INTRODUCTION TO AC MOTOR2

UPON THE COMPLETION OF THIS TOPIC, YOU SHOULD BE ABLE TO:-

1.3 Understand the basic of AC motor 1.3.1 Define synchronous speed,

slip and slip frequency 1.3.2 Determine syncronous speed 1.3.3 Determine slip 1.3.4 Determine slip frequency

SYNCHRONOUS SPEED The "synchronous speed" of

induction motor is the rate of rotation in RPM of the stator magnetic field. It is given by the following equation.

ROTOR SPEED Slip speed is defined as the

difference between synchronous speed and rotor speed.

SLIP PERCENTAGE Slip is defined as the speed of the

rotor in relation to the rotating field. So equation (iv) is the formulae for slip percentage.

VOLTAGE AND FREQUENCY INDUCED IN THE ROTOR The voltage and frequency induced

in the rotor both depend upon the slip. They are given by the equation below:

EXAMPLE1. Calculate the synchronous speed of a

three phase induction motor having 20 poles when it is connecting to 50Hz sources

1. A three phase, 20 poles induction motor is connected to 600V, 60Hz source. Determine:

a) synchronous speed b) find the new synchronous speed if

the frequency reduced to 50Hz c) if the voltage reduced to 300V,

will the synchronous speed change?. State a reason

3. A three phase, 6 poles induction motor is connected to 60Hz supply. The voltage induced in the rotor bars is 4V when the motor locked. If the the motor turn in the same direction as the flux, calculate the approximate rotor change rotor voltage induced and its frequency

4. a) at 300 rpm5. B) at 1000rpm6. C) at 1500rpm