Heating reason of power cable in operation

When the power cable passes through a certain load current, it will be heated. With the increase of the load current, the cable surface temperature will be higher. If it is not handled in time, the consequences can be imagined. For example: PVC cable, the core temperature of 70 degrees is considered as the upper limit, and the surface temperature will be 5-10 degrees lower. Therefore, the cable surface temperature below 60 ℃ is basically safe. Considering the power supply maintenance, of course, the lower the temperature, the better.

The heating reasons of power cable in operation are as follows:

1. Cable conductor resistance does not meet the requirements, resulting in cable heating in operation.

2. Improper selection of cable leads to too small conductor cross-section of the cable used and overload phenomenon in operation. After long-term use, the imbalance of heating and heat dissipation of the cable causes heating phenomenon.

3. If it is too close to the cable, it may cause heat dissipation when the cable is too close to the cable.

4. Poor joint manufacturing technology and loose crimping will lead to excessive contact resistance at the joint and also lead to cable heating.

 

5. The insulation performance of cable phase to phase is not good, resulting in low insulation resistance and heating phenomenon during operation.

6. The partial sheath damage of armored cable will cause slow damage to the insulation performance after water inflow, resulting in the gradual decrease of insulation resistance, and also the heating phenomenon during the operation of the cable.

If the cause is not found out and the fault is eliminated in time, the insulation thermal breakdown will occur after the power cable is continuously energized. This will lead to phase to phase short-circuit tripping of cables, which may cause fire in serious cases.

Treatment method of PVC power cable affected by damp

Cables, especially PVC insulated power cables, have been widely used in urban power grid reconstruction projects. However, due to the particularity of the cable, the installation, operation and maintenance of the cable have special requirements. Cable insulation resistance is reduced by damp or water intrusion, which is an important aspect of cable line operation accidents.

Cause and harm of cable damp and water inflow

PVC power cable affected by damp  (1) When the new cable is delivered from the factory, both ends of the cable are sealed with plastic sealing sleeve. However, after a section of cable is used at the construction site according to the actual situation, the remaining part is simply wrapped with plastic cloth. As it is usually placed in the open air and the sealing is not good, water vapor will inevitably seep into the cable after a long time.

(2) During power cable laying, it is necessary to often cross roads, bridges and culverts. Due to weather or other reasons, a lot of water is accumulated in the cable trench. During the laying process, it is inevitable that the cable head will be immersed in the water, and the water will enter the cable due to loose wrapping or damage of plastic cloth. In addition, the outer sheath and even steel armor will sometimes occur during traction and pipe threading Scrape phenomenon, when using mechanical traction, this phenomenon is particularly prominent.

(3) After the completion of cable laying, due to the limitation of site construction conditions, the cable head can not be made in time, so that the cable fracture without sealing treatment is exposed to the air for a long time, even immersed in water, so that a large amount of water vapor enters the cable.

(4) During the manufacturing process of cable head (including terminal head and intermediate joint), due to the negligence of construction personnel, the newly treated cable end sometimes falls into the water on site.

(5) In the normal operation of the cable, if the breakdown and other faults occur for some reason, the water in the cable trench will enter the cable along the fault point; in the civil construction, especially in the construction site using large construction machinery, the cable damage or breakdown accidents caused by various human factors are also common. When this kind of accident occurs, the cable insulation will be seriously damaged, which will also cause cable water intrusion.

 

After the cable enters water, the aging phenomenon will occur under the action of electric field, which will eventually lead to cable breakdown.

Five aspects of high temperature wire and cable exit

At present, many domestic high-temperature wire and cable enterprises have entered the foreign market, but compared with foreign domestic products, the competitiveness of China’s high-temperature wire and cable products needs to be improved, especially some enterprises act rashly without understanding the foreign industry standards, which leads to an embarrassing situation for the development of enterprises. As a well-known brand in the high-temperature wire and cable industry, Chuncao has made certain achievements in the foreign market. Here are five aspects to be noted in the export of high-temperature wire and cable.

1、 Technical standards: advanced standards such as IEC or British standard, American Standard and other advanced standards are generally required for foreign high-temperature wires and cables. Therefore, it is not enough to be familiar with domestic standards, but also familiar with international standards.

2、 Laying conditions: the environmental conditions in West Asia, Southeast Asia and other regions are relatively special, such as the extreme maximum temperature of 50 ℃ and the maximum daily average temperature of 40 ℃. Therefore, the description of technical parameters related to the environment (such as the correction coefficient of current carrying capacity) should be paid attention to in the technical data.

3、 High temperature wire and cable structure: due to the high temperature wire and cable laying environment, the high temperature wire structure should not only meet the standard requirements, but also have some additional requirements. Therefore, enterprises should pay attention to it in the design and manufacturing process of high-temperature wires and cables.

4、 Packaging of high-temperature wire and cable: for export high-temperature wire and cable, the delivery tray generally adopts large plate or steel plate structure, and is fully enclosed with sheet iron or wood. In addition to the length and minimum allowable bending radius of the high temperature line, the size of the container should also be considered. Strictly follow the order requirements. As the packaging of export high-temperature line is more complicated than that in China, it will affect the cost and delivery time of high-temperature line. Therefore, attention should be paid when signing the contract.

5、 Other precautions: before delivery, the main technical parameters, sectional drawings, laying instructions and other data of high-temperature wires and cables shall be provided to users, and the test reports shall also be delivered with the goods. The technical data shall be complete; the manufacturing length of high-temperature wires and cables shall be strictly controlled, and the error of delivery length shall be minimized. All export products must pass the inspection of the State commodity inspection department and issue the commodity inspection certificate.

With the accelerated process of world economic integration, the market competition of domestic high-temperature wire and cable enterprises will not be limited to the domestic market, and the foreign market is the greater stage. It is hoped that domestic enterprises can carefully consider the above five points before entering the foreign market, and make the most suitable development plan according to their own conditions.

Insulated cable

At present, there are some cables with better temperature characteristics in China, such as:
1. Rubber insulated cables:
The long-term operating temperature of WYJHDP wire core for rubber insulated cables in the field shall not exceed -45 ~ 50℃.
WYJHQ, a mobile rubber insulated cable used in the field, operates at -45 ~ 50℃. The operating temperature of the core shall not exceed 65℃ for a long time.
Rubber insulated cold – resistant cable for field use YHD operating environment is -50 ~ 50℃. The operating temperature of the core shall not exceed 65℃ for a long time.
2. Fluoroplastic insulated cables:
The service environment of AF-200 of fluoro-46 insulated installation line is -60 ~ 200℃.
Copper conductor outdoor PVC insulated wire BVW (NC-BV), laying temperature not less than -20℃.
Ff4-2, FF4H3-2 and other silver-plated copper ptFE insulated wire and cable are fixed and perfunctory, with rated voltage of 600V; Rated temperature: 200℃; The minimum operating environment is -65℃.
Silver plated copper core polyfluoroethylene propylene insulated wire and cable such as FF46-2, FF46P21H6-2, rated voltage of 600V; Rated temperature: 200℃; The minimum operating environment is -65℃.


3. Polyethylene cables
Polyethylene insulated coaxial RF cables, such as SYV-75-1.5-1 and SYV-75-2.5, are used at temperatures ranging from -40 ~ +65℃. Rated voltage: 300V; The temperature of installation and laying should not be lower than -15℃.
BV, BYR, BYR, BYP, BYVP (for fixed laying) RY, RVP, RYVP (for mobile use) can be used under 98% relative humidity at -40 ~ +60℃.
4. PVC cable
Avp-1 and AVP-3 are used for connecting telecommunication equipment with PVC insulated and shielded installation cables. The ambient temperature is -40 ~ 70℃ and the installation temperature is not lower than -15℃.
The lowest operating temperature of VV and VCY of copper conductor PVC insulated and sheathed power cable is -40℃, and the highest allowable operating temperature is 70℃. The ambient temperature for cable laying should be no less than 0℃.

Cable requirements for wind power applications

Generally speaking, wind fields are located in harsh environments with special climatic conditions, such as strong winds, strong ultraviolet rays, and air with high salinity. For this reason, the cable performance in wind power applications is undoubtedly higher than that in other applications. The moving parts in the fan further increase the importance of choosing the right cable.
The maintenance of existing wind farms and the development of new large-scale wind farms need to consider the use of high-grade power cables, data and control cables and communication cables, which determine the interconnection quality of power grids and communication systems. More cables are needed for a single wind turbine than people think. For example, a 1.25MW 90m wind turbine requires about 1km of power cable. In this way, the wind field of 50MW installed capacity will need 40km of cables.


(1) wires
To maximize flexibility, it is recommended that the design engineer use only multiple strands of annealed soft copper wire. The short concentric strand structure is used in bending applications. In torsional winding applications, long concentric strand structures are used. Conductors with an area of more than 6mm2(10AWG) are required to use a composite stranded structure.
(2) the insulation
To increase low temperature flexibility, thermoplastic rubber (TPE), ethylene propylene rubber (EPR, an EPM or EPDM) or silicone rubber (SiR) are usually selected as insulating materials to resist ozone corrosion and heat-induced aging. PVC/ nylon insulation is also widely used due to its high dielectric strength.
(3) the sheath
The cable sheath can be a thermosetting compound such as polyvinyl chloride (CPE), polychloroprene (chloroprene rubber), chlorosulfonated polyethylene (CSPE) synthetic rubber; Similar thermoplastic compounds such as TPE, TPE-PVC alloys, and polyurethane. These materials are resistant to oil, fuel, solvent corrosion, and excellent flexibility at low temperatures. This characteristic makes it an ideal sheath material for wind power cables.
It should be noted that cable structure is also a decisive factor in cable flexibility. Symmetrical conductor designs with balanced structures are usually highly flexible.
Even if these general rules are followed when cables are manufactured, it is highly recommended that a complete test be performed to simulate a “real” application.

What are the common faults of wire and cable?

Common faults of wire and cable lines cause mechanical damage, insulation damage, insulation dampness, insulation deterioration, over-voltage, cable overheating faults. When the above faults occur in the line, the power supply of the fault cable should be cut off, to find the fault point, to the fault.
The direct cause of the cable failure is the breakdown of insulation. Mainly include:
1.Overload operation: long-term overload operation will increase the temperature of the cable and make the insulation aging, which will lead to the breakdown of insulation and reduce the construction quality.

2. Electrical interview: the construction of the cable head fails to meet the requirements, the cable head seals badly, moisture intruded into the cable interior, the cable insulation performance declined, no protective measures were taken when laying the cable, the protective layer was damaged, and the insulation declined.This problem is particularly obvious in all aluminum cables.
3. Civil engineering aspects: poor drainage in working well pipe trench, cable soaked in water for a long time, damaging insulation strength; The working well is too small, the bending radius of the cable is not enough, and the cable is damaged by extruding force for a long time. Mainly in the municipal construction of mechanical barbaric construction, cut and cut the cable.
4. Corrosion: The protective layer suffers chemical corrosion or cable corrosion for a long time, resulting in the failure of the protective layer and the decline of insulation.
5. The cable itself or the cable head accessories are of poor quality, the cable head seals are poor, the insulation glue dissolves and cracks, and the resonant phenomenon of the station is that the phase-to-phase capacitance of the line and the capacitance to the ground and the excitation inductance of the voltage distributor form a resonant circuit, so as to excite the ferroresonance.

Electric wire and cable industry development status

In the 1990s, China’s electric wire and cable industry has achieved rapid development. To become the world’s second largest producer of wire and cable. The development of the industry has given rise to the following problems:
One. The number of wire and cable enterprises is large but the scale is small, and state-owned enterprises have lost their dominant position in the industry. When Shanghai Cable Research Institute conducted the industry survey in 1988, the state-owned enterprises designated by the state accounted for 48% of the total industry output value, but now the collective enterprises, joint-stock cooperative enterprises, foreign enterprises and emerging enterprises such as Hong Kong, Macao and Taiwan investment enterprises have taken the leading position in the industry.

Two. The product structure of the industry has changed. The proportion of wire and cable for winding and electrical equipment decreased, while the proportion of power cable and communication cable increased. This change is related to the rapid development of China’s electric power cables and communication industry, which is expected to continue in the future.


Three. Compared with foreign advanced enterprises, China’s wire and cable industry still lags far behind in terms of management level, technology level, technology content, product quality, etc., and equipment utilization ratio is low. The utilization rate of electric wire and cable equipment in China is about 30% on average, and 70% in advanced countries is normal.Four.Low labor productivity in the industry. Although China’s wire and cable industry has imported a large number of production equipment since the 1980s, which has greatly improved the labor productivity of the industry, the gap with foreign countries is still very large. For example, the per capita sales volume of China’s wire and cable industry is only 10%~20% of that of Japanese counterparts.


Five. Unreasonable product structure. In China’s wire and cable products, the proportion of low-tech products is too large, while the proportion of high-tech products is too small, and the product structure is unreasonable.
Six.Low input and output rate of materials. China’s enterprises in the production process, material consumption and waste is very serious, so that the input output rate is very low.
Seven. Backward management and long production cycle. The turnover of working capital in China’s electric wire and cable industry is less than two times, which is far lower than foreign countries’ 9-11 times.


Eight. The scientific research is weak, the enterprise innovation system establishment progress is slow. The innovation system is not yet in place.
Nine. Market awareness needs to be further enhanced. At present, factories in the industry, especially large and medium-sized state-owned enterprises, have only changed from production-oriented to sales-oriented, but have not yet achieved market-oriented. Large foreign enterprises have invested a great deal of manpower and material resources in market development to highlight the role of market orientation.

Analysis of current situation of wire and cable industry

Wire and cable are used to transmit electrical (magnetic) energy, information and electromagnetic energy conversion wire products. It is widely used in various departments of national economy and provides important supporting facilities for various industries, national defense construction and major construction projects.
China’s wire and cable industry, based on a large number of technology introduction, digestion and absorption and independent research and development, has formed a huge production capacity, product variety satisfaction rate and domestic market share of more than 90%. Large enterprises of wire and cable manufacturing have obvious advantages in market competitiveness and the market develops rapidly.


At present, the market competition in China’s wire and cable industry is fierce, and most small and medium-sized enterprises in China adopt price competition. Wire and cable enterprises lack of development momentum, independent innovation ability is not strong, in the low – and medium-end wire and cable market with relatively low technical added value, price competition is quite common.
As the global wire and cable market matures, wire and cable manufacturing slowdown, growth is not big, falling demand, cable companies relative excess capacity, prices, competition between enterprises, combined with copper, aluminum, plastic and other factors such as main raw materials rose sharply, causing many cable enterprise development difficult.
International cable enterprises occupy the market by means of mergers and acquisitions, external expansion and transfer of production bases, etc., and occupy a large share in the international market.
The relevant personage inside course of study introduces, in recent years foreign capital electric wire and cable enterprise enters, intensified the market competition of domestic electric wire and cable industry further.

China cable industry status and strategy advisory report

On June 30, 2020, the Report on The Current Situation and Strategy Of China’s Cable Industry compiled by the Professional Committee of Wire and Cable was officially released.
Held since July 19, 2019 China cable industry present situation and strategy advice consulting report (hereinafter referred to as the consulting report), since the first compilation work meeting lasted nearly a year, branch organizations invited more than 50 experts of cable industry in our country, to actively participate in data collection, organization and audit work such as writing, successfully completed the consulting report compiled and printed work, to learn the council submitted a satisfactory answer, also for the cable industry enterprise and provide a copy of an influential, cable enterprise innovation and development in China has guidance and reference function of the consulting report.


The official release of the Consulting Report fully reflects the work responsibilities of THE Institute in serving scientific and technological workers in the field of electrical engineering, in serving the innovation and development of industrial enterprises, in serving to improve the scientific quality of the whole people, and in serving the party and the government in making scientific decisions. The institute gives full play to its advantages of intelligence-intensive, talent gathering and extensive connections, and effectively provides a pragmatic and effective service for the development of the electrical engineering field and the electrical industry.
The official release of the consulting report is the first industrial consulting report issued by the Institute in the past 40 years. With the breakthrough of this zero, the society will not only continue to organize and compile around the industrial fields that occupy an important position in the national economy and whose products and technologies cover and are widely used, but also organize and compile relevant consulting reports for the emerging fields and high-end technology fields of national economic development. The first is to give full play to the role of the Institute in leading the development of disciplines, and the second is to guide the technological innovation of relevant industries, so as to make due positive contributions to the institute and provide technical support for the national formulation of relevant industrial development policies for the realization of the goal of transforming from a “manufacturing power in China” to a “manufacturing power in China”.

Cable boosts urban rail upgrades

Urban rail transit is playing an increasingly important role in meeting people’s travel needs, optimizing urban layout, alleviating urban traffic congestion, and promoting economic and social development.
According to statistics, between 2020 and 2025, intercity high-speed rail and rail transit will be the biggest investment in the “new infrastructure” sector. When the new infrastructure becomes the new wind mouth, the wire and cable industry is also about to usher in another period of rapid development.
Deep in the cable industry, Huaxing cable is always committed to the research, development, production and sales of higher-end and higher-quality cables, and keeps investing and improving in product research and development. It can not only live up to customers’ expectations, but also provide a complete set of safe and environmentally friendly cable solutions for urban rail transit.
At present, Huaxing has developed 5 categories of low-smoke, halogen-free and high-flame retardant cables for urban rail transit, including 35kV medium-voltage loop network cables, dc traction cables with rated voltage up to 1500V, low-voltage power cables, control and signal cables, and wire distribution cables, which cover more than 95% of the cable products for urban rail transit.


At the same time, on the basis of these five categories of products, The Technology research and development team of Huaxing continuously innovates and develops high-end products such as intelligent monitoring cables and B1 class new flame-retardant cables to facilitate the construction of smart city rail transit. Among them, dc feed return cables used in rail transit with rated voltage up to and including 1500V are mainly used in dc traction power system of rail transit or transmission and distribution occasions for fixed laying. Can also meet the requirements of flame retardant A and flame retardant B1 level, cable crust and has lower combustion dropped, smoke toxicity and corrosive, waterproof, rat ants, uv protection, effectively reduce the external factors on the cable damage, improve the safety of cable operation, widely used in subway, light rail and other crowded occasion safer, ensure more stable power transmission.
While intensifying the research and development of new products, Huaxin has closely adhered to the comprehensive international business strategy, caught up with the international market, positioned the low-voltage power distribution system mainly used in rail transit and other densely staffed places, and focused on the research and development of low-smoke halogen-free armored cables in line with British standards.
With the development of smart city, the development of urban rail transit in China has shifted from the past “speed and scale” to the new stage of “focusing on high-quality development”, and urban rail transit should also take a good path of independent innovation from technological innovation to industrial innovation. In this trend, Huaxing will seize the opportunity of The Times, and help to create a “safe, reliable and green” new era smart rail transit with more green, efficient and safe modern and intelligent solutions.