At Nuremberg’s transport authority, VAG Verkehrs-Aktiengesellschaft, passengers are the main focus. In addition to buses and trams, the local transportation authority ensures operations of three main subway lines and two auxiliary lines. The subway system is 36 kilometers long and is frequented by an average of 322,000 passengers daily. This presents more than just logistical challenges. As the provider of public transportation, VAG is also responsible for the safety of the passengers. That is why as part of the modernization of the subway stations, the electrical systems were also refurbished – and updated to the latest safety standard by the 5SM6 AFD unit.
VAG was particularly focused on fire prevention. And here the electrical installation plays a key role: So-called serial arcing faults in electric cables are among the most frequent causes of fires. They can occur due to damaged cable insulation or crushed cables, for example, thus leading to fires. Standard protective devices such as RCCBs and miniature circuit breakers, however, are not capable of detecting serial arcing faults. This gap in protection is covered by AFD units. These devices have been required in North America for years. With the 5SM6 AFD unit, Siemens has been one of the first manufacturers to introduce this technology into the IEC market. In the meantime, the standards in Europe have also been evolving. According to IEC 60364-4-42, since 2014 it has been urgently recommended to install AFD units in particularly high-risk areas.
Detection of unwanted arcing faultsAs early as in the planning phase, the City of Nuremberg received a test version of the 5SM6 AFD units from Siemens, which was initially tested along the U2 line. It quickly became clear that the AFD units would become part of the tender for the refurbishing of the stations. In the subway stations remodeled thus far, there are a total of twelve arc fault detection devices, each monitoring its own circuit. The arc fault detection device is driven by Siemens SIARC technology: The device constantly monitors current values and high frequency (HF) noise. The integrated micro-controller detects unwanted arcing faults – and in doing so, can differentiate between harmless sources of interference and hazardous arcs. If an unwanted arcing fault occurs, the AFD unit safely shuts down the circuit. It is not necessary to maintain the arc fault detection device. The integrated self-test function continuously monitors its functionality. Thus in conjunction with a RCBO combination, it provides the perfect all-round protection for persons, plants and assets.
They reliably detect hazardous arcing faults that can occur due to damaged cables. Already today, the devices are considered “generally accepted principles of engineering“ for high-risk areas. The City of Nuremberg relies on the devices to provide all-round protection for people and equipment.