The following should be monitored and recorded by a strip chart recorder during a
load rejection test:
A reference signal to determine exactly when the breaker opens
can be helpful. This can be a signal from the generator current transformer or a
breaker contact that opens or closes with the main breaker.
A string transducer or other position transducer should be
connected to one of the servomotors to monitor wicket gate position. The strip
chart recorder should be calibrated from 100- to 0-percent gate.
Unit speed should be recorded with a tachometer or frequency
transducer with sufficient range to measure the speed from zero to the predicted
Spiral case pressure.-
Spiral case pressure should be monitored by a pressure
transducer connected to a valved tap in the spiral case mandoor. If a tap is not
available in the mandoor, the transducer can be installed directly on the
piezometer ring just upstream from the penstock. Installation on a long line or a
line with a bourdon tube type gauge or sensor can lead to false data.
Surge tank pressure.-
A pressure transducer should be mounted at the base of
the surge tank to monitor water elevation in the tank. Under no circumstances
should the water overtop the tank.
A voltage transducer connected to the generator potential
transformer should be used to monitor generator voltage.
If a pressure regulator or automatic bypass valve is present,
its position should be monitored by a string transducer or other position
Proximity probes should be installed at each of the guide bearing
elevations to monitor shaft runout during the load rejection tests.
After the test, the following data should be recorded:
Wicket gate timing
Maximum shaft speed
Maximum spiral case pressure
Maximum generator voltage
Maximum surge tank pressure or elevation
Regulator valve closure time