Hitachi Relion 670 Series Applications Manual page 115

1MRK506375-UEN Rev. N
OpModetPPZ6: To set the Off/On operation of the phase-to-phase timer of zone 6. The default
setting is Off.
tPPZ6: To set the time delay to trip for phase-to-earth faults in zone 6. It should be set to 0.0 s.
Phase selection
tI0: Delay time for the residual overcurrent start. Residual overcurrent start is delayed by settable
time delay tI0. The default setting is 0.2s.
7.2.3.3 High impedance earthing systems
In isolated/high impedance networks, following types of errors can be anticipated:
• 2-phase short circuit, with or without earth connection
• Single phase-to-earth fault
• cross country double earth faults
For double earth faults, the disconnection by the distance measurement should be selective.
For single phase earth fault in isolated systems, voltage shifts occur and a small capacitive current
generates. Trip will occur after a time delay. In an isolated neutral system, the neutral has no
intentional connection to earth. The system is connected to earth through the phase-to-earth
capacitances. Single phase-to-earth faults will shift the system neutral voltage.
IEC15000384 V1 EN-US
Figure 43:
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
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.
Railway application RER670
Application manual
Earth fault in isolated systems
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Earth fault
IEC15000384-1-en.vsdx
Section 7
Impedance protection
GUID-4A34CA75-7922-4FCD-B078-38AEAD9D8DFC v2
GUID-0D740A9F-64D9-4A0E-80D2-0C71B48E8D35 v2
GUID-F9BB43B1-7A1C-40A4-84DB-58ACE7B12C28 v2
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