Hello all

GT (21 MW, Gas fuel operation) is having high vibration in BB5 and BB6 in exciter end.

The 23/02/2013 generator side vibrations BB11 were found 13.6 mm/s and The turbine not trip after one day the 24/02/2013 BB11 were found 13 mm/s but the turbine was tripped. Can you please suggest reasons for the problem?

Regards

 

MAATALLAH,

A typically configured generator would have two seismic (acceleration) vibration pick-ups on the turbine-end generator bearing and one on the collector end. A properly configured Mark V would have the redundant mask bit set for the generator group, and it would usually take two sensors of a redundant group of working sensors) to trip the turbine. So, presuming the turbine at your site has three sensors (two on the TE and one on the CE), and presuming the Mark V is properly configured, then a single sensor of three would not have caused a trip, but when the second of the group also went above the trip level then a trip would have been annunciated.

We don't have enough information to be of much more help.

And, unfortunately, the redundancy and group masks of many Mark V vibration BBLs were not properly set. It would be necessary to have drawings and a full set of software from the Mark V at your site to be able to determine if the masks were set correctly or not.

BB5 and BB6 are not usually on the collector end of the generator. So, it seems there is something amiss with the configuration or the information you have provided. If this is a Frame 5, there are usually two seismic pick-ups on Bearing #1 (usually called BB1 and BB2); two pick-ups on Bearing #2 (the exhaust end of the turbine; usually called BB4 and BB5); and these two groups of redundant comprise the Turbine Group. There are two or three pick-ups on the Load (Reduction) Gear (usually called BB5, BB6, and BB7); and comprise the Load (Reduction) Gear Group. There are two pick-ups on the TE (Turbine End) generator bearing (usually called BB10 and BB11); and one pick-up on the CE (Collector End) generator bearing (usually called BB12); and these three sensors comprise the Generator Group. Each group of sensors in this configuration example has redundant sensors, and if properly configured the Mark V would require two sensors in each group to exceed the trip level to initiate a trip on high vibration. This is for a unit with all sensors working and enabled in the Mark V (there is a method to disable a non-working sensor, which also changes the requirement for redundant indications for tripping for that group--to protect the turbine).

Lastly, for more information on redundancy and masks, you can refer to the Control Specification provided with your unit, Sect. 09.

So, you can see, we would need a lot of information to be of any further help.