Analysis and Engineering Application of Fireproof Performance of Mine Cable

Due to the increase of wires and cables, the concentration of laying, the poor quality of construction, etc., the danger of wire and cable fires has increased. Therefore, to prevent aerial bundled cable astm b231 fires in actual engineering applications, it is necessary to start with controlling dangerous factors, apply relevant regulations, and take corresponding fire prevention measures.

1 Fire causes and characteristics of wires and cables

Mainly because of overload, short circuit, excessive contact resistance and external heat source. Causes of fire caused by wires and cables under fault conditions such as short circuit, local overheating and external heat. Insulation materials decrease in insulation resistance, lose insulation ability, or even burn, which may cause a fire. The main characteristics of wires and cables in fire are:

In case of fire, the fire temperature is generally 800℃~1000℃. Wires and cables will quickly lose their insulating ability, which will cause secondary electrical accidents such as short circuits and cause greater losses;

2 The conductor cable has a larger overload capacity under the specified allowable current carrying capacity;

The wire and cable will cause the insulation material to melt and burn in an instant, 3 short-circuit conditions. And ignite the surrounding combustible materials.

2 Analysis of fire performance of aerial bundled cable (abc) astm b231 standard 

2.1 Analysis of fire protection mechanism

2.1.1 Flame retardant mechanism

The flame retardant in the condensed phase decomposes and absorbs heat, and is under the heat of the combustion reaction. Slow down the temperature rise in the condensed phase and delay the thermal decomposition rate of the material;

The chain reaction free radical blocker is released, and the flame retardant is decomposed by heat. Interrupt the branches of flame and chain reaction, and slow down the speed of gas phase reaction;

The formation of the coking layer or foam layer strengthens the effect of these layered hard shells in hindering heat transfer; 3 catalyzes the thermal decomposition of the solid phase products of the condensed phase.

The flame retardant has an endothermic phase change, under the action of 4 heat. Physically prevent the temperature rise in the condensed phase.

2.1.2 Fire resistance mechanism

To reduce the heat generated by the polymer, a certain additive is added to the insulation and sheath materials of the wire and cable. Prevent polymer decomposition or promote the carbonization of insulation and sheath materials to form a maintenance layer;

After the insulation and sheath layer is eroded by fire, a layer of mica glass ribbon and other inorganic insulating materials are added to the 2 cores. *The mica refractory tape wrapped around the conductor is maintained and continues to be energized, so as to maintain normal operation for a certain period of time when a fire occurs.

2.1.3 Mechanism of mineral insulated cables

AlOH3 is 34.6% under high temperature operation, and the absorption effect of metal hydrate makes the cable flame-retardant. For example: use AlOH3 and MgOH as flame retardants. MgOHz is 31%, see Reaction Equation 1 and Reaction Equation 2, the reaction is decomposed into an endothermic reaction, which can inhibit the burning of polymers. 2A IOH3–*A lz03+3H20-2648KJ1MgOH2–MgO+H20-93.3KJ2

2.2 Classification of burning characteristics of wires and cables and their standard tests

It can be divided into ordinary wire and cable, flame-retardant wire and cable, fire-resistant wire and cable, halogen-free low-smoke wire and cable, and mineral insulated cable. Wire and cable according to their own burning characteristics.

1 Flame-retardant wires and cables refer to wires and abc cables b230 that are difficult to catch fire and have the ability to prevent or delay the spread of flame. The commonly used standard test is GBT18380. 3 is equivalent to IEC60332-1999

Wire and cable that can still maintain the integrity of the circuit. The commonly used standard test is GBT12666. 6 which is equivalent to IEC60331-21-19992 fire-resistant wire and cable means that it burns under a flame at a specified temperature and time.

When burning, it produces less smoke and has wires and cables that prevent or delay the spread of flames. Commonly used standard tests are GBT17650. 2 is equivalent to IEC60754-2, GBT17651. 2 is equivalent to IEC61034-2 and GBT18380. 3 is equivalent to EC60332-3. On the basis of the above, the flame-retardant and fire-resistant type also need to meet the requirements of maintaining the integrity of the line. 3 There are two types of halogen-free and low-smoke wires and cables. Flame-retardant type means that the material does not contain halogen. At the same time, the commonly used standard test adds GBT12666. 6 is equivalent to IEC60331

How to distinguish between national standard wires and inferior non-standard wires

Before moving into a new house, everyone will check the house first, but most citizens will focus on the structure of the house, and they rarely care about the wires inside the walls. If the house is compared to a person, then the wires hidden in the walls are the vital “arteries”. The wires for home improvement not only concern the normal daily life of the family, but also the safety of the family’s relatives. Inferior wires may cause short circuits, Electric shock, damage to electrical equipment, and even fire, causing casualties. Nowadays, a large number of non-standard wires and low-quality counterfeit wires are flooding the building materials market. Some low-quality wires are broken as soon as they are twisted, making it easier to distinguish. But some low-quality wires are exquisite in workmanship, and at first glance they seem to be even better than the national standard! How to distinguish between national standard wires and inferior non-standard wires? Huaxing Cable‘s professional electrician technicians suggest that you should never think about saving money when buying home improvement wires. The quality of the wires not only affects the service life and safety of household appliances associated with them, but also affects the life safety of our family members. Now let the professional electrician technician of the cable explain to you how to distinguish between the national standard wire and the inferior non-standard wire!

The first step in identifying wires: look at the wire signsThe national standard wire label is the product qualification certificate. Take the wire qualification certificate as an example, it is printed with: wire product trademark, wire product name, wire manufacturer name, wire production site, cable manufacturer contact number, CCC certification and aerial bundled cable b230 factory number, wire model specification , National standard, rated voltage, length of wire, cross-sectional area of ​​wire conductor, production date, inspector’s seal. At the same time, well-known brand wire manufacturers generally have anti-counterfeiting labels that cannot be imitated! Each coil of the aerial bundled cable(abc) b231  has an anti-counterfeit QR code and a barcode, double anti-counterfeiting, just like our ID number

Inferior non-marking signs do not have the above content or are incomplete, and even if they have, they cannot be investigated. The following low-quality line signs are taken as an example; the trademark and company name are all virtual, although the factory address is available, but not specific, there is no way to find the phone number, the model column is blank, and the specification column is only marked 2.52. The formal marking should It is the number of conductor cores × conductor diameter, that is, 1×1.78 mm. The inspector’s seal is printed together with the other contents of the sign, which means that there is no need for inspection at all, and there is no anti-counterfeiting label.

The second step is to look at the copper wire conductor

Qualified copper core wires should be oxygen-free copper, purple-red, shiny, and soft to the touch.

The fake and inferior copper core wire is purple-black, yellowish or white, with many impurities, poor mechanical strength, poor toughness, and it will break with a little force, and there are often disconnections in the wire. The picture below is a low-quality copper-clad copper wire.

The third step is to look at the insulation material

The insulating layer of the national standard wire is made of high-quality insulating plastic, which has a certain degree of mechanical strength and flexibility, and cannot be torn easily. The insulating layer of high-quality wires has a certain flame retardancy. Peel off a section of the national standard wire insulation layer and ignite it with a lighter. After leaving the open flame, it can self-extinguish, and the smoke is light and has a light smell.

The insulating layer of inferior non-standard wire is made of recycled plastic, which has poor insulating ability, which can easily cause the insulating layer to be broken down by current and leak. Great harm to the life safety of users! Inferior wires can be distinguished from the insulating layer with a little attention. Pull off a section of the insulating layer. As shown in the figure below, if the color of the cross section is white, it is the inferior wire. Fold a certain part of the wire several times in succession. If the color of the folded part turns white, it can be judged. It is a low-quality wire. Use a lighter to carry out the igniting experiment, it can still burn after leaving the open flame, and the smoke has a strong smell. Cut a section of the wire insulation layer to see if there are visible pores in the section of the insulation layer and whether the core is located in the middle of the insulation layer. What is not in the center is the eccentricity caused by the low craftsmanship. The presence of pores indicates that the wire insulation material used is unqualified. Severe eccentricity is most likely to leak electricity on the thinner side, and air holes also affect the compressive strength of the wire.

The advantages of copper core cable and aluminum core cable are compared

Copper core cables have more advantages than aluminum core cables:

1. Low resistivity: the resistivity of aluminum core aerial bundled cable BS 7870 is about 1.68 times higher than that of copper core cable.

2. Good ductility: the ductility of copper alloy is 20-40%, the ductility of electrical copper is more than 30%, while aluminum alloy is only 18%.

3. High strength: the allowable stress at room temperature, copper is 7~28% higher than aluminum. Especially the stress at high temperature, the difference between the two is even greater.

4. Anti-fatigue: Aluminum is easy to break after repeated bending, while copper is not easy. In terms of elasticity index, copper is also about 1.7-1.8 times higher than aluminum.

5. Good stability and corrosion resistance: The copper core is resistant to oxidation and corrosion, while the aluminum core is susceptible to oxidation and corrosion.

6. Large current carrying capacity: Due to the low resistivity, the copper core cable of the same cross section is about 30% higher than the allowable current carrying capacity (the maximum current that can pass) of the aluminum core cable.

7. Low voltage loss: Due to the low resistivity of the copper core cable, the same current flows in the same section. The voltage drop of the copper core cable is small. Therefore, the same transmission distance can ensure higher voltage quality; in other words, under the allowable voltage drop condition, the copper core cable can reach a longer distance, that is, the power supply coverage area is large, which is beneficial to network planning and reduces The number of power supply points.

8. Low heating temperature: Under the same current, the copper core cable with the same cross section has much smaller heat than the aluminum core cable, which makes the operation safer.

9. Low energy consumption: Due to the low electrical resistivity of copper, it is obvious that copper cables have low power loss compared to aluminum cables. This is conducive to improving the utilization rate of power generation and protecting the environment.

10. Anti-oxidation and corrosion resistance: The performance of the connector of the copper aerial bundled cable(ABC) B231 is stable, and there will be no accidents due to oxidation. When the connector of aluminum core cable is unstable, the contact resistance will increase due to oxidation and heat will cause accidents. Therefore, the accident rate is much greater than that of copper core cables.

11. Convenient construction: The copper core is flexible and the allowable bend radius is small, so it is convenient to bend and easy to pass through; the copper core is fatigue-resistant, repeated bending is not easy to break, so the wiring is convenient; the copper core has high mechanical strength and can withstand relatively The large mechanical pulling force brings great convenience to construction and laying, and also creates conditions for mechanized construction.

12. Cheap price: Copper pole is 3.5 times the price of aluminum pole, and the proportion of copper is 3.3 times that of aluminum. Therefore, aluminum core cables are much cheaper than copper core cables, and are suitable for low-cost projects or temporary electricity use.

13. The cable is very light: the weight of the aluminum core cable is 40% of the copper core cable, and the construction and transportation costs are low.

14. Anti-oxidation and corrosion resistance: Aluminum quickly reacts with oxygen in the air to form an oxide film, which can prevent further oxidation. Therefore, aluminum wire is a necessary material for high-voltage, large-section, and large-span overhead power transmission.

Although aluminum core cables are cheap, copper cables have outstanding advantages in cable power supply, especially in the field of underground cable power supply. The underground power supply using copper core cables has the characteristics of low accident rate, corrosion resistance, high reliability, and convenient construction and maintenance. This is why copper abc cables are mainly used in underground power supply in China.

Analysis and Treatment of 35kV Cross-linked Cable Water Ingress

Cross-linked polyethylene insulated cables have good mechanical properties, convenient installation and maintenance, excellent insulation performance, larger transmission capacity than oil-paper insulated cables of the same cross-section, simple production process, conducive to mass production, and can transmit power to areas that cannot be reached by overhead lines And other advantages, so it is increasingly widely used in power systems and constitutes an important part of the transmission and distribution network.

Cross-linked polyethylene insulated cables can choose a variety of laying methods according to engineering conditions, environmental characteristics, cable type and quantity, combined with the requirements of reliable operation, easy maintenance, and the principle of reasonable technology and economy, such as direct buried laying, pipe laying, Shallow trench laying, trench laying, tunnel laying, etc. The use of buried aerial bundled  cables ASTM B231 to realize the power transmission and connection between two or more electrical devices can save space and line corridors and reduce the consumption of valuable land resources. The selection of qualified cables and accessories, laying and installation in accordance with the requirements of standards and specifications, and strict guarantee of construction quality are the prerequisite and guarantee for the safe and reliable operation of cable lines.

1. Water ingress analysis inside the cable

Analysis of Causes of Water Ingress As the complete new cable adopts multiple waterproof and water-blocking designs in the internal structure and materials, there will be no internal water ingress under the condition that the two ends are sealed. Aiming at the cause of water ingress into the 35 kV cable, this article conducts an in-depth analysis in connection with the cable manufacturing, transportation, laying and installation links:

(1) Water enters during the production of ABC ASTM B231. The main production process of the cable supplier is: first, a single compact conductor core is formed by wire drawing and twisting; then the conductor semi-conductive shield, XLPE insulation and insulated semi-conductive shield are simultaneously extruded on the outside; then winding Protective tape and metal shielding layer; combine the three cable cores and add fillers to form a cable; wrap the inner sheath and armored steel tape on the outside of the three-core cable, and finally squeeze a layer of polyvinyl chloride outer sheath. In order to control the quality of cable production, the manufacturer adopts many methods in the production process to prevent moisture from penetrating into the cable. For example, advanced production equipment is used to achieve three-layer co-extrusion of conductor semi-conductive shielding, insulation, and insulating semi-conductive shielding; XLPE insulation adopts dry The cross-linking method performs cross-linking. If you strictly abide by the entire production process, with the current advanced technology and production equipment, there will be no water ingress into the cable when manufacturing cross-linked cables.

(2) Water ingress during transportation and construction. There are three possible situations when water enters the cable: one is that the outer sheath of the cable is broken during transportation and installation, and it is exposed to rain or water so that water enters the outer sheath of the cable; the other is that the cable is accidentally used during construction. The head is damaged and water has entered. The third is that when it rains during installation, construction workers forget to cover the sawn cable ports, causing rainwater to flow into the cables.

1.2 Analysis of the influence of water ingress In the first case, water enters the inside of the cable through the crack in the outer sheath, and the steel strip of the armor layer will quickly rust, and then the water will penetrate into the filling material to make it absorb water and become damp. The phase-to-phase insulation of the cable has an impact, but has little effect on the single-phase insulation. In the second and third cases, water can directly enter the bare conductor. If you cut the cable conductor core and observe its cross section, you will find that there is water flowing out of the multi-strand core. If the incoming water is not cleaned up in time, after the cable is energized, water branches can be generated on the side of the main insulation close to the conductor core, which will lead to the generation of branches, and finally lead to the breakdown of the main insulation. Because of the serious consequences of water ingress in the cross-linked cable, as long as water in the cross-linked cable is found, immediately stop laying and installation, analyze the cause of the water in detail, find out the aerial bundied cable(ABC)  damage as soon as possible, and take appropriate measures to deal with it in time.