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RESIDUAL CURRENT OPERATED CIRCUIT-BREAKER`S DEVELOPMENT: A CLASSICAL CHALLENGE FOR HIGHTECH MAGNETIC MATERIALS

VAC has pioneered the application of magnetic cores for Residual Current operated Circuit-Breakers (RCCB) for personal protection. For more than three decades now, VAC has been the market leader in Europe for RCCB cores.

Hardly any other application for soft magnetic cores has driven the development of Crystalline Nickel-Iron (NiFe) materials towards higher and higher permeabilities.

In recent years VAC's development of the rapid solidified nanocrystalline material VITROPERM® resulted in an even further advancement of RCCB technology. Cores from VITROPERM allowed RCCB devices of unprecedented compact design due of their improved soft magnetic features.

Problems & Challenges

Residual Current operated Circuit Breaker devices work by measuring the differential current between the complete number of conductors in an electrical circuit by a differential current transformer. In case of correct operation the differential current is normally equal to zero. A non-zero differential current is detected if a ground fault occurs, i.e. because of an unintended power pathway to ground. As soon as this ground current exceeds the preset threshold, the RCCD disconnects the circuit from the line voltage.

The state-of-the-art technology of the early RCCBs only required the disconnect threshold current to be 300 mA or higher. This 300mA threshold limit was effective to prevent fires and defects of the connected appliances.

The increasing number of accidents through contact with electrical devices fueled the demand for achieving higher sensitivities in RCCBs, so that the disconnect threshold could be set to 30mA or lower to protect human life. However, the standard in most European countries called for purely passive solutions, which were intended to merely avoid the use of an unreliable semiconductor component or line dependent power supplies. The power for the threshold disconnecting action had to be fed only by magnetic induction caused by the ground fault current. At that time, the sensitivity limitation resulted from a limited choice of core materials that were available for differential transformers.

A Schematic Drawing of a Passive Alternative Current Ground Fault Circuit Interrupter.

Last update: 03.12.2012

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