Relevant aspects of Maintenance Management strategies of Itaipu GIS on monitoring and control gas emissions of greenhouse effects

Transcription

1 Relevant aspects of Maintenance Management strategies of Itaipu GIS on monitoring and control gas emissions of greenhouse effects ADRIÁN ¹, DOUGLAS ¹, GREGORIO ², DIEGO ² ¹ Itaipu Binacional, ² Fundación Parque Tecnológico Itaipu Paraguay Paraguay, Brasil SUMMARY The Itaipu Binacional, located at the centre of South America in the border between Brazil and Paraguay, is one of the largest hydroelectric power plants of the world that produces clean and renewable electric energy throughout their twenty generator units of 700 MW each over the Paraná river, totalising fourteen thousand megawatts of installed power, and transmitting its energy to both countries by means of their several high-voltage equipment as step-up transformers, GIS and transmission lines. Over the last years, it has been increasing its levels of electrical energy production and breaking its own records, aiming ever to its corporate mission and vision, which is based on strategic pillars such as Environment and Social Responsibility, Sustainability and Economic Development of the region. Even before launching the first generator unit in the 1980s, Itaipu adopted a special O&M policy related to all equipment to be installed at the dam, and has continued to do so until current days. The 550kV Gas Insulated Switchgear (GIS) is part of the mentioned policy, and from the start of the energy supply, its maintenance technicians staff have been committed to comply with everything related to as well as good practices of maintenance of high-voltage equipment, including the own SF 6 gas sulfur hexafluoride. As any other similar installation, the Gas Insulated Switchgear has inherent factors that may lead to eventual failures, or in the worst case, to undesirable flashovers with the related forced unavailability of the equipment. More than ten years ago, the Electrical Maintenance Engineering Division assembled a PMP Predictive Maintenance Platform composed by monitoring systems to detect longterm abnormalities, such as partial discharges, defects on circuit breakers, supervision of the insulation gas, besides other portable tools based on infrared technologies as for instance surface thermography and gas leakages, X-ray inspection, among other types of inspections, and periodic and aperiodic activities of maintenance. In this specific opportunity, Itaipu wants to share its experience of its SF 6 gas monitoring system such as the humidity level control of the gas chambers as well as early density leakage detection in order to avoid emissions of this gas due to the known harmful effects on the environment, and their incidences on greenhouse effects, thus helping to enhance the high-voltage equipment maintenance of the installation, and consequently making a positive contribution to nature. Keyword Maintenance Management, Gas Insulated Switchgear, greenhouse effects, SF 6 emission reduction, Electric Power System, Predictive Maintenance, High-voltage equipment. 1

2 Main Author Personal Data: Adrián Enrique Osorio Paredes Direct: (PY) Direct: (BR) Mobile: (PY) 2

3 INTRODUCTION The Itaipu Binacional, is located at the center of South America, in the border between Paraguay and Brazil, is one of the largest hydroelectric power plant of the world, that produces clean and renewable electric energy throughout their twenty generator units of 700 MW each over the Paraná river, that totalize fourteen thousand megawatts of installed power, and transmitting its energy to both countries by means their several high voltage equipment as step-up transformers, GIS and transmission lines. Over the last years, comes increasing its levels of electrical energy production and breaking its own records, aiming ever to its corporate Mission and Vision, based-on strategic pillars as: Environment and Social Responsibility, Sustainability and Economic Development of the region. Even before the launching in service of the first generator unit, at the 80 s decade, Itaipu adopted a special O&M policy related to all equipment to be install at the dam, and so on up to on current days. According to the exposed, the 550kV Gas Insulated Switchgear (GIS), is part of the all the mentioned policy, and from the start of the energy supply, its Maintenance technicians staff ever was committed to comply with all related and good practices of maintenance of high voltage equipment, including among them, the SF6 gas: Sulfur Hexafluoride. As any other similar installation, the Gas Insulated Switchgear has inherent factors that can carry out to eventual failures, or even on the worst case, to undesirable s flashovers with the related forced unavailability of the equipment. Since more than ten years ago, the Electrical Maintenance Engineering Division is assembling a PMP Predictive Maintenance Platform composed by monitoring systems to detect long-term abnormalities as: partial discharges, defects on circuit breakers, supervision of the insulation gas, besides other portable tools based-on infrared technologies as surface thermography and gas leakages, X-Ray inspections, among other types of inspections and periodic and aperiodic activities of maintenance. In this specific opportunity, Itaipu wants to share its experience of its SF 6 gas monitoring system, as the humidity level control of the gas chambers, as well as early density leakage detection in order to avoid emissions of this gas due to the known harmful effects over the environment, and their incidences on greenhouse effects, helping thus to enhance the high voltage equipment maintenance of the installation, and consequently contribute with the nature. ITAIPU HYDRO POWER PLANT AND O&M POLICY Most of the rivers in South America have the main profile to born inside the continent and finally goes to find the sea from the highest to the lowest terrain. Figure 1 Map localization of the Itaipu dam over Paraná River 3

4 The opposite happens with The Paraná river, due to the way to the sea is closet by mountain along the both coast of the Atlantic and Pacific seas, that forces the river goes search to encounter the sea below in Argentine, forming the denominated Cuenca del Rio de la Plata (River Plate Basin) joint with the Pilcomayo river [1]. The main basin of the Paraná River is composed of many minor rivers up to reach the actual position of the Itaipu dam, doing of this a strategic localization due to a highest concentration of water over all the year. GAS INSULATED SWITCHGEAR (GIS) PROFILE Nowadays, the use of the gas Sulphur Hexafluoride (commercially known as SF 6) is enough known at the electrical systems and it s currently the most used insulation material, but it is considered on the Annex A of Kyoto Protocol [2] as part of a set of Greenhouse effects gases named as Global Warming Potential (GWP) element, though its harmful capacity to the environment considered on the 3 rd Assessment Report of UNFCCC as WGP , but its total contribution, joint with the Halocarbons group, is around 1% among the total contribution of the remaining groups of GWP [3], due this, Itaipu is aware over the cares on uses and handling this gas. Among the functions of the Itaipu GIS, the main is to serves of link between the generation of electrical energy with the transmission lines, besides the give a support to maintenance flexibility and operation reliability of the high voltage equipment of the installation. The configuration of both GIS (50/60 Hz) are the same and is based on a double busbar with four kind of typical bays, such as: four to generation units compound ten units, four to line exits, one for bus coupler and finally one for auxiliary services supply. At the mentioned configuration above, it s totalized the following amount of high voltage equipment: High voltage equipment Amount Main characteristic Circuit breakers 54 In 4000 A, Icc 63 ka Disconnecting switches 128 Motorized, In 4000 A Earthing switches 154 Manually operated Current Transformer 414 Toroidal and window type, P&M Potential Transformer 24 Inductive type Surge Arrester 132 Metal Oxide Busbar More than 7500 meters Circular and hollow type, painted aluminum SF6 insulation gas More than 110 tons Distributed in 672 sealed compartments Bushings 30 Double SF 6 density, insulation porcelain type Table 1 Profile of High Voltage equipment installed at Itaipu GIS As viewed, Itaipu GIS possess around 110 tons of this gas, and about this considerable amount turn necessary all the cares to keep It under control, not only by maintenance reasons by the electrical strength needs, but by maintain the focus on the around and worldwide environment [4]. 4

5 Figure 2 Aerial partial view of the High Voltage Equipment installed at the Itaipu GIS PREDICTIVE MAINTENANCE PLATFORM (PMP) Since the beginning of the 2000 s, the Electrical Maintenance Engineering division has been working on prospect systems that can be able to forma part of the GIS PMP - GIS Predictive Maintenance Platform, as thus to become one of the tools that their professionals can account, and with support of others auxiliary systems, is expected to compound one of the pillar of a set of make decision related to maintenance activities to be deployed at field. The GIS PMP is centered on three systems to supply of a range of information about abnormalities that can be measured and passible of analysis by their engineers, but they are complemented by other source of information as well as periodic or aperiodic like thermography or gas leakage detection instruments. The objective of this platform is basically collect the information through reliable sensors, concentrators (IED Intelligent Electronic Devices, or simply electronic devices), and pass them to a database to execute the post-processing, calculations, analysis, set alarm levels and possible diagnostics of the equipment or the device under monitoring according on these set of information. Under this approach, the alarms mentioned will be useful to help maintenance staff to plan a future inspection, intervention or even a repair, if necessary. Figure 3 Schedule of the Predictive Maintenance Platform (PMP) 5

6 After an accident in 2006 on a bushing of one phase step-up transformers at elevation 108, for security reasons of the people and equipment, Itaipu determined the definitive closing of the mobile fire doors of the cubicles of the sixty single phase step-up transformers located at the 108 elevation of the power plant. Before this decision, the O&M staff performed regular inspection activities with the transformer energized, and the information would be lost when the fixed fire doors were definitively installed. The existent systems that Itaipu GIS possess are focused mainly on the abnormalities that could affect its performance and are defined as character of predictive in order to avoid a corrective maintenance and to help the maintenance staff proactively and thus to achieve its aims and keep the installation on good reliability indicators, or instead, at low levels of failures. The principals sources of abnormalities are concentered on partial discharges sources (several types), density leakage, moisture on the SF 6, bad functioning of the high voltage of circuit breakers, among others minor elements that can contributes to a fail. Due to the partial discharge detection and high voltage equipment monitoring are out of the scope of this technical paper, the description will be based on a GMS Gas SF6 Monitoring System that monitors the SF 6 gas installed at the Itaipu GIS, and that intuitively try to help the Electrical Maintenance Engineering to avoid increase the gas emissions of greenhouse effects, such as the Hexafluoride Sulphur, supporting thus one of the strategic alignment of the company. GAS MONITORING SYSTEM (GMS) PROFILE Before the definitive closing of the mobile fire doors, the Electrical Maintenance Engineering division begun its prospection at the international market of a complete solution to collect the information of sixty compartments associated to the step-up transformers, and thus maintain the supervision over possible abnormalities on these equipment. As Itaipu didn t find a desired solution, was prospected primary sensors that could help better to achieve this aim, and at first place found a sensor with capacity to measure the following parameters: pressure, density and temperature of the gas, but the manufacturer was developing a new sensor with the same characteristics but added with the measure of humidity of the gas, considerable more interesting of the Maintenance Engineering s point of view. After tests on-site of the sensor, and mechanical adaptations, it was approved to implement on the compartments, but it was necessary to contour other obstacle: communication module. By one hand, the sensor has itself a four wire cables, two of them to receive the source, and the other to communicate the measurements. Although this, would imply the launching of new pipes and cables to install the sensors, but physically there was not enough space to do this. Now, the barrier was thought how to solve a power source and communication option without the need of new cables, and this proposal was given to the staff IPT Itaipu Technological Park to design a probable solution, and they gave two possible options, one based on a wireless system, and another based on a PLC Power Line Communication technology, that uses a pair of cable to do a double function to communicate and to feed the sensors, and when was checked that there was a pair of cable available near from the future location of the sensors, it was the solution adopted by Itaipu, and requested to the ITP to design a prototype. After a time, the ITP developed a prototype, but it up to becoming to the current model (Fig. 4) only after a series of adaptations. 6

7 Figure 4 First prototype of slave node (left hand side) using PLC technology and the current model (right hand side) Basically, the GMS - Gas Monitoring System profile is basically composed of sensors, communication module (slave nodes) associated to each sensor, panels with concentrator node and a central supervisory system. The physical layer used between the sensors and the concentrators are based on the PLC technology (Power Line Communication), and the concentrators can communicate up to 255 slaves nodes. The communication among the panels and the supervisory system is made by means existent optical fiber [6]. At the present, the GMS system covers only sixty compartments that represent around 9% of the total compartments of the installation. The enlargement of the system is still in progress, and the new platform will account with two optical fiber switches and constantly update and upgrading of the software and their respective firmware. FIRST RESULTS AND FUTURE PLANS Installed since 2014, the GMS have been monitoring sixty compartments at the 108 elevation in the industrial area of the dam. As mentioned, the final model was implemented in these compartments and the process of installation was made by Itaipu maintenance staff, and on this specific was made according to the generator unit s stops schedule, due to the prohibition to work inside the cells of the transformers when energized. The measurements of the supervision parameters were made periodically by maintenance staff before the advice of the system, and the periods are varying from semi-annual (simplest), to the most complete around four years. From the compartments the normal parameters extracted are: indirect measure of the density by pressure control, and humidity via dew point instrument of the Sulphur Hexafluoride, due to they are directly related to the dielectric strength under normal operation, and there are alarms levels associated with the SCADA system. With the implementation of this system, in spite of the necessity established by the hermetic closing of the fire-cut doors, the Electrical Maintenance Engineering was needs the means to "predict" anticipately the gas leakage, not only for technical reasons, but due to the strategic objectives of the company. When the maintenance parameters passed from periodic control to an online supervision, the maintenance staff gains a set of information that does possible a better control of the "not 7

8 desirable" gas emissions to the environment, and able them to act proactively on the equipment and programmable [7], [8]. The system acquires periodically four parameters: density, pressure, temperature and humidity and this acquisition rate is user-configurable by the sensors, and the rates are defined on the supervision software. As mentioned, the pair density & humidity give the key to Maintenance make decision about the related compartment and thus enhance the operation performance of the installation, with the collateral effect over availability of the high voltage equipment. As an example, there is showed below one of the cases such as gas leakage detection (Fig. 5) on one of the compartments of Itaipu GIS that has been monitored that were detected by the system and the correction did by maintenance staff of the GIS. Figure 5 Proactive intervention of Maintenance staff on a compartment due to small gas leakage In other hand, as the compartments are hermetically sealed have a controlled humidity (Fig. 6), but in some conditions, the gas SF6 can absorb humidity above the maximum limit defined by the manufacturer as above of 100 ppm for all the compartments, except for the circuit breakers compartments that its maximum level is defined as equal or more than 50 ppm. Figure 6 Normal behavior of the humidity on a compartment As mentioned above, on the cases when is encountered a compartment with excessive humidity, the normal procedure is retire the compartment and treat the gas offline, but recently Itaipu s Maintenance adopted a new online gas treatment below the worst conditions made before on laboratory tests. 8

9 Due to the system is still incomplete, there are exposed on this paper some of the challenges that the Maintenance Engineering would like to mentions such as: the final implementation on all the compartments up to final of 2018, Annual Report of Gas Emissions, Statistical Data of the Mass Losses of the gas by compartment and by installation, among other aims. BIBLIOGRAPHY [1] Itaipu Hydroelectric Project, Engineering Features, Introduction, pages (1.3 to 1.5), January [2] Kyoto Protocol to the United Nations Framework Convention on Climate Change, United Nations, [3] Projection of Greenhouse Emissions 2007 to 2025, National Environmental Research Institute, Aarhus University, NERI Technical Report, 2009 (Pages.) [4] Itaipu Hydroelectric Project, Engineering Features,, Gas Insulation Switchgear, pages ( to ), January [6] O&M, Operation and Maintenance Manual of the Gas Monitoring System (GMS), G6000-E and G6000-E, December [7] Technical Report, Electrical Maintenance Engineering Division, Technical Directory, Performance of Gas Density Sensors, P, January [8] Technical Report, Electrical Maintenance Engineering Division, Technical Directory, Performance of Communication Modules and Supervisory System of the Gas Monitoring System, E, May