Thermal Overload Tripping

[NLLM]

I have 6 thermal overload relays that frequently trip. They each serve a blower with a 3 Phase 460 V 15 horsepower motor. We measured the voltage at the relays and it registered 510 Volts. Could this be causing the trips?

 

[Parchie]

If your problem is overcurrent, you should have measured the line currents.

 

[waross]

Measure the line to line voltages accurately. Unequal line to line voltages will cause greater current inequality. Depending on the impedance of the supply system, a 5% voltage unbalance may cause a 20% or greater current unbalance. The current in the highest phase may be greater than the setting of the O/Ls. Even if your current is not over the rating of the O/Ls, unequal current may be causing differential trips.
Measuring the current is also an excellent idea.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[NLLM]

Thanks. I will measure the current and the line to line voltages.

 

[jraef]

Overload relays react to current, not voltage. But if you have motors that are rated for 460V and the voltage applied to them is 510V, that will cause the motor to go into saturation, which increases the current without increasing the work it performs, so of the motor was fully loaded to start with, the high voltage will cause high current and the OLs are protecting the motor. 510V is out of spec for a 460V motor; 460+10% and it is out of spec for the utility supply, 480+5%. You need to address that no matter what.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington