Eaton Power Xpert PXR 10, Руководство пользователя

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4 Protection settings
4.4 Short-time delayed short-circuit release
PXR Electronic trip unit 01/21 MN012005EN www.eaton.com
27
4.4 Short-time delayed short-circuit release
The short-time delayed short-circuit release I
sd
can be set to 2 to 10 times
the threshold value of the overload release I
r
.
The duration of the short-time delay t
sd
is selected in together with one of
two short delay slopes, “flat” or I
2
t. The duration can be set to a range from
0 seconds (the minimum interval) to 1 second.
Zone selective interlocking (ZSI) may affect the trip times of the short-time
delay protection function and thereby accelerate tripping.
As soon as a short-time delayed overload has caused the circuit breaker to
trip, the
SHORT indicator will light up, provided that auxiliary power is
available (on the PXR20), or a message will appear on the display (on the
PXR25).
4.5 Instantaneous short-circuit release
The instantaneous short-circuit release I
i
can be set to 2 to 18 times of the
rated operational current I
n
. The maximum value depends on the specific
circuit breaker, its rated operational current, as well as the trip unit type.
The instantaneous short-circuit protection trips the circuit breaker without
any time delay.
As soon as an instantaneous short-circuit has caused the circuit breaker to
trip, the
INST indicator will light up, provided that auxiliary power is available
(on the PXR20), or a message will appear on the display (on the PXR25).
4.6 Ground-fault settings
If a PXR20 or PXR25 trip unit is equipped with ground-fault protection, the
characteristics (e.g. the grounding system, the number of sources, and the
number and location of the ground points) of the distribution system must be
taken into account, together with the manner in which the circuit breaker will
be used in the system.
The versatile PXR trip unit can both detect ground-fault currents and respond
to them. A ground-fault alarm ensures early warning in the event of a ground
fault, while a ground-fault trip provides protection in this case.
The following three modes of operation can be selected.
￫
For further information, please refer to
￫ section 4.10, “Zone selective interlocking (ZSI)”, page 31.