Proper Management of operating windfarms is critical to maximising returns from a windfarm investment. Besides day to day management of the windfarm, the Operations Manager will seek to pro-actively extract every possible hour of availability from the turbines. This paper discusses general Operations Management issues and explores some of the emerging trends in condition monitoring.
Unlike traditional electricity generation plants, the operation and maintenance of a windfarm is often outsourced to a third party. This is particularly true given that many windfarm owners are investment consortiums, who have no intention of taking a hands-on approach to managing the operation of their windfarm. The role given to a windfarm Operations Manager varies from site to site, and the scope usually tailored to suit the needs of the windfarm owner. If the owner views the windfarm asset purely as an investment, it may wish to see no more than a monthly production and budget statement. Owners who have a more substantial portfolio of generation facilities may take on the day to day management themselves, and engage assistance for specialised services only.
Wind Prospect has more than a decade of experience in Operations Management of windfarms in the United Kingdom, and they are seeking to expand their operations roles into Australia.
The primary aim of windfarm operations and maintenance is to minimise the production costs per unit of energy generated over the life of the asset. Broadly, this is achieved by:
The scope of a full operation and maintenance contract may extend beyond generating plant to include the entire windfarm site including access tracks, auxiliary buildings and electrical infrastructure.
Liaison is a key role in managing an operational windfarm. The Operations Manager is the conduit for communications between the windfarm owner, turbine manufacturer, maintenance contractors, inspectors, land owners, neighbours, authorities and emergency services. Public relations duties with local press or schools may also be required.
Events which may require immediate response include reports of trespassers, accidents or vandalism on site.
Although modern data systems mean that a full time presence on windfarm sites is not necessary, regular and thorough inspections of the balance of windfarm infrastructure is a must. This includes inspection of gates, fences, access tracks, signage, met masts and electrical infrastructure.When site facilities do require repair or maintenance, it is up to the Operations Manager to organise quotations for the work, ensure its satisfactory completion and certify resulting invoices.
Health and safety management is often included in the scope of the Operations Manager. A Health & Safety Management Plan, incorporating risk assessments, method statements and procedures, must be created and maintained for the life of the windfarm. This document is usually tailored to comply with the windfarm owner’s own health and safety policies.Health and safety auditing of contractors should be carried out on occasion and regular inspection of on site safety equipment should be conducted regularly.
Operations Managers will usually need to guarantee response times to alarms, 24 hours per day, 7 days per week. Depending on the alarm, a local or remote reset may be necessary, or technicians may be asked to attend site for a diagnosis.
Inspection of wind turbines should be conducted on a regular basis, usually at three monthly intervals. The inspection is not just visual in nature. Olfactive and auditive senses can be utilised by the experienced technician too. An abnormal sound or unfamiliar smell can provide tell-tale signs that something is amiss with the mechanical plant. The nacelle should be checked carefully for oil leakage or any other indicators that may suggest an imminent problem.
The Operations Manager is responsible for ensuring scheduled maintenance is carried out. Typically, the Operations Manager will engage a contractor to perform all servicing and repairs of the turbines and it is important that a close relationship be maintained with these parties. Service contractors should be given adequate notice of impending scheduled maintenance.
Non-scheduled repairs and maintenance must be carried out swiftly and in times of low wind to minimise loss of production. Maximum response times for diagnosis and repair must be stipulated in the service contract. Most trip events or breakdowns of turbines occur in strong winds, meaning that every 1% of loss in availability could mean a significantly higher loss in production. Prompt assessment, organisation and supervision of the work is therefore of utmost importance.
To reduce the potential for extended downtime due to lead time in obtaining spares, the Operations Manager may be asked to advise on and maintain an inventory of spares on site, particularly if the windfarm is located in a remote area.
From the enormous amount of data collected on the databases of modern windfarms, the Operations Manager must extract what is most relevant to the windfarm owner and present the information in a concise, readable form. Monthly and annual reports are the norm. This includes production (in MWh and monetary terms) versus budget, scheduled and non-scheduled servicing, availability, capacity factors, alarms, downtime, expenditure and any other information which would be of interest to the windfarm owner.
Figure 1 : Production vs Budget over one month
Figure 1 above is just one example of graphical representation used in a typical report.
The latest trends in wind turbine maintenance and operation strategies incorporate the use of condition monitoring systems. Condition monitoring involves the measurement of physical operating parameters and analysing time based trends and specific characteristics to predict failure of individual components.
Data can be obtained from any or all of the following sources:
Currently, only the first two are commonly used for condition monitoring of wind turbine plant.
The most common form of condition monitoring is the measurement of vibration for moving parts. In the case of a wind turbine this is the mechanical drive train, particularly main shaft, gearbox, coupling and generator. Changes in amplitude of the vibration, both for broadband frequency as well as at specific frequencies tells a story which experienced analysts can use to determine what is happening to the machine.
Use of technology to sample particle levels in oil and thermographic temperature sensing provide further sources of condition monitoring data.
Recent developments in technology specific to wind turbines also include the use of strain gauges (including optic fibre) embedded into structural elements such as blades and towers that are able to monitor and observe changes in the dynamic structural responses. They also allow records to be maintained of load amplitude and frequency changes that can be used to determine whether a structural element has exceeded its design parameters.
Many turbine manufacturers and component manufacturers such as LM Glassfiber are now starting to incorporate condition monitoring technologies into their newer multi MW designs; this includes both building in sensors and integration into SCADA.
Vibration condition monitoring systems are available from traditional suppliers as retrofit systems and are being marketed to wind farm owners. Though becoming common on mainland Europe, the first trial systems are being installed within wind turbines in Australia.
The benefits of continuous condition monitoring include:
Insurance companies are also providing premium benefits where condition monitoring is used.
Condition monitoring has however been slow to be implemented, in a large part due to high cost of the technology and because each individual wind turbine needs to be fitted with sensors and recorders. This is starting to change, as technology improves, cost of technology reduces and the scale of the wind turbines increase (in the last five years we have seen a jump from sub MW scale to multi MW scale). The development of offshore and more remote windfarms also increases viability of condition monitoring as site access costs are significantly higher.
One of the misconceptions of condition monitoring is that it is assumed that if sensors and recorders are installed, then you will have a condition monitoring system and reap the benefits from it. This is not true. Condition monitoring requires also putting in place the systems that can use and respond to the data collected.
Volumes of data will be collected. Modern Condition Monitoring software has the ability to process the data, and isolate specific characteristics. This is not a replacement to a human interface but rather a supplemental tool. It is important to have a knowledgeable operator who is actually looking at the data, interpreting it in relation to experience with that machine. Over reliance on the software can either miss problems or result in an overreaction.
Individual machines have individual characteristics, what is right for one may not be right for another. There needs to be a feedback loop that ensures regular review and adjustment of alarm levels for individual machines.
Service and maintenance personnel need to own the system and incorporate the philosophy of condition monitoring into their planning and service responses. Communications must be established to ensure they are receiving appropriate and timely data.
Many of the wind turbine manufacturers offer centralised remote monitoring centres that are able to monitor the wind turbines, reset remotely and notify local personnel if on site attendance is required. These services are used during the warranty periods but often extend beyond warranty.
Utilities who invest in windfarms generally have 24/7 facilities for their major plant and often elect to monitor the windfarm themselves.It has been observed that these large remote monitoring centres do not always translate to higher levels of performance. It is not clear why this would be but it is suggested that there are several causes.
There is an argument for using smaller, local Operations Managers who have a greater focus on individual performance of the facilities that they monitor. The cost to implement is higher, but the gains in generation income are generally found to offset this.
Manufacturers generally offer availability guarantees during warranty at 97 %. A well run wind farm with the right technology selection can achieve levels higher than this; 99 % is not unheard of. To achieve this requires a far closer and personal relationship between the Operations Manager and the wind turbine that a large remote monitoring facility cannot supply.
With larger windfarms (>100 MW), each percentage point of availability can be worth AU$300-500K of revenue per annum. There is a growing trend towards performance based operations contracts with smaller local operators where the reward associated with increased performance and reliability is shared between the Windfarm Owner and the Operations Manager.
Wind turbine manufacturers are also starting to offer long term warranties up to 12 years or more, with all operations and maintenance bundled at a fixed price. This has the effect of taking all risk away from the owner, though at a cost premium. The growth of this offering is slow as individual manufacturers learn to understand the long term risks for the different regions that they operate in. Performance bonuses will eventually be seen as part of these offerings.
The case study presented illustrates how the monitoring of parameters such as temperature data can provide tell-tale signs of impending doom. Figure 2 below is a plot of gearbox oil temperatures from a windfarm in the UK. The oil temperature traces over a month period indicate a definite trend in increased oil temperatures for turbine 7, despite no reduction in power output. During a low wind period, technicians were sent into the nacelle to diagnose the problem. Sure enough, a small oil leak was discovered and despite a malfunction of the low oil level alarm, the problem was repaired with minimal downtime and virtually no loss in production. It is obvious that the ramifications could have been far worse if the problem had been allowed to deteriorate until catastrophic failure of the gearbox occurred, particularly when the cumulative effects of lead-time, down-time, manpower, transport, cranage and parts are considered for a major component replacement.
Figure 2 : Hydraulic Temperature
The scope of the Operations Manager of a windfarm is wide and varied. However, it is expected that this scope may continue to increase with the trend of using condition monitoring for wind turbines. The viability of these systems has improved due to a maturing of the technology, larger wind turbines and increased remoteness of windfarms (including offshore). In addition, insurers are offering premium discounts for its implementation. The system is no quick fix however. The data must be regularly collated and analysed by trained and experienced technicians, who are intimate with the windfarm to be fully effective.