Chapter 11 Power Cables

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Chapter 11 Power Cables

Touristic Village with Renewable Energy Generation

Chapter 11

Power cables




Touristic Village with Renewable Energy Generation 2

11.1 Introduction

11.1.1 General Layout of the System

The conductor system by means of which electric power is conveyedfrom a generating station to the consumer’s premises may, in general,

be divided into two distinct parts i.etransmission system and distribution

system. Each part can again be sub-divided into two — primary

transmission and secondary transmission and similarly, primary

distribution and secondary distribution and then finally the system of

supply to individual consumers. Atypical layout of a generating,

transmission and distribution network of a large system would be made

up of elements as shown by a single-line diagram of Fig. 11.1 although

it has to be realized that one or more of these elements may be missing

in any particular system. For example, in a certain system, there maybe no secondary transmission and in another case, when the

generating station is nearby, there may be no transmission and thedistribution system proper may begin at the generator bus-bars.

Now-a-days, generation and transmission is

almost exclusively three-phase. The

secondary trans-mission is also 3-phase

whereas the distribution to the ultimate

customer may be 3-phase or single-phase

depending upon the requirements of thecustomers.

In Fig. 11.1 C.S. represents the central

station where power is generated by 3-

phase alternators at 6.6 or 11 or 13.2 or

even 32 kV. The voltage is then stepped up

by suitable 3-phase transformers for

transmission purposes. Taking the

generated voltage as 11 kV, the 3-phasetransformers step it up to 132kV as shown.

Primary or high-voltage transmission is

carried out at 132 kV

The 3-phase, 3-wire overhead high-voltage transmission line next

terminates in step-down trans-formers in a sub-station known as

Receiving Station R.Swhich usually lies at the outskirts of a citybecause

it is not safe to bring high-voltage overhead transmission lines intothickly-populated areas.

Figure11.1





Here, the voltage is stepped down to 33 kV. It may be noted here that

for ensuring continuity ofservicetransmission is always by duplicate

linesFrom the Receiving Station, power is next transmitted at 33 kV by

underground cables (andoccasionally by overhead lines) to varioussub-stations (SS) located at various strategic points in thecity. This is

known as secondary or low-voltage transmission. From now onwards

starts the primary and secondary distribution.

At the sub-station (SS) voltage is reduced from 33kV to 3.3kV 3-wire for

primary distribution.Consumers whose demands exceeds 50 kVA are

usually supplied fromSSby special 3.3 kV feeders.The secondary

distribution is done at 400/230 V for which purpose voltage is reduced

from3.3kV to 400 V at the distribution sub-stations.

Feeders radiating from distribution sub-stationsupply power to

distribution networks in their respective areas. If the distribution network

happens tobe at a great distance from sub-station, then they are

supplied from the secondaries of distributiontransformers which are

either pole-mounted or else housed in kiosks at suitable points of the

distribu-tion networks. The most common system for secondary

distribution is 400/230-V, 3-phase 4-wiresystem. The single-phase

residential lighting load is connected between any one line and the

neutral.

Note: Voltage levels are defined internationally, as follows:

Low voltage: up to 1000 V

Medium voltage: above 1000 V up to 36 kV

High voltage: above 36 kV

Supply standards variation between continents by two general

standards have emergedas the dominant ones:

In Europe

IEC governs supply standards

The frequency is 50 Hz and LV voltage is 230/400 V

In North America

IEEE/ANSI governs supply standards

The frequency is 60 Hz and the LV voltage is 110/190 V.





12.1.2 Difference between over head lines and under ground

systems

Overhead lines are far cheaper than underground cables for long

distances, mainly due

to the fact that air is used as the insulation medium between phase

conductors. The

support masts of overhead lines are quite a significant portion of the

costs, that is the

reason why aluminum lines are often used instead of copper, as

aluminum lines weight

less than copper, and are less expensive.

However,copper has a higher current conducting capacity than

aluminum per square mm, so once again the most economical line

design will depend on many factors.

Overhead lines are by nature prone to lightning strikes, causing a

temporary surge on

the line, usually causing flashover between phases or phase to ground.

This is of shortduration, and as soon as it is cleared, normal operation may be

resumed. Auto-reclosers

are employed on an increasing number of overhead lines.

And this table show the main advantages and disadvantages for both

systems as shown in ( table 1)





Over head lines Under ground systems

Advantages

Less expensive for longerdistances.

Easy to locate fault.

Advantages

Less expensive for shorterdistances

Not susceptible to lightning

Environment-friendly

Not maintenance intensive

Disadvantages

More expensive for shorter

distances

Susceptible to lightning

Not environment-friendly

Maintenance intensive High level of expertise and

specialized equipment needed for

installation.

Underground (buried) cable

installations are mostly used for

power distribution in industrial

applications.

Disadvantages

Expensive for long distances

Can be difficult to locate

fault.

Table 1

Overhead distribution or transmission becomes difficult in populatedarea like cities

and towns. in such areas necessary to use cable laid below the ground

surface . these

are known as underground cables.

All cables are fundamentally similar in that they contain conductors for

carrying current

, insulation for surrounding the conductors , and some form of covering

to provide

mechanical and possible corrosion protection to ensure that theinsulator may continue

to operate is satisfactorily through the life of the cable once the cable

has been installed.

The primary function of the cable is to carry energy reliably between

source and utilization. In carrying this energy ,there are heat losses

generated in the cable that must

be dissipated. The ability to dissipate these losses depends on how the

cable are

insulated ,and this affects their ratings.





The selections of conductor size requires consideration of the load

current to be carried

and the load cycle ,emergency overloading requirements and

duration ,fault clearing

time and interrupting capacity of the cable over current protection orsource capacity,

voltage drop ,d ambient temperatures for particular installation

conditions.

Cable may be installed in cable trays , underground in duct or direct

buried , in cable

bus ,or open runs of the cable.

12.2 cable construction

A typical cable is comprised of

conductors shielded by varioustypes of

material(see Figure 11.2).

Cables may have single core ,two

cores ,three cores

ormore.Cable core is a conductor

surrounded by insulating material which

isolates it from other

cable cores . Single – core cables are

preferred when more flexibility and

installation simplicity are required .

on other hand ,three-core cables are more economical and acquire

better electrical performance in three-phase transmission and

distribution.

11.2.1 Cable conductors:The core conductor is the current carrying conducting material of the

underground

power cable. The two conductor materials in common use are copper

and aluminum.

Copper has historically been used for conductors of insulated cables

primarily for its desirable electrical and mechanical properties. The use

of aluminum is based mainly on its favorable conductivity-to-weight

ratio, its ready availability, and the stable low cost of the primary metal.

Fig 11.2 cable construction





11.2.1.1 Comparison Between Copper and Aluminum.

Aluminum requires largerconductor sizes to carry the same current as

copper. The equivalent aluminum cable, whencompared to copper in

terms of ampacity, will be lighter in weight and larger in diameter . To decrease cross-sectional area of extra high voltage cable,

hard drawn copper core

conductors are used (Aluminum conductivity = 60% Copper

conductivity).

The hard drawn copper conductors are preferred in low-voltage

networks, as copper

material can withstand thermal stress during overloading operations

compared with

aluminum conductors.

The hard drawn aluminum conductors are commonly used inmedium-voltage and

high-voltage distribution networks to decrease costs where the three-

phase load

balancing and hence overloading problem is minimized.

12.2.1.2 Classes of Conductors

Conductors are classified as solid or stranded. A solidconductor is a

single conductor of solid circular section. A stranded conductor is

composed of a group of small conductors in common contact.

A stranded conductor is used where the solid conductor is too large

and not flexible enough to be handled readily. Large solid conductors

are also easily damaged by bending. The need for mechanical

flexibility usually determines whether a solid or astranded conductor is

used, and the degree of flexibility is a function of the totalnumber of

strands.

Fig11.3 Coparison between copper and





The strands in the stranded conductor are usually arranged in

concentric layers about a central core. The smallest number of wires in

a stranded conductor is three. The next number of strands are 7, 19, 37,

61, 91, 127, etc. Both copper and aluminum conductors may be

stranded as shown in figure 12.3

11.2.2 Cable Insulators:

There are many insulations (or dielectric materials) used in producing

the various

cables to deliver electric power. Cable insulation materials include oil

impregnatedpaper,

rubber , and extruded (or polymeric) insulations.

11.2.2.1 Insulating material should achieve the followingrequirement:

Long life

High dielectric strength

High resistance to corona and ionization

Resistance to high temperatures

Mechanical flexibility

Resistance to humidity

Low insulation losses

It is classified into three main categories:

Natural type :Such as Fabrics – Rubber – Wood – Papers.

Synthetic materials : Such asPolymeric Materials for Insulation

Polymeric insulations (known also as Extruded insulations) are long

chainhydrocarbon thermoplastic materials which are produced by the

polymerization

of petrochemical products like ethylene gas under high pressure

andtemperature. Extruded insulations used for wire and cable are

classified into twomain types:

Figure11.3 Stranded wires core conductors





11.2.2.2 Thermoplastic materials

that tend to lose their form upon subsequent heating. Polyethylene (PE)

and Polyvinyl chloride (PVC) are the most common thermoplastic type

extruded insulations.

For the power cable polyvinylchloride (pvc)is the most widely used

thermoplastic

insulation. Polyethylene being used in frequently and then only for high

voltages.

PVC insulating compounds have excellent electrical properties suited

to power cables

used up to including 3.3Kv ,but at higher voltages the material is not

suitable, mainly

because it has a relatively high dielectric constant and dielectric losses

become high.

One electrical characteristics of a PVC which is often not appreciated

in the fact that its

insulation resistance varies quite considerably with temperature .At 70

℃a PVC-insulated cable has an insulation resistance some 700 to1000

times less than the value at20℃.

Being thermoplastic material ,PVC is harder at lower temperatures and

becomes

progressively softer with increasing temperature .The grades of PVC

used for mains cables are designed for conductor continuous

operating temperatures of 70 ℃ and under short-circuit conditions the

conductor temperature should never exceed 1600C ,otherwise the

core insulation would flow and the cable would become permanentlydamaged.





11.2.2.3 Thermosetting materials

That tend to maintain their form upon subsequent heating. These

extruded insulations range from Cross linked Polyethylene (XLPE) and

Ethylene-Propylene Rubber (EPR) to the most recent advances in Tree-retardant Cross linked Polyethylene (TR-XLPE).

Almost all XLBE is made from high density polyethylene (HDPE). XLBEcontains

crosslinkedbonds in the polymer structure , changing the thermoplastic

to a thermoset.

Cross-linking is accomplished during or after the extrusion of the tubing.

The required

degree of cross-linking, according to ASTM (American Society for

Testing andMaterials) Standard F 876-93, is between 65 and 89%. A

higher degree of cross-linkingcould result in brittleness and stress

cracking of the material.

The high-temperature properties of the polymer are improved.

Adequate strength to

120-150°C is maintained by reducing the tendency to flow. Chemical

resistance is

enhanced by resisting dissolution. Low temperature properties are

improved. Impact

and tensile strength, scratch resistance, and resistance to brittle

fracture are enhanced.

XLPE-insulated cables have a rated maximum conductor temperature

of 90°C and an

emergency rating up to 140°C, depending on the standard used. They

have a conductor

short-circuit rating of 250°C. XLPE has excellent dielectric properties,

making it useful

for medium voltage - 10 to 50 kV AC - and high voltage cables - up to

380 kV AC voltage,and several hundred kV DC.




Touristic Village with Renewable Energy Generation

12.2.2.4 comparison the different characteristics of

PVC, XLPE, and EPR

type extruded insulation power cables:

characteristics PVC XLBE

Chemical Structure Thermoplastic Polar Themoset, pure

Hydrocarbon.

Polymer Structure Amorphous Partial Crystalline

Recommended

continuous

working temperature

at

conductor surface in

°c

70 90

Intermittent

temperature

rating during

overloading

in°c

120 130

Maximum

temperature

during short-circuit °c

160 250

Current Carrying

Capacity

___________ 30% Higher than PVC

Dielectric Strength

(KV/mm)

350 550

Low Temperature

Brittleness

Deg. C

-15 -90

Mechanical and

electricalproperties at high

temperature during

overloading and long

shortcircuitperiods

Degraded muchwhen heating over

105 °c

Change slightly as

temperature increasesand does not melt at 105°c

Flexibility Flexible Hard to bend

Application Wiring installation

inside building

Primary feeder in MV

and in HV &EHV

systems

Acid Resistance Fair Excellent





In this project

PVC cables is used for low voltage application.

XLPE cables is used for High voltage application.

11.2.3 Shielding of Higher Voltage Cable

For operating voltages below 2 kV, nonshielded constructions are

normally used.

Insulation shielding is required for all nonmetallic, sheathed,single-

conductor cables operating above 2 kV and all metallic sheathed

cables and multiconductor cables

above 5 kV.

11.2.3.1 Procedure

Shielding is the practice of confining the electric field of the cable to

the insulation surrounding the conductor by means of conducting or

semiconducting layers,

closely fitting or bonded to the inner and outer surfaces of the

insulation. In other words, theouter shield confines the electric field to

the space between conductor and shield. The inner or strand stress

relief layer is at or near the conductor potential. The outer or insulationshield is designed to carry the charging currents and in many cases

fault currents.

11.2.3.2 Purpose

Insulation shields have several purposes:

Confine the electric field within the cable.

Equalize voltage stress within the insulation, minimizing surface

discharges.

Protect cable from induced potentials.

Limit electromagnetic or electrostatic interference (radio, TV,etc.).

Reduce shock hazard (when properly grounded).

11.2.4 Metallic Sheaths:

Materials used for cable sheathing are lead layer, aluminum layer or

copper wire.

The main function of it is to provide:

Good method of cable earthing.

Good path to the fault current.





12.2.4.1 Lead Sheathing:

Lead is one of the oldest sheathing materials used on power cables,

dating back to the

early 1900s. Use of lead sheaths has proven to be a very effective

moisture barriercontributing to long-term reliability of cable systems.

Disadvantage of lead sheaths is that:

They add a great deal of weight to the cable.

Lead sheaths are prone to deformation under continuous load

conditions due to the

creep characteristics of the material.

Also, lead sheaths are susceptible to failure due to metal fatigue

caused by

mechanical vibration or thermal cycling.

11.2.4.2 Aluminum Sheathing

Aluminum sheathing began to appear in the late 1940s. Aluminum is

attractive because

it is much lighter than lead and has good mechanical properties.

However, extra sheath

losses caused by eddy currents can be generated because Aluminummetal has higher

conductivity compared with lead sheath type.

11.2.5 Armoring:

Armoring is primarily used to protect the cable mechanically and add

strength to the

cable A flat galvanized steel metal tape is helically wrapped around

the cable core. The

tape is typically protected by an outer covering. Applications include

commercial or

industrial installations in conduit, ducts, troughs, and raceways.





11.2.5.1 Steel -tape armoring.

the steel tape is provided over the bending and they aren't very

flexible , and their use is limited where the bending of the cables can

not be avoided .

Figure 1

11.2.5.2 wire armoring

It has been found that asingle layer of wire armoring provides abettermechanical protection as against two layer of steel tape

Figure 2

11.2.6 Nonmetallic jackets:

Jackets, also called sheaths, are external covering layers that can

serve several purposes:

They provide mechanical, thermal, chemical and environmental

protection to the

insulated conductors they enclose.

They may act as electrical insulation when used over shields or

armor.

They ease installation and routing concerns by enclosing multipleinsulated

conductors.

They may also protect the characteristics of the underlying

insulation, for example,

a thin nylon jacket over PVC enhances the abrasion and fluid

resistance of a 600v

cable.





11.2.7 Bedding

It is an inner sheath of bituminous paper over the lead metal sheath to

provide: Round cross-section-area of cables to take largest volume in

least space area.

Separate the metallic sheath from the armored layer to prevent

galvanic

corrosion.

12.3 Cable selection

When selecting a cable for your specific application, a number ofvariables

require attention. These are:

Application (voltage rating)

Size and type of load to be supplied.

Emergency overload criteria.

Permissible voltage drop.

Prospective fault current.

Circuit protection.

Installation conditions.

11.3.1 Application

The selection of the cable insulation (voltage) rating is based on: the

phase-to-phase voltage of the system in which the cable is to be

applied, the general system category (depending on whether the

system is grounded or ungrounded), and the time in which a ground

fault on the system is cleared by protective equipment.

11.3.1.1 Low-voltage distribution

For LV distribution purposes, the choice is basically between XLPE and

PVC-

insulatedcables. The XLPE cables have higher current ratings than PVC

cables

for the sameconductor size, Normally XLPE cables tend to be slightly

moreexpensive than PVC cables.





The choice between these two types for LV applications will normally

be

determined by economic considerations (the relative prices at that

stage)andavailability. Bear in mind that a slightly smaller XLPE cable can be

chosen

for the same current requirement, which have other spin-offs, for

example

space-saving on cable racks or in trenches, slightly reduced labor costs

for installation, etc.

12.3.1.2 Medium-voltage distribution

For MV applications, the choice is more involved. First of all, the choice

lies between

overhead lines and underground cables. Nowadays, the tendency is to

move toward

underground cables for distribution purposes, which stated in the

previous.

where they are very economic compared to underground

cables.overhead lines are

mainlyconsidered for applications over relatively large distances,

where they are very economic compared to underground cables.

The next choice is then between aluminum or copper conductors.

Aluminum

conductors are larger than copper conductors for the same current-

carrying capacity,

which may add to installation costs. The choice will mainly be aneconomic one,

influenced by availability and the relative prices of the two metals at

that stage.

Aluminum conductors may be considered in high corrosive areas.

The third choice is the question of cable insulation type. For normal

distribution

purposes, the choice lies between PVC- or XLPE-insulated cables.





11.3.2 Load to be supplied

In order to select the appropriate cable, it is necessary to know the

voltage and the loadcurrent, as the first step in the selection process. The following formulae

apply:

,in case of knowing voltage, and power factor

, in case of knowing the kVA rating and voltage

Use this value of current to determine the cable size by reference to

the relevant

manufacturer’s tables for copper or aluminum conductors.

A slightly larger conductor size may be chosen for safety aspects, and

to provide for the

higher than usual current, which may be according to derating factors

in normal cases.

the starting current of electrical motor should be taken in our

calculation of the cable.

The deratinf factors can be obtained from the tables like in the project

from (ELSEWEDY

Power Cables Catalogue)

Then the manufacturer's ampacity recommendations should be

usedas load current criteria.

Ampacity tables indicate the minimum size conductor required,

however, conservative

engineering practice, future load growth considerations, voltage drop,

and short circuit

considerations may require the use of larger conductors.

IfL = KW× 1000√ 3 × × cos ∅

IfL = KVA× 1000√ 3 ×





11.3.3 Standard Cable Installation Conditions

Standard installation conditions for cables that are installed in free air

includes:

Ambient air temperature is 25 ℃ for transmission and distribution

cables, 30 ℃

forindoor wiring and 35 ℃ for wiring installations in ships.

Minimum distance between cable and wall is 20 mm.

Minimum distance between the cable and neighboring one is

150 cm.

Cable is isolated from direct sun rays.

While the standard installation conditions for cables that are directly

buried in ground

includes:

Soil temperature is 15℃

Thermal resistivity of soil is 1.2 ℃m/W.

Minimum distance between the cable and neighboring one is

1.8 m.

Buried depth is 0.5 m for 1-kV cables and 0.8 m for cables higher

than 1kV.

12.3.4 Emergency overload criteria

Normal loading limits of insulated wire and cable are determined

based on many years of practical experience. These limits account for

a rate of insulation deterioration that results in the most economical

and useful life of such cable systems.

The anticipated rate of deterioration equates to a useful life of

approximately 20 to 30 years. The life of cable insulation may be

halved, and the average thermal failure rate almost doubled for each

5 to 15 ℃increase in normal daily load temperature.

The normal daily load temperature is the average conductor

temperature over a typical 24 hour period. It reflects both the change

in ambient temperature and the change in conductor temperature

due to daily load fluctuations.





Additionally, sustained operation over and above maximum rated

operating temperatures or ampacities is not an effective or

economical practice, because the temperature rise is directly

proportional to the conductor loss, which increases as the square of

the current. The intensified voltage drop may also increase the risks toequipment and service continuity.

Maximumemergency overload temperatures for various types of

insulation have been established and are available as a practical

guide. Operation at these emergency overload temperatures should

not exceed 100 hours per year, and such 100 hour overload periods

should not exceed five during the life of the cable.

11.3.5 Permissible voltage drop:

The supply conductor, if not of sufficient size, will cause excessive

voltage drop in the circuit, and the drop will be in direct proportion to

the circuit length. Proper starting and running of motors, lighting

equipment, and other loads having heavy inrush currents must be

considered. It is recommended that the steady state voltage drop in

distribution feeders be no more than Five percent (5%)

And it will be stated in this chapter in details.

11.3.6 Cable Short Circuit Capacity :

The wiring design and installation of cable circuits requires an

adequate selection of the

nominal cross-sectional area based on:

Continuous current loading under practical installation

conditions of cable circuits.

Cable short-circuit capacity at duration starts from short-circuit

instant untilcomplete interruption by automatic circuit-breakers.

Under short-circuit conditions the temperature of the conductor rises

rapidly then, due to the thermal characteristics of the insulation,

sheath, and surrounding materials, it cools off slowly after the short-

circuit condition is cleared.

A transient temperature limit for each type of insulation for short-circuit

durations not in excess of 10 seconds has been established, and many





times this criterion is used to determine minimum conductor size.

Insulated Power Cable Engineers Association (IPCEA) standards define

the maximum conductor temperature limits allowable under worst-

case fault conditions.

Cable insulations among other cable layers that are affected much

with heat dissipationduring short-circuit, where the maximum

recommended temperature

θmax not toexceed 160 ℃ for PVC-insulation and 2500C for XLPE-

insulation

The maximum short-circuit current period (T) in seconds changes in an

inverse

relationship to the cable r.m.s short circuit capacity (Isc) in amperes as

shown in the

following formula:

S: is the normal cross-section area of core conductor in

mm

θ: is the recommended cable temperature for continuous operation

(70℃ for

PVC insulation, and 90℃ for XLPE-insulation

α, β:are constants depending upon materials of core conductor and

metallic sheath layer

(as indicated in the next )

T:Clearing time in (sec) It is recommended to select an adequate

nominal cross-sectionalarea of core conductor to carry short-circuit current less than short-

circuit current

capacity during 1 or 3 seconds standard interrupting duration

Material

Copper 256 234.5

Aluminum 148 228

Isc = αsT × l n (θmax+β

θo + β )

Diffirent values of ,





11.4 Classification of cables according to voltage

Cables are usually classified according to their operating voltage as

follows:

Low voltage cables (up to 1kv).

Figure 3

Medium voltage cables (3KV to 30KV)

Figure 4

High voltage cables(30KV to 500KV)

Figure 5





12.4.1 Low Voltage CablesThe following tables is up to(0.6/1KV)

300/500 V & 450/750 V

Figure 5

300/500 V & 450/750 V

Figure 6

300/500 V

Figure 7





0.6/1 (1.2) kV

Figure 8

0.6/1 (1.2) kV

Figure 9

0.6/1 (1.2) kV

Figure 10





0.6/1 (1.2) kV

Figure 11

0.6/1 (1.2) kV

Figure 12

0.6/1 (1.2) kV

Figure 13





0.6/1 (1.2) kV

Figure 14

0.6/1 (1.2) kV

Figure 15

0.6/1 (1.2) kV

Figure 16





0.6/1 (1.2) kV

Figure 17

0.6/1 (1.2) kV

Figure 18

0.6/1 (1.2) kV

Figure 19





11.4.2 Medium Voltage Cablesoperating voltage from 6/10 kV up to 18/30 Kv

6/10 (12) kV

Figure 20

6/10 (12) kV

Figure 21

6/10 (12) kV

Figure 22





6/10 (12) kV

Figure 23

8.5/15 (17.5) kV

Figure 24

8.5/15 (17.5) kV

Figure 25





38/66 (72.5) kV

Figure62

38/66 (72.5) kV

Figure 27

11.5 Determination of cable faults:

11.5.1 Reasons of cable faults :

mechanical factors.

Electrochemical factors.

bad industry.

bad burial, elongation and tide.

bad welding.

bad loading.





11.5.2 Types of faults:

single line to ground fault.

Double line to ground fault.

Three phase to ground fault.

Phase to phase fault.

Three phase fault.

11.5.3 Method of fault determination:

1) High voltage test (high voltage with small current).

2) Burning of fault location on the cable (high current with low

voltage).

3) Determine of fault location.

11.5.3.1the high voltage test:

First the faulted cable should be disconnected from starting

terminal and from endingterminal.

this cable is tested to determine the quality of insulation.

Rules of this test:

a)

inject each phase with voltage equal to three times the

operating voltage of the

cable (this voltage around 35KV for the new 11KV cable and 33KV for

the old 11KV

cable)

b) the second test in case of old cables it will be two times the

operating voltage

(25Kv for 11Kv cable).

c) each phase tested for 15 minutes.

d)

if the cable is good ,it will withstand the tested voltage.

e) it is not allowable to leak more than 150 micro ampere foe each

1 K.M from the

length of the cable .if the leakage current more than 150 micro

ampere ,that’s a

good indication that there is a fault.the values of leakage currents in

each phase

should be close to each other.





11.5.3.2 burning the fault location:

Inject the cable with high current and low voltage to burn the fault

location.

11.5.3.3 determination of the fault location:

The distance= speed(V)×time (t)

Distance of fault=×

11.6 Precautions burial of the cable:

it must be the shortest path and has low curvature.

Far from the paths of modern tree planting paths.

Far from the paths of public services.

Far from the ground which has high level from salts and acids, if it

is important

to follow through them. it should be put on special pipes against them.

Far from the paths of electrical trains and if it is important, it

should be made

earthed for the cable with the earthed bars.

Far from the paths of trains to avoid shakings and if it is important,

the cable should

be put in pipe makes from galvanized steel or from PVC .

11.6.1 Cable trenches:

There are different methods for laying depended on cable type, cable

importance & soil

surrounding cable. Such as:

Cables laid in ducts: this method for vital cable and for crossing

ways. Man holes aremade to maintain & repair the cable easily when a fault occurs.

Metallic shield: it

used when the cable is near to railways or duct of pipe lines to prevent

galvanic

corrosion.

Conduits (pipes) which used for buildings (walls & ceilings).

The cables laid in bitumen compound. This method is used where

the soil is

chemically corrosive to the cable.





11.6.2 Rules for burring of cable trenches:

The burial depth not less than 70Cm.

A layer of sands should be put with 10cm then put the cable on it

directly. Again put a layer of sand on the cable until reaches to 20cm

from burial depth.

Put bricks along the path of the cable as guidelines.

Put the original soil which is extracted during the process of burial

until reaches to

20cm from the edge of the hole and put warning strip at this deep then

make the

process of asphalt for the street.

Important note:

In the project, the cables not direct buried into soil but the cable are

put in the ducts.

Figure 28





12.7 cable selection for the project

The Diversty factor of different places in the village used to determining

the rating current is placed in the following table

1-Transformer 1 region cable selection:

Place

Lighting sockets

mosque 1 0.3

Food court 1 1

Hotel 0.5 0.6

Mall 0.7 0.3

administration building 0.7 0.5

chalet 0.5 0.8

cinema 0.2 0.3

Diversty factor

Location Ratedcurrent(A)

Cablecurrent(A)

Cable Type No ofcables

Corresponding

CSA( mm)

Bus way to GRD

Floor panel board

35.89 44.86 Multicore cables,stranded Copper

Conductors PVC Insulated PVC

sheathed laid in duct

1 (3× 1 0 +10)+10

Bus way to Floor 1

panel board




1 (3× 1.5 + 1.5)

+1.5

Bus way to Floor 2

panel board


Conductors PVC Insulated

PVCsheathed laid in duct

1 (3× 1.5 + 1.5)

+1.5

Bus way to Floor 3

panel board




1 (3× 1.5 + 1.5)

+1.5

Bus way to Floor 4

panel board




1 (3× 1.5 + 1.5)

+1.5

Bus way to Floor 5

panel board




1 (3× 1.5 + 1.5)

+1.5

Bus way to Floor 6

panel board




1 (3× 1.5 + 1.5)

+1.5

Bus way to Floor 7panel board

10.44 13.05 Multicore cables,stranded CopperConductors PVC Insulated


1 (3× 1.5 + 1.5)+1.5

Bus way to Floor 8

panel board




1 (3× 1.5 + 1.5)

+1.5

Bus way to Floor 9

panel board




1 (3× 1.5 + 1.5)

+1.5

Bus way to Floor

10 panel board




1 (3× 1.5 + 1.5)

+1.5

Bus way to Floor

11 panel board


Conductors PVC InsulatedPVCsheathed laid in duct

1 (3× 1.5 + 1.5)

+1.5





Bus way to Floor

12 panel board




1 (3× 1 0 +10)+10

Bus way to Floor

13 panel board




1 (3× 5 0 +25)+25

Bus way to Floor14 panel board



1 (3× 1 0 +10)+10

Bus way to Floor

15 panel board




1 (3× 1 0 +10)+10

Bus way to Floor

16 panel board

45 56.25 Multicore cables,stranded Copper



1 (3× 1 0 +10)+10

Bus way to Floor

17 panel board




1 (3× 1 6 +16)+10

Bus way to Floor

18 panel board




1 (3× 1 6 +16)+10

Bus way to Chiller

1




2 (3× 1 5 0 + 7 0)

+70

Bus way to Chiller

2




2 (3× 1 5 0 + 7 0)

+70

Bus way to Chiller

3




2 (3× 1 5 0 + 7 0)

+70

Bus way to Chiller

4



2 (3× 1 5 0 + 7 0)

+70

SDB to Elevator

odd doors




1 (3× 4 + 4)+4

SDB to Elevator

even doors




1 (3× 4 + 4)+4

SDB to Service

lighting

40 50 Multicore cables,stranded Copper



1 (3× 1 6 +10)+10

SDB to Water

Pump




1 (3× 1 0 +10)+10

SDB to Elevator

goods




1 (3× 1 6 +16)+10

MDB to Bus way 1763.28 2204 Multicore cables,stranded CopperConductors PVC Insulated


4 (3× 1 × 240

+120) +120

MDB to SDB 154 192.5 Multicore cables,stranded Copper



1 (3× 9 5 +50)+50

Transformer1 to

MDB

1917.28 2396.6 singlecorecables,stranded Copper

Conductors XLPE InsulatedPVCsheathed laid in duct

4 (3× 1 × 300

+150)+150






Location Rated

current(A)

Cable

current(A)

Cable Type No of

cables

Corres

ponding CSA

( mm)

Bus way to Floor 19

panel board




1 (3× 2.5 + 2.5)

+2.5


37.9 47.38 Multicore cables,stranded CopperConductors PVC Insulated PVC


1 (3× 16 + 16)+10

Bus way to Floor 21

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 22

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 23

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 24

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 25

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 26

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 27

panel board




1 (3× 16 + 16)

+10





Bus way to Floor 28

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 29

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 30

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 31

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 32

panel board



1 (3

× 16 + 16)

+10

Bus way to Floor 33

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 34

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 35

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 36

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 37

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 38

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 39

panel board




1 (3× 16 + 16)

+10





Bus way to Floor 40

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 41

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 42

panel board




1 (3× 16 + 16)

+10

Bus way to Floor 43

panel board




1 (3× 16 + 16)

+10




1 (3× 16 + 16)+10

Bus way to Chiller 1 337 421.25 Multicore cables,stranded Copper



2 (3× 150 +70)

+70




2 (3× 150 +70)

+70




2 (3× 150 +70)

+70




2 (3× 150 +70)

+70

Water Pump 25.5 31.87 Multicore cables,stranded Copper



1 (3× 10 +10)+10

Service lighting 40 50 Multicore cables,stranded Copper



1 (3× 16 +10)+10

MDB to Bus way 2273.78 2842.23 Multicore cables,stranded Copper



5 (3× 1 +300)

+300






MDB to SDB 65.5 81.87 Multicore cables,stranded Copper



1 (3× 50 + 25)

+25

Transformer 2 to

MDB

2339.28 2924 singlecorecables,stranded Copper

Conductors XLPE Insulated


5 (3× 1 × 300 +

150)+150

Location Rated

current(A)

Cable

current(A)

Cable Type No of

cables

Corres ponding

CSA ( mm)

MDB to Mosque

panel board




1 (3× 25 + 25)+10

SDB 3 to GND floor

right panel board




1 (3× 35 + 16)+16

SDB 3 to First floor

right panel board




1 (3× 2.5 +2.5)

+2.5

SDB4 to Chiller 1

Mall




2 (3× 1 8 5 + 9 5)

+95

SDB 4 to Chiller 2

Mall




2 (3× 1 8 5 + 9 5)

+95

SDB 2 to Cinema

chiller



1 (3

× 50 + 25)

+25

SDB2 to Cinema

panel board




1 (3× 6 + 6)+6

SDB4 to Elevator

1




1 (3× 4 + 4)+4

SDB4 to Elevator

2




1 (3× 4 + 4)+4

SDB4 to Elevator

goods




1 (3× 16 + 16)+10

SDB4 to Water

pump




1 (3× 10 + 10)+10

MDB to SDB1 114 142.5 Multicore cables,stranded Copper



1 (3×150+150)

+70

MDB to SDB2 141.76 177.2 Multicore cables,stranded Copper



1 (3× 1 2 0 + 7 0)

+70




1 (3× 70 + 35)

+35

MDB to SDB4 354 442.5 Multicore cables,stranded CopperConductors PVC Insulated


3 (3×300+150)+150






Transformer 3 to

MDB




3 (3× 1 × 300 +150)+150

Location Rated

current(A)

Cable

current(A)

Cable Type No of

cables

Corres

ponding CSA

( mm)

Sub1 to Chalets 1:4

panel board




1 (3× 5 0 +25)+25

Sub1 to Chalets 5:8

panel board




1 (3× 5 0 +25)+25

Sub2 to Chalets

9:13 panel board




1 (3×120+70)

+70

Sub2 to Chalets

14:18 panel board




1 (3

×120+70)

+70

Sub3 to Chalets

19:23 panel board




1 (3×120+70)

+70

Sub3 to Chalets

24:28 panel board




1 (3×120+70)

+70

Sub4 to Chalets

29:33 panel board




1 (3×120+70)

+70

Sub4 to Chalets

34:38 panel board



1 (3×120+70)

+70

GF2 Mall Panel

board to GF 2.1

panel board




1 (3× 10 + 10)

+10

GF2 Mall Panel

board to GF 2.2

panel board




1 (3× 10 + 10)

+10

GF2 Mall Panel

board to GF 2.3

panel board




1 (3× 10 + 10)

+10

Chillers to Chiller 1 294 367.5 Multicore cables,stranded Copper



2 (3×120+70)

+70

Chillers to Chiller 2 294 367.5 Multicore cables,stranded Copper



2 (3×120+70)

+70

Service panel to

Water Pump




1 (3× 4 + 4)+4

Elevator 1,2 Panel

board to Elevator 1




1 (3× 4 + 4)+4

Elevator 1,2 Panel

board to Elevator 2




1 (3× 4 + 4)+4

Service Panel toElevator 1,2 Panel

board

42.4 53 Multicore cables,stranded CopperConductors PVC Insulated


1 (3× 1 0 +10)+10






Location Rated

current(A)

Cable

current(A)

Cable Type No of

cables

Corres ponding

CSA ( mm)

SDB1 to Foad court

panel board




1 (3× 25 + 25)+10

sevice panel to Foad

court elevator




1 (3× 4 + 4)+4

sevice panel to Foad

court water Pumps


Conductors PVC Insulated PVCsheathed

1 (3× 4 + 4)+4

Escalator 1,2 Panel

board to Elevator 1




1 (3× 2.5 + 2.5)

+2.5

Escalator 1,2 Panel

board to Elevator 1



1 (3× 2.5 + 2.5)

+2.5

Service Panel to

Escalator 1,2 Panel

board




1 (3× 6 + 6)+6

SDB1 to SUB1 225.68 282.1 Multicore cables,stranded Copper



2 (3× 70 + 35)

+35




2 (3×120+70)

+70




2 (3×120+70)

+70

SDB1to SUB4 282.1 352.63 Multicore cables,stranded Copper



2 (3×120+70)

+70

SDB2 to GF2 Mall

Panel board




1 (3× 70 + 35)

+35

SDB2 to chiller 1,2

panel board

588 735 Multicore cables,stranded Copper



4 (3×120+70)

+70

SDB2 to Service

Service board




1 (3× 3 5 +16)+16

SDB2 to Mall

second floor 3panel board



1 (3

× 2 5 +25)+10




6 (3×185+95)

+95

MDB to SDB2 1071.98 1340 Multicore cables,stranded Copper



4 (3×240+120)

+120

Transformer 4 to

MDB




6 (3× 1 × 240 +1×240





laid in duct

SDB1 to Foad court

chiller 1



laid in duct

1 (3× 70 + 35)

+35

GF 4 Mall Panel

board to GF4.1 Panel

board



laid in duct

1 (3× 10 + 10)+10

GF 4 Mall Panel


board



laid in duct

1 (3× 10 + 10)+10

GF 4 Mall Panel


board

24.8 31 Multicore cables,stranded Copper


laid in duct

1 (3× 6 + 6)+6

SDB2 to Mall GF4

water Pumps



laid in duct

1 (3× 4 + 4)+4

SDB2 to Chiller 2 294 367.5 Multicore cables,stranded Copper


laid in duct

2 (3×120+70)

+70

SDB3 to Mall GF5Panel board 22.6 28.25 Multicore cables,stranded CopperConductors PVC Insulated PVCsheathed

laid in duct

1 (3× 4 + 4)+4

SDB3 to Chiller 3 294 367.5 Multicore cables,stranded Copper


laid in duct

2 (3×120+70)

+70

Mall GF5 Escalator

1,2 board to

Escalator 1



laid in duct

1 (3× 5 0 +2.5)+2.5

Mall GF5 Escalator

1,2 board to Mall

GF5 Escalator 2



laid in duct

1 (3× 5 0 +2.5)+2.5

Mall GF5 Escalator

1,2 board



laid in duct

1 (3× 6 + 6)+6

GF5 Mallsevicepanel board

to water Pumps

16.95 21.19 Multicore cables,stranded CopperConductors PVC Insulated PVCsheathed

laid in duct

1 (3× 4 + 4)+4

SDB1 to Food

coartsevice panel

board



laid in duct

1 (3× 16 + 16)+16

SDB2 to GF4 Mall

panel board



laid in duct

1 (3× 70 + 35)

+35

SDB3 to GF5 Mall

sevicepanel board



laid in duct

1 (3× 16 + 16)+16

MDB to SDB1 194.85 243.56 Multicore cables,stranded CopperConductors PVC Insulated PVCsheathed

laid in duct

2 (3× 70 + 35)+35



laid in duct

3 (3×120+70)

+70



laid in duct

3 (3× 70 + 35)

+35

Transformer 5 to MDB 968.55 1210.69 singlecorecables,stranded Copper

Conductors XLPE Insulated PVCsheathed

laid in duct

1 (3× 1 × 240 +1 × 2 4 0)+ 1 ×240






Location Ratedcurrent(A)

Cablecurrent(A)

Cable Type No ofcables

Corres pondingCSA ( mm)

Mall GF1 , Floor 2 to

GF1.1 Panel board


Conductors PVC Insulated PVC sheathed

laid in duct

1 (3× 10 + 10)+10


GF1.2 Panel board


Conductors PVC Insulated PVC sheathed

laid in duct

1 (3× 10 + 10)+10


GF1.3 Panel board



laid in duct

1 (3× 10 + 10)+10


Floor 2 Panel board



laid in duct

1 (3× 10 + 10)+10

chillers 1 to Chiller 1 194 242.5 Multicore cables,stranded Copper


laid in duct

1 (3× 1 8 5 + 9 5)

+95

chillers 1 to Chiller 2 194 242.5 Multicore cables,stranded Copper


laid in duct

1 (3× 1 8 5 + 9 5)

+95

Water Pump mall to

Water Pumps



laid in duct

1 (3× 16 + 16)+10

Escalator1,Escalator2

to Panel board

Escalator1



laid in duct

1 (3× 1.5 + 1.5)

+1.5


to Panel Escalator2



laid in duct

1 (3× 1.5 + 1.5)

+1.5

Elevator1, Elevator2 to

Panel board Elevator

1



laid in duct

1 (3× 4 + 4)+4

Elevator1, Elevator2 to

Panel board Elevator

2



laid in duct

1 (3× 4 + 4)+4

Admin1,Admin2

Panel boards to

Admin 1 building

Panel board



laid in duct

1 (3× 10 + 10)+10

Admin1,Admin2Panel boards to

Admin 2 building

Panel board


laid in duct

1 (3× 6 + 6)+6

Chillers 2 to Admin

Chiller 1



laid in duct

1 (3× 70 + 35)

+35

Chillers 2 to Admin

Chiller 2



laid in duct

1 (3× 70 + 35)

+35

water pump admin

to Water pumps



laid in duct

1 (3× 4 + 4)+4

SDB1 to Mall GF1,Floor 2


laid in duct

1 (3× 95 + 50)+50





12.8 Voltage drop:

Voltage drop is a term used to describe any reduction in the supplyvoltage in a complete electrical circuit. The term may be used to

describe a voltage loss across aspecific component in the circuit, the

voltage loss measured across the entire circuit, or as

a broad description of the phenomenon of voltage loss in a circuit in

general.

All electrical circuits, no matter how simple, present a certain amount

of resistance to the

flow of electrical current through them. This resistance effectivelymakes the electrical

SDB1 to chillers 1 338 422.2 Multicore cables,stranded Copper


laid in duct

2 (3× 1 8 5 + 9 5)

+95

SDB1 to Water Pump

mall


Conductors PVC Insulated PVCsheathedlaid in duct

1 (3× 16 + 16)+10

SDB1 to


Panel board



laid in duct

1 (3× 6 + 6)+6

SDB1 to Elevator1,

Elevator2

Panel board

42.4 53 Multicore cables,stranded Copper


laid in duct

1 (3× 16 + 16)+10

SDB2 to

Admin1,Admin2

Panel boards



laid in duct

1 (3× 25 + 25)+25

SDB2 to Chillers 2 230 287.5 Multicore cables,stranded Copper


laid in duct

1 (3×240+120)

+120

SDB2 to water pump

admin



laid in duct

1 (3× 6 + 6)+6



laid in duct

3 (3×240+120)

+120



laid in duct

2 (3× 1 2 0 + 7 0)

+70

Transformer 6 to MDB 947.3 1184.13 singlecorecables,stranded Copper

Conductors XLPE Insulated PVCsheathed

laid in duct

1 (3× 1 × 1000+1 × 5 0 0)+ 1 ×500





current work harder, and thus absorbs energy. This expenditure of

energy is what causes

the reduction in voltage described by the term voltage drop.

For example, a simple circuit can be made up of a 9-volt battery

attached to a simple

flash light bulb with a small switch. If one were to measure the voltage

across the

batteries terminals with the switch open, the multimeter reading would

be

approximately 9 volts. If one were to close the switch and illuminate the

bulb, that

reading would drop by approximately 1.5 volts. That reduction in

voltage is what is

known as a voltage drop, and it comes about as the result of the work

the battery has to

do to illuminate the bulb. Each and every component in a circuit,

including the wiring,

offers a certain amount of resistance to the flow of electrical current

and will cause an

associated voltage drop.

In applications that are extremely supply voltage sensitive, such as

electronic devices,

these voltage losses have to be carefully calculated and the supply

voltage adjusted to

make provision for them. A 12 volt direct current (DC) power supply, for

instance, will

typically produce an output of 13.8 volts to accommodate.

this voltage drop phenomenon. In applications that require very long

cable runs, it is

common practice to uses fairly heavy cables that present less

resistance to the flow of

electric current in an attempt to minimize the effects of voltage losses.

The total

potential loss of voltage in any circuit thus needs to be carefully

calculated during the

design and specification phase of a project to ensure that the finalresult meets all





requirements.

11.8.1 Permissible voltage drop

Calculate the volt drop that will be experienced at the load terminals.

The maximumvolt drop allowed by the Australian Standard for Electrical Installations

(Standard AS

3000; known as the SAA Wiring Rules) is 5%.

11.8.2 The volt drop may be calculated in two different ways:

Multiplying the current by the impedance of the length of cable.

Calculate the

percentage volt drop by reference to the phase-to-earth voltage.

Multiply the current by the length of cable, and then multiply the

result by the volt

drop per amp per meter

12.8.3 Checking for volt drop:

From the previous law as the current increase the impedance increase

and the voltage drop

increase.

11.8.4 In case of low voltage:

The current will be high because the voltage is low compared with high

voltage ,forsame power so the voltage drop will be high . If the voltage drop

exceeded certain limit

(5%) according to IEC standard ,the cable size should be increased to

decrease the overall

resistance hence decrease the voltage drop .which mean you pay

more money.

11.8.5 In case of high voltage:

Vdrop =√ ×Z ××dite




The current will be smaller than it in case of low voltage for the same

power transmitted

,so the voltage drop will be small ,so we volt drop seldom be a problem

a higher voltage

11.8.6 Voltage drop calculation calculated in the project

From TO Rated Current(A) Length mv/Amp/meter Voltage Drop (VD) VD %

Transformer 3 Mosque 61.2 40 1.28 3.13344 0.824589

Transformer 5 Food Court 55 85 1.28 5.984 1.574737

Transformer 6 Adminstration building 26 40 5.199 5.40696 1.422884

Transformer 3 Cinema 28 40 5.199 5.82288 1.532337

Transformer 1 Ground of hotel 36 40 3.101 4.46544 1.175116

Transformer 2 Level 19 of hotel 17.5 19 7.741 2.5738825 0.677338

SDB 1(chalets 1:8) 225.68 40 0.244 2.2026368 0.57964

SDB 2(chalets 9:18) 282.1 80 0.18 4.06224 1.06901SDB 3(chalets 19:28) 282.1 120 0.18 6.09336 1.60352SDB 4(chalets 29:38 ) 282.1 160 0.18 8.12448 2.13802

chalets 1:4 28.21 10 5.199 1.4666379 0.38596chalets 5:8 28.21 40 5.199 5.8665516 1.54383

chalets 9:13 28.21 10 5.199 1.4666379 0.38596chalets 14:18 28.21 40 5.199 5.8665516 1.54383chalets 19:23 28.21 10 5.199 1.4666379 0.38596

chalets 24:28 28.21 40 5.199 5.8665516 1.54383chalets 29:33 28.21 10 5.199 1.4666379 0.38596

chalets 34:38 28.21 40 5.199 5.8665516 1.54383

Trans 4(MDB 1)

SDB 1

SDB 2

SDB 3

SDB 4

Documents

Chapter 11 Power Cables