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

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application, providing uninterruptible power for substation critical loads, has two possible
solutions. The first solution replaces the substation battery by providing short-term
bridging energy to carry critical loads during transfer to an alternate source, or until the
primary source returns to normal operation. The second solution supplements the
substation battery by picking up high inrush loads, allowing reduction in battery size.
These T&D energy storage applications are described below based on the generic need
that they serve. Included in the descriptions are technical specifications such as response
time, run time, duty cycle and power requirements.
Voltage Stabilization Support to the Electric Grid
Problem Description
Need for system stability, in both central and distributed power systems, as well as the
specific functions of reactive power supply and frequency regulation support, are
considered here. The reactive power (VAR) control application solves the problem of
maintaining power flow and voltage stability. The frequency regulation application
solves the problem of controlled injection needed to regulate system frequency. The
latter is particularly relevant for improving stability of relatively weak areas in the T&D
system. These applications are cited as ancillary services in FERC order 888, 1996, and
will eventually carry a location dependent market value in a restructured utility situation.
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 – 2-40 MVA (power may be real, reactive, or both)
• Energy Capacity – .5-10 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 – 80-90% (assumes less than 10% duty cycle)
• No load Losses – less than 3%
• 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.
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