Stator Core Phase Rotation

[mbailey]

Can I test a stator core for proper phase rotation prior to varnish treatment? I know I can power it up and use the spinning can trick but I am hoping there is something we can do at our test stand without high volts or amps. Any comments are much appreciated. Thank you.

 

[electricpete]

Assuming rotor is installed:
For small machines, use standard rotation meter. For larger machines, an oscilloscope can be used as described in my attachment 12 Mar 12 8:11 in the following thread:
thread237-318005
(there may be other stuff in the thread of interest since the subject was basically the same as yours... no difference in determining rotation direction for motor or generator)


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(2B)+(2B)' ?

 

[electricpete]

If rotor not installed (more likely after winding before varnishing), you could arrange a very small cart to roll around the bore of the stator carrying a permanent magnet and use the same oscilloscope approach.

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(2B)+(2B)' ?

 

[Brad1979]

If you have a motor that rotates correctly, you can apply a DC voltage to the lead wires and then record where the north and south poles show up on the stator teeth. As long as you are consistent with how you apply your voltage, you should see the north and south poles in the same places on other motors.

 

[YuriB]

Sorry, but why not to make the correct notes on how the windings get connected during the rewinding work?

 

[mbailey]

Thanks Pete, if I understand you correctly, a small roller skate with a magnet mounted on it could be rolled around the stator bore and monitor the leading phase on the oscope when connected per your rotation check procedure. Would you need to make a full rotation or multiple rotations or would you see this pattern as soon as the skate begins to move? How fast would the skate need to move? Can you push it by hand and get a correct pattern. I assume you would need to adjust the air gap between the magnet and the stator bore to get better results.

This test will be performed on an assembly line and the rotor is not present. It is a green wound stator core and I prefer not to introduce high voltage due to safety concerns.

Thanks for you help. mbailey.

 

[mbailey]

Sorry guys, I should have been more specific; this is not a rewind. We build custom engineered to order motors, one at a time. everyone of them are different and I would like to have a test in place to help identify connection errors before they become problems which can't be corrected without damaging the integrity of the winding. Surge and resistance just won't catch all connection errors whether made at the engineering level or the connection process. With a test like this, my hope is that we can detect a connection that may be one group off but still symetrically balanced or have the jumpers out of sequence. If the wave pattern is distorted or out of sequence, it seems to me that that would indicate a connection issue and require further investigation. If there truly is a problem, we can correct it and not damage the insulation on the wire. After the winding have been through VPI, it is very difficult to separate the connections for repair and we have elected to build a new winding instead of attempt a repair at that stage.

Is this a good approach or should I be going in a different direction? Again, thanks for your help.

 

[petronila]

Hello,

IMO to test if one winding is correct connected(Stator) is connecting all leads(In star or delta)and applying DC low Voltage to the leads 1,2,3.(Use a DC welding machine) then use a compass in order to detect how many south and north poles are. You most see the same north and south poles qty.

Note: The total poles can be calculated from the Motor Synch Speed.

60 Hz: 3600 RPM (2 POLES)-1800 RPM(4 POLES)-1200 rpm(6 POLES)-900 RPM(8 POLES)

50 Hz: 3000 RPM (2 POLES)-1500 RPM(4 POLES)-1000 rpm(6 POLES)-750 RPM(8 POLES)


For other speed apply : RPM Synch = 120*F/P where F is the frequency and P the poles number.

Example: 60 Hz motor with name plate Speed of 1750 RPM this is a Sych speed of 1800 RPM = 4 poles.


Another way is applying three phase voltage to the stator complete connected and if the winding is good connected the Amps per phase most be equal, if you have significative difference then you have a problem, this method require a very large power system due to the currents are high, specialty on medium and large size motors.


Regards

Carlos