An Assessment of PIER Electric Grid Research 2003-2014 White Paper

This white paper describes the circumstances in California around the turn of the 21st century that led the California Energy Commission (CEC) to direct additional Public Interest Energy Research funds to address critical electric grid issues, especially those arising from integrating high penetrations of variable renewable generation with the electric grid. It contains an assessment of the beneficial science and technology advances of the resultant portfolio of electric grid research projects administered under the direction of the CEC by a competitively selected contractor, the University of California’s California Institute for Energy and the Environment, from 2003-2014

Demand Response Benefits for Major Assets of High Voltage Distribution Systems - Capacity Gain and Life Management

Power systems require an adequate capacity and higher utilization efficiency for an economic and reliable supply of electricity. However, their utilization efficiency is ordinary owing to low load factor and reserve capacity needs. Moreover, the growth of electricity demand and aging infrastructure call for massive investments in form of expansions and replacements. Therefore, the power industry is searching for novel solutions to deal with the future needs. Demand response (DR), a load shaping tool in smart grids, can be a potential solution to the future needs. The aim of the dissertation is to assess the DR benefits of capacity utilization gain and better life management for major assets of high voltage grid. The study focuses on subtransmission grids because they have captured least attention in the prior research. Primary substation transformers have given special attention here due to their vital position in the system and high component cost. The aim of the dissertation is further divided into three tasks in order to distinguish the DR benefit among phases of operations and planning and various components. The first task proposes optimization models for utilization gain and life management of transformers by DR during normal and contingency operations. The second task offers tools for optimal capacity planning of transformers in primary distribution substations with and without considering DR. These tools incorporate all transformer related costs, their failure rate increase with age, and their salvage value based on loss-of-life. The third task determines the potential of DR in mitigating the redundancy needs of lines/cables, transformers, and busbars by comparing outage cost due to their contingencies. The simulations are performed using the developed models for typical Finnish systems. The results indicate the following notable deductions. The utilization efficiency of grid components can be substantially improved using DR that depends upon load shape and its DR capability. Also, DR offers significant better life management potential for transformers during both nor- mal and contingency operations. Moreover, the employment of DR along with remote switch- ing of load transfer between substations provides superior savings in transformer capacity planning as compared to that of manual load shifting. Furthermore, the optimal decisions of DR activations are essential in order to gain the intended DR benefits at a minimal expense. The power system utilities can use the models of this dissertation for making decisions of DR deployments. These deployments will be helpful in delaying or eliminating the capacity investments. Moreover, the tools of the second task will help asset managers for taking optimal planning decisions of transformer ratings and their replacement and maintenance schedules.Voimajärjestelmät tarvitsevat riittävästi kapasiteettia ja korkean käyttöasteen taatakseen taloudellisen ja luotettavan sähkön saannin. Järjestelmän potentiaalia ei saada kuitenkaan hyödynnettyä täydellisesti matalan käyttökertoimen ja reservivaatimusten takia, minkä lisäksi kasvava sähkön kysyntä ja ikääntyvä järjestelmä lisäävät painetta investointeihin. Tämän takia sähköteollisuus on kiinnostunut uusista ratkaisuista, joilla järjestelmäresurssit saadaan tehokkaampaan käyttöön. Älykkäiden sähköverkkojen tarjoama kysyntäjousto (demand response, DR) nähdään yhtenä tällaisena ratkaisuna. Tämän väitöskirjan tarkoituksena on tutkia kysyntäjouston hyötyä siirtoverkon kapasiteetin hyödyntämisessä sekä eliniän hallinnassa. Työ keskittyy suurjännitejakeluverkkoon, jonka osalta aihetta ei ole vielä juuri tutkittu. Erityisesti keskitytään muuntajiin niiden tärkeyden ja korkean kustannuksen takia. Jotta kysyntäjouston tarjoama hyöty voidaan erotella tarkemmin verkon eri toimintojen, suunnittelun ja komponenttien kesken, väitöskirja on jaettu kolmeen osaan. Ensimmäinen osa esittelee optimointimallin muuntajan käyttöasteen parantamiseen ja eliniän pidentämiseen kysyntäjouston avulla normaalikäytön aikana sekä vikatilanteissa. Toinen osa tarjoaa työkaluja muuntajan optimaalisen kapasiteetin mitoittamiseen kysyntäjouston kanssa ja ilman. Kolmannessa osassa tutkitaan kysyntäjouston potentiaalia vähentää järjestelmän ylimitoittamista vertailemalla keskeytyskustannuksia. Työssä suoritettavat simuloinnit tehdään Suomen järjestelmää kuvaavalla mallilla. Tulokset osoittavat, että verkostokomponenttien hyödyntämistä voidaan tehostaa huomattavasti kysyntäjoustolla riippuen kuormituksen vaihtelusta ja sen tarjoamasta joustosta. Kysyntäjousto vähentää myös huomattavasti muuntajien vanhenemista normaalin käytön ja vikatilanteiden aikana. Kysyntäjousto optimaalinen aktivointi on kuitenkin olennaista, jotta halutut hyödyt voidaan saavuttaa. Järjestelmävastaavat voivat käyttää työssä esiteltyjä malleja, jos he suunnittelevat kysyntäjouston hyödyntämistä esimerkiksi investointipäätösten yhteydessä. Lisäksi työn toisessa osassa esiteltävät työkalut auttavat suunnittelijoita muuntajien optimaalisessa mitoittamisessa ja ylläpidossa

Reliability Studies of Distribution Systems Integrated with Energy Storage

The integration of distributed generations (DGs) - renewable DGs, in particular- into distribution networks is gradually increasing, driven by environmental concerns and technological advancements. However, the intermittency and the variability of these resources adversely affect the optimal operation and reliability of the power distribution system. Energy storage systems (ESSs) are perceived as potential solutions to address system reliability issues and to enhance renewable energy utilization. The reliability contribution of the ESS depends on the ownership of these resources, market structure, and the regulatory framework. This along with the technical characteristics and the component unavailability of ESS significantly affect the reliability value of ESS to an active distribution system. It is, therefore, necessary to develop methodologies to conduct the reliability assessment of ESS integrated modern distribution systems incorporating above-mentioned factors. This thesis presents a novel reliability model of ESS that incorporates different scenarios of ownership, market/regulatory structures, and the ESS technical and failure characteristics. A new methodology to integrate the developed ESS reliability model with the intermittent DGs and the time-dependent loads is also presented. The reliability value of ESS in distribution grid capacity enhancement, effective utilization of renewable energy, mitigations of outages, and managing the financial risk of utilities under quality regulations are quantified. The methodologies introduced in this thesis will be useful to assess the market mechanism, policy and regulatory implications regarding ESS in future distribution system planning and operation. Another important aspect of a modern distribution system is the increased reliability needs of customers, especially with the growing use of sensitive process/equipment. The financial losses of customers due to industrial process disruption or malfunction of these equipment because of short duration (voltage sag and momentary interruption) and long duration (sustained interruption) reliability events could be substantial. It is, therefore, necessary to consider these short duration reliability events in the reliability studies. This thesis introduces a novel approach for the integrated modeling of the short and long duration reliability events caused by the random failures. Furthermore, the active management of distribution systems with ESS, DG, and microgrid has the potential to mitigate different reliability events. Appropriate models are needed to explore their contribution and to assist the utilities and system planners in reliability based system upgrades. New probabilistic models are developed in this thesis to assess the role of ESS together with DG and microgrid in mitigating the adverse impact of different reliability events. The developed methodologies can easily incorporate the complex protection settings, alternate supplies configurations, and the presence of distributed energy resources/microgrids in the context of modern distribution systems. The ongoing changes in modern distribution systems are creating an enormous paradigm shift in infrastructure planning, grid operations, utility business models, and regulatory policies. In this context, the proposed methodologies and the research findings presented in this thesis should be useful to devise the appropriate market mechanisms and regulatory policies and to carry out the system upgrades considering the reliability needs of customers in modern distribution systems

Feeder flow control and operation in large scale photovoltaic power plants and microgrids : Part I Feeder ow control in large scale photovoltaic power plants : Part II Multi-microgrids and optimal feeder ow operation of microgrids

This thesis deals with the integration of photovoltaic energy into the electrical grid. For this purpose, two main approaches can be identified: the interconnection of large scale photovoltaic power plants with the transmission network, and the interconnection of small and medium-scale photovoltaic installations with the distribution network. The first part of the thesis is focussed on the interconnection of large scale photovoltaic power plants. Large scale photovoltaic power plants are required to provide different ancillary services to the electrical networks. For this purpose, it is necessary to control the active and reactive power injected by photovoltaic power plants at the point of interconnection, i.e. to control the power flow through the main feeder. In this direction, it is developed a central controller capable of coordinating the different devices of the photovoltaic power plants as photovoltaic inverters, FACTS, capacitor banks and storage. The second part is focused on the distributed generation, consisting on small and medium-scale generation facilities connected to the distribution system. In this context, distribution grids, traditionally operated as passive systems, become active operated systems. In this part, the microgrid concept is analysed, which is one of the most promising solutions to manage, in a coordinated manner, the different distributed energy resources. Taking into account the possible transformation of the current distribution system to a multi-microgrid based system, the different architectures enabling microgrids interconnections are analysed. For the multi-microgrid operation, it could result interesting that a portion of their networks operate so that the power exchange is maintained constant, i.e. controlling the power flow at the main feeder. In this thesis, an optimal power flow problem formulation for managing the distributed generation of these feeder flow controlled microgrids is proposed

City-Friendly Smart Network Technologies and Infrastructures: The Spanish Experience

Efficient, resilient, and sustainable electricity delivery is a key cornerstone in increasingly large and complex urban environments, where citizens expect to keep or rise their living standards. In this context, cost-effective and ubiquitous digital technologies are driving the transformation of existing electrical infrastructures into truly smart systems capable of better providing the services a low-carbon society is demanding. The goal of this paper is twofold: 1) to review the dramatically evolving landscape of power systems, from the old framework based on centralized generation and control, aimed at serving inelastic customers through alternating current (ac) transmission networks and one-way distribution feeders, to a new paradigm centered mainly around two main axes: renewable generation, both centralized and distributed, and active customers (prosumers), interacting with each other through hybrid ac/dc smart grids; 2) to illustrate, through featured success stories, how several smart grid concepts and technologies have been put into practice in Spain over the last few years to optimize the performance of urban electrical assets

Distributed resource integration analysis and network design of electric power distribution systems

The integration of high percentages of distributed energy resources and controllable loads into the distribution system coupled with the strict power quality and service reliability requirements at the power distribution level are necessitating a significant change in the planning, operation and control of the traditional power distribution system. The future power distribution circuits should be able to accommodate the new technologies while simultaneously providing a desired level of power quality and service reliability to the customers. This thesis aims to address the current and future grid requirements of both existing as well as new distribution systems with regard to power quality and service reliability issues. Several methods are proposed to evaluate and mitigate power quality and service reliability concerns due to the integration of smart grid technologies into both existing and new distribution circuits. Notably, for the existing distribution circuits, integration studies are simulated to analyze and mitigate the impacts of electric vehicle loads and photovoltaic generation on the distribution voltages. Furthermore, the problem of siting, sizing and deployment of distributed energy storage systems in meeting distribution planning requirements with regard to integrating distributed generation and providing contingency requirements is also addressed. A new distribution system both grid-connected and operating in islanded mode, however, could be designed to the new requirements. The new distribution circuit could be designed to meet the power quality and service reliability standards directly, thus more efficiently mitigating the concerns. In the thesis, the new distribution circuit design is approached from the perspective of maximizing the service reliability. For the new distribution circuit, approaches to reliability based distribution circuit design are proposed.Electrical and Computer Engineerin

Impact of intergrating teebus hydro power on the unbalanced distribution MV network

Small hydro power sources have been identified as one of the renewable energy technologies that the South African government is focusing on in order to generate more electricity from renewable/independent resources. Due to the low carbon output of most renewable energy technologies and the carbon intensive power generation technologies that are currently being used in South Africa e.g. Hydro, coal, gas, and etc. further pressure is increasing to incorporate cleaner forms of generation. In 2002 a study focusing on the hydropower potential was compiled providing an assessment according to conventional and unconventional possibilities for all the provinces. Nowadays, the power electricity demand is growing fast and one of the main tasks for power engineers is to generate electricity from renewable energy sources to overcome this increase in the energy consumption and at the same time reduce environmental impact of power generation. Eskom Distribution Eastern Cape Operating Unit (ECOU) was requested to investigate the feasibility of connecting a small hydro power scheme located in the Teebus area in the Eastern Cape. The Eastern Cape in particular, was identified as potentially the most productive area for small hydroelectric development in South Africa for both the grid connected and off grid applications. These network conditions are in contrast to the South African electricity network where long radial feeders with low X/R ratios and high resistance, spanning large geographic areas, give rise to low voltages on the network. Practical simulation networks have been used to test the conditions set out in the South African Grid Code/NERSA standard and to test the impact of connecting small hydro generation onto the unbalanced distribution network. These networks are representative of various real case scenarios of the South African distribution network. Most of the findings from the simulations were consistent with what was expected when comparing with other literatures. From the simulation results it was seen that the performance of the variable speed generators were superior to that of the fixed speed generators during transient conditions. It was also seen that the weakness of the network had a negative effect on the stability of the system. It is also noted that the stability studies are a necessity when connecting the generators to a network and that each case should be reviewed individually. The fundamental cause of voltage instability is identified as incapability of combined distribution and generation system to meet excessive load demand in either real power or reactive power form

Bulk electric system reliability simulation and application

Bulk electric system reliability analysis is an important activity in both vertically integrated and unbundled electric power utilities. Competition and uncertainty in the new deregulated electric utility industry are serious concerns. New planning criteria with broader engineering consideration of transmission access and consistent risk assessment must be explicitly addressed. Modern developments in high speed computation facilities now permit the realistic utilization of sequential Monte Carlo simulation technique in practical bulk electric system reliability assessment resulting in a more complete understanding of bulk electric system risks and associated uncertainties. Two significant advantages when utilizing sequential simulation are the ability to obtain accurate frequency and duration indices, and the opportunity to synthesize reliability index probability distributions which describe the annual index variability. This research work introduces the concept of applying reliability index probability distributions to assess bulk electric system risk. Bulk electric system reliability performance index probability distributions are used as integral elements in a performance based regulation (PBR) mechanism. An appreciation of the annual variability of the reliability performance indices can assist power engineers and risk managers to manage and control future potential risks under a PBR reward/penalty structure. There is growing interest in combining deterministic considerations with probabilistic assessment in order to evaluate the “system well-being” of bulk electric systems and to evaluate the likelihood, not only of entering a complete failure state, but also the likelihood of being very close to trouble. The system well-being concept presented in this thesis is a probabilistic framework that incorporates the accepted deterministic N-1 security criterion, and provides valuable information on what the degree of the system vulnerability might be under a particular system condition using a quantitative interpretation of the degree of system security and insecurity. An overall reliability analysis framework considering both adequacy and security perspectives is proposed using system well-being analysis and traditional adequacy assessment. The system planning process using combined adequacy and security considerations offers an additional reliability-based dimension. Sequential Monte Carlo simulation is also ideally suited to the analysis of intermittent generating resources such as wind energy conversion systems (WECS) as its framework can incorporate the chronological characteristics of wind. The reliability impacts of wind power in a bulk electric system are examined in this thesis. Transmission reinforcement planning associated with large-scale WECS and the utilization of reliability cost/worth analysis in the examination of reinforcement alternatives are also illustrated