Towards reliability centred maintenance of wind turbines

Reliability centred maintenance applied to a fleet of wind turbines is presented in this paper. The key components and failure modes are identified via analysis of maintenance records. Corrective actions which an operator can take to mitigate such failures are discussed, together with implementation issues. By developing a robust set of RCM tools, wind farm operators can better quantify and minimise operational expenditure of wind farm fleets

Detection of sub-surface damage in wind turbine bearings using acoustic emissions and probabilistic modelling

Bearings are the culprit of a large quantity of Wind Turbine (WT) gearbox failures and account for a high percentage of the total of global WT downtime. Damage within rolling element bearings have been shown to initiate beneath the surface which defies detection by conventional vibration monitoring as the geometry of the rolling surface is unaltered. However, once bearing damage reaches the surface, it generates spalling and quickly drives the deterioration of the entire gearbox through the introduction of debris into the oil system. There is a pressing need for performing damage detection before damage reaches the bearing surface. This paper presents a methodology for detecting sub-surface damage using Acoustic Emission (AE) measurements. AE measurements are well known for their sensitivity to incipient damage. However, the background noise and operational variations within a bearing necessitate the use of a principled statistical procedure for damage detection. This is addressed here through the use of probabilistic modelling, more specifically Gaussian mixture models. The methodology is validated using a full-scale rig of a WT bearing. The bearings are seeded with sub-surface and early-stage surface defects in order to provide a comparison of the detectability at each level of a fault progression

Wind Turbine Reliability Data Review and Impacts on Levelised Cost of Energy

Reliability is critical to the design, operation, maintenance, and performance assessment and improvement of wind turbines (WTs). This paper systematically reviews publicly available reliability data for both onshore and offshore WTs and investigates the impacts of reliability on the cost of energy. WT failure rates and downtimes, broken down by subassembly, are collated from 18 publicly available databases including over 18 000 WTs, corresponding to over 90 000 turbine‐years. The data are classified based on the types of data collected (failure rate and stop rate) and by onshore and offshore populations. A comprehensive analysis is performed to investigate WT subassembly reliability data variations, identify critical subassemblies, compare onshore and offshore WT reliability, and understand possible sources of uncertainty. Large variations in both failure rates and downtimes are observed, and the skew in failure rate distribution implies that large databases with low failure rates, despite their diverse populations, are less uncertain than more targeted surveys, which are easily skewed by WT type failures. A model is presented to evaluate the levelised cost of energy as a function of WT failure rates and downtimes. A numerical study proves a strong and nonlinear relationship between WT reliability and operation and maintenance expenditure as well as annual energy production. Together with the cost analysis model, the findings can help WT operators identify the optimal degree of reliability improvement to minimise the levelised cost of energy

Transmission of Bulk Power from DC-Based Offshore Wind Farm to Grid Through HVDC System

Trends in growth of the wind energy is getting additional pace by offshore technology. This chapter investigates a suitable control strategy for a DC-based offshore wind farm to transmit bulk power to an onshore grid through a high voltage DC (HVDC) transmission line. The offshore wind farm is composed of variable-speed wind turbines driving permanent magnet synchronous generators (PMSG). Each PMSG is connected to the DC bus through a generator-side converter unit to ensure maximum power point tracking control. The DC voltage of the DC-bus is stepped up using a full-bridge DC-DC converter at the offshore HVDC station, and the wind farm output power is transmitted through the HVDC cable. The onshore HVDC station converts the DC voltage to a suitable AC grid voltage. Detailed modeling and control strategies of the overall system are presented. Real wind speed data is used in the simulation study to obtain a realistic response. The effectiveness of the coordinated control strategy developed for the proposed system is verified by simulation analyses using PSCAD/EMTDC, which is the standard power system software package