ABB REL650 series Technical Manual page 158

Section 6
Impedance protection
152
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 /I and V /V is evaluated to determine ground fault or phase- to-phase to ground fault
2 0 2 1
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:
|3I |>IBase · 0.5
0
|3I |>maxIph ·INRelPG
0
where:
maxIph is the maximal current magnitude found in any of the three phases
INRelPG
is the setting of 3I0 limit for release of phase-to-ground measuring loop in % of
In systems where the source impedance for zero sequence is high the change of zero
sequence current may not be significant and the above detection may fail. In those cases
the detection enters the second level, with evaluation of zero and negative sequence
voltage. The release of the ground-fault loops can then be achieved if all of the following
conditions are fulfilled:
|3V |>|V | · 0.5
0 2
|3V |>V | · 0.2
0 1
|V |> VBase · 0.2/√(3)
1
and
/V angle relationship
2 1
1MRK 506 335-UUS A
IBase
Technical manual