In case tripping of cross-country fault is enabled (setting
Enable XC Op mode =
“on”), then operation of IFPTOC requires that simultaneously both the magnitude
of calculated residual current (I
o
) and estimated earth-fault current (
) exceeds
setting
XC stage A Str Val during a detected earth fault:
(Equation 137)
Operate time for cross-country fault operation is given with setting
XC stage Op
time. Typical operate time is 60-100 ms.
The cross-country stage earth fault module always evaluates the true
fault current magnitude (considering the effect of setting
Enable
harmonics) i.e. it is not affected by settings Ena RF Compensation and
Reduction factor.
The cross-country fault indication is given in Recorded data as
XC fault
detection or in Output data as
XC_FLT
.
When start and operate conditions of cross-country earth fault module are fulfilled,
this is indicated by activation of
START
and
OPERATE
outputs and
ST_XC
and
OP_XC
outputs.
In case tripping of cross-country fault is enabled, operate time is given with setting
XC stage Op time. Reset time is defined with setting Reset delay time. Note that
setting
CB Delay comp (circuit breaker delay compensation) is not applicable in
definite time operation, but it must be taken into account in setting
XC stage Op
time.
Applicable settings for cross-country earth fault module are:
Enable XC Op mode, XC
stage A Str Val, XC stage PP V Val, XC stage Op time and Reset delay time.
Intermittent earth-fault protection
Operation time requirement of earth-fault protection in safety standards assumes
continuous flow of fault current. In case of resonant earthed network, earth faults
are often re-striking i.e. fault arc is not continuous, but intermittent. During re-
striking/intermittent earth faults, the very high but narrow current transient may
result to very fast operation times, if operation time is based on IDMT-operation i.e.
Operation curve type = Inverse time EN50522 or Inverse time IEEE80. Requirement
for operation with IDMT-timer is that timer is not reset between successive
current transients i.e.
Reset delay time should be set long enough. However, in
case operation during re-striking/intermittent earth faults is preferably based on
number of counted transients, then setting
Reset delay time should be set to low
value, say 20-40 ms, and dedicated intermittent earth-fault protection functionality
must be enabled.
Intermittent earth-fault module is enabled with setting
Ena Intermit EF mode = “on”.
Module is enabled by default. In case multiple instances of IFPTOC are applied in
the protection configuration, and operation during re-striking/intermittent earth
faults is preferably based on number of counted transients, only single instance
of IFPTOC requires Intermittent earth-fault module functionality to be enabled; in
other instances, Intermittent earth-fault module functionality may be disabled.
Protection functions
1MRS759142 F
630
REX640
Technical Manual