Wind turbine gearbox oil change

In this article, we will discuss how wind turbine gearbox oil change is performed. Why has this particular matter drawn our attention? It is as simple as that. The wind power industry develops rapidly as evidenced by an annual increase in the required power of wind turbines.

Wind energy is relatively inexpensive, environmentally friendly, and renewable. Therefore, its growth trend will persist at least in the near future. However, with discernible advantages, maintenance of wind turbines remains a time-consuming process. GlobeCore produces green energy equipment, including the wind turbine maintenance units. Using this equipment, green energy maintenance becomes fast and convenient.

Repair and maintenance of wind turbines

In addition to time, maintenance and repair of wind turbines also require great financial expenses. For example, in the case of offshore wind farms, wind turbine maintenance ranks first among expense items and accounts for an average of 28% of all cash expenses.

Repairs and maintenance of wind turbines can be of planned and emergency types. Planned wind turbine service maintenance is carried out twice a year. The specific months of carrying it out depend on the particular climatic conditions at the operational location of a wind farm. At least, two technicians are required for planned maintenance.

High-quality wind turbine servicing includes the following main operations:

• checking the status of wind turbine components and mechanisms;
• elimination of cracks and сhips on the blades;
• checking the presence of corrosion and the condition of ropes, if the use of ropes is provided to increase the wind turbine stability;
• diagnostic evaluation of safety systems;
• checking the status of emergency stop system;
• flushing and cleaning the wind turbine;
• diagnostic evaluation of battery and gearbox status;
• monitoring the oil level in the wind turbine gearbox.

Let us dwell on the matters related to gearbox maintenance, because it is the gearbox that largely determines the operational reliability of the entire wind turbine.

Why is a gearbox one of the most vulnerable components of a wind turbine?

A gearbox is used in wind turbines in order to match the rotation speeds of blades and a generator shaft. The wind turbine blades rotate at a relatively low speed, while much higher revolutions are required in order to rotate the generator shaft. These revolutions are ensured by the gearbox.

Large vibrations in the gearbox cause abrasion, wear, and destruction of bearings which, in turn, may entail accidents, expensive repairs, and long downtime of the wind turbine.

In order to reduce friction, a special transmission oil (mineral or synthetic) is used in the gearboxes. An oil film forms on the gears, separates the mating surfaces, and protects the gearing against pitting, micropitting, and wear.

The problem is that as operation progresses, the transmission oil condition gradually deteriorates due to an increase in water content, ingress of metal particles, exposure to high temperatures, etc.

Effect of water on transmission oil properties

One of the most dangerous enemies of transmission oil is water. It gets into the gearbox through the leaking seals of air valves or the holes that have not been properly sealed. Some wind turbines operate at ambient temperature fluctuations which creates moisture condensation inside the gearbox when the hatches and lids are open.

The effect of water on transmission oil and gearbox varies greatly and is expressed in:

• sedimentation of additives;
• oil oxidation;
• oil film deterioration;
• seals hardening and paint flaking;
• rust formation, etc.

 Problem of wind turbine gearbox oil change

The main problems faced by service teams include long oil change time and labor intensity of this process, as well as oil change at high altitudes.

In general, the wind turbine gearbox oil change process can be described as follows:

1. Lifting the technician to the tower together with ropes to subsequently lift the drain hose.
2. Draining the oil from the gearbox using a drain hose. The draining process is lengthy, because depending on the gearbox, the volume of oil may range from several tens to several hundreds of liters.
3. After draining, the filling hose is lifted, and the oil is pumped into the gearbox. Two technicians must be involved here.
4. Lowering the oil filling hose, the related tools and equipment.

How often the oil should be changed in the wind turbine gearbox

The frequency of wind turbine gearbox oil change is determined by the type of oil and lubrication system. The current condition of oil estimated by testing the samples and determining the viscosity, the water content, the acid number, the solids content, and the depletion degree of additives are taken into consideration as well. On average, the wind turbine gear box oil is changed every one to two years.

Automatic wind turbine gearbox oil change equipment

GlobeCore has developed special wind turbine equipment by means of which a three-stage oil change is performed in the gearbox (draining the old oil, flushing the gearbox, and filling it with new oil). This is a mobile oil change unit of CMM-G and CMM-GL types. These units ensure prompt maintenance of the wind turbine oil system and can work with gearboxes from different manufacturers.

The equipment is mounted on a trailer (single-axle — for CMM-GL and two-axle — for CMM-G) and transported by a vehicle of the service team that performs maintenance of wind power plants. Therefore, it is possible to ensure oil change at great distances.

The platform has a booth with ergonomically located doors which is divided into functional zones (machine zone, control zone, zone for storage of spare parts and tools). There are also two reels of hoses. The reels are equipped with geared motors to facilitate and increase the capacity of unreeling and reeling the hoses. The length of hoses may vary from 40 to 230 meters depending on the wind turbine mast height.

CMM-GL is a more compact unit with a lower power requirement. In turn, CMM-G unit has several additional features:

• own tanks for collecting the waste oil, as well as for transporting the clean oil (250 gallons each);
• self-contained operation due to a gasoline generator;
• heating the clean oil before the unit arrives at the wind turbine which allows reducing its viscosity and increasing the capacity of pumping it into the gearbox;
• flushing the gearbox with flushing oil.

In terms of time, the entire process of wind turbine gearbox oil change takes from 2 to 4 hours between starting to prepare the workplace and putting the wind power unit into operation, instead of 7–8 hours required for manual oil change.

Summing it up, we note that the use of special equipment while changing the transmission oil in wind turbine gearboxes makes it possible to obtain the following additional advantages:

• self-contained operation during oil change;
• oil change rate, quick change, efficient change;
• minimum amount of spilled oil and minimum contact of clean oil with the environment;
• within one work shift, the oil can be changed at least in two wind turbines;
• possibility to monitor the volumes of changed oil;
• minimum wind turbine downtime in the electricity generation cycle

Furthermore, using CMM-G units, industrial oil change (not at height) and oil change in places of difficult access can be performed.