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GATE 2020 || Electrical Machines || Quiz 9
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Question 1
A 3 phase, 10 kW, 400 V, 4 pole, 50 Hz, star connected induction motor draws 20 A on full load. Its no load and blocked rotor test data are given below:
No Load test: 400V 6 A 1002 W
Blocked Rotor test: 90 V 15 A /62 W
Neglecting copper loss in no load test and core loss in Blocked Rotor test, estimate motor’s full load efficiency.
No Load test: 400V 6 A 1002 W
Blocked Rotor test: 90 V 15 A /62 W
Neglecting copper loss in no load test and core loss in Blocked Rotor test, estimate motor’s full load efficiency.
Question 2
The torque-speed characteristics of motor (TM) and load (TL) for two cases are shown in the figures (a) and (b). The load torque is equal to motor torque at points P, Q, R and S
A)
B)
The stable operating points are
A)
B)
The stable operating points are
Question 3
The starting current and torque of a three phase induction motor on direct line starting is 30 Amp and 300 Nm respectively. What are the corresponding values with star delta starter?
Question 4
A 400V, 50 Hz, 30 hp, three-phase induction motor is drawing 50 A current at 0.8 power factor lagging. The stator and rotor copper losses are 1.5 kW and 900 W respectively. The friction and windage losses are 1050 W and the core losses are 1200W. The air-gap power of the motor will be
Question 5
The power input to a 400 V, 50Hz, 8 – pole, 3 – phase induction motor is 20k W. Motor is running at 705 rpm. The stator losses are 0.5 kW and friction and windage losses are 1 k W.
The gross power developed by the motor is –
The gross power developed by the motor is –
Question 6
The two cages of a 3-ϕ, 50 Hz, 4 pole delta-connected induction motor have respective standstill leakage impedance of (2+j8) and (9 +j2)-Ω/ph. Estimate the gross torque developed at standstill, the effective rotor voltage being 230 V/ph.
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Dec 18ESE & GATE EE
