IEEE Power & Energy Magazine - November/December 2016 - 34

Voltage of PCC/kV

242
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224

0

5

10

15

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t (s)

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figure 11. Field measurements of bus voltage oscillations.

tripping. The system voltage oscillation curves presented in
Figure 11 are measurements on the transmission line out of
the wind cluster. During the oscillation, active power, voltage of the 220-kV busbar, and system frequency all showed
an oscillation frequency of 1.26 Hz.
An analysis of the oscillation phenomenon showed the
following characteristics:
✔ The phenomenon is different from the low-frequency
oscillations of traditional power systems; the oscillation takes place mainly between the wind farm and
the dynamic reactive power compensators. The mechanical parts rarely participate. That is, variation in
generator speed and mechanical torque are minimal
and do not drive the oscillations.
✔ Although occurring more frequently under weak power grid conditions, the oscillations can also take place
when output power of the wind farm is high or low.
✔ Oscillation frequency varies widely: 1-2 Hz at minimum and dozens of hertz or even higher at maximum.
✔ The amplitude of oscillation is difficult to predict. It is
hard to detect a small oscillation added to the power
frequency, which obscures latent threats to the interconnected power system. Also, a large oscillation can directly damage the stable operation of the power system.
Both dynamic reactive-power compensators and the
electronic power device-based nonsynchronous power
sources (i.e., the wind turbines) were installed with controls that respond in various time scales, including high
bandwidth and very fast behavior. Thus, various fast
dynamic coupling effects were shown to occur between
wind farm groups, between wind farm groups and other
power generating units, between wind farm groups and
flexible dc devices and among nearby electronic driving
devices. The dynamic coupling effects of multiple fast
controllers is the fundamental cause for the observed
oscillation of wind power collecting systems. This behavior can be quite complex.

Conclusions
As large-scale wind power trip-off incidents have taken
place in China, research institutions, grid companies, and

34

ieee power & energy magazine

wind turbine manufacturers have made substantial efforts
to gain insight into the causes of cascading failures and
the critical factors of the response to system contingencies. Great advances have been made in the formulation
of technical standards, wind power testing, FRT capability
improvement, and disturbance testing. Effective solutions
have been found to solve large-scale wind power cascading
failure problems. Large-scale cascading failures due to lack
of FRT capability have been largely eliminated in China.
However, with the increase of wind power capacity and penetration rate, several sub- and super-synchronous oscillation
phenomena have emerged in the regions where wind power
is integrated into the power grid in a centralized way. Thus,
the interaction mechanisms of large-scale wind power with
the grid need careful study. Integration investigations need
to include operational characteristics of wind turbines, wind
farms, and wind power clusters; the interaction mechanism
between wind power and the power grid during faults; and
FRT and dynamic support technology for large-scale wind
power clusters. All of these studies will be necessary to
address the new grid integration challenges of China's ambitious plans for large-scale wind power.

Acknowledgments
This project was supported by the National Basic Research
Program (973 Program) 2012CB215105.

For Further Reading
S. He and X. Dong, "Cause analysis on large-scale wind turbine tripping and its countermeasures," Power Syst. Protect.
Control, vol. 40, no. 1, pp. 131-137, 2012.
Z. Cui, H. Wang, S. Ma, and H. Lui, "Operation situation
analysis and improvement measures for dynamic reactive
compensation equipment applied in large-scale wind power
systems," Power Syst. Technol., vol. 39, no. 7, pp.  1873-
1878, 2015.

Biographies
Wang Weisheng is with the China Electric Power Research
Institute, Beijing, China.
Chi Yongning is with the China Electric Power Research
Institute, Beijing, China.
Wang Zhen is with the China Electric Power Research
Institute, Beijing, China.
Li Yan is with the China Electric Power Research Institute, Beijing, China.
Wang Ruiming is with the China Electric Power Research Institute, Beijing, China.
Nicholas Miller is with GE's Energy Consulting Group,
Schenectady, New York.
Shi Baozhuang is with GE's Energy Consulting Group,
Beijing, China.
p&e

november/december 2016



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