Automatic insulation tester for grounded and ungrounded electrical equipment

摘要

An automatic insulation tester tests the insulation resistance of electrical equipment when the electrical equipment is inoperative. The automatic insulation tester is automatically rendered operative when the electrical equipment is inoperative, and is automatically rendered inoperative when the electrical equipment is operative. The automatic insulation tester applies a voltage on the order of the rated voltage of the electrical equipment to the electrical equipment and measures and displays the insulation resistance of the electrical equipment. When the insulation resistance falls below a predetermined value, an indicator is activated, and remains in an activated state until the insulation resistance of the electrical equipment rises above the predetermined value and the automatic insulation tester is manually reset. In preferred embodiments of the present invention, the automatic insulation tester is provided with a ground interrupter to allow the automatic insulation tester to be used with permanently grounded electrical equipment. A single comparator can be used to monitor several motors or generators by multiplexing the inputs to the comparator and demultiplexing the output from the comparator. The selection means for the motor or generator can be automatic, so that a periodic cycling is performed, or can be manual.