Question

1) explain the principle of construction and operation of universal capacitor start, run and split phase motors.

2)state the principle of motor selection and application

3)show by calculation how to size a single phase motor for a task.

4) state how to choose a motor depending on:

a)temperature, humidity and dust nuance.

b) motor alignment and vibrations

Answer 1

1)

1) Split Phase Induction Motor: In addition to the main winding or running winding, the stator of single phase induction motor carries another winding called auxiliary winding or starting winding. A centrifuga switch is connected in series with auxiliary winding. The purpose of this switch is to disconnect the auxilia winding from the main circuit when the motor attains a speed up to 75 to 80% of the synchronous speed. Vr Ig Stast IStart gun 30 IStart Irun is the current flowing through the main or running winding Lstuct is the current flowing in starting winding and VT is the supply voltage. In this the running winding is inductive in nature and starting winding is highly resistive nature

The starting winding is highly resistive so, the current flowing in the starting winding lags behind the applied voltage by very small angle and the running winding is highly inductive in nature so, the current flowing in running winding lags behind applied voltage by large angle. The resultant of these two curent is IT. The resultant of these two current produce rotating magnetic field which rotates in one direction

Capacitor Start IM and Capacitor Start Capacitor Run IM Starting Winding Centrifugal switch at 0000 C C m Im Squirrel cage rotor Main Winding (b) Phasor diagram (a) Schematic representaion The working principle and construction of Capacitor start inductor motors and capacitor start capacitor run induction motors are almost the same. The current flowing throughthe capacitor leads the voltage. So, in capacitor start inductor motor and capacitor start capacitor run induction motor we are using two winding, the main winding and the starting winding. With starting winding we connect a capacitor so the current flowing in the capacitor i.e Ist leads the applied voltage by some angle, pt The running winding is inductive in nature so, the current flowing in running winding lags behind applied voltage by an angle, Qm.Now there occurlarge phase angle differences between these two currents whichproduce an resultant current, I and this will produce a rotating magnetic field. Since the torque producedby these motors depends upon the phase angle difference, which is almost 90°. So, these motors produce very high starting torque. In case of capacitor start induction motor, the centrifugal switch is provided so as to disconnect the starting winding when the motor attains a speed up to 75 to 80% of the synchronous speed but in case of capacitor start capacitors run induction motor there is no centrifugal switch so, the >capacitorremains in the circuit and helps to improvethe power factor and the running conditions of single phase induction motor