High Impedance Earthing Systems - ABB RER670 Applications Manual

Section 7
Impedance protection
7.2.2.3
124
TimerSelZ6: This is used to set the zone timer selection mode of zone 6. i.e. Timers
separated, Timers linked, General start, PhSel start, Internal start and External
start. The default setting is Timers separated.
OpModetPEZ6: This is used to set the Off/On operation of the phase-to-earth timer
of zone 6. The default setting is Off.
tPEZ6: This is used to set the time delay to trip for phase-to-earth faults in zone 6.
It should be set to 0.0 s.
OpModetPPZ6: This is used to set the Off/On operation of the phase-to-phase timer
of zone 6. The default setting is Off.
tPPZ6: This is used 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.

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 41: Earth fault in isolated systems
GUID-4A34CA75-7922-4FCD-B078-38AEAD9D8DFC v2
GUID-0D740A9F-64D9-4A0E-80D2-0C71B48E8D35 v2
Earth fault
IEC15000384-1-en.vsdx
Railway application RER670 2.2 IEC
1MRK 506 375-UEN A
Application manual