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Introduction

Recently, the wind power industry has been tremendous growth, which focuses largely on better economic conditions, growing market and the development of large offshore wind turbines and farms. High availability of wind turbines are not the result of good management or maintenance of the reliability of wind turbines, it is due to fast and frequent service. Condition Monitoring System (CMS) is better than the traditional maintenance management system increases the reliability of wind turbines. CMS will continue to monitor the wind turbine components e. g. , Transformer, gearbox, generator, etc., and the exact service time is determined by using CMS. Corrective maintenance is maintenance which occurs after the problem and preventive maintenance is maintenance carried out before any problems arise. Reliability Maintenance (RCM) is a structured approach to find a balance between corrective maintenance and preventive maintenance plans and decide to focus on reliability issues.

Reliability Maintenance (RCM) has not yet been implemented tool for wind power in Sweden and Denmark. The United States is the world’s largest producer of wind energy. However, this is a workable solution wind power industry. RCM must be carried out in Norway Vestas. Nordex of Germany and already the reliability-oriented maintenance as part of CMS systems. Application of RCM is the most cost effective planned maintenance program combined with efficient equipment, the monitoring plan for wind power system. This study focuses on condition monitoring such as vibration analysis and oil analysis of the wind power industry in a wide-ranging information about wind, how the CMS could be applied to reliability, centralized maintenance (RCM), and how this has been done earlier eg hydropower.

Few conditions are necessary to understand the maintenance and RCM as a potential tool for wind power. They are:

Failure rate: If the rate is inversely proportional to the Mean Time Between Failure (MTBF).

Reliability: Capacity to take the necessary role in certain circumstances, a certain time interval.

Managed Service Types

There are two kinds of maintenance. They are corrective and preventive maintenance.

1) corrective maintenance: it is carried out when the component fails. No maintenance process takes place before failure of the component. Component, which is not able to repair or replace. It can be replaced by a new technology component or the same as that was available before it is not.

2) Preventive Maintenance: It is a predictive maintenance system is not done before. It reduces the likelihood of failure of components. It is designed and carried out regular maintenance and at regular intervals to prevent the occurrence of failures.

a. Maintenance: Preventive maintenance carried out in accordance with recognized or established by the schedule number of units used.

b. Condition based maintenance: Predictive maintenance based on performance and / or parameter monitoring. The need for maintenance is to predict the statistical methods, it is about when, how and why some have failed.

Maintenance Optimization

Minimize the overall costs and maximize resources, maintenance is the main objective of service optimization. Maintenance is carried out so that the instruments are high and safety equipment are long-lived and its quality is maintained. It is difficult to find a relationship between corrective and preventive maintenance operations and what corrective maintenance costs associated with a certain amount of preventive maintenance.

Wind turbines

Wind power is becoming more prevalent and wind turbines and farms are still, so must be new ways to minimize downtime and maximize availability and profit. You can change the business of wind power electricity wind turbines, machines are used. The main parts are the bearings, gearbox, generator, brakes, steering system, which is part of the balance of electricity and the rotor and the center of the rotor and hub design may vary, but most common is the horizontal axis. Two or three blades, the axis of rotation to rotate simultaneously in the field. Gearbox is to accelerate the rotation from a low speed, the demand generator at a constant speed and it can be cooled in two days with air or water. Wind turbines have two brakes, one brake rotor and the other emergency purposes. The control system is to maximize energy production, machine-room is a part that controls across the wind farm and a small engine that runs on the driving wheels so that the engine room is always the wind direction.

Two vibration frequencies, wind turbines are gears where the frequency spectrum and the typical machinery has two interchangeable frequencies and multiple axes, which are supported by bearings that produce four different frequencies. Technology has become an old wind power and insurance companies complain of substantial harm and to introduce a service restrictions. Monitoring is a solution to avoid damage. Windfarm monitoring periodically inspect all the machinery is a common control procedure for wind power today. While the damage can then be detected, these inspections do not provide answers to when and how the accident occurred.

New monitoring methods

Condition monitoring is carried out in a broad manner to avoid pre-emptive replacement. Condition monitoring is a constant monitoring of each condition. It uses advanced technologies for machinery condition monitoring and prediction of errors in each condition. In practice, there are two ways for condition monitoring, one is a continuous monitoring and the second is the periodic mechanical diagnosis. Continuous monitoring, suitable sensors are linked to the control system, which is linked to an alarm as soon as the information changes, eg faults in the gearbox can be found at an early stage by comparing the current frequency in the original transmission frequency. In the periodic mechanical diagnosis, inspection machines are periodically measuring tools, and compared with the last measurement.

The cost of maintenance of wind power is economically great, condition monitoring put in place to detect deficiencies early to reduce the cost of corrective maintenance and repairs can be better planned and this would give a shorter down times. Some operations control systems of wind turbines is approaching the concept of condition monitoring. Large wind turbines control system is modular security system and it is one of the vulnerable systems and wind power. One cost-effective methods of condition monitoring is visual inspection of the machines, but it is only stationary equipment.

Two condition monitoring techniques explained in this study,

1. Vibration and

2. Oil analysis.

1. Vibration

Vibration is the dominant used for condition monitoring of rotating equipment, in particular, so wind wheels and bearings, gearbox bearings, main bearing and the generator can be controlled properly. Vibration analysis is not new. In the early 80′s instrumentations and systematic skills required for noise or vibration based condition monitoring was fully developed.

Bearing condition for wind noise have been reported higher rotation per minute (rpm) and higher levels of stress fag, where soon. A few years ago, computer-based devices that can measure the volume and evaluate the condition, which has been available, it does not require a person to go to climb the tower, wind turbine and listen to the bearings.

There were no products on the market for monitoring bearings, which are suitable for wind turbines in early 2000. But later, nine of vibration sensors to monitor bearings were assembled main shaft, gearbox, generator and turbine Elida is Risholmen archipelago Gothenburg. This system is called the SKF CMS WindCon.

This analysis is based on two factors, they are;

Vibration and noise is a normal machine, so it is important to remember that:

Benefits, if problems are detected and analyzed at an early stage, are as follows:

Regular monitoring is not suitable for high-performance machines. These machines, on-line, continuous, automatic monitoring is necessary to use the vibration sensor is located in critical points in the machine when the vibration exceeds a predetermined level, alarm or machine should be closed down unintentionally.

Vibration analysis techniques used in the machine Condition Monitoring

Here are some techniques for monitoring air-conditioning machines,

1. Waveform analysis

2. Indices

3. Synchronous average

4. Orbit

5. Statistical Analysis

6. Digital fast Fourier analysis.

Waveform analysis of the records of the history of the events of the storage oscilloscope or a real-time analyzer and wind power. It is easy to identify the damage Gears and bearings, such as broken teeth and cracks.

Indices used to quantify time signals through high-level and the RMS (Root Mean Square) level is not reliable to detect damage to the continuously operating systems.

Synchronous average is useful for diagnosis of vibration of the gear, where many axes are present, it will not only remove noise but also from time to time events are not simultaneous machine will be monitored. Bearing wear, Shaft, the shaft difference, instability in hydrodynamic lubrication of bearings and shaft rub is marked with Orbit.

Statistical analysis is based on the curves of machinery vibration signals which can be used to monitor machine condition. Digital Fourier analysis is based on the frequency spectrum of the signal and the signature will afford important information regarding the condition of the device.

2. Oil analysis

Oil failure of wind power is not always detected, and it is too late, when it is detected. Continuous measurement is necessary to find deficiencies in the oil. Oil analysis is used to determine the status and lubricants commonly used in turbines and accessories. Design and use of dynamics, which, lubrication and rotor support structure is commonly referred to as the machine tripology. Lubricating oil analysis tribology is one technique used in condition monitoring, it assesses the condition of the lubricating oil of mechanical and electrical equipment. Comparison of trace metals in oil samples to demonstrate the model oil wetted parts, which give an indication of the risk of engine failure. Microprocessor-based are available for lubricating oil analysis.

Oil analysis will examine the oil and demonstrates elemental chemical composition of the debris present. Essence of the current oil samples intrusion contaminants such as dust and lubricant additives to combine.

Atomic absorption, infrared Spectro analysis, atomic emission, coupled plasma, X-ray fluorescence and energy dispersive X-ray analysis are examples of oil analysis techniques. Atomic absorption analysis has been used for waste analysis, infrared Spectro analysis indicates and measures the molecular compounds, and atomic-emission analysis of the used litter. Coupled plasma and X-ray fluorescence analysis is used to use garbage and oil additive components and energy dispersive X-ray analysis were analyzed by dry wear debris.

Gearbox

Follow-up gearing is quite a difficult process, because they contain many internal parts. Wind turbines are three stages of gearing, with a number of bearings and gears, it is difficult to find the source does not exist. Gearbox monitoring sensors, and four or six accelerometers. Because it operates in a changing environment, damage can not be detected in the future. Gearbox wear and failure due to load carrying elements, such as shafts, gears and bearings. Cracks in the surface of these parts due to contact with metals during use and the cyclic loading and this will ultimately lead to failure.

Vibration analysis examines the transmission of vibration and it is divided into two categories, and the characteristic spectral analysis. Spectral analysis includes a Fast Fourier Transform (FFT), which plots amplitude of the oscillation signal as a function of frequency.

Reliability Maintenance (RCM)

Reliability Maintenance (RCM) is a structured approach to find a balance between corrective maintenance and preventive maintenance plans and decide to focus on reliability issues. It defines the maintenance plan, e. g. prioritization of critical parts and maintenance tasks through the selection and selects the proper preventive maintenance to operation on the right part is the right time to make the most cost effective solution to adept. Civil aviation is the place for the origin of the reliability maintenance (RCM) and the first description was in 1978, Nowlan and the introduction of nuclear power came in 1980 and hydroelectric power in 1990. RCM is characterized by:

1. System function maintenance.

2. Fault identification

3. Task prioritization

4. Choosing an efficient maintenance operation

Descriptions of the process to define the RCM plan

1. Seven steps Smith 1993

2. First stages of RCM plan – Nowlan

3. Seven questions Moubray.

Seven steps Smith

Theoretical analysis models and decision tree analysis method based on the smith. Seven stages of Smith,

1. Data collection and choose System

2. The system will limit

3. System description and operation of block diagram

4. System functions and operating losses

Fifth Failure Effect and Function (FMEA)

6. Decision tree analysis

7. Maintenance measurement estimate.

Failure to Effect and policy analysis

In reliability analysis, that the effect and operation of FMEA analysis has been used and it may define the connection to troubleshoot the possible causes of failure in the construction and implications. Airplane manufacturer Boeing introduced this method in 1957. Find all the ways in which a product may fail in this method is used. Three questions are answered,

1. What bugs / events could occur?

2. What are the implications faults / events?

3. What are the causes of failures / events?

When the answers to these three questions defect frequency have been reported between the number of eg 1 and 10 These figures demonstrate the seriousness and the probability of discovery. These figures are multiplied by the combined into an index number, which is a higher value represents a worse fault, and it is called the risk priority. Using the whole risk priority assessment of the seriousness of the failures can be determined and then the measurement can be formulated.

First stages of RCM plan – Nowlan

1. Identify matters that require intensive research by dividing it into the hardware object classes.

2. Identify the major items, which are essential for safety or economic consequences.

3. Detect hidden tasks that require regular maintenance.

4. By selecting only those tasks that meet the maintenance requirements by assessing the maintenance requirement for each significant item and hidden functions in respect of the consequences of failure.

5. Identifying items that do not apply or the effective role can be found.

6. Each of the tasks involved, choose a conservative first, and every group of maintenance tasks of the application package

7. To provide factual information necessary to revise the original decisions, though the search program.

 Seven question of Moubray’s RCM II

Identification of system objects to be analyzed is the first step to analyze the system maintenance. Thereafter, according to Moubray we should respond to seven questions,

1. It requires and what?

2. How each can act to fail?

3. What causes each functional failure?

4. What are the effects bug?

5. What are the consequences of failure?

6. How the fault can be prevented?

7. How does one proceed if no preventive action is possible?

Functions which the asset is expected to perform, and when the function is defined, it is important to indicate a certain level, the device must meet. Has two functions, primary and secondary, the primary function is the main purpose of the funds and the secondary task is the additional features of the property must be completed. Failure is then described and the consequences of failure are divided into three groups,

1. Safety and environmental

2. Functional implications

3. Non-operational consequences

If the defect poses an environmental law is broken, it is classified as safety and environmental effects. Environmental and operational consequences for the impact on the cost of production and operation and other operational consequences, only to give the cost in the form of action. Decision on the amount of wood in which maintenance is carried out according to the result of that.

Benefits of RCM

1. Amount of preventive maintenance often can reduce or replace the corrective maintenance through a cautious analysis of the failures

2. Otto spare parts for transport

3. Early stage, poor construction methods was found.

The reliability of a centralized financial management (RCAM)

This method has been developed RCM principle of trying to relate to preventive maintenance to full implementation of the maintenance costs and system reliability. If you want to see the impact of components at the level of preventive maintenance, system reliability, and quantitative methods, the aim is for this technique. This method involves identification of critical components, system reliability has been studied and the relationship between reliability and maintenance is ensured effects associated with preventive maintenance of the reasons that the majority have been assessed. Main stages of RACM approach

1. System reliability analysis

2. Component reliability modeling

3. System reliability and cost-benefit analysis.

Vattenfall Hydropower RCM (RCM convertible) hydro

Vattenfall Vattenkraft development and implementation of RCM model for its hydro power station, it is the same as Moubray’s RCM II in many ways. This model follows the same steps are Moubray’s RCM II but differs from the maintenance strategy.

1. Define the functions

2. Define the function is not

3. Determine failure modes

4. Performance Risk Analysis

5. Determine if the maintenance tasks

6. Analyze and determine maintenance strategies

Each standard function analysis has been studied and the faults are added or removed as necessary. Using standard analysis of all reasonable reference bug causes each functional failure are listed.

Eight different categories of the fault is a consequence,

1. Costs resulting from the break

2. Total cost

3. Environment where the work is done

4. Dam flow

5. Damages in an environmentally

6. Personal needs

7. Production stopped

8. Efficiency

Risk analysis is undertaken for each problem and how often the bug is approximately evaluated. Using the risk matrix, we can get a number between 0 and 5, which describes the risk of failure if that number is three or more than three, preventive maintenance can be used, otherwise the corrective maintenance should be used.

Information, such as staff costs to perform maintenance, stop time and cost due to lost production, the cost of new parts of damaged equipment and other costs associated with maintenance tasks, and specifications needed to decide what kind of economic welfare is used.

The main difference between convertible RCM and RCM II, and convertible RCM II through the risks and costs analysis of the best maintenance strategy to pick up but RCM II is a decision diagram, in which some strategies favoring the maintenance and, if possible, they are then selected.

Conclusion

Planning the maintenance of RCM as a system that collects data needed to wind turbine industry. RCM combined with CMS to monitor the wind power industry equipment, which can not be continuously monitored manually. Of all industries, not just maintenance, but reliability is also an important factor. RCM provides better maintenance management system increases the reliability of wind turbines. RCM offers a lot of preventive maintenance can often reduce or replace the corrective maintenance through careful analysis of the failures. Interaction between the players and the owners of wind power equipment manufacturers (OEM) is very important to plan maintenance process is based on maintenance experience in wind power industry.