Measuring Voltage Transients in Motor application

[noel0589]

Hi all,

It is easy for me to understand transient current surges and how I could measure them in an OPEN TRANSITION WYE start - DELTA run motor application, but all I have is a clamp on ammeter which will not catch or display the transients.
What I do have is a voltmeter which can print a curve to the microsecond. Would someone explain what happens in terms of voltages during the open transition wye to delta switch regarding transients? And also what should I measure voltage across?

As always responses are very much appreciated...
Noel

 

[electricpete]

be careful in that measurement. You likely are dealing with high voltage which gets higher during the transient.

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[electricpete]

Safety issues aside (that is your serious responsbility... but you can tell us the voltage level and instruments and I'm sure you may get some help here)....

Why not monitor the voltage T1-T4, T2-T5,T3-T6.
It should of course increase by square root of 3 during the transition but the peak voltage should not be so high as to damage the winding. How high is ok another question. One might look to surge test standards IEEE522.


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[electricpete]

I should say IEEE522 is just a datapoint, not the answer.

Also the rise time of the voltage spike affects how destructive it is (shorter rise time more destructive). I don't know that much about this type measurement but I think you have to be very careful that your measuring setup does not introduce filtering of the high frequency content. Every setup has some upper frequency limit.

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[noel0589]

EPete,

measuring equipment is an old hioki 8815 memory hi-corder.
I will be measuring on 208V 50HP systems. i'll keep your advice on turning off filtering in mind. Thanks!

 

[electricpete]

I think I was wrong if I suggested that the waveform you will record during monitoring T1-T4 etc would be directly comparable to IEEE surge test waveform in terms of damaging ability. In surge test one end of winding is grounded but not so during system voltage spike. Ground has a significance since there is high capacitive coupling to grounded slot.

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[electricpete]

Maybe I should say another way during surge test you are measuring a voltage to ground. It raises a question in my mind would there be any value in measuring voltage to ground during the transient. I don't know the answer but I don't think so. Anyway it would require more thought to figure out how to relate your waveform to surge test standard.

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