Check list for Commissioning of Steam Turbo Generator at site.

By checking the below points , problems can be avoided during commissioning of STG set at site.

Standstill condition Checks:

• Checking the Generator (both stator and rotor),exciter (both stator and rotor) and PMG stator IR values.
• Over all power circuit HT busduct / HT cables IR value both line and neutral side.
• Healthiness of PTs and CTs by checking IR, resistance , ratio and polarity. CT ratio can be carried out with primary injection kit.
• Configuration and setting verification of Generator protection relay and all other protection relays.
• All protection functions testing in GPR and all other relays by secondary injection method.
• Phase sequence measurement at LAVT panel by back charging the grid voltage to LAVT panel (Generator Line and neutral terminals removed condition). Check the PT voltage inputs to synchronous check relay and check the 12 clock position in synchrono scope, further checking the close command signal to the GCB during this condition. Also measure the PT voltage of bus PT and Generator incoming PT and checking phase out voltages R to R' and Y to Y' between these PTs and should be zero. This back charge test will ensure the phase sequence of grid supply as well as Generator supply.
• Synchronous check relay voltage as well as slip (frequency) setting check.
• AVR Panel setting verification and conducting lamp load test in manual mode.
• Verification of droop CT polarity to AVR panel , in case if it is wrong it will leads to high current and it will lead to under excitation trip.
• Stability test ensuring the line and neutral side CT connection is correct and does not operate the differential protection. during this test generator will be isolated condition and both line and neutral side will be connected.
• Checking turbine trip to Generator master trip relay , Turbine master trip relay to turbine trip , Generator & Turbine master trip relays trip to AVR & GCB, AVR trip to Generator master trip relay.
• GCB tripping and close command circuit checking from remote Generator control protection metering and synchronizing panel in test & service mode.
• Grid CB tripping from Grid master trip relay as wells as close and trip command checking to Grid CB.

Running Condition Checks:

• PMG and main generator phase sequence check with respect to required direction of rotation during rated speed with residual voltage.
• Speed >95% signal interlock to AVR for switching on the excitation.
• Short circuit characteristics test and checking of differential and current operated protections. line side terminals shorting arrangement also to be made after line side differential protection CTs. After SCC test short links needs to be removed in stop conditions.
• open circuit characteristics and reaching voltage up to 110% and check all voltage & frequency operating Protections.
• During SCC and OCC tests AVR shall be manual mode i.e. field current control mode. if SCC and OCC passed without any issues , then it is ready for operation.
• Voltage built of in Auto mode. if it is 2 Auto + 2 Manual channels then, Auto Channel-1 to 2 and vice versa bump less transfer needs to be checked. Further Auto to manual and vice versa transfer also needs to be checked.

After completion of the above checks STG set can synchronized with Grid at GCB and loaded further smoothly.