HIGH VOLTAGE VARIATION ON MOTOR

[Wirenut]

I have a motor running @ 10% above full load current and the voltage is 10% above motor name plate. What will happen to the current if I get the voltage to nameplate????

40 HP motor 3 phase, 460 volts nameplate,

Wirenut

 

[electricpete]

3 effects as you reduce voltage:

1 - the load component of current goes up (assuming constant load)
2- the magnetizing component of current goes down.
3 - there may be a very slight decrease in speed of the load and therefore decrease in real power consumed by load which acts in a direction to decrease load current.

Net result is hard to predict. I think most likely effect #1 wins and current increases.

If #1 doesn't win, it's because you had a core very far into saturation so magnetizing current was big factor and #2 bigger factor.

 

[rbulsara]

Current is inversely proportional to the voltage, assuming HP remains constant.

Howeve HP is proportoinal to the torque which is proportional to the square of the voltage. But it can be decpetive as your load may not need the full torque the motor is able to develope. Assuming the running torque and hence the HP remains constant:

Roughly, the current will go up by another 10% or 120% of (1.1 x 1.1) of the rated FLA. (You can do exact ratio calculations). You will be close to tripping the O/L trip, which normally is set to 125% of rated FLA, or even damage the motor by excessive heat build up.

Your chances of survial are better with slightly higher voltage, the way it is now as it draws less current. Of course,as you understand,this by itself is not the greatest position to be in. You are pushing the envelope.

Real Advice: Instead of going through these type of catch 22 scenarios, lower the voltage by some % and see what happens. Nothing beats a real experiment!! Let us know the results too)

 

[jbartos]

Suggestion: There will some differences between T-Frame motor and U-Frame motor, namely:
T-Frame U-Frame
Current decreases increases
Efficiency increases same
PF increases increases

 

[DanDel]

Within certain parameters, current will typically decrease when the voltage is increased for an induction motor. At 10% above rated voltage, you may have a situation outside of these parameters where the current has started to increase. Why is the motor being run at 110% voltage(506V)?