If the reset timer reaches the value set by
Reset delay time
, the operation timer resets and
the
PICKUP
output is deactivated.
The timer calculates the pickup duration value
PICKUP_DUR
, which indicates the
percentage ratio of the pickup situation and the set trip time. The value is available through
the monitored data view.
The
BLOCK
signal blocks the operation of the function and resets the timer.
4.1.9.5
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 37 with a low three-phase
current. However, this results in an unnecessary event sending when the transformer or
protected object is disconnected.
Phase-specific pickup and trip can give a better picture about the evolving faults when one
phase has picked up first and another follows.
37 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.
4.1.9.6
Signals
Table 165:
37 Input signals
Name
Type
Default
Description
I_A
SIGNAL
0
Phase A current
I_B
SIGNAL
0
Phase Bcurrent
I_C
SIGNAL
0
Phase C current
BLOCK
BOOLEAN
0=False
Block all binary outputs by resetting timers
Section 4
1MRS240050-IB C
Protection functions
220
REF615R
Technical Manual
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