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Design
The short circuit indicator type OK consists of:
1 pcs. reading instrument
3 pcs. sensors
connection cable
The reading instrument is available as a panel-mounted instrument and
as a surface-mounted instrument. Both versions
can be equipped with a remote indication contact.The sensor set
(version type OKS) consists of 3 single sensors.
The cable output of these sensors is combined in one junction. The
cable length from this junction point to the reading instrument is 3000
mm (standard - on request other lengths are possible, too).
The light mains sensors (version OKL) are connected to the reading
instrument via light mains
( standard length 1400 mm - other lengths are possible, too).
Function
The
sensors are installed on the medium voltage cables.
In case of a short circuit, a coil, which is mounted into the sensor's
housing, becomes energized. This coil transmits an impulse to the
reading instrument. Within the reading instrument the impulse is
evaluated.
The monitored net can be used for power supply, because the energy
needed by the indication flags for indication is stored
in a capacitor.
Minimum impulse adjustment: The reading instrument is equipped with a
minimum impulse duration setting. The impulse picked up from the sensor
is checked for its length. If the impulse length is shorter than the
adjusted mininum impulse duration, no fault will be indicated. If the
impulse length is longer than the preadjusted duration,
a short circuit will be indicated.
This equipment allows the filtering of peak currents caused by switch
currents or similar circumstances. Wrong indications
are avoided. The minimum impulse duration can be chosen (between 40 ms
and 300 ms).
Indication: The indication is done by a bistable flag indicator for
every core. In case of a short circuit,
the fault will be indicated by a "red surface". In stand- by- mode the
flag shows a red surface.
The short circuit information transmitted by the sensor controls the
flags, so that a short circuit is indicated.
The reset of the earth fault or short circuit indication can be done in
the following ways:
a) automatic time reset: a time element controls the indication and
resets it after a preadjusted time
(3 values between 0.5 h to 40 h are selectable).
b) manual reset with a push-button.
c) recovering net voltage (if the reading instrument is supplied from
the monitored net).
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