Diagnosing Gears in Wind Turbines
Monitoring the Gears of Your Wind Turbine
Given the significant expansion of wind turbine installations in Brazil and around the world, challenges related to the operation and maintenance (O&M) of these assets are growing each day. Wind farms have hundreds of wind turbines, spare parts logistics are complex, their acquisition costs are high, and turbine unavailability is a recurring issue. In light of these obstacles, routines and systems that aid in O&M processes are essential.
In this context, one of the key components present in wind turbines with a traditional powertrain, featuring a gearbox, is their gears. They primarily serve to increase the inherently low rotational speed of the main rotor of a wind turbine.
Hence, monitoring the vibrations of these components is crucial to ensure their proper operational condition. This technology enables early diagnosis of bearing defects by identifying abnormal vibrational characteristics. As a result, technicians can detect premature defects, allowing maintenance to be conducted in time to prevent equipment unavailability.
In this article, we discuss how the gears of a wind turbine function and how we can monitor them to detect anomalies, thus preventing failures of these components.
What are Gears and What Are They Used For?
Gears are mechanical devices designed to transfer rotational power in one of two ways:
Generate higher torque
Achieve higher rotational speed
They achieve this through the difference in the number of teeth on the gears. The larger gear is called as just gear, while the smaller one is referred to as the pinion.
The following relationship dictates the mechanical behavior of a pair of gears:
Z1 → number of teeth on the crown gear
n1 → rotation speed of the crown gear
Z1 * n1 = Z2 * n2 = GMF Z2 → number of teeth on the pinion
n2 → rotation speed of the pinion
GMF → Gear Mesh Frequency
Using the same variables, a commonly used parameter for gears in parallel stages is the transmission ratio (i):
Z1 / Z2 = n2 / n1 = i
By constructing a pair of gears and properly installing accelerometers, the frequency spectrum of a gear pair is expected to appear as follows:
Gear rotation frequency (typically lower in magnitude than that of the pinion) and its harmonics
Pinion rotation frequency and its harmonics
Gear mesh frequency and its harmonics
Low overall magnitude values (according to ISO 10816-21 standard)
Depending on the gear design quality, certain harmonics of the gear mesh frequency might be more pronounced than others, particularly if the transmission ratio is close to an integer.
Characteristics of Failure Mode
The teeth of a gear pair can be damaged due to the following conditions:
Cracks from manufacturing defects
Misalignments and imbalances
When a tooth is damaged, the gear mesh frequency and its harmonics undergo modulation by the rotational frequency of the gear containing the broken tooth. This modulation is expressed in the frequency spectrum as sidebands generated at a distance equal to the rotational frequency of the broken gear.
The following example illustrates the spectrum of a worn pinion in a gear pair:
The breakage/damage of teeth can result in a frequency spectrum that appears quite "noisy," depending on its severity. This noise might include many harmonics of this modulation overlapping the harmonics of the gear mesh frequency and even the natural frequencies of the system:
Diagnosing Gear Anomalies
Detecting and diagnosing anomalies in gears is a complex activity that involves understanding the theoretical concepts governing the operation of this type of equipment, as well as using tools and vibration analysis techniques.
Despite its complexity, early detection of gear anomalies is of utmost importance for preventing the failure of these components. Not only will the cost associated with materials for repairs be lower, but also the machine's downtime will be shorter and, even more importantly, predictable.
At AQTech, we have a team of engineers specialized in the condition monitoring of rotating machinery, working on developing solutions for the automatic detection of these anomalies. We also have a highly skilled technical team capable of performing monitoring services for these wind turbines. We monitor hundreds of assets, many of which have had anomalies detected. When these anomalies were addressed by turbine operators, they prevented millions of dollars in maintenance expenses.
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