ABB RELION 670 Series Technical Manual page 729

1MRK 502 066-UUS B
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.
• Presence of special railway frequencies (e.g. 16.7Hz or 25Hz) in the three-phase power system
• Sensitive reverse power protection
• Stator or rotor ground fault protection for special injection frequencies (e.g. 25Hz)
• etc.
The filter output can also be connected to the measurement function blocks such as CVMMXN
(Measurements), CMMXU (Phase current measurement), VMMXU (Phase-phase voltage
measurement), etc.
The filter has as well additional capability to report the exact frequency of the extracted signal.
Thus the user can check the actual frequency of some phenomenon in the power system (e.g.
frequency of the sub-synchronous currents) and compare it with expected value obtained
previously by either calculation or simulation. For the whole three-phase filter group the frequency
of the signal connected to the first input (i.e. phase A) is reported. This value can be then used
either by over-/under-frequency protections or reported to the built-in HMI or any other external
client via the measurement blocks such is the CVMMXN.
Technical manual
Section 12
System protection and control
723