timer. This signal is disabled after one or several phase currents have exceeded the
set
Start value
value of the element.
If in the "Single Phase" mode any of the phase current values are less than the value
of the
Start value
setting, the condition is detected and an enable signal is sent to
the timer. This signal is disabled after all the phase currents have exceeded the set
Start value
value of the element.
The protection relay does not accept the
Start value
to be smaller than
Current block value
.
Level detector 2
This is a low-current detection module that monitors the de-energized condition of
the protected object. The module compares the phase currents (RMS value) to the
Start value low
setting. If all the phase current values are less than the
Start value
low
setting, a signal is sent to block the operation of the timer.
Timer
Once activated, the timer activates the START output and the phase-specific ST_X
output. The time characteristic is according to DT. When the operation timer has
reached the value set by
Operate delay time
, the OPERATE output and the phase-
specific OPR_X output are activated. If the fault disappears before the module
operates, the reset timer is activated. If the reset timer reaches the value set by
Reset delay time
, the operate timer resets and the START output is deactivated.
The timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operating time. The value is
available through the monitored data view.
The BLOCK signal blocks the operation of the function and resets the timer.
4.1.10.5 Application
In some cases, smaller distribution power transformers are used where the high-
side protection involves only power fuses. When one of the high-side fuses blows
in a single-phase condition, knowledge of it on the secondary side is lacking. The
resulting negative-sequence current leads to a premature failure due to excessive
heating and breakdown of the transformer insulation. Knowledge of this condition
when it occurs allows for a quick fuse replacement and saves the asset.
The
Current block value
setting can be set to zero to not block PHPTUC with a low
three-phase current. However, this results in an unnecessary event sending when
the transformer or protected object is disconnected.
Phase-specific start and operate can give a better picture about the evolving faults
when one phase has started first and another follows.
PHPTUC is meant to be a general protection function, so that it could be used in
other cases too
In case of undercurrent-based motor protection, see the Loss of load protection.
Protection functions
1MRS757644 H
360 620 series
Technical Manual
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