Rotor Became Overheated After Rewinding and also Taking High Power

03. Pick up the telephone and get the rewinder's technical representative to attend site, investigate and solve the problem. Please state that the invoice hasn't been settled yet!

Yes; if any of the field connections are wrong it definitely could cause high field current.

You need to refer to the OEM drawings and verify all connections are correct.

If you are find that all alternator connections are correct; I would suggest you contact the company that performed the rewind and insist they send a field represenatative to your site before proceeding.

If you cannot get the rewinder to provide competent on-site service, contact the manufacturer (OEM) of the alternator and get their field technical service to provide on-site support.

If you proceed without competent field service the results can be catastrophic not only to the alternator but also life threatening to anyone working in the immediate area and the cost will be extreme.

The rotor can be out of position with respect to the stator bore.

So, do you really have a problem?

The lack of detail you provide says no one knows.

This comment, "the field temperature is 20 degree higher than other genset" may, or may not, be a problem. It would help to know if it's °F or °C, but I assume it's C.

"the excitation voltage and current increase gradually though load and power factor is same" also lacks any real information. From what minimum to what maximum?

The 3 previous posts should be a good start, if followed.

Thanks everyone for the feedback,below some more details:

01. The copper size used for rewinding is same as the original rotor.

02. No of turn also same (as the winding done by square copper bar so it's easy to measure the no of turn and also the copper bar size).

03. There is no OEM drawing for the field and they are not supporting also.

04. Field temperature us 98°C where other Same Alternator with same load is 78°C.

05. Excitation voltage is 47 VDC after immediate full load and slowly it's increased to 56 VDC. where other genset excitation voltage in same load is 43 VDC and as per test report also its 43 VDC.

06. One point I forgot to mentioned, three pole is connected in series and there are two set of field made by six pole. During commissioning we found one set resistance is 680 mili Ohm where other set resistance is 720 mili Ohm.

07. The winder raise his hand as he is not getting anything.

08. The stator is ok and there is not inter-turn short (all three phase resistance is same ).

Please kindly provided your comments to get the rea son of this problem and also let me know if any further information is required.

You still have not explained why the rotor and not the stator coils were rewound.

Your imprecise answer #6 shows that your (stator or rotor) coils are not identical. You have about a 5% difference. If this difference is not due to a faulty measurement or termination then one of every eighteen turns of a coil is shorted.

(720-680)/720=1/18

Notice that this is not approximately 1/18, it is exactly 1/18. This implies that your difference is some form of integer math, like whole turns shorted.

Please check the Gauge of the wire used for rewinding if the gauge is higher than the originally was, you will have the heating effect. this may also happens if the number of turns per pole is reduced.

As mentioned the no. of turn confirm ok. Only thing we are unable confirm is the quality of copper strip that we used.

If the quality of copper is not same as the manufacturer committed than is there any possibility of higher power taken by the field ?

All the connection's seems ok as the genset is still operational with the rewinded rotor Since more than two weeks.

As per your Point no. 6, six set of field coils produce two set of magnetic field.

It has to be three set of magnetic field (each coil produce one magnetic pole N/S) .

Secondly there might be an air crack or air gap in the rotor core which increases the core loss(magnetic field loss) to componsate this loss field current & voltages increase to get the required magnetic flux to generate the same output.

There are number of mandatory tests to be conducted (may call them commissioning tests) before loading the machine. few of them are measurement of winding resistance, impedance test, inter-turn short test (some people cover this by impedance test whereas some conduct RSO test) etc. Have you conducted all such tests and then compared with the original rotor data? Then you are also suppose to conduct OCC and SCC test and compare them with the original curves. Have you done this? If all such test have been conducted and the results are comparable then check the ventilation of the rotor circuit. Increase in voltage with load beyond the normal increase is indicative of excess temperature rise which is causing winding resistance to increase. Have you balanced (including thermal balancing) the rotor? Do the rotor vibrations go up with rise in rotor temperature? Then there is thermal unbalance in rotor and needs to be attended suitably.

Dear Mr.zia6182,

After re-winding, you could have tested the rotor, stator etc.

Pl. compare the test results with the original test reports and understand where the difference has crept in.

What is the cross section of the copper wire/flat used for re-winding.? Does it maintain the same Ampere-Turn Ratio.? If smaller cross section means, the Resistance will be more resulting in excessive heat developed, which results in higher temperature. If lesser Ampere-Turn ratio means, your AVR will regulate or increase the field current in the rotor (increase the current due to lesser Ampere-Turn Ratio) to maintain the Output Voltage.

Pl. inform this forum, how it was sorted out and solved.

DHAYANANDHAN.S

Thanks everyone for the suggestion.

As this alternator operational in IPP and we did periodic checking of all the parameter which is found same as during commissioning after rewinding. So we suggested customer to operate it further until there is no issues.