Application - ABB RELION 620 Series Technical Manual

1MRS757644 F
4.1.10.5
620 series
Technical Manual
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.

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.
Section 4
Protection functions
343