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Introduction of magnesium oxide Cable:
Copper Core copper sheathed Magnesia insulated Fire-proof cable (hereinafter referred to as Magnesia cable), is a kind of outer layer using seamless copper protection cover, the middle filling magnesia crystal powder as insulating material, a single copper rod as a conductor of the new cable. It is not only capable of high temperature, fire, explosion-proof, flame-retardant, but also large load flow, small diameter, high mechanical strength, long service life, generally do not require independent grounding wire. Therefore, Magnesia cable is widely used in dangerous, harsh, high-temperature environment, such as nuclear power plants, metallurgy, chemical industry, mine, kiln and so on. In recent years, with the vigorous development of a variety of technology, Magnesia cable is also more used in high-rise buildings, airports, docks, subways and other civil buildings, to protect the fire in the case of fire pumps, fire elevators, local lighting, emergency evacuation instructions, security monitoring, smoke exhaust system, Self-owned power supply and other fire-fighting electricity and important equipment uninterrupted operation.
Structure and model specification of Magnesia cable:
Magnesia Fireproof Cable Manufacturing process is more complex. There are two main methods, first, the outer layer of seamless copper tube and core copper core conductor between the pouring of Magnesia crystal powder, the second is to press the magnesium oxide powder into a hollow cylinder, which is passed between the conductor and the copper pipe, and then through the pull-annealing-and then pull out of the multi-channel process cycle repeatedly and then made into cable. It should be noted that the Magnesia cable in the processing of the need to continuously detect the density of magnesia and copper pipe tightness and other projects. Through the understanding of the production process and methods of Magnesia cable, we can see that the structure of the cable is mainly composed of three parts: the outer seamless copper casing, the middle of the insulating magnesium oxide crystal powder, the core as a conductor of copper rods.
Magnesia cable models can be divided into BTTQ light cable (500V level) and Bttz heavy cable (750V Class) Two, Kempinski project mainly for Bttz heavy cable. Its specifications are mainly single core, two cores, three cores, four cores, seven cores, 12 cores and so on. Single-core to four-core Magnesia cable is mainly used for power, lighting, more than seven core for communication, control. Single-core cable maximum section can reach 4002m㎡, two cores to four core cable core wire maximum section is 25m㎡.
Second, the advantages of Magnesia cable
1. Complete Fire prevention
Magnesia cable itself completely does not burn, 250 ℃ can run for a long time, 1000 ℃ limit state can also maintain 30 minutes of normal operation, but also does not cause ignition. Even in the case of a flame grill, as long as the flame temperature is lower than the temperature of the copper melting point, the flame eliminates the need to replace the cable can still continue to use. No poisonous fumes or gases will be produced in the event of a flame grill.
2. Strong overload protection ability
When the line is overloaded, the cable will not be damaged as long as the heat does not reach the melting temperature of the copper. Even if the instantaneous breakdown, the breakdown of MgO crystals will not form carbide, overload elimination, cable performance will not change, can continue normal use.
3. High working temperature
4, anti-corrosion, explosion-proof performance is good
As a result of the use of seamless copper pipe sheath, magnesia cable with waterproof, tidal, oil and some chemical damage to the performance of the copper tube has a considerable mechanical strength so there is better explosion-proof performance.
5. Long service life
Magnesia cables are all composed of inorganic materials, so there is no insulation aging, the service life can reach the ordinary cable more than 3 times times.
6, the laying of greater flexibility
Magnesia cable can be laid on the bridge with the ordinary cable, at the same time can be used special stent, more flexible than ordinary cable laying, but also save cable tray input, can reduce the overall cost of the project.
Third, the shortcomings of Magnesia cable
Things have two sides, Magnesia cable is no exception, with many advantages, there are some shortcomings, should be in the selection and construction attention.
1. High investment cost
As a result of magnesium oxide cable sheath is made up of seamless copper tube, the overall copper content far more than ordinary cable, and Magnesia cable construction technology for equipment requirements higher than ordinary cable, resulting in magnesium oxide cable prices and ordinary cable than 30% higher.
2. Easy to damp at joints
Insulating layer is composed of mineral magnesia, it is very easy to react with moisture in air, and generate conductive magnesium hydroxide. In the construction of cable head, when the cable end is stripped of the bare conductor, the insulation resistance of the cable is generally above 10mω, but if the cable head is not finished within 1 hours, the insulation resistance can descend to the 10mω below, May even appear below the 0.5mω condition, if does not pay attention to cut the outer layer, also did not discover in time and seals the damp-proof treatment, the insulating value will descend quickly and will descend gradually to 0, thus will cause this cable to be unable to use.
3, the construction difficulty is big
Magnesia cable hardness compared with the general cable is relatively high, weight of about twice times the general cable, the installation is not easy to achieve a parallel neat impression effect, and the line long, many joints, find fault points difficult, so the construction is more difficult, in and out of the wiring box and the bridge frame bending forming difficulties.
4. Large construction work
Magnesia cable where the specifications of more than 35mm are single core cable, such as 1 70mm of cable, ordinary cable only 3x70+2x35 five conductor in the same outer sheath can, and magnesia to achieve the same specification must be 3 70mm plus 1 35mm of single core cable. Single-core cable delivery length is shorter, such as 240mm cable delivery length of 69 meters, if the laying distance will increase the production of a large number of intermediate joints, so that the construction workload doubled.