Arc-fault circuit interrupter

Indicates a fault arc protection device, in the technical language and in English as Arc Fault Detection Device (abbreviated AFDD ) and in North America as Arc Fault Circuit Interrupter (abbreviated AFCI ) is a protective device in the electrical installation and is used in low voltage distribution systems. The device protects by automatically switching off electrical installations against damage from fault arc and the thermal consequences such as cable fires, which derives the term fire protection switch.

General

AFDDs be mounted in the field of distribution and can detect the consumer electric arcs in series and parallel to the consumer.

Arc in series with the consumer are characterized in that the normal operating current usually is not exceeded, as this is limited by the consumer, and therefore do not respond overcurrent protective device such as fuses or circuit breakers. The arc forms at a defect site of the lead, such as a loose cable clamp or a broken cable. Particularly at higher operating currents and when the arc long periods of time, high temperatures can occur at the fault location by the arc and the application of high current density with the risk of fire.

Arc faults parallel to the consumer are characterized in that adjacent electrical conductors erroneously get electrical contact and cause a short circuit, for example, according to a damage to the cable insulation. In this case, the current is generally higher than operating current, because the current is limited only by the arc and the loop impedance, and it also comes to an immediate tripping of the overcurrent protective device. Depending on the error, such as a ground fault in a parallel arc fault occurring at the consumer and the residual current device (RCD ) can trigger.

Fire Protection Switches for household installations are designed in Europe for 230 V and with a rated current of 16 A usual. In the North American region are used so-called Arc Fault Circuit Interrupter ( AFCI ). AFCIs are available on the U.S. market since the late 1990s and are required by the National Electrical Code (NEC - 2008) for the protection of all living rooms. Other applications lie in the field of avionics, and the power supply of electric components in aircraft.

Operation

To determine whether an arcing fault is present, both the voltage waveform and the current waveform to be measured over time and evaluated by means of digital signal processing from the AFDD. In particular, the current profile has during faults in a characteristic, high-frequency components. It must be noted in the evaluation that even regular fluctuations in the current course, but occurring in normal usage harmonics and transient current waveforms during the switching of consumers should not lead to an erroneous tripping.

In electric arcs in series to the consumer the current-time characteristic is in the range of one second to the area in 100 ms, which is below the trip limit of circuit breakers. In parallel arcing faults resulting from the current-time characteristic that the circuit breaker used in combination triggered even before the detection of the parallel arc fault currents due to the height.