Current situation of power cable and accessories

Insulating materials and shielding materials for power cables, especially materials for high-voltage and ultra-high-voltage XLPE insulated AAAC Cables, are prominent “soft ribs” or “short boards” of China’s cable industry in this field (all sheath materials have been localized).

1. Medium and low voltage power cable materials
Medium and low voltage power cables are mostly insulated with cross-linked polyethylene (XLPE). XLPE takes low-density polyethylene resin (LDPE below) as the main raw material, adds antioxidant and peroxide cross-linking agent, and is made into cable material through mixing, plasticization and granulation. It has many categories, including chemical cross-linking, hospital cross-linking, irradiation cross-linking, ultraviolet cross-linking, etc. XLPE insulating materials of 35kV and below have all been localized.
Among them, chemical crosslinking and silane crosslinking technologies and applications are very mature, irradiation crosslinking and UV crosslinking materials have also been widely used, and water tree resistant materials for medium voltage cables have been more and more applied.
The performance of XLPE insulating materials of 35kV and below fully meets the use requirements, but there are still gaps in process performance stability and long-term service life reliability compared with foreign advanced products: first, the performance stability of synthetic resin in chemical industry; Second, the fierce market competition forces the cable material production enterprises to consider the cost too much and seek to use low-cost raw materials.
Domestic manufacturers with batch supply capacity of 35kV XLPE cable materials mainly include Zhejiang Wanma polymer, Qingdao hancable, Shanghai chemical plant, Henan Wanbo Plastic Co., Ltd.

2. 110kV High Voltage Cable Materials
High voltage and ultra-high voltage ACSR Cables require that the insulating materials must be ultra purified. The main foreign suppliers are petrochemical enterprises, which complete the manufacturing from the fully enclosed ultra purification production process of petroleum cracking ethylene polymerization ultra clean material synthesis, such as Nordic chemical, Dow Chemical of the United States, NUC of Japan, Hanhua of Korea, etc.
At the initial stage of domestic high-voltage cable manufacturing (including the early 35kV cross-linked polyethylene cable material), all imported materials are used, especially Nordic chemical and American Dow Chemical (formerly United Carbon Corporation) account for a relatively high proportion in the domestic market.
During the 12th Five Year Plan period, China’s 110kV high-voltage cable insulation material made a technological breakthrough and realized domestic small batch production. Since 2012, 110kV ultra clean insulation material has been gradually used in cable manufacturing and power engineering.
During the 13th Five Year Plan period, great progress was made through independent research and development, introduction of key process equipment and cooperation with upstream petrochemical enterprises. Among them, major high-voltage cable manufacturing enterprises or cable material manufacturing enterprises jointly with petrochemical enterprises to form a preliminary manufacturing chain from basic resin synthesis to cable material manufacturing and then to high-voltage cable manufacturing and application. For example, the cooperation between Qingdao hancable Co., Ltd. and Yanshan Petrochemical Company, the cooperation between Zhejiang Wanma Gaoli Materials Co., Ltd. and Yangzi Petrochemical Company, the cooperation between Jiangsu Dewei new materials Co., Ltd. and Yangzi BASF company, and the introduction of a full set of equipment and technology by Yanshan Petrochemical Company have formed mass production capacity.
At present, the process technology and production capacity of producing high-voltage cross-linked polyethylene insulating material and shielding material with different equipment and process methods have been formed, with a total production capacity of about 80000 tons / year (including the material capacity for ultra-high voltage cable).

3. EHV cable materials
Insulation and shielding materials for 220kV EHV AAC Cables have higher requirements for purification, such as impurity content, quantity and size. The main bottleneck of ultra clean insulating material is the localized supply of ultra clean special raw material LDPE. In addition to the basic resin, the selection of compounding agent system, formulation technology, storage and transportation environment of insulating materials, factory production environment, etc. will eventually affect the insulation performance of cables.
The main problems of LDPE raw materials are processing rheological properties, melt index, molecular weight distribution uniformity, impurity content and other technical requirements. First, there are strict requirements on the fluctuation range of LDPE melt index, which determines the softening temperature range of LDPE and ensures the uniform plasticization of cable insulation layer, process dimensional stability and surface smoothness under certain process conditions. Second, the requirements for impurity content are very strict. The production workshop is required to reach level 1000, and the special process is even level 100. Materials do not contact with the outside world from production, packaging (tank car or pipeline) to use. Pay attention to the control of impurities and water content from the beginning of resin synthesis.
At present, Qingdao hancable Co., Ltd., Zhejiang Wanma polymer Co., Ltd. and Jiangsu Dewei new materials Co., Ltd. have the batch production capacity of super clean XLPE insulation and shielding materials for 220kV EHV cables, but the actual use is almost imported, with an annual consumption of more than 20000 tons, and the consumption of domestic materials is very small.
Semi conductive shielding materials for high-voltage and ultra-high-voltage cables are mainly used for the internal and external shielding layers of high-voltage XLPE cables. They are also required to be super clean and super smooth. The impurity content in the shielding material, the smoothness of the shielding layer and the adhesion between the shielding layer and the insulating layer will greatly affect the performance of XLPE cable. At present, several domestic semi-conductive shielding materials for 35kV and below cables have been produced and can meet the cable performance requirements, but the semi-conductive shielding materials for 110kV and above have more stringent requirements on basic resin, additives, carbon black types, extrusion equipment, manufacturing process and production environment. China is still in the stage of R & D and trial in this field, The shielding materials used are mainly imported by Nordic chemical and Dow chemical companies, and a small amount are provided by domestic enterprises.
According to statistics, the total domestic annual demand for insulation and shielding materials (including submarine cables and DC cables) for 110kV and above high-voltage and ultra-high-voltage cross-linked cables in 2019 is about 70000 tons, of which the actual use of domestic materials is about 10000 tons (mainly 110kV land AC cables), and another about 2000 tons are exported to the international market.
At present, compared with international advanced technologies, processes and products, the domestic production of 110kV and above XLPE ultra clean cable materials mainly has the following gaps:
1) There is a lack of systematic research on the basic resin of ultra-high pressure and ultra clean polyolefin material, and the development, polymerization, ultra clean synthesis process and material performance evaluation technology of basic resin need to be solved urgently;
2) As the domestic production process from the preparation of ultra clean polyethylene resin to the synthesis of ultra clean materials has not been formed, it brings new difficulties to the storage and transportation guarantee. There are also many new technical problems in the ultra clean technology and process of ultra clean material preparation (including impurity filtration technology, performance evaluation and quality control system) to ensure the stability and continuity of polyolefin cable material preparation;
3) The production time of localization is not long, and more process test and application data still need to be accumulated. In particular, the evaluation and evaluation of the long-term service reliability of the made cable is also an important work to obtain the full confidence of power users in the materials and recognize the application.
4. Materials for high voltage and ultra-high voltage submarine cables
High voltage and ultra-high voltage submarine cables require higher production technology and more complex service environment, so they have higher requirements for cable materials.
At present, the most important raw materials for the production of high-voltage submarine cables – insulating materials and shielding materials have not been localized. Whether it is AC high-voltage submarine cables or DC high-voltage submarine cables, only Nordic chemical and American Dow Chemical Company can provide them in the international market.
The insulation and shielding materials of high-voltage and ultra-high-voltage submarine cables used by China’s submarine cable manufacturing enterprises all rely on imports, including DC cable materials. Due to the imbalance between supply and demand, there is an obvious seller’s market. The R & D and production of high-voltage submarine cable insulation and shielding materials is also an urgent task for China’s cable industry. It is necessary to continue to deepen research and production on the basis of localization of high-voltage and ultra-high-voltage cable materials.

Laying and installation of pre branched cables

1、 Laying and installation of pre branch cable
Prepare for laying and installation according to the requirements of design drawings and be familiar with the laying direction and location of cables.
(1) Formulate construction plan and organize professional construction personnel.
(2) Prepare for installation of tools and equipment.
(3) Verify the abc cable model and specification and packing sequence.
(4) Verify the accessories and assign the installation site of accessories to the construction party.
(5) Place cable tray on the cable release frame.
(6) When the cable is installed vertically, the cable laying frame is lower than the floor, and the cable is lifted by winch or pulley block through the rope. Professional construction personnel shall be required for each floor. As for the terminal, hang the cable on the installed hook
(7) When the cable is installed horizontally, the cable setting out frame shall be set by the professional construction personnel (one person every two meters and the commander) as for the receiving position.

(8) Fix the intermediate part of the main and branch lines of prefabricated branch cables as required.
(9) Connect the main line and branch line with the electrical control device in phase sequence.
(10) After installation, clean the site, measure the insulation resistance of each circuit connected to each phase of prefabricated branch cable.
(11) Fill in the construction record.
2、 Precautions during laying and installation
(1) When laying, it is necessary to use the vertical hoisting as far as possible. When the construction site is restricted or special requirements are required, reverse installation can be used. No matter which setting method, the branch line shall not be released in advance in the process to prevent the branch body from scratching when passing through the hole and avoid being subjected to excessive mechanical external force.
(2) During lifting and hoisting, the cable with a weight of more than 4 times the strength must be selected. After laying, the upper and lower installation and fixing fixture shall be carried out first.
(3) The bending radius of cable shall not be less than 25d during laying and installation.
(4) Metal clamps are not allowed when fixing single core prefabricated branch cables.
(5) When connecting the main line and branch line with the receiving and electric measuring apparatus, the metal clamp must be used and the metal type of the clamp shall be selected correctly.

(6) The spreader must be installed on the load-bearing wall.

A big explanation of high-voltage cables

Power cables have become a necessity in human life and production, and play an important role in many fields and industries, including home appliances, automobiles, houses, engineering, transportation, and so on. The demand for high-voltage power cables has been increasing in recent years, and cable companies have also entered the market.

The main technology for the production of high-voltage cables is CV continuous vulcanization production. This production line converts polymers into high-performance insulating materials and wraps metal conductors to form cables. As far as China’s high-voltage cable market is currently in a state of overcapacity, Chinese cable companies have invested in building a large amount of production capacity, but demand cannot keep up with the substantial expansion of production capacity.

Statistics show that China’s high-voltage power cable production accounted for 40% of the world’s total in 2014. At present, there are more than 185 continuous vulcanization production lines in China that can theoretically produce conductors for high-voltage power cables, accounting for 50% of the global production of high-voltage cable CV continuous vulcanization production lines. Although many of these CV lines are not in production, or have not even obtained relevant approvals, China’s high-voltage cable production capacity still exceeds its demand by three times. Today, the output of high-voltage cables will continue to increase until 2021.
As the traditional high-voltage cable market is saturated with overcapacity and its competition is becoming increasingly fierce, some powerful cable companies have turned to high-voltage submarine cables. This field has higher requirements for technical thresholds. Only a few companies in China have Strong production, and with the construction of wind farm projects in many countries around the world, the demand for high-voltage submarine cables will increase in the future.

The Bare conductor has no sheath, is it safe?

In daily life, many people will see high-voltage power cables in the suburbs. They are often erected in mid-air, but many people may not observe carefully. Many of the high-voltage wires that are erected in the air are bare wires. The so-called bare wires are not insulated. The cable of the skin.

Usually the wires and cables we buy have a layer of insulation. The function of the insulation is to protect the inside of the cable from damage, and to prevent us from getting an electric shock. However, the high-voltage line has no insulation, and the second is a bare wire. Why? What?
The voltage of domestic high-voltage transmission lines is often above 10,000 volts, while China’s unique ultra-high voltage technology has a higher voltage, and the cables used in high-voltage lines are basically bare wires. Generally, lines above 10 kV will be used. .

The reason whyBare conductors are used in high-voltage lines is very simple. If the high-voltage lines are to be insulated for cables, the thickness of the ordinary insulation layer is far from enough. If the insulation layer is to be used, its thickness needs to be increased. , This will make the weight of the cable become very large, will increase the maintenance cost of the later line. Moreover, such a thick insulating layer will also affect the heat dissipation of the cable. The final result of poor heat dissipation is to increase the consumption of electric energy. Therefore, comprehensively considered, the benefits of adding an insulating layer cannot offset the negative effects brought about, so simply don’t need an insulating layer. Attach bare wires directly.
From the design point of view, bare wires are obviously better than cables with insulation, but if you consider their safety issues, will the use of bare wires cause harm to people? In fact, you don’t need to worry. High-voltage lines sound terrible, but the high-voltage lines are difficult for ordinary people to reach. They are all in remote suburbs and are elevated in the air, so ordinary people can hardly touch them.
The operation of the staff also has strict operating specifications in the industry. There are air gaps between the wires and the ground, between the wires and the wires, between the wires and the ground, and between the wires and the tower. Perform accurate calculations and leave a sufficient safety distance.
So generally speaking, it is not very dangerous, but if there are high-voltage lines in the area where you are moving, you should still keep a safe distance.

What is Bare Wire & Bare Conductor ?

Cable products with only conductors without any insulation layer are called “bare wires and bare conductor products”. In order to ensure the current flow along the wire and electrical safety, external insulation suitable for the line voltage must be installed during installation, such as space separation, insulator support, etc. Therefore, this type of product itself does not indicate “use voltage”.

1. Bare single wire
Refers to non-ferrous metal single wires of different materials and sizes, which can be divided into round single wires (copper, aluminum and aluminum alloys cable), flat wires (copper, aluminum and their alloys), single wires with metal plating (tin, silver, nickel) and Bimetallic wires (aluminum-clad steel, copper-clad aluminum, copper-clad steel), etc.
Most of these products are used as materials for the next production of wire and cable products.

2. Bare stranded wire
This is the leading product in this category. Because it is always erected on a pole, it is customarily called an overhead wire. Overhead conductors are not divided into voltage levels. In principle, the same series of conductors can be used from low voltage, medium voltage, high voltage and even ultra high voltage. However, the 330-500kv level has special requirements for the outer diameter of the wire and the surface finish to reduce the corona on the wire surface (that is, the electric field makes the surrounding local air electrically dissociate, which will increase the line loss.
Although the overhead wire structure is simple, its function is extremely important. In the power network, its line length accounts for more than 90% of the total, especially the 110kv-500kv high-voltage transmission and distribution lines. Bare stranded wire can be divided into three types from the structural composition.
One is stranded with a single wire of a single metal material, such as aluminum stranded wire, copper stranded wire, aluminum alloy stranded wire, etc.;

The second type is ACSR cable ,which uses steel stranded wire as the core wire to increase the tensile strength, and the steel core aluminum stranded wire is twisted with one or several layers of aluminum wire or aluminum alloy wire ;The third type is stranded wire made of bimetallic single wire, such as aluminum-clad steel stranded wire.
Steel core aluminum stranded wire (ACSR) is the most widely used variety. Because the steel core can withstand the tensile force suspended on the pole, the spacing between poles can be increased to reduce investment (especially high-voltage lines), extend the life of the wire, and enhance safety.
If there is corrosive gas around the laying line (such as salt spray at the seaside, chemical plant area), anticorrosive steel core aluminum stranded wire coated with anticorrosive paint should be used.

The development trend of new overhead wire and cables products is: ①Increase the tensile strength and vibration resistance without increasing the weight of the wire, such as high-strength aluminum alloy stranded wire, self-damping (anti-vibration) wire, etc.; ②Increase the long-term working temperature of the wire Or conductivity to increase the transmission capacity, such as double-capacity wire, etc.; ③Anti-icing and snow wire to prevent the surface of the wire from freezing in cold areas.

3. Soft wiring and braided wire
This is a kind of special purpose products with a lot of varieties but a small amount; such as brush wires of electric machinery, parallel wires of batteries, antennas, ground wires and shielding nets. This kind of product is made of thin copper single wire stranded and twisted; battery parallel wires are generally made into flat shape (commonly known as braided wire); shielding net sets are woven and sheathed outside the wires that require shielding.

4. Profiles and profiles
The cross-sectional shape of the product is different, and the product that is not round is called the profile; the product that is not used with a larger length is called the profile. According to its purpose, it can be divided into three types:
① As copper and aluminum busbars for high-current bus bars (also called bus bars). Most of them are flat, and some are made into hollow rectangles and semi-arches. Used in power plants and substations to transmit large-capacity streams; and in switch cabinets. In recent years, insulated bus bars with insulating layers have been developed.

②Wires for catenary. This type of wire is used for overhead wires for electrified railways, urban trams, electric locomotives in tunnels (such as subways, underground mine cars). Due to the large-scale development of urban rail transit lines and electrified railways, the use of catenary wires (commonly known as tram lines, now referred to as contact lines) has doubled. In addition to the technical requirements of the contact wire, in addition to good electrical conductivity, sufficient tensile strength and good weather resistance, excellent wear resistance is also very important, which is directly related to the service life.
③Special-shaped strips are mainly used for commutator components in various motors, as well as blade electrodes of various switches and guillotines. The cross-sectional shape is trapezoidal, unimodal, bimodal, and the material is copper or copper alloy.