What are the requirements for the performance of low-temperature flexible cables in China?

In general, wind farms are located in harsh environments with special climatic conditions, such as strong winds, strong ultraviolet rays, and high salinity air. Because of this, cable performance in wind power applications is undoubtedly higher than other applications. The moving parts inside the fan further increase the importance of proper cable selection. ""

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 the power grid and communication systems. A single wind turbine requires more cables than people think. For example, a 90-meter-high 1.25MW wind turbine requires about 1km of power cable. In this way, the wind farm with a 50MW installed capacity will require 40km of cable.

Wind turbines operate in harsh environments that typically have a wide temperature range (about -40°C to 50°C) and are exposed to intense UV light. Therefore, in order to achieve the expected service life, the special cable used needs to be able to withstand low temperatures of -40°C and radiation resistant to ultraviolet light. For moving parts inside the fan, the cable should have excellent torsional and flexural flexibility and have a small bend radius. The cable also needs to be resistant to fuel, anti-refrigerant, oil, and corrosion-resistant chemicals and anti-wear. If the wind farm is on land near the coast or on the sea, the cable must also be resistant to high salt water erosion. For safety reasons, in addition to the above requirements, the cable is also required to have flame retardancy. In some cases, low-smoke, zero-halogen (LSZH) materials and EMI protection are also required.

In summary, the cables used in wind power applications generally should meet the following requirements:

(1) Wire

To maximize flexibility, it is recommended that design engineers only use multiple strands of annealed soft copper wire. In the winding wrap application, short concentric strand configurations are used; in twist wrap applications, long concentric strand configurations are used. Wires larger than 6mm2 (10AWG) require the use of a composite stranded structure.

(2) Insulation

In order to increase the flexibility at low temperature, thermoplastic rubber (TPE), ethylene propylene rubber (EPR, an EPM or EPDM) or silicon rubber (SiR) is generally selected as the insulating material to resist the aging caused by ozone corrosion and heat generation. PVC/nylon insulation has also been widely used due to its high dielectric strength.

(3) Sheath

The cable sheath can be either a thermosetting compound such as polyvinyl chloride (CPE), polychloroprene (chloroprene rubber), chlorosulfonated polyethylene (CSPE) synthetic rubber, or similar TPE, TPE-PVC alloy, and Poly Ester and other thermoplastic compounds. All of these materials are resistant to oil, fuel, and solvents, and have excellent flexibility at low temperatures. This characteristic makes it an ideal jacket material for wind power cables.

It should be noted that the cable structure is also a decisive factor for the flexibility of the cable. Symmetrical wire designs using balanced structures are generally highly flexible.

Even if these general rules are followed when the cable is manufactured, it is highly recommended to perform a full test to simulate "real" applications.

Cable test methods and procedures

Depending on the wind direction, the fan angle needs to be adjusted by the yaw drive. The power, control, and communication cables either bend along the horizontal axis or rotate along the vertical axis. This imposes stricter requirements on torsional flexibility and requires more attention. Although there are currently no standards or regulations to rectify flexing, end-users generally still seek to pass certain tests of cables before they are put into use.

The following is a general test method used by end users in the cable industry.

(1) Torsional stress test of single cable at low temperature (-40°C):

A 10 meter long vertical suspension cable sample is fixed at the top and the bottom is bound to a rotating device. First, twist the cable clockwise four turns (+1440o), and then turn four times counterclockwise to return to the original position. Then twist the cable four turns counterclockwise (-1440o) and then turn clockwise four times to return to the original position. Repeat the entire process 5000 times to simulate 20 years of use. If 5 minutes pass under 2.5U0, the cable is not broken down, the sheath is not cracked, then the cable passes the test.

Note: U0 can be 600, 1000, or 2000V depending on the voltage rating of the cable.

(2) Torsional Stress Test of a Bunch of Cables

The test procedure was the same as (1) except that the cable harness was replaced.

Wind power cable standard

There is no specific standard for the use of cables in wind power applications. Many cable manufacturers comply with IEC 60228 Class 5 or 6 (similar to DIN VDE 0295 Class 5 or 6, HD 383, and GB/T 3956 Class 5 or 6) and use smooth or metal-coated annealed copper strands as wind power. Cable leads to obtain the required flexibility. Interestingly, IEC 60228 only specifies the nominal cross-sectional area of ​​conductors and the number and size of wires in conductors for power cables, which gives cable manufacturers a great degree of freedom. Therefore, even if the cable satisfies the requirements of IEC 60288 Class 5 or 6, the cable performance will often be unsatisfactory. The UL 62 (which refers to multiple ASTM standards) not only specifies the size and number of wires per wire in the wire, but also defines the wire structure (such as the structure of the strand, composite strands, and assembly strands), which are all flexible cables. The key to sexual performance. As for insulation and sheathing, many manufacturers follow DIN VDE 0207-20 and DIN VDE 0207-21. HD 22.1, HD 22.4, UL 44 and UL 62 have also become common standards for cable production.

Other standards such as UL 758, UL 1581, UL 1277, UL 2277, IEC 60332, etc. are also often used to support some additional features such as fan frame cable (WTTC) specifications and flammability rating requirements.

As European countries develop cables for the wind energy market earlier than North American countries, cable manufacturers are now adopting more European standards. However, similar US UL standards have the same function, and in some cases, UL standards have stricter requirements for wind energy applications.

Company Name: Tianjin Cable Plant Rubber Cable Factory

Director: Hao Guozheng Sales General Manager: Ren Dongxia