Wind turbine gearbox: varnish figure from 57.1 to 3.2 in 120 days

The operator runs 117 GE 1.5MW wind turbines and changed the gear oil roughly every four years. Changing from one oil type to another also required the gearbox to be flushed. The question was whether the oil could be kept clean enough to stay in the gearbox longer.

Four turbines at two sites, 15 and 16 years old, were fitted with Delta Xero units on 18 August 2022. The oil was drawn from the gearbox drain plug, through the cartridge and back. The first set of cartridges was full of sludge after 60 days, where the cartridges are normally changed after 12 months or more.

After 120 days the varnish potential (MPC) had fallen from 57.1 to 3.2, and the water content from 87 to 61 ppm. Viscosity and additives such as molybdenum, calcium and phosphorus stayed at much the same level as before, so the cleaning removed the contamination without taking the additives with it.

The particle count did not improve noticeably during the trial, which the manufacturer itself states in the report. The figures come from the manufacturer’s trial report; the laboratory is not named.