Figure 1. Accident number of electric shock injuries
Àâòîðû: O.N. Synchuk, Yu.B.Filipp, M.N.Maksymov
Èñòî÷íèê: Computer science, information technology, automation, 2016, ¹.5
The article sets out the research results of conditions and operation modes for the mine electric locomotives; defined the accumulator parameters and types of traction batteries for the trolley-battery locomotives. In the course were used the methods of system analysis of power consumption for these types of locomotives in the various technological operations, technical and economic performance of batteries of different electrochemical systems, as well as the results of instrumental measurements, mathematical calculations of the parameters of the traction batteries. It was established that the use of the battery-trolley locomotives in the ore haulageways will improve work safety in the load-hauldump underground operations by eliminating the contact wire at low altitudes of an underground working horizon. It was found that the application of lead-acid, nickel-iron and nickel-cadmium batteries for the mine locomotives does not provide necessary levels of reliability, efficiency and safety of operation. Scientific novelty of the work is the analysis of charge and discharge characteristics of various batteries during operation in mines, development of effective control system and traction control of the battery-trolley electric locomotives. To date, the use of lithium-ion and sodium nickelchloride battery types are considered to be a perspective direction. In this regard, development of lithium-iron-phosphate batteries is a useful step towards expelling the above batteries thanks to their lifetime, number of cyclic recharges, charging speed and voltage stability. Another promising type for the mine electric locomotives is the lithium-sulfur battery, which allows to obtain the maximum current density and characteristics similar to lead-acid batteries, and has no risk of fire, explosion, or other hazard.
Introduction. At Ukrainian iron ore enterprises, electric locomotives are used to transport iron ore, to deliver materials and personnel in the underground mine workings [1]. In the mine workings of the analyzed types are operated only the trolley-wire locomotives (overhead wire locomotives). They get their power supply from a trolley traction network (TTN) of DC with 250W voltage in the “trolley wire - rail” circuit. In the process of iron ore mining and delivery, the underground mine workings called haulageways are divided into main and loaddump [2]. Their geometry changes because of the technological structure of the mine workings, namely, the cross section of manufacturing and the height of the trolley wire (TW) suspension relative to the manufacturing floor. In the iron ore loading areas, the height of the TW suspension should be at least 1.8m according to safety regulations. In fact, this height can be lower, which is quite hazardous for miners if they accidently touch a trolley wire [3].
In view of this, in the course of electric locomotive operation, miners’ closeness to TWs results in accidental injuries by electric shock and, as a rule, 100% fatal outcome (Fig.1).
Figure 1. Accident number of electric shock injuries
One of the preventive measures is the introduction of combined electrical locomotives as to their power supply (trolleybattery locomotives). Such foreign producers as A.L.Lee Corporat³on (USA), ASEA (Sweden), Shandong Ch³na Coal Group (China) are developing this type of electric mine locomotives. In this case, at the main haulageways where a trolley wire is at the height safe enough for miners, a locomotive is supplied with power by the TTN. While operating at extremely hazardous places (loading haulageways), the locomotive has a self-contained power supply. Thus, a trolley wire being a major hazard for miners is eliminated.
Different types of storage devices, accumulators, ultracapacitors, etc. can be used as a self-contained power supply for traction electromechanical complexes (TEMC) in electric locomotives. Our research aims at investigating battery traction power supplies.
At the same time, it is worth mentioning that there are two approaches in creating the trolley-battery locomotives. The first approach is realized when the traction battery (TB) voltage is equal to the electric traction network voltage, the second one – when the TB voltage is less than the trolley network voltage and it is sufficient only for a short locomotive transfer at a low speed in case of car transfer in the load and dump mining operations. The authors’ preventive study on haulageway conditions in iron ore mining reveals that the TB position with 250 V voltage of traction engines (if powered by the trolley traction network) is impossible because of space limitations of the mine trolley locomotives as well as haulageway size limits.
Materials and methods. Reasonable choice of the type and parameters TB defines the dynamic characteristics of the electric locomotive and efficiency of the electric locomotive traction system as a whole during operation under the loading points in standalone mode. The level of satisfaction of these requirements is largely determined by the battery as a source of electrical energy. In terms of iron ore mines, electric train is usually formed of 10 trolleys with a carrying capacity of 10 t, driven by an electric locomotive with adhesive weight of 14 t. The nominal value of the current for traction motors in one-hour mode is 200A. Relocation of the trolleys (car transfer) under the loading points is carried out by the electric locomotives according to the loading process technology. The trolleys are relocated twice under the loading points for their completely filling-half of the content for each car. Thus, at least 20 relocations are required to be done by the electric locomotive. Furthermore, due to the inaccurate rearrangements of the train, especially at the end of the loading cycle, the number of permutations increases by on average of 25% that makes up at least 25 movements in total. Referring to the measurements in the mines the duration of the trolley relocation under the loading points is approximately 10 s, and the total time of the reposition is 250 s.
Lead-acid batteries have good performance, and the development of sealed designs raises the question about their use in the mine electric locomotives. The specific weight and volume characteristics of lead-acid accumulators are achieved at the level of 20-50 W•h/kg and 50-100 W•h/l. Unfortunately, the use of active mass coefficient of the lead-acid batteries is low, due to the uneven distribution of the process through the thickness of the electrodes and delivery difficulties of sulfuric acid to the reaction zone. Therefore, the process proceeds mainly on the surface of the plates. At low and intermediate electrode discharge currents is discharged more uniformly and active mass utilization factor is increased, but not more than 65 - 80%. As discharge, internal resistance of a lead-acid battery increases due to increased activity of the masses and the electrolyte resistance. At temperatures below 0 °C increases internal resistance of the battery considerably due to the cooling of the electrolyte.
The discharge capacity of a battery depends on the mode of its charge. The best ratio is achieved using the current when the current decreases at the end of the charge which will provide minimal outgassing. The battery charge is carried out either by stepwise reduction of charging current or charging mode transition to a falling current (at a constant voltage). Fig.5 shows charging characteristics of a sealed lead-acid battery to 100% of discharged current of 0,05 C for 20 hours.
In the lithium-ion accumulators for a negative electrode is used carbon material with incorporated lithium ions. Active material of a positive electrode is cobalt oxide also with incorporated lithium ions. Electrolyte is a solution of lithium salt in nonaqueous solvent. The specific weight and volume characteristics of modern lithium-ion batteries are reached at 100-260 W•h/kg and 250-800 W•h/l. Operating voltage of the battery is 3,5- 3,7 V and remains in operation while reducing capacity to a level of 20% C.
Lithium-ion accumulators have high specific energy, good lifetime and efficiency at low temperatures. Their high specific energy has resulted in their production increase in recent years. Lithium-ion accumulators have only two essential drawbacks: a high price and the need in a special (usually incorporated) charging/discharging system preventing lithium accumulators from spontaneous ignition and even explosions when operation conditions are violated.
the second best after lithium-ion ones on the basis of their specific energy, as they are more efficient under hard operation conditions. This accumulator type also has its advantages and disadvantages. The advantages of this accumulator type include high specific capacity compared to lithiumion accumulators, low price and wide availability of the accumulator basic materials, a higher lifetime (over 1000 full charging/discharging cycles and over 7 years of active operation), resistance to separate elements failure because of low strength of the elements, which are out of order (up to 5% of losses), high environmental safety (basic components of sodium-nickel-chloride accumulators are safe).
Externally, the element is a steel cuboid, which is filled with metallic sodium (negative electrode material), a ceramic tube inserted from beta alumina, which is both an insulator between positive and negative electrodes and the solid electrolyte, permeable to sodium ions A ceramic separator is filled with the material of the positive electrode: nickel chloride and iron chloride, sodium allyumohlorida powder, and inserted into the contact plate, the output of which is located at the end of the battery cell. Since all of the electrode materials are solids under normal conditions, it should be kept in a heated to 300 ° state.
Current batteries are not purely sodium nickel chloride, but nickel-iron-sodiumchloride. The introduction of iron chloride in the positive electrode will result in lower internal resistance of the battery. Also during discharge pure sodium nickel-chloride system at the end of the discharge output falls sharply (almost 2 times). Adding iron chloride enables to avoid this effect. Battery recycling is very simple - they can be sent to the smelter without unmounting. As a result of melting is formed iron-nickel alloy, which can be used in the steel industry. Even during the thermal runaway battery is particularly kind to the environment (the main components and steel body are low-toxic or non-toxic at all for the environment). The external battery case is a double-walled steel body, between the walls of which is a vacuum. This thermos allows to avoid large dissipation by the battery (in normal conditions dissipates about 100W of heat), which is important not only for the functioning of batteries, but for safety use. There is a heater and air cooling system to maintain a constant internal temperature in the battery case. Heating the batteries to the operating temperature takes a heater about 24 hours. The heater maintains the temperature at the set level (above 270°C) from battery power. During the discharge is released about 10% of energy, which requires cooling of the batteries to a temperature below the maximum operating (350°C).
For proper function of a battery is installed smart control system making possible to maintain an internal status of a battery at the optimum level and automatically turn off power at no load in emergency situations (built-in crash sensor). The system can be operated via a serial port on a PC with Windows. Not only is available a function of monitoring the battery status in real time, but also the possibility of tuning the parameters of the battery for a specific application area.
The drawbacks of sodium-nickelchloride accumulators include the need in an intellectual battery control system, the necessity in high operational temperature support inside the battery (level 300°C and about 100W to support this temperature). It takes at least twenty-four hours to heat-up a cold battery to be ready for operation.
Long service life and high performance cycler put the sodium nickel-chloride batteries on one of the first places among the existing battery. At the moment, the only major obstacle is the inflated cost of this type of battery. As soon as the price reduction takes place per kilowatt-hour of battery capacity to 300USD level that can actually be achieved (the cost of production is less than 150USD per 1 kWh), then their use to electric transport, including in electric locomotives, will become a reality.
As outlined in the text previously, when designing the contact and battery electric locomotives is of great importance the choice of the type of battery based on massdimensional values and energy resource. The analysis in this direction showed that in the short term the most appropriate is the use of lithium-ion and sodium nickel-chloride types of batteries in which the specific weight energy will be greater than 200 W h/kg at the resource 3000 cycles (compared to 1 000 cycles to date), and the cost of $ 0,12 / W h.
A promising type of lithium-sulfur batteries was established in 2004 through the use of a different design of the cathode. In lithium-sulfur batteries, it is a liquid that contains sulfur, which increased the maximum current density. When charging, lithium and sulfur becoming lithium sulfide, in turn, during discharge is the reverse process of decomposition of sulfate in sulfur and lithium. The lithium sulfur batteries provide a voltage of about 2,1 V, the same as the lead-acid batteries. Existing examples of lithium-sulfur batteries have the specific capacity of up to 400 W h/kg, theoretically specific capacity of the battery can be up to 2600 W h/kg. The battery is fully safe, the probability of explosion or the risk of fire during operation is minimal. In this regard, this battery can be made simpler and easier in design due to the lack of protection systems.
Fig. 2 shows a diagram of an uninterruptible power supply of the auxiliary loads with electric voltage control UR (SUB sensor, jUR sensor signal). Protection VB diode eliminates battery power from the contact network. In the separation of the current collector from the contact network, the locomotive loses power, the VB diode starts to conduct current from the battery to the circuit auxiliary loads, which provides their uninterrupted supply.
Figure 13. Functional diagram of an uninterruptible power auxiliary loads from the TB
Research and development aimed at reducing the cost of the relatively expensive TB groups definitely will be continued in the future. The decrease in prices for Li-ion, sodium Nickel-chloride batteries in conjunction with solutions on providing secure and high-capacity TB on the basis of these battery electrochemical systems will create more favorable conditions for the expansion of their application as batteries for industrial use.
Meanwhile, it is not necessary to reject the development directed to the establishment of independent power supply for traction electromechanical complexes on the basis of, for example, supercapacitors and other electric energy storage elements.
Conclusions. Presented the methodology and calculations of the parameters of batteries designed for traction batteries of mine battery-trolley electric locomotives for the conditions of the iron ore mines Kryvbas. The calculations of voltage and battery capacity are approximate and should be refined in the course of further studies based on the actual parameter values of the voyage operations of the electric locomotives
The analysis of parameters and characteristics of different types of batteries for forming batteries that can be used for the mine battery-trolley electric locomotives. It was found that a promising direction is the use of lithium-ion and sodium nickel-chloride batteries, but the cost of these batteries is quite high, which limits a wide variety of applications for the mine electric locomotives.
The introduction of lithium-ion and sodium-nickel chloride batteries needs additional research and development of technological processes control system charge/discharge of the batteries. Also it is expected to reduce the cost of these battery types and their availability of subsequent use in the mine trolley-battery locomotives. It is also necessary to consider the prospects of using self-contained power supply on the basis of, for example, other types of supercapacitors and electric energy storage elements.
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