Hey folks,

Hope you are all doing well!

We have a old BRUSH Electric Motor-Generator Set at our site. Recently during servicing, we noticed that the insulation on the Rotor poles was removed/eroding at places(See attached picture). Bare copper can be seen being exposed.

This was concerning but the machine has been running well since past 29 years without any problem and all electrical tests i.e. IR and PI are Okay.
I asked BRUSH rep. about it and he said this happens with old machines and should not pose any imminent threat. I disagree with his statement as I fear an inter-turn short circuit can take place in such a situation if moisture ingress happens or some conductive dusts accumulates over time. I intend to request management for complete rotor removal, dry-ice cleaning and re-varnishing urgently but since a lot of cost is involved I would like to be sure if the threat is real.

Please look at the picture and share your thoughts.

Regards,
Mutahir

 

Hey folks,

Hope you are all doing well!

We have a old BRUSH Electric Motor-Generator Set at our site. Recently during servicing, we noticed that the insulation on the Rotor poles was removed/eroding at places(See attached picture). Bare copper can be seen being exposed.

This was concerning but the machine has been running well since past 29 years without any problem and all electrical tests i.e. IR and PI are Okay.
I asked BRUSH rep. about it and he said this happens with old machines and should not pose any imminent threat. I disagree with his statement as I fear an inter-turn short circuit can take place in such a situation if moisture ingress happens or some conductive dusts accumulates over time. I intend to request management for complete rotor removal, dry-ice cleaning and re-varnishing urgently but since a lot of cost is involved I would like to be sure if the threat is real.

Please look at the picture and share your thoughts.

Regards,
Mutahir

Hey Mutahir,


I would advise at least a re-varnishing for this unit...

Any time!
James

 

MRasool...
1) What service does it provide in your facility?
2) What are the motor's nameplate parameters?
3) What are Wye-winding resistances, Rab, Rbc, Rca: a) while "Cold"; b) when "Hot"?
4) What is the Ambient temperature?
5) Have you considered a new motor's efficiency vs that of the old one?
6) Has the motor been disassembled?
Regards, Phil Corso

 

MRasool...
1) What service does it provide in your facility?
2) What are the motor's nameplate parameters?
3) What are Wye-winding resistances, Rab, Rbc, Rca: a) while "Cold"; b) when "Hot"?
4) What is the Ambient temperature?
5) Have you considered a new motor's efficiency vs that of the old one?
6) Has the motor been disassembled?
Regards, Phil Corso

Hey Phil!

Good to hear from you.

1) What service does it provide in your facility?
It is a frequency converter. We have unit which runs on 60Hz cycle and this unit converts 50 to 60Hz for that unit.

2) What are the motor's nameplate parameters?
Nameplate Generator is(The pictures attached above are for Generator Rotor)

Supply system	2400V / 3 Phase / 60 Hz
Output	4000KW, 5000KVA
Specification	I.E.C 34, Class F Insulation
Temperature Rise	Class B
FLA	1203A
Phase Connections	STAR
Ambient Temperature	50°C

Name Plate Motor is:

Supply system	6600V / 3 Phase / 50 Hz
Output	4158 KW, 5400KVA
Specification	I.E.C 34, Class F Insulation,
Temperature Rise	Class B
FLA	472A
Phase Connections	STAR
Ambient Temperature	50°C

3) What are Wye-winding resistances, Rab, Rbc, Rca: a) while "Cold"; b) when "Hot"?

Generator Stator:

Year​

U-V​

U-W​

V-W​

2021​

12.015mΩ​

12.002mΩ​

11.895mΩ​

Generator Rotor:

Rotor Resistance

0.115 Ω

4) What is the Ambient temperature?
Outside Ambient here is 55 Degree C max. But since it is placed in a building with a natural cooling arrangement, the ambient is around 30Degree C. Also the machine is water cooled with winding coolers.

5) Have you considered a new motor's efficiency vs that of the old one?
This is a 4MW generator working perfectly since past 29 years. We haven't done any efficiency benchmarking as we don't have any newer motor-generator set. What do you recommend?

6) Has the motor been disassembled?
Machine has never been disassembled since commissioning back in 92'. We just open the end covers after every 3 years, do electrical testing, dry air cleaning etc. and close it.


Regards,
Mutahir

 

Mutair...
Can you provide operational V, A, P, Rhot, Tdeg above ambient, so that efficiency can be calculated?
Regards, Phil Corso

 

Mutair...
I forgot to include another variable, i.e., actual speed Srpm!
Regards, Phil Corso