Eaton EDR-5000 Nstallation, Operation And Maintenance Manual page 643

EDR-5000 IM02602007E
Angular or Phase Difference.
Even if the frequency of both systems is exactly identical, usually an angular difference of the voltage phasors is the
case.
Line VA
Bus VA
Angle Diff
Bus f = Line f
Bus VC
Line VB
Line VC
Bus VB
At the instant of synchronization, the angular difference of the two systems should be nearly zero because, otherwise,
unwanted load inrushes occur. Theoretically, the angular difference can be regulated to zero by giving short pulses to
the speed governors. When paralleling generators with the grid, in practice, synchronization is requested as quick as
possible and so usually a slight frequency difference is accepted. In such cases, the angular difference is not constant
but changes with the slip frequency ΔF.
By taking the breaker closing time into consideration, a lead of the closing release impulse can be calculated in a way
that breaker closing takes place at exactly the time when both systems are in angular conformity.
Basically the following applies:
Where large rotating masses are concerned, the frequency difference (slip frequency) of the two systems should
possibly be nearly zero, because of the very high load inrushes at the instant of breaker closing. For smaller rotating
masses, the frequency difference of the systems can be higher.
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