Creating the inductance in the form of a coil, a more intense magnetic field is generated and introducing a solid core made of particular materials the intensity of the magnetic field is further increased. The factors affecting the value of the inductance are the number of turns of the coil and the magnetic permeability of the core.
Permeability (μ symbol, and Tesla units x metres//ampere-turns) is a term used to quantify the capacity of a material to become magnetized. An air core has a permeability value equal to 1 (one), while a soft iron core has a degree of permeability 600 times greater (approximate values).
The intensity of the magnetic field is the measure of the magnet-motive force (MMF) distributed over the length of an electromagnet (symbol H, and unit of measure ampere-turns/metre) and sometimes it is referred to with the name of magnetizing force. The intensity of the magnetic field determines the density of the magnetic flux (induction B and Tesla units).
H is obtained by determining the MMF and dividing it by the length of the material, while B is obtained by dividing the total flux Ø by the cross section of the material. By plotting the trend of B according to H it is possible to obtain a normal magnetization curve (also called a B-H curve) for each specific material. Fig.1 shows two magnetization curves of two different types of silicon steel.
Conventional inductive output reactors have an excellent accumulation capacity and extend motor life.
They reduce the slope of the dv/dt rising edge to earth and between the phases, reduce engine noise and level the current.
They act as a typical series inductance and level both the active symmetrical current and the asymmetrical interference current.
This solution attenuates the cable-conducted disturbances very well also in the lower frequency range. Electromagnetic radiation of the power line is attenuated to a significant degree. Losses and the typical noise of the ferromagnetic pack of the motor caused by harmonics are reduced. .
The diagrams below show the voltage jumps due to pulse-width modulation. With the inductive reactance for motors the maximum value of voltage and the voltage rise rate are clearly lower. In this way the isolation of the motor is protected.
For a correct dimensioning of this type of reactor in addition to the rated data it is also important to know the modulation frequency (PWM) and the percentage of ripples with respect to the nominal value.