FIELD GROUND FAULT DETECTOR AND FIELD GROUND RELAY

摘要

PURPOSE:To sustain the ground fault detection sensitivity at a constant level even upon fluctuation of DC voltage by determining the ratio of ground fault resistance to a specific resistance based on the ratio of voltage across the ground fault resistance to the voltage across the specific resistance. CONSTITUTION:The voltage across a resistor 2 is passed through a low-pass filter 3-1 while he voltage between an N side field circuit E and the earth is passed through a low-pass filter 3-2. DC output voltages from the low-pass filters 3-1 and 3-2 are fed to a level ratio deciding circuit 4. If the criterion for deciding the level is set such that a decision is made that a ground fault has occurred when a detected ground fault resistance is lower than (n) times of the resistance of the resistor 2, a decision is made that a ground fault has occurred when the DC voltage between the N side field circuit E and the earth fed from the low-pass filter 3-2 drops below (n) times of DC voltage across the resistor 2 fed from the low-pass filter 3-1 and it is notified to the outside. This constitution sustains the ground fault detection sensitivity at a constant level even upon fluctuation of DC voltage 1.