At present there is no ISO standard on alignment - maybe they need a voluteer.

indeed a very interesting discussion. However, it did not help me to clarify my doubts with respect to low voltage testing, rather than create more confusion.

I did not ones mention the brand name "AllTestPro" but everybody knew where my posted results came from.

Jank, thanks for sharing my frustration. You are spot on.

El Pete, you are right why did I conclude a "turn to turn" short. I guess the burn pattern.

By the way I will dismantle the motor within the next few days. Pictures and more info will be posted. I had to order the coils in the US as I can not get them locally in Mexico.

El Pete, I share so many doubts with you with respect to the F/I test and I consulted the same publications, standards etc,. and did not find the right reference.

WHAT ME SURPRISES IS THAT "AllTest" HAS NO NEED TO CONTRIBUTE TO THIS FORUM ?

What about PdMA low voltage testing ? Just an other vendor ?

Thanks, guys very interesting

There has already been quite a bit of exchange on this topic, but I will add my two cents. Looking at the supplied photo, it is obvious the winding has failed at the knuckle. At 6300V there was most certainly an arc between the phases. However I do not see evidence of a physical connection between the phases following the fault - no fused copper. In this case, the ALL-TEST results would not indicate the turn fault.

The results do however indicate likely overheated windings. Given these results I would test further with the rotor in a different position and see if the unbalance moves to a different phase or not. Based on my experience, I would expect the unbalance to stay on the same phase regardless of rotor position, and would have removed the motor for service.

I have tested hundreds of motors with the ALL-TEST Pro technology and find it to be reliable and sensitive. You have to understand the technology and its limitations, and know how and when to test further to confirm a fault. It is all well documented and taught in classes.

Any time you are troubleshooting, use all of the tools and information you have at hand. A single test evaluated by itself leaves you open to a missed call.

so mr bob
you mean to say it is reliable to test winding with low voltage?
and as u said you have vast exp in testing of motor with all test pro, can u submit here a perfect algorithm for testing of motor and other equipment. yes obvious it will b found in book but it is better if you can share your practical exp with all test pro.

i personally tested the sample motor provided by the all test pro and accordingly the test points mentioned , atp showing that motor is ok which i have selected test point for on turn to turn short. even that motor is not having rotor.
if it cant perform on test motor then how long is reliable to tested a field motor with this atp?

pls share your exp which is appreiciated and much valuable.

thanks
thanks

Mogli, I am new to this forum yet have many years machinery testing. You stated that the motor had an obvious short, and referenced the pictures. from the picture I downloaded it appeared obvious that some of the insulation was burned off and frayed, but as elect pete asked how did you determine the turns were shorted? Do you have a closer picture that clearly shows the turn to turn short? Just curious.

Thermographer, I'm not sure about a perfect algorithm, but I have distilled the guidelines for evaluating ALL-TEST Pro measurements into a short document which I use. It does not lend itself to posting here, but I would be glad to send it to you via email. Note that in the case of Mogli's failed motor, the measurements do not indicate shorted turns shorted turns, but a damaged insulation system which is consistent with what I can see in the one photo.

regarding your test motor, it sounds like there is a problem with it. The fact that it does not have a rotor should have no bearing. the test motor simulates faults by adding inductors, capacitors, resistors, etc to the circuit in order to simulate measurements that would be seen in a fault. If there is a poor or loose connection within the switch housing, it might cause the simulated fault not to be indicated. I am sure the folks at AT pro would be glad to evaluate and correct it for you.

BobD,

Are you a vendor for ATP?

Dave

Dave,


Yes Bob is a vendor for All Test, but he forgot to mention that in his posts.

Yes I do represent ATP, my profile identifies me as a rep. I know the technology well, have tested hundreds of motors over a 6 year period. I know what Motor Circuit Analysis can do, what it cannot do, and how to use it. I have also helped many facilities implement the technology.

Hello Mr Bob
that sounds good .then can you send me a complete step by step procedure for testing a motor. i have read Dr.Penrose Literature too but in i need some standard procedure for testing a motor. ( i.e. when v should go for rotor testing)also proper data interpretation procedure.
my email id is mr.thermographer@rediff.com

thanks & regards

I had been too caught up in some new projects to post over here, but guess I'll add my two bits.

The impedance unbalance in the AT-IV readings is because the instrument has changed the test frequency for one of the phases (the AT-IV chooses the test frequency automatically, it can be set in the AT-31). I have often asked ATP the reason behind this & they said that this information is proprietory. I hence always preferred the AT-31 to the AT-IV.

We regularly test motors for clients; & as a standard, we perform IR, PI, dielectric discharge, step voltage, surge test, MCA and tan delta & capacitance tests on all. PD measurements are done for 11 KV motors & generators. In addition; we take electrical signature analysis, vibration & acoustic emission measurements in running condition and then compile a report. I have detected faults by MCA,so I would not agree that MCA is a fake test. It works well, if one understands its limitations & looks at other test data too. Recently, we correctly diagnosed shorted turns in the rotor poles of a 30 pole, 5.1 MW synchronous motor using MCA.

I had a case last week where all of the above-mentioned off-line tests were done on a 4500 KW, 6.6 KV slip-ring motor. All results checked okay. The motor failed within a minute of start-up, one coil failed (ground fault) just where the coil comes out of the slot. Does that mean that tan delta & capacitance testing does not work for detecting ground insulation degradation?

Some suggestions regarding MCA tests:
1. If impedance measurements for one phase are approx. double (or half) of those for the other two phases, this is due to change in the test frequency, not due to a winding fault. Some people claim that this change indicates winding problems, I have never seen a confirmed case.

2. Trend absolute values of Fi & I/F, not the unbalance. I have seen these change in motors along with change in IR & the same came back to the baseline values after the IR was improved by heating.

3. Fi & I/F unbalance in synchronous motors at the stator terminals is more often likely to be a rotor fault.

4. Do not rely too much on the unbalance in resistance readings below 0.1 ohm, use a micro ohmmeter instead.

5. Take impedance measurements at different frequencies (AT-31), you can miss faults at lower frequencies. Also, an actual impedance unbalance (not due to frequency doubling) at a higher test frequency is a far more definite indication of a fault than Fi & I/F unbalance.

I have three issues with the surge test:
1. This should ideally be done at hi-pot voltages, but most clients are reluctant & ask that we limit it to operating voltage only. This might work for the line coils but I doubt if it would pick up faults in coils further down.

2. If the motor is in assembled condition, I am unable to interpret the surge waveforms, they are quite messed up. I guess the mutual inductance between the stator & the rotor is the cause. If someone knows how to work around this, would like to know.

3. Surge tester manufacturers rate their instruments as 10 kV or 15 kV, but the actual voltage that can be applied varies with the size of the motor under test. Is there a formula relating the motor KW or impedance to the voltage that the instrument can apply?

Regards,

Aditya