Showing papers by "Matti Lehtonen published in 2017"

A Statistical Model for Hourly Large-Scale Wind and Photovoltaic Generation in New Locations

Abstract: The analysis of large-scale wind and photovoltaic (PV) energy generation is of vital importance in power systems, where their penetration is high. This paper presents a modular methodology to assess the power generation and volatility of a system consisting of both PV plants (PVPs) and wind power plants (WPPs) in new locations. The methodology is based on statistical modeling of PV and WPP locations with a vector autoregressive model, which takes into account both the temporal correlations in individual plants and the spatial correlations between the plants. The spatial correlations are linked through distances between the locations, which allow the methodology to be used to assess scenarios with PVPs and WPPs in multiple locations without actual measurement data. The methodology can be applied by the transmission and distribution system operators when analyzing the effects and feasibility of new PVPs and WPPs in system planning. The model is verified against hourly measured wind speed and solar irradiance data from Finland. A case study assessing the impact of the geographical distribution of the PVPs and WPPs on aggregate power generation and its variability is presented.

An Analysis of Photo-Voltaic Hosting Capacity in Finnish Low Voltage Distribution Networks

Abstract: The ascending trend of photo-voltaic (PV) utilization on a domestic scale in Finland, calls for a technical aspects review of low voltage (LV) networks. This work investigates the technical factors that limit the PV hosting capacity, in realistic case networks, designed relative to different geographical areas of Finland. A Monte Carlo method based analysis was performed, in order to quantify the hosting capacity of the formulated networks, with balanced and unbalanced feeds, in PV systems and their limiting constraints were evaluated. Finally, the effectiveness of on-load tap changer (OLTC) in increasing the PV penetration, when employed in the LV system, was investigated.

Planning to Equip the Power Distribution Networks with Automation System

Abstract: Implementing automation system in distribution networks needs a huge investment that usually cannot be funded entirely in a short period of time. So distribution companies (DISCOs) should develop long-term plans to equip their network with automation technologies as far as economically justifiable. Aiming to provide a methodology for development such plans, this paper presents a novel multistage planning model for implementing distribution automation system considering all main hardware and software infrastructures. The proposed method optimally determines the type, location, and time in which an equipment or infrastructure must be added to network considering the network capacity expansion plan. The objective function of the planning problem is to maximize the net present value of the DISCO's profit in the planning time horizon. In this method, the optimization problem is solved using the genetic algorithm approach as a promising technique in solving the mixed integer nonlinear programming problems. The proposed method is evaluated on an illustrative test network and the obtained results are presented and discussed.

Enhancement of dielectric and mechanical properties of Polyvinyl Chloride nanocomposites using functionalized TiO 2 nanoparticles

Abstract: The current study is to investigate the influence of inserting chemically modified titanium oxide (TiO 2 ) nanoparticles on the dielectric and mechanical properties of the commercial compound Polyvinyl Chloride (PVC) used in insulating power cables. The surface modification of TiO 2 nanoparticles was performed using vinyl silane coupling agent after activating their surfaces with methane-sulfonic acid. The PVC pellets were first dissolved using suitable solvent. Then, PVC/TiO 2 nanocomposites, with different loadings of nanoparticles, were synthesized with the aid of ultra-sonication for better dispersion of nanoparticles. The morphology of the prepared nanocomposites was studied by field emission scanning electron microscopy (FE-SEM), and their mechanical properties were studied by performing tensile test at speed of 50 mm/min. The results showed that the insertion of functionalized nanoparticles is able to increase the tensile strength and the Young's modulus of the prepared samples, however it decreases their elongation. The dielectric properties, such as dielectric constant and dielectric loss, were also studied in a range of frequencies between 20 Hz and 1 MHz. Moreover, AC breakdown voltage of prepared samples was measured under uniform and semi-uniform field, and then, AC dielectric strength was evaluated using Finite Element Method (FEM) for semi-uniform field. For further evaluation, DC breakdown voltage was also measured under uniform field. PVC/TiO 2 nanocomposites with functionalized TiO 2 exhibited better dielectric properties compared to that with un-functionalized TiO 2 or that of base PVC. This may be attributed to the low surface energy of the functionalized TiO 2 nanoparticles that prevented the agglomeration of nanoparticles and restricted the mobility of polymeric chains.

Thermoelectric applications for energy harvesting in domestic applications and micro-production units. Part I: Thermoelectric concepts, domestic boilers and biomass stoves

Abstract: This review aims to present a summary of the current state of art in applications incorporating thermoelectric generator (TEG) units. Description of components critical to TEG system analysis will be provided. Especially practical results available from testing of the experimental systems will be addressed. The review is split in 2 parts, with first part covering TEG fundamental operating principles and materials, the power electronic converters of the TEG loading system, with applications of domestic boilers and biomass stoves. Second part of the review will provide overview of the solar energy harvesting TEG applications.

Experimental measurements of partial discharge activity within LDPE/TiO2 nanocomposites

Abstract: The presence of impurities, voids or gas bubbles during the manufacturing process of insulating materials of power cables leads to electrical degradation in the form of partial discharges (PDs). This paper aims to investigate the influence of incorporated titanium dioxide (TiO 2 ) nanoparticles on the statistical parameters of PD activity within low density polyethylene (LDPE) matrix through using the solvent casting method. The surface morphology of synthesized LDPE/TiO 2 nanocomposites was characterized by field emission scanning electron microscopy (FE-SEM). Then, the internal discharge measurements were performed using the traditional needle-plane configuration with the help of phase resolved partial discharge analyzer (PRPDA). This technique is used to analyze the statistical characteristics and feature of PDs with respect to the phase angle of applied voltage. It is found that the PD activity of all LDPE/TiO 2 nanocomposite samples that represented by discharge magnitude, inception voltage, extinction voltage, and PD generation rate was enhanced compared to that of the pure LDPE. This was explained considering the effect of TiO2 nanoparticles in trapping process and initial electron generation inside the insulation material. Also, governing mechanisms for positive and negative cycle of PD activity were discussed.

Computation of Peak Lightning-Induced Voltages Due to the Typical First and Subsequent Strokes Considering High Ground Resistivity

Abstract: It is essential that the insulation system of the overhead distribution lines should be properly designed to ensure their immunity against lightning-induced overvoltages (LIOVs) caused by nearby return strokes. Therefore, accurate calculation of the peak values of LIOVs is important for the insulation design. In this paper, a formula is proposed to calculate the peak values of LIOVs for both first and subsequent strokes. The typical waveforms of the first and subsequent return strokes are adopted for this study considering a wide range of ground resistivity, from 0.25 to 20 k $\Omega $ m. The 2-D finite-difference time-domain method associated with the Agrawal coupling model is employed for the calculation of LIOVs. In addition, the effect of ground permittivity on the peak values of LIOVs is also investigated. Finally, the proposed formula is applied to calculate the annual number of flashovers per 100 km of the overhead line.

Effect of cumulative moisture content on degradation of transformer paper insulation

Abstract: Nowadays, reliability of power system is of great importance. Therefore, the condition of transformers as the expensive and critical components of a power system should be monitored and assessed. The dominant factor that causes limitation in transformers lifetime is the paper insulation. This paper aims to investigate the conspicuous influence of moisture content, especially in low oxygen and temperature on lifetime estimation under constant conditions, based on the results of previous experiments. Degree of polymerization (DP) is employed to quantify the effects of detrimental parameters with respect to their time-varying nature. This paper proposes a novel lifetime estimation-approach considering a yearly moisture growth for transformers. The results indicate different trend of DP profiles, which lead to an accurate lifetime estimation in comparison with DP obtained through ideal conditions. Furthermore, oscillations in the hot-spot temperature of transformers are demonstrated to have a negative effect on the lifetime.

Evaluation of Fault Levels and Power Supply Network Impedances in 230/400 V 50 Hz Generic Distribution Systems

Abstract: In this paper, typical strengths, fault levels, and source impedances are thoroughly analyzed and calculated for the study of quality of supply in 230/400 V 50 Hz distribution systems. Considering all the disparity in distribution network design, this study is based on a comprehensive database containing typical arrangements and equipment in U.K./European systems, as well as on fully documented generic network models supplying four residential load subsectors in the U.K., i.e., from metropolitan to rural areas. Thus, this paper proposes an alternative method for determining reference values of network supply impedances and short-circuit fault levels at different points and locations of the medium-to-low voltage distribution system. The aim of this study is to provide a wider range of benchmark values than those stipulated in the IEC 60725 Standard, which only defines a single-reference threshold of public supply impedances for all types of distribution systems and residential customers. In order to assist network operators in the planning and design of their distribution systems, these values are further disaggregated and classified in this paper according to network/demand type.

A novel 4-limb earth fault compensation reactor for distribution network

Abstract: Summary This paper presents a novel earth fault compensation solution, which presents high positive sequence impedance and magnetically controllable zero sequence impedance. A 4-limb reactor is introduced to compensate earth fault currents in three-phase power distribution networks without the need of neutral point in substation transformer or separate earthing transformer. This results in considerably lower costs in implementing earth fault current compensation with much faster operation, making it possible to tune for 100% compensation during fault thus improving the probability of arc suppression. The presented reactor is analyzed analytically, and its performance is validated by simulations. The presented solution can significantly improve the reliability of the supply network.

Mitigation of Lightning Flashover from Tree to Medium Voltage Aerial Cable Using Shield Wire

Abstract: This paper presents the performance and protection of medium-voltage (MV) aerial cables against lightning faults by means of laboratory experiment and digital modeling. With the series of laboratory tests, practical examination of lightning hazard to shielded and unshielded aerial cables is conducted, and the need for shield wire protection is established. For the purpose of simulation studies, digital models are developed by using Alternative Transient Program-Electromagnetic Transient Program (ATP-EMTP) and its transient analysis of control system features. The performance of lightning flashover overvoltage on shielded and unshielded aerial cable is evaluated with the developed digital models. The evaluation is made by considering a direct lightning strike on wooden poles, messenger wires, and nearby trees. Based on the experimental and simulation results, practical recommendations are proposed for improvement in lightning performance of aerial cables. This study offers possible solutions for the protection of aerial cables against lightning flashover, induced overvoltage, and direct lightning strike, which may improve electricity reliability and availability to customers.

Impacts of Natural Disasters on Swedish Electric Power Policy: A Case Study

Abstract: The future of climate and sustainable energy are interrelated. Speaking of one without mentioning the other is quite difficult. The increasing number of natural disasters pose a great threat to the electric power supply security in any part of the world. Sweden has been one of the countries that have suffered from unacceptably long blackouts. The tremendous outcomes of the power interruptions have made the field of the economic worth of electric power reliability a popular area of interest among researchers. Nature has been the number one enemy against the supply security of the electricity. This paper introduces a recent and thorough electric power reliability analysis of Sweden and focuses on the country’s struggle against climate change-related natural disasters via updating the country’s electric power policy to improve its service quality. The paper highlights the Gudrun storm of 2005 as a case study to demonstrate the severe impacts of extreme weather events on the energy systems. The economic damage of the storm on the electric power service calculated to be around 3 billion euros.

Statistical wind direction modeling for the analysis of large scale wind power generation

Abstract: Understanding the effects of large-scale wind power generation on the electric power system is growing in importance as the amount of installed generation increases. In addition to wind speed, the direction of the wind is important when considering wind farms, as the aggregate generation of the farm depends on the direction of the wind. This paper introduces the wrapped Gaussian vector autoregressive process for the statistical modeling of wind directions in multiple locations. The model is estimated using measured wind direction data from Finland. The presented methodology can be used to model new locations without wind direction measurements. This capability is tested with two locations that were left out of the estimation procedure. Through long-term Monte Carlo simulations, the methodology is used to analyze two large-scale wind power scenarios with different geographical distributions of installed generation. Wind generation data are simulated for each wind farm using wind direction and wind speed simulations and technical wind farm information. It is shown that, compared with only using wind speed data in simulations, the inclusion of simulated wind directions enables a more detailed analysis of the aggregate wind generation probability distribution. Copyright © 2016 John Wiley & Sons, Ltd.

Assessing the upward demand response potential for mitigating the wind generation curtailment: A case study

Abstract: The increased penetration of intermittent renewable generation has already resulted in spilling and it is projected that renewable energy curtailment level will continue to soar. This paper presents a framework to assess the flexibility of domestic thermal loads and Electric vehicles (EVs) charging load for power sink as a means to reduce wind energy curtailment during different times of a year. The objective of the framework is to jointly optimize the flexible loads to mitigate the curtailment thereby increasing the utilization of intermittent renewable generation. The proposed model is applied to the Finnish power system. The simulation results suggested that the proper activation of demand response (DR) is a feasible curtailment mitigation option but with an important caveat that potential subdued as the renewable penetration increases in the system.

Probabilistic prosumer node modeling for estimating planning parameters in distribution networks with renewable energy sources

Abstract: With the increase in distributed generation, the demand-only nature of many secondary substation nodes in medium voltage networks is becoming a mix of temporally varying consumption and generation with significant stochastic components. Traditional planning, however, has often assumed that the maximum demands of all connected substations are fully coincident, and in cases where there is local generation, the conditions of maximum consumption and minimum generation, and maximum generation and minimum consumption are checked, again assuming unity coincidence. Statistical modelling is used in this paper to produce network solutions that optimize investment, running and interruption costs, assessed from a societal perspective. The decoupled utilization of expected consumption profiles and stochastic generation models enables a more detailed estimation of the driving parameters using the Monte Carlo simulation method. A planning algorithm that optimally places backup connections and three layers of switching has, for real-scale distribution networks, to make millions of iterations within iterations to form a solution, and therefore cannot computationally afford millions of parallel load flows in each iteration. The interface that decouples the full statistical modelling of the combinatorial challenge of prosumer nodes with such a planning algorithm is the main offering of this paper.

A study for improving the energy efficiency of lifts with adjustable counterweighting

Abstract: This article presents a study of the potential energy efficiency improvement by means of adjusting the lift counterweight. The lift energy consumption in different counterweight set-ups is studied ...

Minimization of queuing time of electric vehicles at a fast charging station

Abstract: Parallel developments in electric vehicles' battery technologies and the charging equipment is leading the transportation and logistics sector towards a new era. This paper focusses on the quick charging needs of passenger electric vehicles for their optimal charging in terms of total charging time and network capacity utilization. Power distribution network capacity is utilized in such a way that, charging power to each of the individual charging socket is assigned based on the state of charge of the connected electric vehicle to that particular charging socket. An algorithm has been designed to intelligently allocate the charging power to the individual sockets at the fast charging station to control the charging rate of electric vehicles. Each of the connected electric vehicle could be charged to a certain level of state of charge depending on the length of the queue to avoid congestion of the queue and give chance to other electric vehicles to begin their charging. Simulation results show the relation between available network capacity, number of charging sockets at the charging station and the queuing time of EVs.

Assessing the Potential Benefits and Limits of Electric Storage Heaters for Wind Curtailment Mitigation: A Finnish Case Study

Abstract: Driven by policy changes and technological advancement, wind power installations are booming as compared to any other types of power generation However, the increased penetration of renewable generation in the power systems has resulted in high level of curtailment Advanced energy storage technologies have been increasingly scrutinized as a feasible mitigation option in smart grids This paper investigates the potential of mitigating wind generation curtailment via aggregating the domestic electric storage heaters The key findings show that aggregating domestic thermal storages is a viable option for curtailment mitigation, but with the indispensable caution that mitigation potential significantly saturates as the share of wind generation escalates beyond a certain limit

Block-Layer Reliability Method for Distribution Systems Under Various Operating Scenarios

Abstract: This paper formulates a block-layer method for the reliability assessment of distribution systems. The characteristics of the method include: 1) identifying the impact of distribution component reliability on the system and load points using a block-layer structured assessment; 2) incorporating time-dependent failure parameters; and 3) taking account of the topological, seasonal, and meteorological features of the distribution systems under analysis. The proposed method first identifies the three critical parts of the distribution system: main supply, feeder, and secondary substation. It can also include reserve connections and distributed generation. Second, the method frames these parts into the layered structure, each corresponding to the zone of total load curtailment. To verify this reliability technique, this paper simulates distribution feeders assembled in a number of topologies and compares them with the state sampling technique. Data provided by the local utility company are processed to model the equipment and load for the base year. The results show that the proposed method can provide a wide range of partial and system indices. These values assist in the identification of parts of the distribution system and scenarios with low reliability and to determine possible remedial actions.

Electricity consumption contribution to power system inertia — Case electric vehicles and thermostatically controlled loads in Finland

Abstract: Generation of inverter-connected solar and wind power displaces kinetic energy in power systems, decreasing frequency quality and threatening the system security. As a solution, this paper investigates the potential of electricity consumption to increase the inertial response of the system so that the frequency quality is maintained. The study focuses on three types of consumption: Electric vehicle (EV) charging, direct electric space heating (DESH), and the consumption of refrigerators, which all have different characteristics in terms of their response to the power system frequency. We aim to assess their potential inertia contribution in a Finnish case study. Therefore, the study firstly introduces the consumption models with required load control strategies, after which the performance of the loads as a part of the Nordic power system frequency dynamics is simulated. The results indicate that the loads are able to contribute to the system inertia but their consumption may not coincide with the moments of low system kinetic energy.

System-Level Value of a Gas Engine Power Plant in Electricity and Reserve Production

Abstract: Power systems require a certain amount of flexibility to meet varying demand and to be able to cope with unexpected events, and this requirement is expected to increase with the emergence of variable power generation. In this paper, we focus on gas engine power plant technology and the beneficial influence its flexible operation can have on a power system. The study introduces the concept of a combined-cycle gas engine power plant (CCGE), which comprises a combination of several gas-fired combustion engines and a steam turbine. The operation of CCGE is then comprehensively analyzed in electricity and reserve production in the South African power system and compared with combined-cycle gas turbine (CCGT) technology. Even though CCGE is a form of technology that has already been commercialized, it is rarely considered as a source of flexibility in the academic research. That is the notion providing the motivation for this study. Our core contribution is to show that the flexibility of CCGE can be valuable in power systems. The methodology is based on the unit-level model of the studied system and the solving of a day-ahead unit commitment problem for each day of the simulated 11-year period. The simulation studies reveal how a CCGE is able to offer system flexibility to follow hourly load variations and capacity to provide reserve power effectively.

Predicting the annual escalator energy consumption based on short-term measurements

Abstract: This article presents a novel approach for the annual energy consumption estimation in escalator technology. The method is based on short-term energy measurements of several day types within a week. It suits best for appliances where the passenger flow is weekly recurring. This article explores the implication of the method with seasonal changes, as well as stresses the impact of various day types and holidays on annual energy consumption estimation. The performance of the proposed method was compared with the existing approaches of energy consumption estimation in the standard ISO 25745-3 and annual energy measurement results. The approach is favorable among other existing approaches because it does not require additional passenger measurements, while providing more accurate results.

A distributed ICT architecture for continuous frequency control

Abstract: The active participation of consumers in frequency control can mitigate the negative effects of variable renewable generation in a power system. This study aims at designing a distributed informati ...

Sizing of a photo voltaic-storage system for power system frequency support

Abstract: Power system frequency quality has become topical due to the installation of variable renewable generation. The present paper contributes to the topic by investigating the sizing of a photovoltaic energy storage (PV-ES) system for frequency maintenance. The core content of the paper is threefold. Firstly, an algorithm is proposed to optimize storage capacity required to provide virtual kinetic energy and droop response for the frequency support. Secondly, the required storage and corresponding power capacity are assessed in the case of the frequency dynamics of the Nordic power system. Particular attention is given to the sizing requirements for virtual kinetic energy, replacing the displaced kinetic energy of conventional power plants. Thirdly, a case study is performed to showcase the sizing of several PV-ES systems located in Finland where they are considered to participate in the frequency maintenance in terms of inertial support.

Digital Audio Broadcasting (DAB)-based demand-side management for buildings, virtual power plants and prosumers

Abstract: The main objective of this paper is to present a new and cost-effective ICT tool that can lead to efficient energy management in buildings and optimal operation of electricity networks with increased share of Renewable Energy Sources (RES). The new ICT infrastructure is based on the Digital Audio Broadcasting (DAB) standard and its interoperability with smart metering technology, Intelligent Transportation Systems (ITS) and Building Automation Systems (BAS). The main idea involves the attachment of a DAB receiver to electric devices (from small household appliances up to EVs), and the development of proper DAB interfaces and gateways to building automation systems, in order to enable DAB-based switching of electric loads and implementation of the functionalities for smart metering systems and building automation. The first, necessary step towards the realization of the new technology is the development of a DAB communication protocol.