Moog Pitch System 3: Axis box including pitch servo drive 3 and pitch capacitor module.

“The safety built into Moog Pitch System 3 helps wind farm operators in three important ways,” says Dr. Tobias Theopold, Technology Development Manager Business Unit Wind, for Moog. “The technology avoids hazards from the wind turbine and therefore lowers the insurance fees for a wind farm operators. As the safety-related development of Moog Pitch System 3 required an IEC 61508 and 13849 compliant V-model process including intensive failure insertion testing, this also boosts the reliability of the overall product, which of course lowers downtime and reduces the Levelized Cost of Energy.”

Moog established the benchmark for safety with its previous versions of the Moog Pitch Servo Drive when these were certified by TÜV Rheinland in 2012. With the Moog Pitch Servo Drive 3, Moog has received independent validation that this product will also perform outside the specification at extreme environmental conditions and in cases of unexpected failure.

Along with certifying the safety of its new servo drive, Moog improved the architecture of Pitch System 3 to meet IEC 61508 and ISO 13849, standards governing wind turbine safety. First, Moog’s engineers provide a safety function referred to as Safe Feathering Run (SFR), which automatically moves and stops a turbine’s blades in the feathering position.

Second, Moog included a Safe Stop function called (STOP1) to arrest the motion of an individual blade during manual movement of the blades. The Safe Stop function meets the ISO 13849 standard that addresses the requirements that blades must not perform an unintended move when people are working inside the wind-turbine hub.

“To protect a wind turbine against overvoltage from the grid and lightning strikes, we included a new component called the Moog Pitch Interface Module,” adds Theopold. “Our new interface module is a firewall to protect the blades against extreme environmental conditions and so-called common cause failures (CCFs). These failures are most critical because they can affect each of the pitch axis and therefore can put turbine safety on risk.”

Moog also asked lightning protection specialist DEHN to test Pitch System 3 (including its servo drive and interface module) inside a high voltage lab subjecting the system to multiple lightning strikes reaching more than 260,000 amps. Afterward, the system was still fully operational and performed a Safe Feathering Run.

For more: www.moog.com/wind.

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DTU now has access to a new wind tunnel. The wind turbine blade testing facility will be next.

The test facility at DTU’s Risø Campus will conduct static and dynamic tests of wind turbine blades. The facility will have three test stands capable of delivering static deflection testing and dynamic (directly coupled and mass resonant excitation) testing of wind turbine blades measuring 15, 25, and 45-m long, and the flexibility to test other large structures. The Moog system is an integral part of DTU’s plan to establish a unique research facility that meets the highest international standards and will enable DTU to develop and provide advanced testing methods and research about the strength and fatigue of large structures when exposed to complex loading.

Moog will supply a test system including hydraulic actuation (i.e., winches, linear actuators, and mass resonant excitation units), closed-loop servo control, hydraulic power and distribution pipe work system, project management, design and modeling, installation and commissioning services backed with long term service and support.

“We chose Moog as our equipment provider because its engineering and sales teams were very diligent throughout the tender process to deliver the best technical solution within budget,” said Dr. Kim Branner, senior research scientist and Head of the Structural Design & Testing Team for DTU Wind Energy.  Moog expects the system to be operating in the fourth quarter of 2017.

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A recently released pitch system boasts of 66% fewer parts than the designs installed today on most operating turbines. The new system is also lighter and smaller. As part of its design, its engineering team at Moog also eliminated many problematic components that historically failed at a higher rate than other parts of the pitch system. Using reliability analysis tools commonly applied in the aerospace industry, the design team directly quantified the reliability benefits of the Moog Pitch System 3 based on the system’s configuration.

In late 2016, Moog Inc. launched its next generation of wind turbine pitch-control technology, the Pitch System 3. The first shipment is successfully operating at a wind farm in Brazil. The company improved its earlier pitch-system design to help wind-farm operators and turbine makers meet the growing need to reduce wind farm capital and operating expenses.

Input from DNV GL
It is generally accepted that pitch systems keep a turbine running and ensure its safety in the event of high winds or catastrophic events. Pitch systems monitor and adjust the inclination angle and control the speed of the blades. Although pitch systems play a large role in the safe and the economic operation of a turbine, the devices account for less than three percent of a wind farm’s capital expenditures.

Earlier this year, DNV GL, an international certification body and provider of technical assessments, quantified the impact of pitch-system reliability on turbine failure rates. The organization’s research, in part, examined how innovative designs for advancing pitch-system reliability can improve the Levelized Cost of Energy (LCoE). This figure measures the net cost to install and operate a wind turbine against expected energy output over the course of a turbine’s lifetime.

DNV GL collected data from 69 projects totaling 5.3 GW of capacity across four million turbine days for wind turbines located in China, Europe, and North America. The turbines ranged in size from 1.5 to 3 MW. The organization’s DNV GL benchmarking study confirmed that pitch systems (whether electric or hydraulic) have a high rate of failure and significant effect on turbine reliability, downtime, operating expenses, and LCoE. 

A conventional pitch systems on the left and the simpler System 3 by Moog.

A typical pitch system from five years ago (many of which are operating today in wind turbines globally) can have more than 4,000 individual parts. These components are integrated with thousands of wires and termination points, all potential sources of failure.
Industry-wide performance data from the DNV GL study showed that the current installed base of pitch systems manufactured by a number of providers left a lot of room for improvement. Moog engineers recognized that by increasing pitch-system reliability, it was possible to lower a turbine’s cost of energy. By designing a pitch system with less complexity, far fewer parts, and a modular architecture, the reliability of the system would be greatly improved. As a critical sub-system of the wind turbine, the pitch system has a direct impact on the overall turbine lifetime performance.

Reducing complexity to improve productivity

A cross-functional engineering team first considered how a pitch system might be improved in design. Few systems have changed over the last 10 years. Engineers simplified the basic structure by defining the minimum requirements for a high-performance pitch system in a whiteboard design. Then, engineers integrated functions into core modules that the team designed, optimized, and tested for a service life of more than 20 years. This design approach takes into account a wind-turbine operator’s requirements for improved reliability, ease of integration, interface compatibility and reduction in planned and unplanned maintenance in the field.

Reducing maintenance

The wind sector is under extreme pressure to deliver lower LCoE to grid operators. This requires reducing the capital cost per installed megawatt of capacity and increasing the turbine availability during operation.

Delivering lower LCoE requires the industry to reduce planned and unplanned maintenance costs. Wind-turbine maintenance is challenging and costly because of the difficulty in accessing the nacelle and hub, particularly in remote locations such as offshore. The cost of component failures is amplified by the high cost of accessing equipment for repair.

However, reducing maintenance also lowers LCoE. In fact, the DNV GL study shows that lighter, smaller pitch systems can save up to $1.70/MWh for a typical 3.0 MW turbine. By eliminating required planned maintenance and greatly reducing component failures in general, a wind-farm operator directly benefits from higher availability and lower maintenance costs.

Renewable technologies, such as wind power, have an opportunity to shoulder a larger percentage of the world’s energy needs. The mission-critical nature of a country’s energy grid demands better technology than a general-purpose industrial application, such as many pitch systems developed up to this point.

About the author

Mr. Prasad Padman, an instrumentation and control engineer with a master’s degree in finance and marketing, has been with Moog for eight years in various roles. He is currently responsible for developing next-generation pitch control solutions.

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