Siemens siprotec SJ62, User Manual

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2.2 Overcurrent Protection 50, 51, 50N, 51N
70
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
Inrush current is recognized, if the following conditions are fulfilled at the same time:
• the harmonic content is larger than the setting value
2202 2nd HARMONIC
;
• the currents do not exceed an upper limit value
2205 I Max
;
• an exceeding of a threshold value via an inrush restraint of the blocked element
takes place.
In this case an inrush in the affected phase is recognized (annunciations 1840 to 1842
and 7558
„InRush Gnd Det“
, see figure 2-11) and its blocking being carried out.
Since quantitative analysis of the harmonic components cannot be completed until a
full AC cycle has been measured, pickup will generally be blocked by then. Therefore,
assuming the inrush restraint feature is enabled, a pickup message will be delayed by
a full AC cycle if no closing process is present. On the other hand, trip delay times of
the time overcurrent protection feature are started immediately even with the inrush
restraint being enabled. Time delays continue running with inrush currents present. If
inrush blocking drops out after the time delay has elapsed, tripping will occur immedi-
ately. Therefore, utilization of the inrush restraint feature will not result in any additional
tripping delays. If a relay element drops out during inrush blocking, the associated time
delay will reset.
Cross Blocking Since inrush restraint operates individually for each phase, protection is ideal when a
transformer is energized onto a single-phase fault and inrush currents are detected on
a different healthy phase. However, the protection feature can be configured to ensure
that not only this phase element, but also the remaining elements (including ground)
are blocked (the so-called
CROSS BLOCK
function, address
2203
), if the permissible
harmonic component of the current is exceeded for only one phase.
Please take into consideration that inrush currents flowing in the ground path will not
cross-block tripping by the phase elements.
Cross blocking is reset if there is no more inrush in any phase. Furthermore, the cross
blocking function may also be limited to a particular time interval (address
2204
CROSS BLK TIMER
). After expiry of this time interval, the cross-blocking function will
be disabled, even if inrush current is still present.
The inrush restraint has an upper limit: Above this (via adjustable parameter
2205 I
Max
) current blocking is suppressed since a high-current fault is assumed in this case.