INNOVATIVE LIFE-CYCLE CONCEPTS FOR MEDIUM-VOLTAGE SWITCHGEAR ON BROWN COAL SURFACE MINING DEVICES

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1 INNOVATIVE LIFE-CYCLE CONCEPTS FOR MEDIUM-VOLTAGE SWITCHGEAR ON BROWN COAL SURFACE MINING DEVICES Dr. S. Ruhland, Dr. U. Riedl ALSTOM Sachsenwerk GmbH, Germany The requirements for medium voltage switchgear in brown coal surface mining networks are different from those in the networks of utilities. The main differences are the mobile power consumers in the mine such as mobile transformer stations, power shovels or winding bridges with dimensions of more then 400 meters in length and 50 meters in height. As the power consumption of such a unit is about 30 MW, the distribution network of such a device has a rated voltage of 36 kv respective 7,2 kv. The severe environmental conditions have a major influence to the design, the installation and the operation of the switchgear. Therefore it is evident to think about the full life cycle of these installations. DESIGN AND INDUSTRIAL PHASE The main aspects for the design of distribution equipment for brown coal surface mining are the electrical and mechanical requirements due to the environmental situation. The electrical situation is a network with high probability of faults. The faults can come from the mining process itself (e.g. earth faults coming from damages of cables or lightning impact of the extended metal structures) or from the mechanical movement of the mining devices (permanent vibration and shocks). The switchgear design has to withstand the resulting stresses such as overvoltages and mechanical vibration, therefore it is important to choose the correct materials with minor influence to the environment and with good possibility for the later recycling process, but with high withstand capabilities. The design has to pass several acceptance tests such as vibration tests with accelerations up to 1 g and shock tests with amplitudes up to 5 g. During the tests all mechanical and electrical interlocks have to work safely. The insulation system and the tightness in the case of gas insulated switchgear have to be proven as well to ensure the function during the whole lifetime. All the results and measures taken to fulfil the requirements have to be secured during the assembling process in the factory and have to be documented in the routine test reports. INSTALLATION AND SERVICE PHASE The on site installation is one of the most important milestones during the lifetime of a switchgear. In this period it has to be ensured, that the product attribute s are not influenced by the erection work. Measures have to developed to guarantee e.g. the integrity of the insulation system. That means partial discharge measurements have to be performed on site under a severe electromagnetic environment with disturbance levels. Other points that are important during the service phase are: no maintenance on the active part of the switchgear no maintenance/refilling on the gas system (in the case of GIS) maintenance free mechanical drives choice of resistant lubrication systems easy adaptation of the switchgear to the needs in the network (ratings) zero emission during the normal operation low emission in the improbable case of an internal arc END OF LIFE PHASE In spite of the high lifetime of distribution equipment the disposal at the end of the lifetime has to be considered at the beginning of the development. The usage of environmental friendly materials will reduce the disposal costs and will fulfil strong ecological requirements. Further on the requirements from the client side and from the disposal companies regarding the data of amounts of different materials (kind and amount of metals, plastics..) have to be taken into account during the development phase. A common view on the full lifetime cycle (design, service and disposal) of a medium voltage switchgear has to be developed to tackle the increasing number of ecological requirements in future.

2 INNOVATIVE LIFE-CYCLE CONCEPTS FOR MEDIUM-VOLTAGE SWITCHGEAR ON BROWN COAL SURFACE MINING DEVICES Dr. S. Ruhland, Dr. U. Riedl ALSTOM Sachsenwerk GmbH, Germany INTRODUCTION Using medium-voltage switchgear for brown coal surface mining as an example, we will show the principles according to which particular requirements and installation conditions are taken into consideration for all life phases of a product. ALSTOM concerning design, installation and operation. To this effect, the complete life-cycle of the switchgear was taken into consideration from the start. The following steps are defined as life phases: development, production, local assembly and operation, and disposal. Lignite mining and processing in Lusatia on an industrial scale dates back to the end of the 19 th century. There are lignite fields totalling 13 billion tons in Lusatia, 2.6 billion tons of which, which can be extracted in an economically efficient fashion, taking into account present ecological and social compatibility aspects, are scheduled or planned for mining. In this open cast mining, the lignite stratum to be extracted reaches a thickness of 8 to 12 meters. A typical feature of lignite open cast mining in Lusatia are the big overburden conveyor gantries. They are used to extract the majority of the 60 to 80 m high capping deposited on the stratum. The maximum energy demand of open-cast mining is 60 to 80 MW, depending on the actual extraction technology and utilisation of power. The largest individual energy consumers are the conveyor gantry units F60 with a maximum power utilisation of 25 to 30 MW and an overburden extraction capacity of 90 to 110 million m³ per year. Other main consumers are overburden and lignite conveyor belt systems of max. 15 to 20 MW per operated mining complex. Due to the continuous development of open cast mining with an annual coal advance of 250 to 400 meters, all main consumers, such as conveyor gantries, excavators and conveyor belt systems, are in constant motion. The unfavourable ambient conditions (dust immission, humid climates, vibrations) were of considerable importance for the choice of systems by the operating company, and important for PICTURE 1 Overburden conveyor gantry in lignite open cast mining TECHNICAL IMPLEMENTATION The profiles requested in the table 1 can be covered with the gas-insulated GMA and WSA switchgear series. Moreover, control of the additional mechanical strains imposed on the panels as regards the stability of the drive mechanism, the sealing function parts of the gas compartment and the stable behaviour regarding partial discharge (PD) had to be ensured as well as the condition that operating safety had to be guaranteed in the presence of dust immission and high, alternating air humidity values (condensation hazard). Besides, an internal specification from the manufacturer requires an environmentally compatible design (selection of materials, recycling-oriented design, use of environmentally compatible plastics) and the presence of a disposal concept for switchgear at the end of its service life which includes considerations of

3 ecological regeneration and re-use of the insulating gas sulphur hexafluoride SF 6. TABLE 1 Requirement criterion Technical requirements Service voltage 6 kv Service voltage 30 kv Rated voltage U r 12 kv 36 kv Rated short-circuit 20 ka 16 ka current I k Rated short-circuit 1 second 1 second duration t k Rated (service) current I r for circuit-breaker switchgear for switch-disconnector units Rated insulation level U p U d Insulation level when the insulating gas pressure is reduced to ambient pressure U p 1250 A 630 A 75 kv 28 kv 1250 A 630 A 170 kv 70 kv U d 75 kv 28 kv 145 kv 70 kv Insulation fluid of electrically active part 100% SF 6, no solid insulation 100% SF 6, no solid insulation Leakage rate <<1% p.a. <<1% p.a. Partial discharge (PD) behaviour of overall insulation system: PD intensity at 1.1 U r PD extinction voltage Mechanical endurance: Circuit-breaker mechanism Switch disconnector mechanism Disconnector/Earthing switch Integrated voltage detection system Proof of resistance to vibration strain Vibration Shock Resistance to external environmental influences (dust, humidity, etc.) Proof of staff level safety in case of internal faults Freely configurable interface to BUS systems (Interbus, Profibus etc.) < 15 pc < 15 pc > 0.9 U r > 0.9 U r > > 1000 > 1000 acc. to IEC g 5.0 g IP65 DIN EN 60298, Criteria 1-6 Possible for 100% of internal E/A signals > > 1000 acc. to IEC g 5.0 g IP65 DIN EN 60298, Criteria 1-6 Possible for 100% of internal E/A signals Due to different design characteristics, it was not possible to perform generally valid tests on the GMA and WSA switchgear to confirm the suitability of the types in question, but the inspections had to be adapted to the particularities in question. PICTURE 2 Gas insulated single busbar switchgear type WSA SIGNIFICANCE FOR THE DESIGN PHASE AND FOR THE PRODUCTION PHASE The customer's specific main task profile consisted of the critical ambient conditions of lignite mining. Before the vibration tests were performed in external, independent testing laboratories, the test objects were subjected to the following examinations: Partial discharge measurement Leakage test (test of all single components e.g. electrical and mechanical bushings under thermal cycling conditions -40 C/+105 C, to subject the systems to high mechanical strain; the measurements were performed integrally using highresolution infrared (IR) spectroscopy). After production, each switchgear unit was subjected to an integral test using sensitive IR spectroscopy (exception BB area of the WS switchgear which had been tested over the entire sealing area using a gas sensitive detector after local assembly) Functional inspection of the mechanical drives (in the design phase, the lubricant system was given special consideration as

4 regards stability to moisture and abrasive dusts with partially corrosive action) Determination of the mechanical characteristic data of the drive mechanisms (speeds etc.). Sequence of external inspections following internal inspections: Sweep sine test according to IEC in all three axes Shock test according to IEC in all three axes TABLE 2 Vibration test parameters Type of test Parameter Testing value Vibration Shock Frequency Stroke/ acceleration Frequency change Testing time Shock form Peak acceleration Shock duration Number of shocks Hz 5-58 Hz Hz 1 oct/min 10 cycles half-sine 5 g 11 ms 3 per direction ± mm 0.5 g per axis 6 per axis PICTURE 3 WSA during the vibration test During the tests performed at the Technical University of Berlin and the at the laboratories of the Navy of the armed forces all the functions were controlled. That means manual and electrical operation of the circuit breaker and the disconnectors respective the three position switch, observation of the change of the electrical position indication and check of the gas density control system. After the tests all dielectrical values, power withstand voltage, lightning impulse withstand voltage and partial discharge, could be demonstrated. The materials used for insulation, i.e. duroplastics and thermoplastics, and elastomers (sealing materials) satisfy the requirements to a large extent. Specific accelerated tests under enhanced mechanical strain also allow for conclusions on positive long-term behaviour. The corrosion protection system (painting, electroplating, zinc-plating) also ensures protection over the expected service life. For the painting a combination of a cathodic dip paint and a powder coating with an excellent withstand against moisture and corrosive immissions is used (proofed in time-lapsed tests with salt fog and sulphur-dioxide). The electroplating and hot dip zinc-plating surfaces are optimised with additives (electroplating) and with additional treatment of the protection-layer (hot dip zinc-plating). Graph 1 Measured accelerations during the vibration test All results of the electrical and mechanical parameters determined in type tests are taken over

5 in the routine tests in the production lines, verified there and documented accordingly. SIGNIFICANCE FOR LOCAL ASSEMBLY AND SWITCHGEAR OPERATION Zero fault installation - even under the most difficult installation conditions at the operating company s - is of paramount importance during local assembly. All the relevant systems are checked after assembly work. The on-site partial discharge measurements were particularly sophisticated, as there were powerful interference signals from surrounding electro-technical systems already installed during the testing phase. After installation, all switchgear stations were tested for leakage using mobile analysers, unless this had already been done prior to delivery. for the sealing elastomer systems to support zero leakage condition Zero emission of gas system (only the technically inevitable and extremely low gas losses due to material permeation were detected in the type tests) Low gas emission in the improbable case of an accidental arc (arc resistance of gas compartment, low plastics portion, high recombination capacity of the thermally decomposed insulating gas sulphur hexafluoride) SIGNIFICANCE FOR THE END-OF-LIFE PHASE The preparations for low-cost and ecologically justifiable disposal of the switchgear must be made as early as in the design phase. This step follows the latest state of disposal technology, in spite of the expected long service lives of 30 to 40 years. The use of a maximum recyclable metal portion provides optimum prerequisites to this effect. The metal portion of the GMA and WSA switchgear series amounts to approx. 90 % of the weight, i.e. a very high portion for an electrotechnical mediumvoltage product. The remaining portion consists of the insulating materials duroplastics and increasingly of recyclable thermoplastics), of elastomers (sealing materials), and to a very low extent of special materials and materials such as sulphur hexafluoride (insulating gas), mineral molecular sieves (desiccant in the gas compartment) and ceramics (insulating elements for vacuum interrupter chambers). PICTURE 4 Gasinsulated switchgear type GMA The following aspects were taken into consideration for the operating phase as early as in the design and engineering stage: Zero maintenance in the high-voltage section of the switchgear; this is ensured due to systematic enclosure (gas enclosure without solid insulation) Zero maintenance drive mechanisms over a period of several years, obtained by the specific lubricant and corrosion protection systems and by the selection of the metallic materials Use of a chemically stable lubricant system for the mechanical components, for the movable and fixed contact areas in the gas section and TABLE 3 Materials for the type GMA (average weight values) Steel 150 kg 57 % Stainless steel 70 kg 27 % Copper, aluminium, brass 25 kg 9 % Duroplastics 6 kg 2 % Thermoplastics 7 kg 3 % Other (ceramic, gas, desiccant) 5 kg 2 % The insulating materials have been designed so that the absolute plastics content is reduced even more by reinforcing materials, such as glass fibre. Moreover, all insulating components, if they are adjusted for self-extinguishing action, do not contain any halogen-type flame-retardants. There are effective recycling concepts and proposals for all materials. This is particularly

6 relevant for the insulating gas sulphur hexafluoride which can be recovered effectively, and is recycled after regeneration. To inform customers and disposal companies alike about the type, quantity and installation condition of various materials and the individual channels of disposal, Data Sheets for Materials and Disposal have been prepared for the various switchgear models to inform and instruct about handling after the end of service life. SUMMARY The switchgear project performed together with the operating company demonstrated the great importance of precise determination of a task profile, not only as regards the electro-technical design, but also material and concept selection for operation under extremely difficult ambient conditions. INITIAL OPERATING EXPERIENCE Due to extensions of GMA switchgear and the comments made by a customer, initial information became available after two years about the extent to which switchgear stations prove their functions under the difficult ambient conditions described above. The total period of operation is short compared with the total service life, but further long-term forecasts can be made thanks to certain assessment methods. Compared to the initial values, no increases of partial discharge values were found. The perfect gas tightness of the gas tanks was maintained; gas measurements did not show any leakage and also no change in the dew-point of the gas compartments. The inspection of the mechanical drives showed partially loose screws in one panel, coming from the permanent vibrations of the mining devices. As a precaution the screws in all panels were additional fitted by self securing nuts to avoid any repetition of this. Further the closing/opening coils were replaced in the drive area. However, this was due to the fact that the low-voltage magnets used for closing/opening were actually designed as undervoltage releases, and used at an even higher voltage than the permitted service voltage. PICTURE 5 Transportation of brown coal to the power station When implementing the assembly, testing and installation conditions defined in the development stage, the customer disposes of a switchgear ensuring safe and environmentally responsible operation. In case of malfunctions (power supply faults), operating safety and environmentally compatible behaviour are still ensured. Disposal of the product is due at the end of every service phase. Using environmentally friendly materials and taking account of the aspects of the future regulations on electrical scrap, the operator can rest assured that he has an optimally economical and ecological solution. No corrosion on metals was found, nor soiling in the drive and control section which was due to a sufficiently dimensioned degree of protection. Further dates for regular assessment were agreed upon with the customer, to obtain feedback as to the extent to which the concept of the two variants of gas-insulated medium-voltage switchgear afforded long-term safe operation.

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