Analytic Computation of the Magnetizing Inductance of Current Instrument Transformers Under Consideration of Eddy Currents

The influence of eddy currents on the excitation winding impedance of solid and laminated salient pole synchronous machines

“…Nevertheless, in Dreyfus' work, the magnetic flux density does not result from the interaction between the exciting and the induced MMF, since the flux density distribution is a starting point in his analysis. More recently, Nethe [7] and Jäschke et al [8] have been able to determine the reflected impedance [9] of a winding wound on a ferromagnetic core by making use of very advanced analytical models. Both cited works investigate the subject approached by Dreyfus but from a different perspective.…”

“…In the present paper, a combination of the approaches of [6][7][8] is presented. By using some simplifying assumptions, the eddy current density and flux density in the salient pole rotor are first obtained as solutions of a differential problem as in [6].…”

“…By using some simplifying assumptions, the eddy current density and flux density in the salient pole rotor are first obtained as solutions of a differential problem as in [6]. Said solutions are then related to the main geometric dimensions of the electrical machine as in [7,8], in order to evaluate the AC-resistance and inductance of the excitation winding. Resistance and inductance determined by that way show their dependency on frequency enabling the correlation of their cut-off frequencies with the crosssectional shape of the rotor magnetic circuit and the thickness of its eventually laminated steel.…”

An experimentally determined field winding model with frequency‐dependent parameters

“…Table 8 shows that the values of L p and L' p decrease while the frequency increases. This is due to the degaussing effect of the eddy currents in the solid poles mainly [30–33] and to the skin‐ and proximity‐effect in the winding secondarily. In order to catch how strongly the winding inductance and the frequency are negatively correlated, the following simple inductance law has been introduced where K and γ are constants to be found using the inductance values corresponding to the series resonance frequencies.…”

“…According to the literature, the most used circuits models for studying transients in electric circuits are based on Transmission Line Model (TLM) or Lumped Element Model (LEM) [25][26][27]. Some models assume the circuit parameters to be constant [28,29] even though the winding resistance and inductance show a strong dependence on frequency [30][31][32][33]. Other models assume a constant wave propagation speed in the windings, resulting in an easy extraction of the inductance values from the winding capacitances [24,34].…”