Industrial Power Electronics

7/30/2019 Industrial Power Electronics

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Industrial

applications of

power

electronics

Submitted to: Dr. S. K. Raghuwanshi

Submitted by:

SUMIT SINGH

2010JE1145

B.TECH ECE VI SEM 2012-13


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ACKNOWLEDGEMENTThe achievement, the reward, the pleasure, the satisfaction, the appreciation and the

construction of my project cannot be thought of without the few who apart from their

regular schedule shared their valuable time for me.

I would like to express my gratitude toDr. S. K. Raghuwanshi (Assistant Professor, ISMDhanbad) for giving me the Project in the first instance.

I would also like to thank The Librarian, Central Library of ISM with whose support Icould easily get the books and materials required to complete this project.

I would also like to thank all my friends, my colleagues and all those persons who provided

me feedback and help regarding this project.

Last but certainly not the least; I thank my parents for giving me unflinching support

throughout my project. Their blessings and love ablaze me to reach my goal. They stood rock

solid through ups and downs all through the project period.

Sumit Singh3rd Year Undergraduate Student

Department of Electronics Engineering

Indian School of Mines (ISM), Dhanbad


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Contents :

1. Switching Mode Power Supplies (SMPSs)

2. Static Switches3. High Voltage DC Transmission (HVDC)

4. Uninterruptible Power Supplies (UPSs)5. Static VAr compensator

6.Bibliography


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SMPS:switched-mode power supply

A switched-mode power supply (switching-mode power supply, SMPS, or switcher) is an

electronic power supply that incorporates a switching regulator to convert electrical power

efficiently. Like other power supplies, an SMPS transfers power from a source, like mains

power, to a load, such as a personal computer, while converting voltage and current

characteristics. Unlike a linear power supply, the pass transistor of a switching-mode

supply continually switches between low-dissipation, full-on and full-off states, and spends

very little time in the high dissipation transitions, which minimizes wasted energy. Ideally, a

switched-mode power supply dissipates no power. Voltage regulation is achieved by

varying the ratio of on-to-off time. In contrast, a linear power supply regulates the output

voltage by continually dissipating power in the pass transistor. This higher power

conversion efficiency is an important advantage of a switched-mode power supply.

Switched-mode power supplies may also be substantially smaller and lighter than a linear

supply due to the smaller transformer size and weight.

Switching regulators are used as replacements for linear regulators when higher efficiency,

smaller size or lighter weight are required. They are, however, more complicated; their

switching currents can cause electrical noise problems if not carefully suppressed, and

simple designs may have a poor power factor.


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Theory of operation

A linear regulator provides the desired output voltage by dissipating excess power in ohmic

losses (e.g., in a resistor or in the collectoremitter region of a pass transistor in its active

mode). A linear regulator regulates either output voltage or current by dissipating theexcess electric power in the form of heat, and hence its maximum power efficiency is

voltage-out/voltage-in since the volt difference is wasted. In contrast, a switched-mode

power supply regulates either output voltage or current by switching ideal storage

elements, like inductors and capacitors, into and out of different electrical configurations.

Ideal switching elements (e.g., transistors operated outside of their active mode) have no

resistance when "closed" and carry no current when "open", and so the converters can

theoretically operate with 100% efficiency (i.e., all input power is delivered to the load; no

power is wasted as dissipated heat).


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The basic schematic of a boost converter.

For example, if a DC source, an inductor, a switch, and the corresponding electrical ground

are placed in series and the switch is driven by a square wave, the peak-to-peak voltage of

the waveform measured across the switch can exceed the input voltage from the DC source.

This is because the inductor responds to changes in current by inducing its own voltage to

counter the change in current, and this voltage adds to the source voltage while the switch

is open. If a diode-and-capacitor combination is placed in parallel to the switch, the peak

voltage can be stored in the capacitor, and the capacitor can be used as a DC source with an

output voltage greater than the DC voltage driving the circuit. This boost converter acts like

a step-up transformer for DC signals. A buck

boost converter works in a similar manner,but yields an output voltage which is opposite in polarity to the input voltage. Other buck

circuits exist to boost the average output current with a reduction of voltage.

In an SMPS, the output current flow depends on the input power signal, the storage

elements and circuit topologies used, and also on the pattern used (e.g., pulse-width

modulation with an adjustable duty cycle) to drive the switching elements. The spectral

density of these switching waveforms has energy concentrated at relatively high

frequencies. As such, switching transients, like ripple, introduced onto the outputwaveforms can be filtered with small LC filters.

Static switches:

A transfer switch is an electrical switch that switches a load between two sources. Some

transfer switches are manual, in that an operator effects the transfer by throwing a switch,

while others are automatic and switch when they sense one of the sources has lost or gained

power.

An Automatic Transfer Switch (ATS) is often installed where a backup generator is located,

so that the generator may provide temporary electrical power if the utility source fails.


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Operation of a transfer switchAs well as transferring the load to the backup generator, an ATS may also command thebackup generator to start, based on the voltage monitored on the primary supply. The

transfer switch isolates the backup generator from the electric utility when the generator is

on and is providing temporary power. The control capability of a transfer switch may be

manual only, or a combination of automatic and manual. The switch transition mode (see

below) of a transfer switch may be Open Transition (OT) (the usual type), or Closed

Transition (CT).

For example, in a home equipped with a backup generator and an ATS, when an electric

utility outage occurs, the ATS will tell the backup generator to start. Once the ATS sees that

the generator is ready to provide electric power, the ATS breaks the home's connection to

the electric utility and connects the generator to the home's main electrical panel. The

generator supplies power to the home's electric load, but is not connected to the electric

utility lines. It is necessary to isolate the generator from the distribution system to protect

the generator from overload in powering loads beyond the house and for safety, as utility

workers expect the lines to be dead.

When utility power returns for a minimum time, the transfer switch will transfer the house

back to utility power and command the generator to turn off, after another specified

amount of "cool down" time with no load on the generator.

A transfer switch can be set up to provide power only to critical circuits or to entire

electrical (sub)panels. Some transfer switches allow for load shedding or prioritization of

optional circuits, such as heating and cooling equipment. More complex emergency

switchgear used in large backup generator installations permits soft loading, allowing load

to be smoothly transferred from the utility to the synchronized generators, and back; such

installations are useful for reducing peak load demand from a utility.

Types

Open transitionAn open transition transfer switch is also called a break before make transfer switch. Abreak before make transfer switch breaks contact with one source of power before it makes


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contact with another. It prevents backfeeding from an emergency generator back into the

utility line, for example.One example is an open transition automatic transfer switch (ATS).

During the split second of the power transfer the flow of electricity is interrupted. Another

example is a manual three position circuit breaker, with utility power on one side, the

generator on the other, and "off" in the middle, which requires the user to switch through

the full disconnect "off" position before making the next connection.

Closed transitionA closed transition transfer switch is also called a make before break transfer switch.

A typical emergency system uses open transition, so there is an inherent momentary

interruption of power to the load when it is transferred from one available source to

another (keeping in mind that the transfer may be occurring for reasons other than a total

loss of power). In most cases this outage is inconsequential, particularly if it is less than 1/6

of a second.

There are some loads, however, that are affected by even the slightest loss of power. There

are also operational conditions where it may be desirable to transfer loads with zero

interruption of power when conditions permit. For these applications, closed transition

transfer switches can be provided. The switch will operate in a make-before-break mode

provided both sources are acceptable and synchronized. Typical parameters determining

synchronization are: voltage difference less than 5%, frequency difference less than 0.2 Hz,

and maximum phase angle between the sources of 5 electrical degrees. This means the

engine driving the generator supplying one of the sources generally must be controlled by

an isochronous governor.

It is generally required that the closed transition, or overlap time, be less than 100

milliseconds. If either source is not present or not acceptable (such as when normal power

fails) the switch must operate in a break-before-make mode (standard open transition

operation) to ensure no backfeeding occurs.

Closed transition transfer makes code-mandated monthly testing less objectionable because

it eliminates the interruption to critical loads which occurs during traditional open

transition transfer.

With closed transition transfer, the on-site engine generator set is momentarily connected

in parallel with the utility source. This requires getting approval from the local utility

company.


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Typical load switching applications for which closed transition transfer is desirable include

data processing and electronic loads, certain motor and transformer loads, load curtailment

systems, or anywhere load interruptions of even the shortest duration are objectionable. A

closed transition transfer switch (CTTS) is not a substitute for a UPS (uninterruptible power

supply); a UPS has a built-in stored energy that provides power for a prescribed period of

time in the event of a power failure. A CTTS by itself simply assures there will be no

momentary loss of power when the load is transferred from one live power source to

another

Soft loadingA soft-loading transfer switch actively changes the amount of load accepted by the

generator.

Static transfer switchA static transfer switch uses power semiconductors such as Silicon-controlled rectifiers

(SCRs) to transfer a load between two sources. Because there are no mechanical moving

parts, the transfer can be completed rapidly, perhaps within a quarter-cycle of the power

frequency. Static transfer switches can be used where a reliable and independent second

source of power is available and it is necessary to protect the load from even a few power

frequency cycles interruption time, or from any surges or sags in the prime power source.

Home use

Homes with standby generators may use a transfer switch for a few circuits or the whole

home. Different models are available, with both manual and automatic transfer. Often small

transfer switch systems use circuit breakers with an external operating linkage as the

switching mechanism. The linkage operates two circuit breakers in tandem, closing onewhile opening the other. Manufacturers of transfer switches can provide installation guides

to select the size of switch and provide recommended installation procedures.

Electrical codes require transfer switches, Like all other electrical apparatus, to carry safety

approvals. However, and there have been problems with counterfeit circuit breakers,

particularly those sold via the Internet


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High Voltage DC Transmission (HVDC):

A high-voltage, direct current (HVDC) electric power transmission system uses directcurrent for the bulk transmission of electrical power, in contrast with the more common

alternating current systems. For long-distance transmission, HVDC systems may be less

expensive and suffer lower electrical losses. For underwater power cables, HVDC avoids the

heavy currents required to charge and discharge the cable capacitance each cycle. For

shorter distances, the higher cost of DC conversion equipment compared to an AC system

may still be warranted, due to other benefits of direct current links.

HVDC allows power transmission between unsynchronized AC distribution systems, andcan increase system stability by preventing cascading failures due to phase instability from

propagating from one part of a wider power transmission grid to another. HVDC also

allows transfer of power between grid systems running at different frequencies, such as 50

Hz vs. 60 Hz. Such interconnections improve the stability of each grid, since they increase

the opportunity for any grid experiencing unusual loads to stay in service by drawing extra

power from otherwise completely incompatible grids.

The modern form of HVDC transmission uses technology developed extensively in the1930s in Sweden (ASEA) and in Germany. Early commercial installations included one in

the Soviet Union in 1951 between Moscow and Kashira, and a 100 kV, 20 MW system

between Gotland and mainland Sweden in 1954. The longest HVDC link in the world is

currently the XiangjiabaShanghai 2,071 km (1,287 mi), 800 kV, 6400 MW link

connecting the Xiangjiaba Dam to Shanghai, in the People's Republic of China.Early in

2013, the longest HVDC link will be the Rio Madeira link in Brazil, which consists of two

bipoles of 600 kV, 3150 MW each, connecting Porto Velho in the state of Rondnia to the

So Paulo area, where the length of the DC line is over 2,500 km (1,600 mi).

High voltage transmission :High voltage is used for electric power transmission to reduce the energy lost in the

resistance of the wires. For a given quantity of power transmitted and conductor size,

doubling the voltage will deliver the same power at only half the current. Since the power

lost as heat in the wires is proportional to the square of the current, but does not depend onthe voltage, doubling the voltage reduces the line-loss loss per unit of electrical power


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delivered by a factor of 4. While power lost in transmission can also be reduced by

increasing the conductor size, larger conductors are heavier and more expensive.

High voltages cannot easily be used for lighting and motors, and so transmission-level

voltages must be reduced to values compatible with end-use equipment. Transformers areused to change the voltage level in alternating current (AC) transmission circuits. AC

became dominant after the War of Currents competition between the direct current (DC)

system of Thomas Edison and the AC system of George Westinghouse because transformers

made voltage changes practical and generators using AC were more efficient than those

using DC.

Practical conversion between AC and high power high voltage DC became possible with the

development of power electronics devices such as mercury arc valves and, starting in the1970s, semiconductor devices such as thyristors and later variants such as integrated gate-

commutated thyristors (IGCTs), MOS-controlled thyristors (MCTs) and insulated-gate

bipolar transistors (IGBT)

Advantages of HVDC over AC transmissionThe most common reason for choosing HVDC over AC transmission is that HVDC is more

economic than AC for transmitting large amounts of power point-to-point over long

distances. A long distance, high power HVDC transmission scheme generally has lower

capital costs and lower losses than an AC transmission link.

Even though HVDC conversion equipment at the terminal stations is costly, overall savings

in capital cost may arise because of significantly reduced transmission line costs over long

distance routes. HVDC needs fewer conductors than an AC line, as there is no need to

support three phases. Also, thinner conductors can be used since HVDC does not sufferfrom the skin effect. These factors can lead to large reductions in transmission line cost for a

long distance HVDC scheme.

Depending on voltage level and construction details, HVDC transmission losses are quoted

as about 3.5% per 1,000 km, which is less than typical losses in an AC transmission system.

HVDC transmission may also be selected because of other technical benefits that it provides

for the power system. HVDC schemes can transfer power between separate AC networks.

HVDC powerflow between separate AC systems can be automatically controlled to provide


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support for either network during transient conditions, but without the risk that a major

power system collapse in one network will lead to a collapse in the second.

The combined economic and technical benefits of HVDC transmission can make it a suitable

choice for connecting energy sources that are located remote from the main load centres.

Specific applications where HVDC transmission technology provides benefits include:

Undersea cables transmission schemes (e.g., 250 km Baltic Cable between Sweden and

Germany, the 580 km NorNed cable between Norway and the Netherlands,and 290 km

Basslink between the Australian mainland and Tasmania).

Endpoint-to-endpoint long-haul bulk power transmission without intermediate 'taps', for

example, in remote areas, usually to connect a remote generating plant to the main grid, forexample the Nelson River DC Transmission System.

Increasing the capacity of an existing power grid in situations where additional wires are

difficult or expensive to install.

Power transmission and stabilization between unsynchronised AC networks, with an

extreme example being the ability to transfer power between different countries that use AC

at differing frequencies. Since such transfer can occur in either direction, it increases the

stability of both networks by allowing them to draw on each other in emergencies andfailures.

Stabilizing a predominantly AC power-grid, without increasing prospective short circuit

current.

Uninterruptible Power Supplies (UPSs):

An uninterruptible power supply, also uninterruptible power source, UPS or

battery/flywheel backup, is an electrical apparatus that provides emergency power to a load

when the input power source, typically mains power, fails. A UPS differs from an auxiliary


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or emergency power system or standby generator in that it will provide near-instantaneous

protection from input power interruptions, by supplying energy stored in batteries or a

flywheel. The on-battery runtime of most uninterruptible power sources is relatively short

(only a few minutes) but sufficient to start a standby power source or properly shut down

the protected equipment.

A UPS is typically used to protect computers, data centers, telecommunication equipment or

other electrical equipment where an unexpected power disruption could cause injuries,

fatalities, serious business disruption or data loss. UPS units range in size from units

designed to protect a single computer without a video monitor (around 200 VA rating) to

large units powering entire data centers or buildings. The world's largest UPS, the 46-

megawatt, Battery Electric Storage System (BESS), in Fairbanks, AK, powers the entire city

and nearby rural communities during outages.

Offline / standby type :

Offline / standby UPS. Typical protection time: 020 minutes. Capacity expansion: Usually

not available

The offline / standby UPS (SPS) offers only the most basic features, providing surge

protection and battery backup. The protected equipment is normally connected directly to

incoming utility power. When the incoming voltage falls below a predetermined level the

SPS turns on its internal DC-AC inverter circuitry, which is powered from an internal

storage battery. The SPS then mechanically switches the connected equipment on to its DC-

AC inverter output. The switchover time can be as long as 25 milliseconds depending on the

amount of time it takes the standby UPS to detect the lost utility voltage. The UPS will be


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designed to power certain equipment, such as a personal computer, without any

objectionable dip or brownout to that device

Static VAr compensator:

A static VAR compensator (or SVC) is an electrical device for providing fast-acting reactive

power on high-voltage electricity transmission networks.[1][2] SVCs are part of the Flexible

AC transmission system [3][4] device family, regulating voltage and stabilising the system.

Unlike a synchronous condenser which is a rotating electrical machine, a static VAR

compensator has no significant moving parts (other than internal switchgear). Prior to the

invention of the SVC, power factor compensation was the preserve of large rotatingmachines such as synchronous condensers or switched capacitor banks.[5]

The SVC is an automated impedance matching device, designed to bring the system closer to

unity power factor. SVCs are used in two main situations:

Connected to the power system, to regulate the transmission voltage ("Transmission SVC")

Connected near large industrial loads, to improve power quality ("Industrial SVC")

In transmission applications, the SVC is used to regulate the grid voltage. If the powersystem's reactive load is capacitive (leading), the SVC will use thyristor controlled reactors

to consume VARs from the system, lowering the system voltage. Under inductive (lagging)

conditions, the capacitor banks are automatically switched in, thus providing a higher

system voltage. By connecting the thyristor-controlled reactor, which is continuously

variable, along with a capacitor bank step, the net result is continuously-variable leading or

lagging power.

In industrial applications, SVCs are typically placed near high and rapidly varying loads,such as arc furnaces, where they can smooth flicker voltages


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One-line diagram of a typical SVC configuration; here employing a thyristor controlledreactor, a thyristor switched capacitor, a harmonic filter, a mechanically switched capacitorand a mechanically switched reactor.


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Bibliography:1. A Textbook of Power Electronics byP S Bhimbra

2. Power Electronics by Muhhamed

Rashid

3. Class notes by Dr. S.K.

Raghuwanshi

4. Wikipedia

Documents

Industrial Power Electronics