ABB Relion 670 series, Technical Reference Manual

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so that single phase tripping and autoreclosing can be used plays an important roll in
this matter.
The phase selection function is design to accurately select the proper fault loop(s) in
the distance function dependent on the fault type.
The heavy load transfer that is common in many transmission networks may in some
cases interfere with the distance protection zone reach and cause unwanted operation.
Therefore the function has a built in algorithm for load encroachment, which gives the
possibility to enlarge the resistive setting of the measuring zones without interfering
with the load.
The output signals from the phase selection function produce important information
about faulty phase(s), which can be used for fault analysis as well.
6.8.2 Principle of operation
6.8.2.1 The phase selection function
Faulty phase identification with load encroachment for mho (FMPSPDIS, 21) function
can be decomposed into six different parts:
1. A high speed delta based current phase selector
2. A high speed delta based voltage phase selector
3. A symmetrical components based phase selector
4. Fault evaluation and selection logic
5. A load encroachment logic
6. A blinder logic
The total function can be blocked by activating the input BLOCK.
Delta based current and voltages
The delta based fault detection function uses adaptive technique and is based on patent
US4409636.
The aim of the delta based phase selector is to provide very fast and reliable phase
selection for releasing of tripping from the high speed Mho measuring element and is
essential to Directional Comparison Blocking scheme (DCB), which uses Power Line
Carrier (PLC) communication system across the protected line.
The current and voltage samples for each phase passes through a notch filter that filters
out the fundamental components. Under steady state load conditions or when no fault
is present, the output of the filter is zero or close to zero. When a fault occurs, currents
and voltages change resulting in sudden changes in the currents and voltages resulting
in non-fundamental waveforms being introduced on the line. At this point the notch
1MRK505222-UUS C
Section 6
Impedance protection
289
Technical reference manual