Page 224 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Chart 1
Motor fails to start
S.No Cause Test Remedy
1 Overload relay tripped. Wait for overload coils to cool. If motor could not be started check
Push the reset button if separately the motor circuit for other causes
provided. In some starters the stop as outlined in this chart.
button has to be pushed to reset
the overload relay.
2 Failure of power supply. Test the power supply at the starter If the supply is present in the incoming
incoming terminals. terminals of the starter, check the
starter for fault. If not, check the main
switch and fuses. Replace the fuses
if necessary or restore power supply.

3 Low voltage. Measure the voltage at the mains Restore normal supply or check
and compare with the name-plate the cables for underrating.
rating.
4 Wrong connection. Compare the connection with the Still if motor does not start, reconnect,
original diagram of the motor. after disconnecting the connection
of the motor.
5 Overload. Measure the starting torque Reduce load, raise tapping on auto-
required by load. transformer, install a motor of a
higher output.
6 Damaged bearings. Open the motor and check the Replace if required.
play of bearings.
7 Faulty stator winding. Measure current per phase and Repair the fault if possible or rewind
they should be equal, if required stator.
measure resistance per phase;
check insulation resistance between
winding and earth.
8 Wrong control Check the control circuit and Reconnect the control circuit accord-
connections. compare it with the circuit diagram. ing to the manufacturer’s circuit
diagram.
9 Loose terminal con- Check the terminal connection of Tighten the terminals.
nections at mains or the main switch, starter and motor
at starter or at motor. for discolouring and loose nuts.

10 Driven machine is Disconnect the motor from the load. If the motor starts satisfactorily check
locked. the driven machine and rectify the
defect.
11 Open circuit in stator Check visually and then with Rectify the defect or wind.
or rotor. multimeter/megger.
12 Short circuit in Check the phases and coil groups Repair the winding or rewind.
stator winding. with the help of an ohmmeter or
use internal growler.
13 Winding is grounded. Test with a Megger or test lamp. If the fault is found, repair or rewind.
14 Bearing stiff. Rotate the rotor by hand. If the rotor is stalled, dismantle the
motor and rectify the defect.
15 Overload. Check the load and belt tension. Reduce the load or loosen the
tight belts.

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CITS : Power - Electrician & Wireman - Lesson 93-100 CITS : Power - Electrician & Wireman - Lesson 93-100