New ways to monitor and maintain turbine oil

Olli Rantanen, Heavy Duty Lube and Filtration, Parker Hannifin Corp., Urjala, Finland
parker.com
Maintaining lubricating and hydraulic oil once meant changing it on a set timetable. More recently, it makes sense to keep it as clean as possible, let the oil tell when it needs changing, and let it tell how equipment in the nacelle is performing.

Filters on wind turbine hydraulic systems are essential for removing contaminants from fluids, the primary cause of failure in lubricated and hydraulic equipment. Such failures lose revenue and increase maintenance and associated costs. Worse yet, failures lessen the confidence buyers might have had in a particular machine or manufacturer.
There is a solution to the problem in innovative devices, such as magnetic pre-filtration, which increases the lifetime of hydraulic filters up to 40%. Further development in the use of patented media and element design have seen life of filter elements go from a nominal 3 to 6 months up to 15 months – a significant increase and reduction in maintenance costs for turbine owners. What’s more, the later figure is not a limit. Recent developments will increase the level of reliability of lubrication systems even further.

More complete assemblies
In the recent past, wind turbine OEMs built fluid filtration systems by assembling components not all from the same manufacturer. While such systems worked reasonably well, hydraulic-component companies are now designing complete lubrication-oil systems for the gearboxes of wind turbines. These systems include filters, pumps, valves, coolers, and heaters as well as manifolds and piping to connect components. The advantage is that the assemblies are more thoroughly tested and proven and carry the assurance of reliability from a qualified supplier.

With regards to filtration systems, another emerging design philosophy is to integrate functions and components in a manifold block rather than piping the components individually. Manifolds minimize leak points, reduce assembly time, and provide a more compact, lighter, and reliable unit.
For OEMs that must buy subsystems, another emerging industry trend will assist by providing turbine-specific 3D-models of the hydraulic equipment which can be imported directly into the 3D-CAD-gearbox models or some preferred location in the CAD model of a nacelle. This lets the hydraulic supplier take responsibility for the system and saves the OEMs significant time to accelerate product to market, money, and resources. Further, streamlining the supply chain ensures prompt delivery of consumables and service parts around the globe via a synchronized logistics network.

At least one new filter element designed for wind turbines to ensure sufficient and effective filtration levels and prevent the filter from going into bypass mode, even during cold starts. Also, an integrated offline filter with water removal capabilities secures the best possible conditions of the oil used in these demanding applications. Existing systems on turbines can be upgraded with these new capabilities.

An eye on oil
Oil condition monitoring is gaining favor because turbines are often perched 60 m off the ground and more, making access inconvenient. Some companies maintain condition monitoring centers to manufacture and supply particle counters and detectors as well as moisture sensors, additional indicators of oil cleanliness. One recent oil condition monitoring tool, the iCount Particle Detector (IPD), is a laser-based device intended for monitoring high viscosity fluids. It continuously measures solid contamination levels in the lube oil using laser and light-obscuration principles.

This compact unit qualifies for ATEX ZONE II (meaning it can be assigned to explosive environments ¬ ATmosphere EXplodable or ATEX ¬ in particular locations other than mines and combustible vapors). It can be built into a hydraulic system, such as a lube or power-transmission circuit, and provide end users a real-time look at the solid contamination levels in accordance with ISO cleanliness codes. Users can set limits for the three channel sizes, such as 4µ, 6µ, and 14µ, based on system requirements and their components. Three communication channels then transmit the counts to ground based monitors. The particle detector also has the option for an integral moisture sensor all of which are set up through utility software supplied with the device.

The particle-detector unit includes a small hydraulic pump, pipe work, connectors, check valves, and a soft-start

module, which control oil flow and pressure. A drawback on conventional systems of this sort is that they spot air bubbles in the oil, the result of splash feed lubrication, and identify them as contaminants. That generates spurious results. As such, bubbles must be suppressed before they reach the IPD. To do so, the IPD cleverly raises the oil pressure in the monitoring system in excess of 100 bar which compresses the air bubbles below the unit’s detectable limit so they are not mistaken as debris

The unit typically mounts on the gearbox outlet before the oil pump so it can detect increases in debris from the gears. The use of particle counters in hydraulic systems from oils to fuels is growing as the realization and understanding of the effects of nonvisible debris is factored into component service lives.

It should be noted that traditional wear debris sensors are limited to the size of the particle they can detect, somewhere in the region of 100µ or larger. The IPD, however, measures down to 4µ and so provides an earlier warning of wear and potential component failure than conventional methods.

Another advantage of the particle detector and counter is that it can measure nonferrous particles which are just as dangerous as ferrous ones and in some cases more so. For instance, a turbine operating in a dusty environment may have airborne contamination drawn into the gearbox via the breather. Hard and abrasive silica, more commonly known as sand, is among these contaminants. While wear-metal sensors would not be able to monitor silica, the recent particle detector ensures these are spotted and results transmitted to the turbine control unit. A few systems also come with an optional

integrated moisture sensor that allows monitoring the gradual increase of dissolved water without requiring a separate or stand-alone device. Signals from the detectors can then easily be incorporated into an existing monitoring system or in a stand-alone version.

These recent ideas in oil monitoring allow minimizing or eliminating the use of bottle sampling. Results then become available in real time, instead of waiting days for lab results. This also allows planning the preventative maintenance for turbines, thus reducing downtime and cost of maintenance significantly. WPE