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ETO ETO Exam papers 📅 Dec 2021

Exam Question

(a) Compare the effectiveness of a current limiting circuit breaker with that of a HRC fuse. (6)

(b) A coil having a resistance of 10 ohm and an inductance of 0.15 H is connected in series with a capacitor across a 100 V, 50 Hz supply. If the current and the voltage are in phase what will be the value of the current in the circuit and the voltage drop across the coil? (10)

Reference Answer

A current limiting circuit breaker exhibits a current limiting characteristic. It can reduce the peak apparent fault current to a lesser value and isolate the fault in less than a half cycle time. They can not interrupt currents higher than their nameplate short circuit rating. Current-limiting circuit breakers, provide short-circuit protection without the need for current-limiting fuses. The breaker must be subjected to short-circuit testing at three levels: the threshold current, the intermediate point and the maximum interrupting rating. It can be more expensive to install, repair and replace. When breaker tripped it can be reset. It is most suitable for power circuit.
High Rupturing Capacity (HRC) Fuse can carry short circuit heavy current for a known time period. During this time if the fault gets removed, then it does not blow off, otherwise, it blows off or melts. It is part of the circuit which consists of a conductor which melts easily and breaks the connection when current exceeds the predetermined value. The fuse is the weakest part of an electrical circuit which breaks when more than predetermined current flows through it. It is less expensive to install, repair and replace. It is most suitable for electronic equipment, PLC/ PCB etc . When fuses are blown, they need to be replaced. The materials used for fuse wires are mainly tin, lead, zinc, silver, antimony, copper, aluminium etc
(b) Given:
Input voltage $V = 100V$

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