Motor Overvoltage

[StarCat]

Interesting

Interesting

Two main issues here.

1) The simplest way to look at this is to calculate the ratio of voltage and frequency, then look at what happens when you deviate beyond the stated tolerances. NEMA stipulates +-10%, but IEC might be different, and any motor mfr can stipulate a wider range depending on their intended market. 200V 50Hz is used in Japan, but half of Japan uses 60Hz, so motors designed for use there tend to try to cover that spread. So check with your specific supplier. But if you do have to deviate beyond the tolerance, going UNDER the ratio loses torque, going OVER the ratio increases flux heating. If you are under torque, reducing the load may make it OK, but if you are over saturating, reducing the load makes little difference, other than reducing the load contribution to motor heating. In other words over exciting the motor is going to heat it up more regardless of load, so load reduction has much less effect on motor life.

2) Starting torque (locked rotor torque) varies by the square of the voltage change. So having extra high voltage means a significantly higher risk of torque shock to the load. I have seen it twist shafts off.

There are some soft starters available that will allow you to manually adjust the final output voltage it gets to in order to match what your motor needs. That would also solve your torque shock issue as well. The caveat is, in order to do this, the SCRs are in the circuit full time, you CANNOT use a bypass contactor. That then means you must deal with the running current heat, figure 4-1/2 watts per running load amp in your panel. If you can ventilate, no problem. If you cannot, problem.

What JRAEF is saying about over excitation is interesting and always thoughtful.
I had to make a european pump motor function that had the 50/200 rating. Our supply is 208.
The decision to use a modern drive seemed obvious, but still there were problems.
Then one setting in the drive menu called " flux optimization " essentially was the magic choice after all others.
This essentially cut the current by half and the motor just tools along at about 60% of the RLA and does exactly the duty needed.
So as thus, the expense of the drive paid off while some other long term options were sussed out in the event they became necessary.