Mineral insulation mining cable is also called magnesium oxide cable, the main components are electrical copper, magnesium oxide insulation materials and metal sheath.
The highly conductive copper conductor is embedded in a seamless steel tube made of tightly compacted magnesium oxide material to form an extremely safe mineral insulated cable.
For special needs, a layer of polyethylene outer sheath can be extruded on the metal sheath.
Mineral insulated cables were developed earlier in foreign countries and have been produced for half a century, and are widely used in various fields.
Domestic is still a new topic, although in recent years, some joint ventures with foreign departments, enterprises and imported equipment to use such cables, but is only the beginning.
ArnoldFrancoisBorel, a Swiss engineer, first proposed the idea of a mineral-insulated cable in the late 19th century and patented it in 1936.
Subsequently, France, Britain have been formally put into production, after the rapid development.
Great Britain, France, Italy, Canada, Australia, the United States, the Soviet Union, Japan and other major countries have a large number of production.
The main equipment has been imported from Austria and Italy.
Harbin made use of imported equipment and domestic supporting equipment to develop the cable products and accessories production line, the registered capital of 39 million yuan, so that it has become the first large-scale mineral cable professional manufacturer with an annual production capacity of 1,500 kilometers, filling the domestic gap.
The classification of the mine cable structure according to the foreign usually, mineral insulated cable roughly divided into: distribution cables (WiringCable), heating cables and components (HeatingCableandHeatingElement), thermocouple cables and compensation cables (ThermocoupleCableandCompensatingCable) and special cable (SpecialCable), etc.
According to the voltage grade, mineral insulated cable is divided into heavy load cable (1000 volt class) and light load cable (600 volt class) two kinds.
Cable core number has 1, 2, 3, 4, 7, 12 and 19 cores, 1-4 cores are mainly used for power and lighting, 7 cores or more are mainly used for control and communication.
The maximum manufacturing cross-sectional area of a single conductor cable is up to 400mm2.
According to different requirements, the cable can be made into square, flat or hollow shape and other different shapes.
The cable terminal is made of metal or thermoplastic material.
The long-term use temperature of the bare wire is 250oC, and it can be close to the melting point of copper 1083oC for a short time or in an unusual period.
When used in chemical occasions with corroding copper sheath, a layer of PVC outer sheath (non-flammable) can be extruded on the copper sheath.
Mine cable structure 1) cable sheath 2) conductive wire core 3) insulating material 4)PVC sheath
Main specifications of mine cables: cable type conductor core number and nominal cross section mm2 bare cable outer diameter mm extruded PVC sheath nominal diameter mm conductive wire nominal diameter mm conductive wire core resistivity 20oC copper sheath resistance 20oC finished cable delivery length ± 5% light load cable
Mining cable characteristics The cable is made entirely of inorganic material, which gives it certain properties over any other type of cable
1) fire prevention: copper and magnesium oxide are inorganic, the cable does not burn nor combustion, more will not produce toxic gas, it passed the test of the International Electrotechnical Commission IEC331;
2) explosion-proof: the highly compaction insulation material in the cable and the cable terminal installed with special sealing sleeve can prevent steam, gas and flame from entering the electrical equipment connected with the cable, so it is useful in places with explosion risk and the connection of various explosion-proof equipment and equipment;
3) waterproof and corrosion resistant: the seamless metal sheath of the cable has high corrosion resistance, impermeable to water, oil and gas, almost in all environments, it does not need to take additional protective measures, PVC sheath is only needed in the occasion of individual chemical corrosion;
4) radiation resistance: due to the use of inorganic materials, with an effective neutron capture cross section, and maintain a high insulation resistance, so good stability, suitable for use in nuclear power plants and other nuclear facilities;
5) Large current-carrying capacity: under the same current-carrying condition, the diameter of the cable is smaller than that of the traditional cable section, and the overload (current) energy is large;
6) High mechanical strength: can withstand severe mechanical damage, can still work normally in the case of one-third of cable diameter deformation;
7) Large current carrying capacity: the actual normal continuous operating temperature of the copper core copper sleeve cable can reach 250oC. Under the same load flow condition, the diameter of the cable is smaller than that of the traditional cable section, and the overload (current) energy is large.
8) Safe and reliable: independent grounding conductor is not required. The outer sheath of the cable and the phase wire are installed together to play a grounding role, providing excellent low grounding resistance.
Due to the strength and toughness of the metal sheath, magnesium oxide is highly compressed in the cable processing process, so the cable is subjected to bending, flattening, torsion and other deformation between the core wire and the relative position between the core wire and the sheath will not be broken.
Ensure the stability of the cable, without maintenance in the work;
9) Long service life: the cable is all inorganic material, not aging.
Its life is calculated according to the oxidation corrosion rate of the copper sheath. The sheath is oxidized to 0.25mm, which takes 257 years at 250oC and 583 years at 400oC. The thickness of the general mineral insulated cable sheath is 0.34mm-1.03mm, so the cable has a long life.
As a heating cable, the heating range is wide, the temperature is uniform, and the control is convenient.
As a thermocouple cable, the reaction is sensitive and inert.
Its temperature resistance and electrical properties are very good, almost no change below its melting point of 2800oC.
Each cable is provided with a suitable terminal. A complete terminal consists of a gland which can be extended into the junction box for connection, a terminal which prevents the intrusion of tidal KYDL_SYEY gas and ensures constant insulation resistance, and a corresponding PVC sleeve.
According to the installation method and operating temperature of the cable, three different forms of terminal materials can be used, as shown in the table below: maximum operating temperature sealing material gasket insulation bushing brass pot 105OCCS Moplen BT185OCHT PTFE heat shrinkable end 125oC
Mining cables have special accessories when they are installed and laid: 1) brass ground plate is used for cable sheath grounding;
2) copper strip (12 x1mm);
3) Adjustable plastic mounting sheet;
4) Brass locking nut;
5)"0" type gasket;
6) Brass tight connection cap;
7) Lubricating oil;
8) PVC sheath gland for special occasions;
9) Resin for straight joints and installation;
10)PVC outer sheath;
11) gland.
conclusion
Because of mineral insulated cable has the characteristics above, it has been the international electrotechnical commission, the national institute of electrical engineers, such as the institute of electrical engineers, Germany Lloyd's register many international authoritative organizations, some national standards, and preferable in key areas of electrical engineering, the dangerous area such as: the airport, oil depot and gas station, chemical industry, coal mine, (nuclear) power plant, steel smelting and shipbuilding etc.
Senior important public facilities: satellite earth station, railway wiring, alarm, fire protection, etc.
Places to ensure the safety of personal and property: historic buildings, hotels, high-rise buildings, museums, libraries, banks, hospitals, insurance, shopping malls, scientific research institutions, etc.
The cable, once laid, will last forever, making it worthwhile in terms of a one-time investment.
According to statistics, the fires caused by electrical causes account for about 20-30% of all fires in the world every year.
The loss to our country will not be less than that.
Thus, mineral insulated cable is an essential part of modern engineering cable system.
It will enable the country's oil platforms, nuclear power plants, petrochemicals and high-rise buildings to meet international standards.