The topic of this article is related to electrical equipment that is installed in mines and which requires normal mine performance in order to avoid accidents and accidents. Mine electrical equipment includes apparatuses and machines that convert, distribute and consume electricity in mines, as well as electrical devices and appliances that are used to protect, control, measure and control electrical networks.
Requirements
Mine normal execution must be applied in any external environment where electrical equipment is installed, and this environment can be completely different, it is not the same not only in different areas, but also in the same mine, in its different workings. Therefore, the working conditions of mining mechanisms and machinery with electrical equipment are equally different. The requirements for which the normal mine performance is carried out are also different and depend not only on the manufacture of electrical equipment and its switching methods (inclusion in the electrical network of this mine). The degree of toughening the requirements for how to turn on mine electrical equipment varies and is performed at four levels.
1. RN - mine normal.
2. RP - mine with increased reliability against explosion.
3. RV - mine explosion-proof.
4. RO - mine, especially explosion proof.
PH Features
General industrial equipment is quite different from the equipment that is installed in the mines, since normal mining performance enhances the structural strength, given the operation in difficult mine conditions of high humidity and dust. Conventional electrical equipment is also used.
It has no explosion protection properties, and therefore is used only in mines where dangerous sudden emissions are not expected. It is installed both in the trunks and in the round-bore openings, in stationary installations, that is, in those mine openings where there is ventilation with a fresh air stream due to mine depression. Normal mine performance is used in haulage mines if these are mines of the first and second categories for gas and if there is a constantly fresh stream of air.
RP
Electrical equipment, executed at the RP level, is always equipped with anti-explosive devices (and not only gases, but also coal dust itself explode in the mines). It is installed only in an undamaged condition and working in the correct mode. Normal mine performance is not applicable in dusty mines.
The RP level is set if the mine is non-gas and not dust-hazardous, and fresh air stream is present in the exhaust workings, as well as in dust mines and gas mines of the first and second categories. Execution of RP concerns luminaires, battery boxes, battery electric locomotives, individual parts of transformers and electric motors, if under the conditions it is impossible to mine normal execution.
PH1 and PH2
Mining widely uses electrical equipment in underground mines and mines if there is no danger of ignition. It is made according to general requirements: normal mine performance GOST 24754-81. It does not have explosion protection elements, but on the other hand, it has all types of protection that ensure the safety and reliability of operation. On the marking there is a conditional name - PH and the designation of the insulation level with numbers 1 or 2.
The marking is located in a circle and is made with embossed signs on the passport plate or on the shell. Mine normal performance RN-1 operates in an environment with a humidity of 98.2% and at temperatures up to 35.2 degrees Celsius, it is used in coal mines. RN-2 can work in such and more severe conditions. Normal mine electrical equipment should guarantee the safety of its use. This requires the fulfillment of many conditions, which will be discussed below.
Conditions of use
For the safety of work in coal mines and in mines, it is necessary to use specially designed mine electrical equipment and special mine cables. It is also necessary to comply with all the rules so that the cable and equipment do not receive damage from external factors and work only in the mode calculated for them. In case of loss of safety properties by cables and electrical equipment, a protective shutdown must occur.
Explosive atmospheres should not be created at the locations of equipment and cables and combustible materials should not appear; a whole complex of measures and means is used against this. The risk of electric shock must also be excluded. To prevent accidents and when deviations from normal operation occur, special protective devices exist .
Classification
Mine electrical equipment is classified according to various criteria, and this depends on operating conditions. There is stationary equipment that works without moving from the installation site, there is mobile and portable - this is the first sign. The second one speaks of the presence or absence of explosion protection equipment in the equipment when the environment is ignored or hampered during operation. There are special schemes established by the regulations, according to which mandatory certification is carried out. Mine normal execution also provides for serial production, indicated in the certification scheme as 1s. A 2s, 3s and 4s indicate, respectively, limited lots and certification of individual pieces of equipment.
To work in explosive atmospheres, special indicators are needed: electrical equipment must function safely during the entire service life, as well as when certain external influences occur, when environmental conditions change (the limits are set by the manufacturer). Surface temperatures should not exceed the ignition temperature of an explosive atmosphere in emergency situations. It is necessary to make sure, using the mine normal performance, that this is so. It is necessary to take into account the accessibility of each sample to other parts of the equipment that are dangerous in case of ignition or may themselves be its source. Equipment emitting flammable gases must be in closed structures with the mandatory presence of a manual shutdown.
Fabrication of switchgear
The normal mine version uses high-voltage cabinets with increased reliability, designed to protect and power the equipment of the mine or mine. With its help, underground substations are equipped that operate in explosive and gas hazardous conditions. Protection depending on the conditions - on a mechanical relay or microprocessor, but the following types of protection are required: MTZ (maximum current), ZDZ (from single-phase to ground), ZMN (at the minimum voltage), and also protection against asynchronous running of the motor must be present.
The cabinet can be equipped with any type of vacuum circuit breaker. When using electrical equipment for various purposes, the cabinet allows the use of various cell modifications in a single construct. All equipment must meet the requirements for the safety of their use both in open pits and in underground work in mines and mines that are explosive in dust and gas. According to GOST, it is necessary to check and determine the level of explosion protection.
Circuit protection
Electrical equipment and cables must have a flameproof enclosure that withstands explosive pressure and prevents the explosion from spreading from this enclosure. The electrical circuit must be intrinsically safe, it is designed so that its heating or electrical discharge could not ignite an explosive atmosphere. Electric circuits are divided into three levels of safety: Ua - special explosion protection, Ub - just explosion safety, Uc - only increased reliability. If the electrical equipment or its parts do not have sparking parts, measures are still taken to further complicate the appearance of heat or electrical sparks.
Such additional protection is marked with the letter “P”. There is a shell where live parts and live parts are protected by a liquid non-combustible dielectric, such protection is marked with the letter "M". The letter “K” corresponds to quartz filling. The letter "A" denotes a protective automatic shutdown, which will ensure the release of voltage from all live parts if the protective shell gets damaged, and it will be able to disconnect before ignition of the surrounding explosive atmosphere occurs. As the description indicates, mine normal electrical equipment usually contains several types of such protection at the same time.
Electrical Protection
Three-phase alternating current with a frequency of 50 hertz and a voltage of 1140, 660, 380 and 220 volts is used to power electric receivers in underground workings. To power the lighting systems and electric drills, a three-phase alternating current of 50 Hz and a frequency of 127 volts is supplied. Transformer substations need a transmission of electricity of 3.6 and 10 kilovolts, and for a contact network of electric locomotives - a constant 250 volts. Corresponding to GOST mine electrical equipment should take into account dust and high humidity conditions during maintenance, installation and transportation.
Electrical equipment of increased reliability from the explosion is supplied with means that will prevent the danger of sparks, arcs and provide explosion protection if the working conditions are normal. Explosion-proof electrical equipment is protected even in the event of damage. These are magnetic starters, electric motors, feeder machines and the like.
Additional requirements
The shells of all parts of the electrical equipment must be provided with increased mechanical strength to provide protection against damage and penetration of solid particles, dust and water. The temperature of the outer parts of all shells should not be higher than two hundred degrees Celsius during long-term operation, and for short-term - above four hundred and fifty degrees. All this - no more than three minutes, after which immediate cooling should follow. Electrical equipment should be equipped with heat-resistant, moisture-proof, arc-resistant and oil-resistant insulation, designed for operating conditions at a humidity of up to one hundred percent and at a temperature of thirty-five degrees.
Cable entries with blind or plug connectors are required. All electrical apparatus during operation should be subjected to frequent inspection with a check of protection, contacts and the like. They must be locked mechanically, electrically, or both at the same time, in order to prevent the caps from opening or disconnecting the plugs under electrical load, as well as turning on the device with the cover open. The design of the interlocking unit shall ensure contact breaking. Oil filling can be allowed only for stationary installations (controllers, autotransformers, rheostats and semiconductor rectifiers), and only up to 700 volts.
Degree of danger
Different types of electrical equipment and its individual elements can be hazardous to varying degrees under certain operating conditions. Therefore, the approach to ensuring safety must be differentiated, and the degree of stringency of requirements must be observed depending on the conditions.
For example, an asynchronous squirrel-cage rotor motor, which usually does not have any sparking, is significantly less explosive than a phase-rotor motor, where sparking is always present on contact rings. Or a bus junction box, where the correct installation has been carried out, is not exposed to dangerous heating or sparking, and therefore does not pose such a danger to a mine explosive atmosphere as a switch that always has an electric arc on the contacts when the engine is turned off.
conclusions
Installations that are located in the face or in other explosive places, albeit well ventilated, must be absolutely safe. Usually they save on equipment, using cheaper and not designed for internal pressure, which can be exerted on this equipment by an explosion. They use the usual normal mine performance, even where there are no suitable conditions, in the best case, electrical equipment with increased reliability is installed.
However, it is far from always possible to exclude sparking or heating of hazardous elements. Reliability increases are achieved by enclosing normally sparkling parts of electrical equipment in an explosion-proof enclosure. Or immerse live parts and windings in oil. The manufacture of mining electrical equipment should exclude the slightest possibility of the occurrence of hazardous temperatures, sparks or an electric arc.