Transformer & Motor Specification interview questions
33 real Transformer & Motor Specification questions from the Electrical Design bank, as asked in Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd — free to start.
1. What is Vector group Dyn11?
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A.delta HV, star LV with neutral brought out, LV leading HV by 30°; the standard connection for distribution transformers
B.ONAN uses natural oil and air, ONAF adds fans, OFAF pumps the oil and ODAF directs it into windings, each raising the rating
C.IEC 60529 two-digit code, first digit for solids (6 = dust-tight) and second for water (5 jets, 6 powerful jets, 7 immersion); IP55 is typical for motors
D.IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact
A.Vector group Dyn11 — ONAN uses natural oil and air, ONAF adds fans, OFAF pumps the oil and ODAF directs it into windings, each raising the rating
B.Vector group Dyn11 — delta HV, star LV with neutral brought out, LV leading HV by 30°; the standard connection for distribution transformers
C.Vector group Dyn11 — Indian and international standards for power transformers covering ratings, temperature rise, impedance tolerance (±10%) and type/routine tests
D.Vector group Dyn11 — short-circuit voltage as a percentage of rated voltage, about 4–5% for distribution up to 12.5% for large units; higher limits fault current but raises regulation
A.Cooling designations — ONAN uses natural oil and air, ONAF adds fans, OFAF pumps the oil and ODAF directs it into windings, each raising the rating
B.Cooling designations — insulation ageing rate doubles for every 6 K above the 98 °C reference hot-spot temperature per the IEC 60076-7 loading guide
C.Cooling designations — changes the turns ratio without interrupting supply, typically ±10% in 1.25% steps on the HV side; off-circuit taps only when de-energised
D.Cooling designations — IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact
A.insulation ageing rate doubles for every 6 K above the 98 °C reference hot-spot temperature per the IEC 60076-7 loading guide
B.IEC 60529 two-digit code, first digit for solids (6 = dust-tight) and second for water (5 jets, 6 powerful jets, 7 immersion); IP55 is typical for motors
C.IEC 60034-30-1 defines IE1 standard to IE4 super-premium; IS 12615 adopts them and India's motor QCO makes IE2 the legal minimum, IE3 the usual buyer spec
D.Indian and international standards for power transformers covering ratings, temperature rise, impedance tolerance (±10%) and type/routine tests
8. Which term means: "Indian and international standards for power transformers covering ratings, temperature rise, impedance tolerance (±10%) and type/routine tests"?
A.IS 2026 / IEC 60076 — Indian and international standards for power transformers covering ratings, temperature rise, impedance tolerance (±10%) and type/routine tests
B.IS 2026 / IEC 60076 — IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact
C.IS 2026 / IEC 60076 — insulation ageing rate doubles for every 6 K above the 98 °C reference hot-spot temperature per the IEC 60076-7 loading guide
D.IS 2026 / IEC 60076 — changes the turns ratio without interrupting supply, typically ±10% in 1.25% steps on the HV side; off-circuit taps only when de-energised
A.IEC 60034-30-1 defines IE1 standard to IE4 super-premium; IS 12615 adopts them and India's motor QCO makes IE2 the legal minimum, IE3 the usual buyer spec
B.IEC 60529 two-digit code, first digit for solids (6 = dust-tight) and second for water (5 jets, 6 powerful jets, 7 immersion); IP55 is typical for motors
C.delta HV, star LV with neutral brought out, LV leading HV by 30°; the standard connection for distribution transformers
D.IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact
11. Which term means: "IEC 60529 two-digit code, first digit for solids (6 = dust-tight) and second for water (5 jets, 6 powerful jets, 7 immersion); IP55 is typical for motors"?
A.IP rating — IEC 60529 two-digit code, first digit for solids (6 = dust-tight) and second for water (5 jets, 6 powerful jets, 7 immersion); IP55 is typical for motors
B.IP rating — IEC 60034-1 duties S1 continuous, S2 short-time, S3 intermittent periodic and so on; a motor sized for S1 is over-rated for crane duty
C.IP rating — IEC 60072 designation such as 160M gives shaft-centre height in mm, fixing mounting dimensions independent of manufacturer
D.IP rating — Indian and international standards for power transformers covering ratings, temperature rise, impedance tolerance (±10%) and type/routine tests
A.delta HV, star LV with neutral brought out, LV leading HV by 30°; the standard connection for distribution transformers
B.short-circuit voltage as a percentage of rated voltage, about 4–5% for distribution up to 12.5% for large units; higher limits fault current but raises regulation
C.IEC 60034-30-1 defines IE1 standard to IE4 super-premium; IS 12615 adopts them and India's motor QCO makes IE2 the legal minimum, IE3 the usual buyer spec
D.IEC 60034-1 duties S1 continuous, S2 short-time, S3 intermittent periodic and so on; a motor sized for S1 is over-rated for crane duty
14. Which term means: "short-circuit voltage as a percentage of rated voltage, about 4–5% for distribution up to 12.5% for large units; higher limits fault current but raises regulation"?
A.Percentage impedance — insulation ageing rate doubles for every 6 K above the 98 °C reference hot-spot temperature per the IEC 60076-7 loading guide
B.Percentage impedance — changes the turns ratio without interrupting supply, typically ±10% in 1.25% steps on the HV side; off-circuit taps only when de-energised
C.Percentage impedance — short-circuit voltage as a percentage of rated voltage, about 4–5% for distribution up to 12.5% for large units; higher limits fault current but raises regulation
D.Percentage impedance — IEC 60529 two-digit code, first digit for solids (6 = dust-tight) and second for water (5 jets, 6 powerful jets, 7 immersion); IP55 is typical for motors
A.insulation ageing rate doubles for every 6 K above the 98 °C reference hot-spot temperature per the IEC 60076-7 loading guide
B.IEC 60034-1 duties S1 continuous, S2 short-time, S3 intermittent periodic and so on; a motor sized for S1 is over-rated for crane duty
C.short-circuit voltage as a percentage of rated voltage, about 4–5% for distribution up to 12.5% for large units; higher limits fault current but raises regulation
D.changes the turns ratio without interrupting supply, typically ±10% in 1.25% steps on the HV side; off-circuit taps only when de-energised
17. Which term means: "changes the turns ratio without interrupting supply, typically ±10% in 1.25% steps on the HV side; off-circuit taps only when de-energised"?
A.On-load tap changer — IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact
B.On-load tap changer — IEC 60034-30-1 defines IE1 standard to IE4 super-premium; IS 12615 adopts them and India's motor QCO makes IE2 the legal minimum, IE3 the usual buyer spec
C.On-load tap changer — changes the turns ratio without interrupting supply, typically ±10% in 1.25% steps on the HV side; off-circuit taps only when de-energised
D.On-load tap changer — short-circuit voltage as a percentage of rated voltage, about 4–5% for distribution up to 12.5% for large units; higher limits fault current but raises regulation
A.IEC 60034-1 duties S1 continuous, S2 short-time, S3 intermittent periodic and so on; a motor sized for S1 is over-rated for crane duty
B.short-circuit voltage as a percentage of rated voltage, about 4–5% for distribution up to 12.5% for large units; higher limits fault current but raises regulation
C.IEC 60034-30-1 defines IE1 standard to IE4 super-premium; IS 12615 adopts them and India's motor QCO makes IE2 the legal minimum, IE3 the usual buyer spec
D.IEC 60072 designation such as 160M gives shaft-centre height in mm, fixing mounting dimensions independent of manufacturer
20. Which term means: "IEC 60034-30-1 defines IE1 standard to IE4 super-premium; IS 12615 adopts them and India's motor QCO makes IE2 the legal minimum, IE3 the usual buyer spec"?
A.IE efficiency classes — ONAN uses natural oil and air, ONAF adds fans, OFAF pumps the oil and ODAF directs it into windings, each raising the rating
B.IE efficiency classes — IEC 60034-30-1 defines IE1 standard to IE4 super-premium; IS 12615 adopts them and India's motor QCO makes IE2 the legal minimum, IE3 the usual buyer spec
C.IE efficiency classes — IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact
D.IE efficiency classes — insulation ageing rate doubles for every 6 K above the 98 °C reference hot-spot temperature per the IEC 60076-7 loading guide
A.IK rating — Indian and international standards for power transformers covering ratings, temperature rise, impedance tolerance (±10%) and type/routine tests
B.IK rating — IEC 60034-1 duties S1 continuous, S2 short-time, S3 intermittent periodic and so on; a motor sized for S1 is over-rated for crane duty
C.IK rating — IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact
D.IK rating — IEC 60529 two-digit code, first digit for solids (6 = dust-tight) and second for water (5 jets, 6 powerful jets, 7 immersion); IP55 is typical for motors
A.IEC 60034-30-1 defines IE1 standard to IE4 super-premium; IS 12615 adopts them and India's motor QCO makes IE2 the legal minimum, IE3 the usual buyer spec
B.IEC 60072 designation such as 160M gives shaft-centre height in mm, fixing mounting dimensions independent of manufacturer
C.short-circuit voltage as a percentage of rated voltage, about 4–5% for distribution up to 12.5% for large units; higher limits fault current but raises regulation
D.IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact
A.Motor frame size — changes the turns ratio without interrupting supply, typically ±10% in 1.25% steps on the HV side; off-circuit taps only when de-energised
B.Motor frame size — IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact
C.Motor frame size — IEC 60529 two-digit code, first digit for solids (6 = dust-tight) and second for water (5 jets, 6 powerful jets, 7 immersion); IP55 is typical for motors
D.Motor frame size — IEC 60072 designation such as 160M gives shaft-centre height in mm, fixing mounting dimensions independent of manufacturer
A.Hot-spot ageing rule — IEC 60034-30-1 defines IE1 standard to IE4 super-premium; IS 12615 adopts them and India's motor QCO makes IE2 the legal minimum, IE3 the usual buyer spec
B.Hot-spot ageing rule — insulation ageing rate doubles for every 6 K above the 98 °C reference hot-spot temperature per the IEC 60076-7 loading guide
C.Hot-spot ageing rule — IEC 60034-1 duties S1 continuous, S2 short-time, S3 intermittent periodic and so on; a motor sized for S1 is over-rated for crane duty
D.Hot-spot ageing rule — short-circuit voltage as a percentage of rated voltage, about 4–5% for distribution up to 12.5% for large units; higher limits fault current but raises regulation
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