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

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The technical criteria for grid stabilization, identified here as a “mini-facts” application,
will be somewhat site and utility system specific but likely will fall within these
parameters:
• Application – Reactive power supply and frequency regulation support of T&D
• Power Rating – 2 to 40 MVA (power may be real, reactive, or both)
• Energy Capacity – .5 to 10 kWh at MVA rating
• Duration – Corrective action for cycles up to a few seconds
• Response Time – 5 to 100 Milliseconds
• Duty Cycle – Variable depending on conditions, may be a continuous problem
• Roundtrip Efficiency – 80 to 90% (assumes less than 10% duty cycle)
• Standby Losses – 3 to 4%
• Plant Footprint – .05 MW/m 2 (assumes siting in low density area)
• Environmental Issues – EMI
Other, non energy storage alternatives for solving this problem are: overexcited
synchronous motors and generators, switched capacitors, as well as fast acting static var
compensators (SVCs). Also, utilities traditional options to improve voltage regulation
and control frequency are upgrading transformer and feeder capacity, and cycling power
plants.
Stored Energy for “Distributed-Mini FACTS” Controllers
The energy storage application for improved stability is based on benefits of active power
injection coupled with dynamic reactive power exchange with thee power system. The
need for dynamic reactive power compensation (“fast VARS”) as opposed to fixed or
mechanically switched capacitor banks have long been recognized as a way to improve
T&D system stability and increase power transfer limits. This concept has been applied
in large-scale inverter-based Flexible AC Transmission Systems (FACTS). These
systems have the ability to affect changes of 10 to 100 MVAR and respond in less than
one-quarter of a cycle and they have brought about a new way of thinking regarding
active and reactive power.
An example is the STATCOM, which outpaces switched passive capacitors, reactors, and
LTC transformers in the rapid voltage regulation. STATCOM responds even faster than
conventional generators, SVCs, or synchronous condensers, which in the past were the
main supplier of “fast VAR” to the electric systems. Also, this type of dynamic reactive
compensation is better at supporting voltage during system contingencies than
conventional capacitor banks that loose capacity when system voltage decreases, (See
Figure 9).
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