One of our unit (Frame 5PA) recently had a reverse power, 30 minutes after starting the unit with the power generating 11MW and power dropping (motoring) to -9.52MW for several minutes.
Generator Breaker is still closed at the time of event and can't be manually opened, therefor causing the operator to shutdown the unit via ESD button but the turbine still rotating and Breaker still closed. Operator then activated 12HA (Overspeed Bolt Trip) but the result is still the same. Operators then closed the incoming gas line through manual valve upstream and downstream of strainers with the same result. Operators then finally open 115kV GCB which finally caused the turbine to slow down to 0 RPM.
Flag/alarm that pops up in the HMI at the time of the event is "Manual Trip", followed by "Overspeed Bolt Trip", "Gas Fuel Pressure Low" and "Generator Differential Trip" which in my opinion is a result from the actions of the operators, but does not show flag is active during the initial reverse power/generator motoring.
Note: There is no data trender/logging on this unit, so I can't check parameters such as vibration, winding temp, RPM.
Relay 32 (Directional Power Relay), 40 (Loss of Excitation) and 64F (Field Ground Protection) were found to be active/flag.
The next day, we decide to visually inspect the generator rotor and stator (winding at load gear side and pedestal side), which there seems to be no anomaly or any significant damage other than slightly dirty.
Visual inspection on Busbar, PT, CT Excitation Trafo, Fuse for PT&CT, Fuse Control all seem to be normal.
Resistance test is conducted on generator rotor with result of 76.9 milli ohm and a phase to ground megger resulting in 3.04 Mega Ohm, which seemed acceptable.
Generator Breaker during inspection seemed to be melted, which caused the it to be closed during the event and repairs have been done and also inspection to other generator protection relay is conducted for assurance
Based on the findings above, it is planned that the unit will be started again (at least until full speed no load) in the near future but I still have some doubts whether it is the best path forward as I don't have the winding temperature data and vibration data during the motoring which might give an insight whether damage will likely to occur or not.
But if the turbine is still decided to be started until FSNL, is there any specific parameters that must be observed which might indicate that there is damage from the generator motoring? or is parameters such as generator & load gear vibration, generator RPM, end winding temperature, excitation current monitoring sufficient ?
Is there any further testing required before I can state the unit can be deemed ready to start?
Appreciate your input
*Apologize if there are any error as English is not my first language.
Generator Breaker is still closed at the time of event and can't be manually opened, therefor causing the operator to shutdown the unit via ESD button but the turbine still rotating and Breaker still closed. Operator then activated 12HA (Overspeed Bolt Trip) but the result is still the same. Operators then closed the incoming gas line through manual valve upstream and downstream of strainers with the same result. Operators then finally open 115kV GCB which finally caused the turbine to slow down to 0 RPM.
Flag/alarm that pops up in the HMI at the time of the event is "Manual Trip", followed by "Overspeed Bolt Trip", "Gas Fuel Pressure Low" and "Generator Differential Trip" which in my opinion is a result from the actions of the operators, but does not show flag is active during the initial reverse power/generator motoring.
Note: There is no data trender/logging on this unit, so I can't check parameters such as vibration, winding temp, RPM.
Relay 32 (Directional Power Relay), 40 (Loss of Excitation) and 64F (Field Ground Protection) were found to be active/flag.
The next day, we decide to visually inspect the generator rotor and stator (winding at load gear side and pedestal side), which there seems to be no anomaly or any significant damage other than slightly dirty.
Visual inspection on Busbar, PT, CT Excitation Trafo, Fuse for PT&CT, Fuse Control all seem to be normal.
Resistance test is conducted on generator rotor with result of 76.9 milli ohm and a phase to ground megger resulting in 3.04 Mega Ohm, which seemed acceptable.
Generator Breaker during inspection seemed to be melted, which caused the it to be closed during the event and repairs have been done and also inspection to other generator protection relay is conducted for assurance
Based on the findings above, it is planned that the unit will be started again (at least until full speed no load) in the near future but I still have some doubts whether it is the best path forward as I don't have the winding temperature data and vibration data during the motoring which might give an insight whether damage will likely to occur or not.
But if the turbine is still decided to be started until FSNL, is there any specific parameters that must be observed which might indicate that there is damage from the generator motoring? or is parameters such as generator & load gear vibration, generator RPM, end winding temperature, excitation current monitoring sufficient ?
Is there any further testing required before I can state the unit can be deemed ready to start?
Appreciate your input
*Apologize if there are any error as English is not my first language.