We are operating three numbers of Gas turbines LM6000 PC machines for power generation.
During the shutdown of one of our machines, we faced the following problem.
1.When the machine was given a stop command from Synch Idle "Vibration Summary Malfunction "alarm appeared and the machine went on SML.
2.After Cooldown Crank when the machine went for a stop the speed sensors XNSD/XN25 started showing a value of 3750 / 4005 respectively even though the Machine has come to standstill condition.
3.Even after reset the same speed was displayed on the XYCOM.
4.Tried high speed cranking from local control panel, then the HP speed started showing correct value but after stopping cranking the rpm came down below 600 rpm then suddenly XN25 wen back to frozen value of 4005.

The following actions were carried out but the probem is not yet rectified.

1.The NETCON 5000 control system was rebooted by powering off and on.
2.One speed sensor card was replaced with a new one - P/n 5464-834 rev G - (Pl note that there are 2 speed sensor cards in our system)
3.Checked the power supply to the sensors and the resistance of the speed sensing circuit
as mentioned in TS-28.The values found to be normal.
4.Isolated the speed sensor signals from the vibration monitoring system and other speed switches to avoid any possible interference from these systems to the NETCON. Even then there was no change in the readings.

We request your valuable advice to overcome this problem at the earliest.

Regards

Aashutosh S.Purohit

 

Asshutosh,
I have not worked on LM6000 in several years. Three of us have experience with them here. Have you been able to locate the reading on the netcon 5000 for XN25/XNSD? Does this reading agree with XYCOM and the meter on your control panel?

Some thoughts... GE has had problems on the cable from speed pickups to the remote IO. Have you changed the cable? Also there are two sensors in each pickup. Have you compared these on the netcon? Since you did a local HS crank, were you locked out at the control panel? When you rebooted the Netcon, did you also power down and reboot the remote I/O? I believe either cb1 or cb2 in the right cabinet at control panel or the rio cabinet at the package.

This is a peculier problem. Please post what you have found out.