Figure 346: Permissible time-touch voltage characteristics given in standard
IEEE80 (metal-to-metal contact)
• This operation mode can be also used when maximum allowed earth potential
rise vs. operation speed follows a relationship such as 750 V/√
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 effective earth-fault
current magnitude (considering the effect of settings
Reduction factor
and
Enable harmonics
) exceeds setting
EF current 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. It is important to set setting
EF
current Str Val
according to required protection sensitivity.
• OPERATE and OP_EF-outputs are activated so that the operate time is according
to the touch voltage requirements defined in standard IEEE80. i.e. operate time
is inversely proportional to the estimated fault current.
• 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OPERATE and OP_EF outputs are reset immediately i.e. reset delay time is no
longer valid.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, EF current Str Val, CB delay Comp, IEEE
multiplier, Maximum earthing Ris, 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 50kg:
(Equation 122)
1MRS759142 F
Protection functions
REX640
Technical Manual
607
To Next Page
Loading...
