After major inspection start from October 16th till November 29th, 2017, we can't completely start-up our GT, because at more 4800 rpm (at 14HS sequence) GT trip with "Generator Lockout Relay Trip (86G)" indication and 59EX (Overexcitation Relay) energized. We already checked several components and controls including Excitation Equipment until SVR Control.
Please give us some advice how to troubleshoot this case?
If you're having a generator terminal overvoltage condition, then it would be most likely there is something amiss with the SVR (Static Voltage Regulator), or the terminal voltage feedback (from the generator PTs (Potential Transformers)), or the overvoltage relay itself. Many times during outages the PTs get disconnected ("racked out") and don't get properly reconnected. Or they don't get reconnected at all.
You said you checked the SVR, but you didn't say how or what the result were. You haven't told if the SVR is brushless or brushed. If it is brushed, have you checked the brushes to make sure they are all good? If it's brushless, have you checked to make sure all of the fuses are good to the exciter and the diode wheel?
If you have a Mark V or Mark VI or Mark VIe you have the ability to record data (using the VIEW software tools of the Mark V, or the Trend Recorder of the Mark VI or Mark VIe). Trend the generator terminal voltage during starting and see what it's doing when the SVR is energized. If the generator terminal voltage is really going very high, it's again most likely that the feedback to the regulator (the AUTO regulator) is not connected properly and so the SVR is not limiting the voltage because it's not seeing the voltage.
You could try putting the regulator in MANUAL mode during starting and see if that at least lets you get to Full Speed-No Load.
If the generator terminal voltage is being properly controlled and regulated, then it's likely the problem is with the 59 over-voltage relay.
There's not too much else it can be.
Please write back to let us know what troubleshooting was done, what the results of the troubleshooting were, and what kind of excitation system is in use on the unit.