Power-interruption device uses new operating mode

November 03, 2015 // By Graham Prophet
Researchers in Korea claim to have overcome a long-standing technological limitation by fabricating the world's first “Mott” device that reduces the size and enhances the performance of traditional electromagnetic switches and circuit breakers.

The research team, led by Dr. Hyun-Tak Kim of Korea's Electronics and Telecommunications Research Institute, has developed an innovative power interruption technology based on a Mott metal-insulator transition (Mott MIT) device.

“Mott MIT” indicates the phenomenon that a Mott insulator is abruptly converted into a metal or vice versa without a structural phase transition. The research team previously developed a Mott MIT critical temperature switch (CTS) (or MIT device) which generates a control current (or signal) at a critical temperature between 67C and 85C as the unique characteristic of vanadium dioxide. Subsexquently, the MIT devices were applied to some kinds of electromagnetic switches that interrupt an electric current in case of overcurrent.

The equivalent traditional electromagnetic switch comprises a magnetic contactor, which connects or disconnects signals of main power, and a thermal overload relay with an on-off switching function controlled by temperature, usually via a bimetallic element. Westinghouse patented such a device in 1924. However, the bimetal undergoes a change of the bending characteristic over long-term usage and the accuracy of the overload relay drops. The performance of the electromagnetic switch also degrades.

The Korean research team uses the MIT-CTS instead of the bimetal as a sensor for the on-off switch, creating an electronic overload breaker that remains accurate, over temperature and over long-term use.

The research team confirmed that the developed MIT electromagnetic switch meets Korean published standards; and checked through experiments that a circuit breaker using the bimetal principle, operated below 1 kVac, can be replaced by MIT electromagnetic switching technology.

The part of the figure on the left figure shows the temperature dependence of resistance of the  Mott MIT VO2 device. and its photo. The right side exhibits the commercial overload relay and magnetic contact (electromagnet) and the (developed) electromagnetic switch.

ETRI; www.etri.re.kr/eng/main/main.etri