
Two major earth fault-current limiting factors are possible for the isolated earthing
systems; the zero sequence phase-to-earth capacitance and fault resistance. Since
the voltage and their phase angles are relatively undisturbed, these systems can
remain operational during the sustained low magnitude faults.
Self-extinction of earth faults in the overhead lines is possible for the low values of
earth fault current. At higher magnitudes of fault current, faults are unlikely to self-
extinguish at the natural zero crossing of fault current because of the high transient
recovery voltage.
The zero sequence voltage relays can detect earth faults in the isolated systems.
This method of fault detection is not selective and requires sequential
disconnection or isolation of the feeders to determine the faulted feeder.
Setting guidelines
GUID-F9BB43B1-7A1C-40A4-84DB-58ACE7B12C28 v1
The settings for 2-phase Distance protection zones, quadrilateral characteristic
(ZRWPDIS) are done in primary values. The instrument transformer ratio that has
been set for the analog input card is used to automatically convert the measured
secondary input signals to primary values used in ZRWPDIS.
The default values given should be validated for each application and adopt the
appropriate setting values.
The parameters for ZRWPDIS are set via the local HMI or PCM600.
Common base IED values for primary current (
IBase
), primary voltage (
UBase
)
and primary power (
SBase
) are set in a global base values for settings function
GBASVAL.
General settings
GUID-30CF921D-34EE-4F24-B050-C92036619F59 v2
GlobalBaseSel
: Selects the global base value group used by the function to define
(
IBase
), (
UBase
) and (
SBase
).
Operation
: Sets the protection to
On
or
Off
.
System Earthing
: It is used to select the type of system earthing (i.e.
Compensated
,
Solidly
and
High impedance
).
LineAng
: This is to used set the distance protection characteristic angle. It should
be set to line angle of the protected transmission line. The default value is 75 deg.
IMinOpPE
: It is used to select the minimum operating current for the phase-to-
earth loops. If the minimum current is exceeded, the distance protection calculates
the impedance. The default setting is 10%
IB
.
IMinOpPP
: It is used to select the minimum operating current for the phase-to-
phase loops. If the minimum current is exceeded, the distance protection calculates
the impedance. The default setting is 10%
IB
.
OpLoadEnch
: This setting is used to select the load discrimination characteristic
operation to
On
or
Off
. The default value is
Off
.
1MRK 506 375-UEN A
Section 7
Impedance protection
Railway application RER670 2.2 IEC
125
Application manual
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