Transformer & Motor Specification interview questions
33 Transformer & Motor Specification questions from the Electrical Design bank, written for Indian campus drives and tech interviews. Every question has a verified answer and an AI-tutor explanation on placd.
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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
Answer + AI explanation with Pro
2. Which term means: "delta HV, star LV with neutral brought out, LV leading HV by 30°; the standard connection for distribution transformers"?
Junior
A.Cooling designations
B.Motor frame size
C.Percentage impedance
D.Vector group Dyn11
Answer + AI explanation with Pro
3. Which statement is correct?
Junior
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
Answer + AI explanation with Pro
4. What is Cooling designations?
Junior
A.ONAN uses natural oil and air, ONAF adds fans, OFAF pumps the oil and ODAF directs it into windings, each raising the rating
B.IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact
C.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.IEC 60072 designation such as 160M gives shaft-centre height in mm, fixing mounting dimensions independent of manufacturer
Answer + AI explanation with Pro
5. Which term means: "ONAN uses natural oil and air, ONAF adds fans, OFAF pumps the oil and ODAF directs it into windings, each raising the rating"?
Junior
A.IS 2026 / IEC 60076
B.On-load tap changer
C.Vector group Dyn11
D.Cooling designations
Answer + AI explanation with Pro
6. Which statement is correct?
Junior
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
Answer + AI explanation with Pro
7. What is IS 2026 / IEC 60076?
Junior
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
Answer + AI explanation with Pro
8. Which term means: "Indian and international standards for power transformers covering ratings, temperature rise, impedance tolerance (±10%) and type/routine tests"?
Junior
A.Percentage impedance
B.IP rating
C.Cooling designations
D.IS 2026 / IEC 60076
Answer + AI explanation with Pro
9. Which statement is correct?
Junior
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
Answer + AI explanation with Pro
10. What is IP rating?
Junior
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
Answer + AI explanation with Pro
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"?
Junior
A.IP rating
B.Motor frame size
C.Vector group Dyn11
D.On-load tap changer
Answer + AI explanation with Pro
12. Which statement is correct?
Junior
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
Answer + AI explanation with Pro
13. What is Percentage impedance?
Mid
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
Answer + AI explanation with Pro
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"?
Mid
A.Motor frame size
B.Vector group Dyn11
C.Percentage impedance
D.IK rating
Answer + AI explanation with Pro
15. Which statement is correct?
Mid
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
Answer + AI explanation with Pro
16. What is On-load tap changer?
Mid
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
Answer + AI explanation with Pro
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"?
Mid
A.Hot-spot ageing rule
B.On-load tap changer
C.Motor duty types
D.IK rating
Answer + AI explanation with Pro
18. Which statement is correct?
Mid
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
Answer + AI explanation with Pro
19. What is IE efficiency classes?
Mid
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
Answer + AI explanation with Pro
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"?
Mid
A.Vector group Dyn11
B.IE efficiency classes
C.IP rating
D.Motor frame size
Answer + AI explanation with Pro
21. Which statement is correct?
Mid
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
Answer + AI explanation with Pro
22. What is IK rating?
Mid
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.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.Indian and international standards for power transformers covering ratings, temperature rise, impedance tolerance (±10%) and type/routine tests
D.IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact
Answer + AI explanation with Pro
23. Which term means: "IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact"?
Mid
A.Motor duty types
B.Percentage impedance
C.IK rating
D.Hot-spot ageing rule
Answer + AI explanation with Pro
24. Which statement is correct?
Mid
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
Answer + AI explanation with Pro
25. What is Motor frame size?
Mid
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
Answer + AI explanation with Pro
26. Which term means: "IEC 60072 designation such as 160M gives shaft-centre height in mm, fixing mounting dimensions independent of manufacturer"?
Mid
A.Percentage impedance
B.IK rating
C.Cooling designations
D.Motor frame size
Answer + AI explanation with Pro
27. Which statement is correct?
Mid
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
Answer + AI explanation with Pro
28. What is Hot-spot ageing rule?
Senior
A.Indian and international standards for power transformers covering ratings, temperature rise, impedance tolerance (±10%) and type/routine tests
B.IEC 60072 designation such as 160M gives shaft-centre height in mm, fixing mounting dimensions independent of manufacturer
C.IEC 62262 impact-protection code from IK00 to IK10, where IK10 withstands a 20 J impact
D.insulation ageing rate doubles for every 6 K above the 98 °C reference hot-spot temperature per the IEC 60076-7 loading guide
Answer + AI explanation with Pro
29. Which term means: "insulation ageing rate doubles for every 6 K above the 98 °C reference hot-spot temperature per the IEC 60076-7 loading guide"?
Senior
A.IS 2026 / IEC 60076
B.Hot-spot ageing rule
C.Percentage impedance
D.IE efficiency classes
Answer + AI explanation with Pro
30. Which statement is correct?
Senior
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
Answer + AI explanation with Pro
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