IEEE Power & Energy Magazine - September/October 2015 - 69

In developing a smart grid,
the measurement technology used plays
a crucial role.

access to wind turbine monitoring data. Using PMUs installed
at step-up substations, an intelligent alarm system can detect
when cascading tripping events occur, trace the entire process,
and subsequently assess the impact.
The cascading failures of wind farms can last from several seconds to as much as a minute and are accompanied by
sudden voltage dips because of contingencies, the continuous loss of active power, and the increase in voltage. Meanwhile, under the most violent fluctuation scenarios, the
magnitude and speed of a wind farm's output power ramps
can reach 25% of installed capacity within 5 min; these values are far below those under cascading scenarios, in which
the magnitude and speed can reach 100% of installed capacity within five seconds. The intelligent alarm system detects
large voltage dips at the common coupling points of wind
farms as start-up conditions and then identifies the power
ramps within a minute-based time window. All detected
events are synthesized to obtain a whole picture of the cascading failures. One example is shown in Figures 10 and 11.

Wide-Area Control and Protection
Wide-Area Damping Control

grid. Based on calculations for observability and controllability,
six PMUs across three provinces spanning over 1,000 km as
well as three HVdc links with capacities of more than 11 GW
were chosen for inclusion in this system. The controllers were
coordinated to damp two dominant inter-area oscillation modes
that limited long-distance transfer power. The configuration of
the system is shown in Figure 12.
Some new oscillations with high frequencies (about 5 Hz)
caused by time delays and the characteristics of the quick
response of HVdc were investigated, and a solution using a lowpass filter was proposed. Based on the improved online Prony
identification, the controller parameters can be adapted according to changes in oscillation frequency. The WADC system was
implemented in a real-time system and carefully tested using
the CSG's real-time digital simulation (RTDS) platform, which
comprises more than ten racks of RTDS and real HVdc control
and protection cubicles. After field debugging and trial operations, the performance of the system was validated in 2008 and
2009 through the artificial block and de-block of three different HVdc links and by tripping a 500-kV ac tie-line. The field
test results show that commissioning the WADC system has the
potential to increase the damping ratio of the dominant modes
from 5% to more than 15%. This increase indicates a transfer
limitation enhancement of 650 MW in the CSG. These test
results are shown in Figure 13.

Efficiently suppressing inter-area LFO requires that global
dynamics for different areas be established. Here, PMUs
play a crucial role in realtime and continuous damping control. In designing
wide-area damping control
GZ
(WADC) systems, the folPMU
lowing issues should be
AnShun
GGII
HVDC
GaoPo
considered carefully:
✔ selection of feedback
XingRen
GD
signals and control sites
YN
LuoDong
✔ controller structure,
BaoAn
GGI HVDC
LuoPing
parameters, and adaptCanto
ability
GX
✔ modeling and compensation of random
TSQ HVDC
time delay in the comControl
munication system.
Unit
Central
HN
The WADC system comControl Station
missioned by the CSG in
2008 is a representative project that operates in a par- figure 12. The configuration of the HVdc WADC system implemented by the CSG. GX:
ticularly complicated power Guangxi; HN: Hainan; GG: Guiguang; TSQ: Tianshengqiao.
september/october 2015

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