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CAPACITOR PLACEMENT AND CAPACITOR & VOLTAGE REGULATORS




CAPACITOR PLACEMENT AND CAPACITOR & VOLTAGE REGULATORS
How does capacitor and regulators affect each other during operation?

The installation of capacitors on a feeder can interfere with the proper operation of voltage regulators on that same feeder. This problem is relatively simple to overcome, but should not be ignored. Even fixed capacitors can cause some interference with regulators, but the interference is greater with switched capacitors.

Capacitors, either fixed or switched, installed on the upstream side of the load center of a voltage regulator’s line drop compensator setting can thwart the compensator’s reactance setting. This problem is easily solved by setting the reactance compensation to zero and increasing the resistance compensation enough to achieve the same results previously obtained with both types of compensation.

A voltage controlled switched capacitor on the load side of a voltage regulator can fail to switch properly because of action being taken by the regulator. For example, if the capacitor is on and feeder load begins to decline, the voltage regulator will act to prevent a resulting line voltage rise. Consequently, the capacitor might stay on even to the point of causing a leading power factor instead of switching off to follow the load. Adding complexity to control circuits on the regulator, the capacitor, or both is necessary to address these problems. However, such complexity creates other practical problems and should be avoided if possible.

Potential interaction problems with voltage regulators lead to the recommendation that switched capacitors not be controlled solely by voltage. However, voltage overrides on the other types of controls will create no problems as long as the capacitor voltage action settings lie outside the voltage regulator settings. For example, a capacitor could be controlled by a time switch when line voltage is from 117 to 126 volts on a 120-volt base, and a voltage override control could be set to take appropriate action if the voltage falls below 117 volts or rises above 126 volts. There are some bandwidth complications to address in making the transition between the two types of controls, but these problems are manageable.

Capacitor Placement Studies

Capacitor installations on a distribution feeder will produce greater benefits if an engineering study is performed to determine the size, location, control type, and settings of the individual units. The engineering study should include recommendations on the units to be switched and the type of switching controls to be used. Also, manufacturers’ standard capacitor sizes and the availability of poles with space for the installations should be addressed in such a study. The study settings for switched banks should be fine-tuned after the capacitor has been in operation for a short period of time.
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