Minimizing the impact of EV charging on the electricity distribution network

The main objective of this paper is to design electric vehicle (EV) charging policies which minimize the impact of charging on the electricity distribution network (DN). More precisely, the considered cost function results from a linear combination of two parts: a cost with memory and a memoryless cost. In this paper, the first component is identified to be the transformer ageing while the second one corresponds to distribution Joule losses. First, we formulate the problem as a non-trivial discrete-time optimal control problem with finite time horizon. It is non-trivial because of the presence of saturation constraints and a non-quadratic cost. It turns out that the system state, which is the transformer hot-spot (HS) temperature here, can be expressed as a function of the sequence of control variables; the cost function is then seen to be convex in the control for typical values for the model parameters. The problem of interest thus becomes a standard optimization problem. While the corresponding problem can be solved by using available numerical routines, three distributed charging policies are provided. The motivation is threefold: to decrease the computational complexity; to model the important scenario where the charging profile is chosen by the EV itself; to circumvent the allocation problem which arises with the proposed formulation. Remarkably, the performance loss induced by decentralization is verified to be small through simulations. Numerical results show the importance of the choice of the charging policies. For instance, the gain in terms of transformer lifetime can be very significant when implementing advanced charging policies instead of plug-and-charge policies. The impact of the accuracy of the non-EV demand forecasting is equally assessed.Comment: 6 pages, 3 figures, keywords: electric vehicle charging, electricity distribution network, optimal control, distributed policies, game theor

Effect of variations in load profile on power transformer cyclic ratings

Cyclic rating and demand side management (DSM) schemes are employed by electrical supply authorities to manage peak demand as an alternative to costly network upgrades. This project investigated the currently unknown impact of DSM altered load profiles on the cyclic ratings of power transformers. In response to electricity price increases, supply authorities are employing cyclic rating and DSM techniques to defer capital expenditure. A cyclic rating exploits transformer thermal inertia to permit loading above nameplate for parts of a 24 hour cycle, compensated for by loading below nameplate at other times such that insulation thermal limits are not exceeded. DSM aims to flatten load profiles commonly by transferring load from peak to off-peak times. Both techniques ensure that existing transformers can supply load peaks. Cyclic ratings achieve this by boosting capacity above demand while DSM reduces demand below capacity. In this way, the two techniques permit deferral of network upgrades. Since DSM alters the load profiles on which cyclic ratings are based, a relationship must exist between the two. The plant rating engineer must understand all such dependencies, hence the need for this project. Initially, thermal transformer models proposed by various researchers and AS 60076.7 for the purpose of predicting transformer oil and paper temperatures were studied. The AS 60076.7 models and one selected from the literature were then implemented in Matlab and compared to assess their suitability for use in the project and by plant rating engineers. The selected thermal model then became the basis of a cyclic rating calculator employed to automate the computation of cyclic ratings based on the AS 60076.7 specification. DSM techniques were researched to reveal the load shifting version as the method favoured by supply authorities and a simulator was constructed in Matlab to modify load profiles accordingly. 12 diverse Ergon Energy transformers were then selected along with a set of DSM modified load profiles as inputs to the cyclic rating calculator which computed 600 cyclic ratings for analysis. The final phase of the project then involved analysis of the ratings to determine and quantify the effect of DSM caused load profile changes on cyclic ratings. It was determined that the cyclic ratings of power transformers are negatively affected by load shifting DSM. That is, attening of load profiles causes reduction in cyclic ratings. The amount by which cyclic ratings change given a change in load profile varies according to several factors including: location, size and cooling mode of the transformer. Regression models for simple but approximate prediction of cyclic rating changes were developed. Generalised expressions for predicting the change in cyclic rating with change in peak load or load factor are: ΔCRFd = 0:45 x ΔPLd ΔCRFd = 0:37 x ΔLFi where: ΔCRFd is the percentage decrease in CRF; ΔPLd is the percentage decrease in peak load; & ΔLFi is the percentage increase in load factor. In addition to achievement of the main project objective - determination of the impact on cyclic ratings of load profile changes - a range of other outcomes from the project are useful. These include: a thorough investigation of the techniques and theory involved in transformer thermal modelling, insulation ageing, cyclic rating calculation and DSM; a program which automatically calculates cyclic ratings for power transformers; and a load shifting DSM simulation program, useful for generating altered load profiles for use with the cyclic rating calculator. This collection of knowledge and programs will be of particular use to Ergon Energy, the project sponsor. The impact of load shifting DSM on cyclic ratings, as identified in this dissertation, has the potential to negatively influence factors such as: peak capacity; transformer lifespan and maintenance; planning and budgeting for network augmentation; reduction of capital expenditure; and the valuation of DSM programs. The results and outcomes of this project have the potential to assist plant rating engineers in their understanding and application of cyclic ratings in the context of changing load profiles such that they may anticipate and therefore prevent many of the negative side-effects identified

Smart operation of transformers for sustainable electric vehicles integration and model predictive control for energy monitoring and management

The energy transmission and distribution systems existing today are stillsignificantly dependent on transformers,despite beingmore efficient and sustainable than those of decadesago. However, a large numberof power transformers alongwith other infrastructures have been in service for decades and are considered to be in their final ageing stage. Anymalfunction in the transformerscouldaffect the reliability of the entire electric network and alsohave greateconomic impact on the system.Concernsregardingurban air pollution, climate change, and the dependence on unstable and expensive supplies of fossil fuels have lead policy makers and researchers to explore alternatives to conventional fossil-fuelled internal combustion engine vehicles. One such alternative is the introduction of electric vehicles. A broad implementation of such mean of transportation could signify a drastic reduction in greenhouse gases emissions and could consequently form a compelling argument for the global efforts of meeting the emission reduction targets. In this thesis the topic of a high penetration of electric vehicles and their possible integration in insular networksis discussed. Subsequently, smart grid solutions with enabling technologies such as energy management systems and smart meters promote the vision of smart households, which also allows for active demand side in the residential sector.However, shifting loads simultaneously to lower price periods is likely to put extra stress on distribution system assets such as distribution transformers. Especially, additional new types of loads/appliances such as electric vehicles can introduce even more uncertaintyon the operation of these assets, which is an issue that needs special attention. Additionally, in order to improve the energy consumption efficiencyin a household, home energy management systems are alsoaddressed. A considerable number ofmethodologies developed are tested in severalcasestudies in order to answer the risen questions.Os sistemas de transmissão e distribuição de energia existentes hoje em dia sãosignificativamente dependentes dos transformadores, pese embora sejammais eficientes e sustentáveis do que os das décadas passadas. No entanto, uma grande parte dos transformadores ao nível dadistribuição, juntamente com outras infraestruturassubjacentes, estão em serviço há décadas e encontram-se nafasefinal do ciclo devida. Qualquer defeito no funcionamento dos transformadorespode afetara fiabilidadede toda a redeelétrica, para além de terum grande impactoeconómico no sistema.Os efeitos nefastos associadosàpoluição do arem centro urbanos, asmudançasclimáticasea dependência de fontes de energiafósseis têm levado os decisores políticos e os investigadores aexplorar alternativas para os veículos convencionais de combustão interna. Uma alternativa é a introdução de veículos elétricos. Umaampla implementação de tal meio de transporte poderia significar uma redução drástica dos gases de efeito de estufa e poderiareforçar os esforços globais para ocumprimento das metas de redução de emissõesde poluentes na atmosfera.Nesta tese é abordado o tema da elevada penetração dos veículos elétricose a sua eventual integração numarede elétricainsular. Posteriormente, são abordadas soluções de redeselétricasinteligentes com tecnologias específicas, tais como sistemas de gestão de energia e contadores inteligentes que promovamo paradigmadas casas inteligentes, que também permitem a gestão da procura ativano sector residencial.No entanto, deslastrando significativamente as cargaspara beneficiar de preçosmais reduzidosé suscetíveldecolocarconstrangimentosadicionaissobre os sistemas de distribuição, especialmentesobre ostransformadores.Osnovos tipos de cargas tais como os veículos elétricospodem introduzir ainda mais incertezassobre a operação desses ativos, sendo uma questão que suscitaespecial importância. Além disso, com ointuitode melhorar a eficiência do consumo de energia numa habitação, a gestão inteligente daenergia é um assunto que também éabordadonesta tese. Uma pletora de metodologias é desenvolvida e testadaemvários casos de estudos, a fim de responder às questões anteriormente levantadas

Time domain analysis of switching transient fields in high voltage substations

Switching operations of circuit breakers and disconnect switches generate transient currents propagating along the substation busbars. At the moment of switching, the busbars temporarily acts as antennae radiating transient electromagnetic fields within the substations. The radiated fields may interfere and disrupt normal operations of electronic equipment used within the substation for measurement, control and communication purposes. Hence there is the need to fully characterise the substation electromagnetic environment as early as the design stage of substation planning and operation to ensure safe operations of the electronic equipment. This paper deals with the computation of transient electromagnetic fields due to switching within a high voltage air-insulated substation (AIS) using the finite difference time domain (FDTD) metho

Partial Discharge in Electronic Equipments

Tato disertační práce se věnuje studiu částečných výbojů (PD) způsobených poklesem spolehlivosti a životnosti elektronických zařízení a systémů. Diagnostika PD je dnes známá metoda pro vysoké napětí u vysoko-výkonných zařízení. V případě elektronických zařízení PD testování není ale běžně používáná metoda, přestože je zde také potenciál pro vysoké elektrické zatížení vzhledem k velmi krátké vzdálenosti. Tato práce je zaměřena na vyšetřování PD činnosti u elektronických zařízení. Bylo navrženo a provedeno pracoviště pro diagnostiku PD v elektronických zařízeních. Pracovní frekvence se pohybuje od několika stovek Hz až 100 kHz. Maximální amplituda PD testovaného napětí je vyšší než 10 kV. Navzdory jednoduché konstrukci toto zařízení přináší vysokou spolehlivost měření. Více než 300 PD testů bylo provedeno na různých elektronických zařízeních a elektronických součástí,např. na planárních transformátorech a elektronických komponentách používaných při vysoko-napěťových měničíchThis dissertation thesis is devoted to study of partial discharge (PD) caused decrease of reliability and lifetime of electronic equipments and systems. PD diagnostic is nowadays well known method for high voltage high power equipments but in case of electronic devices PD testing it is not used routinely despite that there is also a potential for high electric load due to extremely short distances. The risk of PD caused failure is here extremely high because of high working frequency and consequently high repetition rate of PD events. Therefore, this work is focused on investigation of PD activity in electronic equipments. The workplace for PD diagnostic in electronic devices based on switched power supply was designed and made. Working frequency ranges from several hundreds of Hertz up to 100 kHz. The maximal amplitude of PD testing voltage is higher than 10 kV. Despite the simple design this equipment brings high repeatability and reliability of measurement. More than 300 PD tests were made on different electronic devices and electronic components, on planar transformers, and on components for voltage gate drivers for use in high voltage power converters. Possibilities of PD tools in investigation and engineering ofd insulation systems were demonstrated.

Power quality and electromagnetic compatibility: special report, session 2

The scope of Session 2 (S2) has been defined as follows by the Session Advisory Group and the Technical Committee: Power Quality (PQ), with the more general concept of electromagnetic compatibility (EMC) and with some related safety problems in electricity distribution systems. Special focus is put on voltage continuity (supply reliability, problem of outages) and voltage quality (voltage level, flicker, unbalance, harmonics). This session will also look at electromagnetic compatibility (mains frequency to 150 kHz), electromagnetic interferences and electric and magnetic fields issues. Also addressed in this session are electrical safety and immunity concerns (lightning issues, step, touch and transferred voltages). The aim of this special report is to present a synthesis of the present concerns in PQ&EMC, based on all selected papers of session 2 and related papers from other sessions, (152 papers in total). The report is divided in the following 4 blocks: Block 1: Electric and Magnetic Fields, EMC, Earthing systems Block 2: Harmonics Block 3: Voltage Variation Block 4: Power Quality Monitoring Two Round Tables will be organised: - Power quality and EMC in the Future Grid (CIGRE/CIRED WG C4.24, RT 13) - Reliability Benchmarking - why we should do it? What should be done in future? (RT 15

Investigating the impact of asset condition on distribution network reconfiguration and its capacity value

Ph. D. ThesisGenerally, decisions regarding Distribution Network (DN) operations are based only on operational parameters, such as voltages, currents and power flows. Asset condition is a key parameter that is usually not considered by Network Management Systems (NMSs) in their optimization process. The work in this thesis seeks to quantify the extent to which asset condition information can positively influence network operation and planning; specifically through Distribution Network Reconfiguration (DNR). Asset condition can be translated into Health Indices (HIs) and failure rates, allowing an NMS – or an optimization algorithm – to make better informed decisions. This is realized via appropriate asset condition assessment and failure rate models. The effect on optimal DNR is evaluated – focusing on substation condition and reliability; the idea of load transfer from one feeder or substation to a more reliable one is key in the proposed methodology. Condition-based risk is considered in the DNR problem, and the impact of transformer ageing on network reconfiguration is examined as well. The effect of asset condition assessment and ageing – which depends on the type of network branches (overhead lines or underground cables) – on the optimal distribution switch automation is also investigated. Finally, a probabilistic method is developed to quantify the contribution of DNR to network security considering asset condition and ageing. The results show that savings can be in the order of tens of thousands of U.S. dollars for a single DN; this corresponds approximately to 10% of the annual cost of active power losses. This can mean hundreds of thousands – or even millions – of U.S. dollars of savings for a single DN operator. Regarding the optimal placement of automated switches, neglecting the effect of asset ageing can result in an underestimation of expected outage cost by as much as $223,000 over a 20-year period. Finally, ignoring the contribution of DNR to security of supply can double the estimation of network risk; in addition to that, disregarding asset condition and ageing results in a reinforcement deferral overestimation of two years

Methodologies for the Evaluation and Mitigation of Distribution Network Risk

Security of supply to customers is a major concern for electricity distribution network operators. This research concentrates in particular on the UK distribution system, and on sub-transmission and extra high voltage networks within that system. It seeks first to understand the principal causes of network risk and consequent loss of supply to customers as a result of faults at these voltage levels. It then develops a suite of methodologies to evaluate that risk, in terms of expected annual cost to the network operator, under a range of different scenarios and for both simple and complex network topologies. The scenarios considered include asset ageing, network automation and increasing utilisation as a consequence of electric vehicles and heat pumps. The methodologies also evaluate possible mitigation options, including active network management, and capital expenditure for both asset replacement and network reinforcement. A composite methodology is also developed, to consider combinations of scenarios and combinations of mitigation strategies. The thesis concludes by considering issues likely to affect the extent and possible increase of network risk over the period 2010-2030