Periodic monitoring of all the turbines at a wind farm is recommended every two or four years. This provides a client with a thorough review of each turbine’s technical condition – information that can be useful in improving performance or obtaining...

By Ritesh Gupta

Let’s set the scene. You either own or operate a wind farm and you are analysing the efficacy of its end-of-warranty (EOW) handover strategy plan. You eventually discover that the wind farm operating profits have dropped or are tapering off. The main reason behind this? The inability to chart out a cost-optimised transition from the warranty to the post warranty period.

The burden and wariness of unexpected costs linked to any turbine component’s post warranty period will eventually be felt by every wind farm owner and operator. These looming feelings of uncertainty are probably most strong as they take over the operations and maintenance responsibility of any project.

Owners/ operators cannot afford any slip up in their understanding of the condition of the wind turbine sub-components at end of warranty (EOW), says Jeremy Parkes, Service Line Leader, Asset Operation & Management, Renewables Advisory, DNV GL – Energy.

“This information [at EOW inspections] can support identification and reporting of serial claims and component failures which can be fixed under warranty. If these are not fixed, then when the warranty expires the owner will be responsible for the costs,” says Parkes.

He adds that for major components these costs could be significantly high.

Without a provision of EOW inspections in contract, there could be a tendency to delay the replacement and rectification of ‘almost failing’ components towards the EOW so that the responsibilities and cost are shifted to owners.

Impact on profitability

EOW inspections need to be spot on as this aspect is being linked to profitability. As Fernando Valldeperes, Services Sales and Marketing Director, Gamesa points out, the long term profitability is linked to the continuous improvement strategies of the servicer and of the turbines’ upgrades. Owners should then select the O&M supplier with the necessary operational experience and technological capability to make the turbines more reliable and easy to maintain.

“This not only improves availability, but also reduces fatigue loads, making possible their operation far beyond the original design life,” says Valldeperes.

Inspection campaigns

Adopting a methodical approach from the outset will help align your plant’s overall performance and inspection campaign. Parkes says during the inspection period the team should focus primarily on three areas of concern: 1) warrantable claims; 2) safety; and 3) maintenance practices.

“These three elements play a very important role in managing possible negative impacts on a wind project from an operation's perspective,” he says.

The first element, warrantable claims, is the most obvious, as identifying component failures prior to the transfer of responsibility from the OEM to the site owner/ operator, will have a very direct impact on reducing unscheduled repair costs during the initial post-warranty period, and will provide an assessment of component issues that can affect overall turbine availability and help define realistic O&M budget expectations.

“Through a SCADA based condition monitoring, two-third of failures can be detected in advance and majority of failures can be detected between four to twelve months in advance,” says Parkes.

The second element, safety, highlights issues that may not be as obvious, but can have a significant impact in employee health and safety, and general project operations.

The third element, maintenance practices, assesses the overall effectiveness of the maintenance plans applied at the site, and may issue recommendations for improved maintenance strategies, or implementation of monitoring systems that could improve project availability.

Martin Molzen, Senior Director, Business, Service, Logistics, LM Wind Power says there are two main requirements which are crucial to ensuring the long term reliability and performance of the wind turbine components.

The first is the correct operation of the wind turbine, which ensures minimum loads on the parts and a consistent high output. Furthermore, inspections at regular intervals need to be in place to spot potential maintenance issues upfront.

“Regular inspections quickly pay off as they ensure minor issues do not develop into more serious ones that require more time and turbine downtime to fix,” says Molzen.

Components

From a manufacturer’s perspective, Gamesa maintains more than 70% of its installed base and includes in its quality process a proactive follow up of any possible premature failure. The team tries as much as possible to replace failing parts with reconditioned ones, says Valldeperes.

There is great focus on certain major components, such as gearboxes, blades, generators, main bearings, and towers.

“(This) is due in large part to the high cost value and long lead-time of replacing any of these components,” says Parkes.

He adds, “However, other sub-components more commonly suffer early wear and tear, such as HV cables, yaw motors, couplers, slip-rings, or accumulators, yet the replacement cost for these components and the downtime associated with their failure is significantly lower.”

Often, sites will continue monitoring issues that may have been observed during EOW inspections at an early stage, to identify wear trends and learn to better predict failure timelines. The “condition based maintenance” and in regular checks by the operator is the successful way to reliability, explains Parkes.

Onshore vs. offshore

Parkes says in offshore, the monitoring of wind turbines is much better and detailed and every job logged on a turbine requires the best preparation by experts for not just the related technology, but the logistics of getting the technicians, vessels, tools and components out to sea and on-site.

“Having in mind that about 30-50% of the work time is for the task itself – the rest is taken up by preparation, transfer and waiting time – the professional operation of an offshore wind farm begins with preventing unforeseen events and a well-structured lessons-learned-process,” explains Parkes.

He says due to the nature of offshore access logistics, there’s a greater push towards the implementation of condition based maintenance strategies and remote sensing, or troubleshooting applications. The lessons learned from this approach, may in turn impact how the team approaches maintenance onshore in the future.

Proper assessment

Clearly a lack of proper understanding of the issues affecting a site can have terrible consequences. There is a high economic cost to the replacement of failed major components, or serial issues that may go undiagnosed.

A proper assessment of the concerns present at the site, can help effectively budget as needed, procure replacement parts in advance, schedule repairs and resources at a favourable time, implement a maintenance strategy that can combat existing concerns, and generally improve the management of the challenges that may arise.