GE PACSystems RX3i User Manual page 18

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Phase Angle
For synchronization, the two grids must be connected when the phase angle difference
between the grids is in the range of ±PHASE_SHIFT_THR, and ideally at the point when
the two grids are exactly in phase. The phase shift threshold represents an angle window
in electrical degrees (usually ±10°) around the 0° value, where it is safe to connect the two
grids. The phase shift between the grids can be a rapidly changing value in a rotating
system.
Additionally, the breaker delay can be significant (hundreds of milliseconds). Therefore, in
rotating phase synchronization, the moment for commanding the sync relay to close must
shift forward to compensate for the time it takes for the contacts to close. For example, the
window of opportunity for commanding relay closure could happen between 25° and 15°,
in order for the contacts to close when the grids are truly in-phase. This angle offset is a
function of the frequency difference (and therefore the rate of change of the phase shift)
and the breaker delay.
Once the CloseRelayOK bit is set, it remains set until either the breaker delay + 24 power
cycles passes, or the phase shift enters and then leaves the ±Phase_Shift_Thr window.
This gives the contacts time to settle, and the two grids time to stabilize into
synchronization.
Angle Delay
Angle Delay is a value, in degrees, that accounts for both the rate of change of the phase
shift between the grids and the breaker delay. Angle Delay is the angle through which the
synchroscope needle travels between the moment the PSM sets the CloseRelayOK bit to
close the IC694ACC200 relay contacts, and when the physical contacts on the sync relay
actually close:
Angle Delay = (360⁰ x ΔF x Bdly)
Where:
ΔF
Bdly = breaker delay in seconds
The Breaker Delay PSM configuration parameter must include all the delays introduced
between the PSM module and the synchronizing contacts. For example, the
IC694ACC200 Terminal Assembly relay outputs have a turn on time of 20ms (see
"Specifications" on page 1-5), and a given contactor has a published closing time of 80ms.
The Breaker Delay parameter should be set to the sum of all delays, or 100ms in this
example. Ideally, the actual breaker delay time will be measured during installation
commissioning and used in the application to compensate for component variations.
PACSystems* RX3i Power Sync and Measurement System – February 2013
= Grid 2 Frequency – Grid 1 Frequency
GFK-2749