Seg WIC1 User Manual

4.4 IH2 - Inrush Blocking
The energization of a transformer and voltage recovery cause inrush currents that can reach
a multiple of the rated current, so that a pickup and even a trip of the overcurrent functions
can be the result.
These pickup and trips are unwanted, and the Inrush module can prevent them (by blocking
the overcurrent protection). But in case of high current faults, the situation is di󰊞erent:
Then the Inrush blocking is unwanted because it will delay the necessary tripping: A
fault with a DC o󰊞set causes a 2
nd
harmonic component. This can potentially result
in CT saturation, especially in case of high fault currents. CT saturation increases the
2
nd
harmonic component furthermore. This can make the Inrush blocking module block
protection stages temporarily, and in such a situation, this results in a delay of protection
operation. Since the Inrush blocking is unwanted in this case the Inrush module does not
operate if a settable threshold »Imax« is exceeded.
The Inrush module checks for the ratio of the 2
nd
harmonic to the 1
st
harmonic and releases
a blocking signal unless at least one phase current is above a settable »Imax« threshold.
NOTICE!
An undelayed /instantaneous overcurrent protection stage always trips earlier than the
Inrush element is able to react. Therefore always use the Inrush element in combination
with a small trip delay, to prevent faulty tripping, instead of undelayed/instantaneous
overcurrent protection.
3-phase Inrush Blocking
The amount of the 2
nd
harmonic can vary in each phase. It is possible that it is not
high enough for an activation of inrush blocking in this phase. If it is required to avoid
false tripping in such a situation the Inrush module can be set to 3-phase blocking (via
setting »IH2 . 3-ph Blo« = “Active”). Then all three phases get blocked as soon as an inrush
is detected in (at least) one phase.
Blocking of Protection Based on Negative-Sequence Current
High inrush currents can lead to a transient saturation of the phase CTs. When this happens
during a transformer inrush the determination of (positive and negative) sequence currents
yields incorrect results. Therefore it is recommended that the Inrush blocking signal blocks
all protection functions that operate on the negative-sequence current. See ╚═▷ “4.4.2
Inrush – Settings” for the settings.
Inrush Blocking of Ground Overcurrent Protection
High inrush currents can lead to a transient saturation of the phase CTs. If the phase currents
are used to determine the ground current (which is the case for calculated ground current),
this transient saturation can result in an incorrect ground current, which can then cause a
false tripping of the ground overcurrent protection.
Therefore one usually wants for these application types, that the Inrush Blocking module
also blocks the ground overcurrent protection. See ╚═▷ “4.4.2 Inrush – Settings” for
the settings.
144 WIC1 WIC1-1.0-EN-MAN
4 Protective Elements
4.4 IH2 - Inrush Blocking

Seg WIC1 Specifications

General

Brand	Seg
Model	WIC1
Category	Relays
Language	English