ABB RELION 620 Series Technical Manual page 805

1MRS757644 F
620 series
Technical Manual
voltage and current distortions, which increases losses and causes overheating of other
equipment in the circuit.
A traditional way of solving the problem is to conduct a detailed system study for each
individual installation and use the results to properly size the capacitors and determine
the right operating range of capacitors to avoid harmonic resonance with other system
components. However, this method is not economical but more time-consuming.
The capacitor switching-resonance protection function can be used as a solution to the
above mentioned problem. The basis for the harmonic resonance protection is the
detection of a current harmonic resonance condition caused by capacitor switching. A
prolonged increase of the harmonic distortion level after a switching operation is a
clear indication of such condition. When a resonant condition caused by capacitor
switching occurs in a circuit, SRCPTOC detunes the circuit by taking the reverse
action, that is, switching the capacitor bank off if switching it on causes resonance. If
the resonance situation has been detected and SRCPTOC has switched off a capacitor
bank, power factor controller should not try to switch on the capacitor bank until the
switching resonance function reset.
The capacitor switching-resonance protection function can also be used to protect
harmonic filters. In harmonic filter bank applications, the SRCPTOC function can be
tuned to harmonic frequency for which the harmonic filter is designed to ensure that
the function does not include thr tuned harmonic frequency current into the
calculation of the resonance current. If there is more than one harmonic filter bank
involved, each SRCPTOC tunes to the harmonic frequency of its corresponding filter
bank. The interlinking between the functions can be done in such a way that if
resonance occurs in a higher harmonic frequency filter bank, all the lower harmonic
frequency filter banks can be tripped immediately by activating the function input
RESO_IN.
The settings Alarm start value and Start value determine the portion of the total
harmonic current (excluding the harmonic defined by the setting Tuning harmonic
Num) in relation to the CT nominal value required for SRCPTOC to give alarm and
operate respectively.
For power factor correction application
• Tuning harmonic Num must be set to 1.
• Alarm start value and Start value must be set according to the standard IEEE519
-1992.
For harmonic filter application
• Tuning harmonic Num must be set to the filter design tuning frequency.
• Alarm start value and Start value must be set according to the standard IEEE519
-1992.
Section 4
Protection functions
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