ABB Relion RES670, Техническое руководство

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Note that the special filtering algorithm is used to extract these phasors. This algorithm
is different from the standard one-cycle Digital Fourier Filter typically used by the
numerical IEDs. This filter provides extremely good accuracy of measurement and
excellent noise rejection, but at the same time it has much slower response time. It is
capable to extract phasor (i.e. magnitude, phase angle and actual frequency) of 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 wye 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.
1MRK 511 408-UUS A
Section 12
System protection and control
Phasor measurement unit RES670 2.2 ANSI 357
Technical manual