Although their basic design remains unchanged, today’s electric motors are more sophisticated when it comes to numerous technical details. This includes the electrical steel strip used, which largely determines the motor’s performance and efficiency. Extremely thin, high-performance grades are in high demand for this application. In terms of efficient use in the stator of the electric drive of a battery-powered car, the NO 20 grade has proven to be an excellent option for electric vehicles.
There are many arguments in favor of using particularly thin electrical steel strip grades in the drive systems of electrified automobiles – a compact design, for example. There is usually only limited space available for the electric motor, and this is particularly true in hybrid vehicles, where the unit is located between the combustion engine and the transmission or is integrated into the belt drive instead of the starter.
At the same time, however, the thin steel strip must be extremely strong in order to withstand the centrifugal forces at speeds of up to 20,000 rpm. Norbert Brachthäuser, responsible for the special product electrical steel strip within Waelzholz’s Materials Technology Department, explains: “Even our thin NO 20 electrical steel strip grade, with a nominal thickness of only 0.20 millimeters (0.008 in), is produced in a high-strength version with a yield strength Rp 0.20 of 500 MPa (73 ksi) – while retaining its excellent electromagnetic properties. As a result, we can offer our customers the assurance that the material will reliably withstand the forces applied to it, including in high-stress applications such as thin bars or rotor teeth.”
And most importantly, the thickness of the electrical steel strip has a major effect on the electric motor’s performance and efficiency. This is primarily related to an effect known as core loss. When an electric motor is in operation, the polarity of the electric steel strip in the rotor changes at a very high frequency. According to electrical steel strip expert Brachthäuser: “When the magnetic field direction alternates, part of the supplied power is lost in the form of heat. These losses increase with increasing thickness of the electrical steel strip. So every hundredth of a millimeter that the material is thinner makes a difference.” As such, thin grades such as NO 20 consume less power, which in turn extends the range of battery electric vehicles.