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E{ectricat jvt&cfrines
I
fftr e e -? fias e Induciion
SYlotors
?art (t)
mffiHs-ffi0f 0{2045000 . 0101I04$$$$
Examole (l)
A 6-pole, 3-phase indu"tion ryg!* i-u_-.,g -. 4 lq Hz supply. If it is running at 970 t'P'ffi',
findthesrip iu H ffi s- ffiExamole (2) 0t01 2015000 . $t $t 104[000
A 3-phase induction motor is wound for 4-poles and is supplied from 50 Hz system. Calculate (i)
the synchronous speed, (ii) the speed of the motor when the slip is 4Yo, and (iii) the rotor current
frequency when the motor runs at 600 r'p'm'I
Examole (3)
A 6-pole alternator is running at 1000 r.p.m. and supplies an 8-pole induction motor. Find the
actual speed of the motor if the slip is 25%'
Examole (4)
A 50 !Iz, 4-pote, 3-phase induction motor has a rotor current of frequency 2l1z' Determine (i)
the slip, and (ii) the speed of the motor'
Examole (5)
A 3-phase, 6-pole induction motor is connected to a60Hzsupply. The voltage induced in the
rotor bars is 4 v when ttre rotor i1y rt*rastill. calculate the.voltage and frequency induced in
the rotor bars at 300 r.P.m.J
Examnle (6)
A 3-phase supply, 400 V wound rotor motor has detta-connected stator-winding and star-
connected rotor-winding.'The stator has 48 tums per phase while the rotor has24 turns per
phase. Find the standstill or open-circuited voltage across the slip rings.
Example (7)
A 6-pole, 3-phase, 50 Hz induction motor is running at full-load with a slip of 4%' The rotor is
star-connected and its resistance and standstill reactanie are 0.25 Q and 1.5 Q per phase' The
_\
e.m.f. between slip rings is 100 V. find the rotor current per phase and power factor assuming
the slip rings are short-circuited.
Examole (8)
A 4-pole, 3-phase, 50 Hz induction motor has a star-connected rotor. The rotor has a resistance
of 0.1 C) per phase and standstill reactance of 2 Q per phase. The induced e.m.f. between the slip
rings is 100 V. if the full-load speed is 1460 r.p.ffi., calculate (i) the slip, (ii) the e.m.f. induced inthe rotor in each phase, (iii) the rotor reactance per phase, (iv) the rotor current, and (v) the,rotor
power factor. Assume slip rings are short-circuited.I
Example (9)
A 150 kW, 3000 V, 50 Hz, 6-pole star-connected induction motor has a star-connected slip ring
rotoi with a transformation ratio of 3.6 (stator / rotor). The rotor resistance is 0.1 Cl per phase
and its per phase leakage inductance is 3.61 mH. The stator impedance may be neglected. Find
the starting current on rated voltage with short-circuited slip rings.
Example (10)
A 3-phase siip ring motor gives a reading of 55 V across slip rings on open circuit when at
standstill with normal stator voltage applied. The rotor is star-connected and has impedance of(0.7 +3 5) Q per phase. Find the rotor current and power factor when the machine is (i) at
standstill with slip rings joined t6"a star-conn'ected starter with a phase impedance of (4 + j 3) O,
and (ii) when running normally with a 5% slip. :i
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