Українська  Русский
DonNTU   Mastersʼ portal

Abstract

The content of the abstract

Introduction

The basis of a technical process in coal mines is the widespread use of high-producing complexes with modern explosion-proof electrical equipment. Currently this development ugolnodobychnyh sites conducted with the help of various mechanized complexes, including: mining harvester, conveyor, powered roof supports.

1. Theme urgency

Phase to phase short circuit (short circuit) is one of the most dangerous states of emergency shaft power, which can not only lead to overheating and damage to electrical components, but also cause fire or explosion of methane-air mixture. The fight against short circuits, their causes, as well as finding ways to improve the reliability of power supply is an urgent task.

Growth of installed power machinery technology makes use of electrical installations with reduced electrical resistance of power circuits (transformer substations and high power induction motors, transmission and flexible cables elevated section), power transfer to higher levels of the rated voltage. This further increases the degree of short-circuit currents in power circuits electrical systems technology areas.

In this regard, the practical relevance is the development of the automatic current limiting short circuit in the cable lines of treatment and development faces, where the probability of their frequent damage. Moreover, short-circuit current decrease leads to the possibility of creating cables providing fire and explosion safety of their use.

So far, the problem short circuit current limiting in mine low-voltage is not solved, because the possibility of using existing resources (limiting reactors) is limited by their great size and a sharp decline in the quality of the voltage (the voltage drop exceeds 10 %), making it difficult to start motors.

2. Analysis process coal mining as building automation

Technological process of coal mining in fully mechanized working face with shearer recess includes the following operations:

  1. Destruction of the coal shearer array and load chipped coal to face conveyor;
  2. Transportation of coal conveyor at the loading point of lava;
  3. Advancing mechanized system composition and conveyor mounting goaf.

The process is characterized by the destruction of the coal array variability of physical and mechanical properties of coal, as well as changes hypsometry seam thickness and includes:

  1. Automatic load control processor. Load regulation of electric motors allows for more efficient use of energy capability of the drive, increase productivity combine to increase its life by reducing the dynamic overloads, free driver continuous control feed rate.
  2. Motion Control harvester profile formation is necessary for maximum mineral extraction and normal working conditions of complex equipment in accordance with the technological requirements.

Figure 1 – Schematic of coal

Figure 1 shows a typical diagram of the process of coal mining:

  1. Haulage drift;
  2. Crushed drift;
  3. Scraper conveyor;
  4. Sections mobile mechanized attachment;
  5. Shearer;
  6. Airway.

Destruction of coal in the recess provided in different ways depending on the type of energy and the method of its application.

The most widely used mechanical method of destruction, which is carried out by the executive bodies of mining machines using cutters, cutters, crowns and others.

Choose how recess depends primarily on the properties and conditions of the formation of coal and surrounding rocks, technical means, the quality requirements of coal, as well as the costs of the recess.

Dredging process involves the destruction of the formation and loading coal recaptured. Both processes can be performed by one or more machines, simultaneously or sequentially, depending on the technology of work and geological conditions [1].

3. Rationale for directions automation process coal mining

Process control of coal mining is to seek the implementation of technological regimes to ensure the safe conduct of the work and the best balance between quantitative and qualitative indicators of the process with a minimum production costs. To achieve this, the process automation system sewage works suggest the following automation subsystems: subsystem control mining machine; management subsystem vehicles; management subsystem fastening goaf; subsystem and control environment and aerological safe operations.

Management Subsystem mining machine performs functions: providing local remote control; automatic maintenance of optimum operation.

Management Subsystem vehicles provides for the possibility of remote control face conveyor of several items and the mode of its operation.

The control segment safe operations performs functions: monitoring of environmental condition in the lava; control and termination process with the advent of an extraordinary situation. Subsystem is realized by means of special signaling, communication and lock.

Management Subsystem provides fastening goaf combined control sections mechanized system: automatic from a central console or remote management positions with lava depending on the specific geological conditions [2].

How important is a device that uses a short-circuit current limiting effect due to the inductive reactance of windings connected individually to each phase. The device is an inductor, wherein the circuit of each phase includes two anti-parallel windings with a predetermined inductance. The windings are geometrically aligned and mounted on a separate frame of a nonmagnetic material.

The device provides automatic inclusion in the work during the first half-cycle; limit short-circuit current in no more than 5 ms, which does not allow the development of surge current, short-circuit characteristic mode, and eliminates the effect of electrodynamic loads; decrease in short-circuit current to the minimum possible value, but not less than 4; self-healing device to normal after the protective current limiting short circuit in the chain of supply; voltage loss in the reactor during normal operation no more than 2 % of the nominal voltage; inductive reactance of the windings of the reactor in the nominal mode is almost zero; permanent inclusion in the work (no switching and control signals for input to the work of the unit); high functional reliability.

Speed current limiting protection allows you to influence even on impact Isc (which occurs no later than the 2nd period of the mains frequency after the emergence of short-circuit).

In order to study the effect of the principle of influential automatic short circuit current limiting computer model was grounded electrical low voltage section of the mine complex, taking into account actions proposed agent.

The main parameters characterizing the performance of electrical complex mine area include:

  1. Secondary winding of the transformer substation mine GSTP-630 (Rtr = 0.018 ohms = 0.078 ohms);
  2. Cable line length of 300 m (cable brand KGESH 3*50, Rk = 0,281 Ohm/km, Lk = 0,252*10-3 Gn/km, Ck = 0,87*10-6 F/km);
  3. Induction motor (1EKV3, 5-200, Un = 660 V, pH = 280 kW);
  4. Circuit breaker (tcp = 5 ms).

The developed model reproduced the behavior of the object graph.

Fig. 2 shows the corresponding SimPowerSystem - model consists of the following parts:

  1. The secondary winding of the transformer substation mine – GSTP-630 – Three-PhaseSeriesRLCBranch;
  2. The cable line length of 300 m – PiSectionLine 1-6;
  3. Asynchronous dvigatel 1EKV3 5-200 – AsynchronousMachineSIUnits;
  4. Circuit Breaker – Three-PhaseBreaker;
  5. Block shorting – Three-PhaseFault.

Figure 2 – Block diagram of the mathematical model of coal mine low-voltage electrical complex

As a result of the research computer model gave the corresponding dependence of current change at the injury site (Fig. 3, Fig. 4).

Duration of short-circuit failure mode in the absence of the device current limit (Fig. 3) is determined by response time overcurrent protection and switching equipment (in accordance with the regulations – 0.2 s).

Fig. 4 shows the current waveform of three-phase short circuit in the same line, but with the action of the automatic short circuit current limiting. In this case, the duration of the dangerous current is reduced to the minimum possible value at which you can virtually eliminate the possibility of ignition of methane-air mixture, fire, and significantly extend the life of switching equipment in connection with relief voltage is switched off in the short-circuit .

Figure 3 – Three-phase short-circuit current waveforms (shown in a phase current)

Figure 4 – Waveform phase short-circuit current, taking into account the action of the automatic current limiting short circuit

4. Development of device protection system automation process of coal mining

Figure 5 – Block diagram of the ultrasonic device short circuit current limiting cable.

Figure 5 shows:

УОТ – current limiting device; тока;

УК – compensation device;

К – key;

В – rectifier;

ТН – voltage transformer;

БИ – the display unit.

On the basis of the structural scheme (Fig. 5) developed a functional diagram of the device, which is shown in Figure 6.

Figure 6 – Functional diagram of the ultrasonic device short circuit current limiting cable
(animation: 5 frames, interval 1000 m/s, 115 kilobytes)

Figure 6 shows:

L1 – inductance;

L2 – inductance;

VS – key;

Z – rectifier;

TV – voltage transformer;

VD – LED.

The scheme works as follows: The voltage supplied to the network. Inductor L1 and L2 cancel each other out, Triac key VS in the closed state, the device is working properly, the green LED light VD. If a short circuit transformer rectifier TV and Z affect Triac key, it opens. Inductance L2 demagnetized and ceases to compensate L1, red light LED VD, L1 starts to limit short-circuit current.

Practical interest in the device, the circuit is shown in Fig. 7. Apparatus comprises a controlled reactor (in the unit current limit БОТ) connected to the mains phases between the power source and the protected connection. In normal operation of counter working through winding L1; L2; L3 and control winding L4; L5; L6 phase reactor rated current line. In this case, since the work of the winding and the control winding is geometrically compatible in space and cover a certain cross-section of the magnetic circuit of the magnetic flux will be fully compensated, and the magnitude of the inductive reactance of the reactor will be close to zero. Voltage drop across the reactor will be determined mainly small size of the active resistance of the windings.

In the event of a short circuit in the controlled lines disappear control signals from the outputs of the control current TUC: voltage in short circuit tends to zero – the signal from the transformer rectifiers through Z1 – Z3 ceases to act on triac gate VS1 – VS3 (semiconductor switches), and disabled control winding L4; L5; L6. Magnetic fluxes working phase windings L1; L2; L3 significantly increased and this increases their inductive reactance. Application controlled reactor can automatically increase the resistance abruptly phase electrical connection with the short-circuit current, and this decrease in the accession to a value commensurate with the operating current. Short Circuit carried a slight delay due to time off triacs [3].

Figure 7 – Scheme means of automatic short circuit current limiting

Speed current limiting protection allows you to influence even on short-circuit current, which occurs not later than second period after the time of the mains frequency of a short circuit.

Effectiveness of the proposed principle of automatic short circuit current limiting can be proved on the basis of computer simulation of low-voltage electrical complex section of the mine in the short-circuit condition, taking into account the action of the device.

Adopted for modeling electrical complex, consisting of the following elements: feeding transformer substation type TPVP-630; trunk cable type EVT 3 × 95 30 m in length; flexible cable type KGESH 3 × 70 300 m length of the linear voltage received on the site – In 1140, a short circuit occurred in the middle of the flexible cable [4].

The proposed device operates automatically and has high speed, as responding to the fact of an emergency, short-circuit mode, and not by the amount of current to prevent the development of shock and short-circuit current to eliminate the influence on the electrical components and cabling electrodynamic overloads. After actuation, the protective short circuit current limiting and removing the supply voltage fails self-healing in its original condition without any additional control signals and switching that ensures high functional reliability. Operation of the device does not affect the parameters of power supply and is characterized by the absence of voltage in the start-up and steady-state conditions.

Relatively small size and versatility in comparison with existing reactors allow the apparatus to implement automatic current limiting short circuit currents in networks of underground power supply voltage of 660 V and 1140 V [5].

Findings

Thus, the urgency of the analysis of processes in the electrical section of the mine complex process in the event of an emergency state-to-phase short circuit in order to justify the automatic short circuit current limiting and developed variant technical implementation of such a device. Computer model of the proposed electrical complex technological section of the mine in the short-circuit condition in a flexible power cord induction motor allowed to establish the character of change of the short-circuit current with the work of the device automatically and without current limit. Analysis of the changes in the magnitude diagrams of the current short-circuit in a network with controlled current limiting reactors in phases confirms the effectiveness and implementation of the proposed device creates the conditions for the safe use of electricity in mines, hazardous gas and dust.

When writing this abstract masterʼs work is not finished. Final completion: December 2014. The full text of the work and materials on the topic can be obtained from the author or his head after the specified date.

References

  1. Справочник энергетика угольной шахты / [Дзюбан В.С., Ширнин И.Г., Ванеев Б.Н., Гостищев В.М.]; под общ. ред. Ванеева Б.Н. – [2-е изд.] – Донецк, ООО «Юго-Восток Ltd.», 2001 – Т2, - С. 404-418.
  2. Муравьев В.П. Расчет электрических сетей угольных предприятий / В.П. Муравьев. – М.: изд- во «Надра», 1975. - с. 184.
  3. Маренич К.Н. Моделирование процесса короткого замыкания в низковольтном электротехническом комплексе участка шахты с учетом влияния электропотребителя / К.Н.Маренич, И.В. Ковалева // Научные труды ДонНТУ, серия электротехника и энергетика. - Донецк: ДонНТУ, 2007. - Вып. 7 (128). - С.146 -149 .
  4. Авт. свид. 913516 СССР, МПК Н02Н9/02 Токоограничивающее устройство / В.А.Машкин, Л.С. Беспалов, В.Г. Савельев. (СССР) - №3000759/24-07. Заявл. 25.07.1980. Опубл. 15.03.1982. Бюл. №10.
  5. Перехідні процеси в системах електропостачання: підручник для вузів. / [Г.Г Півняк, В.М.Винославський, А.Я. Рибалко, Л.І. Несен]; під ред. Г.Г. Півняка. – [2-е вид., доправ. та доп.]. – Дніпропетровськ: НГУ, 2002. – 579 с.