Figure 128: Logic diagram for phase selection module
When the
Number of start phases
setting is set to "1 out of 3" and the fault is in
one or several phases, the phase selection logic sends an enabling signal to the
faulty phase timers. In case the fault disappears, the related timer-enabling signal is
removed.
When the setting is "2 out of 3" or "3 out of 3", the single-phase faults are not
detected. The setting "3 out of 3" requires the fault to be present in all three phases.
Timer A, Timer B, Timer C
The function design contains three independent phase-segregated timers that are
controlled by common settings. This design allows true three-phase overcurrent
protection which is useful in some applications.
Common START and OPERATE outputs are created by ORing the phase-specific start
and operating outputs.
Each phase has its own phase-specific start and operating outputs: ST_A, ST_B,
ST_C, OPR_A, OPR_B and OPR_C.
Once activated, the timer activates the START output. Depending on the value of
the
Operating curve type
setting, the time characteristics are according to DT or
1MRS757644 H
Protection functions
620 series
Technical Manual
259
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