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

EPRI Proprietary Licensed Material
Figure 9
Loss Of Capacitor VAR Output As A Function Of Line Voltage
Combining energy storage with FACTS controllers offers three distinct advantages:
1. Energy storage devices can provide system damping while maintaining constant
voltage following a system disturbance.
2. Energy storage increases the dynamic control range allowing the interchange of small
amounts of real power with the system.
3. Distributed energy storage can maintain the speed of locally connected induction
motors during a power system disturbance, thus helping to prevent a voltage collapse
in areas where there is a large concentration of induction motors.
An EPRI study [1] found that adding energy storage (in this case, SMES) to a FACTS
device increased the control leverage of the reactive power modulation of a FACTS
device by 33% (i.e., operating the FACTS + energy storage in four-quadrant, reactive
plus real power mode provided 33% greater transmission enhancement). Figure 10 shows
the results of a study conducted by Siemens on the effectiveness of short-term energy
storage with a FACTS controller in damping low frequency power oscillations that could
not have been achieved with the STATCOM plus post oscillation damping (POD) alone.
"The results illustrate that a STATCOM alone (i.e. no POD) will regulate voltage in the
post contingency period but will not naturally add much damping to power oscillations.
The STATCOM with POD signal applied to its voltage reference may damp swing
oscillations following a disturbance however this is achieved at the expense of voltage
regulation. The combination of STATCOM plus SMES with POD modulating the SMES
output will allow the system to both regulate voltage and provide oscillation damping."
[2]
Flywheels Page 25