But let's look at the lifetime extension process from the beginning. The traditional assessment and inspection process for extending turbine lifespan includes both practical and analytical components. Deutsche Windtechnik’s Inspection Body conducts the practical part; while the analytical part is carried out by our partner apera engineers (see illustration of the conventional lifetime extension process). The main limitation here is calculating the remaining service life in the analytical part: As a rule, we lack the necessary information to accurately calculate the remaining service life. For example, turbulence or controller behaviour can only be determined approximately. The bearing loads that can actually be borne are only roughly determined, and component reserves are often unknown. Consequently, we make conservative assumptions and counter uncertainties with safety margins. 

Optimising the lifetime extension assessment with LiTEplus  

The measuring system is designed to improve this conventional process. LiTEplus supplements the analytical component of lifetime extension assessments by seamlessly recording the turbine’s load history and monitoring critical structural parameters. The collected data is automatically analysed and enriched with SCADA data. Our partner apera engineers then adapts and validates the calculation model. (see illustration of measurement data-supported lifetime extension process). 

The technology behind LiTEplus 

Technically, the measuring system consists of several cantilever sensors (CLS for short) that continuously measure strains. Usually, only four sensors are installed at the base of the tower. The sensors feature a cantilever clamped on one side and a proximity sensor on the opposite side. Cantilever sensors measure the strain caused by loads and generate a signal comparable to electrical strain gauges. The inductive displacement measurement of the CLS offers advantages over strain gauges by preventing mechanical deformation of the sensor components, which results in long-term reproducibility of the measured values. 

The advantages of LiTEplus 

The main argument favoring installing the measurement system is its potential for lifetime extension and increasing the associated timeframe. Previous projects have achieved extensions of up to eight years for REpower MD77 turbines. Installing of LiTEplus brings further advantages:   

• It can be retrofitted at low cost  

• Minimal downtime through commissioning  

• Expensive requirements can possibly be avoided completely  

• Reducing technical risk by identifying highly stressed componentsContinuous monitoring of the load-bearing structure for safe operation  

• Interesting for systems that are already in lifetime extension 

Is it worth the effort? A practical example provides clarity.  

In 2021, we installed the measurement system at the Südergellersen wind farm on an NM72, 1.5 MW, built in 2001. Initially, Deutsche Windtechnik was commissioned to provide an expert opinion on lifetime extension with a simple load comparison. It turned out that this approach would only allow the turbine to continue operating for 0.4 years. The critical components were the main frame, tower, and blade root. The turbine's position directly behind another one in the main wind direction exposed it to greater air turbulence and tower vibrations. "Because the turbine had been running perfectly up to that point, we were unwilling to accept this result," said Arne Beecken, owner and proprietor of BAE Energieerzeugung GmbH & Co. The installation of LiTEplus measurement technology along with the updated overall assessment backed by data increased the lifetime extension to 6.5 years, especially for critical components. "The turbine continues to run reliably and without damage to the components that were initially considered critical. The cost incurred for the LiTEplus installation in 2021 has paid for itself over the last four years. We are very pleased that we can continue operating the turbine this way for as long as possible," Beecken said. 

Your path to LiTEplus  

Deutsche Windtechnik experts implement LiTEplus, which can be combined with a scheduled inspection to reduce costs. Bachmann Monitoring experts remotely operate the system, minimising turbine downtime. If data cannot be transferred via the park network, we can install LiTEplus with an optional integrated mobile router. Commissioning takes about half a day per turbine. The measurement campaign can last 6 anywhere between three to six months, depending on the location.  

Sounds like LiTEplus is for you? Get in touch!  

Leon Dübbelde 
Sales Manager  
+49 421 69105244 
sales-si@deutsche-windtechnik.com