INNOVATION & NEW TECHNOLOGY FEATURE
Although the basis of the service is straightforward, the implementation is unique, providing facilities unavailable elsewhere in the UK and enabling significantly faster turnaround times than available from original equipment manufacturers situated elsewhere in Europe. The Nottingham site for example boasts the only purpose-built wind turbine
gearbox validation test rig in the UK and the only one in the ZF Group outside of its wind turbine headquarters in Dortmund.
OVERHAUL PROCESS During disassembly, the condition of each internal component is inspected and recorded. Failure mode and cause are noted where applicable, helping to minimise the risk of repeat or premature failure. During overhaul, bearings and seals are replaced with OE parts. Gears, shafts, and bores are measured against OE drawings to assess whether components are within tolerance and can be safely re- used, or require specialist refurbishment or replacement. To save cost and time, damaged gears within tolerance can often be reground using the latest CNC technology and machinery, but where this is not possible they are replaced with OE quality gears. Similarly, bores and shafts can be brought back within specification using proven and accepted recovery techniques.
UNIQUE TEST FACILITY Every wind turbine gearbox overhauled at ZF Services UK undergoes a rigorous test procedure of around eight hours’ duration before release to the customer. This is achieved using a unique, purpose- built validation rig designed for partial load testing of gearboxes from turbines of up to approximately 2.5 megawatts generating capacity. Capable of delivering more than 64,000 Nm torque, the test rig applies a load through the gearbox via a slave gearbox and output motor. Adjustable drive and load motors are used to cope with the variation in height and width of different gearboxes.
The equipment can analyse oil flow and pressure, gearbox temperature, tooth contact pattern, and noise and vibration profiles, and thermal imaging is used to ensure that there are no local hot spots in the gearbox. Current draw, temperature, vibration and torque figures are recorded on the test rig’s human-machine interface (HMI) panel, with a data logging frequency of at least 10 Hz.
SCOPE OF ACTIVITIES To date, the smallest gearbox serviced in the ZF Services UK wind turbine overhaul facility is three tonnes in weight and the largest 11.5 tonnes, but the lifting gear and test rig are capable of handling gearboxes of up to 30 tonnes. Maintenance and repair of gearboxes can include items such as brakes, oil coolers, torque arms, rotor shaft repairs, gear analysis using video endoscopy, vibration/ oil analysis and equipment updates.
Gears and shafts beyond the limits for safe recovery are replaced by OE standard components meeting the rigorous standards demanded by the wind turbine industry. In instances where parts are obsolete or prove hard to obtain, ZF Services UK’s specialist suppliers are capable of reverse engineering these to OE standards.
UPDATES AND UPGRADES ZF Services has access to the latest OE upgrade information, and through its central wind turbine gearbox design and development facility can also offer bespoke solutions to gearbox problems. These services include updating gearboxes to the latest design standards, upgrading lubrication systems, and reprofiling gear teeth to ensure optimum efficiency and increased component longevity.
VITAL CHECKS Wind turbine gearbox bearings may fail prematurely if not correctly installed, so particular attention is given to monitoring that all bearings are precisely set and not preloaded. Cleanliness of the gearbox oil is another critical factor in component longevity. The oil filtering unit checks for correct oil flow and filters oil down to at least 14/11 cleanliness code as defined by the ISO4406:1999 standard, ensuring that the gearbox is free of any particulate contaminants prior to despatch.
FUTURE ENHANCEMENTS The ZF Services UK wind turbine gearbox overhaul facility will shortly have a fully- automated data logging system in place to collect all data and enhance the productivity of the overhaul validation test rig.
ZF Services UK
www.zf.com/uk
e = See enhanced entry online
www.windenergynetwork.co.uk
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