Electrical Machines interview questions

1. A.motor torque is proportional to slip at low slip and inversely proportional at high slip, peaking where slip equals R2/X2
2. B.rms induced voltage equals 4.44 f N Φm, so the volts per turn are fixed by supply frequency and peak core flux
3. C.ratio of energy output to energy input over 24 hours, the correct merit figure for distribution transformers whose load varies
4. D.reversal of current in an armature coil as it passes under a brush, assisted by interpoles to reduce sparking

Answer + AI explanation with Pro

1. A.Torque-slip characteristic
2. B.Synchronous motor V-curves
3. C.Transformer emf equation
4. D.Open-circuit and short-circuit tests

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1. A.Transformer emf equation — difference between synchronous speed and rotor speed expressed as a fraction of synchronous speed, typically 2–5% at full load
2. B.Transformer emf equation — rms induced voltage equals 4.44 f N Φm, so the volts per turn are fixed by supply frequency and peak core flux
3. C.Transformer emf equation — distortion and weakening of the main field flux by the mmf of the armature current, shifting the magnetic neutral axis
4. D.Transformer emf equation — plots of armature current against field current at constant load, minimum at unity power factor and leading when over-excited

Answer + AI explanation with Pro

1. A.motor torque is proportional to slip at low slip and inversely proportional at high slip, peaking where slip equals R2/X2
2. B.distortion and weakening of the main field flux by the mmf of the armature current, shifting the magnetic neutral axis
3. C.oscillation of the rotor about its steady synchronous position after a sudden load change, damped by amortisseur windings
4. D.difference between synchronous speed and rotor speed expressed as a fraction of synchronous speed, typically 2–5% at full load

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1. A.Hunting of synchronous machine
2. B.Slip of induction motor
3. C.Transformer emf equation
4. D.All-day efficiency

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1. A.Slip of induction motor — difference between synchronous speed and rotor speed expressed as a fraction of synchronous speed, typically 2–5% at full load
2. B.Slip of induction motor — oscillation of the rotor about its steady synchronous position after a sudden load change, damped by amortisseur windings
3. C.Slip of induction motor — distortion and weakening of the main field flux by the mmf of the armature current, shifting the magnetic neutral axis
4. D.Slip of induction motor — reversal of current in an armature coil as it passes under a brush, assisted by interpoles to reduce sparking

Answer + AI explanation with Pro

1. A.distortion and weakening of the main field flux by the mmf of the armature current, shifting the magnetic neutral axis
2. B.difference between synchronous speed and rotor speed expressed as a fraction of synchronous speed, typically 2–5% at full load
3. C.motor torque is proportional to slip at low slip and inversely proportional at high slip, peaking where slip equals R2/X2
4. D.reversal of current in an armature coil as it passes under a brush, assisted by interpoles to reduce sparking

Answer + AI explanation with Pro

1. A.Slip of induction motor
2. B.All-day efficiency
3. C.Armature reaction
4. D.Commutation in DC machines

Answer + AI explanation with Pro

1. A.Commutation in DC machines — distortion and weakening of the main field flux by the mmf of the armature current, shifting the magnetic neutral axis
2. B.Commutation in DC machines — reversal of current in an armature coil as it passes under a brush, assisted by interpoles to reduce sparking
3. C.Commutation in DC machines — motor torque is proportional to slip at low slip and inversely proportional at high slip, peaking where slip equals R2/X2
4. D.Commutation in DC machines — difference between synchronous speed and rotor speed expressed as a fraction of synchronous speed, typically 2–5% at full load

Answer + AI explanation with Pro

1. A.ratio of energy output to energy input over 24 hours, the correct merit figure for distribution transformers whose load varies
2. B.reversal of current in an armature coil as it passes under a brush, assisted by interpoles to reduce sparking
3. C.motor torque is proportional to slip at low slip and inversely proportional at high slip, peaking where slip equals R2/X2
4. D.OC test on the LV side gives core loss and the magnetising branch; SC test on the HV side gives copper loss and leakage impedance

Answer + AI explanation with Pro

1. A.Open-circuit and short-circuit tests
2. B.Transformer emf equation
3. C.Torque-slip characteristic
4. D.Hunting of synchronous machine

Answer + AI explanation with Pro

1. A.Open-circuit and short-circuit tests — OC test on the LV side gives core loss and the magnetising branch; SC test on the HV side gives copper loss and leakage impedance
2. B.Open-circuit and short-circuit tests — difference between synchronous speed and rotor speed expressed as a fraction of synchronous speed, typically 2–5% at full load
3. C.Open-circuit and short-circuit tests — rms induced voltage equals 4.44 f N Φm, so the volts per turn are fixed by supply frequency and peak core flux
4. D.Open-circuit and short-circuit tests — plots of armature current against field current at constant load, minimum at unity power factor and leading when over-excited

Answer + AI explanation with Pro

1. A.ratio of energy output to energy input over 24 hours, the correct merit figure for distribution transformers whose load varies
2. B.difference between synchronous speed and rotor speed expressed as a fraction of synchronous speed, typically 2–5% at full load
3. C.oscillation of the rotor about its steady synchronous position after a sudden load change, damped by amortisseur windings
4. D.rms induced voltage equals 4.44 f N Φm, so the volts per turn are fixed by supply frequency and peak core flux

Answer + AI explanation with Pro

1. A.All-day efficiency
2. B.Armature reaction
3. C.Open-circuit and short-circuit tests
4. D.Transformer emf equation

Answer + AI explanation with Pro

1. A.All-day efficiency — rms induced voltage equals 4.44 f N Φm, so the volts per turn are fixed by supply frequency and peak core flux
2. B.All-day efficiency — reversal of current in an armature coil as it passes under a brush, assisted by interpoles to reduce sparking
3. C.All-day efficiency — distortion and weakening of the main field flux by the mmf of the armature current, shifting the magnetic neutral axis
4. D.All-day efficiency — ratio of energy output to energy input over 24 hours, the correct merit figure for distribution transformers whose load varies

Answer + AI explanation with Pro

1. A.distortion and weakening of the main field flux by the mmf of the armature current, shifting the magnetic neutral axis
2. B.plots of armature current against field current at constant load, minimum at unity power factor and leading when over-excited
3. C.motor torque is proportional to slip at low slip and inversely proportional at high slip, peaking where slip equals R2/X2
4. D.difference between synchronous speed and rotor speed expressed as a fraction of synchronous speed, typically 2–5% at full load

Answer + AI explanation with Pro

1. A.Slip of induction motor
2. B.Hunting of synchronous machine
3. C.Open-circuit and short-circuit tests
4. D.Torque-slip characteristic

Answer + AI explanation with Pro

1. A.Torque-slip characteristic — reversal of current in an armature coil as it passes under a brush, assisted by interpoles to reduce sparking
2. B.Torque-slip characteristic — plots of armature current against field current at constant load, minimum at unity power factor and leading when over-excited
3. C.Torque-slip characteristic — distortion and weakening of the main field flux by the mmf of the armature current, shifting the magnetic neutral axis
4. D.Torque-slip characteristic — motor torque is proportional to slip at low slip and inversely proportional at high slip, peaking where slip equals R2/X2

Answer + AI explanation with Pro

1. A.rms induced voltage equals 4.44 f N Φm, so the volts per turn are fixed by supply frequency and peak core flux
2. B.distortion and weakening of the main field flux by the mmf of the armature current, shifting the magnetic neutral axis
3. C.plots of armature current against field current at constant load, minimum at unity power factor and leading when over-excited
4. D.ratio of energy output to energy input over 24 hours, the correct merit figure for distribution transformers whose load varies

Answer + AI explanation with Pro

1. A.Armature reaction
2. B.Commutation in DC machines
3. C.All-day efficiency
4. D.Open-circuit and short-circuit tests

Answer + AI explanation with Pro

1. A.Armature reaction — ratio of energy output to energy input over 24 hours, the correct merit figure for distribution transformers whose load varies
2. B.Armature reaction — distortion and weakening of the main field flux by the mmf of the armature current, shifting the magnetic neutral axis
3. C.Armature reaction — difference between synchronous speed and rotor speed expressed as a fraction of synchronous speed, typically 2–5% at full load
4. D.Armature reaction — reversal of current in an armature coil as it passes under a brush, assisted by interpoles to reduce sparking

Answer + AI explanation with Pro

1. A.plots of armature current against field current at constant load, minimum at unity power factor and leading when over-excited
2. B.ratio of energy output to energy input over 24 hours, the correct merit figure for distribution transformers whose load varies
3. C.rms induced voltage equals 4.44 f N Φm, so the volts per turn are fixed by supply frequency and peak core flux
4. D.distortion and weakening of the main field flux by the mmf of the armature current, shifting the magnetic neutral axis

Answer + AI explanation with Pro

1. A.Transformer emf equation
2. B.Synchronous motor V-curves
3. C.Slip of induction motor
4. D.Commutation in DC machines

Answer + AI explanation with Pro

1. A.Synchronous motor V-curves — OC test on the LV side gives core loss and the magnetising branch; SC test on the HV side gives copper loss and leakage impedance
2. B.Synchronous motor V-curves — oscillation of the rotor about its steady synchronous position after a sudden load change, damped by amortisseur windings
3. C.Synchronous motor V-curves — difference between synchronous speed and rotor speed expressed as a fraction of synchronous speed, typically 2–5% at full load
4. D.Synchronous motor V-curves — plots of armature current against field current at constant load, minimum at unity power factor and leading when over-excited

Answer + AI explanation with Pro

1. A.distortion and weakening of the main field flux by the mmf of the armature current, shifting the magnetic neutral axis
2. B.reversal of current in an armature coil as it passes under a brush, assisted by interpoles to reduce sparking
3. C.oscillation of the rotor about its steady synchronous position after a sudden load change, damped by amortisseur windings
4. D.motor torque is proportional to slip at low slip and inversely proportional at high slip, peaking where slip equals R2/X2

Answer + AI explanation with Pro

1. A.All-day efficiency
2. B.Slip of induction motor
3. C.Commutation in DC machines
4. D.Hunting of synchronous machine

Answer + AI explanation with Pro

1. A.Hunting of synchronous machine — difference between synchronous speed and rotor speed expressed as a fraction of synchronous speed, typically 2–5% at full load
2. B.Hunting of synchronous machine — oscillation of the rotor about its steady synchronous position after a sudden load change, damped by amortisseur windings
3. C.Hunting of synchronous machine — OC test on the LV side gives core loss and the magnetising branch; SC test on the HV side gives copper loss and leakage impedance
4. D.Hunting of synchronous machine — rms induced voltage equals 4.44 f N Φm, so the volts per turn are fixed by supply frequency and peak core flux

Answer + AI explanation with Pro