A 3phase, 50 Hz induction motor has a full load speed of 1440 rpm. The number of poles of the motor is
Since the number of poles must be even and a whole number, therefore the number of poles must be 4.
A properly shunted centrezero galvanometer is connected in the rotor circuit of a 6pole, 50 Hz wouldrotor induction motor. If the galvanometer makes 90 complete oscillations in one minute, the speed of rotor would be
Rotor frequency,
∴ Slip,
So, rotor speed,
A 10pole, 3phase, 50 Hz, delta connected induction motor takes 120 kW during blockedrotor test at rated voltage and frequency. If the stator ohmic loss is equal to rotor ohmic loss during blocked rotor test, then the starting torque if DOL starting is used for this motor will be
During blocked rotor test, power input to a 3phase induction motor appears almost entirely as I^{2}R loss in both stator and rotor windings. Since, stator ohmic loss = rotor ohmic loss
So, starting torque,
A 3phase squirrel cage induction motor has maximum torque equal to twice the fullload torque. The per phase rotor resistance and per phase standstill reactance referred to stator are 0.2 Ω and 2 Ω respectively (Stator impedance is neglected). What is the ratio of motor starting toque to its fullload torque, if the motor is started by directonline starter?
From equations (i) and (ii), we have
A 10 kW, 400 V, 3phase induction motor draw a current of 5 times its fullload current at rated voltage and at standstill developing a starting toque of 1.5 times its fullload torque. An autotransformer is installed to reduce the starting current and to give fullload torque at starting. Neglecting exciting current of autotransformer, the voltage applied to the motor terminals at the time of starting with auto transformer is
A 3phase, 20 kW, 400 V, 1470 rpm, 50 Hz squirrel cage induction motor develops a torque of 100 Nm at a speed of 1400 rpm. if the motor is connected to a 30 Hz supply; for keeping the same airgap flux, the supply voltage and the speed for the same load torque would respectively be
For same airgap flux,
In a 3phase squirrel cage induction motor, applied voltage is reduced to x times its rated value. Then, its starting line current from mains and starting torque by autotransformer starting would reduce respectively from their corresponding direct switching values by a factor of
A 3phase IM with stator in delta draws a line current of 10 A. When connected in star, it would draw a line current of
or,
The power factor of a deltaconnected 3phase, 50 kW, IM is 0.4 when delivering 35% of its rated load. If the stator is reconnected in star, then its
We know that,
∴
Thus, stator current will decrease.
A 3phase, starconnected SRIM is fed from 400 V, 50 Hz source. Stator to rotor effective turns ratio is 2. At a rotor speed of 1440 rpm, the rotor induced emf per phase would be
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