Showing papers by "Matti Lehtonen published in 2015"
TL;DR: In this paper, the authors presented a residential energy hub model for a smart home, where a residential combined heat and power (CHP) as a cogeneration technology, and a plug-in hybrid electric vehicle are employed in the model.
146 citations
TL;DR: A new long-term cost/benefit analysis for an optimal level of distribution network automation is provided and the results show that neglecting the impact of earth fault events can lead to suboptimal solutions.
Abstract: In the past decade, distribution network operators have been broadly engrossed toward automated distribution networks. The operators acknowledge network automation as an efficient investment toward a better service reliability. This paper aims to provide a new long-term cost/benefit analysis for an optimal level of distribution network automation. In the analysis, reduction in customer outage cost is considered as the benefit of implementing automation systems with capital investment, and annual operation and maintenance costs. In the Finnish regulation model, there is a special incentive based on customer outage cost reduction. As the main contribution of this paper, the impact of earth fault events and their required time-consuming fault management process is taken into account within the calculation of the benefit of automation systems. The solution of the analysis consists of the optimal number and location of remote-controlled sectionalizing switches, which are building blocks of automation systems. The problem is formulated in a mixed-integer linear programming format that can be effectively solved by commercially available solvers. The effectiveness of the proposed algorithm is demonstrated by applying it to the Helsinki distribution network. The results show that neglecting the impact of earth fault events can lead to suboptimal solutions.
71 citations
TL;DR: In this paper, a demand response optimization model based on transformer hottest-spot temperature is proposed to enhance the utilization of transformers in a residential primary and secondary distribution system in Finland.
Abstract: Due to load growth, aging infrastructure, and a competitive environment, innovative solutions are required by electrical utilities to enhance the utilization of transformers which are cost intensive. This paper proposes a demand response optimization model based on transformer hottest-spot temperature. The optimization model quantifies the improvement of transformer utilization through DR. The proposed model is applied to a typical Finnish residential primary and secondary distribution transformers for case studies of load with and without DR. The results show that the loading on the transformers can be significantly increased without sacrificing the life of transformers. The gain in utilization depends on the DR capability of the load. Significant monetary benefits can be achieved with the deployment of the proposed model in a real system.
67 citations
TL;DR: In this paper, the authors presented a new hybrid approach to estimate the customer interruption costs of service sector customer segment by making use of a customer survey study conducted in Finland, which benefits from both the reported cost data collected from customers and from the analytical data that are available.
64 citations
TL;DR: In this article, a stochastic model for the medium-term decision-making problem faced by a distribution company (DisCo) dealing with the DisCo's decisions on the level of involvement in forward contracts and in the pool as well as the sale prices offered to customers is presented.
Abstract: Time varying prices by motivating customers to reduce their consumption in peak periods propel the electricity industry towards a higher efficiency compared to that of common flat prices. Focusing on time-of-use (TOU) sale prices, this paper establishes a stochastic model for the medium-term decision making problem faced by a distribution company (DisCo). The developed model deals with the DisCo's decisions on the level of involvement in forward contracts and in the pool as well as the sale prices offered to customers. The demand response to TOU prices is captured using a price elasticity matrix (PEM). The objective is to maximize the DisCo's profit while the exposure risk imposed by uncertainties is limited to a given level. The model is formulated as a mixed integer linear programming (MILP) problem that can be effectively solved via commercial software packages. A typical Finnish 20-kV urban distribution network is used to demonstrate the effectiveness of the developed model.
61 citations
TL;DR: This paper intends to comprehensively assess the potential impacts of DTR on the performance of a realistic Finnish distribution network by following a step-by-step procedure.
Abstract: With anticipated proliferation of electric vehicles and distributed generations in near future, dynamic thermal rating (DTR) as a tool for unlocking network capacities, is becoming critical for distribution network operators. DTR is gaining a great and still growing focus of attention in today’s power industries. However, potential benefits of DTR, although have been envisioned to be significant, have not yet been studied quantitatively. This paper intends to comprehensively assess the potential impacts of DTR on the performance of a realistic Finnish distribution network. For doing so, first a step-by-step procedure is devised. Then, weather data and loading information of circuits in the network are gathered by advanced metering infrastructure available in the network. Thereafter, the gathered data are fed to mathematical models provided by the IEEE Standard 738-2006 and component dynamic thermal models to give thermal rating of circuits. The ratings are then used in reliability analysis where likely system states are simulated. This paper is performed for several cases and the results are discussed.
59 citations
TL;DR: In this article, the authors developed a framework focusing on realization of domestic storage space heating DR capability in balancing market, which consists of two hierarchical stages named energy market stage and balancing power market stage.
47 citations
TL;DR: In this article, a demand response (DR) based optimization model is proposed to limit load on healthy transformers during contingencies, which selects combination of the best remedial actions among DR, load curtailment (LC) and transferring load to a neighboring substation.
Abstract: Severe overloads, caused by the outage of units in multi-transformer substations, may affect transformer life adversely. This paper presents a novel demand response (DR) based optimization model to limit load on healthy transformers during contingencies. The model selects combination of the best remedial actions among DR, load curtailment (LC) and transferring load to a neighboring substation. IEEE standard thermal and aging models are used for transformer loss-of-life (LOL) calculation. For a realistic study, the proposed model is applied to a Finnish residential two-transformer primary substation for case studies of load with and without DR. The load profile and flexibility of the demand are estimated by hourly metered consumption and survey data. Simulations are performed for two situations depending upon availability of connection with a neighboring substation. The results show that the LOL of transformers can be reduced by employing DR following contingency events and the capacity utilization can be increased correspondingly.
46 citations
TL;DR: To establish a circuit-breaker (CB) online monitoring system, the development of an effective diagnosis framework is essential to accurately assess its condition while under operation, and to foresee any risk of failure before it would be possible to plan for the required maintenance on the CB sufficiently ahead of a failure occurrence.
Abstract: To establish a circuit-breaker (CB) online monitoring system, the development of an effective diagnosis framework is essential. The purpose of this online monitoring system is to accurately assess its condition while under operation, and to foresee any risk of failure. Consequently, it would be possible to plan for the required maintenance on the CB sufficiently ahead of a failure occurrence. To fulfill this, a framework is proposed to precisely assess the SF $_{6}$ CBs' condition using its control circuit signals' waveforms as easy-to-access, easy-to-measure, and noninvasive diagnosis parameters. The features found in these waveforms match the characteristics essential for diagnostic purposes, and could cover 50%–60% of CB failures. A data-mining process is employed to cluster the captured data against past-recorded data (in terms of faulty or healthy condition) of circuit breakers (CBs) diagnosis. To determine the probability distribution function of a CB condition cluster, a classifier is developed. In this model, the CB condition (based on its failure risk) is qualitatively classified into normal, alarm, and emergency states. In addition, to avoid any unnecessary maintenance activities during an alarm state, the condition of CBs in each state is quantified in terms of some probabilistic-based indices. The feasibility and applicability of the proposed methodology are verified using recorded data.
45 citations
TL;DR: In this paper, a synergy of real-time dynamic thermal rating (DTR) and coordinated voltage control (CVC) is proposed for solving the voltage quality and thermal limit problems associated with a high penetration level of distributed generation (DG) in an active distribution network.
37 citations
TL;DR: In this article, the authors proposed an implementation of discrete wavelet transform (DWT) to de-noise the measured signals, and compared with a well-known infinite impulse response filtering technique.
Abstract: High energy arc faults in medium-voltage (MV) switchgear are serious hazards to personnel or equipment, and may cause process interruptions. Most of the electrical faults leading to arc are developed slowly, e.g., due to insulation degradation or bad connection. In this paper, the detection of partial discharges (PDs) and low energy arcing between loose contacts has been proposed for online monitoring of MV switchgear. The PD measurements in a switchgear panel and arcing measurements across a 0.2-mm sphere-to-rod gap have been carried out. Measured signals are captured by a differential electric field sensor ( $D$ -dot sensor) and recorded by a high-frequency oscilloscope. In general, online measured signals are suppressed by high-frequency noise, and therefore, de-noising of measurements is of paramount importance to get reliable information about a fault. An implementation of discrete wavelet transform, to de-noise the measured signals, has been proposed in this paper. Comparison with a well-known infinite impulse response filtering technique has been made. Time and frequency domain comparisons between original and de-noised signals reveal the significance of this technique for arc fault prediction in MV switchgear. A layout for the integration of online monitoring to central control is also presented.
TL;DR: In this paper, the potential overall benefit of integrating a resistor for storage heating in the system, which can act as a power sink when needed, was analyzed from the prosumer and power system point of view.
TL;DR: In this article, the authors proposed the possibility for an earth fault localisation with the aid of synchronised data recorded on the lowvoltage side of the medium voltage/low voltage transformers in compensated neutral distribution networks which are equipped with auxiliary resistor for short-time increasing of the active part of the fault current.
Abstract: The main reasons for installation of power quality meters in distribution transformer substations are power quality monitoring and global evolution of electrical network towards the ‘smart grid’. In case that all measurements from the meters are properly synchronised and centralised, new possibilities of control or evaluation of the network are enabled. This contribution proposes the possibility for an earth fault localisation with the aid of synchronised data recorded on the low-voltage side of the medium voltage/low voltage transformers in compensated neutral distribution networks which are equipped with auxiliary resistor for short-time increasing of the active part of the fault current. The described method uses voltage sags evoked by connecting of the auxiliary resistor for locating the faulty section. The proposed method is tested with the help of numerical model which presents a part of the distribution network.
TL;DR: In this article, the authors proposed an autonomous control on automatic switches in electric power distribution networks, which is based on a decentralized control aiming to automatically isolate the faulty section while reducing the overall dependency on the number of fault indicators and communication hops involved in the fault management process.
TL;DR: In this paper, the optimal locations of DSSCs to enhance the system loadability and reliability using the DC load flow model are investigated. And the optimal solution is then selected using the fuzzy satisfying method.
Abstract: Distributed static series compensator (DSSC) is a member of the family of distributed flexible AC transmission system devices that can be attached directly to conductors of transmission lines. DSSCs are able to compensate for and adjust the line reactance; thus, they could be widely used in stability-limited transmission systems. Owing to economic matters, the optimal placement of DSSCs is of a great interest from practical viewpoints. This study presents an approach to find the optimal locations of DSSCs to enhance the system loadability and reliability using the DC load flow model. The optimisation problem is solved using the mixed-integer linear programming. A compromise between improving the system loadability and reliability is fulfilled and a wide range of non-dominated optimal solutions is calculated. The final solution is then selected using the fuzzy satisfying method. Numerical studies are conducted on the IEEE reliability test system (IEE-RTS).
TL;DR: In this article, a concept to create traveling waves is implemented by earthing the neutral via a controlled thyristor that provides a short period of high fault current and produces traveling waves to estimate the fault distance.
Abstract: In Nordic countries, distribution networks are traditionally unearthed and increasingly compensated. For such networks, switching their neutral point to the earth is practically applied through a resistor for better selectivity functions of earth faults. In this paper, the neutral switching and, consequently, an arrival time of the aerial mode traveling wave reflected from the fault point are utilized to accurately determine the earth fault distance. A concept to create traveling waves is implemented by earthing the neutral via a controlled thyristor that provides a short period of high fault current and produces traveling waves to estimate the fault distance. Much higher transient signals are generated by earthing through an opposite charged capacitor. A capacitor-resistor divider is utilized to measure the reflected surge over a heterogeneous distribution feeder. An adaptive setting is proposed for stamping the arrival surge. The results provide evidence of the efficacy of the proposed fault distance estimation.
TL;DR: A decentralized model for the optimal dispatch of DERs in smart grids is established to minimize expected procurement cost of demand while profit of private DER owners is not sacrificed.
Abstract: Proliferation of private distributed energy resources (DERs) necessitates devising effective energy management frameworks. This paper aims at establishing a decentralized model for the optimal dispatch of DERs in smart grids. The objective function is to minimize expected procurement cost of demand while profit of private DER owners is not sacrificed. Unit management modules (UMMs) embedded in private DERs and a central agent are autonomous agents of the model. The approach is iterative. In each iteration, the central agent announces to UMMs its procurement strategy, which contains purchased powers and their prices. Then, UMMs optimize and send back their output power and selling price proposals in the hope of achieving higher profits. The energy service provider (ESP) gathers the bids and modifies the procurement strategy whenever bids are in line with the cost minimization objective. The service provider releases the last procurement strategy in response to which UMMs synchronously update and send back their bids. The mutual interaction between UMMs and ESP is continued to the point in which no further modification in ESP’s procurement strategy is experienced. The effectiveness of the proposed algorithm is demonstrated by its implementation in a system with a few DERs from different types.
TL;DR: In this paper, an online partial discharge (PD) diagnostic system is presented to detect and locate the weak insulation spots developed in the network components spread over the distribution area, where the PD pulses originating and propagating from the defect site arrive at feeder joints, terminals and T-splices and are reflected from there.
11 May 2015
TL;DR: An overview of the state of the art of exhaust waste heat recovery systems utilizing thermoelectric generators (TEGs) can be found in this paper, where the authors present an overview related particularly to vehicle engines exhaust energy recovery systems, introducing the key parameters, components and factors that determine the performance of such systems.
Abstract: Majority of the vehicles commercially available today and on the roads today use internal combustion engines (ICE) for the power source. Such engines utilize only small share of the fuel primary energy converted to kinetic energy, however majority of fuel primary energy is wasted while dissipated in the ambient air as waste heat or as hot exhaust gas. A remarkable potential for improving the efficiency of the ICE systems lies in the recovery of the energy wasted today. This paper presents an overview of the state of the art of current research of exhaust waste heat recovery systems utilizing thermoelectric generators (TEGs). Such systems provide the direct heat-to-electric energy conversion and allow building the exhaust energy recovery systems without adding moving parts to the vehicles. The review will present the overview related particularly to vehicle engines exhaust energy recovery systems, introducing the key parameters, components and factors that determine the performance of such systems.
TL;DR: In this paper, the authors make use of a detailed customer survey study that was conducted in Finland and presents a comparison of five different models: WTA, WTP, direct worth approach, price elasticity approach and a new macroeconomic model.
TL;DR: In this paper, a holistic view on reliability improvement in urban distribution networks and the description of the actual implementations of different methods is addressed, and the impact of the chosen development methods on reliability indices in Helsinki is described.
TL;DR: In this paper, the authors proposed an efficient approach for detecting CT saturation with a generic discrimination index without the need for setting definition, where the simultaneous samples-based multiplication of the secondary current by its derivative is only used to differentiate between saturated and unsaturated wave portions.
Abstract: Derivative-based approaches have been widely used for detecting current-transformer (CT) saturation. This letter proposes an efficient approach for detecting CT saturation with a generic discrimination index without the need for setting definition. For this aim, the simultaneous samples-based multiplication of the secondary current by its derivative is only used to differentiate between saturated and unsaturated wave portions. Reconstructing the detected saturated secondary current is performed by using Kalman filtering to efficiently extract the phasor quantities of the unsaturated current portion. The results provide evidence of the efficacy of the proposed detector and of the Kalman-based waveform reconstruction.
TL;DR: In this article, an online technique of partial discharge (PD) detection and localization in multi-section (straight and branched power lines) MV network is presented by using the conventional Time Domain Reflectometry and Time Difference of Arrival methods.
Abstract: Partial discharge (PD) diagnostic is considered as the main concern while making condition assessment plan for medium voltage assets. PD detection and localization in multi-section (straight and branched power lines) MV network is difficult by using the conventional Time Domain Reflectometry and Time Difference of Arrival methods. It is due to interconnected cables of different lengths and properties which make the interpretation of PD signals quite complex as compared to single cable routes. This paper presents an online technique of PD localization in MV cable network. PD activity emits current pulses propagating away from the PD site. Polarity of the detected PD pulses with reference to polarity of the supply voltage determines the direction of arrival of these pulses. Comparison of the polarity of PD pulses identifies the faulty section of the overhead covered conductor line as well as the cable network. A detailed discussion has been presented to address the practical issues of sensor implementation and polarity comparison in order to ensure the accuracy of polarity based direction of arrival (DOA) assessment during field application. Evaluation of DOA is based on directionally calibrated sensors. Allocated induction sensors are employed along the feeder for integrated implementation of proposed technique in accordance with the distributed agent for improving the network reliability.
TL;DR: In this article, a probabilistic method to assess the risk of insulator flashover in medium-voltage overhead lines due to lightning-induced overvoltages is presented, where a modified Gaussian cumulative distribution function has been used to predict the probability of single-phase, two-phase and three-phase flashover of insulators under combined ac-and lightning induced overvoltage.
Abstract: The effect of lightning-induced overvoltages is more profound in overhead distribution lines due to their limited height and low insulation level. Consequently, there is a high risk of line insulation flashover when exposed to lightning-induced overvoltages. This paper presents a probabilistic method to assess the risk of insulator flashover in medium-voltage overhead lines due to lightning-induced overvoltages. In order to accomplish this, a modified Gaussian cumulative distribution function has been used to predict the probability of single-phase, two-phase, and three-phase flashover of insulators under combined ac- and lightning-induced overvoltages. The validity of the modified probabilistic model is confirmed through experiments carried out in the high-voltage laboratory. Next, Monte Carlo simulations were performed on the simplified Rusck's model to generate the distribution of peak lightning-induced overvoltages. Finally, the risk of insulator flashover is calculated based on the distributions of lightning-induced overvoltages and insulator flashover voltages. The proposed procedure could be considered beneficial to select the optimum insulation level required against lightning-induced overvoltages by distinguishing between single-phase and multiphase flashover faults.
TL;DR: In this article, the authors present a methodology for carrying out statistical analysis of electricity consumption and distributed wind generation in distribution systems in order to investigate their combined effect, e.g., to give a probabilistic estimate of the effective peak net load.
01 Nov 2015
Abstract: Application of renewable sources of energy is vital for the mankind due to global warming. Residential buildings consume major portion of electricity. Therefore, a grid-connected photovoltaic system of domestic level with battery storage backup (PV/storage system) is addressed in this article. This system has a significant effect on decreasing energy costs and contributes to meet the requirements of a nearly net-zero energy building. In this article, Mixed Integer Linear Programming (MILP) is applied to optimize the energy cost of a single-family house with battery energy storage for four different scenarios of installing solar panels. Optimization is performed on monthly scale for a house in Helsinki, Finland. The numerical results indicate that it is reasonable to integrate a storage in grid-connected PV systems in residential applications and represent the impact of battery size on household's monthly energy cost.
TL;DR: In this article, an online system for PD diagnostic system in a distribution network is presented by developing a cascaded organization of the detection, location and quantization features Rogowski coil (induction sensor) is employed for nonintrusive electromagnetic measurement of PD signals.
TL;DR: In this article, the Discrete Wavelet Transform (DWT) has been used to de-noise PD signals in a 20kV switchgear panel and measurements have been carried out by using different non-intrusive sensors including a novel sensor, the D-dot sensor and recorded by a high frequency oscilloscope.
01 Nov 2015
TL;DR: In this article, a centralized framework focusing on realization of domestic heating, ventilation, and air conditioning (HVAC) demand response capability for wind power balancing is developed, where thermal comfort penalty is explicitly integrated in the objective function in order to oblige different customers' thermal preferences.
Abstract: The integration of a great deal of intermittent renewable generation in future grids will require more operational flexibility. Residential demand response can provide the load shaping potentials thereby alleviating the need for operational flexibility. This paper intends to develop a centralized framework focusing on realization of domestic heating, ventilation, and air conditioning (HVAC) demand response capability for wind power balancing. In the proposed optimization model, energy consumption of HVAC loads is optimized to tackle the variability of wind power. The thermal comfort penalty is explicitly integrated in the objective function in order to oblige different customers' thermal preferences. Performance of the framework is verified through simulations on Finnish case studies. The simulation results suggest that the proposed framework will help the network operators to benefit from cheap renewable generation.
26 Jul 2015
TL;DR: In this paper, a demand response (DR) and dynamic thermal rating (DTR) based optimization model was proposed for efficient capacity utilization and life management of transformers during contingencies.
Abstract: Contingencies of transformers in a multi-unit substation may affect life of healthy units severely due to overloads. This paper proposes a novel demand response (DR) and dynamic thermal rating (DTR) based optimization model for efficient capacity utilization and life management of transformers during contingencies. The model opts for the optimal combination of corrective actions among load curtailment (LC), DR, and shifting load to an adjacent substation while maintaining the winding hot-spot-temperature (HST) under a predefined limit. Simulations are performed, on a typical Finnish two-transformer primary distribution substation as a test system, for case studies of demand with and without DR & two situations based on availability of neighboring substation connection. The obtained results indicate that the proposed model offers substantial benefits of life-saving and utilization improvement for transformers present in different ambient conditions.