S. Ž. Djokić

International Industry Practice on Power System Load Modeling

Power system load modeling is a mature and generally well researched area which, as many other in electrical power engineering at the present time, is going through a period of renewed interest in both industry and academia. This interest is fueled by the appearance of new non-conventional types of loads (power electronic-based, or interfaced through power electronics) and requirements to operate modern electric power systems with increased penetration of non-conventional and mostly intermittent types of generation in a safe and secure manner. As a response to this renewed interest, in February 2010 CIGRE established working group C4.605: “Modelling and aggregation of loads in flexible power networks”. One of the first tasks of the working group was to identify current international industry practice on load modeling for static and dynamic power system studies. For that purpose, a questionnaire was developed and distributed during the summer/autumn of 2010 to more than 160 utilities and system operators in over 50 countries on five continents. This paper summarizes some of the key findings from about 100 responses to the questionnaire received by September 2011 and identifies prevalent types of load models used as well as typical values of their parameters.

Performance Assessment of Micro and Small-Scale Wind Turbines in Urban Areas

This paper addresses some general issues related to the difficulties and uncertainties during the assessment and characterization of micro and small-scale wind-based generation in urban areas. This paper proposes four generic wind turbine models, which could be used for the analysis and selection of optimal wind turbines in target applications, as they accurately represent the range of wind turbines currently available on the market. The analysis in this paper compares results for the expected annual energy outputs and cost-benefit analysis obtained using steady state and dynamic wind turbine models of actual and generic micro/small wind turbines, applying both low-resolution and high-resolution measurements of available wind energy resources. The presented results demonstrate the significance of the accurate assessment of wind resources in urban areas, as well as the importance of the correct modeling of wind turbine characteristics. It is shown that substantial errors, typically overestimating wind turbine performance, are obtained if standard assumptions and current recommendations are used for the analysis of wind turbine performance.

Harmonic cancellation of modern switch-mode power supply load

Switch-mode power supplies (SMPS) are one of the most common category of loads, typically found in large numbers in modern power supply systems. These devices usually draw non-linear current and are, therefore, significant sources of harmonics. Although it is well known that the presence of harmonics will result in negative effects (e.g. higher thermal stresses and overloading, or increased neutral conductor currents), the assessment of the actual harmonic levels is not a simple task.

Power Quality and Compatibility Levels: A General Approach

This paper proposes a simple and consistent generalisation of a widely used concept of electromagnetic compatibility. In the paper, only two general conditions/stages for both power supply system and electrical equipment connected to it are used for the description and quantification of possible interactions between them. Different power quality disturbances are discussed, as well as situations in which equipment has a multiplicity of malfunction criteria. The subject is analysed from the equipment point of view.