How do you troubleshoot 3 phase AC motor?

aarohi manager Sep 21, 2023 3 Phase Ac Motor 0 Comment

The table presented below provides a comprehensive insight into the frequently encountered issues that afflict 3-phase squirrel cage induction motors. It not only outlines the root causes behind these problems but also offers effective remedies to rectify them, thereby restoring the motor’s functionality and productivity.

While this troubleshooting guide primarily focuses on 3-phase induction motors of the squirrel cage variety, its principles and solutions are equally applicable to a wide array of other three-phase induction motors.

Whether you’re dealing with issues related to motor efficiency, performance, or reliability, this resource serves as a valuable reference to help diagnose and address them effectively.

Motor Problem	Cause	Remedy
Motor fails to start	Blown fuses	Replace fuse with proper type and rating
		Overload Trips	Check and reset overload in starter
		Improper power supply	Check to see that power supplied agrees with nameplate specifications and load factor
		Improper line connections	Check connections with wiring diagram supplied with motor
		Open circuit in winding or control switch	This is normally indicated by a humming sound when switch is closed. Check for loose wiring connections. Confirm that all control contacts are closing.
		Mechanical failure	Check to see that motor and drive turns freely. Check bearings and lubrication
		Short circuited stator	Indicated by blown fuses. Motor must be rewound
		Poor stator coil connections	Remove end belts. Locate poor connections with test lamp.
		Rotor defective	Check for broken bars or end rings
		Motor may be overloaded	Reduce motor load
Motor stalls	One phase may be open	Check supply lines for open phase
		Wrong application	Change type or size. Consult motor manufacturer
		Overload	Reduce load
		Low voltage	Check that nameplate voltage is maintained. Check connection.
		Open circuit	Fuses blown. Check overload relay, stator and push buttons
Motor runs and then dies down	Power failure	Check for loose connections to line, to fuses and to control
Motor does not come up to speed	Motor is applied for the wrong application	Consult manufacturer for right application of motor
		Voltage too low at motor terminals because of line drop	Use higher voltage on transformer terminals or reduce load. Check connections. Check conductors for proper size.
		Starting load too high	Check load motor is supposed to carry at start.
		Broken rotor bars or loose rotor	Look for cracks near the rings. A new rotor may be required as repairs are usually temporary not permanent
		Open primary circuit	Locate fault with testing device and repair.
Motor takes too long to accelerate and/or draws high current (Amps)	Excessive load	Reduce load
		Low voltage during start up	Check for high resistance. Adequate wire size.
		Defective squirrel cage rotor	Replace with new rotor
		Applied voltage too low	Improve voltage at terminals of transformer by tap changing.
Wrong rotation	Wrong sequence of phases	Reverse connections at motor or at switchboard.
Motor overheats while running under load	Overload	Reduce load
		Frame or bracket vents may be clogged with dirt and prevent proper ventilation of motor.	Open vent holes and check for a continuous stream of air from the motor.
		Motor may have one phase open	Check to make sure that all leads are well connected.
		Grounded coil	Locate and repair
		Unbalanced terminal voltage	Check for faulty leads, connections and transformers.
Motor vibrates	Motor misaligned	Realign
		Weak support	Strengthen base
		Coupling out of balance	Balance coupling
		Driven equipment unbalanced	Re-balance driven equipment
		Defective bearings	Replace bearing
		Bearings not in line	Line bearings up properly
		Balancing weights shifted	Re-balance motor
		Poly-phase motor running single phase	Check for open circuit
		Excessive end play	Adjust bearing
Unbalanced line current on poly-phase motors during normal operation	Unequal terminal volts	Check leads and connections
		Single phase operation	Check for open contacts
		Unbalanced voltage	Correct unbalanced power supply
Noisy Operation	Airgap not uniform	Check and correct bracket fits or bearing.
Noisy Operation		Rotor unbalance	Rebalance
Hot bearings general	Bent or sprung shaft	Straighten or replace shaft
		Excessive belt pull	Decrease belt tension
		Pulley too far away	Move pulley closer to motor bearing
		Pulley diameter too small	Use larger pulleys
		Misalignment	Correct by realignment of drive
Hot bearings ball	Insufficient grease	Maintain proper quantity of grease in bearing
		Deterioration of grease or lubricant contaminated	Remove old grease, wash bearings thoroughly in kerosene and replace with new grease.
		Excessive lubricant	Reduce quantity of grease, bearing should not be more than 1/2 filled
		Overloaded bearing	Check alignment, side and end thrust.
		Broken ball or rough races	Replace bearing, first clean housing thoroughly