This paper presents the preliminary sizing of a High Temperature (HT°) induction motor based on a copper cage rotor and a distributed winding built with an inorganic Electric Insulation System (EIS) able to withstand 500°C. The specific part of the design derives of the poor mechanical and electrical characteristics of the inorganic HT° insulation materials. HT° wires are protected by a cement and form rigid coils. The laminated magnetic core has a specific design for suiting with the rigid coils. An Electrical and thermal models are validated.

Most of electrical machines are wound with enameled copper wires insulated by a thin polymer layer, which has excellent mechanical and insulation properties. However, the organic nature of these insulating layers limit their operating temperatures to more or less 280° C for the best polymers. It is possible to operate at much higher internal temperatures with an inorganic Electrical Insulation System (EIS) made without any polymer. Unfortunately, the available inorganic wires made with a thin ceramic insulating layer have poor electrical and mechanical performances. Therefore, the design of High Temperature (HT ° ) coils, able to work with standard PWM inverters is more difficult. The paper presents a method for computing the voltage spikes that follow each voltage fast edge with a high frequency (HF) equivalent circuits.

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.

Le papier presente les problematiques et les solutions adoptees pour construire le premier prototype d'un moteur electrique tres compact dote de bobinages inorganiques capables de travailler en permanence a une temperature interne de l'ordre de 500°C. L'analyse des verrous technologiques qui empechent de faire des machines tres compactes a fort gradient de temperature interne montre que le principal verrou technologique est lie a la nature organique du Systeme d'Isolation Electrique (SIE). Le prototype de machine synchrone est construit autour de bobines inorganiques rigides montees sur les dents du stator. Ces bobines, testees a 500°C sont capables de resister aux surtensions provoquees par les fronts raides des convertisseurs MLI actuels.

The increase of internal temperature capability of electrical machines is a major challenge for building high power density actuators for many applications in transport systems and in aerospace industry. Today, the main limit is the thermal class of the organic Electrical Insulation System (EIS), but a breakthrough toward very high temperature is possible with inorganic insulation technologies. An inorganic EIS is proposed and tested for designing motors able to work permanently up to 500 degrees C in the heart of windings. After a review of several high temperature (HT degrees) insulation solutions, the paper focuses on currently available ceramic-coated wires insulated with a very thin inorganic layer, which is a favorable solution for high current densities in machines of small sizes. The electrical limits of this technology are investigated, the weak points of the HT degrees wire are circumvented using impregnating cements able to provide adequate mechanical and electrical properties up to 500 degrees C for designing HT degrees electrical machines fed by a standard PWM inverter connected to the HVDC bus of the more electric aircraft, for example.

The paper deals with the general choices made for designing and testing the prototype of a coil able to fulfill the functions required by a Permanent Magnet Synchronous Machine able to work permanently at high internal temperatures, up to 500°C. The specific physical problems are listed and analyzed. The main challenge consists in defining High Temperature (HT°) inorganic coils built without any polymer. The proposed coils are based on a wire insulated by a thin ceramic coating protected by a HT° cement, which gives the appropriate mechanical properties up to 500°C. The deterministic arrangement of the turns compensates weak electrical properties of the turn-to-turn insulation.

The paper deals with the general choices and the sizing problematics of a prototype of a permanent magnet synchronous machine able to work permanently at high internal temperatures, up to 500° C. The specific physical problems are listed and analyzed. The first challenge consists in defining and testing High Temperature (HT°) inorganic coils, built without any polymer. The chosen materials are able to withstand permanently such high temperatures but they have poor mechanical properties. The proposed Electrical Insulation System (EIS) is based on a thin ceramic coating for the wire and a HT ° cement for protecting the brittle ceramic insulation layer between the turns. The second challenge consists in defining the stator core and the magnets that corresponds to the HT ° inorganic rigid coils that must be built separately. Comparing to the usual approach, the design process is reversed: the magnetic circuit must be designed according to the characteristics of the HT ° coils.

The more electric aircrafts require high specific power motors; on the other hand, the design must guarantee long lifetimes. Therefore, most of these motors are synchronous machines, working at high frequencies and made with a large number of coils placed on stator teeth. The Electrical Insulation System (EIS) must be designed for supporting repetitive voltage spikes imposed by modern PWM inverters. Today, most of inverters are built with standard silicon IGBT but, in the near future, faster electronic switches based on silicon-carbide will be used. Consequently the voltage slopes imposed to the motor winding will be much steeper. The paper proposes a method based on equivalent circuits able to predict the voltage spikes distribution in each coil of the motor during the fast transients that follow fast voltage fronts.

Ceramic-insulated wires have very good thermal characteristics. With an adapted motor design, such inorganic wires could be used for building new electric motors able to work at very high internal temperatures, up to 500°C, which opens interesting perspectives for very high power density electric motors. After explaining the advantages of high internal temperatures, electrical characteristics of inorganic coils are compared to conventional enameled wires associated with a polymer impregnation. For classical organic wire, the Partial Discharge Inception Voltage (PDIV) is an important parameter; for ceramic wires, physical phenomena are very different and this concept is not still completely defined. However, the tests performed on ceramic-coated wires show that fast current pulses appears for voltages over a threshold measured for temperatures up to 500°C. This threshold voltage is an interesting indicator for inorganic coil designs: the turn-to-turn voltage must remain below this threshold at any point of the coil.