Protection & Switchgear interview questions

1. A.voltage that appears across breaker contacts immediately after current interruption, which must stay below the breaker withstand to avoid re-strike
2. B.compares current entering and leaving a zone and trips on the difference, with a bias slope to restrain against CT mismatch on through-faults
3. C.arc is quenched in sulphur hexafluoride, whose dielectric strength is about 2.5 times air; standard at 66 kV and above despite being a potent greenhouse gas
4. D.overcurrent relay whose operating time falls as fault current rises, the IEC standard-inverse curve being t = 0.14·TMS/(I^0.02 − 1)

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1. A.IEC 61850 GOOSE
2. B.SF6 circuit breaker
3. C.Transient recovery voltage
4. D.Differential protection

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1. A.Differential protection — high-impedance differential scheme on a transformer winding that detects earth faults near the neutral which biased differential cannot see
2. B.Differential protection — interval of 0.2–0.4 s kept between successive IDMT relays to cover breaker operating time, relay overshoot and CT/relay errors
3. C.Differential protection — compares current entering and leaving a zone and trips on the difference, with a bias slope to restrain against CT mismatch on through-faults
4. D.Differential protection — gas-actuated relay in the pipe between tank and conservator that alarms on slow gas accumulation and trips on a sudden oil surge

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1. A.interval of 0.2–0.4 s kept between successive IDMT relays to cover breaker operating time, relay overshoot and CT/relay errors
2. B.arc is quenched in sulphur hexafluoride, whose dielectric strength is about 2.5 times air; standard at 66 kV and above despite being a potent greenhouse gas
3. C.voltage that appears across breaker contacts immediately after current interruption, which must stay below the breaker withstand to avoid re-strike
4. D.protection CT with 5% composite error at 20 times rated current, unlike metering classes 0.2 or 0.5 that are accurate only near rated current

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1. A.IDMT relay
2. B.Buchholz relay
3. C.SF6 circuit breaker
4. D.Distance relay zones

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1. A.SF6 circuit breaker — high-impedance differential scheme on a transformer winding that detects earth faults near the neutral which biased differential cannot see
2. B.SF6 circuit breaker — voltage that appears across breaker contacts immediately after current interruption, which must stay below the breaker withstand to avoid re-strike
3. C.SF6 circuit breaker — arc is quenched in sulphur hexafluoride, whose dielectric strength is about 2.5 times air; standard at 66 kV and above despite being a potent greenhouse gas
4. D.SF6 circuit breaker — protection CT with 5% composite error at 20 times rated current, unlike metering classes 0.2 or 0.5 that are accurate only near rated current

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1. A.contacts part inside a sealed vacuum interrupter and the arc dies at the first current zero; the dominant choice from 3.3 kV to 33 kV
2. B.arc is quenched in sulphur hexafluoride, whose dielectric strength is about 2.5 times air; standard at 66 kV and above despite being a potent greenhouse gas
3. C.voltage that appears across breaker contacts immediately after current interruption, which must stay below the breaker withstand to avoid re-strike
4. D.gas-actuated relay in the pipe between tank and conservator that alarms on slow gas accumulation and trips on a sudden oil surge

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1. A.Grading margin
2. B.Vacuum circuit breaker
3. C.IEC 61850 GOOSE
4. D.Transient recovery voltage

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1. A.Vacuum circuit breaker — contacts part inside a sealed vacuum interrupter and the arc dies at the first current zero; the dominant choice from 3.3 kV to 33 kV
2. B.Vacuum circuit breaker — overcurrent relay whose operating time falls as fault current rises, the IEC standard-inverse curve being t = 0.14·TMS/(I^0.02 − 1)
3. C.Vacuum circuit breaker — interval of 0.2–0.4 s kept between successive IDMT relays to cover breaker operating time, relay overshoot and CT/relay errors
4. D.Vacuum circuit breaker — gas-actuated relay in the pipe between tank and conservator that alarms on slow gas accumulation and trips on a sudden oil surge

Answer + AI explanation with Pro

1. A.arc is quenched in sulphur hexafluoride, whose dielectric strength is about 2.5 times air; standard at 66 kV and above despite being a potent greenhouse gas
2. B.gas-actuated relay in the pipe between tank and conservator that alarms on slow gas accumulation and trips on a sudden oil surge
3. C.interval of 0.2–0.4 s kept between successive IDMT relays to cover breaker operating time, relay overshoot and CT/relay errors
4. D.contacts part inside a sealed vacuum interrupter and the arc dies at the first current zero; the dominant choice from 3.3 kV to 33 kV

Answer + AI explanation with Pro

1. A.Buchholz relay
2. B.Differential protection
3. C.Grading margin
4. D.Transient recovery voltage

Answer + AI explanation with Pro

1. A.Buchholz relay — high-impedance differential scheme on a transformer winding that detects earth faults near the neutral which biased differential cannot see
2. B.Buchholz relay — peer-to-peer Ethernet multicast message that carries trips and interlocks between IEDs within about 4 ms, replacing hard-wired copper links
3. C.Buchholz relay — compares current entering and leaving a zone and trips on the difference, with a bias slope to restrain against CT mismatch on through-faults
4. D.Buchholz relay — gas-actuated relay in the pipe between tank and conservator that alarms on slow gas accumulation and trips on a sudden oil surge

Answer + AI explanation with Pro

1. A.high-impedance differential scheme on a transformer winding that detects earth faults near the neutral which biased differential cannot see
2. B.overcurrent relay whose operating time falls as fault current rises, the IEC standard-inverse curve being t = 0.14·TMS/(I^0.02 − 1)
3. C.protection CT with 5% composite error at 20 times rated current, unlike metering classes 0.2 or 0.5 that are accurate only near rated current
4. D.contacts part inside a sealed vacuum interrupter and the arc dies at the first current zero; the dominant choice from 3.3 kV to 33 kV

Answer + AI explanation with Pro

1. A.IEC 61850 GOOSE
2. B.Transient recovery voltage
3. C.Differential protection
4. D.IDMT relay

Answer + AI explanation with Pro

1. A.IDMT relay — contacts part inside a sealed vacuum interrupter and the arc dies at the first current zero; the dominant choice from 3.3 kV to 33 kV
2. B.IDMT relay — interval of 0.2–0.4 s kept between successive IDMT relays to cover breaker operating time, relay overshoot and CT/relay errors
3. C.IDMT relay — arc is quenched in sulphur hexafluoride, whose dielectric strength is about 2.5 times air; standard at 66 kV and above despite being a potent greenhouse gas
4. D.IDMT relay — overcurrent relay whose operating time falls as fault current rises, the IEC standard-inverse curve being t = 0.14·TMS/(I^0.02 − 1)

Answer + AI explanation with Pro

1. A.interval of 0.2–0.4 s kept between successive IDMT relays to cover breaker operating time, relay overshoot and CT/relay errors
2. B.Zone 1 covers about 80% of the line instantaneously, Zone 2 reaches 120% with 0.3–0.5 s delay, Zone 3 backs up the adjacent line
3. C.high-impedance differential scheme on a transformer winding that detects earth faults near the neutral which biased differential cannot see
4. D.arc is quenched in sulphur hexafluoride, whose dielectric strength is about 2.5 times air; standard at 66 kV and above despite being a potent greenhouse gas

Answer + AI explanation with Pro

1. A.Grading margin
2. B.Distance relay zones
3. C.IEC 61850 GOOSE
4. D.Buchholz relay

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1. A.Distance relay zones — Zone 1 covers about 80% of the line instantaneously, Zone 2 reaches 120% with 0.3–0.5 s delay, Zone 3 backs up the adjacent line
2. B.Distance relay zones — voltage that appears across breaker contacts immediately after current interruption, which must stay below the breaker withstand to avoid re-strike
3. C.Distance relay zones — compares current entering and leaving a zone and trips on the difference, with a bias slope to restrain against CT mismatch on through-faults
4. D.Distance relay zones — protection CT with 5% composite error at 20 times rated current, unlike metering classes 0.2 or 0.5 that are accurate only near rated current

Answer + AI explanation with Pro

1. A.overcurrent relay whose operating time falls as fault current rises, the IEC standard-inverse curve being t = 0.14·TMS/(I^0.02 − 1)
2. B.peer-to-peer Ethernet multicast message that carries trips and interlocks between IEDs within about 4 ms, replacing hard-wired copper links
3. C.compares current entering and leaving a zone and trips on the difference, with a bias slope to restrain against CT mismatch on through-faults
4. D.protection CT with 5% composite error at 20 times rated current, unlike metering classes 0.2 or 0.5 that are accurate only near rated current

Answer + AI explanation with Pro

1. A.IDMT relay
2. B.Differential protection
3. C.CT class 5P20
4. D.Distance relay zones

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1. A.CT class 5P20 — gas-actuated relay in the pipe between tank and conservator that alarms on slow gas accumulation and trips on a sudden oil surge
2. B.CT class 5P20 — protection CT with 5% composite error at 20 times rated current, unlike metering classes 0.2 or 0.5 that are accurate only near rated current
3. C.CT class 5P20 — arc is quenched in sulphur hexafluoride, whose dielectric strength is about 2.5 times air; standard at 66 kV and above despite being a potent greenhouse gas
4. D.CT class 5P20 — Zone 1 covers about 80% of the line instantaneously, Zone 2 reaches 120% with 0.3–0.5 s delay, Zone 3 backs up the adjacent line

Answer + AI explanation with Pro

1. A.interval of 0.2–0.4 s kept between successive IDMT relays to cover breaker operating time, relay overshoot and CT/relay errors
2. B.peer-to-peer Ethernet multicast message that carries trips and interlocks between IEDs within about 4 ms, replacing hard-wired copper links
3. C.voltage that appears across breaker contacts immediately after current interruption, which must stay below the breaker withstand to avoid re-strike
4. D.contacts part inside a sealed vacuum interrupter and the arc dies at the first current zero; the dominant choice from 3.3 kV to 33 kV

Answer + AI explanation with Pro

1. A.IEC 61850 GOOSE
2. B.Distance relay zones
3. C.SF6 circuit breaker
4. D.Buchholz relay

Answer + AI explanation with Pro

1. A.IEC 61850 GOOSE — peer-to-peer Ethernet multicast message that carries trips and interlocks between IEDs within about 4 ms, replacing hard-wired copper links
2. B.IEC 61850 GOOSE — arc is quenched in sulphur hexafluoride, whose dielectric strength is about 2.5 times air; standard at 66 kV and above despite being a potent greenhouse gas
3. C.IEC 61850 GOOSE — overcurrent relay whose operating time falls as fault current rises, the IEC standard-inverse curve being t = 0.14·TMS/(I^0.02 − 1)
4. D.IEC 61850 GOOSE — Zone 1 covers about 80% of the line instantaneously, Zone 2 reaches 120% with 0.3–0.5 s delay, Zone 3 backs up the adjacent line

Answer + AI explanation with Pro

1. A.peer-to-peer Ethernet multicast message that carries trips and interlocks between IEDs within about 4 ms, replacing hard-wired copper links
2. B.protection CT with 5% composite error at 20 times rated current, unlike metering classes 0.2 or 0.5 that are accurate only near rated current
3. C.interval of 0.2–0.4 s kept between successive IDMT relays to cover breaker operating time, relay overshoot and CT/relay errors
4. D.voltage that appears across breaker contacts immediately after current interruption, which must stay below the breaker withstand to avoid re-strike

Answer + AI explanation with Pro

1. A.CT class 5P20
2. B.Transient recovery voltage
3. C.Distance relay zones
4. D.Vacuum circuit breaker

Answer + AI explanation with Pro

1. A.Transient recovery voltage — gas-actuated relay in the pipe between tank and conservator that alarms on slow gas accumulation and trips on a sudden oil surge
2. B.Transient recovery voltage — voltage that appears across breaker contacts immediately after current interruption, which must stay below the breaker withstand to avoid re-strike
3. C.Transient recovery voltage — overcurrent relay whose operating time falls as fault current rises, the IEC standard-inverse curve being t = 0.14·TMS/(I^0.02 − 1)
4. D.Transient recovery voltage — compares current entering and leaving a zone and trips on the difference, with a bias slope to restrain against CT mismatch on through-faults

Answer + AI explanation with Pro

1. A.peer-to-peer Ethernet multicast message that carries trips and interlocks between IEDs within about 4 ms, replacing hard-wired copper links
2. B.gas-actuated relay in the pipe between tank and conservator that alarms on slow gas accumulation and trips on a sudden oil surge
3. C.overcurrent relay whose operating time falls as fault current rises, the IEC standard-inverse curve being t = 0.14·TMS/(I^0.02 − 1)
4. D.interval of 0.2–0.4 s kept between successive IDMT relays to cover breaker operating time, relay overshoot and CT/relay errors

Answer + AI explanation with Pro

1. A.SF6 circuit breaker
2. B.Grading margin
3. C.IEC 61850 GOOSE
4. D.Distance relay zones

Answer + AI explanation with Pro

1. A.Grading margin — voltage that appears across breaker contacts immediately after current interruption, which must stay below the breaker withstand to avoid re-strike
2. B.Grading margin — interval of 0.2–0.4 s kept between successive IDMT relays to cover breaker operating time, relay overshoot and CT/relay errors
3. C.Grading margin — protection CT with 5% composite error at 20 times rated current, unlike metering classes 0.2 or 0.5 that are accurate only near rated current
4. D.Grading margin — arc is quenched in sulphur hexafluoride, whose dielectric strength is about 2.5 times air; standard at 66 kV and above despite being a potent greenhouse gas

Answer + AI explanation with Pro