Arc fault protection device

from Wikipedia, the free encyclopedia
AFDD as a pre-assembled device. AFD unit with line circuit breaker as separation unit.
AFD unit for top-hat rail mounting for combination with other protective elements such as miniature circuit breakers

An arc-fault circuit interrupter , colloquially fire protection switch or contact failure switch (engl. Arc Fault Detection Device ( AFDD ) or in North America Arc Fault Circuit Interrupter ( AFCI )) called circuits protects against arc faults and is in the narrower sense, a circuit breaker against contact error in the Low voltage installation .

Arc fault circuit breakers analyze the current and voltage curve using digital signal processing and interrupt the circuit with signatures that are typical of threshold arcs. This prevents overheating at poor contact points or flashovers between two conductors and can thus prevent around half of all fires that are caused by electrical installations and devices. The colloquial term fire protection switch is derived from this.

General

Arc fault protection devices are installed in sub-distributions and can detect arcing faults in series and parallel to the consumer.

Arc faults and contact problems in series with the consumer as well as between phase and neutral conductor are characterized by the fact that neither overcurrents nor fault currents arise. Overcurrent protection devices such as line circuit breakers or fuses therefore do not respond. Sources of error can be, for example, loose terminals or a broken cable .

Particularly in the case of long-term, higher operating currents, high temperatures can arise at the fault location with the risk of fire.

Arc faults parallel to the consumer are characterized in that neighboring electrical conductors erroneously come into electrical contact with one another and trigger a short circuit , for example as a result of damage to the cable insulation. In this case, if the insulation is faulty, the current will be higher than the operating current over time; once an arc occurs, the current is then only limited by the loop impedance . The overcurrent protection device is only triggered after a certain time, namely only when the insulation has been damaged by pyrolysis to such an extent that the graphite remaining has a low resistance at a high temperature and creates an arc. The residual current circuit breaker (RCCB) trips immediately only in the event of an earth fault . In the former case, an AFDD can already detect the fault when the charred insulating material begins to partially conduct and, by switching off, avoids high thermal energies and consequential damage at the fault location.

AFDDs are designed in Europe for the usual 230 V operating voltage. The rated currents (I n ) are set to values ​​between 6A and 63A. AFDDs are available as a single device or in combination with a line circuit breaker and / or a residual current circuit breaker. The Arc Fault Circuit Interrupter (AFCI) used in the US have been available on the market there since the late 1990s and have been required by the National Electrical Code since 2008 for the protection of living spaces. Another field of application is in avionics (power supply in aircraft).

functionality

Tripping characteristic as current-time characteristic of an AFDD and in comparison with colored surface circuit breakers with characteristics B, C and D

To determine whether there is an accidental arc, the AFDD measures the voltage and current curve over time and evaluates it using digital signal processing . In particular, the course of the current has characteristic, high-frequency components when there are contact problems. This evaluation is necessary because, in normal operation, regular fluctuations in the current curve, harmonics and transient current curves when loads are switched on must not lead to faulty tripping.

In the case of arcing faults in series with the consumer, the current-time characteristic of the AFDD runs in the range from 0.1 to 1 seconds; miniature circuit breakers cannot detect such errors. In the further course of the triggering characteristic of the AFDD, it can be seen that the triggering time of 0.1 seconds is not exceeded due to the evaluation algorithms. For parallel arcing faults, this means that the AFDD will only trip first if the fault current increases slowly, which is often the case. In the event of a ground fault, the residual current circuit breaker trips faster. In the event of a short circuit, the miniature circuit breaker is only more likely to trip if the fault current increases very quickly to high values.

electronics

AFDDs have active components that are supplied with power via an integrated power supply unit. They are equipped with two main detection stages to detect low frequency (LF) and high frequency (HF) in a frequency band of 10 MHz in the line current . Using suitable algorithms, a microcontroller continuously analyzes the input signals of the two detection stages for unique characteristics that indicate the presence of an arc fault in the line. If an arc fault is detected, the microcontroller switches on an electronic trigger with a thyristor , which acts on the mechanics, triggers them and opens the main contacts.

According to the product standard VDE 0665-10 (IEC / EN 62606), an AFDD must be equipped with at least one test function in order to be able to check the function of the electronic circuit of the AFDD. This can include a test button, an internal self-test, or a combination. The test button acts on the integrated microcontroller, which generates an electronic signal which simulates the real properties of an arc fault and which must trigger the AFDD. An internal self-test monitors all electronic components such as analog circuits, peripheral devices or the memory. An error detected is indicated by a light-emitting diode without triggering the AFDD. If the electronics of an AFDD fail, the physical triggers against overload, short circuit and possibly fault current are still functional.

mechanics

The mechanical structure of an AFDD essentially corresponds to that of a line circuit breaker and consists of

  • a release lever that can be operated by the user and the electronic trigger,
  • a magnetic release to protect against short circuits and
  • a bimetal as overload protection

Regulations

Germany

In Germany, arc fault protection devices have been normatively anchored in the updated DIN VDE 0100-420 since February 2016. AFDDs have been compulsory since the end of the transition period on December 18, 2017, for various uses of space in new buildings or for system changes. This applies to final circuits with operating currents of up to 16 A if they supply bedrooms or common rooms in homes, day-care centers or barrier-free apartments in accordance with DIN 18040-2. The same applies to rooms / places with a particular fire risk (fire-endangered premises), rooms / places with flammable building materials and rooms / places at risk from irreplaceable goods. Use for all other final circuits with operating currents less than or equal to 16 A is recommended.

With the new edition of DIN VDE 0100-420 in October 2019, the areas of application for AFDDs were fundamentally revised. Until the end of the transition period on September 30, 2021, both the version from February 2016 and the current version of the standard from 2019 can be used for systems that are planned or under construction.

According to DIN VDE 0100-420: 2019-10, AFDDs are explicitly recommended in the following areas:

  • Rooms with sleeping accommodation
  • Rooms with an increased risk of explosion or fire according to the model building regulations (MBO)
  • Rooms made of building materials with lower fire resistance than F30 (according to DIN 4202-2)
  • If irreplaceable cultural assets are at risk (e.g. museums, national monuments, train stations, airports, archives, galleries, architectural monuments )

The limit to 16A of the final circuits is no longer applicable.

If the recommendation of the standard is not followed up, a risk analysis must be carried out during planning. If necessary, this reveals the risks from the effects of arcing faults. If risks are identified, structural, organizational or plant engineering measures can be taken. According to VDE 0100-420, the AFDD is a suitable system-technical measure. If at the time of the initial test, according to DIN VDE 0100-600, there is no risk and safety assessment, this must be listed as a defect.

For the evaluation of the legally binding nature of standards, reference is made to DIN.

Web links

Commons : Arc Fault Protectors  - Collection of images, videos and audio files

Individual evidence

  1. ↑ EN 62606: 2013 (IEC 62606 modified; VDE 0665-10: 2014-08) General requirements for arc fault protection devices
  2. ↑ Explanation of the regulation. (PDF; 3.5 MB) Retrieved May 25, 2012 .
  3. ^ A b John Brooks, Gary Scott: Arc-fault Circuit Interrupters For Aerospace Applications . Society of Automotive Engineers, 1999 ( John Brooks, Gary Scott: Arc-fault Circuit Interrupters For Aerospace Applications (PDF; 53 kB)).
  4. ↑ elektro.net from February 19, 2016
  5. ↑ DKE: DIN VDE 0100-420 (VDE 0100-420): 2019-10 . Ed .: VDE Verlag GmbH. Frankfurt am Main October 2019, p. 43 .
  6. ↑ ZVEH; ZVEI: Risk assessment according to DIN VDE 0100-420: 2019-10. December 2019, accessed April 28, 2020 .
  7. ↑ Dr. Thilo Schmidt: Legally binding standards. DIN, accessed on April 28, 2020 .