Running a motor on Low Voltage
Running a motor on Low Voltage
(OP)
Can anyone tell me what will happen if I try to run a motor on a lower than spec voltage?
My application is as follows:
Centrifugal pump
Delta/Y 50Hz 400/690 15kW motor. 1455 rpm
The power system i have is 400/230 3p/4w. The motor is presently running in delta on 400V. I need to slow the motor down and one of the electricians working with me has suggested running the motor in Y. This should work as the load will still be balanced, but what will the power output and new FLA be?
Thanks in Advance.
My application is as follows:
Centrifugal pump
Delta/Y 50Hz 400/690 15kW motor. 1455 rpm
The power system i have is 400/230 3p/4w. The motor is presently running in delta on 400V. I need to slow the motor down and one of the electricians working with me has suggested running the motor in Y. This should work as the load will still be balanced, but what will the power output and new FLA be?
Thanks in Advance.





RE: Running a motor on Low Voltage
RE: Running a motor on Low Voltage
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RE: Running a motor on Low Voltage
RE: Running a motor on Low Voltage
Small reductions in voltage just tends to increase the amperage to the motor.
RE: Running a motor on Low Voltage
RE: Running a motor on Low Voltage
I think the centrifugal pump does not require a constant torque that means the same power for a certain speed. I agree with gepman VFD is the best solution. Also I agree with centripete if the torque would be constant.
I think the centrifugal pump torque is [approximative] proportional with the square of speed[n^2] .Reducing the voltage from 400 to 230 [delta to Y] the motor torque decrease with square of voltage [U^2]. Then the motor and the pump torque curve should meet at another speed.I am afraid this time on the instable region .That means the voltage is reduced too much. Attached jpg may illustrate the case I think.
Best Regards
RE: Running a motor on Low Voltage
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RE: Running a motor on Low Voltage
1) The motor torque will be 33% of normal.
2) The speed will remain the same (or try to).
3) Do the math; the motor output kW will decrease proportionally. kW = Tq (N-m) x RPM / 9550
So you have a 15kW motor at 1455RPM, therefore we can determine that your Tq, is 15 x 9550 / 1455 = 99 N-m
With 33% torque, you have 99 x .33 = 33 N-m
So 33 x 1455 / 9550 = 5kW
If the load power requirement is decreased at that time to 5kW or less, then no problem. But if not, even though the motor current is 33% of normal, the motor will see excessive slip and overload.
RE: Running a motor on Low Voltage
RE: Running a motor on Low Voltage
The voltage reduction (57.73%) due to the wye reconnection will drop the torque similar to the sample lower curve. The load torque will produce high speed SLIP. If the load torque exceeds the new reduced breakdown torque, the motor shaft will stall and the current goes to the locked rotor condition ( around twice the normal full load current for the original voltage). The winding will burn if it is left for extended time under that condition.