Driving wind transformation

Keeping the wind industry in motion

With gearboxes in more than 110GW of installed capacity, ZF Wind Power is at the heart of the global wind supply chain.

Wind turbines are feats of engineering for the 21st century. In many regions and continents they provide the cleanest and lowest-cost source of energy. To the casual observer, they appear to do so effortlessly. Within these machines, the gearbox is at the heart of the system. It converts slowly rotating, high torque power from the wind turbine rotor to higher speed, low torque power, required by the generator, which converts mechanical energy into electricity.
These components perform under challenging conditions for 20 years and often beyond.
ZF Wind Power is a leading designer and producer of wind turbine gearboxes. Since the company first entered the wind turbine market in 1979, its manufacturing plants have shipped more than 65,000 gearboxes, for both onshore and offshore models. Today, ZF Wind Power is the only supplier providing gearboxes for 8MW-plus offshore turbines in serial volumes and, in 2019, it will start the serial production of gearboxes for 9MW-plus offshore turbines.
Back in 1923, the Belgian company started in the industrial gearbox industry, as Hansen Transmissions. In 1979 the company pioneered wind turbine gearboxes. ZF, a global automotive supplier and wind turbine gearbox manufacturer, acquired the company in 2011.

A winning partnership
Merging the strengths of these two organisations has resulted in a winning combination of experience, expertise, innovation and efficient production methods.
In 2015, ZF extended its commitment to the global wind industry, when it acquired Bosch Rexroth’s wind power business. Headquartered in Belgium, ZF Wind Power is able to claim a truly global footprint with a manufacturing presence in Europe, China and India complemented with a global service organisation covering all key markets.
Relied upon by all major wind turbine producers supplying gear-driven machines, ZF Wind Power is a company that passionately shares the industry’s goal of reducing the cost of wind energy and meeting the growing demand for renewable energy.
The company is able to do so through continuous innovation and design of products that meet world-class quality standards, achieving global scale, strengthening quality and reliability, and combining broad customer solutions with strong service.
Its focus on cost-effective designs for onshore and offshore markets optimises lifetime cost.
The company has long-term close customer relationships founded on product development and serial supply and service agreements, resulting in a wide offer of solutions developed for the specifics of each turbine application. Through analytics-based services, the company leverages its expertise and product data to reduce the cost of wind energy, by increasing output, availability and turbine lifetime extension.
Its approach is to always provide extended validation processes ahead of commercialising new solutions. From its 40 years in the business, it has extensive expertise in design and manufacturing and the results speak for themselves: high quality products and efficient manufacturing processes make it the first choice for all major OEMs supplying gear-driven turbines, who have come to expect products available in multi-MW turbine sizes, with high torque density, power-to-weight ratios and low noise and vibration levels.
ZF Wind Power’s commitment to R&D and close collaboration with clients has enabled the company to anticipate new market demands.
The ‘SHIFT’ concept, launched by ZF Wind Power in 2017, is a modular platform, allowing wind turbine manufacturers to reduce the cost of wind energy significantly. As a reaction to the ever-developing market, investing in digitalisation allows ZF Wind Power to provide a truly global full-service approach, through digital birth certificates, constant gearbox monitoring via the cloud and analytics-based servicing to optimise spare parts provision, maximise turbine lifetime and reduce time to market.
Four decades of gearbox innovation, provided by a trusted company with a global footprint and established manufacturing capacity, ensures ZF Wind Power will be a true partner as the wind industry grows and evolves to transform the global energy system over the next 40 years.

Stepping up a gear in the wind industry

Turbine original equipment manufacturers (OEMs) must deliver machines able to achieve optimal output and performance across a widening range of wind environments and regimes. ZF Wind Power’s solution is a combination of advanced technologies, consolidated in the SHIFT gearbox platform that provides the ability to mix and match components to meet the requirements of different projects.

1. Advanced gearbox solutions

Increasing torque density
To reduce the €/kNm, ZF is evaluating approaches to increase gearbox torque density, enabling it to develop gearbox solutions for higher torque levels, for turbines with increasing rotor diameters, while maintaining the same outer dimensions. In order to increase overall gearbox loadability within given outer dimensions, measures have to be taken on different components, including loadability of bearings – either roller or plain bearings – gears, as well as castings and connections. Results so far show an improvement in torque density from 105Nm/kg in classic designs up to 175Nm/kg in the most recent SHIFT 6k platform.

Plain bearings
The potential of a plain bearing solution can be seen in terms of torque density increase. Plain bearings require less space than roller bearings – typically their outer diameter is much smaller than the roller bearing. Of course, replacing a core gearbox technology by one that is new to the wind market requires an extensive technology release trajectory to build-up track record. In the development trajectory ZF has selected and tested plain bearing designs and materials for different positions in the gearbox, both in test rig (see pic) as well as field conditions. Based on positive field test results, ZF considers plain bearing technology to have reached the required Technology Readiness Level for serial production.

Tonal noise mitigation
Wind turbine noise reduction has become a key differentiator, since lower noise levels allow for more wind turbines being installed on the same site without exceeding regulated limits. ZF invests considerable effort to avoid tonal noise. Accurate simulation and measurement of gear excitation is the first step in the optimisation process. However, it should be recognised that there is a major dynamic interaction between the drive train and other wind turbine components. As such, ZF has concentrated on standardisation of its tonality handling process, by cooperating closely with the turbine OEM from the early design phase up to rig and field testing.

Robust bearing solutions
ZF has extensively researched the White Etching Crack failure mode. Based on a broad test program with extensive parameter variation, root causes have been analysed and counter-measures defined. Several counter-measures were implemented in cooperation with bearing suppliers to avoid white etching cracks in wind turbine gearboxes.

2. Advanced drivetrain solutions

In order to keep pace with the trend towards increasing rotor diameters within existing volume of control, ZF is extending the torque density increase efforts from the gearbox level towards the drive train level. By comparing different drive train concepts and architectures, ZF aims to offer optimum solutions in terms of cost (€/kNm), overall dimension (mm/kNm) and weight (kg/kNm), both for onshore and offshore applications.

3. Smart systems

ZF’s approach towards ‘intelligent mechanical systems’ is to use as-built gearbox information, such as configuration, component traceability and design models, in combination with real-performance data from turbines installed in wind farms. The dataset is processed to enable remote self-diagnostics and alerts based recommendations. This supports optimisation of maintenance schedules, reduces operational expenditure and increases turbine availability.

Moving up a gear: SHIFT 6k
SHIFT 6K incorporates ZF’s new generation of high-torque density gearboxes, developed for onshore and offshore wind turbines. This gearbox platform powers new generation wind turbines from 4.5MW up to 7MW, with rotor diameters up to 180m. This covers a torque range of 5500-7300kNm up to a maximum ratio of 195. SHIFT 6K serial production is planned for summer 2020.

The role of digitalisation in driving gearbox operation efficiencies

ZF Wind Power’s state-of-the-art digital analytics system is backed by the company’s 40 years of experience in gearbox manufacture and servicing.

‘Digitalisation’ is a watchword in renewable energy generation, as well as most industries with operational infrastructure, plants and assets. It describes several things happening. First is the gathering of information, sometimes from several disparate sources, such as supervisory data control and acquisition (SCADA), as well as historic servicing records, in the context of an operational wind farm. Then, the information is analysed and insights shared within an organisation, to optimise processes, increase efficiencies and derive cost savings. In this context the driver for digitalisation for wind turbine gearboxes is the same.
Wind turbines should run at an optimal level to harvest as much energy as possible. Disruption from servicing, routine or unplanned, should be kept to a minimum and outside times when the wind resource is available. As turbines are mechanical, fatigue and physical wear in components is normal. Preventative maintenance can address these issues before they become serious, allowing for inspections and mitigating actions to be scheduled based on the condition of components. But when components fail, these need to be repaired or replaced as soon as possible to minimise downtime. Gearboxes are critical components within turbines.
To help its customers optimise the availability of their wind turbines, ZF Wind Power is leading the implementation of digital solutions, powered by state-of-the-art analytics and machine learning across both operational and historical data.
In combination with expertise from manufacturing and servicing gearboxes for 40 years, ZF Wind Power is able to provide a powerful digital offering to the industry. As a gearbox manufacturer, ZF Wind Power holds a range of useful and critical information needed to perform qualitative gearbox servicing. Up-to-date gearbox documentation, such as technical manuals and spare-parts lists, are available in a convenient downloadable format. In case of a gearbox breakdown, service crews can rely on qualitative information at their fingertips to direct the most appropriate course of action.

Insight from 40 years’ experience
Innovations both in hardware, namely sensors, as well as software, such as advanced analytics and cloud computing, mean it is possible for operators to gain access to deep insight into how assets in the field are performing, no matter what their location and in real-time. Similar technological advances allow data from a gearbox to be collected and analysed remotely. ZF is able to use its extensive expertise in designing and manufacturing gearboxes to interpret a gearbox’s performance data, via SCADA systems, to calculate the consumed lifetime of each individual component.

Efficient stock inventory management
Combining consumed and remaining lifetime analysis with ZF’s gearbox expertise provides the operator with a highly reliable spare-parts recommendation, backed up by a comprehensive report identifying which specific parts are needed for each gearbox. When stocks need replenishing, the service contract guarantees fixed pricing for parts and an agreed lead time between ZF and the customer, so they know when it will arrive and can arrange the repair or replacement accordingly, minimising turbine downtime.

Alarm-based recommendations
Optimising spare-parts stock is only a part of the solution towards optimal turbine availability. ZF Wind Power’s digital dashboard captures information from condition-monitoring systems that measure different parameters, such as temperature and oil particles, and generate an alarm when threshold values are reached. After running these alarms through ZF’s analytics platform, recommendations can be made for service interventions to be planned accordingly, also taking into consideration the wind turbine’s optimal operating periods, ensuring servicing can take place at the least productive time.
Qualitative documentation, an optimal spare-parts inventory and recommendations based on live data from each gearbox in the fleet combine into a powerful digitalisation strategy, emphasising on ZF Wind Power’s role as a pioneer in the renewable energy market.

Providing a comprehensive service with a truly global reach

At ZF Wind Power, customer satisfaction with both products and services is a critical objective. It offers service solutions and options that cover the product life cycle, from development until the end of turbine life. Proximity to international customers is central to ZF’s ability to achieve a peerless level of service. It operates state-of-the-art factories, workshops and testing facilities in all key markets. It aims to make customers feel that a ZF technician is working by their side and a replacement component is easily available.

Up-tower repairs
ZF Wind Power’s up-tower solutions and field service offerings are a fundamental part of the aftermarket solutions offered to wind-farm asset owners, to help minimise a wind farm’s levelised cost of energy. Even when working on the development of wind-turbine generator drive-trains, ZF makes important decisions in terms of how it can improve servicing. A careful balance between capital and operational expenditure is a result of concepts integrated into the nacelle and gearbox designs that enhance component-servicing efficiency. Service Readiness is embedded into ZF’s Product Development Process when designing and developing mandatory up-tower solutions. A dedicated group of specialists from ZF and its OEM customers collaborate to engineer the right spare parts, tooling and working methods. The resulting combination of spare-parts kits, tools and skilled technicians ensures an up-tower solution to avoid the potentially high cost of full gearbox exchange.

Workshop repairs: the broadest repair programme, delivered globally
ZF’s main service capabilities are in Belgium, with a repair capability of 400 a year; the US; India; and China. Additionally, it works with partners to strengthen and support capabilities and capacities. Its multibrand service, upgrades, modernisation and differentiated repair levels are key.

Replacement units: fast delivery
ZF has a global pool of replacement units that its experts can access quickly, minimising asset downtime. The customer-specified pooling concept includes gearboxes for different manufacturers’ wind-turbines, all full-load tested; and conversion, inspection and periodical turning are included in the gearbox pool package.

Reliable spare parts availability
ZF Wind Power can combine consumed and remaining lifetime analysis with its network of gearbox expertise to provide wind-farm asset operators and owners with a highly reliable spare-parts recommendation. This is backed up by a comprehensive report identifying which parts are needed. This optimises the levelised cost of energy and means stock inventory is kept at a minimum.