Novel test circuits for protective relays

IN THE TEST, calibration, checking, and setting of protective relays, and in the determination of their characteristic operating curves, it is of course necessary to apply to the relays the quantity or quantities which are expected to operate it. Problems are sometimes encountered in obtaining suitable test facilities, particularly when two or more variable a-c quantities are involved, and the phase angle between the quantities must be known or controlled. The solution to such problems generally may be obtained in the laboratory by special circuits and equipment.