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electronically operated short circuit indicator offers many solutions
to meet the requested conditions. The following figure shows the
different ways of adjusting the indicator and the block diagram of the
function. |
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note: |
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can
be preadjusted in our workshop
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Description
1.)
Sensor
The sensor, which is mounted on
the high voltage conductor, detects the short circuit inductively. |
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operating level is adjusted in each sensor |
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any faulty influence on the data transfer between sensor and reading
instrument is inhibited |
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2.) Impulse
monitoring
The period of the impulses transmitted from
the sensor (= actual short circuit current) can be in the range of 10
ms to 400 ms.
The duration of the impulses is checked by the impulse control in order
to avoid wrong indications.
A minimum impulse duration is adjusted to make sure that a peak current
( e.g. caused by switching processes, e.g.) does not cause an
indication. If the minimum impulse duration has been adjusted to 40 ms,
for example, the sensor has to transmit an impulse longer than 40 ms
before the reading instrument indicates a short circuit.
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| adjustment
of the minimum impulse duration |
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This
serves to avoid wrong indications. |
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3.)
Evaluation
The
short circuit signal impulse transmitted by the impulse control
activates the short circuit indication, the remote indication relay and
the time reset. After the equipment has been reset either by hand, by
operating current or after a pradjusted reset time, the evaluation unit
switches the indicator into stand-by modus.
4.) Indication /
Remote indication
The
short circuit can be indicated visually with LEDs or with flag
indicators. For remote indication, a potential-free alternating contact
is provided.
5.) Reset
The short circuit indicator can
be reset into stand-by modus as follows:
a) by manual reset
The
short circuit indicator can be set into stand-by modus any time with a
trigger switch.
b) by operating current
The
operating current must be deduced from the high voltage system. In case
of a short circuit, this voltage breaks down.
When reclosing the
system, the operating voltage recovers and resets the indicator
automatically. The time between the
recovery of the
operating voltage and and the reset process of the short circuit
indication is adjustable.
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Adjustment of the reset delay after recovery of
the operating voltage
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This
time delay eliminates those disturbances affecting the short circuit
indicator which occur when switching on the network
c.) Time reset
The evaluation unit is equipped with a
timing element. This timing element can be adjusted to every reset
time (0,5 - 1 - 2 - 3 - 4 h standard).
This time starts running at the moment when a short circuit occurs,
respectively when the power supply of the reading instrument recovers. |
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Preadjusting of reset time of the short circuit
indicator
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reset time depends on the maintenance system of the user. |
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Standard
settings
1)
operating point (current) of the short circuit indicator: defined by
customer
2) minimum impulse duration: 40 ms
3) reset delay: 2 sec
4) time reset: defined by customer |
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