ABB RELION 670 Series Technical Manual page 732

Section 12
System protection and control
A
B
C
IEC13000178 V3 EN-US
Figure 386: Example of filter calculation
The data shown in the Figure comes from the comtrade file captured by the IED. The following
traces are presented in this Figure.
a) Waveforms of the stator three-phase currents given in primary kA.
b) RMS value of the sub-synchronous resonance current extracted by the filter in primary amperes.
c) Frequency of the extracted sub-synchronous resonance current provided by the filter in Hz.
Note the very narrow scale on the y-axle for b) and c). Such small scale as well indicates with which
precision and consistency the filter calculates the phasor magnitude and frequency of the
extracted stator sub-synchronous current component.
The following can be observed in the Figure:
• The stator total RMS current value is around 33 kA primary.
• The measured magnitude of the sub-synchronous current is around 173 A primary (that is,
0.5% of the fundamental 50 Hz component).
• The frequency of this sub-synchronous current component is 31.24 Hz.
With above given settings the sub-synchronous current magnitude and frequency are calculated
approximately four times per second (that is, correct value is four times per 1024 ms).
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1MRK 502 066-UUS B
IEC13000178-2-en.vsd
Technical manual