8/4/2019 SVC Tutorials

1/30

STATIC VARCOMPENSATORS

By

Prof. C. Radhakrishna

8/4/2019 SVC Tutorials

2/30

10/17/2010 10:27 AM 2

CONTENTS

STATIC VAR COMPENSATORSSVCs are used for

Types of SVC and Controllers

SVC Control CharacteristicsModelling of SVC

8/4/2019 SVC Tutorials

3/30

10/17/2010 10:27 AM 3

STATIC VAR COMPENSATORS

If the system has to operate close to stability limits insteady state, (with minimum margins), fast control ofreactive power is essential.

In recent years, thyristor controlled static varcompensators are being used for fast reactive powercontrol.

SVCs are used for

1. Increasing power transfer in long lines2. Stability improvement (both steady state and transient)

with fast acting voltage regulation

3. Damping of low frequency oscillations (correspondingto electromechanical modes)

4. Damping of subsynchronous frequency oscillations(due to torsional modes)

5. Control of dynamic over voltages

8/4/2019 SVC Tutorials

4/30

10/17/2010 10:27 AM 4

Types of SVC and Controllers

Three basic types of SVCs1. Variable impedance type2. Current source type

3. Voltage source type

8/4/2019 SVC Tutorials

5/30

10/17/2010 10:27 AM 5

8/4/2019 SVC Tutorials

6/30

10/17/2010 10:27 AM 6

8/4/2019 SVC Tutorials

7/30

10/17/2010 10:27 AM 7

8/4/2019 SVC Tutorials

8/30

10/17/2010 10:27 AM 8

8/4/2019 SVC Tutorials

9/30

10/17/2010 10:27 AM 9

8/4/2019 SVC Tutorials

10/30

10/17/2010 10:27 AM 10

8/4/2019 SVC Tutorials

11/30

10/17/2010 10:27 AM 11

8/4/2019 SVC Tutorials

12/30

10/17/2010 10:27 AM 12

8/4/2019 SVC Tutorials

13/30

10/17/2010 10:27 AM 13

8/4/2019 SVC Tutorials

14/30

10/17/2010 10:27 AM 14

8/4/2019 SVC Tutorials

15/30

10/17/2010 10:27 AM 15

8/4/2019 SVC Tutorials

16/30

10/17/2010 10:27 AM 16

8/4/2019 SVC Tutorials

17/30

10/17/2010 10:27 AM 17

8/4/2019 SVC Tutorials

18/30

10/17/2010 10:27 AM 18

8/4/2019 SVC Tutorials

19/30

10/17/2010 10:27 AM 19

8/4/2019 SVC Tutorials

20/30

10/17/2010 10:27 AM 20

8/4/2019 SVC Tutorials

21/30

10/17/2010 10:27 AM 21

8/4/2019 SVC Tutorials

22/30

10/17/2010 10:27 AM 22

8/4/2019 SVC Tutorials

23/30

10/17/2010 10:27 AM 23

8/4/2019 SVC Tutorials

24/30

10/17/2010 10:27 AM 24

8/4/2019 SVC Tutorials

25/30

10/17/2010 10:27 AM 25

SVC Control Characteristics

The voltage is measured at the high voltage side of the

transformer (or network bus) feeding the SVC and thecurrent is the reactive current, considered to be positivewhen SVC is inductive (absorbing reactive power).

In the control range, the SVC voltage is not maintainedconstant. The slope of the control characteristics is

positive (3 to 5%) and helps in (a) stable parallel operationof more than one SVC connected at the same orneighbouring buses and (b) prevent SVC hitting the limitstoo frequently.

8/4/2019 SVC Tutorials

26/30

10/17/2010 10:27 AM 26

V

ES

Capacitive Inductive ISVC

Figure 1. Steady state control characteristics of variable impedance SVC

The reference voltage of the SVC is chosen such that, undernormal operating conditions, SVC delivers close to zeroreactive power so that the full control range of SVC isavailable for use whenever there is a transient.

8/4/2019 SVC Tutorials

27/30

10/17/2010 10:27 AM 27

Figure 2: Equivalent circuit for SVC in control range

It is to be noted that when the SVC hits the capacitive limit, itbehaves like a fixed capacitor. Similarly, when it hits theinductive limit, it behaves as a fixed inductor. In the controlrange, the SVC can be modelled as a nonlinear voltage source

Es in series with a fictitious, fixed inductor Xs. The phase angle of the voltage source is same as that of the

bus voltage Vs. The value of the inductor is related to the slope of the

control characteristic.

8/4/2019 SVC Tutorials

28/30

10/17/2010 10:27 AM 28

Modelling of SVC

For steady state analysis, it is adequate to model the steady state controlcharacteristics of SVC. Even for transient stability studies, where low

frequency phenomena are of interest, and AC network transients areneglected, steady state representation of SVC may be adequate as a firstapproximation. However to model the damping contribution of SVC, it is

necessary to consider the dynamics of SVC controller. The output of SVC is a time-varying susceptance Bsvc. The inclusion ofthis in the network results in a time varying admittance matrix which can beproblematic. This equivalent has to be updated at every time step when SVC current

is to be calculated.

REFERENCES :

[ 1 ] K.R. Padiyar : Power System Dynamics : Stability and Control , 2nd edition, BSPublications, 2002.

Figure 3: Modelof SVC controller

8/4/2019 SVC Tutorials

29/30

10/17/2010 10:27 AM 29

CONCLUSIONS

8/4/2019 SVC Tutorials

30/30

10/17/2010 10:27 AM 30

THANK YOU