if the estimated busbar phasor, after advance angle adjustment, lies in the zone Z2,
defined by the area under the curve AEFB.
Figure 953: Trajectory of phase-angle in relation to time
Figure 953
shows the trajectory of phase angle between stand-by feeder and
busbar and voltages and time after main supply feeder opening. It is shown
for various linear rates of frequency difference between the stand-by feeder and
busbar, assuming main supply feeder and stand-by feeders were in synch and the
frequency difference is zero prior to circuit breaker opening for main supply feeder.
FBBM transfer mode is suitable for setups having low frequency difference and rate
of change of frequency difference between the stand-by and busbar voltage.
First phase coincidence mode attempts to transfer at the 1
st
phase coincidence,
differential voltage minimum, between the stand-by feeder and busbar voltages
through anticipatory computation. It estimates the phase angle difference between
the stand-by feeder and busbar voltage ahead of CB closing time keeping into
account the prevailing frequency difference and rate of change of frequency
difference between the stand-by and busbar voltage. It attempts to transfer such
that phase angle difference is zero (ideally zero, practically near zero) after stand-
by feeder is completely closed. First phase coincidence transfer can occur if the
estimated busbar phasor, after anticipatory calculation, lies in the zone Z3.
Residual mode attempts to transfer if busbar voltage magnitude drops below
predefined setting,
Res voltage limit
. Residual transfer can occur if the busbar
phasor lies in the zone Z4, represented by the area under the inner most circle with
radius
Res voltage limit
.
Application variants
The following different variants, depending on various circuit breaker
configurations, can be realized with the instances of this function.
1MRS759142 F
Control functions
REX640
Technical Manual
1791
To Next Page
Loading...
