of other mechanisms such as FBBM transfer, first phase transfer, residual voltage
transfer and time delayed transfer.
Z3
Z4
Z1
90
180
270
Zone of operation
Z1. Fast
Z2. FBBM
Z3. First Phase coincidence
Z4. Residual
O
A
B
C
D
E
F
Stand-by voltage phasor
Motor bus voltage phasor
Figure 952: Busbar phasor and zones of operation for different transfer modes
The
Figure 952
provides an insight into the movement of busbar voltage phasor w.r.t
stand-by feeder voltage phasor after the circuit breaker of the main supply feeder is
opened. The busbar voltage phasor starts to move away from the stand-by feeder
phasor. The rate of this movement is guided by the frequency difference and rate
of change of frequency difference between the stand-by feeder and busbar voltage
phasors. The rate of this movement depends upon the moment of inertia of the
motors and the loads connected to the busbar.
The radius of the outermost circle in the
Figure 952
represent the voltage
magnitude of the stand-by feeder. The radius of inner circle represents the setting,
Min busbar voltage
magnitude used for Fast and FBBM transfer. The radius of
innermost circle represents the setting,
Res voltage limit
.
Fast transfer can occur if the busbar phasor lies in the zone Z1, defined by the area
under curve ACDB, after transfer initiation is active. This area reflects the criterion
for the fast transfer to occur i.e., the phase angle difference, frequency difference
between stand-by feeder and busbar voltage phasor must within specified limits
and busbar voltage phasor magnitude must be above the specified limit defined by
minimum busbar voltage setting.
FBBM mode attempts to transfer such that the phase angle difference between
stand-by voltage and busbar voltage phasor lies within a defined limit, represented
by Max Angle Diff FBBM, after the stand-by feeder is completely closed. It estimates
this advance phase angle difference ahead of CB closing time based on the
prevailing frequency difference and rate of change of frequency difference between
the stand-by and busbar voltage. Fast break before make, FBBM, transfer can occur
Control functions
1MRS759142 F
1790 REX640
Technical Manual
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