Dear all,
I hope you are in the best of health and spirits.
I need help in understanding root-cause of a recent tripping on one of the generator units at my workplace. The generator is coupled with Gas Turbine Frame-5001PA.
Generator details are:
Type DG185ZL
Rated Power - 26 MVA
Power Factor - 0.85
Rated Voltage (L-L)- 6600 V
Rated Current- 2295 A
Rated Frequency-50 Hz
Year of Manufacture- 2009
Number of Poles - 4
Rated Speed - 1500 rpm
What happened?
Recently the generator tripped on Seismic probe security i.e. going beyond the trip limit.
There are two Seismic probes installed on the generator(See the Train Diagram attached), 1ea on the in-board and 1ea on the outboard along with 2ea proximity probes. Bentley Nevada system is installed which feeds their value to Mark 6 system for Turbine control. The Sequence-of-Events was as follows:
Note: We do not have any trending of probe value for both Seismic and Proximity Probes in Mark-6. Only events are logged i.e. if something goes above alarm limit or trip limit.
Our Instruments team has checked both the seismic probes by knocking on them and seeing the response signal on Mark-6, checked the cabling and the Bentley cards. All was found Okay. There was no seismic activity in area nor any sudden load change on generator i.e. All the parameters were running business as usual. (There was a road being made about 50m away form the generator and a roller was being used on it.)
The machine was started again after forcing the seismic probes and it is running normally now.
Questions?
I would request the forum to give their insights on following questions:
The generator was running normally, no sudden load changes and no lightening strikes or seismic activity observed/recorded in the areas.
We have already floated the queries to OEM, so please don't suggest that. Posting here to benefit from collective wisdom.
Looking forward to your responses.
Regards,
MRasool
I hope you are in the best of health and spirits.
I need help in understanding root-cause of a recent tripping on one of the generator units at my workplace. The generator is coupled with Gas Turbine Frame-5001PA.
Generator details are:
Type DG185ZL
Rated Power - 26 MVA
Power Factor - 0.85
Rated Voltage (L-L)- 6600 V
Rated Current- 2295 A
Rated Frequency-50 Hz
Year of Manufacture- 2009
Number of Poles - 4
Rated Speed - 1500 rpm
What happened?
Recently the generator tripped on Seismic probe security i.e. going beyond the trip limit.
There are two Seismic probes installed on the generator(See the Train Diagram attached), 1ea on the in-board and 1ea on the outboard along with 2ea proximity probes. Bentley Nevada system is installed which feeds their value to Mark 6 system for Turbine control. The Sequence-of-Events was as follows:
- Both the Seismic probes started to go above the alarm limit of 4.5mm together. This kept happening for 5 minutes.(Both went above alarm limit and came back, then again both went above alarm limit and came back and this repeated)
- Then finally one of them went above the trip limit of 7mm(followed by the other) and this tripped the machine as the logic is 1oo1 for these probes in Mark-6.
- It is important to note that the proximity probes did not read any abnormality during this time. It was only the seismic probes.
Note: We do not have any trending of probe value for both Seismic and Proximity Probes in Mark-6. Only events are logged i.e. if something goes above alarm limit or trip limit.
Our Instruments team has checked both the seismic probes by knocking on them and seeing the response signal on Mark-6, checked the cabling and the Bentley cards. All was found Okay. There was no seismic activity in area nor any sudden load change on generator i.e. All the parameters were running business as usual. (There was a road being made about 50m away form the generator and a roller was being used on it.)
The machine was started again after forcing the seismic probes and it is running normally now.
Questions?
I would request the forum to give their insights on following questions:
- What can cause Seismic probe to read the values in this manner i.e. as mentioned above, one by one going above alarm level?
- Can something inside the generator i.e. excitor/PMG assembly, cause the seismic probe to detect intermittently?
- Is the Seismic probe even needed here when we have proximity probes as well? The machine is well protected with the proximity probes as well.
- Should we change the trip logic on Seismic probes from 1oo1 to 1.5oo2 or 2oo2 and increase the limits?(Current values are for: Alarm: 4.5mm, Trip: 7.5mm)
- What is recommended maintenance or replacement regime for Seismic probes on this application? Do they have a life after which they need replacement?
- What more should we be looking at to identify Root- Cause of Event?
The generator was running normally, no sudden load changes and no lightening strikes or seismic activity observed/recorded in the areas.
We have already floated the queries to OEM, so please don't suggest that. Posting here to benefit from collective wisdom.
Looking forward to your responses.
Regards,
MRasool