Design
The earth fault and short circuit indicator consists of:
3 pcs. short circuit sensors
1 pc. earth fault sensor
1 pc. reading instrument
connecting cables and / or light mains
The reading instrument is incorporated in a plastic housing together
with the electronics for the time reset and the evaluating electronics.
Each type of fault, short circuit and earth fault, is indicated by one
blinking LED.
The fault is remotely indicated over one relay (1x changer) for earth
fault and short circuit.
The reading instrument is equipped with a test/reset button.
Each sensor consists of a plastic housing, which contains a coil to
detect impulses caused by a short circuit or an earth fault. Depending
on the version, a connection cable is fixed to the sensor, or the
sensor is prepared for connection to a light mains. The housing is
fully sealed and follows the standards of IP 67.
The light mains are applied for a potential-free data transmission
between the short cicuit sensor and the reading instrument through a
high voltage area. These light cables are made of PMMA and are
available up to a length of 15m.
Function
The
sensors detect earth faults and short circuits inductively. The
operating points for earth fault and short circuit are adjusted with
electronics for threshold levels. When the current picked up by the
coil exceeds the preadjusted threshold level, an impulse is sent to the
reading instrument for evaluation. The respective LED indicates a short
circuit and/or an earth fault.
Minimum impulse adjustment: The reading instrument is equipped with a
setting for minimum impulse duration. The impulse picked up from the
sensor is evaluated regarding its duration. If the impulse duration is
shorter than the adjusted value of the mininum impulse duration, no
fault will be indicated. If the impulse duration is longer than the
preadjusted duration, an earth fault or short circuit is indicated.
This equipment allows the filtering of peak current caused by switch
currents or similar circumstances. Wrong indications are thus avoided.
With the instrument 4 values for minimum impulse duration can be
adjusted (times follow request of customer).
The reset of the earth fault or short circuit indication can be done by:
a) automatic time reset. A time element controls the indication and
resets it after a preadjusted time
(4 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).
Assembling
-Please
refer to the assembling instructions delivered with each instrument -
The reading instrument has to be installed outside the high voltage
area. It is possible to install the short circuit sensors on screened
and unscreened cables. The earth fault sensor must be installed around
all three cores to assure that the sum current of all three cables is
picked up.
The frames of the sensors can be opened for installation.
The short circuit sensors are connected to the reading instrument via
light mains.
The earth fault sensor is connected to the reading instrument via cable.
|
|
