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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Function of auxiliary relay is as
Change over relay
Supervisory relay
Tripping relay
All of above
All of above
Quick Summary: An auxiliary relay is a secondary switching device used to multiply the number of contacts, amplify signals, or perform logical functions in a protection scheme. It acts as an intermediary between the main protective relay and the circuit breaker or alarm circuits.
An auxiliary relay is a secondary switching device used to multiply the number of contacts, amplify signals, or perform logical functions in a protection scheme. It acts as an intermediary between the main protective relay and the circuit breaker or alarm circuits.
Pcoil=RV2 — Power consumed by the relay coil
T∝Φ1Φ2sin(θ) — Basic torque principle for electromagnetic operation
When a main protective relay detects a fault, it operates to energize the auxiliary relay coil. The auxiliary relay then operates its multiple contacts to perform various functions simultaneously, such as tripping the circuit breaker, initiating reclosing, triggering local/remote alarms, and providing indication signals.
Auxiliary relays serve as 'signal multipliers' in protection circuits.
They provide electrical isolation between the sensing circuit and the high-power control circuit.
Common configurations include hand-reset, self-reset, or electrical-reset types.
They ensure reliable operation of circuit breakers by providing sufficient contact capacity.
Contact multiplication allows one relay to perform multiple simultaneous actions.
Increases the flexibility of protection schemes.
Introduces slight time delay in the protection sequence.
Requires additional DC control power supply.
Circuit breaker tripping control.
Alarm and indication lamp circuits.
Interlocking logic for complex switchgear operations.
An auxiliary relay is often termed a 'slave relay' when operated by a main sensing element.
The term 'tripping relay' specifically refers to a high-speed auxiliary relay that holds the circuit breaker trip coil energized until the mechanical trip latch is cleared.
D is correct — Auxiliary relays are versatile devices capable of functioning as change-over, supervisory, or tripping elements within electrical protection systems.
In competitive exams, remember that auxiliary relays are primarily used to increase the contact capacity of a low-power output signal, which is critical for operating heavy trip coils of EHV circuit breakers.