Seg XRI1-IR, Руководство пользователя

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10 TB XRI1-IR 02.00 E
By means of accurate hardware design and by using
an efficient directional algorithm a high sensitivity for
the voltage sensing circuit and a high accuracy for
phase angle measurement are achieved so that a cor-
rect directional decision can be made even by close
three-phase faults.
As an addition, to avoid maloperations due to distur-
bances, at least 2 periods (40 ms at 50 Hz) are
evaluated.
For the MRI1 -overcurrent relays with directional feature
different time delays or time multipliers can be set for
forward and backward faults (ref. to chapter 6.1.3
and 6.1.6).
If the trip delay for backward faults is set longer than
the one for forward faults, the protective relay works as
a "backup"-relay for the other lines on the same bus-
bar. This means that the relay can clear a fault in the
backward direction with a longer time delay in case
of refusal of the relay or the circuit breaker on the
faulted line.
If the trip delay for backward faults is set out of range
(on the display "EXIT"), the relay will not trip in case of
backward faults.
4.4 Requirements on the main
current transformers
The current transformers have to be rated in such a
way, that a saturation should not occur within the fol-
lowing operating current ranges:
Independent time overcurrent function: K1 = 2
Inverse time overcurrent function: K1 = 20
High-set function: K1 = 1.2 - 1.5
K1 = Current factor related to set value, at which the
C.T. is not yet saturated
Moreover, the current transformers have to be rated
according to the maximum expected short circuit cur-
rent in the network or in the protected objects.
The low power consumption in the current circuit of
XRI1-IR , namely <0.2 VA, has a positive effect on the
selection of current transformers. It implies that, if an
electromechanical relay is replaced by
XRI1-IR , a high
accuracy limit factor is automatically obtained by using
the same current transformer.