초록 ▼

An earth fault detection circuit employs a differential current transformer and burden resistor to sample circuit current for potential earth fault current. A second order low pass filter circuit is employed to filter out harmonics within the protected circuit and a time delay circuit is used to ins

An earth fault detection circuit employs a differential current transformer and burden resistor to sample circuit current for potential earth fault current. A second order low pass filter circuit is employed to filter out harmonics within the protected circuit and a time delay circuit is used to insure the occurrence of a true earth fault leakage condition. A circuit with an operational amplifier is used to create a symmetric power supply for the rest of the circuits from a full wave rectified AC source.

대표청구항 ▼

[ We claim:] [1.] A control circuit for an earth leakage relay comprising:a detection circuit for monitoring earth leakage current within an electrical system;a filter circuit for attenuating multiples of a frequency of a circuit current; anda comparator circuit for comparing a signal representative

[ We claim:] [1.] A control circuit for an earth leakage relay comprising:a detection circuit for monitoring earth leakage current within an electrical system;a filter circuit for attenuating multiples of a frequency of a circuit current; anda comparator circuit for comparing a signal representative of said earth leakage current with a threshold value and outputting a control signal to an electric relay to interrupt said circuit current when said signal exceeds said threshold value.