UPTEC ES 17017

Examensarbete 30 hpJuni 2017

Technical Feasibility Study of an IGBT-based Excitation System

Johan Frisk

Teknisk- naturvetenskaplig fakultet UTH-enheten Besöksadress: Ångströmlaboratoriet Lägerhyddsvägen 1 Hus 4, Plan 0 Postadress: Box 536 751 21 Uppsala Telefon: 018 – 471 30 03 Telefax: 018 – 471 30 00 Hemsida: http://www.teknat.uu.se/student

Abstract

Technical Feasibility Study of an IGBT-basedExcitation System

Johan Frisk

This thesis aims to design a cabinet to house some of the requiredhardware to realize a 1000 A IGBT inverter controlled staticexcitation system. In the thesis practical design considerations areidentified and solved.

The suggested excitation system requires a cabinet to house theinverters. Together with inverter requirements stated by the invertermanufacturer and possible electromagnetic interference from switchingof the IGBT:s, practical design considerations arise when realizingthe system. Identified design considerations are heat dissipation,EMI, IP-code requirements and mechanical stresses at inverterconnections.

In this study, the design considerations are addressed and a cabinetdesign with required components inside is suggested. The suggestedcabinet together with its components could fulfil the suggestedsystem's- and the inverter's requirements. However, the IP-codeallowed by the suggested EMC-seals might be lower than the IP54required by the inverter. The cabinets EMC-properties will probablybe lowered if regular rubber gaskets are used.

The study suggests one possible configuration which is possible torealize. It is suggested that further consideration is dedicated tothe EMI reducing properties of the cabinet if it is to be installedin an environment sensitive to EMI.

ISSN: 1650-8300, UPTEC ES17 017Examinator: Petra JönssonÄmnesgranskare: Urban LundinHandledare: Johan Abrahamsson

Populärvetenskaplig sammanfattning Magnetiseringssystemet styr strömmen till generatorns fältlindningar och rotorns magnetfält

ändras efter strömmen genom fältlindningarna. Magnetfältet från rotorn bestämmer vilken

spänning som generatorn ger ifrån sig till elnätet.

För att styra strömmen i rotorn kan tyristorer användas för att likrikta en växelström som

sedan leds till generatorns rotor. Storleken på den likriktade spänningen kan ändras genom att

kontrollera tyristorerna. Genom att styra spänningen över rotorns fältlindningar styrs indirekt

även strömmen, som bestämmer magnetfältet, som bestämmer spänningen som generatorn ger

ifrån sig.

Ett annat sätt att styra strömmen till generatorns rotor, är att använda en likriktare tillsammans

med en växelriktare, en så kallad H-brygga. Att använda en H-brygga medför att spänningen

över rotorns fältlindningar kan anta endast två värden, VDC eller -VDC. Den applicerade

spänningen över rotorlindningen kan inte varieras, tillskillnad mot spänningen som appliceras

i ett tyristorbaserat system. Detta gör att strömmen styrs direkt i det växelriktarstyrda system,

tillskillnad mot i det tyristorbaserade systemet där strömmen styrs indirekt genom att variera

spänningen över rotorlindningen. I den förslagna växelriktaren finns transistorer, så kallade

IGBT:er (eng. Insulated Gate Bipolar Transistor). Dessa IGBT:er används för att styra

strömmen genom rotorns fältlindningar.

Att använda växelriktare är förknippat med värmeutveckling från förluster som uppstår när

IGBT:erna slår av och på. Värmeutvecklingen kan, om effekten är hög, bli betydande. Den

värme som utvecklas tillsammans med de krav som tillverkaren av den förslagna

växelriktaren har på montering av den, skapar design problem.

Det här examensarbetet syftar till att designa ett skåp som kan uppfylla de krav som det

föreslagna magnetiseringssystemets ska uppfylla. Även de krav som tillverkaren av den

föreslagna växelriktaren har på dess installation ska uppfyllas. Tillvägagångssättet har varit

litteraturstudier, 3D-modellering och diskussioner med leverantörer. Att hitta de krav som

ställs på växelriktarens installation har varit centralt i litteraturstudien och kraven har legat till

grund för de designkrav som ställts på elskåpet.

Under litteraturstudien framkom att växelriktaren måste monteras inuti ett elskåp, vilket gör

att värmeförluster från den måste tas om hand. Det framkom också växelriktaren kräver:

En separering mellan kylflänssida och framsida. Separeringen ska åtminstone vara av

kapslingsklass IP54

Ett luftflöde över sin framsida. Luftflödet ska minimalt vara 2 m/s för att undvika heta

områden.

Att åtgärder vidtas för att minimera mekaniska krafter på anslutningsterminaler för AC

och DC.

I en elektrisk komponents kapslingsklass är den första siffran i IP-koden en indikering på hur

beständig komponenten är mot inträngande föremål. I den ena änden av skalan (låg siffra)

indikerar siffran hur beständig komponenten är mot inträngande föremål, i den andra änden av

skalan står den första siffran för skydd mot damm. Den andra siffran i IP-koden står för skydd

mot vatten, där en hög siffra betyder högre motståndsförmåga än en låg siffra.

Växelriktaren kan även orsaka elektromagnetiska störningar (EMI) i sin omgivning på grund

av att spänningen bryts och slås på med en frekvens på upp till 15 kHz. För att skapa

elektromagnetisk kompatibilitet (EMC) med omgivningen kan elskåp tillverkas i ett särskilt

EMC-utförande och skärmade kablar användas. Att jordning utförs på ett korrekt sätt är

viktigt för att få EMC.

Genom att skapa 3-D modeller av föreslagna elskåp i SolidWorks och sedan föra diskussioner

med skåptillverkare, har en föreslagen lösning tagits fram som uppfyller de krav som

växelriktaren ställer på elskåpet. För att minska risken för mekaniska spänningar på

växelriktarens kopplingspunkter har diskussioner förts med en tillverkare av

strömfördelningskomponenter.

Resultatet visar att det kan vara tekniskt möjligt att bygga ett elskåp som uppfyller de krav

som tillverkaren ställer på installation av växelriktaren. Detta kommer att bero på om flänsar

tillsammans med tillhörande packningar uppfyller IP54. En leverantör av elskåp hittades som

kunde bygga en föreslagen lösning på skåpkonstruktion.

En färdig strömfördelningskomponent som kunde överföra 1000 A och utgöra en övergång

mellan kabel och växelriktare hittades inte. En specialtillverkad lösning togs fram genom

diskussion med en leverantör av strömfördelningskomponenter. Den framtagna lösningen

består av en solid kopparskena till vilken kabelskor för anslutning av kablar samt anslutning

av flexibel skena kan ske. Den flexibla skenan (Flexibar) bockas i U-form för att kunna

absorbera krafter från termisk expansion av kopparen. Bockningen är avsedd att förhindra

mekaniska krafter på växelriktaren.

Luftflödet mot växelriktarens framsida åstadkoms genom att montera en fläkt framför, snett

nedanför växelriktaren. Fläktens förväntade livstid samt dess strömförsörjning har varit

avgörande vid val av fläkt.

Kablar innehållandes en ledare har valts för överföring av ström till generatorn. Detta val har

gjorts på grund av ett högre strömvärde jämfört med kablar innehållande flera ledare (till

exempel en trefaskabel).

Executive summary In this thesis the technical feasibility of a new concept of static excitation system is studied.

The new concept of excitation system uses an inverter with IGBT:s to control the output

voltage of the generator.

The study shows some practical problems that can be encountered when designing a cabinet

to house high power inverters (1000 A) and how to meet them. The result shows that it is

technically feasible to build the system. Components needed for current distribution and

cooling of the inverters are designed and presented.

It is suggested that further consideration is dedicated to the EMI reducing properties of the

cabinet if it is to be installed in an environment sensitive to EMI.

Table of Contents

1 Introduction ........................................................................................................................ 1

1.1 Purpose ........................................................................................................................ 1

1.2 Problem formulation .................................................................................................... 1

1.3 Scope ........................................................................................................................... 2

1.4 Aim & limitations ........................................................................................................ 2

1.5 Background .................................................................................................................. 2

1.5.1 Static exciter system ............................................................................................. 3

1.5.2 Thyristor controlled static exciter system ............................................................ 4

1.5.3 IGBT controlled static exciter system .................................................................. 6

2 Pre-study ............................................................................................................................. 8

2.1 Laws, regulations and recommendations ..................................................................... 8

2.2 EMI & radiated emissions ........................................................................................... 8

2.2.1 Cabinet to reduce EMI ......................................................................................... 8

2.2.2 Shielded cables to reduce EMI ........................................................................... 10

2.3 Inverter requirements ................................................................................................. 11

2.3.1 Inverter cabinet ................................................................................................... 11

2.3.2 Inverter temperatures .......................................................................................... 11

2.3.3 Inverter electrical connections............................................................................ 13

2.3.4 Inverter heat sink cleaning ................................................................................. 13

2.4 Ampacity & principles of cable- and busbar dimensioning ...................................... 14

2.4.1 Principles of cable dimensioning ....................................................................... 15

2.4.2 Principles of busbar dimensioning ..................................................................... 16

2.5 Final cabinet design criterions ................................................................................... 17

3 Method ............................................................................................................................. 18

3.1 Dassault Systemes' SolidWorks................................................................................. 18

3.2 Component selection ................................................................................................. 19

3.2.1 Cabinet ............................................................................................................... 19

3.2.2 Forced air cooling at inverter front .................................................................... 20

3.2.3 Electrical connections ........................................................................................ 20

3.3 Assembly ................................................................................................................... 21

4 Result & Analysis ............................................................................................................. 22

4.1 Cabinets ..................................................................................................................... 22

4.1.1 Inverter cabinet ................................................................................................... 22

4.1.2 Control equipment cabinet ................................................................................. 24

4.2 Components in inverter cabinet ................................................................................. 26

4.2.1 Electrical connections ........................................................................................ 26

4.2.2 Fans .................................................................................................................... 30

4.2.3 Cable glands and flanges .................................................................................... 31

4.3 The completed cabinet ............................................................................................... 33

5 Discussion ........................................................................................................................ 38

6 Conclusion ........................................................................................................................ 43

7 References ........................................................................................................................ 44

8 Appendix .......................................................................................................................... 47

Appendix A - Porjus U9SR - Konstruktionsdokumentation .................................................... 47

Appendix B - Material .............................................................................................................. 61

Appendix C1 - Inverter cabinet drawing .................................................................................. 63

Appendix C2 - Control cabinet drawing .................................................................................. 64

Nomenclature

IGBT - Insulated Gate Bipolar Transistor

EMI - Electromagnetic Interference

EMC - Electromagnetic Compatibility

RFI - Radiofrequency Interference

XLPE - Cross-linked Polyethylene

PAC - Programmable Automation Controller

1

1 Introduction Excitation of the rotor field winding inside a generator can be achieved in different ways and

two examples are the brushless AC- and the static excitation systems [1]. Nowadays, the static

excitation system is the preferred system [2] and in the static exciter system, the components

used are, as implied by the name, static and non-moving [3]. A static exciter system uses a

power rectifier bridge to rectify AC into DC. The power rectifier bridge consists of power

electronics, which can be thyristors [4]. The output voltage from the thyristor rectifier can be

controlled and used to control the voltage on the output terminals of the generator. [4]

A novel way to obtain a static excitation system is to use a H-bridge inverter with IGBT:s to

control the voltage on the output terminals of the generator. If the field winding can withstand

the fast and large voltage transient across it, a chopper based control offers better

controllability than a thyristor based system [5]. However, the use of inverters are coupled to

heat generating switching losses. In this study the heat generated could be significant since the

exciter system can attain power levels in the hundreds of kW area. [6]

The heat generated from the inverter will have to be dissipated and this can become

troublesome since the chosen inverter manufacturer states that the inverter has to be installed

inside a cabinet. The cabinet allows for a certain IP-code separation between the heat sink

side and the electronics side of the inverter. Protection against accidental touch of electrically

conductive, and accessible parts, with up to 1000 VDC is also obtained by mounting the

inverters inside a cabinet. The requirement of cabinet installation from the manufacturer also

helps to assure only authorized and qualified personnel can access the inverters [7].

Since the system in the study is dimensioned for currents up to 1000 A the size of the required

cables can make them cause mechanical stress to their connection points. The chosen

inverters' AC- and DC terminals are sensitive to stresses and measures have to be taken to

minimize them [7]. Also, since switching of an inductive load can give rise to EMI [8]

measures will be taken to reduce EMI.

1.1 Purpose The purpose if this study is to investigate the technical feasibility of an IGBT controlled

exciter system.

1.2 Problem formulation To realize the IGBT controlled static exciter system the necessary hardware needs to be found

and made compatible with the inverters.

The inverters must be installed in some sort of casing with the required IP-code to protect the

electronics from dust and protect from accidental touching of electrical connections.

The switching losses coupled to the inverters may cause heat dissipation problems as they are

mounted inside a casing.

2

The inverters heat sinks must be cleaned in recommended intervals. Hence the heat sinks must

be installed in a way which allow access to them for cleaning.

The switched output voltage from the inverters will cause harmonics and could thereby cause

EMI-problems to its surrounding.

The DC-link and cables which connect the inverter to the generator have to be connected to

the inverter without causing mechanical stresses at the inverters AC- and DC-terminals. Since

the system is dimensioned for 1000 A, the risk of mechanical stress from cables can be

substantial.

1.3 Scope This study will address problems coupled to housing IGBT based inverters inside a cabinet.

Problems regarding heat dissipation, IP-code separation, electrical connections and EMI will

be looked into and technical solutions will be found to meet them.

The hardware required for rectification, control system and software are deemed out of scope

and will not be covered in this study.

1.4 Aim & limitations The aims of this study are:

Perform a literature study to get knowledge of required design criteria

Create a 3-D drawing of a cabinet containing the required components needed for an

IGBT controlled excitation system handling 1000 A

Create a guide for assembly of the proposed cabinet

The study does not include:

Hardware in control system

Software

Electrical connections to the slip rings on the rotor shaft

Hardware for rectification

1.5 Background The basic function of any excitation system is to provide direct current to the field winding of

the synchronous machine. The excitation system also performs control and protective

functions. The protective functions of the exciter system consists of ensuring that the

capability limits of the generator are not exceeded. The excitation system can also control the

power system by controlling the field voltage, and thereby controlling the field current. These

functions are essential to make the power system perform in a satisfactory way. [3]

Excitation of the field windings inside a generator can be obtained in different ways. One of

them is the static excitation system. In contrast to DC excitation systems and AC excitation

systems, all the components in the static excitation system are still, or static [3]. The

maintenance of excitation systems with moving parts to supply the excitation field to the

generator is not needed in the static excitation system [9]. Replacement of rotating exciters

3

and its associated equipment with static excitation systems provides a solution to this problem

[4]. However, the static excitation system can introduce problems with harmonics due to

thyristor switching. [9]

1.5.1 Static exciter system

The static excitation system consists of three basic components. These components are power

control devices such as the power rectifier bridge, a voltage regulator and the power potential

transformer. Together these components provide field control to maintain the output voltage

of the generator. [4]

Voltage regulator

To obtain an automatic voltage control of the generator, an automatic voltage regulator

(AVR) is used [4]. The AVR is used to maintain a steady armature voltage and the voltage to

be maintained is set to some predefined limits [10]. To achieve an automatic voltage control,

some components have to be used together. The components required are sensing

transformers, a firing circuit and an automatic voltage regulator [4].

The sensing transformers provides an insulation and a voltage matching between the

automatic voltage regulator and the generator instrument transformer [4].

The firing circuit generates the turn-on pulses to the rectifier bridge if thyristors are used for

rectification (see section 1.5.2). By changing the time relationship between the firing pulses,

the output from the rectifier bridge is increased or decreased [4].

The automatic voltage regulator rectifies a sample from the output of the generator and

compares it to a reference dc voltage. If the voltages deviate to much from one another, a

signal is sent to the firing circuit. The firing circuit then alters the firing angle according to the

error signal to restore the output voltage of the generator to the set value. [4]

Power transformer

The power potential transformer provides power to the excitation system. The output voltage

on the generator terminals is stepped down by the transformer to make it compatible with the

requirements of the field windings in the generator [4].

Power rectifier bridge

The power transformer supplies the power rectifier bridge with an AC voltage. The AC

voltage is rectified to supply the generator field windings with a DC voltage [4].

4

A principal sketch of the static exciter system is shown below.

Figure 1.1 A principal sketch of the static exciter system. The power and sensing is taken from the generator output via a

transformer and is rectified with thyristors to feed the rotor with a DC current. The DC current is fed to the rotor windings via

slip rings on the rotor shaft.

In Figure 1.1 it can be seen how the power needed to excite the rotor is taken from the

generator output terminals. It is then sent to the thyristor rectifier bridge, which output voltage

is set from the AVR. By comparing a rectified sample from the output voltage of the

generator to a reference value, the AVR alters the firing angle to the thyristors. The firing

angle of the thyristors determines the output voltage from the rectifier bridge and hence the

voltage across the field windings.

1.5.2 Thyristor controlled static exciter system

The thyristor is a device which have the ability to control the start of conduction by delaying

it from when it gets forward biased to a desired time. Because of this, the thyristor is named a

semi-controlled device [11].

The thyristor is an electrical switch which can be turned on to start conducting when it is

forward biased. The turn on is accomplished by sending a current pulse to the gate of the

thyristor and in its on-state, the thyristor works as a diode. It is not possible to turn off the

thyristor with a current pulse to its gate. Instead, the thyristor turns off when the current

through it falls to zero [11].

When using thyristors to rectify an AC-voltage, the DC-voltage output is set by the firing

angle, α. The firing angle can be seen as the delay from when the thyristor gets forward biased

to when the gate pulse is sent to it. This means a larger firing angle will reduce the output

voltage.

5

How the firing angles affect the output voltage is graphically shown in Figure 1.2.

Figure 1.2 Output voltage from a thyristor rectifier. The average output voltage decreases as the firing angle increases.

The firing angle α, dictates the field voltage, which in turn is proportional to the field current.

As the firing angle is changed, so is the field voltage.

The rotor field current is what determines the excitation of the stator winding, which in turn

determines the output voltage of the generator. This means, by applying a certain DC-voltage

to the rotor field winding (altering the firing angle α of the thyristors), the rotor field winding

current can be controlled and thereby also the output voltage of the generator.

A schematic picture of a thyristor controlled exciter system can be seen in Figure 1.3

Figure 1.3 A principal sketch of the thyristor controlled excitation system. An AC-voltage is rectified by a 6-pulse thyristor

bridge. By altering the firing angle of the thyristors, the output DC-voltage can be controlled. The current through the rotor

field winding is indirectly controlled by the field voltage. The thyristor firing circuit has been left out in the figure.

The voltage sources in Figure 1.3 is the excitation transformer (see Figure 1.1) used in the

thyristor controlled static excitation systems. The voltage of the secondary winding in the

6

excitation transformer will determine the maximum voltage, the ceiling voltage, which can be

applied to the rotor field winding.

1.5.3 IGBT controlled static exciter system

IGBT modules have a history of being widely used in converters for electric-motor drives.

The IGBT modules used in these converters can be seen as reliable components and their

reliability are equal to or even greater than that of thyristors. [12]

In the IGBT controlled static excitation system shown in Figure 1.4, the IGBT:s will be

supplied with a DC-voltage. This means, the rotor field winding (the RL-load in Figure 1.4)

will be subjected to the ceiling voltage as the IGBT:s switches, and not to of a variety of

voltages in-between as in the thyristor controlled system.

Figure 1.4 A principal sketch of the IGBT controlled exciter system. An AC voltage is rectified by a 6-pulse diode bridge

and the resulting DC-voltage is supplied to the H-bridge constructed with IGBT:s. The rotor field winding is represented by

the RL-load in the H-bridge.

The current is controlled with a current sensor placed in one of the legs of the H-bridge. The

measured output current from the H-bridge will be compared to a reference value by a

Programmable Automation Controller (PAC). The reference current value is determined from

the output voltage of the generator. A lower output voltage than required will lead to an

increased reference value of the rotor field current in the PAC.

The voltage applied to the rotor field winding will determine how steep the slope of the

current ripple will become. A higher voltage will mean a steeper slope and possibly a faster

current control. In the IGBT controlled exciter system in the study, the same voltage, the

ceiling voltage, will always be the voltage applied to the field winding. A sketch of the

current wave form in the rotor field winding can be seen below in Figure 1.5.

7

Figure 1.5 Sketch of the field current wave form in the rotor winding of the IGBT controlled exciter system. The slopes of

the wave form will approximately attain the value or .

The graph in Figure 1.5 appears as it does due to the altering ceiling voltages. As the ceiling

voltage attains a positive value, the current is increasing. As the current reaches some

tolerance value, the two conducting switches in the H-bridge will open and the other two

switches will close (see Figure 1.4). This causes a negative voltage to be applied across the

field winding. The applied voltage will be the ceiling voltage but with an opposite sign as

before the opening and closing of switches. The now negative voltage will start to limit the

current in the field winding until it reaches a tolerance value below the reference value, the

switches will then change state again, and the procedure continues.

If the field winding can withstand the fast and large voltage transient across it, a chopper

based control offers better controllability than a thyristor based system. This way of field

control opens up possibilities. Possibilities as e.g. a segmented field winding where different

poles are excited by different choppers. [5]

Because of this possibility, it is interesting to look into if the suggested IGBT controlled static

exciter system can be realized. The realization should be made with components, preferably

on-shelf than tailor-made, which can be bought and made fit together to allow implementation

of the system.

8

2 Pre-study Except from laws and regulations, information regarding EMI and EMC was also gathered

since the switching together with an inductive load gives rise to transient interference [8].

The pre-study also aimed to acquire knowledge about the inverter specific needs regarding its

housing. Specific requirements in mind were the inverters IP-code, guidelines regarding

electrical connections and conductor sizing.

2.1 Laws, regulations and recommendations The technical feasibility study is at this state, a research project and does not intend to provide

a ready to sell product on the market. Hence, the rules of electrical equipment from the

National Electrical Safety Board will not apply. Because of this, there are no demands on how

electrical connections are designed nor any demands on providing user manuals and storing

documentation of the product in a certain amount of years. [13]

In "starkströmsföreskrifterna" [14] advice is given about dimensioning conductor cross

sectional area. It is written that the smallest cross sectional area of the conductor should be

chosen with consideration to:

Highest allowed temperature of the conductors.

Acceptable voltage drop.

Electromagnetic stresses which can arise due to a short circuit.

Other mechanical stresses which the conductors may be subjected to.

2.2 EMI & radiated emissions Electromagnetic interference is an increasing form of pollution. It's effect can vary from a

disturbing noise on a radio receiver to more severe effects such as potential fatalities due to

corruption of safety-critical control systems. As electrical and electronic equipment penetrates

more into society, the risk of EMI increases and so does the possible damage. [15]

To dampen the electric- and magnetic fields originating from an electrical circuit, shielding

can be used. Shielding means an electrically conducting surface (a barrier) is placed around or

around a part of the electrical component. The barrier can be made completely out of metal if

protection against low frequency EMI is desired. If protection against higher frequency EMI

(30 MHz or more) is desired, a thin conductive layer placed on e.g. plastic is sufficient to

achieve a shielding effect. [15]

2.2.1 Cabinet to reduce EMI

To shield against EMI, a cabinet constructed of a conductive material can be used. Principles

of absorption and reflection of electric fields are presented in Figure 2.1

9

Figure 2.1 Description of how an impinging electric field is absorbed and reflected from a barrier surface.[15]

The shielding effectiveness of a barrier is a result of both reflection and absorption. As an AC

electric field impinges on a conductive surface, a current in that surface will be induced. The

induced current flow (J in Figure 2.1) is attenuated a certain amount each skin depth of the

barrier. Skin depth depends on material properties such as conductivity, permeability and

frequency. The skin depth is defined as (1). [15]

(1)

As an example, steel can offer higher absorption than copper at low frequencies due to its

high relative permeability. The absorption loss is the same whether the field is electric or

magnetic. [15]

The reflection loss depends on the wave impedance of the field. In the near field, when the

distance from the source to barrier is less than the E-field impedance will be high and it

causes the reflection loss to be high. For magnetic fields, the wave impedance in the near field

is low, and correspondingly, the reflection loss is low. Barrier material also affects the

reflection loss. For materials as copper and aluminium which are high conductive, the

reflection loss is higher than for lower conductive materials such as steel. [15]

Chassis radiation

A common source for radiation is the seams of the chassis. Higher frequency emissions,

typically greater than 200 MHz, are more common to originate from the chassis of the

equipment. [16]

An electromagnetic shield commonly consists of more than one part which is joined together

in seams. When two parts are joined together, the joint will not be perfect, which will cause

the electrical conductivity in the joint to be non-perfect. The reason for this may be more than

one and distortion, painting and corrosion are a few examples of things which can create an

10

insulating layer which reduces electrical conductivity. As a consequence, problems will arise

from an EMC-perspective when removable panels and doors are used. [15]

Circuit boards placed inside a cabinet can generate high-frequency currents on the inside of

the chassis and the high-frequency currents can leak out from gaps or seams. These leaked

currents will then flow around the outside of the chassis. The chassis then becomes an antenna

which radiates. [16]

Seams

When a high frequency current flowing on the inside of the chassis come to a seam it must be

able to pass it easily. A small impedance (a few milliohms) will create a voltage drop, which

means an electric field, that radiates. [16]

Holes

To keep the EMC-performance of the cabinet if a hole has to be made for e.g. a display, a sub

shield can be used. The sub shield have to be made sure to surround the back side of the

display and have a good electrical contact with the door/wall in which is placed. [15]

2.2.2 Shielded cables to reduce EMI

Shielding of cables can be obtained in several ways. Foil-shield, braided shield and

Helical/spiral shield are just a few examples. The shields differ in design and material

properties, and hence also in shielding properties. [8]

Braided shields are effective in both reducing emissions and increasing immunity against

EMI. The braided shield is effective when possible sources of interference are e.g. switches

which are operating an inductive load or when the source is e.g. motor control circuits. [8]

Braided shields offer protection against magnetically induced interference in the frequency

range 30 to 100 MHz. Generally, EMI protection is increased with higher grade of braid

coverage and typical values are 80-95 percent coverage. 100 percent shield coverage is

unattainable, but if the braid covers 85 percent or more of the conductor, the braided shield

can offer significant lowering of the radio-frequency interference (RFI) [8]. Radio-frequencies

have traditionally been defined as frequencies ranging from a few kHz to roughly 1 GHz. [17]

A spiral shield can be used to shield against inductive coupling and capacitive coupling when

possible sources of interference are for example power lines. [8]

Overall shields are effective against power line frequencies. The overall shield is also

effective against high frequency electromagnetic and electrostatic interference if the shield is

grounded at both of its ends. A counter current that cancels out the interfering current

interacting with the protected current, is induced when the shield is grounded at both ends. [8]

To reduce radiated emissions, it is important to assure that all shielded cables have a low

impedance bond at both ends. The shields should be terminated with direct contact to the

connector or the chassis and the use of pigtails should be avoided unless absolutely necessary.

If pigtails must be used, assure they are made as short as possible. [16]

11

A metallic shield is a barrier to high-frequency fields on one side of the barrier and the other.

Since it is important that all parts of an enclosing barrier are well bonded together, problems

arise when a cable needs to be penetrated through a barrier. To prevent noise current from

leaking outside the barrier, following the outside of the cable shield or the cable wires, the

cable needs to be bonded to the enclosure. The bonding should be made with a low-

impedance connection to the chassis, and ideally made with a 360° connection. [16]

2.3 Inverter requirements The manufacturer of the proposed inverter provides some requirements for the operation of

the inverter. There are certain requirements on the cabinet which are to house the inverters

and there are also requirements regarding temperatures and electrical connections on the

inverter.

2.3.1 Inverter cabinet

When the inverters are mounted, there must be a separation between the inverters front and

the heat sinks on its back. This separation must fulfil at least IP54. [7]

The National Electrical Safety Board explains the first- and second figure in the IP-code as

can be seen in Table 2.1.

Table 2.1 Explanation of the figures in the IP-code system. The explanations are made by the Swedish National Electrical

Safety Board. Values in the table are adopted from [18].

IP-code

First figure Second figure

0 No protection. No protection

1 Protection against penetration of solid

objects larger than 50 mm.

Protection against dripping water.

2 Protection against penetration of solid

objects larger than 12 mm.

Protection against dripping water. The apparatus is

not allowed to lean more than 15°. 3 Protection against penetration of solid

objects larger than 2.5 mm.

Protection against sprinkling water. Maximal angle

60°. 4 Protection against penetration of solid

objects larger than 1.25 mm.

Protection against sprinkling water. All angles.

5 Dust protection. Protection against rinsing water from a nozzle.

6 Dust tight. Protection against heavy rinsing with water.

7 Can be temporarily submerged in water without

taking damage.

8 Suitable for long term submersion in water.

According to manufacturer directions.

The IP-code specifies the protection degree of the electrical equipment and the higher figure

in the IP-code the higher protection is offered.

2.3.2 Inverter temperatures

The inverter manufacturer specifies maximum temperatures for different components on the

inverter. They also specifies a minimum airflow across the snubbers on the front of the

inverter. An air flow ≥1 m/s is required, but if the air flow is <2 m/s the maximal operating

temperature of the snubbers risks to be exceeded. [7]

12

A snubber is an electric circuit typically placed in parallel with each semiconductor element.

The snubber circuit is used to provide a protection against voltage- and current transients and

often consists of a resistor and a capacitor. [19]

The specified temperatures are shown in Table 2.2.

Table 2.2 Temperature limits at certain components on the inverter specified by Semikron. The table is adopted from [7].

Temperature limits

Component Maximal surface temperature

which is not to be exceeded

Recommended maximal surface

temperature during operation

Thin film capacitors 85 °C 80 °C (1)

Snubbers 95 °C 90 °C

AC- and DC-busbars 105 °C 100 °C (1)Lifetime of the capacitors is reduced if operating between 85 °C and 90 °C for extended periods of time

To verify that the internal air cooling is sufficient, measurements have to be made to ensure

temperatures does not exceed the values in Table 2.2. [7]

The placement of the components mentioned in Table 2.2 is shown in Figure 2.2 below.

Figure 2.2 A sketch of Semikron's SlimLine 150. The red and green rectangles show the DC- and AC-terminals respectively.

The yellow rectangle shows the snubbers and the blue rectangle shows where the thin film capacitors are placed. The thin

film capacitors cannot be seen in the sketch.

13

2.3.3 Inverter electrical connections

The electrical connections on the AC-terminals of the inverter are made out of aluminium or

tin plated copper. To ensure electro-galvanic compatibility of the materials in the electrical

connection to the inverter, tin plated copper should be used. Tin plated copper is compatible

with bare copper, bare aluminium, tin plated copper and nickel plated copper. [7]

The manufacturer of the inverter issues precautions to be taken during its installation. The

precautions regards the mechanical stresses which the electrical terminals of the inverter

might be subjected to. Mechanical stresses may come into existence during connection of

cables or busbars to the inverter. [7]

The manufacturer of the inverter also specifies the maximum allowed temperatures for the

AC- and DC-terminal connections. The temperature of the AC- and DC-terminal on the

inverter is not allowed to exceed a temperature of 100 °C (Table 2.2) [7]. This has to be taken

into account when choosing the conductors which are to be connected to the inverter. The

chosen conductors ampacities have to be high enough to allow for a continuous load current

without exceeding 100 °C.

2.3.4 Inverter heat sink cleaning

If dust accumulation on the heat sink fins starts, the thermal efficiency of the heat sink may be

reduced. Recurring stops due to overtemperature may be an indicator of dust accumulation on

the heat sink fins and it is advised to add an air filter if dust accumulation becomes a problem.

Maintenance intervals of the inverters in the SlimLine series are shown in Table 2.3.

Table 2.3 Cleaning interval recommendation and replacement interval of some components of the inverters in the SlimLine

series. The table have been adopted from the SlimeLine series user manual [7].

Year 0 1 2 3 4 5 6 7 8 9 10 11 1

2

next

Cleaning

Heat sink fan

X X X X X X X X X X X X

Het sink fins and

capacitor bank

According to the environmental conditions the inverter is

installed in

Replace

Capacitor bank

and heat sink fins

X Every 100 000 h

Heat sink fans X Every 70 000 h

To clean the heat sink fans, the fans have to be dismounted from the heat sink. The fans are

then to be blown down in a separate area. [7]

If the inverter is mounted with a IP54 separation between its heat sink side and its front side,

the inverter does not have to be dismounted to clean the heat sink and capacitors. If it is not

mounted with the stated IP-code separation, the inverter have to be removed and transported

to a separate area for cleaning. [7]

14

2.4 Ampacity & principles of cable- and busbar dimensioning Ampacity is a measure of conductors ability to carry electrical current. All metals will carry

electrical current, but copper and aluminium are the most commonly used materials for

conductors. Copper is the most widely used because it is a better conductor and is physically

more strong than aluminium. The weight of copper is about three times that of aluminium

and due it's low density, aluminium is the most common choice for over head power lines.

However, the resistance of aluminium is more than 150 percent higher than that of copper.

[20]

Copper's higher conductivity compared with aluminium reduces the heat losses for a copper

conductor compared to an equally sized aluminium conductor. The lower heat losses for a

copper conductor infers a higher ampacity than that of an equally sized aluminium conductor.

[21]

The ampacity of a conductor will depend on several factors. The material of the conductor,

the area in which it is installed and it's cross sectional area are some of the factors affecting

the ampacity [20]. When dimensioning the required cross sectional area needed to provide a

certain amount of current to a load, ampacity tables and reduction factors are used.

The required ampacity tables are found in IEC standard 60364-5-52 Low-voltage Electrical

Installations Part 5-52: Selection and erection of electrical equipment - Wiring systems [22].

Also the necessary reduction factors, which derates the ampacity of conductors depending on

their way of installation, ambient temperature and number of circuits can be found there.

15

2.4.1 Principles of cable dimensioning

The dimensioning of cables is done with respect to their ampacity, which is their maximum

current carrying capacity. The ampacity will differ between two same sized conductors

depending on if they are single core cable or multi core cable. A sketch of a single core and a

multi core cable is shown in Figure 2.3.

Figure 2.3 Single core and multi core conductors. The single core conductor to the left offers higher ampacity for a given

conductor size. The conductors in the picture uses one single copper strand, to increase the cable's flexibility, more strands

can be used.

Also, the choice of insulation material of the conductor will affect it's ampacity. A PVC-

insulated conductor will have a lower ampacity than a XLPE insulated conductor, since the

highest temperature it can withstand is lower. [22]

In order to take into account the ambient temperature and the method of installation of the

conductors, reduction factors are used. The ampacities in [22] are calculated at an ambient

temperature of 30 °C. This means the ampacity for a given conductor will increase if the

ambient temperature is lower, and decrease if it is higher. If conductors are placed together on

e.g. a cable ladder with no spacing in-between, their ampacity is reduced. [22]

To calculate the required ampacity of a conductor at a given installation (2) is used [23]:

(2)

where is the rated load current and is the correction factor which changes the required

conductor ampacity given the way of installation.

In Table 2.4, the ampacities of two loaded, horizontally placed single-core, PVC-insulated

and XLPE insulated copper conductors can be seen. The ampacity of an equal sized multi-

core, PVC-insulated cable is also shown for comparison. The ampacities of the conductors are

16

at 30 °C ambient temperature for a copper conductor with a maximal conductor temperature

of 70 °C for a PVC insulated conductor and 90 °C for a XLPE insulated conductor. [22]

Table 2.4 Ampacities of a few chosen conductor sizes. The values in the tables are adopted from table B.52.10 and B.52.12

in IEC 60364-5-52. The ampacities are valid for conductors installed horizontally on a cable ladder.

Single-core cable Multi-core cable

Cross sectional area

[mm2]

2 loaded conductors

70 °C

2 loaded conductors

90 °C

3 loaded conductors

70 °C

185 463 A 575 A 364 A

240 546 A 679 A 430 A

300 629 A 783 A 497 A

Correction factors for the ambient temperature are shown in Table 2.5.

Table 2.5 Correction factors for different ambient temperatures which are to be used if the ambient temperature at the

installation differs from 30 °C. The values in the table are adopted from table B.52.14 in IEC 60364-5-52.

Ambient temperature [°C] Correction factor for PVC-insulated

conductor

20 1.12

25 1.06

30 1.0

35 0.94

Correction factors to be used when more than one conductor is used in parallel can be seen in

Table 2.6.

Table 2.6 Correction factors which takes number of circuits into consideration. If a group of cables consists of n cables, it

may be considered as n/2 circuits of two loaded conductors or n/3 for a multi-core cable with three loaded conductors. The

values in the table are adopted from table B.52.17 in IEC 60364-5-52.

Arrangement: cable ladder and cables touching

Number of circuits or multi-core cables Single layer on cable ladder system

7 0.79

8 0.78

9 0.78

The correction factors in Table 2.6 are used to take into account for more than one circuit of

two loaded conductors placed on the same cable ladder. The highest correction factor in the

table are for a group of 9 cables placed tightly, touching each other on a cable ladder. [22]

Finally, the corrected ampacity can be calculated with (2).

2.4.2 Principles of busbar dimensioning

A busbar is a conductive bar, usually made of copper or aluminium. The busbar enables

connection between two or more electrical circuits and it can be used in e.g. substations. [24]

Busbars can be made more flexible by using sheets of copper to create a laminated busbar and

the lamination allows for more flexibility during installation. [25]

The dimensioning of these insulated busbars, Flexibars, from Mericon is made from a table in

one of their product catalogues. The dimensioning is made from the maximum allowed

temperature of the conductor, the ambient temperature, the load current in the conductor and

the width of the connection point [26]. The connection points are the AC- and DC-terminals

of the inverter.

17

In Table 2.7, the maximal current which do not cause the conductor to exceed 50 K (ΔT =

50K) of the ambient temperature is shown. The choice of ΔT = 50 K is a result from

discussions with Mericon.

Table 2.7 Maximal allowed current to not exceed a conductor temperature which is higher than 50K than that of the ambient.

N in the leftmost column shows the number of copper sheets in the Flexibar and W is the width of the Flexibar. The thickness

of the sheets are 1 mm for all the conductors shown in the table. In the rightmost column, the recommended overlap at the

point of connection is shown, the recomended overlap is 5xW mm. The values in the table are adopted from the table

"Dimensionering av Flexibar" at page 6 in [26].

Dimension (NxW) [mm] Allowed current [A] (ΔT = 50 K) Overlap [mm]

8x40 1040 A 40

8x50 1175 A 40

6x63 1215 A 30

4x80 1015 A 25

5x80 1175 A 25

The Flexibars can be delivered with a conductor material consisting of bare copper or as tin

plated copper [26]. A sketch of the Flexibar with its laminated tin plated copper sheets is

shown in Figure 2.4.

Figure 2.4 Sketch of the insulated Flexibar with laminated conductor material of tin plated copper.

2.5 Final cabinet design criterions The pre-study resulted in a list of design criteria. The design criteria are mostly specified by

the inverter manufacturer. The EMC design criteria was added since switching together with

an inductive load can give rise to transient interference [8].

The list of design criteria becomes as follows:

IP54 separation between front and heat sink side of the inverter

Mechanical stress of AC- and DC-terminals must be lowered as much as possible

Airflow over the front (≥2 m/s)

Allow for cleaning of fans and heat sinks

A cabinet to reduce EMI from the inverters

18

3 Method When the design criteria had been determined, 3-dimensional models of cabinets were created

in SolidWorks. The models were created in an iterative process where a manufacturer of

cabinets was contacted to discuss designs and their ability to fabricate the proposed designs. A

reseller of busbars and current distributing components was also contacted for discussions.

Selection of components could be made when the pre-study was finished and it followed the

procedure presented in section 3.2.

3.1 Dassault Systemes' SolidWorks SolidWorks is a tool for computer aided design and it has been used to create 3-D models of

cabinets. The modelled cabinets were housing the inverters together with the components

needed to power and cool the inverters. An example of such modelled component is the fan

mounting structure (Figure 4.9) and fan used to provide forced air cooling on the inverter's

front side.

The 3-D modelling could show distances between parts and cabinet walls and how much

room was left for e.g. the installation of a transition from cable to busbar for connection to the

inverter. Room for bending radii of cables and routing of cables are examples of other

limiting parameters which became visible when creating the models.

One of the main issues during the design was to keep an IP54 separation between the heat

sinks and the front side of the inverter. The 3-D modelling helped when trying to create paths

for the air to flow towards the heat sinks when at the same time keeping the required IP-code.

Different topologies and the possibility of them fulfilling the inverter criteria were evaluated

using the 3-D models.

The modelling in SolidWorks was an iterative process which followed the procedure in Figure

3.1.

Figure 3.1 The iterative procedure used when designing the cabinets in SolidWorks.

The flow chart in Figure 3.1 describes the designing procedure. A sketch of an idea of a

design was created and contact was taken with the cabinet manufacturer for discussion and to

see if it was possible for them to fabricate the design. In the discussions, pictures of the

cabinets were used as a foundation for better understanding and reduce risk of

misunderstanding when details about the designs were discussed.

19

3.2 Component selection The selection of components to realize the IGBT controlled exciter system followed the

procedure seen in Figure 3.2.

Figure 3.2 The applied procedure in choosing components to the IGBT controlled static exciter system.

The adopted procedure consisted of the steps seen above in Figure 3.2. Firstly, the system

specifications were studied to get knowledge of what components were need. The second step

consisted of finding the required component. In a third step, the components specifications

were compared to the system requirements, if it fulfilled them, the component selection

moved on to a fourth step. In the fourth step, the recently found component were sketched in

SolidWorks. The sketch was made to get an in-scale model of the component which could be

fitted together with the other components to see if and how they fitted together. If the recently

sketched component could be made to fit together with the other components and it had an

acceptable price, the component could be bought and used in the technical feasibility study.

To start the study, the inverters were used as a starting-point. Inverters from the SlimLine

series from Semikron (SL150) have been used to design a cabinet and the electrical

connections needed to connect conductors to the inverter.

3.2.1 Cabinet

The cabinet design started with contacting two companies which manufactures cabinets to

house electrical equipment. One of the companies responded and the design work were

continued with them. The cabinet needed to fulfil the design criterions in section 2.5 was not

among the chosen manufacturer's product range. Hence, a tailor made design had to be

produced.

The cabinet design had to fulfil the criteria mentioned in the Pre-study, section 2.5 and

different designs of cabinets were produced in an iterative process. A cabinet which could

fulfil the requirements were drawn in SolidWorks and then discussed with the manufacturer.

During the discussions it became clear how the production machines at the manufacturer and

the materials they used limited how the cabinets could be designed.

Problems to produce suggested designs resulted in a final design which originates from the

manufacturers own cabinet design with slight changes to it.

20

3.2.2 Forced air cooling at inverter front

To keep the cabinet integrity as much as possible, a decision was made to not use an inlet-

outlet air cooling system.

The forced air cooling is attained from a fan mounted in front of the inverters. The fan will

cause an airflow over the snubber circuits, which is specified by the inverter manufacturer.

Since the excitation system is crucial for power production and the inverters risk to shut down

if their maximum temperature is exceeded at some part, a fan with long lifetime is desirable.

The power supply to the fans were decided to be taken from the control cabinet next to the

cabinet housing the inverters. In the control cabinet, there is an available power supply of

24 VDC which provides power to the fans pushing air through the inverters heat sinks.

Together with the design criteria in section 2.5 this infers that the criterions for fan selection

become:

24 VDC

As long lifetime as possible

Produces an airflow of ≥ 2 m/s

Mounted in such a way that it forces air over the front side of the inverter

3.2.3 Electrical connections

When the design criterions of the system had been determined, it became obvious some

components were needed in order to connect cables connecting the DC-link and generator to

the inverter. This was deemed necessary to reduce risk of mechanical tension on connection

terminals on the inverter.

To solve the problem, a company selling current distributing products were contacted.

Discussions containing inverter specifications, required currents and desired possibility to

connect more than one cable to each output terminal led to a solution.

An electrical connection forming a bridge between cable and inverter is used to prevent

mechanical tension from cables and from thermal expansion of conductor material. The

bridge is used to fulfil the design criterion regarding mechanical stress in section 2.5.

The same solution can be used to connect to the output terminals (AC-terminal) and the input

terminals (DC-terminal).

21

3.3 Assembly To reduce the risk of metallic splinters finding their way into the inverters, the suggested

order of installation is:

Place the cabinet on the supportive leg structure, fasten the cabinet to the structure and

fasten the supportive leg structure to the floor if needed.

Install flanges, gaskets cable glands and cable routing inside the cabinet. Make the

necessary holes for fastening of the heat sinks protective cage to the supportive leg

structure, to each other and to the cabinet.

Make the required FL21 sized holes for cables to pass between the control- and

inverter cabinet.

Fasten the two cabinets into each other.

Install the inverters.

Attach the inverters heat sink fans.

Install the electrical connections at the AC and DC-terminals of the inverters.

Install the fans which provides airflow over the inverters fronts inside the cabinet.

Install the heat sinks protective cage on the cabinets back side when the system is up

and running.

More details (e.g. torques) regarding assembly can be found in Fel! Hittar inte

referenskälla.. However, it is advised to read the section regarding installation in [7] before

installing the inverters.

22

4 Result & Analysis The result from the technical feasibility study of an IGBT controlled excitation system is

presented in this section. Firstly, the results regarding cabinets are presented. Results

regarding the component selection are presented in section 4.2 and onwards. A bill of

materials can be found in the Fel! Hittar inte referenskälla..

4.1 Cabinets The system is suggested to make use of two cabinets. One cabinet is to contain the inverters

with the components required to make the system function and fulfil the design criterions in

section 2.5. A second cabinet is used to house the control equipment used in the IGBT

controlled exciter system.

4.1.1 Inverter cabinet

The proposed cabinet is a result from using the cabinet manufacturer's original design,

without any significant changes to it. In the manufacturer's design, there is a metal sheet

mounted close to the back of the cabinet. The function of the metal sheet is to be a surface

onto which electrical equipment can be mounted. In the proposed design, this sheet has been

removed to give room for the inverter heat sinks to be placed outside the cabinet. The

placement of the heat sinks outside of the cabinet is a result of the limitations in fabrication

and required IP-code separation between the heat sink side and the front side of the inverter.

The proposed cabinet is shown below in Figure 4.1.

Figure 4.1 The proposed design of the inverter cabinet. The cabinet has pre-fabricated holes for flanges and holes in its back

to make room for the inverters' heat sinks. The back of the cabinet is made in two parts due to fabrication limitations.

23

The cabinet is fabricated in IP-code 55 prior to making the holes in the back to fit the

inverters' heat sinks. Also, the cabinet is fabricated in the manufacturers EMC-design to

reduce the risk of EMI from the inverters.

The proposed cabinets dimensions and approximate weight are presented in Table 4.1

Table 4.1 The proposed cabinets dimensions and approximate weight.

Cabinet data

Width 160 cm

Height 160 cm

Depth 40 cm

Weight 200 kg(1)

(1)The cabinet is tailor made and have not yet been built. Because of this, the weight is approximated with a similar sized

cabinet found in the manufacturers range of products.

Pre-fabricated holes for flanges have been tailor fitted to accommodate the outgoing cables

from the inverter to the flanges. One flange is used for each inverter. The pre-fabricated holes

for flanges in the top of the cabinet are placed to accommodate for electrical connection of the

DC-link to the inverter. An extra set of flanges have been fitted to allow for the incoming DC-

link to be connected to either side of the row of inverters.

The cabinet is placed on supportive legs to give room for bending the radii of the outgoing

cables to the generator. The distance between the floor and the bottom of the cabinet is 50 cm.

Since the heat sinks of the inverters add significant weight to the back of the cabinet, the

supportive legs have been designed to compensate for this. The supportive leg structure

continues further back to prevent a bending force from the cabinets centre of mass to tip the

cabinet. The supportive legs have feet which could be fastened in the floor to even further

prevent the cabinet from tipping. The supportive leg structure is shown in Figure 4.2.

Figure 4.2 The supportive leg structure. In the right picture the holes in the structure feet is shown. The holes permits

fastening to the floor. Fastening prevents the cabinet from tipping.

Since the supportive leg structure is constructed with a larger depth than the cabinet itself, a

metal bar is added to the place where the back edge of the cabinet will be placed. The metal

bar permits the cabinets back lower edge to rest and not be suspended hanging in the air. The

24

supportive leg structure is fabricated in 35x35 mm square pipe steel. The choice of using nine

legs is discussed in section 5.

The heat sinks sticking out of the back of the cabinet is a crucial part of the system. Without

proper cooling, the switching losses will cause the inverter to get overheated. The protective

cages seen in Figure 4.3 were added to prevent damage to the heat sinks and also to prevent

accidental touching of the warm heat sinks.

Figure 4.3 The inverter cabinet with the protective cage. The protective cage gives some protection against mechanical

damage and also offers protection against accidental contact with the heat sinks.

The protective cage is made out of 2 mm thick cold-rolled steel sheets and there are two

mirrored halves creating one cage. The two halves is a result from limitations in fabrication.

The two parts of the cage are fastened to the supportive leg structure with screws which

allows for easy dismounting. The easy dismounting helps fulfilling the design criterion

regarding cleaning of fans and heat sinks in section 2.5.

The perforation of the cage seen in Figure 4.3 is mainly used to reduce weight.

4.1.2 Control equipment cabinet

The cabinet housing the control equipment is placed next to the inverter cabinet. This

placement of the cabinets close to each other ease the connecting of cables for measurements

on the inverter. The placement also eases the connection of power supply to the fans in front

of the inverters as well as connecting the power supply to the heat sink fans. The control

equipment cabinet placed to the right of the inverter cabinet is shown in Figure 4.4

25

Figure 4.4 The control equipment cabinet and the inverter cabinet. The control equipment cabinet placed to the right of the

inverter cabinet.

The suggested control cabinet's dimensions and weight are presented in Table 4.2

Table 4.2 The proposed control cabinet's dimensions and approximate weight.

Control cabinet data

Width 50 cm

Height 200 cm

Depth 50 cm

Weight 82 kg(1)

(1)The cabinet proposed cabinet is fabricated in an EMC-design and the weight found is valid for a non-EMC cabinet. Slight

difference in weight may occur.

The control cabinet is fitted with holes for flanges to allow for cables passing through the

control cabinet into the inverter cabinet. However, the inverter cabinet is not pre-fitted with

these holes for flanges. This is due to the precise alignment of the cabinets which is needed if

26

the holes are to be pre-fitted cannot be guaranteed on site. Hence the holes in the inverter

cabinet have to be made on site.

The flanges on top of the control cabinet is a dividable type of flange. This eases the passing

of measurements cables into the cabinet and reduces the need of cable glands.

The control cabinet is placed on a socket which panels can be removed to allow cables to

enter from the bottom of the cabinet. The removable panels also permits cables from the

inverter to be laid underneath the control cabinet on their way to the generator if needed.

In Figure 4.4 a hole can be seen in the door of the control cabinet. The hole will hold a screen

to show system parameters of interest.

4.2 Components in inverter cabinet To make the IGBT based excitation system work, more components than the inverters are

needed. Components to allow for electrical connections, flanges and cable glands as well as

fans to cool the inverters' fronts are some of the components required.

4.2.1 Electrical connections

The electrical connections in the system can be divided into three parts. The first part is the

flexible busbar connecting the inverter to a solid busbar mounted on insulators some distance

from the AC- and DC connection point of the inverter. The solid busbar forms a bridge

between the inverter and the cables. The second part is the bridge itself and the third part is

the connection of cables to the bridge.

The connection points are summarized below:

The connection of cables to the bridge with cable shoes

The bridge

The flexible busbar connecting the inverter to the bridge

4.2.1.1 Cables

The recommendations regarding voltage drop, electromechanical stresses and other

mechanical stresses in section 2.1 have been disregarded. The voltage drop will not cause any

issues since the system uses current control to obtain its desired function. Furthermore, the

recommendations regarding stresses have not been considered since the inverter will measure

and cut the current fast if a fault occurs. No cause of other mechanical stresses have been

foreseen.

In the process of choosing cables, two main types of cables have been considered. The two

types of cables are the single core cable and the multi core cable. The single core cable consist

of one single conductor (could have more than one strand) and the multi core cable which is

made with three or more conductors, e.g. three phases and a neutral.

The chosen cable is of a single core type. The single core cable have a higher ampacity for a

given conductor size and a comparison between the ampacities of single- and multi core

cables can be seen in Table 2.4.

27

The required conductor ampacity is calculated with (2) at an ambient temperature of 20 °C.

The number of parallel circuits are chosen as 9, which allows for a worst case scenario if

more cables than the ones from the inverters are installed on the same cable ladder. The

correction factors used can be found in Table 2.5 and Table 2.6.

The minimum ampacity for two current carrying conductors placed in parallel with 9 other

circuits is 572 A. When compared to the ampacities in Table 2.4, it can be seen that the

minimum required conductor cross sectional area is 300 mm2. The ampacities of the other two

conductors in Table 2.4 are not sufficient to fulfil the dimensioning ampacity of 572 A.

A single core conductor which fulfils the required minimum cross sectional area and the EMC

design criterion in section 2.5 is the Single 602-RC-CY-J/O from Helu Cable. This cable have

a braided shield with approximately 80% coverage. Its insulation is PVC and it can withstand

a conductor temperature of 90 °C.

The cables will connect the inverters to the generator. To connect the cables to the inverters,

they will be connected to a bridge, forming a connection to the inverters.

4.2.1.2 Bridges

The bridges forming a connection between cables and the inverters are made up of a copper

busbar placed on two insulators mounted on a rail. The two insulators are used to prevent any

bending moment which can create a twist of the bridge. The bridges have been designed by

Mericon and they can be seen in Figure 4.5 and Figure 4.6. Below, the bridge used on the AC-

side of the inverter is shown.

Figure 4.5 The bridge which forms a connection between the AC-terminal of the inverter and the cables. The bridge is used

to prevent mechanical stresses to the inverters AC-terminals during and after installation of the cables connecting to the

generator.

The width of the copper busbar in Figure 4.5 is dimensioned to fit two 300 mm2 cable shoes

installed next to each other. The cable shoe used in the dimensioning is the ELPRESS

KRF12A-300

28

Another bridge is used on the DC-link side of the inverter. The design is roughly the same as

the AC-terminal bridge. However, since the DC-link is connected to one of the inverters and

transferred between them using conductive plates, the one inverter which is connected to the

DC-link will have a similar connection as the AC-terminals.

The bridge used to connect the DC-link to the inverter is shown in Figure 4.6.

Figure 4.6 The bridge used to enable connection of the DC-link to the inverter. The bridge is dimensioned to allow for two

parallel conductors to connect. The conductor cross sectional area of the two parallel conductors can be up to 300 mm2.

The dimensions of the copper busbars in Figure 4.5 and Figure 4.6 are 100x150x10 mm

(WxHxD).

4.2.1.3 Flexible busbar

The flexible busbar is the Flexibar from Mericon. The Flexibar was chosen because of its

flexibility and ability to bend. These properties allows for the Flexibar to be bent in a U-shape

to absorb forces occurring from thermal expansion. The ability to absorb mechanical forces

helps to fulfil the design criterion regarding mechanical stresses on the AC- and DC-terminals

on the inverter.

The widest possible Flexibar was chosen since a wider conductor means it can be thinner and

still have a large enough cross sectional area to allow for the required current. The thinner the

Flexibar is, the more flexible it will be and the less the force from thermal expansion will be

on the AC- and DC terminals of the inverter. The chosen dimensions of the Flexibars are

shown in Table 4.3.

Table 4.3 The dimensions of the Flexibars used to connect to the AC- and DC terminals on the inverter. The values in the

table are taken from Table 2.7.

Connection point Connection width [mm] Chosen Flexibar

width [mm]

Maximum allowed

current (ΔT=50K) [A]

AC-terminal 83 80 1175

DC-terminal 95 80 1175

The conductor material of the Flexibar can be chosen to be either sheets of bare copper or tin-

plated copper. The chosen material is tin-plated copper sheets. The tin plating is used to

29

ensure electro-chemical compatibility with the inverters AC- and DC terminals. The copper

sheets are 1 mm thick and 5 of them are used in the chosen 80 mm wide Flexibar.

Figure 4.7 shows the bent Flexibar used to connect the inverters AC-terminal to the bridge.

The upper side, with the diagonally placed holes, will connect to the inverter.

Figure 4.7 The Flexibars used to connect to the AC-terminals of the inverters. The Flexibar is bent in a U-shape to be able to

absorb mechanical tension resulting from thermal expansion of the copper. The holes for bolts to connect to inverter and

bridge are tailor fitted to the user's needs.

The tin plated copper sheets used in the Flexibar provides flexibility and allows for bending as

seen in Figure 4.7.

30

4.2.1.4 The complete electrical connection design

The choices and designs in the three previous sections result in the complete electrical

connection design. The result is shown in Figure 4.8.

Figure 4.8 The connection method used to connect the cables from the generator to the inverter's AC-terminal. The

connection of the DC-link to the inverters DC-terminals is made in a similar way.

The connection to the inverters AC terminal is made as seen in Figure 4.8. In the figure, the

bent Flexibar is connected to the bridge and the cable shoes is used to connect the cables from

the generator. The size of the cable shoe is what has been used to determine the minimum

width of the copper busbar used in the bridge.

4.2.2 Fans

The fan used to provide the forced air cooling at the inverters fronts was chosen because of its

power supply voltage, air flow and life time. Its name and data can be seen in Table 4.4

Table 4.4 The chosen fan and fan data.

Fan NMB TECHNOLOGIES 4710KL-05W-B30-E00

Power supply 24 V

Air flow 3.75 m/s

Lifetime 100,000 h (25 °C)

The fan is to be mounted in a way which causes the air flow from it to flow over the snubbers

on the front of the inverters. The structure used to mount the fan will be mounted on the rail

of the AC-terminal bridge seen in Figure 4.8.

The fan structure consists of two metal brackets onto which a bent plastic plate is mounted.

The plastic plate is screwed onto the brackets and the brackets are attached to the rail of the

bridge. A support is mounted on the inner side, the fan-side, of the plastic plate. The support

will prevent the angle in which the plastic plate is bent, from changing over time. The fan

mounting structure is shown in Figure 4.9.

31

Figure 4.9 Forced air cooling over the snubbers on the inverter's front side is achieved by mounting a fan in a slight angle

below the snubbers. The structure is mounted with the metal brackets on the same rail as the bridge between the cable and

inverter is mounted.

The fan mounting structure seen in the figure above will allow for an air flow over the

snubber circuits at the front of the inverters. The chosen fan provides a higher airflow than the

minimum required 2 m/s, but due to the fan's placement some distance away from the

inverter, a higher airflow is used.

4.2.3 Cable glands and flanges

The pre-fabricated holes in the cabinet are all of the standardized FL21 size. The use of

standard sized holes allow for easy change of flanges if the suggested flanges for any reason

have to be exchanged.

The cabinet is fabricated in an EMC-design and to keep the EMI-protecting properties of the

cabinet there are demands on the cable glands and the flanges' gaskets used together with the

cabinet. As an example, the cables shields should be grounded with a 360 ° connection to the

chassis. This is accomplished with certain cable glands for EMC purposes. The EMC cable

glands have metallic surfaces inside them which allow for electrical connection between the

cable shield and the cable gland. When the metallic cable gland is connected to the flanges,

which are ensured to have electrical connection to the chassis by using certain EMC gaskets,

electrical connection between the cable's shield and the chassis is obtained. The proposed

M63 cable glands permits a cable diameter of 32-42 mm. The suggested cable 602-RC-CY-

J/O from Helu Cable, have an outer diameter of 36 mm.

32

A sketch of the flanges and gaskets used together with the cabinet is shown in Figure 4.10.

Figure 4.10 A 2xM63 flange and a blind flange with their gaskets to the left. To the right, the gaskets are mounted onto their

respective flange.

If the suggested cable glands were not to fit the suggested cable, a reducing nut can be

inserted which can lower the thread size to M50.

The IP68 EMC cable glands and the electrically conductive gaskets used together with the

flanges helps to fulfil the EMC design criterion in section 2.5. Regarding the IP-code

separation, no information have been found on what separation the EMC-gasket allows for.

This results in an uncertainty whether the IP-code design criterion is fulfilled or not.

33

4.3 The completed cabinet In this section, the inverters are mounted inside the cabinet and the electrical connections are

fitted to them. The result first presented is the inverters and electrical connections mounted on

the back plates of the cabinet. The result is presented in this way since it will show the design

in a better way than when placed inside the cabinet. The result is presented in Figure 4.11.

Figure 4.11 The inverters mounted in the back of the cabinet, to provide a clearer image of the inverters and their electrical

connections, the cabinet have been left out. The DC-link is connected to the leftmost inverter and distributed to the other

inverters by the plates connecting the inverters. In the picture to the right, the heat sinks and their fans can be seen sticking

out the back side of the cabinet.

In Figure 4.11 it can clearly be seen how the Flexibars are bent and connected to the inverter

and the bridge. It can also be seen how the cable shoes connect to the bridge. The cables have

been left out in the figure. Between the modules three plates can be observed. These plates

from Semikron are interconnecting busbars used to connect the DC-link to all the inverters,

which reduces the need for installing own current distributing systems inside the cabinet.

34

Figure 4.12 shows the same installation as the previous figure, but now also with the fan

structures installed.

Figure 4.12 The fan structures mounted in front of the AC-terminals. The fans provides the required airflow over the snubber

circuits on the inverters front sides.

35

The final proposed cabinet on its supportive legs, inverters installed, electrical connections

made, fan structure fitted and flanges mounted is presented in Figure 4.13.

Figure 4.13 The final inverter cabinet with the control equipment cabinet to its right.

Inside the final cabinet a plastic duct is mounted horizontally above the inverters. The duct

will provide a path for the measurement cables connecting the inverters to the control

equipment cabinet.

In the cabinet top, four flanges are mounted and fitted with EMC gaskets. Only two of the

flanges are used to connect the DC-link to the inverters. The other two flanges are blind and

covering two holes which also can be used to connect the DC-link depending on which side is

more favourable. In the bottom of the cabinet there are four flanges. Each of the four flanges

is a 2xM63 flange which are to be fitted with certain EMC cable glands to ground the cables

shield in a 360 ° connection to the cabinet.

36

The distance between the cabinet ceiling and the solid copper busbar is 28 cm. The distance

between the cabinets bottom and the bottom part of the solid busbar on the AC-side of the

inverter is 27 cm.

The control equipment cabinet placed to the right of the inverter cabinet in Figure 4.13 have

two dividable flanges fitted on its top. The dividable flanges are available in an EMC-model

and have been fitted to ease the installation of cables transferring measurements to equipment

inside the cabinet. At the bottom there are two blind FL21 flanges which can be exchanged if

cables need to be routed from the bottom and outside e.g. to the power supply of the heat sink

fans. The base of the control equipment cabinet is fitted with removable panels to allow for

routing of cables underneath the cabinet. In the side of the control equipment cabinet, there is

a dividable flange. This flange is fitted there to permit the D-sub cable routing to the inverters.

In contrast to the inverter cabinet, the control equipment cabinet is fitted with a mounting

plate in its back. The mounting plate allows for fastening rails to mount electrical equipment.

37

The back side of the cabinets is shown in Figure 4.14.

Figure 4.14 Back sides of the two cabinets. One protective cage have been dismounted to show the heat sinks of the

inverters. The ducts seen underneath and up towards the inverter fans are routes for cables connecting to the fans.

Cable routing to the heat sink fans from the control cabinet can be made in the horizontal

plastic duct seen mounted on the legs beneath the cabinet. The routing to respective fan is

made in the vertical ducts seen in Figure 4.4. The vertical ducts are screwed to the horisontal

rails seen in the figure. The rails are welded to the back of the cabinet to keep the cabinets

integrity regarding EMC and IP-code.

38

5 Discussion Cabinets

In the proposed cabinet design, the heat sinks of the inverters are placed outside the cabinet

and this placement is a result of limitations in fabrication. If the heat sinks were to be placed

inside the cabinet or in some other way be enclosed it would offer more protection to the heat

sinks. The highest risk of damage to the heat sinks will probably be the time of installation of

inverters and cabinet on site. With people moving in proximity, an enclosure of the heat sinks

would offer a more sturdy protection but would on the other hand increase the difficulty to

clean the heat sinks.

The dividable flanges used in the control equipment cabinet are quite expensive but will ease

installation of cables. Especially if many thin cables were to be used. If the cost is deemed too

high, cable glands could be used together with regular FL21 sized flanges instead.

One more dividable flange will probably have to be used to allow for the power supply cables

to enter the inverter cabinet from the control cabinet. This extra flange has not been added to

the design seen in Figure 4.13.

As mentioned, the dividable flange seen in between the cabinets in Figure 4.13 is used by the

D-sub cables transferring measurement data from the inverters to the control equipment.

These D-sub cables are thought to be placed on top of each other as they pass through the

dividable flange.

Regarding the IP-code separation attained when using the EMC-gaskets together with the

flanges, it cannot be said certain that they fulfil the IP54 design criterion. Here, a trade of

might have to be made regarding EMC-properties and IP-code separation.

A mindset used in the design process of the cabinets has been to let the cabinet manufacturer

fabricate as many parts as possible. The result of this is that fewer manufacturers and/or

companies will be involved in the process of creating the cabinet. The result of this mindset is

less work for a presumptive customer to obtain their ready-to-use cabinet. The price of the

cabinet might thereby be reduced if components are bought from other suppliers. The

protective cage, flanges and lighting are examples of such components.

Supportive legs structure

The choice of using three legs in the front-to-back-direction of the supportive legs structure is

a result from discussions with the cabinet manufacturer. The manufacturer could not

guarantee the sturdiness of the square pipe steel used to construct the supportive legs if only

one leg at each corner were used. As a precaution against the pipes flexing when the cabinet

with inverters and its installed components are placed on the supportive legs, it was decided to

use a set of legs in the middle of the structure. However, simulations of the mechanics of

materials could show the extra legs are not needed.

Electrical connections to inverter

The Flexibar connecting to the AC- and DC-terminals of the inverters is a flexible conductor,

which if it is not fastened correctly might (as any other conductor) result in heat generation at

39

the connection point. A chance to look at the Flexibar and evaluate how an accidental bending

of it might affect the contact area have not been given in the study.

Since the temperatures on the AC- and DC-terminals of the inverters are of importance, the

overheating risk (due to an unintentional errant connection) might be reduced if solid busbars

are used at these connection points. The resulting way to electrically connect the inverters to

the generator would then be: inverter-solid busbar-flexibar-bridge-cable. This connection will

take up more space in the cabinet, resulting in less room for the cables to enter and connect to

the bridge. The suggested change in design is only needed if the Flexibar's contact area might

compromised due to accidental bending. The use of Flexibar in the connection is a good

solution to prevent mechanical forces on the inverters connection terminals resulting from

thermal expansion of the copper.

If it is decided to change the proposed single core cable to a multi core cable. It have to be

remembered that the required number of conductors required to transfer the 1000 A current

will probably increase from the proposed two in parallel. An increase of the number of

conductors will cause the bridge to be too narrow and a wider bridge have to be designed on

the inverters AC-side. Alternatively if the bridge is installed with a larger distance from the

back of the cabinet, cables might be able to connect to the back side of the solid copper bus

bar as well.

No unauthorized personnel should ever get access to the cabinet and the people working with

it or inside it should have adequate knowledge. However, some protective plastics could be

added over electrically conductive parts inside the cabinet. An addition of protective plastic

will reduce the risk of accidentally touching bare copper parts in the system which are

conducting current.

The Flexibar is dimensioned to maximum reach a ΔT of 50 degrees ( ).

The temperature inside the cabinet will hence be of importance to assure the Flexibar does not

get to hot to compromise the temperature limits on the AC- and DC-terminals. The maximum

allowed temperature of the copper conductor in the Flexibar is 105 °C.

Forced air cooling inside the cabinet

In Figure 4.13 the brackets of the fan structure is attached to the same rail as the bridge. A

different way of fastening the brackets of the fan structure might be needed. The reason to this

is that the brackets are 200 mm long and the bent plastic plate which the fan is mounted on,

might subject the bridge to a bending force. If a bending force results in an actual bending of

the rail, the solid copper busbar attached by insulators to it will also bend, and hence the

Flexibar will also bend. If this will cause a mechanical force large enough to matter on the

inverters AC-terminal is not sure but some force might be applied.

To prevent this bending, another set of vertically mounted rails beneath the rail holding the

bridge could be installed. The orientation of the vertically mounted rails might prevent the rail

from being bent in the same way as it could be in the suggested design when the fan structure

is fastened to it.

40

An estimation of the cabinet's heat removing capacity can be made with (3) (4) and (5). [27]

(3)

(4)

(5)

The calculation of can be made with (5) for a forced, turbulent airflow and over a rolled

surface with an airspeed <5 m/s. [27]

The variable's meanings are shown in Table 5.1

Table 5.1 Variables used in equation (3), (4) and (5).

Variable Description Value

Surface area of the cabinet [m2] 4.48 m

2

Heat transfer coefficient [W/(m2*

K)] Airspeed dependant

Temperature difference between in- and outside [K] [0, 50] K

Thickness of the wall [m] 2e-3 m

Heat conductivity of the wall (steel) [W/(m*K)] 50 W/(m*K)]

Convective heat transfer coefficient (air) [W/(m2*

K)] Airspeed dependant

Airflow [m/s] [0, 3] m/s

The estimated temperature inside the cabinet at an ambient temperature of 20 °C is shown in

Figure 5.1.

Figure 5.1 Estimation of temperature inside the cabinet, the outside temperature is approximately 20 °C. The temperature

inside the cabinet will depend on the airflows on the inside and outside of the cabinet. The fans inside the cabinet provides an

airflow of 3.75 m/s over the inverters fronts. The dashed black line shows a cooling capacity of 1 kW, which can be

considered high, since the total losses of the four inverters is approximately 16 kW [6].

41

To determine the heat transfer capability of the cabinet, the airflow close to the walls inside

the cabinet must be approximated, so does the airflow close to the outside of the cabinet's

walls. The airflow provided by the internal fans is 3.75 m/s at the fan outlet. At the cabinet's

walls this airflow will be lower. The airflow close to the outside of the cabinets steel walls

cannot be determined with certainty at this point and measurements have to be made to

achieve a more accurate estimation. However, if one assumes an airflow which is non-zero

outside the cabinet, the could obtain a value of roughly 50 °C.

A of 50 °C means a temperature of 70 °C inside the cabinet is high and even though the

calculations are made on assumptions caution should be taken when the inverters are started

and observations made to the temperature inside the cabinet.

The of 50 °C in the estimation will occur if the losses to the inside of the cabinet is 1 kW.

1 kW losses inside the cabinet can be considered high since the total losses of the 4 inverters

is 16 kW and the heat generated inside the cabinet will probably be lower. However, the

cabinet is recommended to be installed in a ventilated area which produces an airflow outside

the cabinet due to the estimations made in Figure 5.1.

Cables

The proposed cables used to connect the inverter to the generator is of a single core type.

Given a conductor size, the single core type have a higher ampacity compared to the multi

core cable. During the study, there have been trouble finding the required sizes of single core

cables. The troubles could be a result of it being unusual to use a shielded 300 mm2 single

core cable, this would explain the pricing of the single core cables found.

During the selection process of cables, another cable manufacturer than the now selected one,

were contacted. The suggestion from them was to use their FXQJ EMC 1kV 3x240 mm2

which is spiral shielded and also uses a 100 % covering foil outside the spiral shield. The

shield in this cable is probably constructed to shield against the frequencies in the power grid,

which contain lower frequencies than the switched voltage and current in the studied system.

The dimensioning of the cables have been made from tabled values of apacities for PVC-

insulated copper conductors with a maximal allowed conductor temperature of 70 °C.

However, the chosen cable's insulation can withstand a conductor temperature of 90 °C in

continuous operation. This means the ampacity of the conductor is higher than the calculated

one. The dimensioning have been made in this way to keep some margin to the recommended

maximum temperature of the AC- and DC terminals of 100 °C. Also, it is uncertain how the

shield affects the cooling of the conductor, and a dimensioning after the 90 °C conductor

temperature might show too high ampacity. The tabled values used in the dimensioning are

not valid for armoured single core cables, but nothing is said about shielded single core

cables.

Even though the dimensioning of cables have been made to keep margin to maximal

recommended temperature of the AC- and DC-terminals of the inverter, it is possible they

have been made without cause. This is due to the fact the cables are not connected directly to

the inverters. The bridge and the Flexibar both have a larger cross sectional area than the two

42

cables together, which mean they will not get as hot as the conductors inside the cables. The

solid copper bar of the bridge is not insulated which allows for better cooling than that of the

cables' conductors, which are insulated. With this is mind, some margin might be achieved to

maximum recommended temperatures of the AC- and DC terminals of the inverter even if the

tables values at 90 °C are used in the dimensioning. Heat simulations to show how much the

temperature is lowered from the connection point of the cables to the connection point on the

inverters could hence be of interest. The heat transfer to the surroundings will however

depend on the ΔT between conductors an ambient air, which is hard to know at this point.

Accurate results from a heat simulation will hence be hard to achieve.

Protective cage

The design of the protective cage which surround the inverters can cause inconvenience if the

heat sinks accumulate dust faster than the cleaning schedule says the heat sinks should be

cleaned. If dust accumulation becomes troublesome, the heat removing capability of the heat

sinks will get reduced. If reduced too much, the system might turn off due to too high heat

sink temperatures. This will mean air filters have to be added to filter the air before it is

pushed through the heat sinks. The addition of air filters will get obstructed by the perforated

cage. To obtain filtered air through the heat sinks, all air which can possible be pushed

through the heat sinks must be filtered and proposed solution of protecting the heat sinks

make filtering the air hard. A possible solution is to attach a duct to the inlet of the heat sinks

to obtain a desirable air filtering.

However, the proposed solution offer easy access to the heat sinks when they are to be

cleaned. The removal of the protective cages is easy due to the fact that they are screwed onto

the supportive leg structure and into the back of the cabinet.

EMC

The cabinet is fabricated in an EMC design. However, since it is needed to cut open holes in

the back of the cabinet to allow for the heat sinks to stick out, the barrier which shields against

EMI is compromised. The barrier will be compromised by the holes for flanges as well, but

the special electrically conducting gaskets used together with the flanges will, if not keep,

reduce the effect of the holes in the barrier.

The inverters will probably not be fastened to the back of the cabinet with an electrically

conducting gasket as the flanges are. Due to this, the holes made for the heat sinks will

probably reduce the EMC-properties of the cabinet.

If the cabinet is to be used in an environment which is known to be sensitive to EMI, it is

suggested more time is spent on investigating the effect of the heat sink holes in the cabinet.

To achieve EMC it is of importance that holes and seems are avoided in the barriers shielding

against EMI.

43

6 Conclusion During the iterative process of designing the cabinet, learning from proposed designs and

discussions have contributed to the final design. During the design process, non thought of

issues as bending radii of cables and limitations in manufacturing showed to have an impact

on the possible design.

The technical feasibility study show it is technically feasible to build the system described in

the report, however a trade-off will probably have to be made regarding EMC or IP-code

properties. A manufacturer of cabinets have been found which can fabricate a cabinet that

meet the requirements of the inverter. A solution to provide airflow over the inverters front

side have been found and the electrical connections have been designed in a way that fulfils

the inverters requirements.

The EMC properties of the cabinet are compromised by holes made to allow for the heat sink

to stick out through the cabinets back. In a future work it is suggested that time is spent on

investigating how much the EMC properties are affected by the holes made for the heat sinks.

The systems EMC properties will be important if it is to be implemented in an environment

sensitive to EMI.

44

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45

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46

[Accessed 15-5-2017].

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47

8 Appendix

Appendix A - Porjus U9SR - Konstruktionsdokumentation

Porjus U9SR - Konstruktionsdokumentation

Johan Frisk

___________________________________________________________________________

1FA392, Examensarbete i Energisystem, 30 hp 2017:05

Civilingenjörsprogrammet i energisystem Uppsala 2017

Innehållsförteckning

1 Inledning ........................................................................................................................... 50

2 Installation ........................................................................................................................ 51

2.1 SL150 ......................................................................................................................... 51

2.2 Fläktar på kylflänsar .................................................................................................. 51

2.3 Skena på isolatorer ..................................................................................................... 51

2.4 Kabelkanal för D-sub-kablar ..................................................................................... 52

2.5 Kablar för spänningsmatning och styrning av fläktar ............................................... 52

2.6 Fästen för fläktar inuti skåpet .................................................................................... 53

3 Åtdragningsmoment för elektriska förbindningar ............................................................ 54

3.1 SL150 ......................................................................................................................... 54

3.2 Generella åtdragningsmoment ................................................................................... 54

4 Elektriska förbindningar ................................................................................................... 55

4.1 Kabelskor och pressbackar ........................................................................................ 55

4.2 Skena - flexibar .......................................................................................................... 55

4.3 Flexibar - AC-terminal .............................................................................................. 56

4.4 Flexibar - DC-terminal .............................................................................................. 56

5 Jordning ............................................................................................................................ 57

6 Plåtar/beröringsskydd för kylflänsar ................................................................................ 57

7 Kablars böjningsradie ....................................................................................................... 57

8 Genomföringar ................................................................................................................. 58

8.1 Flänsar ....................................................................................................................... 58

8.2 Förskruvningar ........................................................................................................... 58

8.3 Oanvända genomföringar .......................................................................................... 58

9 Lyft ................................................................................................................................... 59

10 Utbyte av SL150 ............................................................................................................... 59

11 Referenser ......................................................................................................................... 60

50

1 Inledning Detta dokument sammanfattar information som kan vara till hjälp under installation av

utrustningen i U9SR.

I dokumentet finns information om bland annat åtdragningsmoment för bultar/muttrar på olika

anslutningspunkter.

Information om skåpets vikt, böjradie för kraftkablar och minsta anläggningsyta för flexibla

skenor (flexibar) återfinns också.

Tillverkaren av frekvensomriktarna (Semikron) kräver att kapslingsklassen för

frekvensomriktarens framsida är minst IP54. På grund av detta är det viktigt att hål som tas

upp eller hål för flänsar (FL21) som inte används, tätas.

Skåpen (för frekvensomrikatare samt kontrollutrustning) är tillverkade i ett EMC-utförande av

Elkapsling. Det innebär att samtliga genomföringar måste dessa vara av en EMC-typ för att

behålla det EMC-utförande som de levererats i. Till exempel behöver en särskild EMC-

packning, som har elektriskt kontakt med både fläns och skåp, användas vid tätning av hål av

typ FL21 (de rektangulära hålen). Den täckfläns som används måste dessutom vara tillverkad

i metall.

Systemet består av flera skåp. Ett skåp per fyra frekvensomriktare. Ett skåp som innehåller

kontrollutrustning som kan styra och övervaka fyra frekvensomriktare. Samt ett skåp

innehållandes den likriktningsutrustning som förser alla frekvensomriktare med den DC-

spänning de behöver.

En skiss av skåp för frekvensomriktare samt kontrollutrustning visas i Figur 1.1.

Figur 1.1 Skiss av de färdigmonterade skåpen. Framifrån (t.h.), från vänster (mitten) samt snett uppifrån vänster (t.h.)

51

2 Installation I detta avsnitt beskrivs tillvägagångssätt för installation av komponenter, till exempel

frekvensomformaren SEMIKUBE SlimLine (SL150) och tillhörande fläktar.

2.1 SL150

Lyft eller handha inte modulerna på någon annan plats än den som är avsedd för

modulerna. Idealt ska temperaturen vid installation vara mellan 5 °C och 30 °C.

Minst två hanteringspunkter på modulen ovansida måste användas vid lyft.

Skydda alla externa elektriska kontakter med kontaktfett (Electrolube ref: CG53A)

Installatören ska se till att anslutningar, kablar och skenor inte applicerar några

mekaniska spänningar på de elektriska terminalerna på SEMIKUBE SlimLine

Följ alla rekommendationer gällande ESD-skydd

o Använd alltid jordade armband vid anslutning eller urkoppling av kontrollern.

o Efter urkoppling av kontrollern, återmontera det skyddande skummet direkt

innan nedmonteringen av SEMIKUBE SlimLine fortsätter.

Vid montage av frekvensomformaren SL150 placeras de i hålbilden i skåpets ryggplåt men

skruvarna dras ej åt helt. Placera alla fyra SL150 och skruva ihop dem med varandra innan de

skruvas fast helt i plåten. (Semikron, 2016, sid. 20-21)

Fastsättningen i plåten görs med skruvförband M8 hållfasthetsklass 8.8 med räfflad

spännbricka, planbricka och mutter som i Figur 4.1. Åtdragningsmomenten får vara högst

18 Nm (Semikron, 2016, sid. 20-21)

2.2 Fläktar på kylflänsar Monteringen av fläktar görs efter att frekvensomriktarna har monterats i skåpet. Fläktarna

monteras i en push-konfiguration med fläktarna placerade på kylflänsens nedre kant.

Fläktarna monteras så att luft blåses genom kylflänsen. Uppmärksamma att pilen som visar

vilket håll fläkten flyttar luften pekar in mot kylflänsen.

Enligt kontaktpersonen på Semikron är fläktarnas prestanda i push- och pull-konfiguration

likvärdig. Hur de olika konfigurationerna påverkar kylflänsens värmeavgivande förmåga har

inte utvärderats. Valet att placera fläktarna på kylflänsarna nedkant har gjorts med avseende

på skydd mot fallande föremål. Sådana föremål kan vara en kvarglömd mutter eller

skruvmejsel på skåpets tak.

2.3 Skena på isolatorer Den skena som bildar övergång mellan kabel till generator och Flexibar till

frekvensomformarens AC-terminal svetsas fast i skåpets bakkant alternativt fastsättes med

minst två stycken skruvförband M8 och momentdrages enligt Tabell 2.

Om skenan väljs att fastsättas med skruvförband kommer skåpets IP-klass och separeringen

mellan frekvensomrikarnas fram- och baksida att äventyras. Separeringen mellan

frekvensomriktares fram- och baksida ska enligt tillverkaren vara IP54. Om infästning ändå

väljs att göras med skruvförband ska hålen göras så små som möjligt för att behålla skåpets

EMC-utförande i högsta möjliga grad.

52

Säkerställ att den metallskena (ankarskena) som isolatorerna är monterade på har elektrisk

kontakt med jord efter montering. Det högsta tillåtna elektriska motståndet till jord återfinns i

avsnitt 5.

2.4 Kabelkanal för D-sub-kablar

Kabelkanalen ovanför frekvensomriktarna är tänkt att vara en kabelväg för D-subkablar som

löper mellan skåpet med kontrollutrustning och skåpet med frekvensomriktare.

Kabelkanalen skruvas fast i fästen i skåpets bakkant. Fästena består av svetsade eller

punktsvetsade bitar av ankarskena. Ankarskenan är orienterad så att dess sida med störst

anläggningsyta är riktad utåt, mot en tänkt betraktare som tittar in i skåpet.

Detta sätt att montera kabelkanalen skapar inga skruvhål i skåpet. Hål kan försämra EMC-

egenskaper samt äventyra den kapslingsklass som separerar frekvensomriktarnas fram- och

baksida. Monteringssättet kräver svetsarbeten. Dessa utföres innan montering av

frekvensomriktarna för att minska risken att de tar skada av värme etc.

2.5 Kablar för spänningsmatning och styrning av fläktar Plastkanal som utgör kabelväg för spänningsmatning och signalkablar till de fläktar som sitter

monterade på frekvensomriktarnas baksida monteras på skåpets stödben. Plastkanalen skruvas

fast med lämplig skruv i skåpets stödben. Kablarna förläggs i vertikal stigarkanal till

respektive fläkts anslutningspunkt. Tänkt montagesätt visas i Figur 2.1.

Figur 2.1 Montering av kabelkanaler för kablar till kylflänsarnas fläktar. Svetsning eller punktsvetsning av ankarskena enligt

figuren för att inte äventyra kapslingsklass och eventuellt försämra skåpets EMC-egenskaper.

I Figur 2.1 visas hur de vertikala stigarkanalerna kan monteras utan att äventyra

kapslingsklass och EMC-egenskaper. Ankarskenor svetsas eller punktsvetsas fast och de

vertikala kanalerna kan sedan skruvas fast i dessa. För att minska risken för skada på

frekvensomriktarna kan svetsarbeten med fördel utföras innan montering av

frekvensomriktarna i skåpet.

Kablarna från skåpet för kontrollutrustningen kan dras genom de löstagbara sidorna på den

sockel som skåpet står på. Alternativit kan en vertikal kabelkanal monteras på kontrollskåpets

baksida och kabeldragningen ske ut från kontrollskåpets överdel.

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2.6 Fästen för fläktar inuti skåpet Fästen för de fläktar som blåser luft över frekvensomriktarnas framsidor skruvas fast med

mutterbricka eller T-skruv i samma skena som kopparskenan som bildar övergång från kabel

till Flexibar sätts fast i. Hålen i ankarskenan är 9 mm breda, om större skruv väljs behöver

uppborrning av de prefabricerade hålen i skenan göras.

Fästet består av en 200 mm lång montagevinkel och en bockad plastskiva. Den bockade

plastskivan och hur montagevinklarna är tänkta att monteras kan ses i Figur 2.2.

Figur 2.2 Fästplatta för de fläktar som monteras inuti skåpet

I Figur 2.2 går det även att se de utskurna vinklar som monteras på plastplattan insida. Dessa

vinklar är utskurna i samma vinkel som plastplattan är bockad och ska förhindra att den vinkel

som fläktarma monteras i inte ska förändras över tid.

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3 Åtdragningsmoment för elektriska förbindningar

3.1 SL150 Det vridmoment som anslutningarna ska dras åt med på Semikron SEMIKUBE SLIMLINE

150 (SL150) kan hittas i användarmanualen till SLIMLINE-serien. Anslutningarnas storlek

samt åtdragningsmoment kan ses i Tabell 1. (Semikron, 2016, sid. 27)

Tabell 1 Terminaler och deras respektive anslutningar samt åtdragningsmoment

Referens SL150

U, V, W 2xM12 - 50 Nm

PE M10 - 40 Nm

DC+, DC- 6xM8 - 15 Nm

Semikron specificerar inte om spännbrickor skall användas vid anslutningarna.

3.2 Generella åtdragningsmoment För skruvförband där inget moment är specificerat kan följande åtdragningsmoment

användas. Ett exempel på var dessa åtdragningsmoment kan användas är för anslutning av

kabelsko på kopparskena.

Den använda skruvens ytbehandling påverkar åtdragningsmomentet. För åtdragningsmoment

av en elförzinkad + blankkromaterad stålskruv plus mutter med hållfasthetsklass 8.8 används

Tabell 2. (Bulten, 1999)

Tabell 2 Åtdragningsmoment för elförzinkade + blankkromaterade stålskruvsförband. Åtdragningsmomenten är ett resultat

av multiplikation av omräkningsfaktor 0,96 med angivet åtdragningsmoment för obehandlad, anoljad stålskruv (Bulten,

1999).

Skruvstorlek Åtdragningsmoment

M6 9,5 Nm

M8 23 Nm

M10 45 Nm

M12 78 Nm

M16 200 Nm

För skruvförband med gjorda av andra material eller med andra ytbeskaffenheter hänvisas till

tabell 9.1 och 9.2 i Bultens Teknikhandbok. För att beräkna åtdragningsmoment för en

elförzinkad + blankkromaterad M14 används omräkningsfaktorn 0.96 (se tabell 9.1)

multiplicerat med det moment som anges i tabell 9.2. Det moment som en M14 elförzinkad +

blankkromaterad stålskruv skulle dras åt med blir enligt detta 0.96*128 Nm = 123 Nm.

(Bulten, 1999)

55

4 Elektriska förbindningar I detta avsnitt beskrivs hur de elektriska anslutningarna av frekvensomriktarna ska utföras.

4.1 Kabelskor och pressbackar För pressning av kabelskor finns pressverktyg från olika tillverkare. Här informeras endast om

ELPRESS men fler tillverkare och deras verktyg för kontaktpressning kan hittas i till exempel

produktkatalogen från Onninnen. I katalogen finns leverantörer som Pfisterer, ABB kabeldon,

Tyco Electronics och Ensto samt deras tillgängliga förbindningselement.

På kopparförbindningarna från ELPRESS framgår vilken ledararea de är avsedda för.

Typnummer för den back som skall användas vid kontaktpressning står också ingraverat på

förbindningarna. Om ledararean överstiger en viss storlek kan fler än en kontaktpressning

krävas. Pressningarna görs i dessa fall bredvid varandra, utan något överlapp. (Onninnen,

2017)

I Tabell 3 visas vilka pressbackar som ska användas för två av ELPRESS pressystem.

(Onninen, 2017, sid. 8 & sid. 11)

Tabell 3 System för kontaktpressning och backar för olika ledarareor

System V1300, Cu-ledare System V250, Cu-ledare

Ledararea

(mm2)

Back Antal pressningar Back Antal pressningar

240 13B30 2 B30 1)

1

300 13B32 2 B32 1)

1

400 13B38 3 B2538

2

500 - B2542

2

630 - B2553 3 1) Backhållare erfordras

För pressning av ELPRESS rörkabelsko för kopparförbindningar typ KSF/KRF med system

V1300, Cu-ledare används sexkantsbackar. För ledarareor i Tabell 3 behövs inga backhållare.

(Onninnen, 2017)

För pressning av ELPRESS rörkabelsko för kopparförbindningar typ KSF/KRF med system

V250, Cu-ledare används sexkantsbackar. Använd backhållare V2506 (E 08 200 60), V2608

(E 08200 61).

Det finns även kabelskor med skruvanslutning i produktkatalogen från Onninnen.

4.2 Skena - flexibar Anslutning mellan Flexibar och skena görs med skruvförband. Skruvförbandet består av bult,

spännbricka, planbricka och mutter. Anslutning görs enligt specifikation av Mericon och kan

ses i Figur 4.1.

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Figur 4.1 Anslutning av flexibar mot skena

Den yta som flexibar ansluts mot måste vara flat, men behöver inte vara polerad. Ytan måste

vara ren samt fri från oxid och fett. (Mericon, 2015, sid. 6)

Ytan på flexibar som anlägger mot skena måste vara minst 5 gånger flexibarens tjocklek

(Mericon, 2015, sid. 6). Exempel: Flexibaren har en dimension på 80x5 mm (bxh). Den

överlappande ytan får inte vara mindre än 5x5 mm = 25 mm.

4.3 Flexibar - AC-terminal Anslutning görs med tennpläterad flexibar från den skena som bildar övergång mellan kabel

och flexibar, se Figur 4.1. Momentdrages med momentet 50 Nm (enligt Tabell 1).

Anslutningen på AC-terminalen på SL150 är gjord av tennpläterad koppar eller av aluminium.

4.4 Flexibar - DC-terminal Anslutning görs med tennpläterad flexibar. Skruvförband på frekvensomriktaren åtdrages på

med moment 15 Nm enligt Tabell 1.

Rengör anslutningen på frekvensomrikaren. Under transporten eller under förvaringen av

frekvensomformaren hos leverantören kan damm ha ansamlats på anslutningen. (Semikron,

2016, sid.)

57

5 Jordning I användarmanualen till Semikrons SlimLine-serie (avsnitt 5.10) kan läsas att varje KUB

måste anslutas till skåpet och jordas. För SL150 som består av flera enheter specificeras inte

jordningsförfarandet men det antas vara detsamma som för övriga moduler i serien SlimLine.

Alla metalldelar vars uppgift inte är att eda elektricitet måste jordas. Efter jordning måste det

kontrolleras att motståndet mellan komponent och jord är högst 3 mΩ (Semikron, 2016)

6 Plåtar/beröringsskydd för kylflänsar Dessa kommer att leveras i ett delat utförande eftersom Elkapsling inte kunde tillverka dem i

ett stycke. Plåtarna ställs på stödbenen i samma nivå som skåpet och skruvas fast i den ram

som de ställs på.

Eftersom plåtarna levereras i ett två-delat utförande kan de komma att överlappa något där de

möts. Här kan det vara bra om de monteras så att ingen vass kant sticker ut utanför den ram

som de ställs på eftersom att plåtarna kommer att behöva demonteras för rengöring av

kylflänsarna och fläktar. Vid demontaget kan det finnas risk för skärskador på ben om

plåtarna monteras med utstickande kanter.

7 Kablars böjningsradie Den maximala böjningsradien för en kabel med motsvarande uppbyggnad som FXQJ, FXQJ-

EMC, AXQJ, AXQJ-EMC är åtta kabeldiametrar (8*D). Den maximala böjradien avser

kabelns böjradie efter installation. (Nexans, uå)

I examensarbetet har kabeln 602-RC-CY-J/O från Helu Cable hittats. Denna kabel går att

beställa med ledararea upp till 300 mm2. Kabeln är tillverkad i flertrådig koppar och har en

ytterdiameter på cirka 63 mm. Den minsta tillåtna böjningsradien vid fast installation är 3*D.

(Helu Kabel, 2015)

58

8 Genomföringar Tillverkaren av frekvensomriktarna (Semikron) kräver att kapslingsklassen för

frekvensomriktarens framsida är minst IP54. På grund av detta är det viktigt att hål som tas

upp eller hål för flänsar (FL21) som inte används, tätas.

För genomföringar i skåpet måste därför en sådan genomföring användas som inte reducerar

skåpets kapslingsklass till lägre än IP54.

8.1 Flänsar Vid montage av flänsar i skåp med EMC-utförande ska särskild flänspackning användas.

Kontaktytan mellan flänspackning-skåp samt kontaktytan mellan flänspackning-fläns måste

vara elektriskt ledande för att behålla skåpets EMC-utförande.

Att skrapa bort eventuell färg så att skruv och mutter får elektrisk kontakt med fläns kan vara

en god ide eftersom de särskilda EMC-förskruvningarna ska jorda kabelns skärm.

Flänspackningen ska vara elektriskt ledande men kontrollera ändå att fläns och skåp har

elektrisk kontakt.

8.2 Förskruvningar Vid montage av förskruvningar i skåp med EMC-utförande ska dessa vara av EMC-typ.

8.3 Oanvända genomföringar Oanvända genomföringar måste tätas med täckfläns och EMC-packning för att behålla

skåpets EMC-utförande. Kontaktytan mellan skåp och packning samt kontaktytan mellan

täckfläns och packning måste vara elektriskt ledande för att behålla det EMC-utförande som

skåpen levererats i.

Om blindproppar används för att täta hål i flänsar, måste dessa vara tillverkade i metall.

59

9 Lyft Vid lyft av skåpet används de lyftöglor som finns monterade. Information om skåpets vikt

utan komponenter har vid upprättandet av konstruktionsdokumentationen inte varit

tillgänglig. På Elkapslings webbsida finns information om att ett liknande skåp (USO 180

80/80 50) väger 200 kg. Det föreslagna skåpet i examensarbetet återfinns inte i tillverkarens

produktkatalog (det föreslagna skåpets mått: 160 80/80 40).

De fyra frekvensomriktarna väger 130 kg med fläktar monterade. Vid lyft av

frekvensomriktarna används de lyftöglor som finns. En frekvensomformare utan fläkt väger

30.8 kg. Vid lyft av frekvensomriktare se avsnitt 2.3, 3.1 samt 8.7 för lyftanvisningar.

(Semikron, 2016)

10 Utbyte av SL150 Se avsnitt 8.7 i användarmanualen

Ta bort alla elektriska anslutningar till frekvensomriktaren i följande ordning:

Lossa alla kraftkablar från AC- och DC-terminaler. Notera deras respektive

anslutningspunkt.

Lossa de kablar för styrning och kontroll som är anslutna på frekvensomriktaren

Säkerställ att SEMIKUBE SlimLine har svalnat

Modulerna är ömtåliga och känsliga mot skada - hantera varsamt

Lyft eller flytta dem genom att använda lyftpunkterna

Lägg dem ned på den plana sidan när de inte är monterade i en ram.

Lämna inte modulerna utan stöd i deras upprätta position

När en modul ska bytas ut eller lossas krävs en kran och att två personer är närvarande.

Lossa på fläktarna

Lossa modulen från sin ram genom att skruva loss de 8xM8-skruvar som håller fast

modulen.

Dra ut modulen tills lyftöglan i modulen överkant är åtkomlig, fäst sedan kranens

schackel i lyftöglan i modulen övre del.

Låt kranen ta upp modulens vikt och dra försiktigt ut modulen från dess ram.

Med kranen fullständigt lyftandes modulens vikt, dra ut modulen helt från sin ram.

Med modulen hängandes i kranen och med person två som håller den i en vertikal

position, flytta modulen till en säker plats och placerad den med sin undersida

(Semikron, 2016, avsnitt 8.7)

Det rekommenderas starkt att läsa detta avsnitt i användarmanualen för att förhindra att

eventuell misstolkning vid översättning orsakar olägenhet.

60

11 Referenser Bulten. (1999). Ordning ur kaos. Hallstahammar: Bulten. [Broschyr] Tillgänglig:

http://www.exx.se/techinfo/docs/bultens_teknikhandbok.pdf [2017-02-15]

Helu Kabel. (2015). Single 602-RC -CY -J/O special single core cable

for drag chains, 90°C, 600 V, EMC-preferred type, meter marking. [Broschyr] Tillgänglig:

https://www.helukabel.de/pdf/ks/1KS_69631_en.pdf [2017-04-26]

Mericon. (2015). Distrubutionskomponenter Nr 2015:1. Hammarö: Mericon. [Broschyr]

Tillgänglig: http://www.mericon.se/wp-content/uploads/2015/08/Mericon-huvudkat-dist-

komp.pdf [2017-02-14]

Nexans. (uå). Kabelboken Eldistribution - Installation. Grimsås: Nexans Sweden AB.

[Broschyr] Tillgänglig: http://www.nexans.com/Sweden/files/Kabelboken140630.pdf [2017-

02-11]

Onninnen. (2017). Produktkatalog - Förbindninngsmateriel. [Broschyr] Örebro: Onninnen

AB. Tillgänglig:

http://www.onninen.com/sweden/produkter/onnline/Documents/Flik_04_Forbindningsmtrl.pd

f [2017-02-14]

PBM kabel. (2017). PBM 901NCP – Högflexibel skärmad enkelledare för släpkedjor.

Enköping: PBM kabel. [Broschyr] Tillgänglig: http://www.pbmkabel.se/wp-

content/uploads/2014/09/PBM-901NCP-%E2%80%93-H%C3%B6gflexibel-

sk%C3%A4rmad-enkelledare-f%C3%B6r-sl%C3%A4pkedjor.pdf [2017-03-06]

Semikron. (2015). SKS SL SL150 GD 50/10 - E4 P1. Semikron [Broschyr] Tillgänglig:

https://www.semikron.com/dl/service-support/downloads/download/semikron-datasheet-sks-

sl-150-gd-50-10-e4-p1-af-08801380 [2017-02-16]

Semikron. (2016). SEMIKUBE SlimLine User Manual.

61

Appendix B - Material

62

63

Appendix C1 - Inverter cabinet drawing

64

Appendix C2 - Control cabinet drawing