FACTS 1

Shunt compensators

Presented by

T.S.L.V.AyyaraoAssistant ProfessorGMRIT

FACTS 2

Objective of Shunt Compensation

The objective of shunt compensation is to change the natural characteristics of the line and make it more compatible with load demand.

Shunt connected reactors minimize the overvoltage under light load conditions.

Shunt connected capacitors maintain voltage levels underge under heavy load conditions.

The ultimate objective of shunt compensation is to increase the power transfer of the line.

FACTS 3

Mid point voltage regulation Consider a simple two bus transmission line as shown in fig Ideal VAR compensator is shunt connected at mid point

The compensator is represented with a sinusoidal AC Source with fundamental frequency.

Here Vs = Vm = Vr. The compensator divides the line into two segments.

Fig.1 Two bus power system with VAR Compensator

FACTS 4

Mid point voltage regulation The segment includes line of X/2 impedance and carries

power from sending end to mid point. The second segment includes line of X/2 impedance and

carries power from mid point to receiving end. The Phasor diagram is as below

Fig.2 Phasor diagram of the line

FACTS 5

Mid point voltage regulation For lossless system, active power is same at each terminal. From phasor diagram,

Vsm = Vmr = V cos(δ/4)

Ism = Imr = I = 4V/X*sin(δ/4)

The transmitted power is P = VsmIsm

= VIcos(δ/4)

P = 2V2/X *sin(δ/2) Similarly Reactive power is Q = 4V2/X*(1-cos(δ/2))

FACTS 6

Mid point voltage regulation The relation between P , Q and δ is shown below

Fig.3 Variation of P,Q with δ

FACTS 7

Mid point voltage regulation Mid point compensation significantly increase the power

transfer by supplying reactive power demand. Mid point location is the best location of the compensator

because

1. voltage sag is maximum at mid point.

2. compensator breaks the line into two equal parts. This concept can be expanded to use of multiple

compensators. Increase in no. of segments rapidly decrease the voltage

variation of the line.

FACTS 8

Mid point voltage regulation .

Fig.4 Two bus system with multiple compensators

FACTS 9

Mid point voltage regulation But the system too complex and too expensive.