k Var Compensation

8/13/2019 k Var Compensation

1/22

REACTIVE POWER

COMPENSATION

8051.inwww.8051.in


2/22

CONTENTS

Introduction

Reactive power

Need for reactive power

Need for reactive power compensation

Shunt compensation

Series compensation

Static VAR compensators (SVC)

Static compensators (STATCOM)

Synchronous Condensor

Conclusion

References

www.8051.in


3/22

INTRODUCTION

Reactive power (VAR) compensation is defined as themanagement of reactive power to improve the performanceof ac systems. There are two aspects:-

a) Load CompensationThe main objectives are to :- i)

increase the power factor of the systemii) to balance the real power drawn from the system

iii) compensate voltage regulation

iv) to eliminate current harmonics.

b) Voltage Support The main purpose is to decrease thevoltage fluctuation at a given terminal of transmission line.

Therefore the VAR compensation improves the stability of acsystem by increasing the maximum active power that can betransmitted.

www.8051.in


4/22

WHAT IS REACTIVE POWER ?

Power is referred as the product of voltage andcurrent

i.e. power = V x I

In an ac transmission, when the voltage and current goup and down at the same time, only real power istransmitted and when there is a time shift betweenvoltage and current both active and reactive power aretransmitted.

when the average time is calculated, the average activepower exists causing a net flow of energy whereasaverage reactive power is zero. In the case of reactivepower, the amount of energy flowing in one direction isequal to the amount of energy flowing in the opposite

direction. That means reactive power is neitherwww.8051.in


5/22

Power Triangle

Power factor = cos

= real power / apparent power

= kW/ kVA

Whenever there is a phase shift

between V and I we have:-

a) real power (kW)

b) reactive (imaginary ) power (kVAR)

c) The combination is a complex or

apparent power (kVA)=(kW) + (kVAR)

www.8051.in


6/22

WHY DO WE NEED REACTIVE

POWER?

In resistive loads the current produces the heat energy

which produces the desired output but incase of

inductive loads the current creates the magnetic field

which further produces the desired work. Therefore

reactive power is the non working power caused by themagnetic current to operate and sustain magnetism in

the device .

Reactive power (vars) is required to maintain the voltage

to deliver active power (watts)through transmissionlines. When there is not enough reactive power the

voltage sags down and it is not possible to deliver the

required power to load through the lines.

www.8051.in


7/22

IMPORTANCE OF REACTIVE

POWER

i)It is the circulating power that does no useful work which

results from the storage elements mainly inductors and

capacitors.

ii)It has a strong effect on the power factor and system

voltages and hence must be compensated to prevent

voltage problems.

LIMITATIONS :-

Reactive power does not travel very far and is necessaryto produce it close to the location where it is required .

www.8051.in


8/22

Need for Reactive Power

Compensation

Reactive power generated by the ac power source is

stored in a capacitor or a reactor during a quarter of a

cycle and in the next quarter of the cycle it is sent back

to the power source. Therefore the reactive power

oscillates between the ac source and the capacitor orreactor at a frequency equals to two times the rated

value (50 or 60 Hz). So to avoid the circulation between

the load and source it needs to be compensated .

Also to regulate the power factor of the system andmaintain the voltage stability we need to compensate

reactive power .

www.8051.in


9/22

Methods of Reactive Power

Compensation

Shunt compensation

Series compensation

Synchronous condensers

Static VAR compensators

Static compensators

www.8051.in


10/22

Shunt compensation

The device that is connected in parallel with the transmissionline is called the shunt compensator. A shunt compensator isalways connected in the middle of the transmission line. Itcan be provided by either a current source, voltage source ora capacitor.

An ideal shunt compensator provides the reactive power tothe system. The voltage equation is given as :-

P + jQ = -j4V(1-cos/2)/xSince the real part of the power is 0 therefore the shunt

compensator injects only the reactive power in the system. Shunt-connected reactors are used to reduce the line over-

voltages by consuming the reactive power, while shunt-connected capacitors are used to maintain the voltage levelsby compensating the reactive power to transmission line.

www.8051.in


11/22

Transmission line with shunt

compensation

www.8051.in


12/22

Series compensation

When a device is connected in series with the

transmission line it is called a series compensator. A

series compensator can be connected anywhere in the

line.

There are two modes of operationcapacitive mode ofoperation and inductive mode of operation.

A simplified model of a transmission system with series

compensation is shown in Figure .The voltage

magnitudes of the two buses are assumed equal as V,

and the phase angle between them is .

www.8051.in


13/22

Transmission line with series

compensation

www.8051.in


14/22

Static VAR compensators

A static VAR compensator (or SVC) is an electrical device for

providing reactive power on transmission networks. The term

"static" refers to the fact that the SVC has no moving parts (other

than circuit breakers and disconnects, which do not move under

normal SVC operation).

The SVC is an automated impedance matching device, designed to

bring the system closer to unity power factor. If the power system's

reactive load is capacitive(leading), the SVC will use reactors

(usually in the form of 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.

www.8051.in


15/22

www.8051.in


16/22

ADVANTAGES

a) Static VAR compensation is not done at line voltage; a

bank of transformers steps the transmission voltage

(for example, 230 kV) down to a much lower level (for

example, 9.5 kV).This reduces the size and number of

components.

b) They are more reliable .

c) Faster in operation .

d) Smoother control and more flexibility can be provided

with the help of thyristors.

www.8051.in


17/22

Static Compensator

The devices use synchronous voltage sources for

generating or absorbing reactive power. A

synchronous voltage source (SVS) is constructed

using a voltage source converter (VSC). Such a

shunt compensating device is called staticcompensator or STATCOM .

A STATCOM usually contains an SVS that is driven

from a dc storage capacitor and the SVS is

connected to the ac system bus through aninterface transformer. The transformer steps the ac

system voltage down such that the voltage rating of

the SVS switches are within specified limit.

www.8051.in

COMPARISON OF VI


18/22

COMPARISON OF VI

CHARACTERISTICS OF SVC AND

STATCOM

www.8051.in


19/22

Synchronous Condensor

A device whose main function is the improvement of pf

of the electrical system is known as the synchronous

condensor. It is installed at the receiving end of the line .

When a synchronous condensor is introduced it supplies

the kVAR to the system , and hence the current is

reduced .

Therefore the losses are reduced and provides a better

efficiency . Hence more power can be delivered to the

load and improves the pf of the system.

www.8051.in


20/22

CONCLUSION

From all the previous discussion we can

conclude reactive power compensation is a

must for improving the performance of the ac

system. By reactive power compensation wecan control the power factor and reduce the

consumption of electricity.

www.8051.in


21/22

References

[1] Juan Dixon and Luis Moran - Reactive PowerCompensation Technologies.

[2] Yongan Deng - Reactive Power Compensation OfTransmission Lines.

[3] Hong Chan- Practices of Reactive PowerManagement and Compensation.

T.J Millen- Reactive Power Control in ElectricalSystems.

Canadian Electrical Association-Static Compensators

For Reactive Power Control.

www.8051.in


22/22

VISIT www.8051.in for more.

THANKS

www.8051.in
http://www.8051.in/http://www.8051.in/

k Var Compensation

Documents

Transcript of k Var Compensation