Jesse A. Andrawus

Wind Turbine Maintenance Optimisation: principles of quantitative maintenance optimisation

Maintenance optimisation is a crucial issue for industries that utilise physical assets due to its impact on costs, risks and performance. Current quantitative maintenance optimisation techniques include Modelling System Failures MSF (using monte-carlo simulation) and Delay-Time Maintenance Model (DTMM). The MSF investigates equipment failure patterns by using failure distribution, resource availability and spare-holdings to determine optimum maintenance requirements. The DTMM approach examines equipment failure patterns by considering failure consequences, inspection costs and the period to determine optimum inspection intervals. This paper discusses the concept, relevance and applicability of the MSF and DTMM techniques to the wind energy industry. Institutional consideration as well as the benefits of practical implementation of the techniques are highlighted and discussed.

The Selection of a Suitable Maintenance Strategy for Wind Turbines

Common maintenance strategies applied to wind turbines include ‘Time-Based’ which involves carrying out maintenance tasks at predetermined regular-intervals and ‘Failure-Based’ which entails using a wind turbine until it fails. However, the consequence of failure of critical components limits the adequacy of these strategies to support the current commercial drivers of the wind industry. Reliability-Centred Maintenance (RCM) is a technique used mostly to select appropriate maintenance strategies for physical assets. In this paper, a hybrid of an RCM approach and Asset Life-Cycle Analysis technique is applied to Horizontal-Axis Wind Turbines to identify possible failure modes, causes and the resultant effects on system operation. The failure consequences of critical components are evaluated and expressed in financial terms. Suitable Condition-Based Maintenance activities are identified and assessed over the life-cycle of wind turbines to maximise the return on investment in wind farms.

Modelling System Failures to Optimise Wind Turbine Maintenance

Modelling System Failures (MSF) is a unique quantitative maintenance optimisation technique which permits the evaluation of life-data samples and enables the design and simulation of the systems model to determine optimum maintenance activities. In this paper, the approach of MSF is used to assess the failure characteristics of a horizontal axis wind turbine. Field failure data are collated and analysed using the Maximum Likelihood Estimation in the Weibull Distribution; hence shape (β) and scale (η) parameters are estimated for critical components and subsystems of the wind turbine. Reliability Block Diagrams are designed to model the failures of the wind turbine and of a selected wind farm. The models are simulated to assess the reliability, availability and maintainability of the wind turbine and the farm; taking into account the costs and availability of maintenance crew and spares holding. Optimal maintenance activities are determined to minimise the total life-cycle cost of the wind farm.

A SMART software package for maintenance optimisation of offshore wind turbines.

Offshore Wind Turbine (OWT) maintenance costs in between 20 – 35% of the lifetime power generation cost. Many techniques and tools that are being developed to curtail this cost are challenged by the stochastic climatic conditions of offshore location and the wind energy market. A generic and OWT centric software packages that can smartly adapt to the requirement of any offshore wind farm and optimise its maintenance, logistics and spares-holding while giving due consideration to offshore climate and market conditions will enable OWT operators to centralise their operation and maintenance planning and make significant cost reductions. This work aims to introduce the idea of a comprehensive tool that can meet the above objectives, and give examples of data and functions required. The package uses wind turbine condition monitoring data to anticipate component failure and proposes a time and maintenance implementation strategies that is developed as per the requirements of HSE and government regulations for working in the offshore locations and at heights. The software database contains key failure analysis data that will be an invaluable asset for future researchers, turbine manufacturers and operators, that will optimise OWT power generation cost and better understand OWT working. The work also lists some prevalent tools and techniques developed by industries and researchers for the wind industry.

Significance of Effective Lubrication in Mitigating System Failures - A Wind Turbine Gearbox Case Study

The effectiveness of lubrication in machines mainly depends on the physical and chemical properties of lubricating oil, like quantity, level of suspended particles, effect of external load/shear forces, temperature amongst others. Periodic inspection of lubricating oil for its grade of viscosity, H2O content, fuel content, amount and nomenclature of suspended particles etc. assists maintenance personal in assessing the quality of oil and its residual life. Such assessments are also useful in determining health of the system in which the lubricating oil was used. This work discusses about industrial Wind Turbine Gearbox lubrication, its importance, applications, oil analysis method and lists constituents found in the oil. Results lead us to the conclusion that additives in the oil protect the gearbox from wear and tear during initial years of operation. Analysis also suggests that re-lubrication process should be performed every 18 months time interval to optimise the life of gearbox components. Other results and advice for lubrication are also listed.

Offshore Wind Turbine Blade Coating Deterioration Maintenance Model

Maintenance of offshore wind turbine blades has significant impact on the overall cost of managing offshore wind farms. Effective maintenance of protective coatings of wind turbine blades is one of the key challenges of offshore wind farms given that the current condition monitoring systems for wind turbines are limited in detecting coating deterioration. The durability and adhesion of coatings are affected by varying complex offshore weather conditions. This impact is further aggravated as access to offshore wind farms are costly and weather dependent. In this paper an effective predictive maintenance strategy for protective coating of wind turbine blades is developed. The strategy is based on risk analysis approach and coating codes for offshore installations. Practical implementation of the developed strategy will significantly reduces the overall maintenance cost of offshore wind farms.

Calculating Hydrodynamic Loads on Pipelines and Risers: Practical Alternative to Morison’s Equation

Hydrodynamic stability analysis is one of the major tasks in the design of subsea pipelines and risers. The analysis is important to ensure stability of pipelines and risers under the action of the hydrodynamic forces produced by waves and currents during construction and operation stages. Morison related these hydrodynamic forces to kinematic wave properties, water particle velocity, and acceleration. However, previous studies show that Morison’s equation does not describe accurately the forces for combined wave and steady current flow. The actual measured forces differ significantly from the forces calculated using Morison’s equation. Though Morison’s equation leads to easy computer application for design purposes, it is a very conservative approach resulting in high cost of construction of offshore structures. In this paper the Wake II Model is incorporated into MathCAD software to practically determine hydrodynamic forces acting on cylindrical offshore structures. The Wake II Model takes into account the vortex shedding effect in the wake of a bluff body resulting in velocity reversal, thus the velocity is modified to include this effect. The modified velocity, time dependent drag and lift coefficients are then used to calculate hydrodynamic forces of lift and drag using MathCAD software. The results showed that the forces predicted using the Wake II Model is significantly less in comparison to the Morison’s equation. The results achieved in this project are consistent with results achieved by Lambrakos in his comparison of the Wake Model predictions with measured forces (actual loads) from the Exxon Pipeline Field Measurement Project (PFMP). The Wake II Model lends itself to easy computer application such as MathCAD so ftware and will also reduce the overall construction cost of cylindrical offshore structures such as pipelines and risers.