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).
1MRK502052-UEN B Section 12
System protection and control
601
Technical manual
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