User Manual Chapter 1
GFK-2749A Jan 2020
PSM Module Description and Specifications 12
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 = (360
⁰
x
Δ
F x Bdly)
Where:
Δ
F = Grid 2 Frequency – Grid 1 Frequency
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
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.
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:
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