Experimental research of transition processes of asynchronous motors of belt conveyors on mathematical modeling

. The purpose of the study. increasing the performance of belt conveyors and reducing transportation costs based on the developed mathematical modeling of transient processes of asynchronous motors of open-pit conveyor transport. The object of the research is the operating modes of asynchronous motors of belt conveyors of mining enterprises. The subject of research is the starting and braking modes of operation of asynchronous motors of belt conveyors of mining enterprises. Research methods are based on the modern theory of electrical machines, methods of linear and nonlinear mathematical programming, mathematical statistics, as well as methods of system analysis. The practical results of the study are as follows: the actual coefficient of resistance to the rotation of the conveyor rollers and the coefficient of resistance to the movement of the belt, leading to a decrease in the tractive effort, were determined; a method was developed for determining the additional power consumption of electric motors of belt conveyors, taking into account the overall volume, weight and speed of transported lumpy cargo; a mathematical model of braking and starting modes of induction motors of belt conveyors of mining enterprises was developed, taking into account the resistance coefficient of the belt and rollers.


Introduction
In the global mining industry, it is important to improve the energy efficiency of conveyor belts and save energy. "The use of conveyor belts in quarries around the world is dramatically reducing rock transport distances, reducing shipping costs by 30-40% and doubling labor productivity." In this regard, much attention is paid to the optimization of asynchronous motors of belt conveyor transport, normalization of consumed electricity, the search for combination methods for extracting minerals from the horizons of deep quarries and increasing the reliability of conveyor equipment.
In the world, research is being carried out aimed at increasing the productivity of a quarry, reducing the cost of mining and transporting rocks, developing energy-efficient control algorithms and reducing losses during transient processes of asynchronous motors. In addition, asynchronous motors are considered, including mineral quality metrics to

Methodology
The research methods are based on the modern theory of electrical machines, methods of linear and nonlinear mathematical programming, mathematical statistics, as well as methods of system analysis of conveyors, depending on the length and slope of the conveyor.
Scientific research is aimed at improving the efficiency of belt conveyors using advanced methods for calculating belt conveyors and determining the prospects for their development, are carried out in leading research centers and universities in the world, However, despite significant advances in improving the method for calculating the transient processes of belt conveyors, the determination of the drag coefficients of conveyor belts and rollers, the determination of the overall volume, weight and speed and power consumption of belt conveyors depending on the length and slope of the conveyor have not been studied enough.

Discussion
In steady-state modes, asynchronous motors of conveyor belts are characterized by a nominal mode [1,2].
Transient processes are much more diverse and more complex than steady-state processes [1,2].
Transient processes in asynchronous motors of a belt conveyor occur when the frequency and voltages at the motor terminals change and when it is disconnected from the braking network, etc. [1,2].
Belt conveyors as the most economical, productive and reliable type of transport of bulk cargo are widely used in our republic and abroad. With the increase in the length of the conveyors and their productivity, the dynamics of the start-up is of particular importance. Therefore, the start-up of the belt conveyors is very important. Dynamic processes in belt conveyors are characterized by the appearance of dynamic tension, which, algebraically summing up with static, significantly increase the resulting tension in the conveyor belt and the forces in the elements of the conveyor. At start-up, these changes can lead to unstable operation of the drive drum, for example, partial or complete slipping [2, 3].
Slipping is unacceptable for many reasons: heating the drum, a sharp decrease in the coefficient of adhesion, which makes it difficult to start the conveyor, etc. All this can cause emergency situations and even cause a fire, which is unacceptable in the Angren Mine because it leads to property damage, in addition, dynamic forces increase the loads in the tensioning device mechanisms, in the gearbox and other elements of the conveyor. Therefore, the analysis of the processes of starting and braking belt conveyors is of great importance.
An analysis of these processes makes it possible to accurately determine the values of dynamic loads, which will help to avoid irrational technical solutions, increase the reliability of the belt conveyor-motor system, and therefore, sharply reduce the likelihood of emergencies and increase the productivity of the belt conveyor [1,2].
Calculation of starting modes of operation of asynchronous motors of conveyor belts As you know, the transportation of coal mined from the face at the Angrensky open pit is carried out by combined transport: dump trucks, conveyor transport (downhole and main conveyors) [4].
In Fig. 1 shows the layout of the conveyors of the Angren open-pit mine.Asynchronous motors with squirrel-cage rotors are used as a drive on the belt conveyors of the Angren open pit mine [4].
In these engines, the starting characteristics of the computer were calculated. Fig. 2. dependences М м = ( ) and = ( ) are shown when starting an asynchronous motor with a power of 55 kW, = 380V, when there is no load on the conveyor.
In Fig. 3 for the same motor, the current dependences in the stator and rotor , = ( ), are shown when there is no load on the conveyor.   In Fig. 4. dependencies М м = ( ) and = ( ) are given when starting an asynchronous motor with a power of 55 kW, 2 = 4, = 380V, when the belt conveyor is loaded.
In Fig. 5. for the same engine, dependencies , = ( ), are shown when the belt conveyor is loaded. The starting time is = 9,5s.   In Fig. 7. for the same motor, the time dependences of the currents in the stator and rotor are shown, i.e. , = ( ), when there is no load on the conveyor. As seen from Figure 6 and 7 during t = 3.5 s, the currents in the stator and rotor have a maximum value, which determines the maximum values М м . In Fig. 8. shows the dependences М м = ( ) and = ( ) when starting an asynchronous motor with a power of 75 kW, 2 = 6, = 380V, when the belt conveyor is loaded. In Fig. 9 for the same engine shows the dependencies , = ( ), when the belt conveyor is loaded. The starting time is = 7,5 s.
In Fig. 14-17 shows the dependences М м = ( ), = ( ) and , = ( ) at idle and at load of an induction motor with a power of 160 kW, 2 = 6, 380 V.         From a qualitative analysis of the start-up of asynchronous motors of belt conveyors, it follows that these processes differ from each other in the nature of the change in currents, shock torques and angular velocity.
Modeling an asynchronous motor in the Matlab package. When modeling asynchronous motors of belt conveyors, the program in the Matlab package is used, which shows the model of the conveyor electric drive in Fig. 18. To do this, differential equations are collected in a certain order, based on the principles of analog modeling [5].
Simulation of an induction motor in the Matlab package. When modeling asynchronous motors of belt conveyors, the program is used in the Matlab package which shows the model of the conveyor electric drive in Fig. 18. To do this, differential equations are collected in a certain order, based on the principles of analog modeling [5].
Waveform analysis in Fig. 19 allows one to determine [13]: -when starting with loaded tapes, the starting current of the stator of an asynchronous motor is 850 A and exceeds the rated current value by 3,5 times, such a current flows in the stator circuit for 6,5 seconds; in the future, the current transient is of an oscillatory nature with damping, the time of the current transient to a steady-state value of 250 A is 12 sec; -when starting with loaded tapes, the starting current of the rotor of the asynchronous motor is 800 A and exceeds the rated current value by 10 times, such a current flows in the stator circuit for 5 seconds; in the future, the current transient is oscillatory with damping, the current transient to a steady state value of 80 A is 11 seconds; A mathematical model was developed on the Matlab package of an asynchronous belt conveyor motor, taking into account the following parameters distributed along the length of the conveyor, namely: mass of the transported load, mass and elasticity of the traction member, and forces of static and dynamic resistance.
Modes and oscillograms of transient processes are calculated for the parameters of the stator and rotor current of the motor, speed, torques and resistance forces on the shaft of an asynchronous motor when starting a belt conveyor.
The developed mathematical model of the belt conveyor makes it possible to study the static and dynamic modes of operation of both the drive motor and the mechanical part of the conveyor, on each of which the tension forces can be calculated at starts with different loads.

Conclusion
1. The calculation and modeling on the Matlab package of the mode of starting the asynchronous motors of belt conveyors, taking into account the resistance coefficient of the belt and rollers.
2. From the analysis of the start-up of asynchronous motors of belt conveyors, it follows that these processes differ from each other in the nature of changes in shock currents, shock moments and angular velocity.
3. The developed mathematical model of the belt conveyor makes it possible to study the static and dynamic modes of operation of both the drive motor and the mechanical part of the conveyor, on each of which the tension forces can be calculated at starts with different loads.