GE PACSystems RX3i User Manual page 19

GFK-2749
Slow Rotating Phase Angles
In rotating phase angle synchronization, the PSM sets and clears the PhaseShiftOK
status bit based on the Angle Delay value. In slowly rotating phase angles where
Angle Delay ≤ (Phase_Shift_Thr - 2º)/2, noise-induced jitter in the zero-crossing detection
can make the phase angle difference from one power line cycle to the next appear to
change direction. For this reason, 2º of hysteresis is added to the trailing edge of the
PhaseShiftOK window:
PhaseShiftOK = On @ Angle Delay
PhaseShiftOK = Off @ –(Angle Delay+2º)
Slow Rotation: Angle Delay ≤ (Phase_Shift_Thr - 2º)/2
If the request to sync is on, or received by the PSM module at any time in the green
region (while PhaseShiftOK = on), the CloseRelayOK status bit will be set and the
IC694ACC200 output contacts will close.
Once CloseRelayOK is on and the IC694ACC200 output contacts are closed, they remain
on and closed, regardless of grid alarms, until after the breaker delay plus 24 power line
cycles pass, to allow the newly synchronized grids to settle. After the settling time, all
ANSI protections are reinstated and the PSM monitors the Delta Frequency, Delta Voltage
and Phase Shift status bits again.
In the absence of other alarms, the phase shift is allowed to drift within the phase shift
threshold (the yellow region) indefinitely as the PSM waits for the physical contacts to
synchronize the grids.
Chapter 1 PSM Module Description and Specifications
0º
-Phase_Shift_Thr
SYNCHROSCOPE
1
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