In this research, signals from the transducers were recorded and processed by using an SKF WindCon 3.0 unit, a commercial CMS producing FFT spectra, as currently used on the full-size operational WTs. This was done to demonstrate that the research proposals in this Thesis could be implemented on a practicable, industrial CMS.
Figure 4.11 shows the operational structure of the SKF WindCon system installed on the test rig. MasCon 16W is the WindCon hardware and has 16 analogue and 2 digital inputs. Each channel is equal to a sensor input. In its current configuration there are 6 active analogue channels enabled in MasCon configured to record: the vertical and horizontal shaft proximeter signals, the 2 accelerometer signals (named Accelerometer 1 and Accelerometer 2, respectively), HSS torque and one phase stator line current.
Figure 4.11: Architecture of the SKF WindCon system installed on the WTCMTR.
For operation and analysis purposes the system requires that a pulsed speed signal be applied to one of the digital inputs as a reference signal for other measurements and as a trigger for Fourier transform analysis, as all
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frequency analysis and diagnosis is reliant on the machine operating condition. For the test rig this requirement is met by the shaft tachometer signal, set as a digital channel, named Generator Speed, with 60 pulses per revolution.
The configuration of the MasCon unit can be done remotely via the WindCon software, SKF @ptitude Observer, which has been installed by the Author to replace the old SKF ProCon version. This software is also used for data management and analysis. Data are stored on a recently built dedicated server, called ReliaWind, accessible, via @ptitude Observer, across the Durham University School of Engineering and Computing Science network. @ptitude Observer Monitor is the server software which works as the connector between MasCon system, database, and @ptitude Observer users. This software performs the communication and database storage allowing the use of @ptitude Observer as an on-line system.
Different types of measurement points are available and can be performed in the channels of the WindCon MasCon 16W unit. Several measurement points can be attached to one channel. They are classified into two main categories, details of which are available in (SKF Reliability Systems, 2010):
Spectra and time waveform based measurement points, which include
Vibration, Envelope, Harmonic, Process FFT;
Trend based measurement points, which include Process, Speed,
Running hours, Counts, Counts rate, Derived point.
For the purpose of this research, according to the sensors currently connected to the test rig, 7 measurement points have been set and are listed in Table 4.3.
Main feature of the vibration points in WindCon is the possibility to set the spectral analysis, which is carried out using FFT and so requires
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stationary input signals. In order to analyse CM data of variable speed and load WTs, for each point the spectral analysis can be configured according to an active range, which sets the limits for operating conditions under which spectra are sampled. In particular, the measurement point active range is set in terms of speed, load and the allowable change in these during the measurement period. In this way quasi-stationary signals can be processed avoiding issues associated with variable speed and load conditions and increasing the confidence in the resultant spectra which are directly comparable by the operator. During the test rig operation, time series data have been configured to be recorded at 0.08 minute intervals, while spectra from the vibration signals at 1 minute intervals, when the speed is within the active range set in the spectral analysis settings.
The Observer software features a powerful diagnostic tool, the machine parts, which allows the creation of a mechanical model of the machine, where the features of its main components can be specified, as, for example, the gear type and tooth number. The software also features a large bearing database which stores geometrical data from approximately 20,000 different bearings
Table 4.3: Test rig WindCon system measurement point configuration. Measurement
Point Name Point Type MasCon Channel
HSS Speed Speed Generator Speed (digital)
HSS Torque Process HSS Torque
Accel1 Vibration Accelerometer 1
Accel2 Vibration Accelerometer 2
Line Current Vibration Line Current
VertProx Vibration Vertical Proximeter
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from several different manufacturers. This allows detailed specifications to be attached to each individual bearing. The WTCMTR mechanical model is shown in Figure 4.12.
Figure 4.12: SKF Observer machine parts of the Durham WTCMTR, equipped with the gearbox, including main component of interest.
The machine parts mechanical data provides a tool aiding the user to automatically calculate the characteristic frequency signature of each component at any rotational speed. For a given FFT spectrum, the component-specific, speed dependent characteristic fault frequencies can be easily identified by selecting them from a menu of all possible components in the machine diagram and displayed as vertical bars. The cursor function enables user to select peaks, harmonics and sidebands in the spectrum to aid FFT interpretation and to increase the diagnostic capability of frequency analysis. A harmonic cursor is a set of markers indicating all members of a specific harmonic family with a very fine resolution. A sideband cursor similarly depicts a family of sidebands with a given spacing around a specified central carrier frequency (Randall, 2011). The software built-in diagnostic system also provides the user with the probability that a selected unidentified frequency in a spectrum, including harmonics, belongs to a specific machine part. This allows the identification of the part of the machine which causes a high peak at a specific frequency.
As a result, the software user, however inexperienced, has a much improved ability to understand vibration spectra from the complex drive train
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and to find out which machine component is generating a certain anomaly in the frequency spectra. However, accurate fault detection and diagnosis still require time-consuming and costly manual analysis for spectra comparison as specialised knowledge is required for signal interpretation.
For each measurement point, individual automatic or adaptive warning and alarm settings can be configured in Observer. The level for the active alarms can be set by the user or automatically calculated by the system after a minimum specific number of historical values have been stored in the database. The alarms can be used to give an overall picture of the machine health, but do not necessarily indicate the exact location of a fault, due to their general nature. In order to speed up the diagnostic process, alarms can be set based on the fault frequencies for different components within the drive train. However, recent work about the use of WindCon on operational onshore WTs in the field (Crabtree, 2011) has shown that, given the WT noisy variable speed and load environment, alarms could not be relied upon with any great confidence and, albeit following an alarm signal, faults always required manual investigation in order to gain confidence in the result.
The current status of the machine can be visualised through the process overview graphic interface, configured to display the rig measurement point alarm status. For operational onshore and offshore WTs, once reliable and effective alarms are set, the process overview represents an easy to use and understandable tool for control rooms and operators.
The software also features the machine diagnosis tool, including ready- made formulas which link together frequencies and harmonics with the correct machine part and correct cause of error. Sophisticated built-in diagnosis rules, derived from SKF’s understanding and experience of rotating machine diagnostics, can be applied using defect frequencies of the whole machine, with individual alarm level for each overall or enveloped vibration measurement point and for each type of fault. Customized diagnosis rules can
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also be created by the software user. In the diagnosis display, all the different diagnoses attached to a measurement point and calculated using the spectrum data stored in the database, are trended and are related to the alarm level set by the user. This allows displaying and following the progression of machine faults more simply than the alternative of manually inspecting each spectrum.
The aim of this research is to investigate and expand the potentiality of current commercial WT CMSs, such as the SKF WindCon system, by experimentally developing fault detection algorithms, with instruction sets optimised for real-time manipulation of sampled signals, which could be implemented into their software diagnosis tool. This will contribute to automate the fault detection and diagnosis process for the main WT components, improving the confidence in the alarms produced by the system and reducing uncertainty and risk in applying CM techniques directly to field data from operational WTs.