Question
a) With reference to single phasing applied
to a.c motors
i) Explain the
meaning of single phasing
ii) Describe it's
effect
iii) State the most common cause of single
phasing.
a)
[Single Phasing is where one of the 3-phase's
supplying the Motor becomes disconnected.
The Motor will continue to run if this happens and can
result in Motor Burnout.
The effect of Single Phasing is to increase the
Current in the two remaining Lines and cause the Motor to become very noisy due
to uneven Torque produced.]
1) The meaning of single phasing is where one of the
three phases is lost in an AC motor.
2) The effect of single phasing is an imbalance in the
other two phases, which can lead to rough operation of the motor, or if the
motor is stopped and you try starting the motor, it will make a humming noise
and will not start.
3) The most common cause of single phasing, is poor or
loose terminal connections on one of the phases or a fuse that has blown in one
of the phases.
b) Sketch a simple diagram of a direct on
line starter, showing in detail, the overload and single phase Protection trip.
Answer
