Applicability of Power-Line Communications to Data Transfer of On-line Condition Monitoring of Electrical Drives

The research of power-line communications has been concentrated on home automation, broadband indoor communications and broadband data transfer in a low voltage distribution network between home andtransformer station. There has not been carried out much research work that is focused on the high frequency characteristics of industrial low voltage distribution networks. The industrial low voltage distribution network may be utilised as a communication channel to data transfer required by the on-line condition monitoring of electric motors. The advantage of using power-line data transfer is that it does not require the installing of new cables. In the first part of this work, the characteristics of industrial low voltage distribution network components and the pilot distribution network are measured and modelled with respect topower-line communications frequencies up to 30 MHz. The distributed inductances, capacitances and attenuation of MCMK type low voltage power cables are measured in the frequency band 100 kHz - 30 MHz and an attenuation formula for the cables is formed based on the measurements. The input impedances of electric motors (15-250 kW) are measured using several signal couplings and measurement based input impedance model for electric motor with a slotted stator is formed. The model is designed for the frequency band 10 kHz - 30 MHz. Next, the effect of DC (direct current) voltage link inverter on power line data transfer is briefly analysed. Finally, a pilot distribution network is formed and signal attenuation in communication channels in the pilot environment is measured. The results are compared with the simulations that are carried out utilising the developed models and measured parameters for cables and motors. In the second part of this work, a narrowband power-line data transfer system is developed for the data transfer ofon-line condition monitoring of electric motors. It is developed using standardintegrated circuits. The system is tested in the pilot environment and the applicability of the system for the data transfer required by the on-line condition monitoring of electric motors is analysed.

Vaihtosuuntauksen ja suodatuksen toteuttaminen tasasähkönjakeluverkossa

Pienjännitejakeluverkko Suomessa on toteutettu 400 V:n kolmivaiheisella vaihtosähköllä. Pienestä jännitteestä johtuen 20/0.4 kV:n muuntajat täytyy sijoittaa lähelle kuluttajaa, jotta siirtohäviöt eivät nouse liian suuriksi. Suuremman vaihto- tai tasajännitteen käyttö pienjännitejakelussa kasvattaisi verkon tehonsiirtokapasiteettia ja mahdollistaisi pidempien siirtomatkojen käytön. Käynnissä olevassa tutkimushankkeessa käsitellään vaihtoehtoa, jossa tasajännitettä käytettäisiin 20 kV:n verkon ja kuluttajan välisessä tehonsiirrossa ja kuluttajalla sijaitseva vaihtosuuntaaja muodostaisi tasasähköstä standardien mukaista yksi- tai kolmivaiheista vaihtosähköä. Tässä diplomityössä käsitellään tehoelektroniikan soveltamista kuluttajalle sijoitetussa vaihtosuuntaajassa. Työssä tarkastellaan yksivaiheisia invertteritopologioita, niiden ohjausta ja soveltamista erilaisissa vaihtosuuntaajaratkaisuissa sekä LC- ja LCL-suotimien soveltuvuutta invertterin lähtöjännitteen suodatukseen. Lisäksi esitellään erilaisia rakenneratkaisuja vaihtosuuntauksen toteutukseen ja tarkastellaan näiden järjestelmien vikatilanteita ja sähköturvallisuutta. Lopuksi käsitellään koko järjestelmän häviöitä ja hyötysuhdetta eri suodinkomponenteilla sekä kytkentätaajuuksilla ja esitellään laboratorioprototyyppi. Työssä saatiin selville, että puolisiltainvertteri ei sovellu suurten kondensaattorien vuoksi syöttämään verkkotaajuista kuormaa, vaan joudutaan käyttämään kokosiltainvertteriä. Kokosiltainvertterin ja LC- tai LCL-suotimen käsittävää kokonaisuutta tarkasteltaessa havaittiin, että pienimmät häviöt saavutetaan LC-suotimella 5 %:n ja LCL-suotimella 1 %:n särövaatimuksella. Hyötysuhdekäyrää tarkasteltaessa saatiin sama tulos läpi koko invertterin tehoalueen. Suotimen häviöiden tarkka laskenta on kuitenkin erittäin haasteellista, joten tulokset ovat suuntaa-antavia.

Change of Electricity Distribution Industry: Drivers and Opening Business Opportunities

As a result of the recent regulatory amendments and other development trends in the electricity distribution business, the sector is currently witnessing radical restructuring that will eventually impact the business logics of the sector. This report represents upcoming changes in the electricity distribution industry and concentrates on the factors that are expected to be the most fundamental ones. Electricity network companies nowadays struggle with legislative and regulatory requirements that focus on both the operational efficiency and the reliability of electricity distribution networks. The forces that have an impact on the distribution network companies can be put into three main categories that define the transformation at a general level. Those are: (1) a requirement for a more functional marketplace for energy, (2) environmental aspects (combating climate change etc.), and (3) a strongly emphasized requirement for the security of energy supply. The first point arises from the legislators’ attempt to increase competition in electricity retail markets, the second one concerns both environmental protection and human safety issues, and the third one indicates societies’ reduced willingness to accept interruptions in electricity supply. In the future, regulation of electricity distribution business may lower the threshold for building more weather-resistant networks, which in turn means increased underground cabling. This development pattern is reinforced by tightening safety and environmental regulations that ultimately make the overhead lines expensive to build and maintain. The changes will require new approaches particularly in network planning, construction, and maintenance. The concept for planning, constructing, and maintaining cable networks is necessary because the interdependencies between network operations are strong, in other words, the nature of the operation requires a linkage to other operations.

Tasasähkönjakeluverkon vaihtosuuntaaja galvaanisella erotuksella

Suomessa sähkönjakeluverkko koostuu pääasiassa 20 kV ja 400 V jännitetasoista. Tällöin sähkö viedään lähelle kuluttajia suuremmalla jännitetasolla ja muunnetaan alhaisemmaksi lähellä asiakkaita. Haittapuolena on se, että haja-asutusalueilla jakelumuuntajien määrä kasvaa suureksi, koska ne täytyy sijoittaa lähelle kuluttajaa. Vaihtoehtona on toteuttaa osa sähkönjakelusta tasajännitteellä, jolloin tehollinen jännite olisi suurempi. Tällöin sähköä voitaisiin siirtää pidempiä matkoja ilman, että asiakaskohtaisia tai muutaman asiakkaan kattavia 20 kV siirtolinjoja tarvitsisi käyttää. Tämä taasen edellyttää asiakaskohtaisien vaihtosuuntaajien käyttöä. Tässä työssä esiteltävällä 1 kVA vaihtosuuntaajalla muodostetaan tasasähköjakeluverkosta saatavasta 750 V tasasähköstä yksivaiheista (230 VRMS, 50 Hz) verkkojännitettä. Laite on suunniteltu toteuttamaan galvaaninen erotus mahdollisimman hyvän hyötysuhteen puitteissa. Vaihtosuuntaaja on toteutettu käyttämällä resonanssikonvertteria, joka vaihtosuuntaa jakelujännitteen korkeataajuiseksi vaihtojännitteeksi. Tämän jälkeen toteutetaan galvaaninen erotus käyttäen suurtaajuusmuuntajaa. Tätä seuraa syklokonvertteri, joka pulssintiheysmodulaatiota soveltaen muodostaa lähtöjännitteen. Tämä suodatetaan lopuksi LC- alipäästösuotimella säröltään standardin mukaiseksi. Laite on jaettu työssä kolmeen osaan, joista jokaisen toiminta on selitetty ja simuloitu itsenäisesti. Lopussa koko järjestelmä on simuloitu yhtenä kokonaisuutena. Hyötysuhteeksi arvioitiin karkeasti 94 % ja lopullisista tuloksista voidaan päätellä, että laitteen toteuttaminen prototyypiksi voisi olla kannattavaa.

Distribution development in global business environment

The purpose of this master’s thesis was to analyze a case company’s distribution and its elements. With different distribution structure options a customer can be served with different ways. However, cost elements and service elements create different trade-offs. In this work the case company’s distribution’s present state was analyzed and conclusions were made. Based on these conclusions different alternatives for distribution were created. These different alternatives were analyzed through simulations and with more traditional calculations to compose the total operative costs of each alternative. Also other aspects were considered, such as required organizational changes and the possible better customer service. With the suggested 3-stock distribution structure shorter delivery times and possibly more punctual deliveries for products kept in stock could be achieved with the same operative costs as in current direct delivery model. Also, similar benefits could be achieved with other products with the 3-stock model.

Galvaanisen erotuksen toteuttaminen tasavirtasähkönjakelun asiakaspäätelaitteessa

Suomessa sähkönjakeluverkon pääasialliset jännitetasot ovat 20 kV ja 400 V. 20 kV jännitetasolla sähkö viedään lähelle kuluttajia ja muunnetaan pienemmäksi lähellä asiakkaita. Haittapuolena on se, että 20 kV avojohtosähkönsiirtoverkko on hyvin vika-altis ja usein yhden haaran vikaantuessa monta muutakin jää ilman sähköä. Lisäksi hintavien ja suurien jakelumuuntajien määrä on suuri. Vaihtoehtona on toteuttaa osa sähkönjakelusta tasajännitteellä, jolloin tehollinen pienjännite olisi 400 V:a suurempi. Tällöin sähköä voitaisiin siirtää pidempiä matkoja ilman, että asiakaskohtaisia tai muutaman asiakkaan kattavia 20 kV siirtolinjoja tarvitsisi käyttää. Tämä edellyttää vaihtosuuntauksen toteuttamista kuluttajan päässä. Tässä työssä esiteltävällä 1 kVA:n tehoisella vaihtosuuntaajalla muodostetaan tasasähköjakeluverkosta saatavasta 750 V tasasähköstä yksivaiheista (230 VRMS, 50 Hz) verkkojännitettä. Laite on suunniteltu toteuttamaan galvaaninen erotus mahdollisimman hyvällä hyötysuhteella. Suurtaajuusmuuntajan mitoitus mahdollisimman hyvälle hyötysuhteelle on haastava tehtävä, koska vaatimuksia sille asettavat sekä syöttävä resonanssikonvertteri että syötettävä syklokonvertteri. Mitoituksessa on pyrittävä löytämään mahdollisimman hyvä hyötysuhde kustannusten ja toteutettavuuden suhteen.

Techno-Economic Feasibility of Novel On-Line Condition Monitoring Methods in Low Voltage Distribution Networks

The focus in this thesis is to study both technical and economical possibilities of novel on-line condition monitoring techniques in underground low voltage distribution cable networks. This thesis consists of literature study about fault progression mechanisms in modern low voltage cables, laboratory measurements to determine the base and restrictions of novel on-line condition monitoring methods, and economic evaluation, based on fault statistics and information gathered from Finnish distribution system operators. This thesis is closely related to master’s thesis “Channel Estimation and On-line Diagnosis of LV Distribution Cabling”, which focuses more on the actual condition monitoring methods and signal theory behind them.

Aging based maintenance and reinvestment scheduling of electric distribution

The maintenance of electric distribution network is a topical question for distribution system operators because of increasing significance of failure costs. In this dissertation the maintenance practices of the distribution system operators are analyzed and a theory for scheduling maintenance activities and reinvestment of distribution components is created. The scheduling is based on the deterioration of components and the increasing failure rates due to aging. The dynamic programming algorithm is used as a solving method to maintenance problem which is caused by the increasing failure rates of the network. The other impacts of network maintenance like environmental and regulation reasons are not included to the scope of this thesis. Further the tree trimming of the corridors and the major disturbance of the network are not included to the problem optimized in this thesis. For optimizing, four dynamic programming models are presented and the models are tested. Programming is made in VBA-language to the computer. For testing two different kinds of test networks are used. Because electric distribution system operators want to operate with bigger component groups, optimal timing for component groups is also analyzed. A maintenance software package is created to apply the presented theories in practice. An overview of the program is presented.

Control of transients in water distribution networks by H¥ Control

In this work, a controller for regulating the transients in water distribution networks is established. The control technique is the H¥ Control. The developed controller is applied to a water distribution network and the results of this application demonstrate that the technique allowed the establishment of a robust controller, capable of attenuating the disturbances in a suitable way, being effective in controlling the oscillations of the state variables in question.

Impact of reliability of supply on long-term development approaches to electricity distribution networks

The Finnish electricity distribution sector, rural areas in particular, is facing major challenges because of the economic regulation, tightening supply security requirements and the ageing network asset. Therefore, the target in the distribution network planning and asset management is to develop and renovate the networks to meet these challenges in compliance with the regulations in an economically feasible way. Concerning supply security, the new Finnish Electricity Market Act limits the maximum duration of electricity supply interruptions to six hours in urban areas and 36 hours in rural areas. This has a significant impact on distribution network planning, especially in rural areas where the distribution networks typically require extensive modifications and renovations to meet the supply security requirements. This doctoral thesis introduces a methodology to analyse electricity distribution system development. The methodology is based on and combines elements of reliability analysis, asset management and economic regulation. The analysis results can be applied, for instance, to evaluate the development of distribution reliability and to consider actions to meet the tightening regulatory requirements. Thus, the methodology produces information for strategic decision-making so that DSOs can respond to challenges arising in the electricity distribution sector. The key contributions of the thesis are a network renovation concept for rural areas, an analysis to assess supply security, and an evaluation of the effects of economic regulation on the strategic network planning. In addition, the thesis demonstrates how the reliability aspect affects the placement of automation devices and how the reserve power can be arranged in a rural area network.

Energy Management System for LVDC Island Networks

Recent developments in power electronics technology have made it possible to develop competitive and reliable low-voltage DC (LVDC) distribution networks. Further, islanded microgrids—isolated small-scale localized distribution networks— have been proposed to reliably supply power using distributed generations. However, islanded operations face many issues such as power quality, voltage regulation, network stability, and protection. In this thesis, an energy management system (EMS) that ensures efficient energy and power balancing and voltage regulation has been proposed for an LVDC island network utilizing solar panels for electricity production and lead-acid batteries for energy storage. The EMS uses the master/slave method with robust communication infrastructure to control the production, storage, and loads. The logical basis for the EMS operations has been established by proposing functionalities of the network components as well as by defining appropriate operation modes that encompass all situations. During loss-of-powersupply periods, load prioritizations and disconnections are employed to maintain the power supply to at least some loads. The proposed EMS ensures optimal energy balance in the network. A sizing method based on discrete-event simulations has also been proposed to obtain reliable capacities of the photovoltaic array and battery. In addition, an algorithm to determine the number of hours of electric power supply that can be guaranteed to the customers at any given location has been developed. The successful performances of all the proposed algorithms have been demonstrated by simulations.

Modelling of changes in electricity end-use and their impacts on electricity distribution

The electricity distribution sector will face significant changes in the future. Increasing reliability demands will call for major network investments. At the same time, electricity end-use is undergoing profound changes. The changes include future energy technologies and other advances in the field. New technologies such as microgeneration and electric vehicles will have different kinds of impacts on electricity distribution network loads. In addition, smart metering provides more accurate electricity consumption data and opportunities to develop sophisticated load modelling and forecasting approaches. Thus, there are both demands and opportunities to develop a new type of long-term forecasting methodology for electricity distribution. The work concentrates on the technical and economic perspectives of electricity distribution. The doctoral dissertation proposes a methodology to forecast electricity consumption in the distribution networks. The forecasting process consists of a spatial analysis, clustering, end-use modelling, scenarios and simulation methods, and the load forecasts are based on the application of automatic meter reading (AMR) data. The developed long-term forecasting process produces power-based load forecasts. By applying these results, it is possible to forecast the impacts of changes on electrical energy in the network, and further, on the distribution system operator’s revenue. These results are applicable to distribution network and business planning. This doctoral dissertation includes a case study, which tests the forecasting process in practice. For the case study, the most prominent future energy technologies are chosen, and their impacts on the electrical energy and power on the network are analysed. The most relevant topics related to changes in the operating environment, namely energy efficiency, microgeneration, electric vehicles, energy storages and demand response, are discussed in more detail. The study shows that changes in electricity end-use may have radical impacts both on electrical energy and power in the distribution networks and on the distribution revenue. These changes will probably pose challenges for distribution system operators. The study suggests solutions for the distribution system operators on how they can prepare for the changing conditions. It is concluded that a new type of load forecasting methodology is needed, because the previous methods are no longer able to produce adequate forecasts.

Visual management of sags and incidents gathered in distribution substations for power quality management

Monitor a distribution network implies working with a huge amount of data coining from the different elements that interact in the network. This paper presents a visualization tool that simplifies the task of searching the database for useful information applicable to fault management or preventive maintenance of the network

The real-time optimisation of DNO owned storage devices on the LV network for peak reduction

Energy storage is a potential alternative to conventional network reinforcementof the low voltage (LV) distribution network to ensure the grid’s infrastructure remainswithin its operating constraints. This paper presents a study on the control of such storagedevices, owned by distribution network operators. A deterministic model predictive control (MPC) controller and a stochastic receding horizon controller (SRHC) are presented, wherethe objective is to achieve the greatest peak reduction in demand, for a given storagedevice specification, taking into account the high level of uncertainty in the prediction of LV demand. The algorithms presented in this paper are compared to a standard set-pointcontroller and bench marked against a control algorithm with a perfect forecast. A specificcase study, using storage on the LV network, is presented, and the results of each algorithmare compared. A comprehensive analysis is then carried out simulating a large number of LV networks of varying numbers of households. The results show that the performance of each algorithm is dependent on the number of aggregated households. However, on a typical aggregation, the novel SRHC algorithm presented in this paper is shown to outperform each of the comparable storage control techniques.

Control methodologies: Peak reduction algorithms for DNO owned storage devices on the Low Voltage network

The Distribution Network Operators (DNOs) role is becoming more difficult as electric vehicles and electric heating penetrate the network, increasing the demand. As a result it becomes harder for the distribution networks infrastructure to remain within its operating constraints. Energy storage is a potential alternative to conventional network reinforcement such as upgrading cables and transformers. The research presented here in this paper shows that due to the volatile nature of the LV network, the control approach used for energy storage has a significant impact on performance. This paper presents and compares control methodologies for energy storage where the objective is to get the greatest possible peak demand reduction across the day from a pre-specified storage device. The results presented show the benefits and detriments of specific types of control on a storage device connected to a single phase of an LV network, using aggregated demand profiles based on real smart meter data from individual homes. The research demonstrates an important relationship between how predictable an aggregation is and the best control methodology required to achieve the objective.