Slitevind owns 29 wind turbines in Sweden where 18 is on the island Gotland in Sweden. Ten wind turbines are located in the park Smöjen in the north part of the island. Smöjen consists of four Vestas V66 (1,5 MW), four Vestas V47 (0,66 MW), and two Enercon 0,5 MW.

The Vestas V66 was built in 1999, and the warranty period ended during 2004. Anders Gahne (owner and technician) wanted to install a system that could prevent the high cost of replacement of damaged gears in the wind park. The first SPM monitoring system was installed in mill nr 1504 (Vestas V66). The system VCM20 measuring the running condition on the main shaft, gearbox, and the generators with SPM Spectrum online and vibration measurements with EVAM.

The first indication showed a reduced condition in the bearing located on the output shaft from the gear to the main generator after a few months. The indication was increased values for the symptom BPFI (inner ring). Later on, the values increased even more and during a period with strong wind and high production, the values showed really high peaks (see diagram).

Almost a year after the first installation of the SPM monitoring system, the service team from Vestas opened the high-speed end of the gearbox and replaced the damaged bearing and also the bearings at the rotor end of the shaft. All work was done on-site. The bearing showed a broken inner ring and some metal pieces had contaminated the oil that needed to be replaced as well.

The total cost for the repair was 10% of what the cost would have been to replace the gearbox. Three more V66 wind turbines in Smöjen got VCM system from SPM installed.

Measuring points:

• Shock pulse transducers at main shaft bearings.
• Shock pulse and vibration transducers on the gearbox.
• Shock pulse on the main generator.
• Shock pulse on the secondary generator.
• Vibration on a cooling fan for the main generator.