Jump to content

motor burn out with inverter


Recommended Posts

Dear sir,

I have just tried an inverter for my machine.

My machine use 10 HP (7,5 kW) 380V. but this motor have been rewinding because of burn out.

When I install the inverter to this motor, the motor burn again at one phase.

I set the inverter for base frequency at 60 Hz (my motor is 50 Hz).

and then I run the inverter at 700 RPM (about 28 Hz) for 1 hour. then my motor become too hot and when I checked it was any burn at the phase.

when I measure the current in the inverter output it shows about 15 A each phase.

measurement at inverter input it showed 8/9 A at two phase and 10/11 A at one phase.

my motor nameplate is 380V delta, 10 Hp, 15,7 A (FLA I think), and has 4 pole, and 1448 RPM.

when motor run for no load it takes 4 A each phase.

my question is : what makes my motor burn ?

is it because the wire sizes is not correct?or the inverter setting is wrong

that can make the motor burn?

when I run this motor with inverter I forgot to place a fan in the back of motor , is it influence very much to motor burned cause I work at 700 RPM at full load ?

Do I need auto tuning at inverter cause i work only at V/F control not PID or sensorless vector control?

Is it true that inverter current is higher at 50 Hz (cause when I set for above or below 50Hz the current output from inverter seem lower) ?

thank you very much for answering my questions, Cause I want to know what makes my motor burn.

Link to comment
Share on other sites

Hello Cahya


Your motor is rated at 10HP at 50 Hz.

When you slow th motor down, you reduce the cooling considerably. If you run the motor continuously at rated current and part speed, you will have the same losses in the motor as at full speed, but due to the reduced cooling, the temperature rise will be much higher. This will cause the insulation to overheat and fail early.


With induction motors, it usually said that the life of the insulation halves with each10 degree C increase in temperature. This is true up to a "plastic" temperature where the insulation changes state. At thsi temperature, failure is much quicker.

I suspect that at 28 Hz, the cooling on your motor will be less than half the required cooling and so the temperature rise would be more than double the design temperature rise. This would take the insulation through the "plastic" region and result in an insulation failure.


If you wish to run your motor continuously at rated current at much reduced speed, you must provide additional cooling for the motor. This is a case where the use of thermistors in the motor windings would probably prevent a failure.


PID control will not prevent this from occurig. PID control is a means of providng a feedback mechanism so that the drive will operate at a set point.


Best regards,

Link to comment
Share on other sites

So I guess, motor burn out is caused the wire insulation size for the motor is wrong and not enough cooling air inside the motor.

If I want to use external cooling fan, where I must take the fan?

Is it in the back of built in fan (back of motor)?

How about base frequency at 60 Hz when I use 50 Hz motor? Is it become an over-energised for the motor or not with V/Hz control method?

Link to comment
Share on other sites

Hello Cahya


The insulation is not necessarliy wrong for the conditions that the motor was designed to be used under. You are using it under different conditions and so the insulation requirements change.

Positioning and sizing of the external cooling fan depends on the motor. You are best to talk to the motor supplier and ask them. Some have kits available to add additional external cooling.


If you set the base speed to 60Hz with a 50Hz motor, and you set the voltage at that speed equal to the rated voltage of the motor, you will be underfluxing the motor and this will tend to increase the slip and rotor heating. You should set the base speed and voltage equal to the motor ratings. You can still run up to 60Hz, but you will get the correct voltage at 50Hz. If you set the base speed to 60Hz and the voltage to the design voltage, then at 50 Hz, you will have a reduced output voltage and this will under flux the motor, increase the rotor losses and increase the stator current.


Best regards,

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...