Fig. 2,459.—General Electric line drop compensator. It has two dial switches with many taps to the resistance and reactance in the box so that it can be adjusted to compensate accurately for line losses with loads of varying power factor. Dial R changes resistance, and dial X, reactance.
Fig. 2,460.—General Electric line drop compensator. This compensator contains besides resistance and inductance, a current transformer, the secondary of the transformer being connected in series with the resistance and inductance; the primary of the contained current transformer is connected to an external current transformer. The reactance and resistance are both so wound that any proportion of the winding can be cut in or out of the voltmeter circuit. Both elements have 12 points of adjustment of one volt each, giving a total combined drop at maximum setting of about 17 volts.
Ques. How can the voltmeter indicate the pressure at the center of distribution?
Ans. If the amount of inductance and resistance be properly adjusted, there will be produced a local circuit corresponding exactly in all its characteristics to the main circuit. Hence, any change in the main circuit produces a corresponding change in the local circuit, and causes the voltmeter to always indicate the pressure at the end of the line or center of distribution or at any point for which the adjustment is made.
Fig. 2,461.—Westinghouse line drop compensator. For single phase circuits, one compensator and one series transformer, that is the instrument as listed with transformers, will give correct indications for a single phase circuit. The same voltage transformer serves for both voltmeter and compensator. For balanced two phase circuits one compensator and one transformer connected in one of the phases is sufficient. Two single phase compensators should be used for unbalanced two phase circuits. For three phase circuits the compensator should be connected by means of two series transformers.
Ques. How should the adjustment be made?
Ans. It is advisable to calculate the ohmic drop for full load and set the resistance arm at the point which will give the required compensation and then adjust the inductance arm until the voltmeter reading corresponds to the voltage at the point on the line selected for normal voltage.