With the increase and accumulation of cable service time, the cable is most likely to have problems with insulation aging. The reason for this may be that the cable was not selected for the appropriate model when it was laid, resulting in the long-term work of the cable under overvoltage or the cable line. There are close to heat sources around, so that part of the cable or the entire cable line is heated for a long time and prematurely aged. The working environment of the cable is also a factor that affects the life of the cable insulation layer. If it is used in an environment with adverse chemical reactions, or multiple cables run in parallel but one or several of them are in poor contact, it will also cause other parallel cables to overheat. The load operation causes failure. When the cable accessories are made, the cable connection tube is not crimped firmly, resulting in an increase in contact resistance and causing overheating. These are the causes of insulation failure and must be avoided reasonably.

Accessories are also very prone to problems, and this ratio is also very high. The reason is that the cable intermediate joints and terminals are usually completed by the installers on the laying site. Problems with accessories will affect composite interface discharge and material aging of accessories. The problem of accessories is often due to the poor production process and poor product quality. During the production process, defects such as air bubbles, moisture, and impurities appear inside the accessories, which cause partial discharge and cause insulation breakdown. Not only must you choose high-quality accessories, but also Nor can it be neglected.

The problem of the outer sheath is also relatively common. In the medium and high voltage power grid, the outer sheath of the wire and cable is the first line of defense to protect the cable. Whether it is intact or not is directly related to the safety of the internal structure and the length of the cable's service life. The reasons for the problems of the outer sheath are: there are hard objects on the top and bottom of the direct-buried cable, and the sharp corners directly contact the outer sheath, especially in the section where vehicles pass, and the road vibrates for a long time, and the sharp corners of the hard objects may pierce the outer sheath. As a result, the internal structure is damaged, coupled with the change of the cable load, the thermal expansion and contraction of the cable itself and the uneven distribution of the electric field at the damaged part, resulting in damage to the insulation layer; It may cause damage to the outer sheath; mechanical construction or pipe jacking operations around the cable path may cause damage to the outer sheath.

During the laying construction process of the cable, the outer sheath is pulled and the cracked part is in the pipe, so it will not be found in time; after a period of operation, cracks will occur, the insulation of the outer sheath will be reduced, the metal sheath will be grounded at multiple points, and the circulation will increase. Large, eventually lead to thermal aging breakdown of insulation. Termite erosion is also one of the reasons for the appearance of the outer sheath. Once a termite erosion site is found, there should be multiple corrosion areas on the cable line, and we should pay enough attention to it. Termites are dangerous to eat and eat, relatively speaking, they rarely appear in the north.

The advantages of single-core cables are small cross-sectional area ratio, not easy to oxidize, short-circuit capacity impact resistance, and long service life. The disadvantage of single-core wires is that the wire is relatively hard, and it is difficult to pull the wire in some places, so it is difficult to straighten after bending, and it is easy to damage the wire after repeated bending. Advantages of multi-core cable Multi-core cable refers to a cable with an upper insulating layer of copper core, which can reduce the skin effect of the cable, thereby reducing line loss.

The disadvantages of multi-core cables are poor strength, easy to break, poor surge resistance, and inconvenient forming. Single-core or multi-core cables are the best wires with the same cross-sectional area. The cost of single copper core cable is cheaper than multi-copper core cable, while the cost of multi-copper core cable is slightly higher.

Single copper cables look a bit stiff when installed and conduit, while multi-copper cables should be softer and have stronger wires. After installation, single-core and multi-core are similar in specific applications.

The difference between multi-core cables and single-core cables is that in terms of circuit capacity, the rated current capacity of single-core cables is greater than that of three-core cables with the same cross-section; in terms of insulation performance, both single-core and three-core cables need to meet national standards. Under the premise of meeting the national standards, a certain safety margin needs to be left, which can be understood as the insulation performance is qualified and there is no difference;

In terms of cable use, the heat dissipation performance of single-core cables is greater than that of three-core cables (cables of the same type), plus the rated current carrying capacity of single-core cables of the same cross-section > three-core cables, which can be achieved under the same load or short circuit conditions Next, the calorific value of a single-core cable is less than that of a three-core cable, which is safer to use;
In terms of cable laying, single-core cables are more convenient to lay and easier to bend, but the difficulty of laying long-distance single-core cables is greater than that of three-core cables;
From the installation of the cable head, the installation of the single-core cable head is easier and the wiring is convenient;

multi-core cable

A multi-core cable is a cable with more than one insulated core. Cables play an important role in electronic products and electronic systems. They are the key links connecting various functions of electronic products, and are widely used in aerospace, marine warships and other fields.

single core cable

Single core means that there is only one conductor in one insulating layer. When the voltage exceeds 35kV, most single-core cables are used. The relationship between its core and the metal shielding layer can be regarded as the relationship between the coil and the iron core in the primary winding of a transformer. When the single-core cable core passes current, there will be magnetic force lines interlinked with aluminum cladding or metal shielding layer, causing induced voltage to appear at both ends of it.

1. BBTRZ flexible mineral insulated cable fireproof cable

General wires and cables use organic polymer materials for insulation, so they are easily carbonized under flame conditions and lose their insulating effect. Since the main material of the flexible mineral insulated fireproof cable (BBTRZ) is composed of mineral compounds, it will not cause fire by itself, and it is impossible to burn or support combustion. These materials generally have a higher melting point above 1500°C, so the fireproof cable can also perform normal power transmission functions even under flame conditions, and it is a real fireproof cable. And can pass BS6387 C, W, Z test.

This type of cable can guarantee emergency use after installation, and can also be used as a temperature-resistant 125°C halogen-free flame-retardant cable and fire-resistant cable. Because this series of cables covers a wide range, it not only overcomes the defects of rigid MI cables, but also gives full play to flexible MI cables. The advantages of cables, and provide practical products for various key projects, so that modern engineering can achieve the effect of short circuit without burning, burning without short circuit. The application cases used in this paper prove that flexible mineral insulated cables are not only used in fire alarm and emergency rescue It can be successfully applied in the fire protection performance of the circuit, and can also be popularized and applied in the case of high-density current and other special performance requirements.

2. BTLY isolated (flexible) mineral insulated cable fireproof cable

Using aluminum as the main material for metal tube extrusion instead of copper tube drawing not only simplifies the process and improves efficiency, but also greatly reduces the product cost (aluminum is only 1/10 of the comprehensive cost of copper). The reason why the aluminum tube can replace the copper tube is that it does not melt under high-temperature flames, thanks to the expansion refractory layer extruded on the outside of the aluminum tube: the expansion layer foams and solidifies under the attack of the flame, forming a thick barrier that blocks the impact of the flame on the aluminum tube. Tube for direct injection. Not only the integrity of the aluminum tube is preserved, but also the heating temperature of the mica tape is reduced to below 600°C, and the insulation stability of the mica tape is undoubtedly improved (the insulation resistance of the mica tape increases with the decrease of temperature)

The fire-resistant standard can pass the three assessments of BS6387: that is, it will not break down under the flame of 950°C for 3 hours, withstand water spraying for 15 minutes after 30 minutes at 650°C (directly immersed in water), and withstand knocking and vibration for 15 minutes under the flame of 950°C without damage. In terms of fire resistance, it can fully meet the assessment standard of BTT.

3. BTTW (YTTW, BTTRZ, BTTE) flexible copper sheath inorganic mineral insulated fireproof cable

The conductor of YTTW series metal sheathed inorganic mineral insulated power cable is made of multi-strand copper stranded wire, the insulation is mechanically wrapped with high temperature resistant synthetic mica tape, the insulation layer is densely filled with non-alkali glass fiber, and the sheath is welded longitudinally with copper tape It is formed into a copper tube, and then formed by continuous rolling and corrugation. If the metal sheath is not exposed to specific requirements, a layer of polyolefin (low-smoke and halogen-free) sheath can be added outside.

1. Cable conductor: twisted with multiple strands of copper wire, it has good bending properties.

2. Insulation layer: High temperature resistant, non-combustible inorganic mineral insulation material.

3. Copper sheath: Copper material, which has good bending properties after special processing, and is used as PE wire.

4. BTTZ copper sheathed magnesium oxide mineral insulated cable

Fireproof and explosion-proof, waterproof, high temperature, radiation resistance, anti-electromagnetic interference, high mechanical strength, good grounding performance, halogen-free, smoke-free, non-toxic, strong corrosion resistance, large current carrying capacity, strong overload capacity, small size and light weight ,long life

1. Look at the appearance and certificate: We look at the certification certificate of the quality system required by the manufacturer to see whether the certificate is standardized; whether there is a factory name, factory address, inspection stamp, production date, etc. It also depends on whether the cable itself has trademarks, specifications, voltage, etc. It also depends on the cross-section of the copper core of the wire. The high-quality copper is bright and soft in color.

2. Weighing: Good quality wires are generally within the specified weight range. For example, the commonly used plastic insulated single-strand copper core wire with a cross-sectional area of 1.5 square meters has a weight of 1.8~1.9KG per 100m, and the plastic insulated single-strand copper core wire of 2.5 square meters has a weight of 3 per 100m. ~3.1kg. Poor quality cables have insufficient weight, or are not long enough, or have too many impurities in the copper core of the wire.

3. To try: Take a section of wire and bend it repeatedly. The wires that feel soft, have good strength, plastic or rubber feel elastic, and have no cracks on the wire insulation are generally national standard wires.

4. Look at the price: Because poor wires are generally produced with poor materials to reduce costs, price is generally one of the important means of differentiation.

5. Look at the copper quality: the copper core of qualified copper core wire is purple red, shiny and feels good. Inferior copper cores are purple-black or yellowish, white, with many impurities, poor mechanical strength, and insufficient flexibility, and will break with a little force. And there are often short lines in the wire. We usually peel off the wire head and scratch it on the white paper with the copper core. If there is black residue on the white paper, it means that there are more impurities in the copper core, which is a non-marking line.

1. The difference in principle

The principle between fire-resistant cables and flame-retardant cables is different. The flame retardant principle of the halogen cable is mainly based on the halogen flame retardant effect, and the flame retardant principle of the non-halogen cable is to rely on the precipitated water to lower the temperature to extinguish the fire. The fire-resistant cable relies on the fire-resistant and heat-resistant performance of the mica material in the fire-resistant layer, so it can ensure that the cable can work normally in the event of a fire.

Second, the difference between structure and material

The structure and material of fire-resistant cables are also different from those of flame-retardant cables. The basic structure of the flame retardant cable is:

(1) The insulating layer is made of flame retardant material.
(2) The sheath and outer sheath are made of flame retardant materials.
(3) Taping and filling are made of flame retardant materials.

Fire-resistant cables usually add a fire-resistant layer between the conductor and the insulating layer, so in theory, a fire-resistant layer can be added to the structure of the flame-retardant cable to form a cable that is both flame-retardant and fire-resistant, but it is not practical. There is no need for this. Because of the refractory layer of the fire-resistant cable, multi-layer mica tape is usually used to wrap directly on the wire. It can withstand long-term burning, even if the high polymer where the flame is applied is burned, it can also ensure the normal operation of the circuit.

flame retardant cable

3. The clear concepts and advantages and disadvantages of flame-retardant cables, halogen-free cables, and fire-resistant cables

The characteristic of flame retardant cable is to delay the flame along the cable so that the fire will not expand. Because of its low cost, it is a cable variety widely used in fireproof cables. Whether it is a single cable or laid in bundles, the flame can be controlled within a certain range when the cable burns, so it can avoid major disasters caused by fire and delay, thereby improving the fire protection level of the cable line.

The feature of the halogen-free low-smoke flame-retardant cable is that it not only has good flame-retardant properties, but also does not contain halogen, which is less corrosive and toxic when burned, and produces a very small amount of smoke, thereby reducing Damage to personal instruments and equipment is conducive to timely rescue in case of fire. Although it has good flame retardancy, corrosion resistance, and very little smoke concentration. But its mechanical and electrical properties are slightly worse than ordinary cables.