How to Detect Burnt or Malfunctioning 3-Phase Motors: Inspection Tips and Troubleshooting

Question

as above. I know that this type of engine burns in different ways, but how to detect if such an engine is actually burnt or not? Last year, in the work I was doing, the saliva burned down and I was called for a so-called inspection, is it really so? Basically, having a small idea about it, I...

POL02 · Answer

Hello.
You can check the engine as follows.
1. Breakdown test (whether the insulation between the winding and the motor housing is not damaged. This is done either with a breakdown tester at U = 1250V or IMI (inductor insulation tester)
2. Measure the winding resistance (for a three-phase motor they should be equal to each other)
3. Measurement of the idling currents in each phase (they should be equal).
This is a basic check.

gmp · Answer

You can still disconnect the windings and check for breakdowns between them. Sometimes the cause of the damage is sometimes the bearings or bearing seats, the motor then jerks - and then the stator rubs the winding.

stasiekm · Answer

It is also very useful to measure the inductance of the windings - the same principles as when measuring resistance

vymiathatch · Answer

I know the first two methods described by my colleague POLO2, but I do not know what it is about, i.e. I interpret it like this, you should turn on the motor itself without any load on the shaft and then measure the currents coming to the motor, if they are equal, the motor is operational and if they are different then where there is more current the winding is burned out

Spiderek · Answer

It is best to measure the resistance of individual windings, they should be equal to each other, although the value is relatively small, then it will turn out if it makes sense at all to do something with it

Czesiek · Answer

It happens that everything looks fine from the measurements and the squirrel cage motor has no "power". The cause may be a crack or a burnout in the aluminum rotor winding. Often invisible to the eye.
What is best for a different rotor to be checked. Determining such damage is sometimes only possible with an industrial X-ray, and it is profitable with larger motors.

Anonymous · Answer

And often by smell you know (after unscrewing the cover of the can). Just the smell of burning, not hot paint, that's the difference .

vymiathatch · Answer

and what row are the resistances of these windings? kilo ohms or maybe ohms? and if I do not have the windings drawn on the box, I will put the meter to the end of two neighbors. then my measurement was for nothing. what do you say?

Anonymous · Answer

If you conventionally label the three-phase windings as U, V and W, then the connection layout on the 6-terminal plate is usually as follows:

UVW
VWU

that is, diagonally, not horizontally or vertically.

This is done in order to easily assemble a triangle with the help of the plates:

UVW
lll
VWU

or stars:

U_V_W

VWU

(In the star configuration, the motor is less powerful and consumes less current, often starting in a star configuration and operation - after delta switching).
A motor above a kilowatt will have a winding resistance of maybe 2 ohms, certainly not a kilowatt. A motor a few hundred watts can have more - maybe even more than 10 ohms.

(This forum compresses spaces - the letters and the connecting dashes above should be evenly spaced, but this won't display as I entered.)

tprzemko · Answer

Hello
Most three-phase motors burn when they run on two phases. You can add some security.
To check the motor is not damaged, it is best to immediately treat it with an inductor if it has the appropriate resistance to ground. Usually, when the insulation drops, the winding will have a breakdown on the motor body and a specific smell. After positive insulation measurement, check whether the transition is between the windings, and finally measure the currents with clamps. It very often happens that the engine in the machine cannot start and most often it is a mechanical fault, something that is obliterated. Just check that the motor shaft can be turned by hand

belka3 · Answer

You can also check the current during operation at individual phases, sometimes only a few windings will stick in the middle of the motor will work,
electronic omomież will show a slight difference like everything is ok.
But while you work, you may notice significant current differences.

ACULA · Answer

can be checked on one phase: connect in a delta, then connect the wires 220 to the third to the two terminals and, for example, to the second one connect a capacitor. Of course, the real strength of the engine cannot be checked in this way.
This way you can check if it works at all, broken bearings, bent axle etc. You can also more or less check the power by trying to stop the axis rotation.

piotrpak · Answer

Once upon a time I had a case that the entire rotor package was displaced .... The current at idle speed was only half lower than the rated current

macher · Answer

If you have a drop in power, it may be due to the gearing of the motor and short-circuit between turns on some phase. The motor will consume more than the nominal current and it will be weaker. You will detect this with an ohmmeter.
If you have 3 terminals, you measure each with each other, you have 3 measurements and these are the resistances of the windings in the 3 phases of the stator should be the same.
If you have 6 clamps, it's like a gulson.
8O
trickster

How to Detect Burnt or Malfunctioning 3-Phase Motors: Inspection Tips and Troubleshooting

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