An algorithm is presented for the computation of the saturation characteristics of transformer iron cores based on supplied conventional V/sub rms/-I/sub rms/ curves and no-load losses at rated frequency. Laboratory measurements on a steel sample were carried out. It is shown that the iron core losses are a nonlinear function of the applied voltage. Taking these losses into account improves the nonlinear flux-current characteristics. >

On modelling iron core nonlinearities

A rational function approximation for magnetization curves and hysteresis loops is presented. This approximation leads to Rayleigh relations and the law of approach to saturation as limit forms. Furthermore, the magnetic permeability and the magnetic energy density is computed. Finally, this analysis is applied to commercial ferrite cores and pure ceramic samples.

Simple approximation for magnetization curves and hysteresis loops

In this thesis a general purpose transformer model for low and medium frequency transient studies is developed and verified. The inrush current phenomena during no-load energization of power transf ...

Power Transformer Modeling for Inrush Current Calculation

An algorithm is described for the computation of the saturation characteristics of three-phase delta-connected transformers from measured V/sub rms/-I/sub rms/ curves and no-load losses at rated frequency. For these transformers, positive sequence excitation tests are usually carried out with the delta connection closed. While triplen harmonic currents are present in the delta-connected windings, they do not appear in the line connections to the three-phase source. This paper presents an algorithm which accounts for the missing triplen harmonics on the line side in the derivation of the saturation characteristics. >

Saturation curves of delta-connected transformers from measurements

This paper investigates the effect of supply voltage harmonics on the excitation current of a typical 25 kVA single-phase distribution transformer. A complete analytical model is developed to calculate the time domain waveform and the harmonic components of the excitation current. The key findings are: the phase angles of the supply voltage harmonics determine whether or not those voltage harmonics increase or decrease the distortion of the input current (with respect to the sinusoidal supply voltage case). A peaked input voltage wave distorted by 3rd, 7th, 11th, etc. harmonic components, or a flattened input voltage wave distorted by 5th, 9th, 13th, etc. harmonics, creates a flattened current (i.e., decreases the current harmonics and distortion). A flattened input voltage wave distorted by 3rd, 7th, 11th, etc. harmonic components, or a peaked input voltage wave distorted by 5th, 9th, 13th, etc. harmonics, creates a peaked current (i.e., increases the current harmonics and distortion): The 3rd harmonic component in the supply voltage has the highest effect on the current harmonics and distortion. The effect of higher voltage harmonics gradually diminishes with frequency. The magnitudes of the individual current harmonics follow the same decreasing/increasing pattern of changes as does current distortion variation. The corresponding variations in harmonic current phase angles is negligible.

An investigation of the harmonic characteristics of transformer excitation current under nonsinusoidal supply voltage

An analytical technique has been suggested for predetermination of true saturation characteristic of transformers and reactors from the manufacturer data giving the conventional rms saturation characteristic. The method has some advantages over that suggested by Talukdar et al.

M. Rao

Papers

A direct piecewise linearized approach to convert rms saturation characteristic to instantaneous saturation curve