Fig. 2,462.—Diagram of automatic voltage regulator, using line drop compensator. For ordinary installations the compensating winding on the alternating current control magnet is connected to a current transformer in the main feeder. A dial switch is provided by which the strength of the alternating current control magnet can be varied and the regulator made to compensate for any desired line drop up to 15 per cent. according to the line requirements. Where the power factor of the load has a wide range of variation, a special line drop compensator, such as shown in fig. 2,459, adapted to the regulator would be desirable. The connections are readily understood by the diagram. The number of condenser sections which will prevent undue arcing at the relay contacts depends on the characteristics of the exciter. They may be roughly estimated by allowing one section for each 15 kw. capacity for exciters with laminated poles, and one for each 22 kw. capacity for exciters with solid steel poles. It is necessary though to have one condenser section for each pair of relay contacts, and at times it becomes necessary to apply a double section for each pair of contacts. In the lower part of the figure the line drop compensation and connections is reproduced in more detail on a larger scale.[2]
[2] NOTE.—It is desirable, in any system of distribution, to read the active voltage at the point of distribution, by means of the voltmeters in the station. A compensator proper consists of a variable resistance and a variable inductance, and sometimes a current transformer. In wiring, the voltmeter, instead of being connected directly across the secondaries of a pressure transformer, has inserted in series with it, portions of the resistance and inductance of the compensator. These are so connected that the drop in pressure across them will be combined with that of the pressure transformer, so that the voltmeter reading indicates the pressure at the center of distribution or end of the line.
Starting Compensators.—These are used for starting induction motors and consist of inductive windings (one for each phase) with a number of taps connecting with switch contacts as shown in fig. 2,463. A starting compensator is similar to a rheostat except that inductive windings are used in place of the resistance grids.
Fig. 2,463.—Diagram of connections of General Electric two phase starting compensator with no voltage release and fuses.
Ques. Describe the inductive windings.
Ans. The compensator winding consists of an inductive coil in each phase with each coil placed on a separate leg of a laminated iron core. Each coil is provided with several taps so located that a number of sub-voltages may be obtained.