Load Rejection Tests

A full series of load rejection tests should be performed and the results documented. These tests should include all conditions that can occur during the full range of operation. The data from these tests are needed to determine the maximum and minimum operating pressures and unit speeds.

Based upon data obtained from the hydraulic transient analysis, stop nuts on the governor main distributing valve servomotor are then set to limit the full rate opening and closing times of the wicket gates with the turbines unwatered, the governor in “main valve,” and the shutdown solenoids blocked in the running position. Rapid operation of the gate limit between 0 and 100 percent will then cause the gates to operate at maximum rate. Experience has indicated that full rate closure under actual operating conditions tends to be about 10 percent faster than the unwatered setting.

To set the gate timing accurately, the stopwatch has been replaced with a position transducer attached to the servomotor and a strip chart recorder. Minimum test equipment for the load rejection tests, if required to verify the computer model, includes:

  • Results of the hydraulic transient study to allow safe initial adjustments.
  • Pressure transducers on the penstock and/or spiral case.
  • A tachometer to measure unit overspeed.
  • A position transducer on the wicket gates.
  • A voltage transducer to measure the generator voltage transient.
  • A strip chart recorder with at least 4 channels.