Innovative Life-Cycle Concepts for Medium-Voltage Switchgear on Brown Coal Surface Mining Devices

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 assembling process in the factory and have to be in brown coal surface mining networks are documented in the routine test reports. different from those in the networks of utilities. The main differences are the mobile power consumers INSTALLATION AND SERVICE PHASE in the mine such as mobile transformer stations, power shovels or winding bridges with dimensions The on site installation is one of the most important of more then 400 meters in length and 50 meters milestones during the lifetime of a switchgear. In in height. As the power consumption of such a unit this period it has to be ensured, that the product is about 30 MW, the distribution network of such a attribute’s are not influenced by the erection work. device has a rated voltage of 36 kV respective 7,2 kV. Measures have to developed to guarantee e.g. the integrity of the insulation system. That means The severe environmental conditions have a major partial discharge measurements have to be influence to the design, the installation and the performed on site under a severe electromagnetic operation of the switchgear. Therefore it is evident environment with disturbance levels. to think about the full life cycle of these installations. Other points that are important during the service phase are: DESIGN AND INDUSTRIAL PHASE · no maintenance on the active part of the switchgear The main aspects for the design of distribution · no maintenance/refilling on the gas system (in equipment for brown coal surface mining are the the case of GIS) electrical and mechanical requirements due to the · maintenance free mechanical drives environmental situation. The electrical situation is a · choice of resistant lubrication systems network with high probability of faults. The faults · easy adaptation of the switchgear to the needs can come from the mining process itself (e.g. earth in the network (ratings) faults coming from damages of cables or lightning · zero emission during the normal operation impact of the extended metal structures) or from · low emission in the improbable case of an the mechanical movement of the mining devices internal arc (permanent vibration and shocks). END OF LIFE PHASE The switchgear design has to withstand the resulting stresses such as overvoltages and In spite of the high lifetime of distribution mechanical vibration, therefore it is important to equipment the disposal at the end of the lifetime choose the correct materials with minor influence has to be considered at the beginning of the to the environment and with good possibility for the development. The usage of environmental friendly later recycling process, but with high withstand materials will reduce the disposal costs and will capabilities. fulfil strong ecological requirements.

The design has to pass several acceptance tests Further on the requirements from the client side such as vibration tests with accelerations up to 1 g and from the disposal companies regarding the and shock tests with amplitudes up to 5 g. During data of amounts of different materials (kind and the tests all mechanical and electrical interlocks amount of metals, plastics ..) have to be taken into have to work safely. The insulation system and the account during the development phase. tightness in the case of gas insulated switchgear have to be proven as well to ensure the function A common view on the full lifetime cycle (design, during the whole lifetime. service and disposal) of a medium voltage switchgear has to be developed to tackle the All the results and measures taken to fulfil the increasing number of ecological requirements in requirements have to be secured during the future. 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 ALSTOM concerning design, installation and operation. To this effect, the complete life-cycle of the switchgear was taken into consideration from Using medium-voltage switchgear for brown coal the start. 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.

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 19th 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. PICTURE 1 Overburden conveyor gantry in lignite open cast mining A typical feature of lignite open cast mining in Lusatia are the big overburden conveyor gantries. TECHNICAL IMPLEMENTATION 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 The profiles requested in the table 1 can be technology and utilisation of power. The largest covered with the gas-insulated GMA and WSA individual energy consumers are the conveyor switchgear series. gantry units F60 with a maximum power utilisation of 25 to 30 MW and an overburden extraction Moreover, control of the additional mechanical capacity of 90 to 110 million m³ per year. Other strains imposed on the panels as regards the main consumers are overburden and lignite stability of the drive mechanism, the sealing conveyor belt systems of max. 15 to 20 MW per function parts of the gas compartment and the operated mining complex. stable behaviour regarding partial discharge (PD) had to be ensured as well as the condition that Due to the continuous development of open cast operating safety had to be guaranteed in the mining with an annual coal advance of 250 to 400 presence of dust immission and high, alternating meters, all main consumers, such as conveyor air humidity values (condensation hazard). gantries, excavators and conveyor belt systems, are in constant motion. Besides, an internal specification from the manufacturer requires an environmentally The unfavourable ambient conditions (dust compatible design (selection of materials, immission, humid climates, vibrations) were of recycling-oriented design, use of environmentally considerable importance for the choice of systems compatible plastics) and the presence of a by the operating company, and important for disposal concept for switchgear at the end of its service life which includes considerations of ecological regeneration and re-use of the Due to different design characteristics, it was not insulating gas sulphur hexafluoride SF6. possible to perform generally valid tests on the GMA and WSA switchgear to confirm the suitability TABLE 1 Technical requirements of the types in question, but the inspections had to be adapted to the particularities in question. Requirement criterion Service Service voltage 6 voltage 30 kV kV Rated voltage Ur 12 kV 36 kV Rated short-circuit 20 kA 16 kA current Ik Rated short-circuit 1 second 1 second duration tk Rated (service) current Ir for circuit-breaker switchgear 1250 A 1250 A for switch-disconnector units 630 A 630 A Rated insulation level Up 75 kV 170 kV Ud 28 kV 70 kV Insulation level when the insulating gas pressure is reduced to ambient pressure Up 75 kV 145 kV U 28 kV 70 kV d PICTURE 2 Gas insulated single busbar Insulation fluid of 100% SF6, 100% SF6, electrically active part no solid no solid switchgear type WSA insulation insulation Leakage rate <<1% p.a. <<1% p.a. SIGNIFICANCE FOR THE DESIGN PHASE AND Partial discharge (PD) FOR THE PRODUCTION PHASE behaviour of overall insulation system: PD intensity at 1.1 Ur < 15 pC < 15 pC The customer's specific main task profile consisted PD extinction voltage > 0.9 Ur > 0.9 Ur of the critical ambient conditions of lignite mining. Mechanical endurance: Circuit-breaker > 30000 > 30000 Before the vibration tests were performed in mechanism external, independent testing laboratories, the test Switch disconnector > 1000 - objects were subjected to the following mechanism examinations: Disconnector/Earthing > 1000 > 1000 - Partial discharge measurement switch Integrated voltage - Leakage test (test of all single components detection system acc. to IEC acc. to IEC e.g. electrical and mechanical bushings 61243-5 61243-5 under thermal cycling conditions Proof of resistance to -40°C/+105°C, to subject the systems to vibration strain high mechanical strain; the measurements Vibration 0.5 g 0.5 g were performed integrally using high- Shock 5.0 g 5.0 g resolution infrared (IR) spectroscopy). After Resistance to external IP65 IP65 production, each switchgear unit was environmental influences subjected to an integral test using sensitive (dust, humidity, etc.) IR spectroscopy (exception BB area of the Proof of staff level safety DIN EN DIN EN WS switchgear which had been tested over in case of internal faults 60298, 60298, the entire sealing area using a gas sensitive Criteria 1-6 Criteria 1-6 detector after local assembly) Freely configurable Possible Possible interface to BUS for 100% for 100% - Functional inspection of the mechanical systems (Interbus, of internal of internal drives (in the design phase, the lubricant Profibus etc.) E/A E/A system was given special consideration as signals signals 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 60068-2 in all three axes - Shock test according to IEC 60068-2 in all three axes

TABLE 2 Vibration test parameters

Type of Parameter Testing value test Vibration Frequency 5-150-5 Hz PICTURE 3 WSA during the vibration test Stroke/ 5 - 58 Hz ± 0.035 acceleration mm During the tests performed at the Technical 58 - 150 Hz 0.5 g University of Berlin and the at the laboratories of the Navy of the armed forces all the functions were Frequency 1 oct/min controlled. That means manual and electrical change operation of the circuit breaker and the Testing time 10 cycles per axis disconnectors respective the three position switch, observation of the change of the electrical position Shock Shock form half-sine indication and check of the gas density control system. Peak 5 g acceleration After the tests all dielectrical values, power Shock duration 11 ms withstand voltage, lightning impulse withstand voltage and partial discharge, could be Number of 3 per 6 per demonstrated. shocks direction axis 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).

All results of the electrical and mechanical Graph 1 Measured accelerations during the parameters determined in type tests are taken over vibration test in the routine tests in the production lines, verified for the sealing elastomer systems to support there and documented accordingly. zero leakage condition · Zero emission of gas system (only the technically inevitable and extremely low gas SIGNIFICANCE FOR LOCAL ASSEMBLY AND losses due to material permeation were SWITCHGEAR OPERATION detected in the type tests) · Low gas emission in the improbable case of an accidental arc (arc resistance of gas Zero fault installation - even under the most difficult compartment, low plastics portion, high installation conditions at the operating company’s - recombination capacity of the thermally is of paramount importance during local assembly. decomposed insulating gas sulphur All the relevant systems are checked after hexafluoride) assembly work. The on-site partial discharge measurements were particularly sophisticated, as there were powerful interference signals from SIGNIFICANCE FOR THE END-OF-LIFE PHASE surrounding electro-technical systems already installed during the testing phase. The preparations for low-cost and ecologically After installation, all switchgear stations were justifiable disposal of the switchgear must be made tested for leakage using mobile analysers, unless as early as in the design phase. This step follows this had already been done prior to delivery. 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 medium- voltage 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).

TABLE 3 Materials for the type GMA (average weight values) PICTURE 4 Gasinsulated switchgear type GMA Steel 150 kg 57 % The following aspects were taken into Stainless steel 70 kg 27 % consideration for the operating phase as early as Copper, aluminium, brass 25 kg 9 % in the design and engineering stage: Duroplastics 6 kg 2 % Thermoplastics 7 kg 3 % · Zero maintenance in the high-voltage section Other (ceramic, gas, 5 kg 2 % of the switchgear; this is ensured due to desiccant) systematic enclosure (gas enclosure without solid insulation) The insulating materials have been designed so · Zero maintenance drive mechanisms over a that the absolute plastics content is reduced even period of several years, obtained by the more by reinforcing materials, such as glass fibre. specific lubricant and corrosion protection Moreover, all insulating components, if they are systems and by the selection of the metallic adjusted for self-extinguishing action, do not materials contain any halogen-type flame-retardants. · Use of a chemically stable lubricant system for the mechanical components, for the movable There are effective recycling concepts and and fixed contact areas in the gas section and proposals for all materials. This is particularly relevant for the insulating gas sulphur hexafluoride SUMMARY which can be recovered effectively, and is recycled after regeneration. The switchgear project performed together with the To inform customers and disposal companies alike operating company demonstrated the great about the type, quantity and installation condition importance of precise determination of a task of various materials and the individual channels of profile, not only as regards the electro-technical disposal, Data Sheets for Materials and Disposal design, but also material and concept selection for have been prepared for the various switchgear operation under extremely difficult ambient models to inform and instruct about handling after conditions. the end of service life.

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 PICTURE 5 Transportation of brown coal to gas tightness of the gas tanks was maintained; gas the power station measurements did not show any leakage and also no change in the dew-point of the gas compartments. When implementing the assembly, testing and installation conditions defined in the development The inspection of the mechanical drives showed stage, the customer disposes of a switchgear partially loose screws in one panel, coming from ensuring safe and environmentally responsible the permanent vibrations of the mining devices. As operation. In case of malfunctions (power supply a precaution the screws in all panels were faults), operating safety and environmentally additional fitted by self securing nuts to avoid any compatible behaviour are still ensured. repetition of this. Disposal of the product is due at the end of every Further the closing/opening coils were replaced in service phase. Using environmentally friendly the drive area. However, this was due to the fact materials and taking account of the aspects of the that the low-voltage magnets used for future regulations on electrical scrap, the operator closing/opening were actually designed as can rest assured that he has an optimally undervoltage releases, and used at an even higher economical and ecological solution. voltage than the permitted service voltage.

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.