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The effect of a loss of transmission line (TL) and generation on the behaviour of
the WF was studied. For the TL, the circuit breakers at both ends of the lines were
opened at 1s for the 400kV, 100km line and then for 20kV, 50km line in turn. The
circuit breaker at bus 4 connecting the synchronous generator (SG) to the grid was
opened at 1s to disconnect the SG from the power system. The results are shown in
Fig 19. A loss of line causes a surge in the system frequency at the PCC; this caused a
reduction of active power to the network by the WF to restore the frequency to the
prefault value. The 20kV, 50km line has a severe impact compared to the 400kV,
100km line due to close proximity to the WF. At the instant the SG (generation) was
lost; a sudden dip in the system frequency was experienced, this in turn resulted into
an instant injection of active power from the WF to the grid to restore the system
frequency.
The terminal voltage reduces from the prefault value of 0.655kV to a new value of
0.638kV, 0.641kV and 0.650kV for the loss of 50km line, 100km line and SG
respectively as a result of change in the system configuration.
-0.64
0.66
0.655
-0.66
0.65
-0.68
0.645
-0.7
0.64
0.635
-0.72
0
1
2
3
4
5
0
1
2
3
4
5
(a) Time (s)
(b) Time (s)
0.81
50.15
0.8
50.10
0.79
50.05
0.78
50.00
0.77
49.95
0.76
0
1
2
3
4
5
0
1
2
3
4
5
(d) Time (s)
(c) Time (s)
20kV,50km line loss
400kV,1000km line loss
SG loss
Fig. 19.
Response to loss of transmission line
5
Conclusions
The behaviour of a wind farm consisting of DFIG in response to different
disturbances emanating from the power system has been studied. From the study, the
effect of the rotor controller on the stability of a wind farm has been shown to be
significant to the stability of the wind farm following a disturbance. Without
controller, prefault condition was achieved after about 3s. With a controller, the
prefault condition was achieved almost immediately.
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