Close Signal; Load Picture After Synchronising - Deif GPC-3 Designers Reference Handbook

GPC-3 DRH 4189340587 UK
The intention of the synchronising is to decrease the phase angle difference between the two rotating sys-
tems. These two systems are the three-phase system of the generator and the three-phase system of the
busbar. In the illustration above, phase L1 of the busbar is always pointing at 12 o'clock, whereas phase L1 of
the synchronising genset is pointing in different directions due to the slip frequency.
Of course both three-phase systems are rotating, but for illustrative purposes the vectors for
the generator on load are not shown to be rotating. This is because we are only interested in
the slip frequency for calculating when to release the synchronisation pulse.
When the generator is running with a positive slip frequency of 0.1 Hz compared to the busbar, the two sys-
tems will be synchronised every 10 seconds.
Observe the chapter regarding PID controllers and the synchronising controllers.
In the illustration above, the difference in the phase angle between the synchronising set and the busbar gets
smaller and will eventually be zero. Then the genset is synchronised to the busbar, and the breaker will be
closed.

7.2.1 Close signal

The unit always calculates when to close the breaker to get the most accurate synchronisation. This means
that the close breaker signal is actually issued before being synchronised (read L1 phases exactly at 12
o'clock).
The breaker close signal will be issued depending on the breaker closing time and the slip frequency (re-
sponse time of the circuit breaker is 250 ms, and the slip frequency is 0.1 Hz):
The synchronisation pulse is always issued, so the closing of the breaker will occur at the 12
o'clock position.
The length of the synchronisation pulse is the response time + 20 ms (2020 Synchronisation).

7.2.2 Load picture after synchronising

When the incoming genset has closed its breaker, it will take a portion of the load dependent on the actual
position of the fuel rack. Illustration 1 below indicates that at a given positive slip frequency, the incoming gen-
set will export power to the load. Illustration 2 below shows that at a given negative slip frequency, the incom-
ing genset will receive power from the original genset. This phenomenon is called reverse power.
DEIF A/S
Synchronisation
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