Vibration monitoring boosts performance of wind turbines
Catastrophic machine failure is the worst fear of any maintenance engineer, who feels huge responsibility if it happens. At the same time, business managers will understand the full economic consequences of such an event.
In an industry like wind energy, where the cost of repairs is astronomical, these problems are only magnified. There have been recent instances in Poland and Scotland, for instance, of wind turbines exploding through gear failure, due to very high winds. As well as the repair bill, there may also be fines and compensation to pay in cases like these.
An enhanced maintenance and monitoring regime can help to cut the risk of such occurrences, and one of the most tried and tested techniques is vibration monitoring. Here, the vibration ‘signature’ of bearings and other moving parts is monitored using sensors. Any variation from a ‘normal’ signal – which can indicate early signs of failure – can be picked up and corrected before small problems turn into big ones.
Detecting the vibration of a bearing within a noisy machine may sound difficult, but modern sensors are perfectly capable of such a task. The sensors – also referred to as accelerometers – usually come in two broad variants: low- and high-frequency. For an application like wind turbines, low-frequency accelerometers are the ‘weapon of choice’ for detecting anomalies. In general, the models used on wind turbines are 100mV/g, or the higher sensitivity 250 or even 500mV/g. These might be used to monitor the low speed aspects of the generator – such as output shafts.
Hansford Sensors has been involved in many such projects, and most of them required the use of a local junction box to house the accelerometer cabling at the top of the turbine. This is usually fed back down to the ground using multi-core (screened twisted pair) cable to connect it to an online monitoring system – allowing operators to monitor turbine conditions in real time, using a handheld device with internet access. Such a system will identify faults and predict failures before they get out of control.
Online or offline
From this, operators can develop a predictive maintenance strategy that will help to save resources, time and money. This type of online, instantly connected system can form the basis of a sophisticated remote monitoring regime – in which data is delivered to a remote ‘control centre’. Experts then interpret and analyse the data, in order to make more informed decisions regarding machine health.
A stripped-down version of this full online system is achieved by terminating the sensors in a switchbox on the ground. Then, a vibration analysis team will be dispatched to take regular readings – and act fast if necessary.
It makes sense to use this method if budgets are limited. If required, it can later be upgraded to a full online system by replacing the switchbox with a monitoring station.
It’s always best to work with an experienced partner when considering which option is best, so that an effective system can be designed for the right price.
Fix it quick
There is a pressing reason for introducing more sophisticated condition monitoring technology to wind turbines: to keep maintenance costs under control. A recent report from GlobalData estimates that turbine maintenance bills will rise to around $17bn in 2020, which is nearly double that of 2014. This is because the number of turbines is increasing, including many old ones that require frequent maintenance. For an offshore wind farm, around one-quarter of total cost is accounted for by operation and maintenance.
Employing vibration monitoring to keep tabs on a turbine’s rotating parts helps maintenance teams to spot potential problems and carry out necessary repairs at the earliest opportunity in order to avoid breakdowns.
While the 4-20mA sensors used in high spec applications like wind turbines are top of the range, their price has come down far enough to justify the use of multiple sensors – and hence better data gathering. Using multiple sensors helps to boost techniques such as acceleration enveloping, which ‘extracts’ the vibration signal of a failing bearing by filtering out the ‘noise’ of other components.
Wind power is an expanding – yet demanding – area of engineering. Recent estimates put global capacity for 2016 at 340,000 wind turbines with a capacity of more than 430GW. This figure is due to quadruple by 2030.
Operators are under constant pressure to run operations as efficiently as possible, by raising output and controlling costs. By using a predictive maintenance regime based on vibration monitoring – especially for offshore wind turbines, which are more expensive to repair due to their remoteness – they can reduce catastrophic breakdowns, boost turbine availability, and increase the economic viability of wind energy.