Switched Banks
Switched banks provide benefits under the following situations:
• More loss reduction — As the reactive loading on the circuit changes,
we reduce losses by switching banks on and off to track these
changes.
• Voltage limits — If optimally applied banks under the average loading
scenario cause excessive voltage under light load, then use
switched banks.
In addition, automated capacitors — those with communications — have
the flexibility to also use distribution vars for transmission support.
Fixed banks are relatively easy to site and size optimally. Switched banks
are more difficult. Optimally sizing capacitors, placing them, and deciding
when to switch them are difficult tasks. Several software packages are available
that can optimize this solution. This is an intensely studied area, and
technical literature documents several approaches (among these Carlisle and
El-Keib, 2000; Grainger and Civanlar, 1985; Shyh, 2000).
To place switched capacitors using the 1/2-kvar method, again place the
banks at the location where the line kvar equals half the bank rating. But
instead of using the average reactive load profile (the rule for fixed banks),
use the average reactive flow during the time the capacitor is on. With timeswitched
banks and information on load profiles (or typical load profiles)