Up-tower cylinder maintenance on Vestas V126 at EnBW Fichtenau

Background

After six years of operation, several Vestas V126 turbines at EnBW’s Fichtenau wind farm in Germany began to show signs of degradation in the hydraulic pitch system.
The original pitch cylinders started leaking hydraulic oil into the hub, increasing the risk of contamination.

Early warning signs were detected through oil analysis.
Increasing chromium levels in the hydraulic oil, typically starting in the range of 2–4 ppm, indicated surface wear on the cylinder rod. When dismantled, the rod showed visible colour change in the short-stroke area, confirming surface degradation.
Additional indicators included blocking of in-line filters, caused by extruded sealing material entering the oil system.

“We have started to suffer from leaking cylinders and high chromium levels, and we wanted to stop this before the hub was covered in oil”, tells @Philip Waczowicz, Work Preparer at EnBW.

The challenge

Hydraulic oil leaking into the hub can dilute the blade-bearing grease.
A reduction in grease viscosity increases wear and, in the worst case, can lead to catastrophic blade-bearing failure.

At the same time, the Fichtenau wind farm had moved out of OEM service.
This required EnBW to strengthen its in-house capability and take responsibility for planning and executing preventive maintenance on the pitch system.

“Our wind park is now out of OEM service and therefore we need to upgrade our know-how on optimized maintenance. With UWF, we are now training the site teams and our maintenance engineers to drive, plan and perform the up-tower maintenance in the future”, says Philip Waczowicz.

Initial assesment

The observed wear pattern followed a clear and repeatable trend.
Chromium was released from the cylinder rod due to surface degradation, and sealing material entered the hydraulic system as wear progressed.Rather than waiting for full cylinder replacement, EnBW chose an up-tower repair strategy aimed at addressing the root cause while limiting downtime, risk and hub exposure.

Technical approach

An up-tower repair solution (CIM 3846) was applied, where the internal components of the existing cylinder were exchanged with LJM parts.
The solution allowed the cylinder to be repaired in the hub without removing it from the turbine.

The repair kit reduces installation time, HSE risk and CO₂ emissions, while maintaining product quality.
The mechanical lifetime of a repaired cylinder corresponds to that of a new LJM cylinder.

As part of the intervention, the hydraulic oil system was flushed to remove contamination and stabilise operating conditions.

Execution

Kristian Vissing, United Wind training manager, visited the site and trained local technicians directly in the hub.
Training focused on up-tower handling and repair, using OEM-approved repair kits, the OEM lifting bag, and special tools designed for the V112, V117 and V126 platforms.

During the visit, the first V126 turbine was repaired using three original OEM cylinder repair kits.
All spare parts, tools and lifting equipment were prepared for HSE-approved handling and approved by Vestas.With the established setup, the team is now able to repair up to two cylinders per day, depending on site conditions.

Results

The intervention stabilised the hydraulic system and reduced the risk of oil contamination inside the hub.
At the same time, EnBW established readiness to perform preventive up-tower cylinder maintenance using its own technicians.

Maintenance can now be planned and executed proactively, rather than being driven by leakage events.

Closing

The solution applied at Fichtenau was developed together with LJM.
It reflects an approach where preventive maintenance and knowledge transfer support long-term turbine operation.