IEEE Power & Energy Magazine - November/December 2016 - 29

Voltage/kV

260
240
220
200
180
160
140
120
100
22:22:44.500

22:22:45.000

22:22:45.500

22:22:46.000

Reactive
Power/MVAr

Active
Power/MW

Muchang Wind Farm 220-kV Bus
100
80
60
40
20
0
-20
22:22:44.500

22:22:45.000

22:22:44.500

22:22:45.000

22:22:45.500
22:22:46.000
Muchang WF Reactive Power

10
5
0
-5
-10
-15
-20
22:22:45.500

22:22:46.000

Muchang WF Reactive Power

figure 5. Event recording at the Muchang wind farm.

buses close to the fault location during the fault are very
similar to the mean voltages in recordings.
The Muchang wind power plant is in the Guyuan regional
cluster. The total installed capacity is 100.5 MW (Sinovel
wind turbines). When the fault occurred, the PCC voltage
experienced a deep depression of more than 50%, causing
the wind turbines to immediately disconnect from the grid
due to the excessively low voltage at their terminals. The
fault caused the passive crowbar of the wind turbines to act.
The crowbar short-circuits the rotor circuit, causing the
wind turbines to exhibit the super-synchronous characteristics of asynchronous machine with lost excitation. During
the first 20 ms after the fault occurred (between the vertical
green line and the first red line), the wind turbines released
reactive power and then kept absorbing reactive power
until the wind turbines tripped. The wind turbines tripped
on low voltage, with switching acting after 60-80 ms. By
60 ms later (at the second red line), most of the wind turbines had disconnected from the grid, and the active power
output dropped rapidly to zero. Figure 5 shows the event
recording. Simulations successfully captured the essential
aspects of the event.

Incorrect Switching of Reactive Power
Compensation
On 14 May 2012, another incident occurred, also in Guyuan,
Hebei province. This event was caused by voltage fluctuanovember/december 2016

tion. As a result, 584 wind turbines tripped offline, resulting
in a power loss of 737 MW.
Before the event took place, the total power output of the
1,191 wind turbines in the wind power cluster was 1,298 MW.
At the time, the wind speed increased vigorously in Guyuan,
which led to a rapid and substantial increase of wind power
output. The reactive power supply of the regional system
became insufficient to support the voltage of Chabei Station
and Yiyuan Station buses. To support the 220-kV voltage of
these stations, four sets of reactors in Chabei Station and two
sets in Yiyuan Station were switched off gradually. Then, three
sets of capacitors in Chabei Station were switched online. This
caused the system voltage to increase, as desired, but the voltage increased too much and caused a large number of wind
turbines to disconnect from the grid due to the high voltage.
Among the wind turbines integrated into the grid through
the Guyuan transformer station, there were 607 wind turbines that remained connected to the grid, accounting for
51.5% of the operating wind turbines before the incident.

Fault Analysis Conclusions
The recordings and simulations are representative of analyses
on wind plant disconnection events occurring before remediation, and these indicate that the major causes were as follows:
✔ Issues with the wind plant collector designs result in
faults not being cleared quickly. This leads to cascading
impacts on other wind plants in the cluster.
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