From what is visible on the angle taken, I would say that the insulator on the radial stud connecting the rotor lead to the thru-shaft portion failed. Probable causes include: mechanical abrasion (vibrating in the shaft exit hole), contamination (something conductive got close and bridged the gap between live conductor and grounded shaft - usually across the top of the insulating tube), or significant thermal load (high current draw heats up conductor, which deteriorates the insulating and mechanical properties of the insulating tube).

Converting energy to motion for more than half a century

Fatigue failure of current carrying bolt/stud. About 20 years back, our client had one such failure in a GE 20 MW GTG. Luckily, the thread on the rotor current bar was not damaged. We cleaned up the thread and provided new bolt/stud. Still running. GE wanted to ship the rotor across continents from Asia to US.

Muthu
www.edison.co.in

Intriguing Connection Failure.
There does not appear to be any means for inspecting the hidden damage.

The entire rotating portion of the machine needs to be dismantled.
It's a connection problem, not a slip ring failure.

John

El AABD Jamal By the way - this specific type of failure occurs fairly frequently in mining applications (crushers, shredders) and wind generators (doubly fed induction designs) - anywhere there are high peak instantaneous torque loads and/or high frequency vibration.

Converting energy to motion for more than half a century

El ABBD Jamal ,
I don't see data related to motor power , voltage and rotor current. In any case, while you waiting for rotor repair , you should carefully check and look at the condition of the rotor resistor and switching equipment .
Good luck !

Thank you for your replies,
The motor Data:
- Nominal power : 2800 KW
- Voltage : 5,5 KV
- Nomiunal Current : 364 A
- Speed : 994 RPM

By monitoring the power and the current we observed that before the breakdown by 4 days,an abnormal current fluctuation Min-max difference of 200 Amps, compared to what was recorded before (a more or less stable current), now that we have replaced the motor with a another one new the same fluctuation persists I'm afraid that the same failure will happen again for the new motor, for information it's a raw mill application in a cement plant.

Does a current fluctuation below the rated current cand do a damage to the motor?

For illustration please see picture attached (in green the power, in pink the current)

• https://files.engineering.com/getfile.aspx?folder=43156622-288f-4dd1-b42e-5

Since the same current hunting is seen, I would check the rotor resistors for loose connections or about to fail resistors and the shorting contactor for loose connection and burnt out contacts.

Muthu
www.edison.co.in

drive chain also contains a turn group dedicated to starting the application the latter is composed of a squirrel cage motor and a gearbox the same phenomenon of current fluctuation was observed which made us suspect less the rotor circuit of the MV motor.

Attached the rotor electrical measures

• https://files.engineering.com/getfile.aspx?folder=5398dd3e-6f92-4c41-b0cf-c

Stator electrical measures

• https://files.engineering.com/getfile.aspx?folder=d79c2bef-eba9-4be9-b0db-1

Quote (drive chain also contains a turn group dedicated to starting the application the latter is composed of a squirrel cage motor and a gearbox)

Are you saying this failed motor is a synch motor? You should post the motor nameplate details.

Muthu
www.edison.co.in

No its Not a synchronous Motor,the LV motor is used to start the application not the MV motor!

• https://files.engineering.com/getfile.aspx?folder=b5e13f75-1d28-465b-8272-a

MV motor nameplate

• https://files.engineering.com/getfile.aspx?folder=e4b369be-c59e-4a11-afac-0

Still not clear why a MV slipring motor would require a LV starting motor. And your GA drawing doe snot show a LV motor (unless 6 is the LV motor).

Muthu
www.edison.co.in

the MV motor is for a vertical raw mill before starting it a prepartion need to be done by the operator it consist of Preparing a layer of material on the table, this is only possible by turning the table at low speed in the first place, that's why the LV motor(6) and its gearbox are needed. the MV motor for its starting it only needs an electrolytic starter.

Have been looking at the original photo posted by the OP.

This is a warranty repair.
The failure is hidden from view inside a tube. The end user didn't cause this.
The manufacturer of the apparatus needs to explain why their product failed.

John

Edit: Yes, the connection nut locking devices do not appear to be "factory", [but] it still looks like a warranty.