Figure 353: Permissible time-touch voltage characteristics given in standard
IEEE80 (metal-to-metal contact).
• This operation mode can be also used when maximum allowed earthing voltage,
i.e. earth potential rise, vs. operation speed follows a relationship such as 750V/
√
t
[
sec
].
• Time margin for practical circuit-breaker operate time can be applied with
setting
CB delay Comp
. Default setting is 0 ms.
• START and ST_EF outputs are activated when estimated touch voltage
(considering the effect of settings
Reduction factor
and
Enable harmonics
)
exceeds setting
Touch Vol Str Val
and earth fault is detected and earth-fault
current estimate is validated. Note that
Ena RF Compensation
= “Enable” does
not affect this start condition.
• OPERATE and OP_EF outputs are activated according to time-touch voltage
characteristics given in standard IEEE80 i.e. operate time is inversely
proportional to the estimated touch voltage.
• 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
Reset delay time
). After OPERATE output activation, START, ST_EF,
OPERATE and OP_EF outputs are reset immediately i.e. reset delay time is no
longer valid.
• During re-striking/intermittent earth faults, the very high current transient may
result to very fast operation times. In case longer operation during re-striking/
intermittent earth faults is preferred and operation should be based preferably
on counted number of transients, then setting
Reset delay time
should be
set to low value, say 20-40 ms. Dedicated intermittent earth-fault protection
functionality based on counted number of transients is described in
Chapter
4.2.10.5.6 Intermittent earth-fault protection
.
• Applicable settings are:
Reduction factor, Maximum earthing Ris, Touch Vol Str
Val, CB delay Comp, IEEE multiplier, IDMT stage Min Op Tm, IDMT stage Max Op
Tm, Reset delay time
.
According to the standard IEEE80, the values of the permissible touch voltage U
Tp
as a function of the fault duration t
f
are defined as follows:
For body weight of 50 kg:
Protection functions
1MRS759142 F
620 REX640
Technical Manual
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