Siemens 7SC80 Manual page 232

Functions
2.12 Monitoring Functions
times the nominal current, and depending on the transformer size and design, can last from several tens of
milliseconds to several seconds.
Although filtering of the measuring currents only evaluates the fundamental component, disturbances could
occur when energizing transformers, because the inrush currents created when energizing transformers can
also contain a considerable amount of fundamental component depending on size and design.
7SC80 therefore features and integrated inrush-current detection. It prevents "normal" pickup of the elements
in the phases and in the ground path of the non-directional and directional overcurrent protection. The same
is true for the alternative pickup thresholds of the dynamic cold load pickup function. When setting the param-
eters of the overcurrent protection elements, you can enable or disable the inrush-current detection for each
single element. See Section
If inrush currents are detected, special inrush pickup signals are generated. These signals also initiate fault
recording and start the associated trip delay time. If inrush conditions are still present after the trip time delay
has elapsed, a corresponding indication (
diagrams of the non-directional and directional overcurrent protection in Section
50, 51, 50N, 51N
The inrush current contains a relatively large second harmonic component (twice the rated frequency), which
is nearly absent in the fault current. The inrush-current detection is therefore based on the evaluation of the
second harmonic present in the inrush current. For frequency analysis, numerical filters are used to conduct a
Fourier analysis of all three phase currents and the ground current.
Inrush current is recognized if the following conditions are fulfilled at the same time:
•
The harmonic is larger than the setting value 2202 2nd HARMONIC (minimal 0.125 * I
•
The currents do not exceed an upper limiting value 2205 I Max nicht;
•
A threshold is exceeded in an element that can be blocked by the inrush-current detection.
In this case, an inrush current in the affected phase is recognized (indications 1840 to 1842 and 7558
Gnd Det , see Figure
Since a quantitative analysis of the harmonic cannot be completed until a full cycle has been measured, pickup
will generally be blocked by then. This means that a pickup indication with active inrush-current detection will
also be delayed by one cycle if no energization has taken place. On the other hand, trip delay times of the
overcurrent protection functions are started immediately even when the inrush-current detection is active and
continue during the inrush duration. If inrush blocking drops out after the time delay has elapsed, tripping will
occur immediately. Thus the inrush-current detection does not cause any additional trip delays. If the element
drops out during inrush blocking, the associated time delay is reset.
The inrush-current detection is no longer effective above a current value that can be specified in address 2205
I Max, because it can only be a high-current internal fault in this case.
Depending on the setting at address 2206 INRUSH DET. BY, inrush-current detection is initiated by Phase,
Cross or Sum.
Blocking Phase
If you have selected the value Phase at address 2206 INRUSH DET. BY, blocking will affect the phase in
which the inrush current is detected.
Cross Blocking
If you have set the value Cross at address 2206 INRUSH DET. BY, blocking will affect all phases, including
the ground path, once the inrush current is detected for one phase.
An inrush condition in the ground path does not block the phases.
Cross blocking is reset if no inrush current is detected anymore in any phase. Furthermore, the cross blocking
function can also be limited to a certain time. You can specify this time at address 2204 CROSS BLK TIMER.
After expiry of this time, the cross blocking function will be disabled, even if inrush current is still present.
Blocking Sum
If you have selected the value Sum at address 2206 INRUSH DET. BY, the root of the sum of squares of the
second harmonic of the phase currents is compared to the individual phase currents.
232
2.2.12 Setting Notes
....Timeout. ) is output, but the tripping is blocked (see also logic
and Section 2.3 Directional Overcurrent Protection 67,
2-71) and it is blocked.
and 2.3.10 Setting Notes for more information.
67N).
E50417-G1140-C486-A8, Edition 07.2017
2.2 Overcurrent Protection
);
Nomsec
InRush
SIPROTEC Compact, 7SC80, Manual