ABB RELION REX640 Technical Manual page 1146

Protection functions
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
harmonic current (excluding the harmonic defined by the setting
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.
4.12.4.7 Signals
1146
Alarm start value and Start value determine the portion of the total
Alarm start value and Start value should be selected as such that
Settings
in normal operation SRCPTOC should not operate.
1MRS759142 F
Tuning harmonic
REX640
Technical Manual