Electrical Power Plant Design: Distribution System

WEEK 13: DISTRIBUTION: EQUIPMENT

Voltage Regulators is generally used to maintain the voltage of a line. The primary feed voltage generally drops when a large load current is drawn and less voltage is available across the primaries of the distribution transformers. The regulator maintains the voltage at the proper rated value at all times. Most of the voltage regulators for distribution systems are pole-mounted.

The principle of operation of a voltage regulator is somewhat similar to that of a transformer having taps. This form of a regulator has two fixed windings, a primary (high-voltage) winding connected in shunt or across a line, and a secondary or low-voltage winding connected in series with the line. The secondary series winding is provided with as many taps as necessary to vary the voltage across this winding. This equipment operates as a voltage regulator by means of a control circuit which automatically changes the tap setting on the series winding, while leaving the voltage applied to the primary (high-voltage) winding alone. The variable voltage in the series winding can thus be added or subtracted from the incoming (or primary) voltage, resulting in an outgoing voltage which can be kept approximately constant even when the incoming primary voltage may vary.

An older type, known as the induction -type voltage regulator, accomplishes the same effect by having the primary coil voltage rotate, changing the position in relation to the secondary coil, which in this case has no taps.

Voltage regulators are either hand or motor-operated. When a motor is used, it is usually automatically controlled by a means of relays.

Distribution Capacitors

Purpose It is the job of capacitors to keep the power factor as close to one (1) as possible. Capacitors counteract inductance and usually consists of two conductors separated by an insulating substance. Among other materials which may be used are aluminum foil separated by oil-impregnated paper or synthetic insulating material. Introducing capacitors into a circuit causes the current to lead the voltage in phase.

Mounting Capacitors are mounted on crossarms or platforms and are protected with lightning arresters and cutouts, just as transformers. Auto-Switched and Fixed Pole-Top Capacitors improve phase relation between line voltage and line current in a distribution system. Series Pole-Top Capacitors improve voltage, reduce flicker, connected in series with a distribution transformer. Residential Secondary Capacitors improve voltage, reduce flicker, connected in series with a distribution secondary lines.