Optimal passive filter design for effective utilization of cables and transformers under non-sinusoidal conditions

Transformers and cables have overheating and reduced loading capabilities under non-sinusoidal conditions due to the fact that their losses increases with not only rms value but also frequency of the load current. In this paper, it is aimed to employ passive filters for effective utilization of the cables and transformers in the harmonically contaminated power systems. To attain this goal, an optimal passive filter design approach is provided to maximize the power factor definition, which takes into account frequency-dependent losses of the power transmission and distribution equipment, under non-sinusoidal conditions. The obtained simulation results show that the proposed approach has a considerable advantage on the reduction of the total transmission loss and the transformer loading capability under non-sinusoidal conditions when compared to the traditional optimal filter design approach, which aims to maximize classical power factor definition. On the other hand, for the simulated system cases, both approaches lead to almost the same current carrying (or loading) capability value of the cables.

I. Introduction

Present day's power systems invariably have nonlinear loads, which inject harmonics into the system and give rise to nonsinusoidal voltages and currents. Accordingly, in the literature, considerable interests have been focused on the adverse effects of the harmonics on the power distribution equipment such as cables [1] [4] and transformers [5] [9]. These studies reveal that the resistances of the cables and the winding resistances of the transformers increase with the frequency. Due to this, cables and transformers have excessive losses under distorted (or non-sinusoidal) current conditions even if the rms values of the distorted currents delivered by them are lower than their sinusoidal rated currents. As a result, the distorted currents cause the reduction of the useful life of transformers and cables.