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.
4.1.9.6 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.
4.1.9.7 Signals
Table 468: PHPTUC Input signals
Name Type Default Description
I3P SIGNAL – Three-phase currents
BLOCK BOOLEAN 0=False Block all binary outputs by resetting
timers
Table 469: PHPTUC Output signals
Name Type Description
OPERATE BOOLEAN Operate
OPR_A BOOLEAN Operate phase A
OPR_B BOOLEAN Operate phase B
OPR_C BOOLEAN Operate phase C
START BOOLEAN Start
ST_A BOOLEAN Start phase A
ST_B BOOLEAN Start phase B
ST_C BOOLEAN Start phase C
Protection functions 1MRS759142 F
408 REX640
Technical Manual
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