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Method of Arc Suppression for Mechanically Operated Switches

IP.com Disclosure Number: IPCOM000187264D
Published in the IP.com Journal: Volume 9 Issue 9B (2009-09-25)
Included in the Prior Art Database: 2009-Sep-25
Document File: 4 page(s) / 138K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

Mechanical switches are widely used to control the flow of the current in electrical circuits. Their main constituents are the electrical contacts which will be opened ore closed mechanically. The major challenge by the improvement of these switches is the increasing of their breaking capacity without increasing their size. During switching operations especially in high current applications electric arcs can occur. Consequently the contact surfaces ablates caused by high temperatures, which melts or vaporizes particles out of the contact material. Thus, electric arc is the major challenge for any attempt to improve the breaking capacity of a mechanical switch. The rated current and voltage of a switch is the current and voltage that can be interrupted by typical mechanical contacts safely. The shaded area in figure 1 represents this safe operating region for all currents and voltages encountered during breaking.

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Method of Arc Suppression for Mechanically Operated Switches

Idea: Yi Rong Yang, CN-Shanghai; Zhaohui Du, Ph.D., CN-Shanghai; Jian Guo Ma, CN-Shanghai;
Stefan Cordes, DE-Amberg

Mechanical switches are widely used to control the flow of the current in electrical circuits. Their main constituents are the electrical contacts which will be opened ore closed mechanically. The major challenge by the improvement of these switches is the increasing of their breaking capacity without increasing their size. During switching operations especially in high current applications electric arcs can occur. Consequently the contact surfaces ablates caused by high temperatures, which melts or vaporizes particles out of the contact material. Thus, electric arc is the major challenge for any attempt to improve the breaking capacity of a mechanical switch. The rated current and voltage of a switch is the current and voltage that can be interrupted by typical mechanical contacts safely. The shaded area in figure 1 represents this safe operating region for all currents and voltages encountered during breaking.

There are two main approaches of handling the arc problem. At the one side the use of expensive contact materials like silver alloy which has a lower resistance and at the other side the reduction of high currents which has to be switched. The latter approach is often realized by using PTC resistors (PTC: Positive Temperature Coefficient) which provides a safe operating region at high current levels. PTC devices are popular current limiters because they increase their electrical resistance if their own temperature rises. That heating can be caused by the ambient temperature surrounding the individual device but also by self heating which is again caused by the running current. Figure 2 shows a combination of the rated current and voltage of one specific mechanical contact. Whereas the shaded area OABCD depicts the rated range in which the contacts can resist arc. The area framed with EFG is the region in which the current and voltage are able to trip the PTC device within a fixed time period at room temperature. A PTC device can therefore be employed to suppress the arc occurring in this additional region. However, there is still an area between area OABCD and EFG that is vulnerable to arc. Moreover, the PTC working region EFG changes with the ambient temperature. The working region EMN relates to low ambient temperature and region EPQ to high temperature. The applications which use such devices are for example a combination of sequential breaking and PTC current limiter or for extinguishing the arc in low voltage switches. A drawback of PTC devices is the need of lot of thermal energy to get to the high resistance state which is depending on the running current, the applied voltage, the trip time, and the thermal dissipation. Als...