Why Protection Relays and LSIG release same LV side?
On the LV (Low Voltage) side of transformers (or) switchgear, protection relays and the ACB/MCCB’s LSIG (Long, Short, Instantaneous, Ground) release are employed to protect against electrical faults.
Why are they on the same LV side?
Faults like as overload, short-circuit & earth fault are most common on the LV side, where current is high.
The LSIG release (built-in trip unit for breakers) provides rudimentary protection against these faults.
Protection relays (such as differential, REF, overcurrent, and earth fault relays) offer sophisticated, selective & backup protection with additional parameters, logic, and coordination.
Both collaborate to rapidly detect and isolate LV faults, assuring transformer, busbar & feeder safety.
LSIG provides primary breaker protection whereas relays provide selected system-level protection. Both are necessary on the LV side wherein most protection activities are required.
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