JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III POWER SYSTEM PROTECTION Previous Question Paper (February - 2023 - R18)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, Answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
What is primary and back – up protection?
Answer
Primary protection is the first line of defense that acts as the main protection system for a specific zone. It is designed to operate immediately when a fault occurs within its protected area to isolate the faulty component.
Back-up protection is the second line of defense that operates only if the primary protection fails to clear the fault within a predetermined time interval. It ensures system security by isolating the faulty section when the primary system is unable to do so.
Draw and explain the basic components of a protection system in brief.
Answer
A power system protection scheme consists of three primary components that work in coordination to isolate faulty sections:
- Instrument Transformers (CTs and VTs): These step down high voltage and current levels to safe, manageable values for the protective relays while providing electrical isolation.
- Protective Relays: These are the decision-making units. They continuously monitor the inputs from instrument transformers and compare them against pre-set threshold values to detect abnormal conditions like faults.
- Circuit Breakers: These are the final switching devices. Upon receiving a trip signal from the relay, they physically open the electrical circuit to disconnect the faulty equipment from the healthy system.
What is an impedance relay? Explain its operating principle.
Answer
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Distinguish between current setting and time setting.
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What is wire pilot protection?
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How do you protect a bus bar? Give brief explanation.
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List the limitations of Static relays.
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Explain how microprocessor-based relays are different from electromechanical relays.
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Define the term Fuse and explain its usage.
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Explain different ratings of circuit breakers.
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Part B
Explain the following protective schemes in brief: Overcurrent protection, Distance Protection, Carrier – current protection, Differential Protection.
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Explain the basic principle of operation of electromagnetic relay. State different types of electromagnetic relays.
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What are the various overcurrent protective schemes? Discuss their merits, demerits and field of applications.
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An earth-fault starting relay has a setting of 35%, and a current rating of 5 A. It is connected to a CT of ratio 500/5. Calculate pick-up current in primary for which the earth fault relay operates.
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Discuss how (i) an electromechanical and (ii) a static MHO relay is realized. Explain its characteristic on the R-X diagram.
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Explain the effect of power swings on the performance of distance relays.
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What is carrier aided distance protection? What are its different types? Discuss the permissive under-reach transfer tripping scheme of protection.
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What type of protective device is used for the protection of an alternator against overheating of its (i) stator, (ii) rotor? Discuss them in brief.
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A three-phase, 132 kV/33 kV star-delta connected power transformer is protected by differential protection scheme. Determine the ratio of CTs on the HV side of the transformer, if that on the LV side is 300/5. How are the CT secondaries connected?
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Explain the following types of Static Amplitude comparators: Integrating comparators and Instantaneous comparator.
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Explain the working of static IDMT over current relay with a neat block diagram.
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What is an Arc Interruption and explain the following methods of Arc Interruption: High resistance interruption and Current zero interruption.
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Explain the operation of H. V. D. C. circuit breakers.
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Explain the working of SF6 Circuit breaker with a neat circuit diagram.
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