Motor voltage & frequency

Hello nambiathiri

If the motor is a squirrel cage induction motor, it will run slower, of course, at 5/6 of the nameplate speed, on the lower frequency supply.

We commonly have connected 60Hz 380v motors to 400v supply here, without any bother at all, apart from the speed difference, and our Mains Voltage varies from the nominal 400 V to 380V minimum - 420 V maximum as allowed by local Electrical Supply Regulations.

In most Electrical Supply areas, Mains Voltage range is normally +/- 5% which at 380 Volt Supply +5% is 399 Volts, and your 415 Volt supply should probably be safe to use, even though a small increase above normal nameplate voltage.

Carefully check motor current in your situation, at both No Load and Full load, should you intend using the motor on a permanent basis.

Remember that at the lower speed, there is less fan cooling on a Fan Cooled motor, and if you note the motor case getting too hot, arrange for extra cooling.

Kind Regards....

dear

the reason is at 60hz the impedance of the motor matches to 380V.this is desided by the ampereturns of the coil and core maximum flux density.

the only remedy is to reduce suply voltage at 50hz.

but the power remains the same after reducing(stepdown) 415volte to apropriate value.

thanQ

RRekhapalli

Since inductive reactance is proportional to frequency, the stator current at a given voltage will be higher at 50Hz compared to the current at 60Hz.

European standards permit 10% variation on mains supply. Thus 415 VAC is permissible for motor rated at 380VAC.

The cumulative effect of decreasing the frequency and increasing the voltage would be net increase in stator current and the resultant increasse in winding temperate.

This will result in reduced life-span of the motor because of the rise in insulation temperature. Joule heat will increase and efficiency will come down. There would be slight increase in the motor torque and motor kW.

Dear Members,

What will happen if a motor designed for 415 V power supply is connected to 380 V power supply, the frequency being the same?

Regards.

R.Thiyagarajan

A motor designed for 415 V and used at 380V (in both cases at the same frequency)will turn a little bit slower, (the slip will increase ...)

but the torque that the rotor can deliver will only be 84%

so the total output power is +/- 80% of the original motor.

Keep in mind that when the motor is driving the same tool at 415 and at 380V, the needed torque on the motor shaft, will be the same. The motor will, despite the lower voltage, try to deliver this needed shaft torque. So the motorcurrent will increase and the motor will warm up.

Nambiathiri,

The ratio of voltage to frequency should remain fairly constant. This is basic to how VFD's work--as they decrease the frequency they also decrease the voltage. In your question, the voltage is going up and the frequency going down. This is just the opposite of the desired relationship. Not a good idea, as others have noted. If you "must" do it, then make sure you have the best flow of air for cooling and that your running overload protection is set at or slightly below the motor's nameplate current.

--JMM