The plug-together wind turbine

The plug-together wind turbine

Hybrid connector systems are proving to be helpful in getting wind turbines up and running quickly

Wind turbine systems encompass a wide variety of integrated components and subsystems. These subsystems all use several types of wiring and cables for electrical power, data communications, and control signals. In the nacelle, for example, cabling has a key role in integrating such devices as generators, generator slip rings, and inverters. It is also important for wind anemometers, pitch and yaw controls and motors, brake, collision lighting, plus other elements and control systems. The wind turbine manufacturer typically assembles and tests most of the systems before shipping them to the installation site. There technicians assemble the nacelle, tower, and base control station, make the remaining electrical connections, and commission the completed wind turbine.

Hardwired point-to-point cabling has been the typical way of making connections between major subsystems and assemblies. It has also traditionally been a source of problems. Typically, this type of wiring runs through rigid or flexible conduit. Conduit complicates the testing, troubleshooting, and debugging of major system elements. The same is true at the jobsite when the wind turbine is assembled. Hardwiring errors are likely, particularly on work done by independent contractors having no experience with the specific brand of wind turbine at hand. Problems multiply in the tower installation, which includes the turbine control center (base station), data communication system, internal and collision-warning light systems, and may also involve power and control wiring for an elevator.

The direct and indirect costs associated with hardwiring problems can be substantial. There is labor associated with point-to-point wiring and similar costs to disassemble the system for shipment to the jobsite. Inevitably problems are uncovered during testing in the plant, and troubleshooting often involves disconnecting wires at terminal points to isolate the causes.

The situation is not much different at the jobsite when the system is assembled. In a worst-case scenario, wiring errors can damage equipment during start-up. Severe difficulties may necessitate bringing in factory engineers and technicians to correct the situation. No one is ever happy with this course of events.

A point to note is that a wind turbine installation has several different types of wiring. This would seem to require several different connectors and individual cable assemblies. However, recent developments in connector technology are making that thinking obsolete. Today, modular connector designs make it possible to devise hybrid, or mixed purpose, connectors. In other words, designers can customize connectors to accommodate optical fiber, Ethernet, coax, pneumatic lines, electric power, and many other specialized connections. The resulting mixed-use cable assemblies can replace several kinds of point-to-point wiring.

At first, the idea of a hybrid cable might seem counter to the quest for simplified system wiring, but it’s not. Such cables are easy to assemble with crimp, screw, cage clamp, and axial screw wire terminations. Their testing can be automated to quickly ensure there are no wiring errors. If wiring errors arise, connector wires are easy to remove and replace. The result is a prewired, pre-tested, known-good cable assembly for interconnecting major parts of a wind turbine system.

At the equipment end of a pre-assembled cable, a mating connector can handle short wiring runs to components or subassemblies. Alternatively, the cable can have individual connectors or wiring fan-outs going to subassemblies. For example, consider a cable with a wiring fan-out at the connector ends. This would be typical of connections to a panel board. However, individual connectors could be used in a fan-out to mate with connectors on subassemblies or components.

Although the addition of connectors makes a cable run more expensive, there are several advantages, including a few that might not be immediately evident. Besides reducing job-site labor, warranty costs often go down, as do maintenance inventories. It can also be easier to effect field modifications with upgrades, options, and so forth.

The reduction in initial wiring cost comes from use of staged subsystem and electrical panel assembly with pre-wired and tested cable assemblies. Testing and debug time drops because it’s easier for technicians to isolate and test individual system components by removing cables with connectors. Standardized, pre-built subassemblies promote modular system design. Using connectorized cable assemblies makes much of the wind turbine system “plug and play” for start-up. Turbine owners are happy because they see fewer start-up problems and lower service costs when turbines are up and running. Both maintenance and many repairs take less time because many components and subsystems are “plugged-in” vs. “wired-in”.

The payback from many of these benefits is difficult to quantify, but it is possible to make reasonable estimates. In the case of wind turbine systems, a good rule of thumb for fully burdened hard wiring labor costs is $80 for both ends of a single cable run. Experience shows there is 40% added cost for the initial installation of connectors on each end of the same cable, plus the cost of the connectors themselves. With two connectors typically costing $60, that brings the initial connectorizaton cost to $60 + (1.4 × $80) = $172 at the wind turbine plant.

However, experience in the field shows there is about a 30% premium on field wiring labor costs compared to doing the same hard wiring in the plant. Assuming major assemblies ship to the jobsite fully assembled, hard-wired cables must be un-wired in the field and then rewired for installation. Thus the total installation cost for a single hard-wired cable at the jobsite is ($80 × 2) × 1.3 = $208. The cost of unplugging and replugging two connectors on a cable is negligible. So this brings a net savings from connectorization of $208 - $172 = $36. Any subsequent disconnect/reconnect because of field repairs, less downtime, and ease of adding options will save more if connectorized cables are used. Each case is different, but we have seen wind turbine makers calculate savings in the thousands of dollars from actual equipment installations.

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