Siemens 7SJ82, Руководство пользователя

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Detuning Supervision for Capacitor Banks
AC-Filter Detuning Supervision
Tuned AC filters serve to provide reactive power and to absorb specific frequencies from the busbar. They
usually consist of the upper-voltage side capacitor (for providing reactive power) and the tuning section (for
tuning to the frequencies to be absorbed). The tuning section consists of primary C, L and, if required, R
elements, refer also to
Figure 7-67 .
Under normal operation, the RLC characteristics of the filter – the impedances – are identical per phase. A
change in the impedance of one phase indicates that the filter characteristic of this phase has changed. This
situation (a detuned filter) is not wanted and shall be detected.
The primary elements of the AC filter shall be subject of regular maintenance intervals where the compliance
with the tolerances of the rated values specified in the design need to be checked. For the detection of
detuning between the maintenance intervals, the protection device can be applied. Detuning supervision for
the upper-voltage side voltage capacitor can be achieved by applying the phase-selective Current unbalance
function (ANSI 60C), especially by using the counter function.
A criterion for the supervision of the primary elements of the tuning section is the ground or zero-sequence
current (3I0) of the AC filter. The fundamental phase current of the AC filter is determined by the phase capac-
itance of the upper-voltage side capacitor. Consequently, a difference in the phase capacitances of the upper-
voltage side capacitor will cause a fundamental ground current. Therefore it is not sufficient for the tuning-
section supervision to evaluate only the fundamental ground current. Under normal operation and symmet-
rical network conditions, the fundamental ground current will be 0. An unbalance in the phase impedances
(detuning) will cause a ground current. A detuning of the tuning section will mainly cause harmonics in the
ground current. Thus, the RMS value of the ground current needs to be evaluated. For a detuning supervision
of the tuning section, the function OCP, ground (ANSI 50N) with the measuring method RMS value is applied.
This allows detecting harmonics up to the 50th harmonic with high precision (refer also to Technical data).
When selecting the settings (pickup value, operate delay and function mode) for the function OCP, ground
(ANSI 50N) the present network connecting conditions must be considered! Otherwise short-term power-
system unbalances (for example, 1-pole fast auto reclosing) or statically present harmonics in the zero-
sequence system may cause an overfunction. Since the primary elements of the AC filter are directly or inher-
ently protected by other protection functions and due to the possible influence of the network conditions on
the function OCP, ground (ANSI 50N), this function should be configured only as alarm function and not as
tripping function.
7.9
7.9.1
Capacitor Bank Protection
7.9 Detuning Supervision for Capacitor Banks
1070 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017