ABB RELION REX640 - Fault resistance estimation; Trip logic

Faulted phase information is not given in case of cross-country fault
(XC_FLT = TRUE).
Fault resistance estimation
Protection function IFPTOC includes fault resistance (R
F
) magnitude estimation
based on information on the faulted phase, the faulted phase voltage and estimated
earth fault current magnitude (fundamental frequency). Fault resistance magnitude
can be estimated with equation:
(Equation 141)
Where
= Faulted phase voltage magnitude, fundamental frequency [V]
= Estimated earth-fault current magnitude, fundamental frequency [A]
Actual implementation utilizes Cumulative Phasor Summing (CPS).
Magnitude of estimated fault resistance in primary ohms is available in
Recorded data: Fault resistance . In monitored data this information is
given: RF.
Fault resistance estimation is not done in case of cross-country fault
(XC_FLT = TRUE).
In case of intermittent earth fault, fault resistance estimation is not
accurate.
Trip logic
Protection function IFPTOC supports both tripping and alarming earth-fault
handling defined with setting Operation mode = “Alarming EF” or “Tripping EF”.
With Operation mode = “Alarming EF”, OPERATE and corresponding OP_EF/OP_XC/
OP_SOTF/OP_INTR outputs are not activated. Operation mode = “Alarming EF” is
applicable in networks, where due to low touch voltages tripping of earth-fault
is not required (requires existence of Global Earthing System, GES). Monitoring
of prevailing earth-fault current and/or touch voltage magnitude can be done via
Monitored data.
When start conditions of touch voltage protection, earth-fault current protection,
cross-country fault protection, intermittent earth-fault protection or switch
onto fault protection are fulfilled, this is indicated by activation of START
and corresponding ST_EF/ST_XC/ST_SOTF/ST_INTR outputs. When operate
conditions are fulfilled and setting
Operation mode = “Tripping EF”, this is indicated
by activation of OPERATE and corresponding OP_EF/OP_XC/OP_SOTF/OP_INTR
outputs.
1MRS759142 F
Protection functions
REX640
Technical Manual
635