By James Moorman, Vice President of Sales

Legacy fleets that are operating today and approaching the end of their service life will be analyzed by asset owners and technicians on whether these aging turbines can be overhauled to continue operating or be decommissioned. For wind farm operators who decide to overhaul and repower their existing machines, re-using their existing infrastructure is a possibility as long as the components that are put into the existing towers are compliant with the current standards.

Cables that have been exposed to oil and other lubricants for long periods can begin to crack as the plasticizers have been removed from the insulation causing it to harden.

Meeting Today’s Standards for Wind Turbines

Underwriters Laboratories (UL) standards 6141 and 6142, which were enacted in 2016/2017, aim to simplify the process of receiving final approval for wind turbines through local Authorities Having Jurisdiction (AHJ) inspectors. In the US, local AHJs need to certify that products are safe to use in accordance with general American installation regulations such as the National Electric Code (NEC), National Electrical Safety Code (NESC) and American National Standards Institute (ANSI)/ Institute of Electrical and Electronics Engineers (IEEE) C2, among others. It is not always clear whether components that originally complied with the European CE standards also comply with American installation regulations. If there is any doubt, an AHJ inspector may shut down the project. UL 6141 and UL 6142 are the first American safety standards developed specifically for wind turbines. They provide a set of rules that help AHJ inspectors with the approval process, making it more transparent and predictable for everyone involved.

Cables used in the drip loop that have low abrasion resistance often show wear due to the constant rubbing that occurs as the nacelle rotates. Over time, abrasion can wear down the jacket and insulation exposing the conductor and creating risk to technicians and the machine. It’s important to use cables with high abrasion resistance to maximize their longevity in this critical area of the turbine.

UL Aims to Harmonize with IEC 61400

For many years there were no national safety standards specifically for wind turbines in North America. The only guidelines AHJs had for reference was IEC 61400, which is the international standard for wind turbines issued by the International Electrical Commission (IEC). However, the IEC standard has been criticized in North America since it was published. Critics claimed that it did not include enough provisions regarding the electrical safety of components, controls and protection devices.

Therefore, UL developed national standards to supplement IEC 61400. These standards refer directly to IEC 61400-1 (Design Requirements) and IEC 61400-2 (Small Wind Turbines), and add technical requirements primarily focused on electrical safety, control, safety devices and fire protection within the wind turbine. These UL standards – 6141 and 6142 – thereby bridged the gap between the IEC standards.

ANSI issued UL 6141 as an American National Standard for Wind Turbines Permitting Entry of Personnel. UL 6141 applies to large-scale wind turbines, typically 1MW and above, that can or may be entered by operators or service technicians for operation or maintenance.

UL 6142 has been acknowledged as a national standard for small wind turbine systems by ANSI since it was first proposed in 2012. It applies to smaller, commercial-kW wind turbines that are found closer to residential areas, and typically have a nominal capacity of up to 1,500 V AC. Due to their size, most smaller turbines aren’t large enough for operators/technicians to enter inside to perform maintenance or inspections, so they are either hinged to be laid down or climbed externally. There are smaller turbine types that are large enough to be entered and climbed by a tech, but are still classified as a “small turbine”. For these turbines, there are lock-out/tag-out procedures for operators and technicians to enter the turbine to perform maintenance.

Both UL standards apply exclusively to on-shore wind turbines and only affect new constructions or the refurbishing of wind turbines with a capacity greater than 500 kW. Existing legacy fleet systems do not need to be refitted to meet the UL standards until their end of service life date comes due.

The power and data cables within the tower should also be inspected and replaced, if needed, during the retrofit.

How Does UL 6141 Impact the Use of Cables?

UL 6141 focuses primarily on electrical safety and introduces several restrictions on how cables may be used in the future. The bottom line is that appliance wiring material (AWM) – in other words, cable that is UL Recognized but is not UL Listed – may only be used minimally within the turbine. Up until now, AWM cables were frequently used throughout the various sections of the wind turbines. UL 6141 stipulates that all accessible cables need to be installed in cable ducts or trays. If this is impractical or impossible, e.g. in the cable loop, only so-called tray-rated cables, more specifically cables that are approved for exposed run (TC-ER), are allowed. The -ER or “exposed run” approval allows cable to come out of the cable tray unprotected for ≤6 ft. (1.8m) if it passes crush and impact tests. Cables in the down tower and nacelle are usually accessible and therefore must be certified for exposed run as well.

Tray cables that are designed to be used for exposed run applications are oil and flame resistant, and fulfill the increased safety requirements of UL 6141. In fact, cables need to be UL Listed to be classified as tray cable. Tray cable rated for 600 V falls under UL 1277 (Electrical Power & Control Tray Cable), while wind turbine tray cables (WTTC), which are rated up to 1000 V, are listed under UL 2277 (Flexible Motor Supply Cable and Wind Turbine Tray Cable). Unlisted AWM cables have not passed the specified tests and therefore are not suitable for exposed run applications. UL standards were already in place to regulate components in certain wind turbine subsystems such as generators. These standards will continue to apply. Furthermore, UL 6141 will apply to areas that were not previously regulated by a standard.

The cables replaced during an overhaul can vary based on what equipment is being upgraded or repaired. With thousands of components in an entire turbine, a majority of the cables replaced are located in the nacelle, and the drip loop, where cables experience millions of torsion cycles over their lifespan.

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By Michael Hamsa, Head of Supply Chain Management

The Corona crisis has exposed weaknesses in the supply chains of many companies. There are several ways though that they can be made more crisis- and future-proof. From our perspective, the primary leverages for this are short distances, secure supplies and the increased digitalization and automation of processes. HELUKABEL’s basic strategy has always been to maintain close proximity to customers with a comprehensive and very diverse range of products. In order to be able to supply our international customers with this diversity quickly and reliably, we have set up an integrated supply chain that reflects the motto “think global, act local”. From over 55 locations worldwide, we punctually deliver to local markets in a staggering total of 160 countries. The continental logistics hubs in Germany, the USA and China as well as the affiliated production plants act as backups for the local warehouse locations.

A Supply Chain that Meets Customer Needs

This regional production and storage concept enables us to keep transport distances short which not only boosts supply chain resilience, but also reduces costs for the customer and keeps the ecological footprint low. Another important factor positively affecting supply chain resilience is a long-term relationship with customers and service partners based on trust. Reliability, flexibility and high-quality levels, together with responsible cooperation, are core values at HELUKABEL. The second key ingredient for a future-proof supply chain is consistent implementation of the “digitalized supply chain“ as part of Industry 4.0. The pivotal concept here is the topology and best possible optimization of the supply chain. To this end, we are pushing hard to create the paperless nexus between the multiple value-added stages that this requires. For example, highly automated high-bays warehouses contribute to customer-specific control, coupled with high levels of guaranteed stock. On request, HELUKABEL operates an active inventory management at the customer’s premises, enabling them to benefit from reduced inventory levels and smaller capital tie-up. The digitalized supply chain allows us to think in new dimensions and improve the way we integrate customers into shared processes.

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Copper or aluminum? Choosing conductive metals for different industries and applications can be a challenge. Copper has become the standard in cables and wires because of its excel-lent conductivity and malleability. However, it is relatively heavy and expensive compared to aluminum. Switching to aluminum, which is lighter and significantly less costly than copper, is a via-ble option in many cases. Using aluminum successfully is a matter of understanding the capabilities of this conductive metal and how to deal with the challenges it presents. Copper is typically more than twice as expensive as aluminum. This significant difference in price is due to the greater availability of raw aluminum compared to copper. After oxygen and silicon, aluminum is the third most common element in the Earth’s upper crust, while copper is ranked 25th in availability on the list of raw materials. Assessment of current prices is further reinforced by the volatility of the raw materials market. The fluctuations of aluminum are not as volatile as copper, which allows for better material planning.

If aluminum is used as a conductor material, its lower conductivity requires a wire size that is approximately one-third larger than that of a copper wire. In the end however, the insulating material used with the wire plays a crucial role in performance; an aluminum wire can possess the same current carrying capacity as a H07RN-F copper wire. Aluminum’s larger wire size would only be a disadvantage in applications requiring tight spacing, such as when installed in densely packed control cabinets. The facts for aluminum speak for themselves when it comes to the issue of weight. As a raw material, aluminum is approximately 70% lighter in weight than copper. This can be helpful in the efforts of numerous application fields looking to reduce the weight of all components. Naturally, when used in electrical cables, the lower weight makes them easier to install. High-voltage cables have long been made from aluminum; the lighter weight reduces the tensile force placed on wire and masts significantly. But even industries such as auto-motive manufacturing and the aerospace industry are switching to aluminum wires. All the cable harnesses in the Airbus A380 are already made of aluminum. Aluminum wires can be up to 60% lighter than copper wire with comparable current-carrying capacity. Even for applications that re-quire flexible cable connections, copper must not always be the first choice. The HELUWIND® WK POWERLINE ALU series provides a range of fine-wired cables and connection technology.

For more information about HELUKABEL’s WK POWERLINE ALU, please visit https://www.helukabel.com/publication/us/brochures_flyers/wind/wk-powerline-alu.pdf

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