Series-Shunt Compensation

It is clear from the above analysis, that the advantage of both shunt and series compensation of an AC capacitor can be made use of. In shunt compensation, the capacitor is used to compensate the individual induction generators. In series com­pensation, the capacitor is used to compensate the line impedance. The overall result will be an improvement in the voltage and lower losses on the transmission line.

To know the effect of the combined series and shunt compensations, simula­tions are carried out for two different combinations of series-shunt compensation. The same 10 wind turbines are connected at bus 9. Figure 7.21 illustrates the real power generated by WECS versus the voltage at the WECS terminals with various combinations of series-shunt compensations. It is seen that the voltage profile is high compared to individual series or shunt compensation. In fact, there is over compensation with series capacitor equal to 75 % of line reactance and shunt compensation of 200 kVAR.

Figure 7.22 shows that reactive power demand decreases significantly when compared to those with series compensation alone. As shown in Figs. 7.20 and 7.23, a comparison between the line current for series compensation and series-shunt compensation, it is observed that the transmission line current is reduced signifi­cantly with series-shunt compensation.

Comparing Figs. 7.12, 7.18 and 7.21, which show the variation of voltage with power for different types of compensation, it is evident that series-shunt

Series-Shunt Compensation
image107,image108,image109

compensation provides a very good voltage profile at WECS terminals and increases the wind power penetration, as more turbines can be connected.

From Fig. 7.24, it is observed that series-shunt compensation with 50 % series compensation and 150 kVAR shunt compensation gives better voltage profile than that obtained by strengthening the grid with 5 parallel lines. Also, for such capacitor combination, the reactive power demand and transmission line current are reduced significantly as seen from Figs. 7.22 and 7.23. Thus it can be con­cluded that series-shunt compensation is an economical alternative to grid strengthening.

Table 7.2 Summary of results

Max. no. of turbines that can be connected

V (PU)

P (MW)

Q (MVAR)

I (PU)

A1

2

0.9329

1.56

0.88

0.0735

A2

5

0.9389

3.89

2.21

0.1833

A3

13

0.9472

10.12

5.79

0.4325

B1

9

0.9788

3.89

1.49

0.1807

B2

13

0.9912

389

1.25

0.1771

B3

17

1.0031

3.89

1.01

0.1729

C1

18

0.9580

7.77

4.43

0.3604

C2

22

1.0090

7.77

4.68

0.3443

D1

13

1.0014

7.77

2.27

0.1782

D2

20

1.0619

7.77

1.91

0.1253

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