ABB Relion 650 Series Technical Manual page 128

Section 5
Impedance protection
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 ground-to-phase 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 for example, all three
phases are faulty.
Symmetrical component based phase selector
The symmetrical component phase selector uses preprocessed calculated sequence voltages and
currents as inputs. It also uses sampled values of the phase currents. All the symmetrical
quantities mentioned further in this section are with reference to phase A.
The function is made up of four main parts:
A Detection of the presence of ground fault
B A phase-to-phase logic block based on V
C A phase-to-ground component based on patent US5390067 where the angle relationships
between V
ground fault
D Logic for detection of three-phase fault
Presence of ground-fault detection
This detection of ground fault is performed in two levels, first by evaluation of the magnitude of
zero sequence current, and secondly by the evaluation of the zero and negative sequence voltage.
It is a complement to the ground-fault signal built-in in the Symmetrical component based phase
selector.
The phase-to-ground loops are released if both of the following criteria are fulfilled:
IBase · 0.5
|3I |>
0
|3I |>maxIph ·
0
where:
maxIph
INRelPG
122
/I and V /V is evaluated to determine ground fault or phase- to-phase to
2 0 2 1
INRelPG
is the maximal current magnitude found in any of the three phases
is the setting of 3I0 limit for release of phase-to-ground measuring loop in % of
IBase
© Copyright 2011 ABB Power Grids. All rights reserved
/V angle relationship
2 1
1MRK 506 326-UUS B
SEMOD153832-58 v3
SEMOD153832-70 v5
Line distance protection REL650
Technical manual