What is Load rejection test (governor test) in commissioning?

Electrical
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What is load rejection?

Load rejection is a situation in an electrical system where there is a sudden loss of load in the system that causes over-frequency generation of equipment. A station can experience a load rejection, where the generator would unexpectedly remove the load.

Load rejection test (Governer test):

Load rejection test is a part of commissioning of a power system to confirm that the system can withstand the sudden loss of load and return to the normal condition using its governer.

The objective of the Turbine Load Rejection Test is to verify and demonstrate the role of the governor to maintain a load rejection to prevent the turbine from Overspeed tripping, steady speed control at no-load operation and to remain in service without any adverse effect on the turbine.

Load rejection testing is done to test engine performance with no-load condition after operating with 100 percent load, for example, when the circuit breaker generator unexpectedly trips due to upper network failure.

Load rejection test procedure:

Before Load Rejection Test:

  1. Confirm steady condition of load operation.

  2. Perform mechanical Over Speed Oil trip Test

  3. Perform Lub. oil pump auto start test

  4. Switch the auxiliary unit bus to power the transformer from the auxiliary unit.

  5. Confirm that level of( Condenser, Deraerator and HP/LP feed water heaters are within range.

  6. Confirm that HP and LP Turbine bypass ( valves and Sprays ) are in automatic mode.

  7. Confirm the defined load dispatcher time.

Load rejection test:

  • Open Circuit breaker of the Generator

  • If the Overspeed trip system does not work contrary to expectations even if the turbine speed reaches 111 percent of the rated speed, the turbine will fly immediately.

  • During transient conditions, all observers shall read and record “Maximum or Minimum” of the measuring objects.

  • If the maximum instantaneous speed is restricted below the limits of the overspeed trip (111 percent), the load rejection test is therefore considered successful.

  • Throughout transient times, all observers shall read and record “Maximum or Minimum” of the measuring objects