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.

Discussion on environmental protection requirements of PVC cables and wires

The use of non environmental protection cables is strictly prohibited in developed countries, and China also attaches great importance to this field. China’s relevant laws and regulations clearly require the use of PVC wires and cables in important buildings. Halogen free and low smoke crosslinked PVC wires and cables must be used to avoid heavy smoke and chlorine gas causing casualties in case of fire.

Environmental protection cable will effectively drive the development of cable industry, enhance the competitiveness of cable manufacturer, and make the cable industry more and more stable on the road of sustainable development in green practice and innovation. In recent years, China’s cable enterprises have gradually made efforts to environmental protection cables and low smoke and halogen-free cables. As far as possible, they do not contain heavy metals such as lead, cadmium, mercury, bromine flame retardants, harmful halogen gases, corrosive gases, less heat during combustion, and no soil pollution. Environmental protection cables will be more favored by the market, and will be recruited by power grid companies It is easier to get high order in the bid.

The user’s requirements for environment-friendly wires and cables can be summarized as follows:

1. Low content of lead and heavy metals is required

It is well known that lead and some heavy metals will have adverse effects on human health. In PVC formulation, additives such as lead, cadmium, barium and other heavy metal compounds are usually needed. However, since the 1990s, some developed countries and large electric companies have successively formulated laws and regulations. In the PVC wires and cables used, there are eight kinds of heavy metal content shall not be greater than the regulations. These new regulations not only bring new business opportunities to wire and cable manufacturers, but also bring serious challenges to PVC cable manufacturer.

2. Low smoke and low hydrogen oxide are required

Good flame retardant performance is a very obvious advantage of PVC wire and cable. However, when ordinary flame retardant PVC cable is on fire, it will release thick black smoke and a large amount of HCI gas, which will cause “secondary disaster” after the fire, and seriously affect personnel evacuation and fire rescue work. Therefore, in addition to the flame retardant requirements for wires and cables, the requirements of “low smoke” and “low HCI” will be put forward in some applications.

3. Low toxicity or non toxicity is required

In addition to lead-free and heavy metal free, non-toxic (or low-toxic) cables are required for some household appliances, medical and health appliances and children’s electric toys that may come into contact with food and blood products. This means that all constituent materials used in PVC formulations should be non-toxic. There are a lot of plasticizers in cable materials, but the non-toxic plasticizers must be used to manufacture non-toxic materials. Therefore, the requirements of this PVC material are higher than that of lead-free and heavy metal free materials, and the price is naturally more expensive.

4. Other prohibited items

At present, the regulations being reviewed by the EU impose restrictions on the following items to ensure that wires and cables meet the requirements of environmental protection. For example: 1) asbestos; 2) biphenyl and its ethers, polybrominated phenol; 3) polychlorinated biphenyls; 4) short chain (C10-C13) chlorinated paraffin.

With more and more attention to environmental issues, many countries have formulated a variety of environmental protection policies, so people prefer to use green cable. Low smoke halogen-free flame retardant cable material is one of the most popular environmental protection cables. Although China’s market demand for green cable is growing, compared with developed countries, China still has a long way to go in terms of relevant policy formulation and mandatory application. China should improve the environmental protection cable standards as soon as possible.

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.

The global subsea power cable market will grow at a compound annual rate of over 4% from 2020 to 2024

The market for subsea power cables is expected to grow at a compound annual rate of more than 4 percent from 2020-2024, driven largely by surging demand for electricity, according to Technavio.

According to the report, 47 percent of the market growth in the forecast period will come from Europe, with Italy, Denmark and Finland being important markets for European subsea power cables.

Europe is the largest subsea power cable market in 2019, and government support and growing concern about wind power will significantly drive growth in the subsea power cable market in the region during the forecast period.

Offshore wind turbines can produce more energy using fewer turbines than conventional ones. As a result, the Asia-Pacific region will enjoy rapid growth during the forecast period. Thanks to heavy investment in offshore wind projects over the past few years, China and India will account for most of the region’s share of the forecast period.

According to the IEA, demand for electricity will rise by 40 per cent by 2024. Similarly, growing environmental concerns will force economies to use renewable energy to generate electricity. As a result, the number of renewable projects such as wind and tidal power projects is increasing in most countries, which in turn will increase the demand for undersea power cables or submarine cables. The growing demand for intercountry and island connections will be one of the main drivers of market growth. Subsea power grid interconnection projects in France – UK, Belgium – UK and Ireland – UK are under construction.

On the other hand, the growing demand for high-voltage direct current (HVDC) power cables will also drive the market growth. These HVDC cables are more and more popular compared with traditional cables because they are safe and reliable and can transmit power over long distances. These factors will drive the global subsea power cable market to grow at a compound annual rate of over 4% over the forecast period.

From the manufacturers’ point of view, Prysman, Nexans, Sumitomo Electric, Lenny Cable, Ankart Cable, Tengura Cable, Guhe Electrician, LS cable will continue to dominate the global subsea power cable market in the forecast period.