Single Phase Induction Motors Emec Practice Questions

Stepping rate is 100 steps/sec. Step required for one revolution $=\frac{360^{\circ}}{1.8}=200$ steps. Therefore, time required for one revolution= 2 seconds rev/sec=0.5 rps rev/minute =30rpm

$L_s=\frac{N_s^2}{Rl_s}$ and $L_r=\frac{N_r^2}{Rl_r}$ where, $L_s$ and $L_r$ are self inductances of stator and rotor. $N_s$ and $N_r$ are no. of turns energized in stator and rotor. $Rl_s=$ Reluctance seen by the stator flux. $Rl_r=$ Reluctance seen by the rotor flux. As $L_s$ and $L_r$ are independent of the rotor position, the reluctances $Rl_s$ and $Rl_r$ does not vary with the rotor movement. Therefore, reluctance torque terms. $\frac{1}{2}I_s^2\frac{dls}{d\theta }$ and $\frac{1}{2}I_r^2\frac{dL_r}{d\theta }$ become zero.

Brushless dc motor definitely has a permanent magnet.

Detent torque: It is amount of torque that the motor produces when it is not energized. No current is slowing through the winding. Holding Torque: It is amount of torque that the motor produces when it has rated current flowing through the winding but motor is at rest.. Pull-in Torque: Shows the maximum value of torque at given speeds that the motor can start, stop, or reverse in synchronism with the input pulses. Pull-out Torque: Shows the maximum value of torque at given speeds that the motor can generate while running in synchronism. If the motor is run outside of this curve, it will stall.

Where, $\lambda =N\phi =$ Flux linkage Field energy is the energy absorbed by the magnetic system to establish flux $\phi$ . For a linear electromagnetic circuit Field energy = Co-energy $=\frac{1}{2}\lambda i$

Capacitor start type motor has high staring torque and therefore is used for hard starting loads such as compressor, conveyors, pumps et. Capacitor-run type motor has better running power factor and efficiency and a quiter and smoother operation. It is used for both easy and hard to start loads. Moder applications of such motors are ceiling fans, blower etc.

Universal motors are used where light weight is important., as in vacuum cleaners and portable tools e.g. food mixer which usually operate at high speed (1500-15000 rpm). Domestic water pump are usually of low rating. So single phase induction motor can be used for such application. Three phase induction motor is suitable for escalator as it has high starting torque.

A $1-\phi$ induction motor with only the main winding excited would have forward rotating field is more than the backward rotating field at synchronous speed.

The area under the hysteresis wave is ameans to measure the hysteresis loss per cycle. Area under the curve

For a cycle of 50 Hz, $\text{Loss}=500mW \times 50Hz=25W$