Download Assignment-1

Assignment-1
Electrical Engineering
Subject: EMEC-II, TEE-501(V sem)
Q.1. Explain with the help of suitable diagrams, how rotating magnetic field is produced in a 3-Ø
induction motor. Explain why the rotor of SCIM rotates in the same direction as the rotating
magnetic field.
Q.2. Give the expression for an I.M. for
I.
II.
III.
Full load torque.
Max. torque.
Relation between rotor reactance & rotor resistance for max. torque.
Q.3. By means of a power-flow diagram, describe power flow in a 3 Ø induction motor and
show
Pg: Pr(cu):Pmd:=1:s:(1-s)
Q.4. The power supplied to a 3 Ø I.M. in 40 KW & the corresponding stator losses are 1.5KW.
calculate
I.
II.
The total mechanical power developed & Pr(cu) when the slip is 0.04.
Efficiency of the motor neglecting rotor Iron loss.
Q.5. The following data referred to a 12-pole, 420V, 50Hz, 3- Ø mesh connected I.M. :
R1=2.95,
R2’= 2.08,
X1= 6.82,
X2’=4.11 Ohms/Phase.
On no load the line value of magnetizing current is 6.7A. and core losses are 269 Watt.
Determine: power factor, Input current, equivalent rotor current & torque at slip of 3% from
approximate equivalent circuit.
Q.6. A 3 Ø induction motor has starting torque of 100% and a maximum torque of 200% of the
full load torque, find slip at maximum torque.
Q.7 .Show the following points on torque slip curve:
I.
II.
Starting torque.
Break down torque/pull out torque.
III.
Full load torque.
Also explain the condition & stability of I.M. in terms of load torque and show the stable &
unstable region on Torque vs slip curve.
Q.8 . A 4- pole, 50 Hz 3- Ø I.M. has rotor resistance and standstill rotor reactance of 0.04 Ω and
0.16 Ω per phase respectively. Calculate the value of the external rotor resistance per phase to
be inserted to obtain 70% of maximum torque at starting.
Q.9. The stator of a 3- Ø, 4- pole slip ring I.M. is connected to 50 Hz supply. At the rotor
terminals a frequency of 30 Hz is required. Find the possible speed at which the rotor must be
driven. What is the ratio of slip ring emf at this speed at no-load.
Q.10. A 20 hp, 440V, delta connected, 50Hz, 4pole, 3 phase induction motor gave the following
test results:
No-Load Test:
440V, 10A, 1.5kW
Blocked Rotor Test: 120V, 30A, 2.25kW
Calculate the equivalent circuit parameters. Stator dc resistance per phase is given as 0.6 Ohm.
Q.11. A 450V, star connected, 50Hz, 6pole, 3 phase induction motor gave the following test
results:
No-Load Test:
450V, 20A, p.f. =0.15
Blocked Rotor Test: 200V, 150A, p.f. =0.3
The ratio of standstill leakage reactance stator and rotor is estimated as 2, if the motor is
running is running at the speed of 960 RPM determine
i)
ii)
iii)
Net mechanical power output
Net torque
Efficiency of the motor
Assume stator and rotor cu-losses to be equal.