Hv shunt reactors: an overall comparative analysis between dry-type air core and oil-immersed iron core technologies

Shunt reactors in high-voltage and extra high-voltage, have historically been manufactured using oil-immersed iron core technology, mainly due to issues related to the insulation of the reactor windings. However, with the improvement of the insulating films as well as on the manufacturing techniques, it has been possible the manufacturing of these equipment using dry-type air core technology, which has demonstrated to be efficient, environmentally friendly and, in many cases, with lower costs in short, medium and long-term basis. It is required therefore, the study of which are the changes when it is adopted this air core technology, which has been the more and more accepted on worldwide market. The main aspects regarding the application of these equipment are disclosed, stablishing a parallel between both technologies, with regards to the construction aspects, the viability of replacement (which are the cases at which they are or not indicated), the losses comparison, all the precautions and remarks in terms of magnetic field, the protection and the transients aspects (including a study case of two identical equipment in both technologies, with calculations and simulations of transient frequency and voltage, TRV and RRRV, as well as a percentage comparative analysis between the calculated and simulated results). These comparisons, aim to contribute with technical community and the global trend in adopting dry-type technology, highlighting the main differences and particularities to be considered when replacing traditional type.Reatores em derivação em alta e extra alta tensão, historicamente sempre foram fabricados em tecnologia com núcleo de ferro imersos em óleo, devido prioritariamente a questões relacionadas ao isolamento dos enrolamentos. Contudo, com o avanço dos materiais isolantes e de técnicas de fabricação, tem sido possível a fabricação destes equipamentos utilizando tecnologia com núcleo de ar, a qual tem se demonstrado eficiente, ambientalmente amigável e, em muitos casos, com menores custos de curto, médio e longo prazo. Fazendo-se necessário portanto, o estudo de quais as implicações quando se opta por esta tecnologia, que tem sido cada vez mais aceita no mercado mundial. São abordados os principais aspectos da aplicação destes equipamentos, estabelecendo um paralelo entre ambas tecnologias, no que tange os aspectos construtivos, a viabilidade de substituição (quais os casos em que ela é ou não indicada), comparativo de perdas, aspectos de proteção, todas as precauções e observações em termos de campo magnético, aspectos transitórios (incluindo estudo de caso de dois equipamentos idênticos nas duas tecnologias, com cálculos e simulações das frequências e tensões transitórias, TRT e TCTRT, bem como um comparativo percentual entre os resultados calculados e simulados). Tais comparações visam auxiliar a comunidade técnica, de modo a contribuir com a tendência global em adotar a tecnologia do tipo seco, enfatizando as principais diferenças e particularidades a serem consideradas quando da substituição da tecnologia tradicional

Transformer innovation in a changing energy landscape – Part II

Reliability and resilience are two different concepts but closely related. Power grids need to be prepared to secure a continuous sourcing energy, and at the same time, be ready to react in case of incidents or events. The integration of renewables also possesses challenges to the efficiency and reliability of the transmission grids and distribution networks. Digitalization is a powerful tool to strengthen the power and distribution systems, but other traditional alternatives are also used with good results

Standards relevant to transformers – Part VI

Due to the wide use of transformers, their specification is very important. Transformer specification is a “common language” between manufacturers, suppliers, vendors, engineers, or any other parties that work with transformers on the technical level. That is the reason why the transformer specifications are well defined by standards

Standards relevant to transformers – Part II

The first step taken by the American Institute of Electrical Engineers (AIEE, formed in 1884) towards the standardisation of electrical apparatus and methods, was a discussion on the standardization of generators, motors and transformers, which took place simultaneously in New York and Chicago on 29 January 1898. A committee was appointed by the Council of the Institute under the chairmanship of Prof. Francis B. Crocker, and included eminent electrical engineers of the day, such as Charles P. Steinmetz, Lewis B. Stillwell (Niagara Power Company) and Elihu Thomson. The first standard (or ‘rules’, as they were called then), was presented and adopted by the Institute on 26 June 1899. This common standard for generators, motors and transformers was subsequently revised ten times during the next 22 years. In 1907, a standing committee, called the Standards committee, was constituted to continually monitor and revise this standard. This committee continued to grow over the years with several subcommittees to work on individual products required for electric power industry. Over the years, the input into the standardisation rules was also obtained from the Association of Edison Illuminating Companies (AEIC), the Electric Power Club (later to become the National Manufacturers Association, NEMA), the National Electric Light Association (NELA, the forerunner to the Edison Electrical Institute, EEI), and others. In parallel to AIEE, these organisations also began to issue standards. For example, in 1916, NELA issued a report on the standardisation of power ratings, voltages and taps for transformers (probably the first exclusive US), and NEMA standards on transformers that are still in vogue today. AIEE standards committee formed a separate subcommittee (No. 8) for transformers in 1918. Until 1921, transformer standard was a chapter in the common rules of standardization, titled Stationary induction apparatus

Modelling of a 400-kV MSCDN reactor for computation of voltage and field distributions during switching transients

In this paper, a model for the reactor of a 400-kV mechanically switched capacitor with damping network (MSCDN) based on an equivalent circuit representation is developed. The model is based on sub-dividing the physical reactor into sections which are sufficiently small to be represented by a lumpedparameter equivalent circuit. The circuit parameters are obtained for each section using analytical formulae based on the physical configuration of the reactor, the winding layout, and the insulation material. The model is then simulated in the ATP/EMTP program for the evaluation of transient voltage and field distributions along of the reactor. This helps in identifying possible failure scenarios which will allow designing measures to mitigate failures effectively during transients arising from switching operations. Further analysis of the results has revealed that there are substantial dielectric stresses imposed on the winding insulation that can be attributed to a combination of three factors. First, the surge arrester operation during the MSCDN energization, which causes steep voltage change at the reactor terminal. Second, the non-uniform voltage distribution, resulting in high stresses across the top inter-turn windings. Third, the rapid rate-of-change of voltage in the assumed worst-case reactor winding location. This is accompanied by a high dielectric (displacement) current through the inter-turn winding insulation. The results of this paper indicate that a synergistic effect of high electric field and high dielectric current occurring at worst energization, followed by the thermal effects of steady state operation may contribute to the failure of air-core reactors used on the 400-kV MSCDN

Improved power losses calculation model for air core reactors

Air core reactors (ACR) have been widely used in power systems in several different applications like harmonic filters, thyristor-controlled reactors (TCR) for static var compensators (SVC), mechanically switched reactors (MSR) for shunt compensation of long transmission lines, smoothing and valve reactors for line commutate converter (LCC) and for voltage sourced converted (VSC), respectively, in HVDC systems, onshore and offshore. As a global trend, the pursuit of environmentally friendly equipment has increased, leveraging the use of ACRs in ultra-high voltage (UHV) systems. Applying that equipment in such voltage levels demands very accurate calculation models to establish the proper design parameters (e.g., inductance values, power losses and audible noise levels) as well as the stresses (dielectric, thermal and mechanical) that the equipment will have to withstand during operation, for their lifecycle. One typical concern related to those calculation models is regarding the prediction of the eddy current winding losses by analytical models. Several models have been proposed for this type of calculation for transformers and electrical machines, but usually with some constraints that make those models more suitable to that equipment than to others. With the crescent demand for ACR with lower power losses levels, it makes sense to look for improvements on those calculation models. One way of supporting the enhancement of those models is using software based on finite element methods (FEM) that allows for very detailed simulation of the physical phenomena related to the air core reactors and their applications. Although the FEM is a powerful tool for complex simulations, it is usually very time consuming and may require sophisticated computational apparatus to run more complex models. Air core reactors are equipment composed by one or several concentric windings made of conductive material (aluminum or copper) and their design may vary significantly, from a few kilograms to some dozens of tons. The simulation, in a reasonable time, of that equipment with several windings and sometimes thousands of turns would require computers that are not easily found in regular industries. In this work an optimized modeling process for simulating ACR using a 2-D equivalent geometry method in a finite element-based software was developed to allow for faster simulations. The validation of the method is performed by running a full factorial design of experiments (DOE), screening four design parameters of windings: winding diameter, winding height, number of strands and strand diameter, as these parameters significantly affect the two main design characteristics of the air core reactors: inductance and winding power losses. The results of the finite element simulations are statistically compared to the results of analytical calculations. With the deployment of this process, an improvement for the calculation of the eddy current winding losses of that equipment is proposed

Análise comparativa do desempenho das manobras de religamento monopolar e tripolar para eliminação de faltas monofásicas em linhas de transmissão

Orientador: Maria Cristina Dias TavaresDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: Um sistema de energia elétrica compreende geração, transmissão e distribuição de energia elétrica. As linhas de transmissão são usadas para transmitir energia elétrica a centros de carga distantes. O rápido crescimento dos sistemas de energia elétrica nas últimas décadas resultou em um grande aumento do número de linhas em operação e seu comprimento total. Para níveis de transmissão EHV (extra alta tensão), entre 90-95% de todas as falhas de linha envolvem apenas uma única fase. Destes, mais de 90% são temporários e podem ser compensados ??por três fases de religamento; Conseqüentemente, faltas fase-terra têm recebido a maior atenção em estudos de sistema. Este projeto analisa as entidades da linha de transmissão resultantes da eliminação de uma falta monofásica usando o SPAR (Auto-Reclusão Monofásica) e o religamento automático trifásico na linha de transmissão de 400 kV. O projeto analisa a influência de diferentes parâmetros do sistema, como nível de compensação, comprimento da linha e local da falta, juntamente com o método de mitigação. Para o estudo de simulação, PSCAD / EMTDC é selecionado como o software de simulaçãoAbstract: An electric power system comprises of generation, transmission and distribution of electric energy. Transmission lines are used to transmit electric power to distant large load centers. The rapid growth of electric power systems over the past few decades has resulted in a large increase of the number of lines in operation and their total length. For EHV (extra high voltage) transmission levels, between 90¿95% of all line faults involve only a single phase. Of these, more than 90% are temporary and can be cleared by three phase reclosing; consequently, phase-to-ground faults have received the most attention in system studies. This project analyzes the transmission line entities resulting from elimination of a single-phase fault by using the SPAR (Single-Phase Auto-Reclosing) and three-phase auto-reclosing on the 400 kV transmission line. The project analyzes the influence of different system parameters like compensation level, line length and fault location together with the mitigation method. For the simulation study, PSCAD/EMTDC is selected as the simulation softwareMestradoEnergia EletricaMestre em Engenharia ElétricaCAPE

Transients in reactors for power systems compensation

This thesis describes new models and investigations into switching transient phenomena related to the shunt reactors and the Mechanically Switched Capacitor with Damping Network (MSCDN) operations used for reactive power control in the transmission system. Shunt reactors and MSCDN are similar in that they have reactors. A shunt reactor is connected parallel to the compensated lines to absorb the leading current, whereas the MSCDN is a version of a capacitor bank that has been designed as a C-type filter for use in the harmonic-rich environment. In this work, models have been developed and transient overvoltages due to shunt reactor deenergisation were estimated analytically using MathCad, a mathematical program. Computer simulations were then undertaken using the ATP/EMTP program to reproduce both single-phase and three-phase shunt reactor switching at 275 kV operational substations. The effect of the reactor switching on the circuit breaker grading capacitor was also examined by considering various switching conditions. The main original achievement of this thesis is the clarification of failure mechanisms occurring in the air-core filter reactor due to MSCDN switching operations. The simulation of the MSCDN energisation was conducted using the ATP/EMTP program in the presence of surge arresters. The outcome of this simulation shows that extremely fast transients were established across the air-core filter reactor. This identified transient event has led to the development of a detailed air-core reactor model, which accounts for the inter-turn RLC parameters as well as the stray capacitances-to-ground. These parameters are incorporated into the transient simulation circuit, from which the current and voltage distribution across the winding were derived using electric field and equivalent circuit modelling. Further analysis of the results has revealed that there are substantial dielectric stresses imposed on the winding insulation that can be attributed to a combination of three factors. (i) First, the surge arrester operation during the MSCDN energisation, which causes steep voltage change at the reactor terminal. (ii) Second, the nonuniform voltage distribution, resulting in high stresses across the top inter-turn windings. (iii) Third, the rapid rate-of-change of voltage in the assumed worst-case reactor winding location. This is accompanied by a high dielectric (displacement) current through the inter-turn winding insulation. Work within this investigation proposes that a synergistic effect of high electric field and high dielectric current occurring at worst energisation, followed by the thermal effects of steady state operation contributes to the failure of air-core reactors used on the 400 kV MSCDN