any signal (e.g. 37,2Hz) present in the waveforms of the connected CTs and/or VTs.
The magnitude and the phase angle of this phasor are calculated with very high
precision. For example the magnitude and phase angle of the phasor can be estimated
even if it has magnitude of one per mille (i.e. 1‰ ) in comparison to the dominating
signal (e.g. the fundamental frequency component). Several instances of this function
block are provided. These instances are fully synchronized between each-other in
respect of phase angle calculation. Thus if two multi-purpose filters are used for some
application, one for current and the second one for the voltage signals, the power
values (i.e. P & Q) at the set frequency can be calculated from them by the over-/under-
power function or CVMMXN measurement function block.
In addition to these phasors the following quantities are internally calculated as well:
• Phasors for the individual phases as well as phase-to-phase phasors
• True RMS value of the input signal over all samples available in the memory
• Positive sequence phasor
• Negative sequence phasor
• Zero sequence phasor
• etc.
In order to properly calculate phase-to-phase phasors from the individual phase
phasors or vice versa, the setting parameters ConnectionType is provided. It defines
what quantities (i.e. individual phases or phase-to-phase quantities) are physically
connected to the IED analogue inputs by wiring. Then the IED knows which one of
them are the measured quantities and the other one is then internally calculated. This
setting is only important for the VT inputs, because the CTs are typically star
connected all the time.
Thus when this filter is used in conjunction with multi-purpose protection function or
overcurrent function or over-voltage function or over-power function many different
protection applications can be arranged. For example the following protection,
monitoring or measurement features can be realized:
• Sub-synchronous resonance protection for turbo generators
• Sub-synchronous protection for wind turbines/wind farms
• Detection of sub-synchronous oscillation between HVDC links and synchronous
generators
• Super-synchronous protection
• Detection of presence of the geo-magnetic induced currents
• Overcurrent or overvoltage protection at specific frequency harmonic, sub-
harmonic, inter-harmonic etc.
• Presence of special railway frequencies (e.g. 16.7Hz or 25Hz) in the three-phase
power system
• Sensitive reverse power protection
• Stator or rotor earth fault protection for special injection frequencies (e.g. 25Hz)
• etc.
1MRK502052-UEN B Section 12
System protection and control
597
Technical manual
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