CONMOW: Condition Monitoring for Offshore Wind Farms H. Braam,
[email protected], Tel. +31 224 564657 L.W.M.M. Rademakers,
[email protected], Tel. +31 224 564943 T.W. Verbruggen,
[email protected], Tel. +31 224 564046 ECN Wind Energy, P.O. Box 1, 1755 ZG Petten, The Netherlands, Fax. +31 224 568214 ABSTRACT. To investigate whether a cost-effective integral condition monitoring system can be realised in practice the European project CONMOW (Condition Monitoring for Off-shore Wind Farms) was started at November 2002. In the first phase, one single turbine, the GE 1.5S located at Zoetermeer, is being instrumented extensively, not only with condition monitoring techniques but also with the “traditionally” measurement systems. In this paper the objectives and the approach of the project are outlined. Furthermore the instrumentation of the single wind turbine is explained. 1. INTRODUCTION Offshore turbines are being placed at remote sites under harsh conditions. The demand for high reliability and low operational costs becomes higher than for onshore turbines. From recent studies for developing operation and maintenance (O&M) plans for offshore wind farms, it appears that the costs for maintenance are too high, approximately 25 - 30% of the energy generation costs. These costs are dominated by unexpected failures leading to corrective maintenance. These figures emphasise the need for an adequate O&M program that makes use of good diagnostics and condition monitoring techniques to lower the number of corrective maintenance actions and the related costs and downtime. Condition monitoring techniques are being used successfully already for a long time in many branches of industry. In the past, many attempts have been made to apply condition monitoring in wind turbines in order to improve the maintenance procedures and to predict failures and wear in an early stage. Suppliers and manufacturers of condition monitoring systems have driven many of these attempts and as a result several different systems are commercially available for application in wind turbines, f.i. vibration control systems for bearings and gearboxes or oil monitoring systems. These systems are usually additional, high-tech systems. It has been proven that the systems will function under the conditions a wind turbine is operated, only little attention has been given to actually demonstrate the added value of the advanced condition monitoring techniques and signal analyses. A main problem is the interpretation of the measured signals, as a wind turbine is operated under strongly fluctuating wind loads. Hence condition monitoring is not applied on a large scale, and before somebody is going invest money in condition monitoring he should answer the following questions. • Which condition monitoring system has added value for the operation of the farm? • Is the system suitable for diagnostics only or can it be used to predict the remaining lifetime? • What kind of data should be measured, analysed and stored? • What kind of data analysis and signal processing techniques are available? • What kind of information should be dealt with automatically by the turbine controller or the park controller and what kind of data should be provided to an operator? So for a successful introduction of condition monitoring in wind offshore wind farms these questions have to be addressed. Furthermore introduction of condition monitoring can be speeded up by considering an integral condition monitoring system, instead of separate
specialised devices. In such an integral system the measured data of specialised devices are considered, analysed and interpreted in coherence with data and signals that are available in the turbine already. One could think of temperatures in the generator and the gearbox, variations in the power curves, trends in the pitch and yaw speed, etc. To investigate whether a cost effective integral condition monitoring system can be realised in practice the European project CONMOW (Condition Monitoring for Off-shore Wind Farms) was started at November 1st, 2002. This project aims at further developing techniques for diagnostics and condition monitoring for offshore wind farms and selecting and demonstrating a suitable set of techniques, in order to change from corrective maintenance to condition based maintenance. In the following a brief outline of the project is presented. 2. OBJECTIVES AND APPROACH The project CONMOW aims at developing techniques for diagnostics and condition monitoring of wind turbines (and farms) at remote areas and selecting and
Fig. 1: GE 1.5 Wind Turbine at Zoetermeer
demonstrating a suitable set of techniques. The objectives in fact are fourfold. 1. Development of new algorithms for data processing by a case study of a turbine with variable speed and pitch control. 2. Improvement of currently available condition monitoring techniques and SCADA systems to the specific wind turbine needs and to make sure that they will meet the newly developed wind turbine communication standards as being developed for instance in IEC TC88 WG 25. 3. Investigating and demonstrating the benefits of condition monitoring techniques and generic SCADA systems in a wind farm and assessing the added value in the operation of large wind farms at remote (offshore) locations. 4. Implementing the selected procedures and techniques for condition monitoring into the O&M plan for the offshore wind farm with the aim to change from preventive and corrective maintenance to condition based maintenance. The project is separated into two main phases. In the first phase, which started in November 2002, one single turbine, the GE 1.5S located at Zoetermeer (Fig. 1), is being instrumented extensively, not only with condition monitoring techniques but also with the “traditionally” measurement systems like load measurements in the blade root, torque of main shaft, tower bending moments, speed, etc. This turbine is owned and operated by Siemens Nederland BV. The instrumentation plan is described in Section 3. The objective of this phase is to carry out an extensive measurement campaign on a pitch controlled turbine with variable speed under normal and faulted conditions. With data from the extensive measurement campaign, inter-relationships will be determined between various turbine parameters and condition monitoring results. The condition monitoring techniques will be assessed on their added value for wind farm operation. Assessment criteria that are thought of are: 1. does the technique have added value for diagnostics, detection of early failures, verification of design assumptions, or predicting the remaining lifetime of a component; 2. is the data accurate enough to apply it for turbine and park control applications; 3. is a substantial price reduction possible? In the second phase, which will start in the beginning of 2004, the selected and improved methods will be integrated into one system and applied on a larger scale (5 turbines) in a wind farm. The systems will be tested over a longer period of time. A generic SCADA system will be used to collect and store the data and to make the data accessible for the various users. In this testing phase, the condition monitoring techniques as well as the SCADA system will be improved continuously. Experiments will be done with automated surveillance. 3. INSTRUMENTATION PLAN As part of the 1st phase the GE 1.5S wind turbine located at Zoetermeer is being instrumented. The initial focus of CONMOW is to apply condition monitoring on gearbox, main bearing, generator (mechanical part) and pitch mechanism. The lay-out of of the measurement system is depicted in Fig. 2. To monitor the structural vibrations in
total seven accelerometers of Prüftechnik of the type VIB 6.122 or VIB 6.102[1], are installed at the following locations: • Main bearing, 2 sensors, both in radial direction, 90 deg shifted; • Gearbox, planetary side, horizontal/radial direction; • Gearbox, output side, axial direction; • Bearing output shaft, vertical/radial direction; • Bearing generator, gearbox side, horizontal/radial direction; • Bearing generator, back side, horizontal/radial direction.
Nacelle Nacelle
Nacelle Pall
Nacelle, Trafo
Prüftechnik Vibronet Signalmaster
ECN Vibronet Signalmaster
Nacelle. PT
G&J
Gram & Juhl
Switch
Ethernet / Opto Tower
Tower base
PC ECN Intermediate storage
Opto / Ethernet Switch
Router IP ADSL modem
Remote Access
Internet
Fig 2: Instrumentation scheme
stat. Hub/blades
Also Gram&Juhl Dynamic Analysis Modules [2] will be mounted to: • Main bearing, DAM-XY-01; • Gearbox, 2 x DAM-Z08; • Generator, DAM-Z08. For the gearbox the following systems of Pall [3] are foreseen: • The Pall M&E DeltaSense Differential Pressure transmitter to measure to quality of the oil filter; • The Pall M&E water sensor for monitoring of the gearbox lubrication system water contents; • The Pall PIM400 for inline fluid cleanliness monitoring. Furthermore the following “traditionally” measurements are performed by ECN: • Blade moments; • Temperature and current of pitchmotors; • Acceleration of nacelle; • Rotor speed; • Azimuth angle; • Yaw misalignment; • Air temperature; • Pitch angle; • Yaw angle; • Wind speed; • Electrical power; • Rotor shaft torque. All signals are supplied to three measurement systems in the nacelle. Which are used for data acquisition and intermediate data storage. These system are connected to a PC in the tower base, which is accessible by internet.
4. ANALYSIS OF RESULTS In order to be able to produce meaningful algorithms to predict failure, it is necessary to identify the key failure modes that can be identified by condition monitoring and it is necessary to analyse how these failure modes are likely to manifest themselves. For this purpose a Failure Mode and Effect Analysis (FMEA) is under preparation. The FMEA is generally intended to identify all possible failure modes of a system, their likelihood, and their consequences in terms of costs, downtime, safety, etc. The result of an FMEA is a list with the most vulnerable items and recommendations on how to reduce their criticality. A possibility is to reduce the likelihood, e.g. by choosing components with a lower failure rate, or limiting the consequences, e.g. by lowering the repair costs or downtime. The CONMOW project is intended to determine applications for condition monitoring with which it is possible to reduce the number of unexpected failures and thus of unwanted downtimes due to difficult access. By performing a FMEA and conceiving corrective measures it will become clear which failures occur suddenly and which failures show up gradually. The first category cannot be predicted and will always occur unexpectedly. The latter category can probably be detected at an early stage with the use of an adequate condition monitoring system. (Condition monitoring in this context here is very broad. It includes all technologies ranging from visual inspection to vibration analysis.) The objective of the FMEA within this CONMOW project is to identify those failure modes that show up gradually and can be identified at an early stage. 5. CONSORTIUM The project CONMOW is undertaken by: • ECN Wind Energy (NL) • Siemens Nederland BV (NL) • Loughborough University (UK) • Risø National Laboratory (DK) • Garrad Hassan and partners Ltd. (UK) • Pall Corporation (E) • Gram&Juhl APS (DK) • Prüftechnik CM GmbH (D) REFERENCES [1] http://www.pruftechnik.com [2] http://www.gramjuhl.dk [3] http://www.pall.com ACKNOWLEDGEMENT This work is partly funded by the EC under contract ENK5-CT-2002-00659 and by Novem under contract 2020-02-11-10-006.
Fig. 3: Instrumentation cabinet
