Electronic Overload Relay:
Electronic overload relay consists of a solid state circuit which operate the electromagnetic switching device to protect the load from overload.
The load current is sensed by using a transducer such as current
transformer (CT).
The output of current transformer is converted to voltage signal as required by electronic circuit.
The electronic circuit consists of RMS-to-DC conversion, threshold detection, time-setting & relay driver sections.
The output of relay driver section sends trip signal to electromagnetic switching device.
On the occurrence of over-load, the current magnitude is sensed by CT and current sensing circuit. The difference between full-load and over-load current is determined by electronic circuit. The differential current RMS value is converted to DC and according to this differential current value and time-setting, the relay driver section trips the electromagnetic switch with time delay.
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