ABB RELION 670 Series Technical Manual page 250

Section 7
Impedance protection
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 value. Both
voltages and currents are filtered out and evaluated. The condition for fault type classification for
the voltages and currents can be expressed as:
FaultType
EQUATION1808-ANSI V1 EN-US
FaultType
EQUATION1809-ANSI V1 EN-US
The value of FaultType for different shunt faults are as follows:
Under ideal conditions: (Patent pending)
Single phase-to-ground;
Phase-to-phase fault
Three-phase fault;
The output signal is 1 for single phase-to-ground fault, 2 for phase-to-phase fault and 3 for three-
phase fault. At this point the filter does not know if ground was involved or not.
Typically there are induced harmonics in the non-faulted lines that will affect the result. This
method allows for a significant tolerance in the evaluation of FaultType over its entire range.
When a single phase-to-ground fault has been detected, the logic determines the largest quantity,
and asserts that phase. If phase-to-phase fault is detected, the two largest phase quantities will
be detected and asserted as outputs.
The faults detected by the delta based phase selector are coordinated in a separate block.
Different phases of faults may be detected at slightly different times due to differences in the
angles of incidence of fault on the wave shape. Therefore the output is forced to wait a certain
time by means of a timer. If the timer expires, and a fault is detected in one phase only, the fault is
deemed as phase-to-ground. This way a premature single phase-to-ground fault detection is not
released for a phase-to-phase fault. If, however, ground current is detected before the timer
expires, the phase-to-ground fault is released sooner.
If another phase picks up during the time delay, the wait time is reduced by a certain amount. Each
detection of either phase-to-ground or additional phases further reduce the initial time delay and
allow the delta phase selector output to be faster. There is no time delay if all three phases are
faulty.
The delta function is released if the input DELTAREL is activated at the same time as input
DELTABLK is not activated. Activating the DELTABLK input blocks the delta function. The release
244
å D D D
( VA VB , , VC
=
D D D
Max IA IB ( , , IC
å D D D
( IA IB , , IC )
=
D D D
Max IA IB ( , , IC
FaultType=1
FaultType=2
FaultType=3
)
)
)
1MRK 502 066-UUS B
(Equation 62)
(Equation 63)
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