ABB REL650 series Technical Manual page 156

Section 6
Impedance protection
150
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.
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 filter
produces significant non-zero output. The filter output is processed by the delta function.
The algorithm uses an adaptive relationship between phases to determine if a fault has
occurred, and determines the faulty phases.
The current and voltage delta based phase selector gives a real output signal if the
following criterion is fulfilled (only phase A shown):
Max(ΔVA,ΔVB,ΔVC)>DeltaVMinOp
Max(ΔIA,ΔIB,ΔIC)>DeltaIMinOp
where:
ΔVA, ΔVB and ΔVC
DeltaVMinOp and DeltaIMinOp
The delta voltages ΔVA(B,C) and delta current ΔIA(B,C) are the voltage and current
between sample t and sample t-1.
The delta phase selector employs adaptive techniques to determine the fault type. The
logic determines the fault type by summing up all phase values and dividing by the largest
are the voltage change between sample t and sample t-1
are the minimum harmonic level settings for the voltage and current filters
to decide that a fault has occurred. A slow evolving fault may not produce
sufficient harmonics to detect the fault; however, in such a case speed is
no longer the issue and the sequence components phase selector will
operate.
1MRK 506 335-UUS A
Technical manual