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Mining industry is currently one of the biggest industries in the world. All mines produce “indispensable” minerals, starting from fuels such as coal and ending with noble metals such as gold or copper. Mines in the world compete in the volumes of mined minerals what requires use of state-of-the-art, more efficient and, and what is more important, safer machines. Such trend favors development of technology and mobilize engineers to adapt the technologies that were used so far in easier environment to the needs of the mining industry. The article presents the issue of energy recuperation in mining battery locomotives. Simulation tests of the power supply and control system of the Lea type battery locomotive are discussed. The results of tests on the electric energy consumption of the locomotive during the operational change in the mine were presented, which were referred to the simulation results. Factors influencing the efficiency of energy recovery and the risk resulting from hydrogen emission in the recuperation process have been indicated. Also discussed is the study of the concentra- tion of hydrogen concentration emitted from the battery of lead-acid cells during their recharging in the process of electrical braking with energy recuperation. Key words: battery supply, energy recuperation, hydrogen emission, mine locomotive unit, PMSM drive INTRODUCTION of diesel locomotives, outperforming them with efficiency When it comes to hard coal mines in Poland 99% of all mi- and lower emissions of harmful gases. Higher energy effi- ning plants are the mines with methane or coal dust ciency of battery locomotives additionally reduces the explosion hazard. Besides of basic coal dust sources there heat emission to the mine atmosphere . Traction loco- are many secondary coal dust sources, which extends the motives give way to battery machines, mainly due to re- use of machines in difficult conditions [6, 23]. Working in strictions resulting from the possibility of conducting elec- that specifically conditions increase machine failures, tric traction in selected areas of the mine. However The which have destructive effects on continuity of operation source of power for mining battery locomotives are lead- and lead to production losses in long-wall mines . The acid cells, which emit hydrogen during charging or rechar- transport of people in underground mining excavations ging (e.g. during electric braking) . The amount of hy- and the transport of materials and spoil in mines is one of drogen emitted from the cell depends, among others, on: the most important processes affecting the efficiency of charge level, charging current, charging duration, elec- raw material production. The means of transport used in- trolyte temperature. The analysis shows that the effec- clude floor locomotives and suspended tractors [10, 21]. tiveness of battery ventilation during operation of the ma- There are three types of floor locomotives: diesel, traction chine is not verified in any way, and the level of energy and battery-operated. Due to the emission of harmful recuperation during the electrical breaking is extremely substances from diesel locomotives, efforts are being important for the hydrogen gas emission. For this reason, made to reduce them and replace them with electric tests were carried out to check whether there was a need drives. In the deepest seams of mines, when driving he- to monitor the concentration of hydrogen in order to en- adings, combustion engines are practically not used. The sure safety and maintain the efficiency of the electric bra- extraction of ore and the transport of materials is carried king process, with energy recovery. out by means of electrically powered transport systems . The accumulator locomotives used match the mobility 254 Management Systems in Production Engineering 2020, Volume 28, Issue 4 LITERATURE REVIEW traction drives, the life of engines and mechanical gears of The most popular, operated battery machine in Polish locomotives was extended. hard coal mining is the Lea locomotive (version BM-12 or 12P3) - Fig. 1, which has been in operation for almost fifty SIMULATION TESTS OF THE POWER SUPPLY AND CON- years. TROL SYSTEM OF THE MINING LOCOMOTIVE WITH ENERGY RECUPERATION Simulation tests of the power supply and control system of the mining battery locomotive, intended for energy re- covery, were conducted in the PSIM simulation environ- ment. The scope of the simulation included the passage of the locomotive from the firehouse towards the loading point (driving on a slope without loading), and then the passage from the loading point to the place of unloading (driving after falling with loading). Simulated acceleration of the locomotive, coasting and braking with energy re- covery. The model of the power supply and control sys- tem for the Lea Bm-12 locomotive is shown in Fig. 2. The study took into account the profile of the transport route Fig. 1 Lea 12P3A battery mine locomotive previously identified in one of the mines as real, on which mining battery locomotives move. A route with unfavora- This locomotive is powered by a LDs-245 DC (Lea BM-12) ble traction parameters was selected. The route length or LDs-327 (Lea 12P3) DC motor. Motors, due to the in- was about 3000 m (from the loading point to the unlo- stalled electric power, have different rotational speed ading point) and the average slope 0.4% (towards the un- (LDs-245 nN = 2910 rpm, LDs-327 nN motor = 1450 rpm). loading station). The following parameters of the battery In the first solutions, resistors were used in the battery lo- locomotive were assumed for simulation tests: maximum comotive drive system to control the start-up and to re- tractive force Fp = 30 kN, maximum speed V = 6 m/s, max max gulate the speed of traction motors . The machine gear ratio with = 1:19.26, wheel diameter d = 560 mm, ra- speed control consisted of connecting series starting resi- ted battery voltage Un = 144 V, five-hour capacity of C5 stors and switching traction motors from serial to parallel batteries = 840 Ah. connection. These systems had a number of disadvanta- ges, such as: difficulty in adjusting the angular speed of motors, large power losses on starting resistors and the need to use a large number of contactors and adjusters switching high currents, which caused rapid wear of con- tact elements. However, the biggest disadvantage of this type of control system was the inability to return energy to the battery during the electric braking process. All energy recovered during braking was dissipated as heat. The disadvantages of the original control systems deter- mined the low efficiency of the locomotive's propulsion system. Therefore, locomotive designers and manufactu- rers sought to develop a higher efficiency powertrain so- lution. Nowadays the series DC motor was eliminated to be replaced by one or two brushless permanent magnet synchronous motors (PMSM). The main advantages of IM over DC machine for the same performance are cost, ro- bustness and reliability [1, 2, 14, 18, 19], also the perma- nent magnet synchronous motor has the advantages of large energy density, high efficiency, long service life and low complexity [8, 13, 15, 16, 17, 20, 22]. Supply and ro- tational speed control is based on DC thyristor switch, which is DC/DC converter of forced-commutation. Bidi- rectional DC/DC converter with isolated structure is most popular [7, 11, 12]. It can operate in a switch on or switch off position for any time interval. The power-electronic Fig. 2 Simulation model of the power supply and control system key allows for smooth step less motor startup and energy for the Lea BM-12 locomotive, powered by a DC motor type recuperation to the battery. The energy efficiency of loco- LDs-245 motives equipped with this type of control system, com- pared to resistor control systems, is about 25% higher. In The most unfavorable conditions from the point of view addition, as a result of the controlled flow of current in of hydrogen emissions were simulated, i.e. acceleration of B. POLNIK et al. – Energy Recuperation as One of the Factors Improving… 255 the transport set (with loading), after a fall with a slope of The measurement of the intensity and shape of the elec- 0.4%, in the speed range of 0-3.2 m/s. After reaching the tric current was recorded using an appropriate current steady speed, braking followed until the locomotive probe (Fig. 3). Since hydrogen emission only took place stopped. The following parameters were recorded during during charging (recharging) of the battery, current wave- the simulation: locomotive speed, electromagnetic forms were recorded only during braking with an electric torque of the engine, motor armature current, average motor, with energy recuperation. The guidelines set by battery current, energy absorbed and transferred to the National EV IWC, recommend a minimum total power fac- accumulator battery. Based on the recorded parameters, tor of 95% and a maximum current THD of 20% . the mechanical power on the motor shaft was calculated. The simulation results are shown in Table 1. Table 1 Simulation results Series 15kW DC motor type LDs-245 driven on a 0.4% incline track with a load Energy Electrical Speed Distance Energy recuperated breaking road [m/s] [m] [Wh] [Wh] [m] 3.2 516 1224 168 33.6 Fig. 3 The measurement devices for measure and registration In simulation studies, only two sections of the route were of the current and shape analyzed in which electric braking with energy recovery occurs. The route profile and load of the battery locomo- Hydrogen concentration measure methodology tive were unfavorable for the machine, which in relation The measure of the hydrogen concentration was made ac- to information obtained from the mine are very rare. De- cording to the standard methodology shown of Fig. 4. spite this, energy of 168 Wh was recovered. In typical ope- rating conditions, the battery locomotive moves with lo- wer loads, traveling on milder sections of transport rou- tes, on which electric braking with energy recovery occurs much more often. TESTS IN THE REAL CONDITIONS The test object in real mine conditions was the power sup- ply and control system of the Lea-type mining battery lo- comotive. This system consisted of a power supply bat- tery, converter and drive motor. Technical parameters of individual components of the power supply and control system are presented in Table 2. Fig. 4 Hydrogen concentration measure methodology Source: . Table 2 Technical parameters of the tested power supply The measurement of hydrogen concentration was carried and control system out using two catalytic sensors located in the battery enc- Rotatory Battery Type Power Voltage Current losure (Fig. 5). speed capacity of locomotive [kW] [V] [A] [rot/min] [Ah] Lea 15.2 144 2910 840 120 BM-12 Lea 18 144 1450 840 140 12P3A The tests was carried out on a single-track drift of one of the hard coal mines. The following parameters were re- corded during the tests: − the intensity and shape of the electric current flowing to the battery during braking with an electric motor, Fig. 5 Preparation of the tested object – arrangement of hydro- with energy recuperation, gen concentration sensors − hydrogen concentration inside the accumulator bat- tery (according to standard methodology). The location of the hydrogen concentration sensors resul- ted from the construction of the SBS-4 flameproof battery 256 Management Systems in Production Engineering 2020, Volume 28, Issue 4 enclosure and the direction of driving of the locomotive. Hydrogen concentration sensors placed inside a charged battery, recorded hydrogen concentrations during the operation of the mining locomotive until it was dischar- ged. The measurement took approx. 4 working shifts (approx. 24 h). The percentage of LEL hydrogen concen- tration (Lower Explosion Limit) was recorded. The conver- sion from percentage to volume resulted from the need to determine the explosive concentration of hydrogen (hydrogen in air is an explosive gas at a concentration of 4 to 75% by volume). The value of 100% LEL was set to 4% by volume The % LEL reference to the entry in PN-EN Fig. 6 Variation of selected electric quantities in time during the real object testing 1889-2 + A1 (2010), regarding the ventilation of the bat- tery box (so that the hydrogen concentration does not ex- Rapid transfer of high intensity electricity to batteries may ceed 2% by volume), resulted in the measurement of hy- cause an intensive emission of electrolytic gas – hydrogen, drogen concentration below 50% LEL meant compliance which in certain concentrations may become an explosive security requirements. It should be emphasized that exce- gas. The design of explosion-proof boxes allows, however, eding the level of hydrogen concentration above 50% LEL to vent accumulated hydrogen. Frequent skipping of the was not a threat, but only signaled the failure to meet the coasting stage and the rapid transition to electric braking requirements of the standard. A real threat of hydrogen with energy recovery may cause the accumulation of large explosion occurs when its concentration level is exceeded amounts of hydrogen and require effective ventilation of by 90% LEL. the battery enclosure. The results of the hydrogen con- centration recorded during the mine battery locomotive RESULTS AND DISCUSSION operation has shown in Table 3. As The analysis of the obtained test results was made in terms of the impact of current intensity and distortion on Table 3 the intensity of hydrogen evolution. Fast Fourier Trans- Hydrogen concentration measured under the tests form (FFT), used for periodic waveforms, was used to ana- Measurement 1 Measurement 2 lyze current waveform deformation. The current wave- forms recorded during the tests were periodic, however The maximum value they were of a vanishing nature, which significantly hinde- of the concentration of hydrogen [% vol.] red their analysis. Each mileage consisted of two parts: Location of measurement The average value of hydrogen work and braking. points concentration Fig. 6 presents examples of voltage and current curves for [% vol.] accumulator batteries recorded during actual mining ope- The standard deviation ration of the Lea BM-12 battery locomotive. Color blue re- of the mean value presented the voltage, color green is the current under [% vol.] the acceleration, color black is the current during the ope- point 1A - half the di- 0.92 0.64 ration, color purple is the current under the electrical bre- stance between 0.73 0.47 aking and color red is the current under the electrical bre- the upper surface of the cell aking with energy recuperation. During 800 seconds of ±0.16 ±0.13 and the cover operation of the locomotive transporting several tons of 0.52 0.52 material, electric braking with energy recovery was regi- point 1B - near stered. During braking, the average effective value of the the corks filling 0.46 0.48 current flowing to the battery was 100 A. The course of and ventilation ±0.05 ±0.05 the battery current was cyclical. Each cycle is divided into point 2A - half the di- three stages: acceleration, coasting and electric braking 0.76 0.40 stance between with energy recovery. The direct transition of the accele- 0.74 0.34 the upper surface rated machine into electric braking mode with energy re- of the cell and the covery, due to the generation of a current of about 400 A, ±0.02 ±0.05 cover can adversely affect the power electronics system. This si- 0.44 0.64 tuation, however, usually does not occur during normal point 2B - near machine operation. The exception is emergency braking. the corks filling 0.43 0.56 and ventilation Currently, power supply and control systems are not ±0.02 ±0.09 equipped with a system limiting the current flowing to the battery during electric braking. Chamber 2 Chamber 1 B. 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Bartosz Polnik ORCID ID: 0000-0002-6803-3090 KOMAG Institute of Mining Technology Pszczyńska 37, 44-101 Gliwice, Poland e-mail: firstname.lastname@example.org Krzysztof Kaczmarczyk ORCID ID: 0000-0002-3205-1238 KOMAG Institute of Mining Technology Pszczyńska 37, 44-101 Gliwice, Poland Andrzej Niedworok ORCID ID: 0000-0001-5234-0531 KOMAG Institute of Mining Technology Pszczyńska 37, 44-101 Gliwice, Poland Ralph Baltes ORCID ID: 0000-0002-0655-9468 RWTH Aachen University Institute for Advanced Mining Technologies Wüllnerstr. 2, 52062 Aachen, Germany e-mail: email@example.com Elisabeth Clausen ORCID ID: 0000-0002-2085-1879 RWTH Aachen University Institute for Advanced Mining Technologies Wüllnerstr. 2, 52062 Aachen, Germany e-mail: firstname.lastname@example.org
Management Systems in Production Engineering – de Gruyter
Published: Dec 1, 2020
Keywords: battery supply; energy recuperation; hydrogen emission; mine locomotive unit; PMSM drive
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