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MINIMIZING VOLTAGE REGULATOR LOSSES


How to minimize loss on Voltage Regulators Operation?

To minimize losses on substation regulators, either separate units or substaton load tap changers, the high-voltage tap setting on the substation transformer should be set so the regulators will spend the maximum amount of time near the neutral position, since regulator losses increase as the regulator tap position farther away from neutral. Ideally substation regulators should spend approximately the same amount of time bucking voltage as they do boosting voltage. This keeps the regulators near neutral under average system conditions.

Regulator Settings
Line and transformer losses on a distribution system are minimized by the proper operation of voltage regulators. As explained earlier, line voltage should be kept as high as possible without causing overvoltage conditions on distribution transformers and on consumers' equipment. Consequently, care should be taken to set regulators correctly and to use the line drop compensators. The issue of increased distribution transformer core losses when energization voltage is set above normal is especially important for distributors because of their high costs of core losses. If most of the transformers on a feeder are of low-loss design, and if the transformers are fully loaded at peak load, then a line voltage of approximately 105% of nominal (126 volts on a 120-volt base) is definitely the most economical operating practice. However, during off-peak periods the transformers are lightly loaded and the economy chages in favor of a lower energization voltage.

A feeder that supplies transformers that are mostly either high-loss or not fully loaded at peak, or both of these conditions, is very susceptible to excessive core losses at high line voltage. For such feeders, a maximum voltage setting somewhat less than 105% would be more economical. However, voltage setting that does not support a voltage of at least 114 volts on a 120-volt base at the end of the line during peak load conditions will, in most cases, result in higher overall costs than would be incurred at a higher voltage.

Voltage regulator line-drop compensators provide the valuable capability of automatically reducing line voltage during off-peak periods and keepin voltage high during peak-loads periods. This is the cost-optimal way to operate a feeder, so distributors are urged to properly apply these devices. Methods for calculating and making settings can be found in voltage regulator manufacturers' literature.

Under no circumstances should regulators be set such that a voltage in excess of 105% of nominal is impressed on distribution transformers. The core losses of distribution transformers begin to increase to very large levels when the voltage exceeds 105% of nominal. Furthermore, voltages in excess of 105% of nominal can be damaging to distribution transformers and other devices installed on primary lines.

On feeders where switched capacitors are in service, careful coordination is necessary between controls on voltage regulators and the switched capacitors.
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