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The following should be monitored and recorded by a strip chart recorder during a
load rejection test:
load rejection test:
Breaker position.-
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.
breaker contact that opens or closes with the main breaker.
Gate position.-
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.
chart recorder should be calibrated from 100- to 0-percent gate.
Unit speed.-
Unit speed should be recorded with a tachometer or frequency
transducer with sufficient range to measure the speed from zero to the predicted
maximum speed.
maximum speed.
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.
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.
should the water overtop the tank.
Generator voltage.-
A voltage transducer connected to the generator potential
transformer should be used to monitor generator voltage.
Pressure regulator.-
If a pressure regulator or automatic bypass valve is present,
its position should be monitored by a string transducer or other position
transducers.
transducers.
Shaft runout.-
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