A Survey on Wind Turbine Condition Monitoring and Fault Diagnosis—Part II: Signals and Signal Processing Methods

Abstract

This paper provides a comprehensive survey on the state-of-the-art condition monitoring and fault diagnostic technologies for wind turbines. The Part II of this survey focuses on the signals and signal processing methods used for wind turbine condition monitoring and fault diagnosis. ). respectively. A. VibrationMany WT faults induce vibrations of the corresponding WT subsystems, which can be detected by using the signals acquired from vibration sensors. Vibration monitoring is the dominant technique used in almost all commercially available WT condition monitoring systems (CMSs), in which the vibration sensors are usually installed on the casing of the gearbox, generator, main shaft and bearing, and blade surface.The major types of vibration sensors include accelerometers, velocity sensors, and displacement sensors. Accelerometers have the widest working frequency range from 1Hz to 30 kHz, In contrast, velocity sensors have a working frequency range from 10 Hz to 1 kHz and displacement sensors have a working frequency range of 1-100 Hz. Accelerometers are the most widely used vibration sensors in CMFD of WTs for their wide working frequency range. The signals acquired from accelerometers contain the information of accelerations of WT components caused by faults [1]. Displacement sensors have also been used in WT CMFD systems for diagnosing the faults leading to lowfrequency vibrations of WT components. Vibration monitoring has been used for CMFD of WT gearbox [2], [3], bearing [4], rotor and blade [5], generator, tower, main shaft, etc. The amplitude of the vibration signal can indicate the severity of a fault [6]. For example, the amplitude of the 1P frequency components in vibration signals provides a measure of rotor asymmetries [5].Through years of applications, the vibration-based CMFD technologies have been mature and standardized by ISO10816. However, this approach requires the installation of the capital cost and wiring complexity of the WT system. The vibration sensors are usually mounted on the surface or are buried in the body of WT components, making them difficult to access during WT operation. Moreover, the sensors and data acquisition devices are also inevitably subject to failure. Sensor failure may further cause the failure of WT control, mechanical, and electrical subsystems. These could cause additional problems with system reliability and additional operation and maintenance (O&M) costs. In addition, vibration signals usually have a low signal-to-noise ratio (SNR) when used to diagnose an incipient fault. B. AEMaterials that are subjected to stress or strain may emit sound waves, which is called AE [7]. The sources of AE can be located to detect possible defects of a structure using one or more AE sensors. The AE monitoring technology has been used for CMFD of WT blades [1], gearboxes [8], [9], and bearings [10]. As a blade is usually made of various materials and components, damages often grow over critical areas and the interfaces of different internal components inside the blade. Therefore...

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