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    Talking about the Performance Requirement and Testing Method of Low Temperature Flexible Cable


    In general, the wind field is located in harsh environments with special climatic conditions, such as strong winds, strong ultraviolet rays, and high salinity air. For this reason, cable performance in wind power applications is undoubtedly higher than other applications. And the movement of the fan parts to further improve the importance of the correct choice of cable. "

    Existing wind farm maintenance and new large-scale wind farm development need to consider the use of high-grade power cables, data and control cables and communication cables, which determine the grid and communication system interconnect quality. The number of cables required for a single wind turbine is greater than people think. For example, a 90-meter-high 1.25 MW wind turbine requires about 1 km of power cables. In this way, the 50MW installed capacity of the wind field will require 40km of cable.

    Wind turbines work in harsh environments, which generally have a wide temperature range (about -40 ° C to 50 ° C) and are exposed to extreme ultraviolet radiation. Therefore, to achieve the expected service life, the use of special cables need to be able to withstand -40 ℃ low temperature and can withstand ultraviolet radiation. For moving parts within a fan, the cable should have excellent twisting and bending flexibility and a small bend radius. The cables also need to be resistant to fuels, antifreeze, oil resistant, corrosion resistant chemicals and abrasion resistant. If the wind field is close to the coast of the land or located at sea, the cable must also be resistant to high salt water erosion. For safety reasons, in addition to the above requirements, but also requires the cable has a flame retardant. In some cases, other characteristics such as low smoke, zero halogen (LSZH) materials and EMI protection are also required.

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

    (1) wire
    To maximize the flexibility, it is recommended that the design engineer use only multiple stranded annealed soft copper wires. In the application of bending around the fold, the use of short concentric twisted wire structure; in the twist around the folding application, the use of long concentric strand structure. Wires with an area greater than 6 mm2 (10 AWG) require the use of composite stranded structures.

    (2) insulation
    To increase the low temperature flexibility, thermoplastic rubber (TPE), ethylene propylene rubber (EPR, EPM or EPDM) or silicone rubber (SiR) are usually used as insulating materials to resist ozone corrosion and heat aging. PVC / nylon insulation has been widely used due to its high dielectric strength.

    (3) Sheath
    The cable sheath may be a thermosetting compound such as polyvinyl chloride (CPE), polychloroprene (chloroprene rubber), chlorosulfonated polyethylene (CSPE) synthetic rubber, or TPE, TPE-PVC alloy and poly Amylate and other thermoplastic compounds. These materials have the ability to resist oil, fire resistance, solvent resistance, and have excellent flexibility at low temperatures. This feature makes it ideal for wind power cables.

    It should be noted that the cable structure is also a decisive factor in cable flexibility. Symmetrical conductor designs with balanced structures are usually highly flexible.

    Even when the cables are manufactured to follow these general rules, it is strongly recommended to perform a complete test to simulate "real" applications.

    Cable test methods and procedures

    Depending on the wind direction, it is necessary to adjust the fan angle by the yaw drive. The power, control and communication cables either bend along the horizontal axis or rotate along the vertical axis. This requires more stringent torsional flexing and requires more attention. Although there is currently no reversal of the standards or regulations in terms of flexibilities, end users often still pursue cables that can be tested in some way 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)
    The top of a 10-meter-long vertical suspension cable is fixed and the bottom end is tied to a rotating device. First, turn the cable clockwise by 4 turns (+ 1440o), then turn it counterclockwise for 4 turns and return to its original position. Then turn the cable counterclockwise 4 turns (-1440o), then turn clockwise 4 turns to return to the original position. Repeat the whole process 5000 times to simulate 20 years of use. If 5 minutes after 2.5U0, the cable is not broken, the jacket is not cracked, then the cable passed the test.
    Note: Depending on the voltage level of the cable, U0 can be 600, 1000 or 2000V.

    (2) Torsional stress testing of a bundle of cables
    The test procedure is the same as (1), except that it is replaced by a cable bundle.
    Wind power cable standard

    There is currently no standard for the use of cables in wind power applications. Many cable manufacturers follow the IEC 60228 Class 5 or 6 (similar to DIN VDE 0295 Class 5 or 6, HD 383, GB / T 3956 Class 5 or 6) standards using smooth or metallized annealed copper wires as wind power Cable wire to achieve the required flexibility. Interestingly, the IEC 60228 only specifies the nominal cross-sectional area of the wire and the number and size of the wires in the wire for the power cable, which gives the cable manufacturer a great deal of freedom. Therefore, even if the cable meets the requirements of IEC 60288 Class 5 or 6, cable performance is often unsatisfactory. The UL 62 (involving multiple ASTM standards) not only specifies the size and number of wires per wire in the wire, but also specifies the structure of the wire structure (such as concentric stranded, composite stranded and stranded wire, etc.) The key to sexual performance. As for insulation and sheathed, 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 a common standard for cable production.

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

    As European countries earlier than North American countries to develop for the wind energy market cable, cable manufacturers are now more use of European standards. Nonetheless, similar US UL standards have the same function, and in some cases, UL standards have more stringent requirements for wind energy applications.