How do you change the oil on an operational wind turbine? This is a rather niche question, even for engineers well-versed in all-things renewable. The answer, it turns out, involves several steps – perhaps the most important being to “ask an expert”.
Renewable Oil Services (ROS)
One key expert in this sector is Renewable Oil Services (ROS), which is a leading supplier of oil products and oil exchange services to the wind turbine industry, covering both the onshore and offshore wind markets. The company has been carrying out gearbox and hydraulic oil exchanges on wind turbines across the UK and Ireland with the use of its specialised oil pump trucks for over 12 years. Back in 2013 it was the first company worldwide to carry out a vessel-mounted combined gear and hydraulic oil exchange on an offshore wind turbine using its specially designed and manufactured vessel-mounted pumping system.
The specialised trucks and offshore units are fully bunded and have an in-house developed oil heating, filtration and pumping system that allows the new gear oil products to be pre-filtered and heated to between 40⁰C and 55⁰C, which is for ease of pumping the viscous 320ct gear oil products up the 180m hoses to the wind turbine nacelle and into the gearbox. With the truck or vessel in place at the base of the turbine, ROS’s engineers start with winching their hoses up to the nacelle; from there they connect the waste oil hose and pumping system to the gearbox drain point or points and drain the full system of the old oil.
The Four Procedures In Oil Exchange
The next steps to be taken depend on any oil sample results that show the contamination level of the gearbox oil, which will determine the level of system flushing required. There are four basic ‘levels’ of procedures that are followed.
Level 1 is a basic oil exchange with no flushing required, where a routine oil exchange is taking place with no or minimal contaminates currently found within the oil sample.
Level 2 is an oil exchange with single flush: this is if low to moderate levels of contaminates are found in the oil sample. For this, a pre-defined system volume quantity of oil is used and this quantity will vary depending on the turbine and gearbox type.
The new oil is pumped up to the gearbox via a closed system. The reason for carrying this out in a closed system is so as not to open the gearbox lid, as this one of the main points of contaminates being introduced into the gearbox itself. To achieve this closed system oil exchange the company uses specialised fittings to connect to the gearbox, keeping the gearbox lid sealed and contaminate free.
The oil enters the gearbox at between 40⁰C to 50⁰C to allow the operation of any internal system thermostats to open fully, allowing the flow of oil to pass through all of the gearbox auxiliary systems freely (oil coolers, filter blocks, etc.). The oil is then circulated and flushed through the gearbox and ancillary systems with the use of the gearbox’s own internal or external gear oil pump for a set time period. Once complete, the flush oil is then drained from the gearbox via the sump drain point as before.
Level 3 is an oil exchange with double flush. This is if moderate to high levels of contaminates are found in the oil sample or if a change of product type was taking place. The procedure for this would be exactly the same as the Level 2, only carried out in its entirety twice as two full flushes.
Level 4 is an oil exchange with full invasive system flushing. This is where extremely high levels of contaminates or sludge are found in the oil sample. If this is the case it may be required for a high-viscosity gear oil detergent to be put into the gearbox several days prior to the oil exchange taking place to break down any heavy sludge or contaminate build up within the gearbox and associated systems.
The procedure would require some gearbox pipework disassembly then a full individual component system flushing of coolers, filter blocks and all associated pipework to ensure all contaminates are removed from each of the individual parts of the system. ROS recommends that the inline filter should be replaced during this flushing procedure to capture additional contaminates during the flushing.
Opening of the gearbox lid will also be required to carry out internal gearbox rinsing of the surfaces with pressurised hot oil to ensure any build-up of sludge in the gearbox casing surfaces. Webbings and ledges are rinsed down into the sump for removal and pumped out via the drain point as before.
Once this is completed the systems are reassembled and lid placed back onto the gearbox in preparation for full closed system flushing (the same as the Level 2 flush) to ensure all residuals and any introduced contaminates with having the systems and lid opened are fully flushed out.
Once the emptying of the gearbox has taken place, along with any flushing required, the filters are replaced with new units and then the gearbox and associated systems are refilled with new clean oil to the specified levels. This is conducted via a pump and hose system, again filling the gearbox via a closed system to ensure the new oil pumped directly into the gearbox is contaminate free.
Suitable For Hydraulic Systems
These procedures and principles for the gear oil exchange are also applicable for the wind turbine hydraulic system and can be carried out on the turbine at the same time as the gearbox oil exchange to reduce the turbine downtime.
Recently ROS has been approached by several companies from other industrial and marine sectors to bring its oil exchange expertise to these industries for machinery and system oil exchanges, which they are now looking to develop over the coming months.
Barry Sutherland i9s managing director of Renewable Oil Services