High Temperature (HT°) motor coils open new perspectives for extending the applications of electrical motors or generators to very harsh environments or for designing very high power density machines working with high internal temperature gradients. Over a temperature of 300°C, the classic enameled wire cannot work permanently, the turn-to-turn insulation must be inorganic and made with high temperature textiles or vitro-ceramic compounds. For both cases, a diffusion barrier must protect the copper wire against oxidation. The usual solution consists of adding a nickel layer that yields an excellent chemical protection. Unfortunately, the nickel has ferromagnetic properties that change a lot the skin effect in the HT wire at high frequencies. For many applications such as aeronautics, electrical machines are always associated with PWM inverters for their control. The windings must resist to high voltage short spikes caused by the fast fronted pulses imposed by the feeding inverter. The nickel protection layer of the HT° inorganic wire has a large influence on the high frequency behavior of coils and, consequently, on the magnitude of the voltage spikes. A good knowledge of the non-linear magnetic characteristics of this nickel layer is helpful for designing reliable HT inorganic coils. The paper presents a method able to characterize non-linear electromagnetic properties of this nickel layer up to 500°C.
 Aymonino F., Lebey T., Malec D., Petit C., Michel J., Anton A., Gimenez A., Degradation and dielectrics measurements of rotating machines insulation at high temperature (200-400EC), IEEE International Conference on Solid Dielectrics, July 2007, pp. 130-133 (2007).
 Hooker M., Hazelton C., Kano K., Tupper M., High-temperature electrical insulation for EGS downhole equipment, Thirty-Fifth Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, California (2010).
 Iosif V., Roger D., Duchesne S., Magnetic characterization of the nickel protection layer of wires used for high temperature motors, XXIV Symposium on Electromagnetic Phenomenon and Nonlinear Circuits (EPNC), Helsinki (2016).
 Iosif V., Roger D., Takorabet N., Duchesne S., Meibody-Tabar F., Technological assessments for designing machines able to work at very high internal temperatures (450-500EC), International Conference on Electrical Machines (ICEM), Lausanne (2016).
 Zaimovski A., On the temperature dependence of magnetic permeability in weak fields, Journal of Physics (1941).
 Néel L., Propriétés magnétiques du nickel pur a proximité du point de curie, Société Française de physique (1933).
 Iosif V., Roger D., Duchesne S., Malec D., Assessment and improvements of inorganic insulation for high temperature low voltage motors, IEEE Transactions on Dielectrics and Electrical Insulation, vol. 23, no. 5, pp. 2534-2542 (2016).
 Iosif V., Duchesne S., Roger D., Voltage stress predetermination for long-life designof windings for electric actuators in aircrafts, IEEE - Annual Report Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), Ann Arbor, pp. 319-321 (2015).