The importance of maintaining proper lubrication of a wind turbine’s gears and bearings has long been understood. Unfortunately, the infrequency of lubricant sample collection along with inconsistencies in sampling procedures has meant that the current method has shortcomings. This may be about to change as several online continuous oil health monitoring devices have recently been released. ONYX reliability engineers became curious about the new technologies and launched a multi-phase research project to gain a deeper understanding of the new sensors and their potential benefit to the wind industry.
At ONYX’s upcoming 4th NA Annual Technical Symposium, Mechanical Engineer Jesse Graeter will share the knowledge we’ve gained with his presentation “Online oil sensor performance”.
In 2018 ONYX purchased a selection of oil quality sensors and tested them in the Castrol Laboratory in Pangbourne, UK. The lab test apparatus consisted of a steel vessel with oil temperature control, forced mixing, and automatic syringe drivers for introduction of test substances. Some of the tests performed were water ingress, increased acid content to simulate aging, additive dropout, and cross contamination with other oils. As a preview to the Symposium, we’ll discuss how an oil quality sensor can detect additive depletion.
Figure 1: The test bench setup for multiple oil quality sensors
Many of the wind turbine drivetrain gears and bearings operate in the thin-film lubrication regime thus relying on extreme pressure and anti-wear additives in the oil to prevent metal-to-metal damage. A key use of an oil quality sensor is to detect reductions in these additives thus enabling maintenance actions such as oil changeout or additive top off. Oil quality sensors utilize capacitance transducers to measure the permittivity of the oil. Permittivity is a material property (farad per meter) that quantifies the ability of a substance to store electrical energy. In our case the oil is the capacitor, or dielectric material. Lubricating oils typically have a relative permittivity (aka dielectric constant) between 2.0 to 3.0. The molecular composition of the base oil and it’s additives determines the conductivity and capacitive effect of the lubricant. As oils age and/or the additive concentration is reduced, the permittivity will drop. In lab testing we simulated additive depletion by slowly diluting the test oil with a base oil, while recording how the oil quality sensor responds with a reduction in the relative permittivity measurement. During the Symposium other oil health sensing technologies such as conductivity and relative humidity will be discussed in detail.
Figure 2: Comparison of oil permittivity readings for three oil types during additive depletion simulations
This fall the field testing will involve installation of multiple oil sensors side-by-side on 10 turbines consisting of 2 turbine OEMs, 3 gearbox models and 2 gear oil types. This research project is one of the most thorough independent tests in the industry. It utilizes multiple sensing types: basic chip detectors, advanced debris probes, conventional particle counters and oil quality sensors.
We look forward to sharing what we learn from the field testing and invite you to join our Technical Symposium to learn more on this subject throughout the 2.5 day event. To support the oil sensor discussion, we will cover the fundamentals and application of oil analysis during the “Pre-Symposium Training” on September 16th 2019.