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______ combines the function of isolators and a switch.
Circuit breaker
Load interrupter switch
Earth switch
Line trap unit
Load interrupter switch
A load interrupter switch (also known as a switch-fuse unit or load break switch) is designed to interrupt normal load currents, effectively combining the load switching capability with the physical isolation required for safety and maintenance. Unlike a simple isolator, which is intended to be operated only when the current is zero, the load interrupter switch includes arc-quenching mechanisms to safely break the current under load conditions.
A load interrupter switch (also known as a switch-fuse unit or load break switch) is designed to interrupt normal load currents, effectively combining the load switching capability with the physical isolation required for safety and maintenance. Unlike a simple isolator, which is intended to be operated only when the current is zero, the load interrupter switch includes arc-quenching mechanisms to safely break the current under load conditions.
P=3тАЛVLтАЛILтАЛcos╧Х тАФ represents the load power handled during interruption
IarcтАЛ=RarcтАЛVarcтАЛтАЛ тАФ represents the current dynamics during the interruption process
The device operates by using a spring-assisted quick-make/quick-break mechanism to minimize the arcing period. When opening under load, the contacts move rapidly to draw an arc, which is subsequently extinguished by an arc-chute or gas/vacuum medium. Once the current is broken, the device maintains a visible air gap, satisfying the requirement for an isolator.
Load interrupter switches are limited by their short-circuit breaking capacity.
They are distinct from circuit breakers, which can handle full fault current interruption.
Commonly used in ring main units (RMUs) and distribution substations.
The arc quenching medium can be SF6 gas, vacuum, or air with arc chutes.
Cost-effective alternative to circuit breakers for light loads.
Provides a clear visual indication of disconnection (isolation).
Space-saving design as two devices are integrated into one unit.
Limited fault current breaking capability.
Not suitable for heavy-duty protection without supplementary fuses or breakers.
Distribution network switching.
Transformer primary side switching.
Motor starter circuits in industrial plants.
An isolator is strictly a no-load device meant for maintenance isolation only.
Circuit breakers possess high-speed protection mechanisms for clearing faults which a load interrupter switch typically lacks without add-on fuses.
Option A (Circuit breaker) is designed for fault current interruption, not simply as a combination switch.
Option C (Earth switch) is used for discharging trapped charges, not for load switching.
Option D (Line trap) is a coupling device for Power Line Carrier Communication (PLCC).
B is correct тАФ A load interrupter switch integrates the arc-quenching capability required to break load current with the mechanical isolation feature of a standard isolator.
In competitive exams, always distinguish between a device that handles 'load current' (interrupter switch) and one that handles 'fault current' (circuit breaker).