Showing papers by "Matti Lehtonen published in 2016"

Value of Distribution Network Reconfiguration in Presence of Renewable Energy Resources

Abstract: Proliferation of renewable energy resources in distribution networks has captured distribution companies' attention towards more active management tools. Thanks to the smart grid paradigm, hourly network reconfiguration, which is still among immature ideas, can bring the activeness required to handle fluctuating output of renewable resources. The aim of this study is to analyze the worthiness of the hourly reconfiguration in the presence of renewable energy resources. For doing so, a mathematical model is devised to minimize daily network losses via applying hourly reconfigurations. The model is a mixed integer second-order cone programming problem and is solved via MOSEK solver. The electrical demand variations as well as renewable power generation fluctuations during a day are taken into account. The proposed method is applied to the Baran 33-bus system and the results including a great deal of sensitivity analyses on key parameters are presented and discussed.

Benefits of Demand Response on Operation of Distribution Networks: A Case Study

Abstract: Despite of the great focus of attention dedicated to demand response (DR), the potential benefits of DR on distribution networks have not yet been quantitatively studied. This paper aims to assess DR potential impacts on major attributes of the operation of a residential distribution network. For doing so, grossly metered usage of more than 1600 residential consumers from Kainuu, Finland, is disaggregated to appliance-level load profiles. The flexibility of the load profiles is also estimated from the survey data and questionnaires. The individual profiles are then adjusted within their flexibility such that the most evenly distributed aggregated load profile is realized. Finally, the resulted load profile is applied to a Finnish distribution network, and the impacts of the DR on different aspects of the network operation such as the network losses, voltage profiles, and service reliability are studied. The observations certified significant benefits of the DR potentials for the network operation and reliability. It is also revealed that almost all of the benefits can be achieved by enabling the potential of responsive heating and ventilation systems.

Optimal Residential Load Management in Smart Grids: A Decentralized Framework

Abstract: Severe peak rebounds are likely in absence of a system-wide coordination among customers participating in demand response programs. This paper aims to establish a decentralized system-wide framework to coordinate demand response of residential customers in a smart grid. The objective of the framework is to modify system load profile provided that customers’ payments are minimized, and their comfort and privacy are preserved. Home load management (HLM) modules, embedded in customers’ smart meters are autonomous agents of the framework. The energy service provider iteratively exchanges load information with HLM modules in the hope of achieving his desired load profile. In each iteration, the service provider announces system load profile to HLM modules. The modules, keeping in mind their own financial and comfort constraints, nonsequentially send back load reschedule proposals to modify system load profile. The received proposals are judged whether they improve system load profile or not. HLM modules with accepted proposals apply their proposed schedules. The modified system load profile is then released, and HLM modules’ new proposals are gathered and judged. This procedure is repeated to the point at which no further improvement in the system load profile can be experienced. Performance of the framework is shown by applying it to a system with 50 customers.

Increased Utilization of Wind Generation by Coordinating the Demand Response and Real-time Thermal Rating

Abstract: Demand response (DR) will play an essential role in smart grids by contributing to the operational flexibility requirement arising from the increased penetration of intermittent renewable generation. However, DR activation could be hampered in the absence of intelligent network management. Real-time thermal rating (RTTR) functions as a smart network management tool for unlocking the network capacities by allowing the network to safely operate during overload states. This paper offers an optimal residential DR approach integrated with RTTR to balance the hourly wind power production. The proposed framework is modeled from the perspective of an electrical aggregator that manages the population of heating, ventilation and air-conditioning (HVAC) loads for wind power balancing considering the RTTR of a distribution network. The model schedules the HVAC loads without deterioration of the customers' temperature preferences. To demonstrate the performance of the proposed approach, simulations are performed on a typical Finnish distribution network plan. The results demonstrate the considerable benefits that can be realized by coordinating the DR and RTTR in a distribution network for wind generation balancing.

Explicit method to predict annual elevator energy consumption in recurring passenger traffic conditions

Abstract: This paper proposes a method for simple projecting of annual elevator electricity consumption based on short-term energy measurements and identifies challenges in the determination of actual energy consumption based on kWh meter readings. The study also analyzes the impact of the employed elevator technology, building type, and seasonal variations in elevator usage on the calculation of the annual consumption. Thus, the method can be adopted in different regions with varying elevator usage. The approach employs elevator specific daily energy consumptions measured on the prevailing day types. The reliability of the proposed approach was analyzed and the performance compared to actual measured annual consumption and estimates provided by commonly adopted energy efficiency classification schemes, VDI 4707-1:2009 and ISO 25745-2:2015. The results of the monitored office elevator indicated that the proposed method performs generally better than the competing approaches.

Investigation of Lightning Electromagnetic Fields on Underground Cables in Wind Farms

Abstract: Due to the current spreading of wind farms all over the world and their vulnerability to lightning strikes, it is important to investigate the lightning electromagnetic transients in wind farms. Underground cables are one of the essential parts in wind farms that link the turbines with the electrical grid. This paper investigates how the ground conductivity and relative permittivity, struck wind tower position, and rise time of lightning current influence the lightning electromagnetic fields impinging the underground cable sheath. The three-dimensional finite-difference time-domain method is implemented for this study. The lightning current through the cable sheath and its associated electric field can be effectively mitigated by connecting the grounding systems of the wind towers by underground bare wires called as counterpoise. Accordingly, the mitigation effect of counterpoise on the lightning current through the sheath and its associated electric field is also investigated. The results show that the lightning current through the cable sheath and its associated electric field is higher with lower ground conductivity. Moreover, it is revealed that the effect of both ground permittivity and struck wind tower position on the associated electric field and the sheath current is dependent on the ground conductivity.

Analysis of power network loading due to fast charging of Electric Vehicles on highways

Abstract: Limited range of Electric Vehicle's (EV) battery in terms of number of miles per recharge, requires EV to recharge the battery at least once during the long trip However, long charging durations are not acceptable in these cases, therefore fast charging of EV is needed Fast charging of EV needs more charging power for relatively shorter period of time, which gives rise to overloading of the power network due to simultaneous charging of multiple EVs at the fast charging stations This paper studies the power network requirements to meet the EV fast charging needs on highways Different parameters are considered in the study, for instance, arrival order of EVs at the charging stations, number of charging slots per charging station, power rating of installed chargers, distance between charging stations, state of charge (SoC) of EVs arriving for charging, battery capacities, waiting time at charging stations and the duration of charging Various scenarios are simulated using Monte Carlo Simulations (MCS) to see the impact of fast charging on the power network loading The key finding is the peak load on individual fast charging stations with respect to different penetration levels of EVs on the road A real highway case in Finland is considered in this study to show the rationality of the results

A review on the theory of electric power reliability worth and customer interruption costs assessment techniques

Abstract: As the society gets more dependent on continuous electricity supply, the impacts of disruptions in the service yield significant economic losses for all customer segments. There is crucial need for understanding the worth of reliability improvements in the power systems for planning purposes of the transmission and distribution systems. That is why, there has been an increased attention by the researchers in the field of economic worth of electricity service reliability. This review summarizes the academic work done in the fields of worth of electric power reliability and customer interruption costs assessment techniques from the year 1990 to 2015.

Incorporating earth fault location in management-control scheme for distribution networks

Abstract: This study integrates earth fault location computation with fault management-control schemes for distribution networks. To realise this target, a panel substation is located at the lateral outlet. The faulted section is identified precisely via a fault-location algorithm. Then, isolating the faulted section is accomplished through control signals between the lateral-panel substation and the faulted section isolators. The service restoration is achieved by a direct communication between the lateral-panel substation and the feeder primary substation. The proposed fault-location algorithm is based on the pure fault circuit with the initial condition of the earth fault using the measurements at each lateral panel. For phase-to-ground fault, the initial condition is the series connection for the sequence networks from the fault point. For phase-to-phase-to-ground fault, the initial condition is that the summation of the sequence currents at the fault point is equal to zero. The proposed fault-location algorithm is, therefore, suitable for equipping distribution systems with distributed generation. Moreover, it is applicable for earthed or unearthed networks with all possibilities of transformer connection and load taps. For investigation purposes, simulation tests are performed using the IEEE 33-bus automated feeder example. The simulation test results corroborated the efficacy of the proposed fault management system.

Influence of Highly Resistive Ground Parameters on Lightning-Induced Overvoltages Using 3-D FDTD Method

Abstract: It is important for the proper insulation design of the distribution system that lightning-induced overvoltages ( LIOVs ) are accurately computed. This paper investigates the impact of ground resistivity, considering wide range up to 20 kΩm, on LIOVs impinging an overhead line due to nearby return stroke using the three-dimensional finite difference time domain (3-D FDTD) method. The investigation considers two values of both ground permittivity as well as the rise rate of lightning current. Subsequently, it is inferred that the influence of both ground permittivity and rise rate of lightning current on the peak values of LIOVs depends on the ground resistivity. Furthermore, horizontal conduction and displacement current densities are also calculated on the ground surface under the line to analyze the behavior of ground surface impedance. Consequently, it is deduced that the behavior of the impedance changes from inductive to capacitive at high values of ground resistivity, thus increasing the time to the peak value of LIOVs . The peak values of LIOVs computed using the 3-D FDTD method are compared with those calculated using Darveniza's formula. It has been revealed that this formula considerably underestimates the peak values of LIOVs at high values of ground resistivity. Thereby, an interpretation is presented for the reason of this underestimation from an electromagnetic perspective. Accordingly, Darveniza's formula is appropriately modified to improve the computation accuracy.

Macroeconomic assessment of voltage sags

Abstract: The electric power sector has changed dramatically since the 1980s. Electricity customers are now demanding uninterrupted and high quality service from both utilities and authorities. By becoming more and more dependent on the voltage sensitive electronic equipment, the industry sector is the one which is affected the most by voltage disturbances. Voltage sags are one of the most crucial problems for these customers. The utilities, on the other hand, conduct cost-benefit analyses before going through new investment projects. At this point, understanding the costs of voltage sags become imperative for planning purposes. The characteristics of electric power consumption and hence the susceptibility against voltage sags differ considerably among different industry subsectors. Therefore, a model that will address the estimation of worth of electric power reliability for a large number of customer groups is necessary. This paper introduces a macroeconomic model to calculate Customer Voltage Sag Costs (CVSCs) for the industry sector customers. The proposed model makes use of analytical data such as value added, annual energy consumption, working hours, and average outage durations and provides a straightforward, credible, and easy to follow methodology for the estimation of CVSCs.

Optimal Capacity Management of Substation Transformers Over Long-Run

Abstract: The management of transformers’ capacity is a vital task for planners and asset managers due to their high cost. This paper proposes an optimization model for capacity management of transformers in a substation over long-run. The model considers the present worth costs of investment, losses, maintenance, reliability, and the salvage value of transformers for providing the optimal selection and scheduling of multistage transformer installations and their refurbishments. In the optimization model, growing failure rate of transformers along with their age is incorporated and the cumulative loss-of-life (LOL) of transformers is also used in determining their salvage value. The developed model is applied for planning and management of transformer capacities for a residential load dominant two-transformer primary distribution substation over a period of 40 years. The simulations are performed for various case studies representing the situations encountered by utilities. An extensive sensitivity analysis is also conducted for several conditions of the system parameters. The numerical results indicate the worth of inclusion of variable failure rate and LOL of transformers in their capacity management.

Survey of harmonic emission of electrical vehicle chargers in the European market

Abstract: This paper presents results of comprehensive tests of 18 different on-board electric vehicle battery chargers (EVBCs), representing the majority of currently available passenger-car-type EVs in the European market. The presented analysis compares the harmonic characteristics of EVBCs, concentrating on the impact of variations in supply voltage magnitude on emission of low frequency harmonics, as well as their total harmonic distortion and total harmonic current indices. The results provide information on the harmonic performance of EVBCs, classification of their harmonic characteristics and their potential impact on harmonic power flows in residential networks.

A User-centric Demand Response Framework for Residential Heating, Ventilation, and Air-conditioning Load Management

Abstract: The domestic heating, ventilation, and air-conditioning load promises a good prospect for electrical aggregators to consider it for demand response. This article presents a user-centric demand response control for scheduling the electric space heating load under a price and load uncertainty environment. The objective of the framework is to minimize a weighted sum of the expected payment, loss of comfort, and financial risk of a customer while strictly considering the end-user preferences. The household thermal behavior is modeled via an accurate two-capacity building model. The price and load uncertainty is modeled using a scenario-based stochastic programming approach. The proposed decision model is formulated as a non-linear programming problem that can be simply solved via commercially available solvers. The effectiveness of the formulation is demonstrated by applying it to a typical customer. The simulation results demonstrate that the decision mechanism allows consumers to compromise among el...

Analysis of partial discharge signals in medium voltage XLPE cables

Abstract: The partial discharge measurements have been widely used in the field of insulation diagnostics. The presence of partial discharges inside the cable indicates the degradation of insulation material. This paper deals with the development of insulation diagnostic method based on the partial discharge (PD) measurements. The useful information about the partial discharge activity and insulation defects is extracted by the experimental results. Artificial cavity was introduced inside the medium voltage XLPE cable by using the traditional needleplane configuration. The statistical characteristics formulated with the help of PRPDA technique and ultra-wideband discharge characteristics by using HFCT sensor was studied and analyzed. Paper is related to study about the partial discharge phenomenon in detail. The aim is to interpret the variations in the partial discharge characteristics over the insulation ageing period in terms of physical phenomenon's taking place in PD sources. The results of this work are based on the partial discharge measurements for lifetime tests conducted over the medium voltage (MV) XLPE cable samples at high voltage laboratory.

MAS-Based Modeling of Active Distribution Network: The Simulation of Emerging Behaviors

Abstract: Agent-based modeling of active distribution network helps to understand the dynamics and to design the control strategies for overall system efficiency. There is, however, a lack of generic and multipurpose agent definitions in existing studies. In this paper, a multi-agent system-based modeling of an active distribution network is presented using cooperative agents. A method to solve a network-wise objective of state estimation is explained with the proposed model. The network component agents are defined to be cooperative to meet the overall objectives and greedy to fulfil individual objectives such as energy cost minimization. A token-ring protocol is deployed for the agent communication among themselves, as well as with market and network operator agents. Furthermore, a MATLAB/Simulink model of active distribution network is used to simulate the emerging stochastic loading scenario, while the autonomous prosumer agents optimize their total energy cost responding to market price variations.

Induced Voltages on Overhead Line by Return Strokes to Grounded Wind Tower Considering Horizontally Stratified Ground

Abstract: Wind power plants are one of the most widespread sources of electric energy during the last few decades. Wind towers are quite often exposed to lightning strikes due to their tall height and long blades. In this paper, the lightning-induced voltages (LIVs) on a three-phase overhead line are computed for both first and subsequent strokes to a nearby grounded wind tower using the three-dimensional finite-difference time-domain method with homogeneous and horizontally stratified grounds. The horizontal electric fields are computed on the line and on the ground surface considering the transient grounding and characteristic impedances of the struck wind tower. The impact of the existence of wind tower on LIVs and horizontal electric fields is illustrated by removing the tower (i.e., return stroke to the ground surface). Finally, the influence of ground permittivity on the peak values of LIVs is investigated.

Evaluating and improving the energy efficiency of counterbalanced elevators based on passenger traffic

Abstract: Passenger traffic has been widely neglected when considering the elevator energy consumption. Earlier, the consumption has been typically estimated in the design phase of the building by a simple energy per square meter approach. Recently, energy efficiency classification schemes for elevators, VDI 4707-1 and ISO 25745-2, have presented computational methods applying reference power measurements from the installation site to determine specific energy usage categories and to provide an estimate of annual consumption. The ratio of standby and running energy demand are based on the building type related to a certain number of starts per day. The usage of the elevator directly derives from the passenger traffic profile. Therefore, this paper highlights the importance of analyzing the passenger flow, car loading in each direction, length of trips, and their impact on the elevator energy consumption. The modeled results of the case building imply that a substantial share of the total electricity consumption is related to other forms than transporting the passengers between floors. The main cause is considered to be the low average loading in contrast to a commonly used heavy counterbalance. Thus, the paper suggests measures to decrease the energy consumption by resizing the counterbalance and compares the results to regenerative solutions. When the counterbalance is sized optimally, the modeled efficiency improvement of the counterbalance resizing nearly equals the regenerative system with approximately 60% total savings in the case office building.

Multi-agent system based distributed voltage control in medium voltage distribution systems

Abstract: Due to the penetration of Distributed Generation (DG), distribution systems are advancing towards the smart grid technologies for voltage control strategies. In this paper, a Multi-Agent System (MAS) Based, two stage algorithm is proposed that removes the inadmissible voltages on the nodes of distribution system, in distributed manner. Furthermore, the algorithm also minimizes the overall losses. The proposed scheme utilizes minimum data in the voltage control strategies. The effectiveness of the proposed method is investigated by conducting simulations in Matlab software, on a typical Finnish residential medium voltage distribution system with varying DG penetration. Results indicate validity of the approach in distributed voltage control and give the sensitivity analysis based on DG penetration for both stages.

Optimized residential load scheduling under user defined constraints in a real-time tariff paradigm

Abstract: Peak demand is a one of the major problems in an electricity grid and it has been solved by supply side management in the past. But nowadays the existence of potential in the demand side management has drawn attention due to its economic and environmental advantages. In this paper, the potential of demand response in reducing the peak load demands as well as electricity bills to the domestic electricity users is evaluated. For this purpose, domestic appliances are modeled in MATLAB Simulink and controlled by the energy management controller. The devices are categorized into controllable or uncontrollable. Energy management controller decides the switching instants of the controllable appliances based on the results from optimization algorithms. MILP (mixed integer linear programming) algorithm is used for optimization in GAMS software. In different cases, different constraints are used for optimization considering the comforts, needs and priorities of the end users. Results are compared and the savings in electricity bills is discussed in this paper considering real time pricing and fixed tariff pricing, which exhibits the existence of potential to reduce electricity bills and peak loads in demand side management.

Improve capacity utilization of substation transformers via distribution network reconfiguraion and load transfer

Abstract: Nowadays, the essentiality of asset management in power systems and higher utilization of resources have become more critical to keep pace with the radically growing demand of today's networks. Power transformers are amongst the most important equipments installed in power distribution systems. Therefore, this paper presents a novel methodology to improve the utilization of substation transformers. In this methodology, the transformer utilization of a two-transformer substation is increased via reconfiguration considering the single contingency policy (SCP). The online reconfiguration helps to maximize the amount of load transferred from a substation with a failed transformer to its neighboring substation. This load transfer maximization provides higher transformer capacity utilization possible. In the presented methodology, the load transfer is optimized through two hierarchical stages. In the first stage, the best configuration of the assisting substation is achieved. Then, in the second stage, load points that can be transferred from the substation with a failed transformer to its neighboring healthy substation are determined. In both of the stages, the reconfiguration problem is modeled as a mixed integer second-order cone programming problem. The IEEE 33 bus distribution network is considered as the test system and the results illustrate the effectiveness of the proposed methodology in transformer utilization improvement.

Practices to improve the annual elevator energy consumption estimates and measurements

Abstract: Elevators form a crucial service of a functioning modern society, and the amount of installed units will continue to rise with increasing urbanization. Consequently, the energy efficiency of elevators has begun to attract more attention. However, elevators are rarely being monitored with energy meters, and the actual energy consumption of these devices is therefore commonly based on estimates. This paper provides useful measurement data from a mid-rise office building and analyzes the gathered readings against two energy efficiency classification schemes: the VDI 4707-1 guideline and the ISO 25745-2 standard. This study presents key points for improving the annual consumption estimates provided by these two commonly applied schemes. Furthermore, this paper identifies challenges in the determination of actual energy consumption based on kWh meter readings. The findings of this paper can be applied at any site to reduce errors in the energy consumption modeling of elevators. The results highlight the significance of correctly interpreting the methods of the classification schemes and knowing the total amount of starts of an elevator or an elevator group. Most importantly, the paper finds the elevator usage and consumption to depend heavily on the installed elevator technology as well as the people flow characteristics of the building.

Agent based bidding architecture in electricity markets for EVs as V2G and G2V

Abstract: Due to the expected high penetration of intermittent renewable energy sources in power grid, such as solar and wind, the issue of matching demand and supply would become more critical. In order to address the issue, this paper investigates the potential of Electric Vehicles (EVs) for the short term power imbalances in smart grid. This paper proposes a simple bidding algorithm for energy market for EV's participation in V2G and G2V. The key finding is the initial cost of the EV battery which could make EV as a market player for maintaining short term balances.