For AC-type RCCBs that are sensitive to sinus exciting currents, toroidal cores made of Permalloy-type materials are used for decades. The application of nanocrystalline alloy NANOPERM in RCCBs were limited to a region where the special annealing cycle leads to flat or round ferromagnetic hysteresis loop with a remanence ratio smaller than 0,7 with a maximum permeability less than 250,000. The actual trend – for technical as well as for cost reasons – is to make magnetic cores much smaller than their existing counterparts with extremely high permeability. This reveals a new generation of extremely small toroid soft-magnetic cores that can be used in AC-type RCCBs with the following exceptional properties:
- the magnetic core weight can be reduced down to 40 – 70 % compared to the Permalloy-type cores for similar applications
- the maximum permeability is at least 400,000 for typical applied maximum magnetic fields of Hmax = 7 – 20 mA/cm
- the output voltage ratio measured between magnetized and demagnetized states is at least 3 times better for small maximum magnetic field of Hmax = 4 mA/cm than for Permalloy-type cores
- the temperature variation of the permeability at the operational magnetic field is between 80 % and 120 % compared to room temperature (20±5 °C) for temperatures between –25 °C and +100 °C
- the remanence ratio is bigger than 0.7.