Tension Variation - Electrical Power

Equipment (in North America) such as a motor, is generally designed to operate with +- 10% voltage variation and maintain nominal speed and torque (NEMA Standard MG-1). But if you run it at either limit continuously, the life of the motor will be shortened. Utilities are typically required to maintain +- 5% nominal voltage for most customers, but are "allowed" to get away with up to a 10% swing for short durations, i.e. a few seconds.

One problem is, the Utility is only required to maintain that at the terminals of your incoming service. You may have a problem after that, but it would not be their fault. For instance if you have too much of a load on your service, they have to be told and they will charge you more of course. So often times, people try to get away with not upgrading a service when they should and the end result is things like this. You may also have inadequately sized conductors feeding the service panel for the elevator, which causes a voltage drop. You may also have a loose connection somewhere. The list goes on and on.

Does the motor fail and they repair or rewind ?Elevator motor comes under a different category.The motor starts and stops frequently and correctly designed motor with a different duty cycle is to be used.If its a question of voltage do u always have low voltage? as Rightly said motors are designed for 10% Voltage and can continuously operate at +- 10%.I think motor name plate details can reveal lot of Information.

Hi Brim, #s 1 and 2 gave good advice. You need to measure the voltage and current at the input of your motor, under operating conditions, to determine if it is being supplied properly or whether there is a load or motor problem. On all phases by the way.

What does the voltage variation mean? If it's under or over voltage, your facilities should be ok because manufacturer made their goods based on approved standard, except the under/over beyond the standards. Fellas here have explained to you the voltage tolerance.

But if it's transient voltage, electronic components in PLC, PC, Drive, etc without proper protection devices, will fail. AC motor should be ok against this transient. Then power metering system should be developed to accomodate this such situation.

Transient will cause PLC to "lock out".

If its voltage imbalance, the motor's temperature will get hot. 3.5% imbalance will significantly increase the temp. to about 25%. Voltage imbalance shall be limited to below 1% at all voltage levels.

Anyway, what cause the motor to stop? Circuit breaker trip, TOL work, etc, briefly does your system provide "alarm/fault history"?

Another thought - when applying all of the good suggestions for testing that previous posts suggested, it might be wise to have a disinterested 3rd-party electrician do them - one that knows you won't be having him in to do service work. The service provider may be giving you insufficient information. After all, he has an interest in further service calls... Couldn't hurt.