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Arc fault protection
system DEHNshort

DEHNshort is a modular arc fault protection system
which detects arc faults with the help of current and
light sensors. Thanks to its short response time of a
few milliseconds, the incident energy is reduced to a
minimum. DEHNshort takes the protection of persons 5
and systems to another level and by far exceeds
the requirements of the currently applicable IEC TR
61641* standard.

Detection:
The current transformers at the infeed detect the
overcurrent resulting from the arc fault and transmit this 2 4
information to the relevant detection device. Sensors
detect the light emitted by the arc fault and also transmit
this information to the detection device. Depending on
the application, fibre optic and optoelectronic sensors are
available.
1
Evaluation:
In the detection devices, the sensor signals are converted
into digital information and are linked together logically.
If all arc fault detection criteria are fulfilled, quenching
and disconnection commands are issued. The quenching
devices are immediately activated via fibre optic cables, the
shunt releases via relay contacts. LEDs indicate the current
status of the system. Since the detection devices are
integrated in the assembly door, the system status can also
be evaluated if the assembly door is closed.

Arc fault quenching:
In order to quench the arc fault as quickly as possible, the
detection device activates the relevant quenching devices.
The current commutates from the arc fault to the low-im-
pedance bolted short-circuit of the two quenching devices
and the voltage drops, thus quenching the arc fault. Power
thyristors ensure short commutation times which cannot
be achieved by previous solutions. 3

Disconnection:
At the same time as the quenching devices, the detection
devices transmit a trip command to the shunt releases of
all incoming circuit breakers via a floating relay contact
and disconnect the part of the switchgear assembly where
the arc fault occurred.

Recommissioning:
The switchgear assembly can be recommissioned after the
fault has been rectified, the quenching devices have been 2
replaced and the arc fault protection system has been
reset.

* IEC TR 61641: Low-voltage switchgear and controlgear assemblies; Guide for testing under conditions of arcing due to internal fault
** IEC 60364-4-42: Low-voltage electrical installations – Part 4-42: Protection for safety – Protection against thermal effects
6 *** IEC 60364-5-5: Low-voltage electrical installations – Part 5-53: Selection and erection of electrical equipment – Switchgear and control gear