Motor starting by reactor

[47651]

I have a motor , which is designed on 80% reactor starting.
Can I set the starter with 65% tap to start this motor

 

[dpc]

Sure - you can set it on the 50% tap too. Whether or not the motor will actually start is another question (and one you didn't ask).

Torque varies with the square of the voltage.

 

[47651]

Thanks for your information.

So, with 65% tap reactor starter, the starting torques is smaller, the starting time will be longer. Am I correct?

Motor manufacturer torqe vs. speed characteric curve, it nly show 100%, and 80%. So, this motor still can be started at 65% or 75% with longer starting time.

 

[edison123]

To paraphrase dpc, the question is will the load allow the motor to start and reach the speed at that torque level. So, you need to study the load torque requirement and check at what level of voltage, the motor will match it.

 

[dpc]

Yes, at 65% tap, the torque is about 42% of a full voltage start.

As edison said, you have to consider the torque requirements of the driven equipment, not just the motor. If this is a centrifugal pump starting with discharge valve closed, or a fan starting with dampers closed, the starting torque requirements are generally low enough to allow starting at a reduced voltage. The acceleration will take longer.

If you are trying to start a high-inertia load, it could be a problem, since the starting and accelerating torque requirements will be higher.

 

[LionelHutz]

The only reason the motor would be designed to work on 80% reactor starting is if the whole system, starter, motor and load, was already engineered and 80% was chosen as the best starting voltage.

I have seen lots of motor curves giving 100% and 80% voltage characteristics. Have we started any of those motors at 80% voltage? No.

I also think you mean autotransformer starting. A reactor starter does not apply a fixed voltage level to the motor. The voltage varies inversely with the starting current.

As the others have posted - you need to determine if using 65% voltage will allow the motor to accelerate close to full speed.

 

[dpc]

Good point Lionel, I assumed OP was referring to autoxfmr start, not reactor.