Which relay type is favored for protecting short transmission lines against phase faults?
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Answer: B. Reactance
Explanation
Reactance relays are well-suited for protecting short transmission lines because their operation is practically unaffected by arc resistance. Short lines have very low line impedance, making arc resistance a significant error source for other relay types. By measuring only the reactive component of impedance, reactance relays maintain accurate tripping boundaries during short-circuit faults. Transmission line protection relies on distance relays that measure the impedance between the relay location and the fault point. Arc resistance can vary unpredictably during a fault, introducing measurement errors in impedance calculations. Reactance relay operating characteristics form horizontal lines on the resistance-reactance plane, focusing strictly on reactive impedance.
Induction type describes a general mechanical construction rather than a specialized distance measurement characteristic for short lines. Impedance relays are heavily influenced by fault arc resistance, making them unsuitable for very short transmission lines. None of the above is incorrect because reactance relays are specifically designed and favored for short-line phase fault protection.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
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