Standalone hybrid systems based on renewable energy sources may represent a convenient and cost effective option for powering isolated consumers located far from the existing grid. In this study the focus is on particular photovoltaic-wind-diesel-battery systems which supply mobile telephony base stations. In the study, both the consumption of telecommunication electronic equipment and the consumption of cooling devices are taken into account. Nine characteristic locations across Europe with different climatic conditions were selected for comparative techno-economic assessment. For each location, a comprehensive simulation and optimization routine was performed, in order to find the optimal system configuration and the minimum amount of total annualized costs. The obtained results are discussed and some conclusions regarding system sizing at different locations are drawn.

In contemporary electrical power systems real-time power line monitoring and supervision are commonly performed using simple non-invasive devices with contactless magnetic field measurement. Measured magnetic fields are commonly employed for fault detection in fault passage indicators, but they can also be used to determine electrical and non-electrical power line variables. In this paper a novel adaptive method for conductor sag estimation is proposed, using magnetic field measurement. The method is based on the properly calibrated approximate power line magnetic field model, in which catenary-shaped conductors are modeled by tilted straight-line conductors of infinite length. By this approximation, the overhead power line model can be used in simple devices for power line monitoring in real-time. Applicability and accuracy of the proposed method for power line conductor sag estimation is verified by computer simulations and measurements on a three-phase overhead line model, scaled to laboratory conditions.

In recent years, the number of requests for connection of PV systems to the medium voltage distribution network has been significantly increasing. In order to approve a connection, it is necessary to comprehensively consider the integration impacts on the grid. In this paper, a two-step quasi-dynamic network simulation in DIgSILENT PowerFactory automated by Python scripting is proposed. In the first step, based on statistics of meteorological parameters and consumer load profiles, long-term hourly sequences of PV system power production and load of all consumers were artificially generated. In the second step, a Monte Carlo simulation applied to IEEE 33-bus system with an integrated PV system was performed. As illustrative results, the voltage profile and active power losses are shown and discussed.

This paper presents a laboratory setup for testing and experimental verification of fault detection methods based on contactless measurement of power line magnetic field. The setup consists of a physical power line model scaled to laboratory conditions with two orthogonal measuring coils installed on one support pole underneath phase conductors. Voltages induced in the coils are amplified and filtered out by using analog electrical circuits and are fed to a digital data acquisition board. The sampled voltages are digitally processed by employing a generalized fault detection method previously developed by the authors. In this paper the main steps for designing the measuring coils, analog amplifying and filtering circuits are described in detail. The developed laboratory setup is verified by experiments for different shunt and series faults.

Optimal sizing of standalone hybrid renewable power supply for mobile telephony base stations is considered in this paper. This task is very complex due to stochastic nature of input variables such as wind speed, solar irradiance, ambient temperature and electric load. Further concern is modeling of the power consumed by cooling devices which is also uncertain variable dependent both on ambient conditions and power dissipation of telecommunication equipment. The realistic behavior of the station both in electrical and thermal terms can be analyzed only by a comprehensive probabilistic simulator. The basic idea of this paper is to systematically vary the main input parameters (rated powers of wind turbine and photovoltaic system along with battery capacity) and to run a Monte Carlo simulation for each considered variant observing the technical and economic indicators. Based on the minimum annual costs, it is possible to choose the best available investment solution. Simple optimization can be extended to multi-objective by adding some additional goals, such as minimizing the operating time of a diesel backup generator. The optimization method is tested on an illustrative example of a base station located in the Mediterranean area.

Bifacial photovoltaic modules have gained increasing attention in the last decade due to their potential to achieve higher annual energy yield in comparison to conventional monofacial modules. Since the higher energy production is also accompanied by higher investment costs, it is necessary to conduct a careful techno-economic analysis in order to provide the investors an answer about their accurate cost efficiency. The achievable energy output of a bifacial photovoltaic power plant is influenced by many factors such as module geometry, row spacing, orientation of the modules and ground albedo. Since the methodology for prediction of the energy yield has not yet been standardized, the main target of this paper was to create one version of a comprehensive standalone energy calculator that would serve as a useful performance assessment tool for designers and investors. The developed software tool was tested on several characteristic scenarios and the obtained results were compared with the results provided by two freely available online calculators.

This paper discusses the problem of powering a remote rural mobile base station using a standalone hybrid renewable energy system. A wind turbine and photovoltaic system are employed as the complementary power generation technologies, while the diesel generator serves as a backup power supply. A battery is required to reduce the impact of intermittency of renewable sources. On the consumption side, along with telecommunication electronic equipment, the consumption of cooling devices as a result of the ambient temperature, is also taken into account. The behavior of the base station in electrical and thermal terms is tested using the sequential Monte Carlo simulation. Adequate models have been used to generate wind, irradiance, and temperature input series, using the monthly averages for calibration, as the statistic information that is widely available in meteorological atlases, even for remote rural locations. The developed software provides all the variables of interest either in the form of chronological diagrams or probability histograms. The simulation platform can also be incorporated as a module of an algorithm for selection of optimal capacity of the generating system elements and for the optimal control of the cooling devices.

Noninvasive contactless methods for electric power line monitoring based on magnetic field measurement have become an interesting topic for researchers and the electric power industry since introduction of the Smart Grid concept. By measuring and analyzing magnetic field originating from currents in power line conductors, it is possible to detect faults in the network. In medium voltage distribution networks, where a variety of different pole geometries are present, different criteria for fault detection have to be employed for each geometry, which complicates detection and influences accuracy. This paper proposes a novel approach for fault detection in medium voltage distribution networks which is based on processing of signals measured by low cost contactless magnetic field sensors. In order to create a generalized method for fault detection, a sequence of mathematical transformations of the measured magnetic field components is applied. A novel geometric transformation which eliminates influence of pole geometry is introduced, providing signals from which steady-state symmetrical components of the rotating magnetic field are computed. Those components are used as general fault detection criteria. The proposed approach is confirmed to be applicable for different fault types by a set of experiments on three-phase overhead power line model scaled to laboratory conditions.

- The paper gives an overview of methods for efficiency optimization in electric drives. A historical overview of these method is given and in a more detailed actual trends are described through presented control models, simulation and experimental results. Possible directions for further research and the challenges in this field are also given in the paper.