During the operation of single-phase ac motors, it experiences various faults at the time of starting or stopping or while running. The faults in single-phase motors are due to many reasons like overcurrents or undercurrents, over or under voltages, starter failure, motor overheating, over-loading, etc. Hence, it is essential to protect the motor from faults. Let us see the various faults and rectification or remedies for faults in single-phase ac motors.
Main Faults in Single-Phase Induction Motors :
Motor fails to start :
| Causes | Remedies |
|---|
| Supply may be cut off. | Check the main supply with a test lamp at the terminals of the motor, at starters terminals. or in the main switch of the motor. |
| Overload or low starting torque. | Rotate the rotor by hand and if it is free to move, then reduce the load. |
| Stator winding may be open-circuited or reversed coil connections. | Check the windings and polarity of coils with the test lamp and if any end is found broken. join it or solder it and if the polarity is wrong. correct them by doing the connections of ends of each coil polarity. |
| Open circuit in relay circuit or centrifugal switch. | Check with a test lamp in series of the supply and correct them. |
| The capacitor may be defective in a capacitor-type motor. | Check the capacitor with a series test lamp and replace it. |
| The rotor shaft may be jammed in the bearings or brushes. | Rotate the rotor shaft to see its free motion and check the bearings and play. |
| Belt may be too tight. | Check and set it in the correct order. |
Fuses blown off as soon as the motor is started :
| Causes | Remedies |
|---|
| Protective gear may be defective. | Check and set it in the correct order. |
| Motor may be overloaded. | Check and reduce the load. |
| Starter winding may be short-circuited or earthed. | Check the winding with a series test lamp or megger and correct it. |
| Connections of stator windings may be wrong. | Check the connections physically and also with a series test lamp and correct them. |
Motor starts and then stops :
| Causes | Remedies |
|---|
| Supply voltage may be too low. | Check the supply voltage with a voltmeter and switch off the motor till the voltage increases. |
| Motor may be overloaded. | Check the load physically and reduce it. |
| Connections of stator windings may be wrong. | Check with a series test lamp and correct them. |
Bearings over-heated :
| Causes | Remedies |
|---|
| Bearings may be squeezed. | Check and grease them. |
| Belt may be too tight. | Check and lose the belt. |
| Motor may be overloaded. | Check and reduce the load. |
| Bent shaft of the rotor. | Check and straighten it. |
| Rotor may be rubbing the stator cores. | Check and set the rotor shaft position. |
Motor's frame may be over-heated :
| Causes | Remedies |
|---|
| Misalignment of the drive. | Check and correct it. |
| Adjustment of the pulley may not be proper. | Set it correctly. |
| Ventilation may not be proper. | Maintain the proper ventilation. |
| Drive troubles. | Check and correct. |
| Supply voltage may be too high. | Check and switch off the motor till the voltage is reduced. |
| Motor may be over-loaded. | Check the load on the motor physically and reduce it. |
| Short-circuit of stator winding or centrifugal switch may be short-circuited. | Check the winding and check with a series test lamp or megger and correct it or get the motor re-wound. |
Motor giving noise :
| Causes | Remedies |
|---|
| Motor loosely fitted on the foundation. | Check and tighten the nuts. |
| Any part of the motor may be loosely fitted. | Check and tighten it. |
| Rotor may be rubbing the stator core. | Check and set the rotor shaft properly. |
| Bearing may be squeezed. | Check and grease the bearings. |
Speed of motor is reduced suddenly :
| Causes | Remedies |
|---|
| Supply voltage may be reduced. | Check with the voltmeter and stop the motor till the voltage is increased. |
| Open circuit in the stator winding. | Check with the voltmeter and stop the motor till the voltage is increased. |
| Motor may be electrically or mechanically loaded suddenly. | Check and reduce the load. |
Speed of motor is increased suddenly :
| Causes | Remedies |
|---|
| Supply voltage is increased suddenly. | Check the voltage with a voltmeter and stop the motor till the voltage falls to normal. |
| Load on the motor is reduced too much. | Check and increase the load on the motor up to normal. |
Heavy sparking at brushes in case of repulsion or universal motors :
| Causes | Remedies |
|---|
| Brushes rocker may not be on the magnetic neutral axis. | Set the rocker in the magnetic neutral position. |
| Pitted commutator. | Get the commutator to be turned on the lathe. |
| Open, short, or earth fault may be in the armature. | Check the armature for these faults and replace it. |
| Armature coils connections may be reversed. | Check the connections with a series test lamp and correct them. |
| Motor may be overloaded. | Check and reduce the load. |
Hunting of repulsion or repulsion start induction motor :
| Causes | Remedies |
|---|
| Pitted commutator. | Get it turned on the lathe. |
| shorting in gear or brushes. | Check and overhaul the gear and brushes. |
