The purpose of Turbine Load Rejection Test is to verify and demonstrate the governor function to sustain a load rejection in order to prevent the turbine from overspeed tripping, steady speed control at no-load operation and remain in service without any adverse effect to the turbine.
The test requires skillful and appropriate operation not only for turbine , but also for boiler and its auxiliaries.
Items to be confirmed for Load Rejection Test
1-Turbine main valves
2-GV no load valve position
3-Lube oil pump auto start test
4-Protective device test
5-Valve transfer from MSV mode to GV mode
6-Overspeed tripping point (111% speed)
7-OPC (Overspeed Protection Controller) function
8-Exclusion of Interlocks (Turbine Trip due to Boiler Trip)
TEST PROCEDURE
*Before Load Rejection Test (one hour)
1-Confirm steady condition of load operation
2-Perform mechanical Over Speed Oil trip Test
3-Perform Lub. oil pump auto start test
4-change over unit auxiliary bus from unit auxiliary transformer to start up transformer.
*Before Load Rejection Test (30 minutes)
1-Confirm that level of( Condenser , De aerator and HP/LP feed water heaters are within range
2-confirm that AVR in automatic mode
3-Confirm that HP and LP Turbine bypass ( valves and Sprays ) are in automatic mode
*Before Load Rejection Test (10 minutes)
1-confirm the appointed time with the load dispatcher
2- Exclude the interlock of (Turbine Trip due to Boiler Trip)
*Before Load Rejection Test (0 minute)
1-Open Circuit breaker of the Generator.
2-If the Overspeed trip device doesn’t operate contrary to expectations even when the turbine speed exceeds 111% of the rated speed , Trip immediately the turbine.
3-All observers shall read and record “Maximum or Minimum” of the measuring objects during transient condition
After Load Rejection
Pay attention to the following points and see that there is no distinction about them.
-Turbine speed
-Rotor Position & Vibration
-BRG temp. and Vibration
-Condenser Vacuum and hotwell level
Stabilization
-Stabilization will be judged when turbine speed is stabilized approx. 3000 rpm by GV & ICV speed control
Test Acceptance Criteria
If maximum instantaneous speed is restricted below overspeed trip limits (111 %) ,therefore the load rejection test is regarded as successful.
Confirmation items after Stabilizing
-GVs are restored in no load position
-turbine speed is controlled at near synchronous level
-No abnormality is observed at electrical room and local positions.
Emergency Case
If boiler trips by boiler protection , turbine shall be immediately tripped.