How electrical discharge can damage bearing

J

Thread Starter

johnahuja

We have three gas turbine of model-MS6001B. we are facing problem in one of gas turbine regarding high vibration since back 2 years. so we are not able to load more than 18 mw. so as per OEM recommendation in recent MI we replace turbine rotor, All 9 cpital spares with uprated compressor blade and IGV, exhaust casing and also uprate our machine to PG 6581 model. Then we started our machine and same is loaded up to 35.6 mw with max. vibration 8.8. but after running of 10 days. brgg-2 metal temperature start increases, then we took shutdown of machine and found BRG-2 in damage condition. now our doubt is can electrical discharge damage BRG-2. or please suggest what may be root cause for that.
 
T
There could be many reasons for the Bearing damage like whether lube oil pressure is sufficient, lube oil temperature is well maintained, etc. Please provide more details on the Lube oil cooling system.

Please provide additional information like-

1) What was trend of lube oil pressure and temperature.
2) What was trend of bearing#2 temperature

In addition, I think bearing#2 is located in the hot zone and cooled by external means. Please provide details for the same.

Why you are suspecting only Electrical current? Was there any past history of such event?

Regards,
 
I had an 8MW motor (11kV) driving a ball mill (mining). The white metal bearings were destroyed in the first 2 months of start up
Reason: Depending on the thrust location the Rotor was not grounded correctly and the earth path that it found was via the bearing.

Solution was an earth strap on the rotor

This may be your issue.
 
Thanks for your prompt reply. detail of machine parameter is as under
load-16.6 mw
Lube oil header temperature- 58 degree
header pressure- 1.8 kg/ sq cm
MOP discharge pressure- 4.6 kg/ sq cm
Brg-2 metal temperature- 65 degree
BRg-2 Drain Temperature- 78 Degree

But after running of 7 days Brg-2 metal temp. start increases from 65 to 75 and drain temperature start increase 78 to 85.

We are suspected for electrical discharge by seeing the damage pattern of BRG-2.

Reason- Brg-2 has minimum clearance so oil film thickness is very less.

there is no past history for damage of BRg-2 due to electrical discharge.
 
Top