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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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In which case HRC fuse provide best protection?
Overload
Open circuit
Short circuit
None of above
Short circuit
Quick Summary: HRC (High Rupturing Capacity) fuses are specifically designed to handle high fault currents with extremely fast operation. They provide their most effective protection during short-circuit conditions where the prospective fault current is significantly higher than the rated current.
HRC (High Rupturing Capacity) fuses are specifically designed to handle high fault currents with extremely fast operation. They provide their most effective protection during short-circuit conditions where the prospective fault current is significantly higher than the rated current.
I2t=constant — represents the pre-arcing energy limit of the fuse element
Q=∫i2Rdt — represents the total heat energy generated during the fault
The HRC fuse consists of a silver element embedded in a quartz powder filler. Upon the occurrence of a short circuit, the current rises rapidly, causing the element to melt. The arc generated is extinguished by the surrounding quartz powder, which absorbs the energy and fuses into a non-conductive solid (fulgurite), effectively interrupting the circuit within a few milliseconds.
HRC fuses exhibit an inverse time-current characteristic.
They provide excellent discrimination, meaning only the fuse nearest to the fault operates.
The quartz powder prevents the re-establishment of the arc even at high recovery voltages.
They are primarily used in high-voltage and low-voltage distribution systems for backup protection.
Extremely fast clearing of short-circuit faults
High breaking capacity
Maintenance-free and no aging effect if operated within limits
Requires replacement after every operation (non-reusable)
Can lead to single-phasing in 3-phase systems if only one fuse blows
Industrial distribution boards
Motor starter backup protection
Transformer primary side protection
Option A (Overload) is incorrect because while HRC fuses can operate on overloads, they are not optimized for this compared to circuit breakers or thermal relays, which offer better inverse-time features.
Option B (Open circuit) is irrelevant as a fuse cannot detect an open circuit.
C is correct — HRC fuses are explicitly designed to interrupt the high magnitude currents associated with short-circuit faults before peak values can damage equipment.
In competitive exams, remember that HRC fuses are 'current limiting' devices; their primary purpose is the rapid disconnection of prospective fault currents, not routine overload management.