ABB RELION REX640 Technical Manual page 598

Protection functions
Earth-fault current and touch voltage protection
Based on the practical experience from real earth faults, some faults have re-
striking/intermittent characteristics, where the voltage and current waveforms
generated by earth fault are rich with harmonics and non-sinusoidal content. In
such fault type the operation of IFPTOC can alternatively be based on the counted
number of transients instead of estimated fault current or touch voltage. Dedicated
functionality to allow this type of operation is described in
Intermittent earth-fault protection
Principle based on earth fault current estimate
The operation of IFPTOC based on earth-fault current estimate is described next.
In case
the estimated effective earth-fault current magnitude taking account the effect
Reduction factor . The harmonic content of fault current can be included into
of
estimate with setting
Operation time can be either definite time or inverse time, selected with setting
Operating curve type = "Definite time", "Inverse time EN50522" or "Inverse time
IEEE80".
When
• Operate time is according to definite time (DT) operation
• START and ST_EF outputs are activated when estimated earth-fault current
magnitude (considering the effect of settings
harmonics ) exceeds setting EF current Str Val and earth fault is detected, and
earth-fault current estimate is validated. Note that
"Enable" does not affect this start condition. It is important to set setting
current Str Val according to required protection sensitivity.
• OPERATE and OP_EF outputs are activated after operation timer has elapsed,
defined with setting
• Reset timer is started if any of the above conditions for START is not anymore
valid. START and ST_EF outputs stay activated until the reset timer expires
(setting
OPERATE and OP_EF outputs are reset immediately i.e. reset delay time is no
longer valid.
• During re-striking/intermittent earth faults, in case operation should be
based preferably on counted number of transients, then setting
delay time should be set to low value, say 20-40 ms, thus definite time
operation is ineffective during re-striking/intermittent earth faults as DT-timer
becomes reset between re-strikes. Dedicated intermittent earth-fault protection
functionality based on counted number of transients is described in
4.2.10.5.6 Intermittent earth-fault protection
• Applicable settings are:
and
• Note that setting
applicable in definite time operation, but it must be taken into account in setting
DT stage Op time .
598
Operation principle = "EF current based", then operation is based on
Enable harmonics = "Enable".
Operating curve type = "Definite time" is selected, then
DT stage Op time .
Reset delay time ). After OPERATE output activation, START, ST_EF,
Reduction factor, EF current Str Val, DT stage Op time
Reset delay time .
CB Delay Comp (circuit breaker delay compensation) is not
Minimum practical value for setting
primary current. For example, in case CT primary current is 200 A, then
minimum practical value for setting
1 A. For CT with 400 A primary current, then minimum practical value
for setting EF current Str Val is 0.5%*400A = 2 A. The lower setting EF
current Str Val is used, the higher sensitivity in terms of fault resistance
.
Reduction factor and Enable
Ena RF Compensation =
.
EF current Str Val is 0.5% from CT
EF current Str Val is 0.5%*200A =
1MRS759142 F
Chapter 4.2.10.5.6
EF
Reset
Chapter
REX640
Technical Manual