After my country's cable industry surpassed the United States to become the world's largest in terms of production capacity in 2011, the issue of its large size but lack of strength and overcapacity became a major topic of discussion within the industry. How to grow bigger and stronger became a critical question facing the cable industry. Since the beginning of the 21st century, the world has been vigorously promoting the development of new energy sources, and my country's new energy industry is booming. Broadly speaking, new energy sources include solar energy, wind energy, nuclear energy, biomass energy, and chemical energy. The construction and development of these new energy sources are inseparable from cables. Therefore, new energy cables can be divided into: photovoltaic cables, wind power cables, cables for offshore oil platforms, cables for nuclear power plants, electric locomotive cables, and cables for inland conventional and unconventional natural gas development. This article will provide a detailed analysis of the product categories and performance, domestic and international application standards, and development prospects of these new energy cables.
Wind power cables
Wind energy, as a clean and renewable energy source, is currently the largest, most technologically mature, and most commercially promising power generation mode among many new energy sources. According to publicly available data, my country's mainland and near-coastal areas have nearly 1 billion kW of usable wind energy resources. my country's "Medium and Long-Term Development Plan for Renewable Energy" points out that by 2020, my country's total installed wind power capacity will reach 30 million kW, making the period from 2013 to 2020 a golden period with great potential. Wind power cables include control cables, signal cables, and torsion-resistant power cables within the wind turbine nacelle and tower. Due to the harsh wind farm environment and the torsion of the power cables caused by the rotor's oscillation, wind power cables generally have high requirements, such as resistance to low temperatures, oil, torsion, weathering, ultraviolet radiation, and acids and alkalis. Currently, my country lacks national standards for wind power cables, with only industry standards such as TICW01-2009 "Torsion-resistant Flexible Wires for Wind Power Generation with Rated Voltage of 1.8/3kV and Below" issued by the National Wire and Cable Quality Supervision and Inspection Center.
Tower cables are the most widely used cables in wind power generation systems; the term "wind power cable" often refers to this type of cable. Because tower cables constantly oscillate forward and backward with the wind turbine, their performance requirements are extremely stringent. They must ensure structural flexibility while possessing high tensile strength, low-temperature resistance (-40℃), UV resistance, torsion resistance, salt spray resistance (required for offshore wind farms), seawater corrosion resistance, abrasion resistance, weathering resistance, and flame retardancy. Figure 2 shows a schematic diagram of the cables used in the main components of the wind turbine. The numbers represent the following: 1—blade actuator, 2—pitch and azimuth adjustment actuator, 3—blade pitch and azimuth control system, 4—deflection actuator, 5—gearbox, 6—impeller anemometer, 7—control box, 8—inverter, 9—generator, 10—pump, wind turbine, heater. The cables required for these components are primarily flexible motor power cables, flexible servo cables, and VFD cables.
Standards for wind power cables vary across countries. In my country, the main standards are TICW01-2009 "Twist-resistant Flexible Cables for Wind Power Generation with Rated Voltage of 1.8/3kV and Below" and NBT31034-2012 "Twist-resistant Flexible Cables for Wind Power Generation with Rated Voltage of 1.8(3)kV and Below - Part 1: Cables with Rated Voltage of 0.6(1)kV". There are currently no industry standards for higher voltage levels; they are generally manufactured according to IEC standards. In North America (Canada/United States), wind power cables generally refer to the UL/CSA series. The standard is based on the US National Electrical Code NPFA70, with cable models WTTC and TC. In the UL certification system, WTTC is covered under the ZGZN product category, with voltage levels of 0.6/1kV and 1.8/3kV. Different models correspond to different standards, as shown in Table 1.
Standard Number | Standard Name | Standard Description UL44 Thermosetting Insulated Wires and Cables: Covers cables with four voltage levels: 600V, 1000V, 2000V, and 5000V. Conductor, insulation, sheath, and other structural details and thicknesses can all be found in this standard. UL1072 Power and Control Cables (Optical Units): Medium Voltage Power Cables: Covers medium voltage cable standards and is similar to GB/T12706. UL1581 Wires, Cables, and Flexible Wires: Covers conductors, insulation, sheath, and related testing methods. UL2277 Wind Power Cables: WTTC and TC power cables are related to other standards. ASTM-B33 Conductor Standard: The American standard classifies conductors in great detail, such as AA, A, B, C, D, I, and K.
It is worth noting that the classification of conductors is different in UL1581 and ASTMB33. Class AA - bare conductors for overhead use; Class A - bare conductors that are more flexible than Class AA; Class B - conductors with insulation materials such as rubber and insulating paper that are more flexible than Class A; Class C and Class D conductors are more flexible than Class B conductors; Class G conductors are made of 7-61 strands and are typically used for flexible cables with rubber sheaths and for mobile equipment.
When manufacturing wind power cables according to UL standards, attention should be paid to the way conductor specifications are expressed, i.e., the conversion relationship between AWG and metric millimeters, the selection of dry and wet conductors at different temperatures, the selection of insulation and sheath materials, and the selection of relevant tests in UL44, etc. It is worth noting that the UL standard does not distinguish between halogen-containing and halogen-free materials for wind power cables.
For a considerable period of time, wind power cables will continue to occupy the main position in new energy power generation cables, and the products tend to have more comprehensive performance across multiple standards, such as meeting the low temperature torsion resistance test in TICW1 and FT4 in UL1581, and so on.
Photovoltaic cables
The development of solar energy has seen explosive growth in recent years. By the end of 2010, my country's installed solar photovoltaic (PV) power generation capacity had reached 893 MW, ranking 7th in the world. It is projected that by 2020, my country's total installed solar PV power generation capacity will exceed 30,000 MW. The government is also providing support for PV projects. PV power generation has spurred the rapid development of related products, such as PV cables. Typically, the low-voltage DC power generated by PV power generation needs to be converted to AC power; the connecting cable between the PV cells and the AC/DC inverter is the PV cable. Theoretically, a PV module generally requires two single-core cables between 0.8 and 1 meter in length. Therefore, based on the current development speed of PV modules, the usage of PV cables in my country will reach approximately 150,000 km by 2020, indicating significant demand.
Photovoltaic cables, abbreviated as PV cables, have a relatively simple structure consisting of a conductor, insulation, and sheath (see Figure 5). Currently, my country does not have national standards for photovoltaic cables. Internationally, the most authoritative certifications for photovoltaic cables are TÜV Rheinland, TÜV MARK, and UL certifications, primarily referencing standard 2 Pfg 1169 or UL 4703. Samples must be sent to Germany or the United States, resulting in a long certification cycle, high costs, and varying design focuses for each sample. Generally, photovoltaic cable performance requirements are as follows: the thermal life of the cable insulation and sheath should be no less than 25 years at 120℃; the cable must pass a dynamic penetration test; the cable must pass a single-strand vertical burning test; the cable must pass a -40℃ low-temperature test; and the cable must pass acid and alkali tests, damp heat tests, ozone tests, and weather resistance tests. However, the application environments for photovoltaic cables vary, so the design should consider the installation location, such as protection against rodents and other small animals.
nuclear-grade cables
The construction and decision-making regarding nuclear power plants is one of the most pressing issues for countries worldwide in the 21st century. From the Iranian and North Korean nuclear crises to the Fukushima nuclear disaster in Japan, and referendums in some European countries, all have revolved around the question of whether or not to use nuclear power. A map showing the distribution of nuclear power plants in my country is shown in Figure 6. However, regardless of the decision, the number of cables required for each nuclear power plant is enormous.
International standards IEEE 383 "Type Testing of IE Cables, Field Joints and Connectors for Nuclear Power Plants" and RCC-E "Code for Design and Construction of Electrical Equipment in Nuclear Islands" specify emergency reactor shutdown, containment isolation, emergency core cooling, residual heat removal from the reactor, and residual heat removal from the reactor building. Chinese standard GB 22577—2008 "General Requirements for 1E Class Cables for Nuclear Power Plants" specifies general requirements for nuclear-grade cables. Electrical systems and equipment designed to prevent the large-scale release of radioactive materials into the surrounding environment are defined as 1E class. In my country, IE class equipment is classified into three categories—K1, K2, and K3—based on the operating environment and quality assessment requirements. The K3 quality assessment procedure verifies the ability of equipment installed outside the containment to perform its specified functions under normal environmental conditions and, for some equipment, under specified accident conditions. Cables certified by the K3 quality assessment procedure are called "K3 category cables". The insulation cores of K3 category control and instrumentation cables of grade 1E used in nuclear power plants must meet excellent mechanical, electrical and heat resistance properties, pass the single-core vertical burning test, have low smoke, halogen-free, low toxicity and low corrosion characteristics, and their service life should exceed 40 years.
In addition to the aforementioned new energy cables, there are also cables for offshore oil platforms, electric vehicle charging cables, and natural gas development cables. These cables are basically not regulated by national standards in my country, and most are produced in accordance with the standards of developed countries. Previously, domestic and foreign customers may have mostly used products from certain global cable giants. With the rise of Chinese cables, these customers will place their procurement in China where product prices are more competitive. These customers will then require Chinese cable companies to digest and absorb foreign standards and promptly launch projects when they are ready, in order to avoid vicious competition due to homogenization when many companies rush into the market.
The development prospects of new energy cables are very broad. We should digest foreign standards such as UL, VDE, and BS, actively transform them into internal enterprise standards, and maintain good communication with customers to ensure smooth technical exchange channels.
