INTRODUCTION
URGENCY OF WORK
SURVEY OF RESEARCH AND DEVELOPMENTS
RESULTS
CONCLUSIONS
REFERENCES

INTRODUCTION

Conveying an integral process of the mining enterprise. Its effectiveness has a significant impact on coal mining enterprise in general. Automation of conveyor transport is to increase the efficiency of the delivery process by reducing the cost of maintenance and repairs, as well as by reducing downtime and increasing productivity.

The purpose of automation conveyor transport is to increase efficiency and safety of the conveyor line. To achieve this requires to solve two main tasks:
1) process control start and stop conveyors;
2) automatic control of conveying to stabilize cargo.

From the foregoing it is evident that among the pressing questions relating to modes of pipeline and efficiency of its operation, is the question concerns starting.

URGENCY OF WORK

In existing soft starter uses phase control supply voltage realized by a thyristor converter. But the phase regulation at the converter output voltage is obtained by poor quality, which is characterized by a start-up transients, as in the electric and the mechanical part design. Transient processes are accompanied by drastic changes in various parameters of the state in time, including an effort in the tape. Moreover, the value of this variable may vary to a large extent, beyond the permissible or even critical. Overload during start-up pipeline could lead to a dangerous reduction in safety factor of drive and tape. Therefore, analyzing the above, we can conclude that the problem of the soft starter is very relevant today.

This means that there is a need to find alternative means of voltage control of induction motors with squirrel cage rotor. One such alternative is to replace the principle of phase control - pulse-width voltage regulation. In accordance with this principle, the power switches between the power supply and the load switched at high frequency during the period of supply voltage. Controlled quantity - on-time of power key for a constant carrier frequency. The average value of output voltage during the period of the carrier frequency is determined by the duty cycle control of power switches, as well as the instantaneous values of supply voltage. The implementation of this method is possible when using transistors with insulated gate (IGBT), which are characterized by high energy and dynamic performance [1].

SURVEY OF RESEARCH AND DEVELOPMENTS

From the point of view of the requirements to drive conveyor belts, the drive has some drawbacks. The disadvantages of electric drive with an asynchronous squirrel-cage motors include a sharp increase starting torque, and hence the possibility of high tension in belt and slip on the driving drums.

Significant improvement in performance enabled by the electric circuit to drive special starters:

1. Starter coupling of the closed type, to ensure smooth start-up and the necessary load sharing between motors multi-motor drive stations. Fluid has serious drawbacks, because mechanical coupling characteristics do not allow for acceleration traction belt body with the necessary intensity, motor protection is a danger to staff and a simple pipeline, due to the time to re-fill it emulsions, installing a new fuse plug.

2. Electromagnetic clutch slip. The disadvantages of electromagnetic clutches slip include the following: during the acceleration conveyor eddy currents arising in the anchor sleeve, causing her strong heating, which requires, especially at high drive power, a rather complicated cooling system coupling, inductor, which supplied a constant current through thering must be explosion-proof to meet the conditions of work in an explosive atmosphere of coal mines; drive with magnetic clutch slip and a short-circuited induction motor requires two types of current - AC and DC, which also complicates the supply system of the drive. Therefore, for these reasons the work in the field of electromagnetic slip clutch for belt conveyors is currently being developed.

3. Slip-ring motors. Ensure a smooth start in the electric drives is carried out by introducing resistance in the rotor circuit of the motor. As the resistance to use a metal step rheostat or variable - liquid. Liquid rheostats are available on a wide range of power and made an explosion-proof, allowing you to use drives of this type in the coal mines. He was less widespread drive an electric motor with a phase rotor and metal dimmer included in the rotor circuit. Introduction of resistance carried out by means of electromagnetic contactors. There are also drives with motors with phase rotor, a chain which includes unmanaged inductive resistors. This method has several disadvantages such as wear slip-rings, heavy losses of the adjustable resistance, decrease stiffness characteristics with increasing resistance, high cost otnostelno cage motors.

4. Drives on the basis of the induction motor with slip-ring motors for brushless cascade induction system. Disadvantages of this scheme - the high cost of implementation and the accompanying disadvantages motor with a phase rotor.

5. Scheme of the pulse speed control induction motor with slip-ring motors. Regulation of the rigidity of mechanical characteristics in this scheme by changing the resistance in the circuit of rectified current pulse method. The drive belt conveyor with an asynchronous motor squirrel pulsed current regulation is possible only in the stator circuit. Pulse method for controlling an induction motor is the most simple and easily implemented. However, this method has some significant drawbacks. With this method of control is a continuous flow of transients and the associated flow of the motor operates free components of transient currents, causing heating of the motor and the appearance of alternating moments of shock, degrade the quality of the transition process when starting the conveyor.

6. Frequency regulation of induction motor with frequency converter. The frequency converter provides a smooth adjustment in the desired range. The main disadvantage of the drive - it is expensive and large dimensions.

7. Parametric method for controlling an induction motor. If this method impact on the value attached to the drive motor voltage. Realized when the engine is started with a squirrel cage by two basic methods:

1) Deterministic phasing, ie, alternately switching the stator windings of the motor on the network at time instants corresponding to certain phase voltage, which eliminates the appearance of aperiodic component of inrush current and allows us to obtain the dynamic mechanical characteristics close to static.

2) Gradual increase in a linear or exponential voltage supplied to the engine.

Suppression of alternating moments of shock greatly increases the smoothness of start-up and, consequently, the durability and reliability as the electric drive, traction and organ [2].

Explosion-proof soft starter conveyors of this kind are issued by several foreign firms, among them the leading position occupied by such companies as «Hansen & Reinders», «Elgor & Hansen», «Hamacher» and others. The domestic industry produces two devices starter АПМ-200 and the УКТВ-400 ("Makeevsky plant mine automation") [5]. Also in УкрНИИВЭ was created explosion complete soft starter type КУВПП-250УХЛ5. A distinctive feature of foreign devices is that they are represented in the form of complete devices in large buildings and for domestic consumers are too expensive.

АПМ apparatus designed for soft start-up production and developing single-engine belt conveyors and cableway, equipped with asynchronous motors with squirrel cage, as well as for soft dynamic braking of electric conveyor belt after turn it off.

The electrical circuit apparatus provides:

• soft start working organ belt for a given program;
• changing the acceleration conveyor;
• dynamic braking of electric drive after turn it off;
• change brake torque;
• reverse actuator using magnetic starter disconnector;
• protection of power thyristors unit from overheating from short circuit currents, the loss of control of power thyristors with the disappearance of the pulse control in one or more channels, the loss of phase input voltage;
• indication of the switching on (off) state apparatus and the actuation of protection.

Apparatus is equipped with a contactor, which bypasses the power thyristors after the soft start working organ the conveyor. If necessary, they can make direct start the motor.

The cost of the apparatus АПМ is considerably inferior cost of similar foreign units, which together with its functionality makes the device particularly attractive АПМ for domestic consumers.

Thus, the existing device unit for a smooth launch phase induction motors using the principle of regulating the source voltage - due to the formation of the given angle α thyristor control. In this case, disable the power key natural - while reducing the current to zero. This allows the use of relatively inexpensive single-purpose thyristors, which are characterized by high energy performance.

Along with the obvious advantages (reliability, the lack of artificial switching devices), such a system has significant flaws that affect the quality of the original parameters, the impact on the nutrient and energy data network drive [3].

Explosion-proof complete soft starter type КУВПП-250УХЛ5 designed for soft start three phase induction motors with squirrel cage rotor used in the drive belt conveyors and other mining machines in underground coal mines, dangerous on gas or coal dust.

The device provides a soft start induction motor with squirrel cage rotor with adjustable duration from 5 to 20 seconds.

The device allows for no more than four starts with an interval of 1 minute or up to eight starts per hour under the terms of heating the engine.

The device provides the ability to switch back to operate without a soft starter. In this case, device works like an ordinary starter.

The basis of the soft-starter on the principle of supply three-phase induction motor is by increasing the voltage at start-up provided by a thyristor switch, consisting of six thyristors included two back-to-parallel in each phase of the mains.

Static switch allows you to smoothly change the voltage at a constant frequency of the network by the time of opening the thyristor. Management slew rate is provided a microprocessor control unit.

Starting torque of the motor varies in proportion to the square of the voltage at a fixed frequency. Smooth increase in voltage eliminates inrush current at the time of inclusion, while also excluded mechanical shock to the system motor-reducer mining machine.

The program incorporated a microprocessor control function of load current. This function performs a protection against phase failure, motor overload protection and supports the multiplicity limit the starting current from the nominal given by the user by means of switches.

Figure 1 – Block diagram of the soft starter
Animation: the number of slides - 10; delay between slides – 1с;
looping – 7; size - 42Кб.
T – sensor; K – unit complex protection;
MK – microprocessor control; 1 – thyristor switch;
KM – vacuum contactor; М – induction motor

Thyristor switch is designed as a module, which consists of six thyristors, mounted on common heat sink. For forced air cooling thyristor switcher is equipped with radiator fan. Control the radiator temperature by solid-state sensor signal from which is passed to the microprocessor control. The temperature is displayed. When heating radiator over 80 °С microprocessor control disables the device. The module also has a board transformer provides galvanic isolation circuit thyristor control of the power and timing control circuit board with each phase of the network.

The device incorporates two vacuum contactor. Contactor KM1 shunts thyristor switch at the end of dispersal, to prevent excessive temperature rise of thyristors in a confined space explosion proof casing. Contactor KM2 provides a disconnected state, compared with thyristors, more reliable isolation of outgoing power circuit.

The algorithm works microprocessor control is constructed in such a way that when you run the command "START" (illustrated in the animation) to ensure switching contactors, is included KM2, open thyristors, turn KM1, closed thyristors off KM2. When the command "STOP" is included KM2, open thyristors off KM1, closed thyristors off KM2 [4].

RESULTS

The studies were made in the modeling of induction motor at a phase (Fig. 2) and pulse width (Fig. 3) regulate voltage supplied to the engine.

Figure 2 – Principle of phase control variable voltage

Which:

α – angle unlocking thyristor;

T – switching period;

t – duration of switching;

uв – output voltage converter;

uс – voltage

Figure 3 – The principle of pulse-width control AC

The simulation processes in an asynchronous motor with phase regulation, it was determined that the current drawn by the load differs from the sinusoidal and the amplitude of the 5 th, 7 th, 11 th, 13th harmonic currents are comparable to the 1-th harmonic component, especially when small values of the relative stress (Fig. 4.б). Also has a significant impact on the power factor of the network(Fig. 5). All this adversely affects the electromechanical performance and service life of the drive.

Figure 4 – The dependence of the harmonic content of current asynchronous motor output voltage with a pulse width regulation (a) and phase regulation (b)

Which:

v1w, v5w, v7w, v11w, v13w и v1f, v5f, v7f, v11f, v13f – 1 st, 5 th, 7 th, 11 th, 13 th harmonic components of current induction motor with pulse-width regulation and phase regulation, respectively;

Uw, Uf – the relative values of voltage.

The results of simulation processes in an asynchronous motor during the pulse-width regulation have shown that the amplitude of current harmonics, except the 1 st, are negligible (Fig. 4.а), that causes substantial proximity to sinusoidal current consumption.

Figure 5 - Dependence of the power network from the output voltage with a pulse width(χw) and phase regulation(χf)

All this and no effect on the power factor (Fig. 5) suggests that the use of PWM voltage regulation in the starter allows you to: bring the adjustment signal to sine wave, to optimize the starting and stopping points for the unstressed acceleration and stops reducible mechanisms, extend the use of bearings, gear teeth gears, belts, etc. [1]

CONCLUSIONS

During of the study were the main requirements to electric drive belt conveyors, analyzes the main tasks of automation of conveyor transport and lit probelema start. Had reviewed the main existing technical solutions to ensure a smooth start-up conveyor belt. These solutions were analyzed in terms of reliability, functionality and economic viability, highlighted the main advantages and disadvantages of any method.

At the conclusion of the work were considered modern soft starters, there were advantages and disadvantages. Were presented to the benefits of applying PWM control to phase control based on the simulation results of both methods. Formulated by the prospect of further research.

REFERENCES

1. Ставицкий В.Н., Горбунов Е.Ю. Применение широтно-импульсного регулирования переменного напряжения в устройстве плавного пуска (УПП) привода ленточного конвейера. // Материалы IX Международной научно-технической студенческой конференции. – Донецк: ДонНТУ, 2010. – с. 133 – 136
2. Малиновский А.К. Автоматизированный электропривод машин и установок шахт и рудников: Учебник для вузов. – М: Недра, 1987. – 277с.
3. Ставицкий В.Н., Маренич К.Н. Полупроводниковый преобразователь для автоматизированного электропривода горной машины. // Наукові праці Донецького національного технічного університету. Серія: обчислювальна техніка та автоматизація. Випуск 58. – Донецьк: ДонНТУ, 2003. – с. 122 – 129
4. «Взрывозащищенное устройство плавного пуска типа КУВПП-250 УХЛ5». Электронный ресурс. Режим доступа: http://ukrniive.com.ua/ru/article/soft_start.htm
5. «Макеевский завод шахтной автоматики». Электронный ресурс. Режим доступа: http://mzsha.inf.ua
6. Воронин П.А. Силовые полупроводниковые ключи: семейства, характеристики, применение. М: Издательский дом Додэка-XXI, 2001. – 384с.
7. Справочник по автоматизации шахтного конвейерного транспорта / Стадник Н.И. и др. К.: Техника, 1992. – 438с.
8. Технические средства автоматизации в горной промышленности: Учебное пособие / В.И. Груба, Э.К. Никулин, А.С. Оголобченко. – К.: ИСМО, 1998. – 373 с
9. Батицкий В.А., Куроедов В.И., Рыжков А.А. Автоматизация производственных процессов и АСУ ТП в горной промышленности: Учебник для техникумов. – 2-е изд., перераб. и доп. – М.: Недра, 1991. – 303 с.
10. Руденко В. С. Преобразовательная техника. Київ: Вища школа, 1983. – 431 с.
11. Автоматизация подземных горных работ / Под ред. Проф. А.А. Иванова. – К.: Вища школа, 1987. – 328с.

When writing this master of the abstract work is not completed yet. Date of final completion: December 2011. Full text of the work and materials on the subject can be obtained from the author or his supervisor after this date.

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