signal has an internal pulse timer of 100 ms. When the DELTAREL signal has disappeared the delta
logic is reset. In order not to get too abrupt change, the reset is decayed in pre-defined steps.
Symmetrical component based phase selector
SEMOD153832-58 v3
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
2
/V
1
angle relationship
C A phase-to-ground component based on patent US5390067 where the angle relationships
between V
2
/I
0
and V
2
/V
1
is evaluated to determine ground fault or phase- to-phase to
ground fault
D Logic for detection of three-phase fault
Presence of ground-fault detection
SEMOD153832-70 v8
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 complementary based zero-sequence current function evaluates the presence of ground fault
by calculating the 3I
0
and comparing the result with the setting parameter
INRelPE
. The output
signal is used to release the ground-fault loop. It is a complement to the ground-fault signal built-
in in the sequence based phase selector. The condition for releasing the phase-to-ground loop is
as follows:
The output from this detection is used to release the ground-fault loop.
|3I
0
|>maxIph ×
INRelPE
where:
|3I
0
| is the magnitude of the zero sequence current 3I
0
maxIph is the maximum magnitude of the phase currents
INRelPE
is a setting parameter for the relation between the magnitude of 3I
0
and the
maximum phase current
The ground-fault loop is also released if the evaluation of the zero sequence current by the main
sequence function meets the following conditions:
|3I
0
|>
IBase
× 0.5
|3I
0
|>maxIph ×
INRelPG
1MRK 502 066-UUS B Section 7
Impedance protection
245
Technical manual
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