Handbook of Energy Storage for Transmission or ... - W2agz.com

EPRI Proprietary Licensed Material
Figure 10
Damping Of Post Fault Oscillation With And Without Energy Storage
The use of large-scale (100 MVAR or more) FACTS controllers to provide dynamic
reactive compensation has already been demonstrated through several landmark projects.
However, because of high initial cost, the alternative of a smaller scale, modularized,
distributed real, and reactive VAR injection has recently received considerable attention.
The key to this application is the injection of real energy storage to maintain speed of
motor, which in turn reduces the inrush current for feeders heavily loaded with motor
loads. This minimizes bus voltage depression and thus helps with both rotor angle and
voltage stability. By providing a critical boost to the system both during faults and
following the clearing of faults helps avert instability. This type of distributed dynamic
reactive compensation with energy storage is particularly suitable for solving transient
voltage stability problems in a weak portion of the network with a high concentration of
induction motor loads during peak loading conditions.
The advantage of energy storage under these conditions is mainly in reducing the
maximum transient voltage dip, which is a measure of the dynamic performance of the
system Based on Western Systems Coordinating Council (WSCC) criteria as shown in
Figure 11, the voltage at any load bus should not dip below 20% of the initial value for
more than 20 cycles.
Estimating the total portion of induction motor loads is becoming a critical issue for
power system stability. This was recognized in a study conducted for model validation
and analysis of WSCC System Oscillations following Alberta Separation on August 4,
2000. Figure 12 shows the modeling result of the system oscillation following the
separation for different percentages of induction motor loads. Based on this study, one of
the recommendations was to increase the portion of induction motor load representation
in selected areas for future system stability study models.
Flywheels Page 26