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
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