MODERNIZATION, AUTOMATION AND RELIABILITY ON CEMIG DISTRIBUIÇÃO S.A. s UNDERGROUND DISTRIBUTION NETWORK SYSTEM Cortez, A. N. CEMIG Distribuição Belo Horizonte/MG - Brazil Franceschini, L.B. CEMIG Distribuição Belo Horizonte/MG - Brazil Silva, M.R. CEMIG Distribuição Belo Horizonte/MG - Brazil Cleverson Shindi Takiguchi S&C Electric Europe LTd. Cape Town/WC South Africa
Abstract This article describes the currently executing plan for modernizing underground electric energy distribution systems in the concession area of Cemig Distribuição S.A. branch of Grupo Cemig enterprise. The highlight among the many projects is the supervision, control and automation system implementation, whose agility for interventions and recovery actions exponentially increases the system s reliability. Index-terms - Underground distribution system, modernization, automation, reliability. I. INTRODUCTION Cemig is one of the most solid and important groups of the electrical energy segment in Brazil, participating in more than 100 undertakings, in addition to consortia and a private equity fund. As a publicly traded company controlled by the Minas Gerais State, it has 114 thousand shareholders in 44 countries. Its shares are traded at stock exchanges in São Paulo (Bovespa), New York and Madrid. The Company is today a reference in the global economy, recognized for its sustainable practices. For the last 12 consecutive years, is part of the Dow Jones Sustainability World Index (DJSI World). Cemig s field of work extends to 22 brazilian states, and to Chile, with the operation of a transmission line in consortium with Alusa. It controls Light, utility responsible for the distribution network that serves the city of Rio de Janeiro amongst other cities in the state. It also holds stakes in electric energy transmission companies (TBE e Taesa), investment funds in the natural gas segment (Gasmig), telecommunication (Cemig Telecom) and energy efficiency (Efficientia). The company also invests in renewable energy sources, where it has acquired share participation in three wind farms of Energimp S.A. (Impsa), with installed capacity of 99.6 MW in Ceará State, besides other projects such as biomass, small hydroelectric power plants, solar energy and cogeneration projects. The Cemig Group is also recognized by its dimensions and technical competence, being considered the largest integrated company of the electricity sector of Brazil. It is the biggest energy supplier utility for free customers of the country, with 25% of the market, responsible for the operation of 65 power plants, with an installed capacity of 6,925 megawatts. In Minas Gerais State, it accounts for 96% of the concession area, with more than 7 million consumers in 774 municipalities. In the area of concession of Minas Gerais State, since March 2011, Cemig has initiated the conception of a bold plan for modernizing the underground network, following the base
premise of replacing the existing assets for new ones with the integration of supervision, control and automation systems, technologically placed amongst the world s most developed systems, providing an even bigger reliability, quality and security level for the electric grid and it s served customers. Inherently, the asset renovation for automatized systems will provide a considerable reduction in operational costs (OPEX) II. TOPOLOGIES Taking into account financial criteria and the required level of reliability, the following topologies of underground distribution system (UDS) can be chosen, such as radial, radial with resources, selective primary or double feeding, loop primary-circuits, ring secondary and networked seconday, also known as Network systems, as shown on Fig. 1. In the coverage of Cemig Distribuição s concession area, considering its network length, the most adopted systems are mainly Network and selective primary/double feeding systems. Fig. 1: Underground distribution topologies 1. THE SPOT NETWORK (OR RETICULATED) SYSTEM Belo Horizonte s downtown region underground power distribution system was built following the Network topologies, which offers the highest level of service continuity in high load density areas. This system is basically composed of two or more primary feeders, with one or more transformers connected to each other on their secondary terminals, creating a
secondary network mesh, which is interconnected through wells and passage boxes equipped with bus bars. The transformers are installed on transforming vaults, integrated with medium voltage switchgears and network protectors connected to the low voltage bus bars. The implementation and start-up of the Spot Network grid in Belo Horizonte were performed progressively as shown of Table 1, composed by five distinct network meshes, shown on Fig. 2, named Redes Praça Sete (A), Afonso Arinos (B), Alfredo Balena (C), Raul Soares (D) e Rio Branco (E). Table. 1: Beginning of operation - Belo Horizonte s Spot Network system Mesh Praça Sete Afonso Arinos Alfredo Balena Raul Soares Rio Branco Beginning of operation 1973 1973 1978 1984 1987 2. DOUBLE FEEDING OR SELECTIVE PRIMARY In this system, the feeding circuit is always composed of a pair of feeders, with a main circuit and an alternate circuit. The transformers are fed through 3-way switchgears, with the sources connected to ways 1 and 2, and the transformer on way 3. In the event of a fault on the main feeder, all transformers of this circuit can be transferred to the alternate circuit. This system shows enhanced levels of reliability, with the advantage of an inferior cost in comparison to the Spot Network system. This system serves several areas of high importance in the metropolitan area of Belo Horizonte, besides the downtown areas of the cities of Juiz de For a, Montes Claros, Uberlândia, Uberaba, and historical centers such as the cities of Ouro Preto and Diamantina, and great condominiums as the Alphaville complex in Nova Lima. 3. OTHER TOPOLOGIES The radial system is used in cities with lower load densities and historical cities of Minas Gerais, amongst them the condominiums (Vale dos Cristais, Riveira, Qintas do Sol, Quintas do Morro, Veredas, Morro do Chapéu and Reserva Leal) and historical centers of the cities of Mariana, Nova Lima, sabará, Santa Luzia, etc
A E D C B Fig. 2: Belo Horizonte Central Region III. MOTIVATION From 2011 on, CEMIG has started a revitalization plan in its underground distribution network seeking improvement in reliability, as the network began to present failures due to aging of its equipment and cables. Other than that, the events of the Confederations Cup, held in June 2013, and the 2014 World Cup, both promoted by the Federal Government along with the Fédération Internationale de Football Association, FIFA, would result in the affluence of people coming from different parts of Brazil and the World to the cities of Minas Gerais, especially to Belo Horizonte. Thus Cemig took part in several works to adjust the electric system to serve this increase in demand and enhance the level of reliability of the system, within which the plan for the modernization of the underground distribution system is allocated. It s also valuable to mention that the actions proposed in the modernization plan are coherent with the criteria of investments considered prudent by the Electrical Energy National Agency, ANEEL, regulatory agency responsible for the brazilian electrical system, in terms of depreciation time of the network assets, apart the significant reduction in operational costs (OPEX). IV. UNDERGROUND NETWORK S MODERNIZATION PLAN Once the alternatives and associate costs were defined, it was decided that three projects would be led: a. Double feeding system equipment: Replacement of 232 manual medium voltage switchgears, by switchgears with remote supervision, control and automation in the
UDS of the cities of Belo Horizonte, Juiz de For a, Uberlândia, Uberaba, Montes Claros, Diamantina, Ouro Preto and Varginha; b. Spot Network system equipment: Replacement of 115 sets of 500kVA transformers, network protectors and manual medium voltage switchgears by switchgears with integrated remote supervision, control and automation of the switchgear/protector. c. Spot Network system medium voltage cables: replacement of 360 km of medium voltage cables (400, 120 and 50 mm²) of the feeders in Belo Horizonte s system. 1. DOUBLE FEEDING SYSTEM - EQUIPMENT The switchgears for the double feeding systems were specified to the following criteria: a. Three three-phase terminals, with two for connection with the feeder s circuits, main and alternate, and the third for the connection with the transformer; b. Grounding terminal and window for visualization of the internal contacts (visible gap), in accordance with the regulatory standard Segurança em Instalações e Serviços de Eletricidade, NR10; c. Submersible enclosure, for compatibility with the other equipment already installed in the transforming vaults; d. SF 6 or vacuum insulation; e. Auto-transfer system, self-healing, between the feeding sources, in the event of an accidental shutdown of the main feeder s circuit; f. Supervision, control and automation system integration with the equipment in the submersible control panels, with electric quantity measurement (voltage, current, power), switchgear status (open, closed, grounded), vault monitoring (motion sensor and water level), transformer monitoring (temperature, pressure and oil level alarms) and remote opening and closing commands, as detailed on Fig. 3; g. Dimensions compatible with the vault, avoiding civil work execution to adapt the transforming vaults due to restricted physical space; The switchgear replacement of the Savassi region, in Belo Horizonte, were performed between August/2012 and June/2013, with the replacement and automation commissioning of 105 switches. The equipment communication and SCADA, Supervisory Control and Data Acquisition, interface will be concluded until April/2014. In the countryside of the State, the
works were initiated in October/2012 and are still in execution. On 05/10/2013, at 16:40h (+3h GMT), there was a blockage of the BHCN32 feeder that serves the Savassi region in Belo Horizonte. This feed possesses 16 switchgears that feed 500, 750 and 1000kVA transformers, apart two costumers fed in medium voltage (13.8 kv). Since the switchgears of this feeder did not yet posesse a fully functional supervision, control and automation system, the inspection of all transforming vaults was needed along with manual transfer to the alternate feeder, BHCN30. Since the time of the event coincided with the time of highest vehicle flow in the city of Belo Horizonte, only finished at 20:05h on the same day, time when the last transformer load was manually transferred. In the event of a fault upstream to the switch (without circulation of short circuit current through the equipment), the self-healing function would automatically transfer all load to the alternate feeder seven seconds after the interruption on the main feeder, drastically reducing the recovery time of over three hours to seconds of energy supply interruption. Fig. 3: Automation system overview 3-way solution 2. SPOT NETWORK SYSTEM EQUIPMENT With the replacement of 115 sets of transformers, network protectors and medium voltage switchgears, Fig. 4, the main goal is the reduction of failure rates, asset renewal and the improvement of the energy supply quality in the served region, with the inclusion of automation, supervision and control equipment, switchgears and network protectors. The criteria of the network protector switches were the same presented for the double feeding system, whit the following exceptions: a. The switches for the network protectors should possess only two three-phase terminals, one for the source feeding and the other for the transformer connection;
b. The supervisory, control and automation system of the switchgear should integrate the network protector automation, as detailed on Fig. 5; Fig. 4: Transforming vault of network protector in Belo Horizonte This project covers the Praça Sete network, which corresponds to the capital s hyper central area, the busiest area of the city of Belo Horizonte. Among the criteria adopted for the definition of this Network system, highlights are the obsolescence of the equipment (see Table 1), failure rates and project execution feasibility. Fig. 5: Automation system overview 2 way solution and switchgear, transformer and network protector integration 3. SPOT NETWORK SYSTEM MEDIUM VOLTAGE CABLES Comprises the replacement of 100% of the medium voltage cables of Belo Horizonte s Network system, totaling 120 km of three-phase circuits already depreciated and compromised by electric weariness and with crescent failure rates, as shown on Fig. 6.
Fig. 6: Medium voltage failure rate evolution The coverage of this project comprises the hyper central area and the hospital region of Belo Horizonte, where most touristic sites of the city are located, among them the Central Market, the Praça da Liberdade complex, the Mina Centro and the Municipal Park, places with great touristic movement. Thus the goal is to reduce the system s failure rate and to improve the safety to the utilities working teams and to general citizens. V. MINEIRÃO STADIUM S ENERGY SUPPLY The automation solution engineered for the double feeding system (3-way switchgears with supervisory, control and automation resources along with transformer and vault monitoring) was also applied to the energy supply of the Governador Magalhães Pinto Stadium, the Mineirão, re-opened in 12/21/2013, after three years of modernization works performed with Minas Gerais State Government s resources, to hold the Confederations Cup games, held in 2013, and for the 2014 World Cup. The energy supply concept for Mineirão Stadium was engineered with two feeding sources in 13.8kV, Fig. 7, from two different substations: Main feeder, BHMR27, of Maracanã substation, with the installation of a section of 13.8 kv and the construction of 4.73 km of underground network at 13.8 kv, employing 400 mm² XLPE cables; Alternate feeder, BHPM15, of Pampulha substation, with the installation of a section of 13.8 kv and the construction of 6.48 km of underground network at 13.8 kv, employing 400 mm² XLPE cables; Installation of a 4-way SF 6 switchgear with supervisory, control and automation system, with the same requirements as presented for the 3-way switchgear solution.
Figure 7: Feeder sources for Mineirão Stadium The supervision, control and monitoring system for the 4-way switchgear and for the monitoring of the transformer vault are in operation since April 2013, under the coordination of Cemig s Centro de Operação da Distribuição (COD) (Distribution Operation Center) through SCADA, without fail logs, including all the Confederations Cup period - second half of June 2013. Since the entry into service of the supervisory system, maneuvers were carried out remotely for both, load transfer between the main and alternate feeders and even for scheduled shutdown, resulting in cost savings related to the team s displacement to the substation. In addition, the Mineirão Stadium will be equipped with a solar plant, with 1.42 MWp (megawatt peak) installed power, placed on the Stadium s roof with the installation of nearly six thousand photovoltaic modules. The energy generated by the solar plant will be injected in the distribution electric system through the fourth way of the 4-way switchgear, as shown in the single-line diagram of the Figure 8.
Figure 8: Single-line diagram of the power input of Mineirão Stadium VI. CONCLUSIONS Although yet with phases running, gains can be measured with the execution of the modernization plan for the underground network systems in the concession area of Cemig. The medium voltage cables replacement in the Alfredo Balena network were prioritized, for this network serves the hospital care area of Belo Horizonte city and, since the installation of the new conductors, between October 2012 and January 2013, there were no registered events related to insulation failures in cables and splicings in these circuits. At the same time, there were prioritization in the replacement of 3-way switchgear of the Savassi underground system, in which the old switches did not have grounding terminals for the circuit, and some presented SF 6 gas leakage and were not adaptable for automation. Once the replacement of the equipment and the commissioning of the supervisory system were finished, the transformers of the feeding circuits of the Savassi network can be transferred from the main source to the alternate one in the event of a problem in the feeding branch, reducing the recovery time from hours to seconds. If an internal failure occurs in one of the transformers, the switchgear isolates this transformer, keeping the remaining equipment operational. The modernization improves the reliability of the underground network system, enabling them to be more robust and, with the availability of the supervisory and automation system, reducing the recovery and maneuvers times, resulting in a reduction of the operational costs in both, the emergency care and in the routine inspections, taking full account of the project objectives. VII. REFERENCES [1] Ortiz, G.T, Gilmer, D.L., Dupy, D.D, Primary-selective system chosen over spot networks to serve new downtown loads, Transmission & Distribution, July, 1991. [2] Wagner, V.E, Reliability and cost comparison of power distribution configurations Industrial and Commercial Power Systems Technical Conference, 2008. ICPS 2008. IEEE/IAS [3] Sanabria, D.R. Comparative Framework for Service Reliability in Electric Distribution Systems. Thesis presented to the master of science in electrical engineering at the University of Puerto Rico, 2005.
VIII. BIOGRAPHIES Anderson Neves Cortez was born in Divinópolis, Brazil, on January 12th, 1967. He graduated as Electrical Engineer at the Pontifícia Universidade Católica de Minas Gerais and obtained his Master Degree in Electrical Engineering at the Universidade Federal de Minas Gerais. He works at CEMIG (Companhia Energética de Minas Gerais) managing Distribution Engineering and Planning Areas. His special fields of interest include planning and engineering of transmission and distribution systems. Luiz Braz Franceschini was born in Juiz de Fora, Brazil. Graduated as Electrical Engineer and Bachelor in laws at Federal University of Juiz de Fora. Specialist in Systems Information Analysis at Faculdade Estácio de Sá, Rio de Janeiro and MBA in Business Management at Instituto Brasileiro de Mercado de Capitais IBMEC, Belo Horizonte. Worked at Cemig Distribuição S.A. since 1987, where held various positions. Currently is responsible for the management of Construction and Field Services. Marcelo Róger da Silva was born in Caratinga, Brazil, on October 7th, 1973. He graduated as Electrical Engineer at the Pontifícia Universidade Católica de Minas Gerais and obtained his Master Degree in Electrical Engineering at the Universidade Federal de Minas Gerais. He works at Cemig (Companhia Energetica de Minas Gerais), in coordinating services construction, maintenance and operation of underground networks of metropolitan region Belo Horizonte. His areas of interest include engineering, maintenance and automation of distribution systems. Cleverson Takiguchi has extensive knowledge in the energy sector. With almost 20 years of global industry experience, and over 30 published papers, Cleverson Takiguchi has become a thought leader in the area of Smart Grid applications and Power Systems. Cleverson has worked in the Brazilian operation of S&C for 14 years, 7 years of which were spent in leadership roles. Cleverson has now taken his skills and experience to Cape Town, with the aim to develop business across Sub-Saharan Africa.
In his current position, Cleverson will cover the full range of S&C products and services and also provide sales and engineering support. Furthermore, Cleverson will take an active approach to engaging new target markets and enhancing S&C s brand in the region. Cleverson is heavily involved with several trade associations including: South African Wind Association, as well as being on the advisory board for both the African Utility Week and Distributech Africa conferences. Cleverson regularly engages with media and often speaks on the opportunities facing the African Grid, as well as: transmission and distribution, energy security, energy storage, energy supply, Smart Grid and automated communications. Presenter: The paper is presented by Serge Kabunda