Handbook of Energy Storage for Transmission or ... - W2agz.com
Handbook of Energy Storage for Transmission or ... - W2agz.com
Handbook of Energy Storage for Transmission or ... - W2agz.com
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EPRI Proprietary Licensed Material<br />
• Duty Cycle – Variable depending on type <strong>of</strong> fluctuating loads and power sources,<br />
may be a continuous duty such as <strong>f<strong>or</strong></strong> automatic welding equipment.<br />
• Roundtrip Efficiency – >90% (assumes less than 10% duty cycle)<br />
• Standby Losses - < 3%<br />
• Plant Footprint – .1 MW/m 2<br />
• Environmental Issues – EMI, EMF, Aesthetics<br />
Non-energy st<strong>or</strong>age alternatives <strong>f<strong>or</strong></strong> solving this problem in the distribution system <strong>or</strong> at<br />
end-user facilities include dynamic voltage rest<strong>or</strong>er <strong>or</strong> related ride-through power<br />
conditioning equipment, increased service size, and modifying <strong>or</strong> isolating fluctuating<br />
loads. In the transmission system and at higher voltage levels alternate feeders may be<br />
used to separate <strong>of</strong>fending loads; substation static VAR <strong>com</strong>pensat<strong>or</strong>s and FACTS can<br />
<strong>com</strong>pensate <strong>f<strong>or</strong></strong> momentary reactive power demand; and utilities have the option to add<br />
faster regulat<strong>or</strong>s and beef up trans<strong>f<strong>or</strong></strong>mer and feeder capacity to reduce voltage<br />
fluctuations.<br />
St<strong>or</strong>ed <strong>Energy</strong> Solution <strong>f<strong>or</strong></strong> Inrush Current and Voltage Control<br />
The most direct approach to mitigate fluctuating loads is to provide distributed <strong>or</strong> local<br />
<strong>com</strong>pensation. This relieves the rest <strong>of</strong> the power system <strong>of</strong> momentary overloads and<br />
related line losses <strong>f<strong>or</strong></strong> power delivery. Reactive power <strong>com</strong>pensation, such as fixed shunt<br />
capacit<strong>or</strong>s is usually the most economic <strong>com</strong>pensation. Series capacit<strong>or</strong>s have also been<br />
successfully applied <strong>f<strong>or</strong></strong> <strong>com</strong>pensating fluctuating reactive loads. However, when<br />
fluctuations are caused by high power fact<strong>or</strong> loads, such as a resistive welder, than the<br />
most effective <strong>com</strong>pensation must have a real power <strong>com</strong>ponent.<br />
Distributed energy st<strong>or</strong>age interfaced via power electronics <strong>of</strong>fers real and reactive power<br />
<strong>com</strong>pensation capability. Also, if four-quadrant (real, reactive, bi-directional) power<br />
electronics are used it is possible to source <strong>or</strong> sink power acting as a stabilizer <strong>f<strong>or</strong></strong> the<br />
electric grid. In this case the system can be sized <strong>f<strong>or</strong></strong> the aggregate <strong>of</strong> expected local load<br />
and source fluctuations, and thereby provide local stabilization. Assuming moderate<br />
series impedance, and a lag time in the response from other grid sources, a simple<br />
voltage-based control will pick up momentary voltage excursions and feedback demand<br />
<strong>f<strong>or</strong></strong> sourcing <strong>or</strong> sinking power with the grid. A conceptual diagram <strong>of</strong> this dynamic<br />
voltage regulat<strong>or</strong> and current inrush controller is shown in Figure 14.<br />
Flywheels Page 29
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