Motor downtime can mean lost revenue, product spoilage, equipment failure and employee downtime. A motor could be out of commission for several reasons, and by understanding the fundamentals, you can avoid motor failures in your plant or project. Simply replacing the motor may not solve the problem, which is why diagnosing the problem itself can save your company time and money.
1. Failure to Start
When your electric motor fails to start, begin by checking the motor and the load are turning freely. Ensure the load does not require more power than the motor can deliver. If the motor is being operated for the first time, ensure the wiring is correct.
Next, check the motor circuit. Make sure the correct voltage is present at the motor terminals. The poor connections, faulty switches, and relays can create high resistance in the line, creating a voltage drop when power is applied to the motor. Confirm the motor switch is turned on.
If the voltage is too low or at 0, look at fuses and overload protectors designed to cut off power to the motor and protect it from damaging current surges. If these are fine, work backwards from the motor to find the point where power is lost.
If the correct voltage is found at the motor terminals, it may be time to dis-assemble and inspect the motor. If the stator windings are damaged, contact the manufacturer to be repaired and rewound.
2. Stoppage
Sometimes an electric motor will operate normally and suddenly experience a stoppage. This is usually caused by an overload where a safety protection device such as a fuse or overload protector is tripped to prevent high currents from damaging the motor windings.
It is important to figure out what caused the safety protection to trip. Review operation and ensure the load is free and is not encountering intermittent resistance. In some cases, overload can happen intermittently. Overload will not always trip the safety protections, which could create damaging current surges and heat spikes that reduce the motor’s service life.
If the motor safety protections do not trip, move on to the steps laid out in the previous section to check the motor circuit, power supply and eventually the motor itself.
3. Failure to Reach Speed
If the motor starts but does not reach up to speed, check whether it can deliver the power required by the load. A motor that’s too small for the job will struggle to perform and may experience damaging current levels and overheating. Also, check for damaged bearings, which are usually accompanied by increased noise and vibration. This can cause resistance that prevents the motor from reaching its full operating speed.
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If you already know you have the right motor for the job, check the voltage at the motor terminals during operation. Poor connections and faulty fuses, switches and relays can cause voltage drops that only appear when the motor is drawing full power.
Check the length of power cables – long cable runs can create small electrical resistances that significantly impact the upper end of motor performance.
4. Overheating
Overheating can quickly degrade the motor’s internal components and reduce its service life. The motor temperature should be checked regularly to ensure it operates within the manufacturer’s safe temperature range. If the motor is too hot, the root cause may be the way it is operated, its cooling system, or a combination of both.
When an electric motor starts, it typically experiences a surge of current during acceleration that builds heat inside the motor. This heat may dissipate quickly once the motor has reached its normal speed. However, if the motor is stopped and started frequently, the heat may not have time to dissipate and will continue to build up. In this case, it is recommended to use either a soft starter or a speed controller such as a Variable Frequency Drive (VFD) to gradually accelerate the motor and prevent current surges from happening.
If the load changes continuously and is highly variable during operation, current surges can occur as the motor is forced to draw sudden bursts of power to overcome the resistance. This quickly builds up damaging levels of heat inside the motor. It may be necessary to review the motor’s suitability for the application and consider using a larger motor or one with a better cooling system.
A motor with a shaft-mounted fan is risky to operate at low speeds because the cooling system is less effective as speed is reduced. In this case, it may be necessary to switch to a motor with a separate blower that provides maximum cooling regardless of speed.
Finally, check that the motor cooling is working properly. Clear air intake vents and ensure the fan is clean and is capable of moving air through the motor.
5. Vibration and Noise
Excessive or unusual vibration and noise are signs that something is wrong. Begin by removing the load and running the motor freely. If the vibration and noise continue, check the motor bearings for damage, misalignment and excessive play. Replace or realign the parts if necessary. If the problem persists, the motor may have come out of balance, and it will require rebalancing.
If the problem only occurs with the load attached, ensure the motor is properly mounted and the mounting bolts are tight. The motor should align with the load, and the coupling should be secured. Lastly, check whether the load is balanced and secure.
Another possible cause of vibration is the loss of one phase of power, accompanied by reduced power output from the motor. Check that sufficient power is available for each phase of the motor.
Summary
These tips should give you the knowledge to undertake basic electric motor troubleshooting, enabling you to quickly move from diagnosis to solution and get your operation back online.
