Multi-dredge electric dredges are powerful floating units operating in placer deposits for mining gold, platinum and other minerals. The modes of operation of electric drives of the main mechanisms of the dredge are not studied sufficiently yet.In the present article as a result of analysis of the constructed and taken from nature load diagrams, a possible method of selection of the power of the main electric motor of the dredge - the motor of its scoop chain is offered.
This work was completed in 1950 as a joint venture between the Department of Mining Electrical Engineering of the Leningrad Mining Institute and one of the coal trusts. The electric motor of a submersible motor-pump designed for pumping water from wells in the conditions of the Leningrad coal deposit was tested. Both the pump and the electric motor are completely immersed in water during operation, which significantly distinguishes the design of this motor-pump from all existing ones, in which the electric motor is installed at the top of the wellhead and connected to the pump submerged in water by means of a long shaft (motor-pumps of the ATN type, etc.). The electric motor is made with moisture-resistant insulation of an open type without a hermetic shell.
Determining the power of the main drive of multi-bucket electric dredges, i.e., the drive of their bucket device, encounters the following difficulties. 1. Insufficient study of the physical properties of the soils of dredged placers leads to the fact that the cutting force of the soils by the buckets cannot be determined with the necessary degree of accuracy. The soils are, for the most part, not homogeneous. As follows from the classification of soils for dredging operations (Table 1), established in 1937, soils may contain peat, sand, clay, crushed stone, sandstone, boulders, igneous rocks and other components, and their percentage composition varies widely. Therefore, using physical constants obtained from testing homogeneous soils for such soils would not be entirely correct. 2. During dredge operation, various obstacles may be encountered (large boulders, support timber from old workings, etc.), which cause overloads of the bucket drive motor. The duration and magnitude of overloads cannot be accounted for theoretically. Identifying the nature of such overloads and the magnitude of the cutting force can be accomplished using load diagrams recorded by self‑recording electrical measuring instruments. The selection of the type of drive for the bucket device presents fewer difficulties.
The present work is the result of creative collaboration of the Department of Mining Electrical Engineering of the Leningrad Mining Institute with one of the coal trusts. Electric motors of two submersible motor-pumps were tested. The design data of both motor-pumps are absolutely identical. Only their electrical parts differ slightly: the stator of the electric motor of one of them (motor-pump No. 7) has slightly larger slot dimensions than the stator of the electric motor of the other motor-pump (motor-pump No. 9). Therefore, 16 wires are laid in each slot of the stator of the electric motor of motor-pump No. 7, and 11 wires are laid in the electric motor of motor-pump No. 9. The main data of the submersible motor-pumps with a star connection of the stator winding of the electric motor are as follows: electric motor power on the shaft Pn = 9.2 kW; voltage Un = 380 V; revolutions n = 2900 rpm. The motor is a three-phase asynchronous squirrel-cage induction motor (Fig. 1); pump capacity Qн = 30 m³/h; pump head Ha = 50 m. The total height of the motor-pump is 1400 mm, the height of the electric motor is 930 mm, the diameter of the unit is 183 mm. The electrical and mechanical parts of the submersible motor-pumps are manufactured by the assembly and mechanical workshops of the trust. Submersible motor-pumps of the proposed design, used for pumping water from wells, compare favorably with those currently existing in the following features.
The power of the scraper winch motor is known to be determined based on the expression ... (see the article). Thus, it is assumed that the scraper traction force is constant during the entire time of its operation, i.e., in essence, the choice of motor power for the scraper drive is carried out as in a continuous duty mode. In fact, the operating mode of the scraper winch drive should be classified as repetitive short-time duty, since the periods of working and idle runs of the scraper alternate, which is evident from the load diagrams given below, taken by the author in the mines of the Cheryomkhov coal basin. Therefore, from the point of view of the operating mode, the choice of scraper winch motor power based on expression (1) can hardly be recommended. In this sense, it would be most appropriate, using load diagrams similar to the one given in the figure, to determine the drive power as the root‑mean‑square value. Unfortunately, this is practically almost impossible to implement, since the scraping conditions are so varied with respect to the angle of inclination of the plane of movement of the load, the nature of the scraped material, the length of the delivery route, etc., that in each specific case it would be necessary to have either load diagrams taken from actual operation, or a large number of load graphs recorded on tape, on the basis of which experimental coefficients could be derived.
As is known, the following resistances act during the movement of a loaded scraper: 1. resistance to movement of the material captured by the scraper, 2. resistance to movement of the scraper itself, 3. resistance to movement of the ropes, 4. resistance in the blocks and from the rigidity of the ropes, 5. resistance to scooping up the scraped material. During the movement of an empty scraper, only resistances (2), (3) and (4) act, resistances (1) and (5) are equal to zero. However, the pattern of change in the resistance to movement of the material captured by the scraper (hereinafter designated z₁) and the resistance to scooping up the scraped material (hereinafter designated z₅) during filling the scraper has not been studied in essence. Meanwhile, knowledge of this pattern is highly desirable from the point of view of overloading the scraper winch engine and, consequently, a more theoretically justified choice of the power of this engine. Based on existing data on the operation of scraper installations, in particular, on the existing coefficients of friction and the values of the specific work of scooping, below we offer the following interpretation of the pattern of change during filling of the scraper of the two types of resistance indicated above.
