Can a Loss of 30 Volts Cause an Electric Motor to Overheat?

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Discussion Overview

The discussion revolves around the potential causes of overheating in an electric motor that is experiencing a voltage drop of 30 volts under load. Participants explore the implications of this voltage loss on motor performance, the suitability of overload protection, and the relationship between generator output and motor specifications.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant questions whether the 30-volt loss could be responsible for the motor overheating, given that the motor is running hot but not tripping overload relays.
  • Another participant notes that without details on the overload relay sizing and the motor's mechanical load, it is difficult to provide specific recommendations.
  • Concerns are raised about the acceptability of a 30-volt loss in wiring, even if it results in the desired voltage at the motor.
  • There is speculation that the motor itself could be malfunctioning, potentially contributing to the voltage drop.
  • One participant mentions that elevated voltage could increase no-load current and suggests checking this aspect.
  • Discussion includes the possibility that the motor's insulation class allows for high temperatures, which may explain the overheating without triggering overload protection.
  • Another participant emphasizes the importance of ensuring that the generator's frequency matches the motor's specifications.

Areas of Agreement / Disagreement

Participants express various viewpoints on the causes of the motor's overheating, with no consensus reached on whether the voltage drop is the primary issue or if other factors, such as motor malfunction or environmental conditions, are at play.

Contextual Notes

Participants acknowledge the need for more readings and checks against motor specifications to better understand the situation, indicating that current information may be incomplete.

Joe P
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Hello, looking for some information on electric motor theory for a problem I encountered on a friends machine. An on site generator is our power supply, our motor requires 480v/ac 3phase, our generator is providing 500v/ac but we are losing 30 volts under load from our extension leads. our motor is running very hot but not tripping overload relays. My question is - could the 30 volt loss of power cause this problem. Also if I increase the voltage output on my generator will it solve the problem. Thanks joe
 
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Without knowing how the overload relays are sized, the mechanical load and current drawn by the motor vs. the nameplate max current it is hard to recommend anything. Accepting 30 volts of loss in the wiring is not exactly good practice even if it does put the voltage at the motor right where you want it. Also, 'very hot' is a relative term. It can depend on if the motor is ventilated in the way that the designers intended.
 
Is it possible the motor has a problem? If so, maybe that's where the 30 volt drop is coming from.
 
Presuming the overload protection is suitable set on then the current it is in its correct limits. Elevated voltage could raise the no-load current-this could be checked of course. Usually the rated voltage is 460 V so 500 V [if this is the measured voltage at motor terminals] but 8.7% more it is not so elevated voltage.
The motor could be “very hot” if the insulation permits this. Insulation class H permits a conductor temperature of 180 dgr.C and 70-80 dgr.C outside stator surface could be permissible.
However the overload protection does not “protect” the motor against a defective ventilation or if a heat source in vicinity may deliver a substantial heat –even sunshine or else.
 
Joe P said:
our motor is running very hot but not tripping overload relays.

Hi Joe P. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

Check that the generator is matched to the motor's frequency, e.g., both 60Hz.
 
Last edited by a moderator:
Thank you for the the helpful info, We are going to take more readings and check the motor tag specifications,
Thanks all Joe
 

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