threshold is active for the set hold time for the “dynamic parameters” (see
Section 3.12.8, (p. 3-88)) and the “normal” threshold is active when no hold time
is running.
It is also possible to select whether the starting decision shall be based on the
fundamental or on the r.m.s. value.
The IDMT protection will trigger when the 1.05-fold of the set reference current
value is exceeded by the residual current. Dependent on the characteristic
selected and the residual current magnitude the P634 will determine the tripping
time. Moreover the tripping time will under no circumstances fall below a
settable minimum time threshold irrespective of the residual current flow
magnitude.
The inverse-time stage can be blocked by an appropriately configured binary
signal input. In addition the inverse-time stage can also be automatically blocked
by singlepole or multi-pole starting (depending on the setting).
3.24.6 Hold Time
The setting of the hold time defines the time period during which the IDMT
protection starting time is stored after the starting has dropped out. Should
starting recur during the hold time period then the time of the renewed starting
will be added to the time period stored. When the starting times sum reach the
tripping time value determined by the P634 then the corresponding signal will be
issued. Should starting not recur during the hold time period then, depending on
the setting, the memory storing the accumulated starting times value will either
be cleared without delay or according to the characteristic set. In Fig. 3-124,
(p. 3-172), the effect of the hold time is shown by the example of a phase
current stage.
3 Operation P634
P634/EN M/R-42-A // P634‑311‑653 3-171
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