Selcuk Sakar

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.

Optimal design of single-tuned passive filters using Response Surface Methodology

This paper presents an approach based on Response Surface Methodology (RSM) to find the optimal parameters of the single-tuned passive filters for harmonic mitigation. The main advantages of RSM can be underlined as easy implementation and effective computation. Using RSM, the single-tuned harmonic filter is designed to minimize voltage total harmonic distortion (THDV) and current total harmonic distortion (THDI). Power factor (PF) is also incorporated in the design procedure as a constraint. To show the validity of the proposed approach, RSM and Classical Direct Search (Grid Search) methods are evaluated for a typical industrial power system.

Hosting capacity assessment and improvement for photovoltaic-based distributed generation in distorted distribution networks

In this paper, the hosting (or maximum allowable) capacity of a photovoltaic (PV)-based distributed generation (DG) unit for a typical two bus distorted distribution system, is analyzed. The harmonic constraints, total and individual harmonic distortion limits stated in IEEE Standard 519, and the conventional hosting capacity constraints, bus rms voltage limit and the current carrying capability limit of the supply cables are taken into account. In the analysis, various simulations are carried out to show the effect of the nonlinearity degrees of the loads on the systems hosting capacity. It is clearly seen from the analysis results that the harmonic distortion limits significantly constrain the PV-based DG unit hosting capacity for the higher nonlinearity levels of the consumer. Accordingly, a C-type filter is designed to maximize the hosting capability of the studied system while providing desired power factor and satisfying the harmonic and conventional hosting capacity constraints. Besides, the numerical results are given to point out that a higher allowable hosting capacity is obtained with the proposed filter design approach compared to two traditional filter design approaches, which aims to attain minimization of voltage total harmonic distortion and minimization of current total demand distortion by considering the same constraints of the proposed approach. It is found that passive filters, already planned in the original system, helps in improving the PV-based DG hosting capacity of distribution feeder.

On the no-load loss of power transformers under voltages with sub-harmonics

Power transformers are traditionally designed for their utilization in sinusoidal voltage and current conditions. However, the non-linear loads are largely proliferated in the modern power systems. Thus, pec (point of common coupling) voltages and line currents usually have harmonically distorted or non-sinusoidal waveshapes. This study focuses on the parametrical analysis of transformer no-load loss under the excitation voltage with several sub-harmonic contents. For this aim, a computationally efficient technique is developed by combining both the harmonic-domain model of transformer windings and Finite Element Method (FEM) based modeling of transformer core. The obtained simulation results figured out that effect of sub-harmonic voltages on the transformer core loss is negligible. However, it is also seen that small amount of sub-harmonic voltages may highly contribute the winding loss under the no-load condition, and they should carefully be handled for the derating of power transformers.

A filter design approach to maximize ampacity of cables in nonsinusoidal power systems

This paper presents an optimal design of the C-type passive filters for the effective utilization of the power cables under nonsinusoidal conditions based on maximization of the harmonic derating factor (HDF) of a power cable, where maintaining the load true power factor at an acceptable range is desired. According to IEEE Standard 519, the total harmonic distortions of the voltage and current measured at the point of common coupling are taken into account as main constraints of the proposed approach. The presented numerical results show that the proposed approach provides higher current carrying capacity, or ampacity of the cables under nonsinusoidal conditions when compared to the traditional approaches based on minimization of the current total harmonic distortion and maximization of the true load power factor. A numerical case study is presented to demonstrate the proposed approach.