Reliability Centered Maintenance Combined with the condition monitoring systems for wind energy systems

Author: Malarvizhi.G

Introduction

In recent times, the wind industry has experienced exceptional growth, focusing largely on improving the economic condition, market growth and development of large offshore wind farms and farms. Higher availability of wind turbines is not because of good reliability and maintenance management in the wind because of the rapid and frequent. Condition Monitoring System (CMS) is better than the maintenance the traditional management system for increasing reliability of wind turbines. CMS monitors the performance of wind turbine parts, for example, the processor gearbox, generator etc, and accurate maintenance work time is determined by using CMS. Corrective maintenance maintenance is to be held after the problem arose and preventive maintenance is carried out before any maintenance problem. Reliability Centered Maintenance (RCM) is the structured approach to find the balance between corrective maintenance and preventive maintenance and identify terms of reliability, focusing on those aspects.

Reliability Centered Maintenance (RCM) has not yet been implemented as a of wind power in Sweden, and Denmark. United States is the largest producer of wind energy. This is a solution for the industry wind. In Norway a MRC was carried out by Vestas. And German Nordex reliability is already oriented towards maintaining the their CMS systems. The application of the MRC is a cost-effectiveness of planned maintenance combined with a monitoring plan equipment for wind power. This study focuses on the supervision of the state, such as vibration analysis and oil analysis for industry of wind energy, vast knowledge of the wind, how CMS could be applied to Reliability Centered Maintenance (RCM) and how it was done earlier, for example, in hydropower.  

Few words are required to include the maintenance and MRC as a possible tool in the wind. They are:

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

Reliability: Ability of a point to perform a required task under given conditions, for a time interval.   

Types of maintenance

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

1) Corrective maintenance: It is done after the component fails. No interview takes place before failure of the component. The element which has failed can be repaired or replaced. It can be replaced by the new technology component or the one that was available before, he failed.

2) Preventive Maintenance: This is a proactive maintenance before the system fails. It reduces the likelihood failure of components. This is a planning and maintenance and conducted at regular intervals to avoid cases failures.

a. Maintenance: preventative maintenance carried out in accordance with a timetable established or recognized number of units of use.

b. Condition Maintenance: preventative maintenance based on performance and / or monitoring parameters. The need for maintenance is provided with statistical methods, it is about when, how and why the element failed.

Maintenance Optimization

Minimize costs and maximize resources for maintenance is the main objective optimization of maintenance. Maintenance should be carried out so that the tools have a high level of security and equipment has a long shelf life and its quality is preserved. It is difficult to find the relationship between preventive and corrective maintenance and determine the cost of corrective maintenance, which is associated with an amount of preventive maintenance.

Wind Turbines

Production of wind energy is becoming more frequent and wind turbines and farms are increasingly, therefore, it must have new ways to minimize downtime and maximize availability and profit. To transform kinetic wind power electricity wind machines are used. The main components are the bearings, gears, generators, brakes, control system, part balances of power and of the rotor and hub and the rotor hub of this design may vary but the most common is the horizontal axis. With two or three blades, the axis of rotation runs in parallel with the ground. Gearbox is to accelerate the rotation of a low speed, the generator constant speed and the application, it can be cooled within two days with air or water. Wind has two brakes, a brake rotor and one for emergency purpose. Control system is to maximize energy production, the platform is a party that controls the various parts of the wind turbine and a small engine manages a spiral so that the platform is always in the direction of the wind.

Two frequencies of vibration in the wind turbines are often Gear and on the frequency, type mechanisms are two frequency devices and there are several areas that are supported by bearings that produce four frequencies. The former technique is in wind power and insurance companies are complaining about large damages and to introduce restrictions maintenance. Monitoring is a solution to avoid damages. Wind farm monitoring that periodically inspects the entire mechanism is the control of wind power today. While the damage may be discovered, these controls do not provide answers to know when and how the damage occurred.

New ways of monitoring

Condition Monitoring is implemented in a to avoid a widespread preventive replacement. Condition Monitoring is a regular monitoring of each state. It is the use of advanced technology for the monitoring of a state machine and predicting failures in each state. In practice, there are two means of monitoring the state, there is a monitoring and another is a periodic mechanical diagnosis. In a continuous monitoring of sensors appropriate are connected with the control system that raises an alarm as soon as the data is modified, such as failure of the gearbox can be found at an early stage, by comparing the current frequency of the gearbox with frequency. Periodic mechanical diagnosis, inspection machines are performed periodically with tools to measure and compare with the most recent.

The cost of maintaining a Wind is economically high condition monitoring must be submitted to the discovery of failures at the beginning to reduce costs for maintenance and repair could be better planned giving short time. Some of the functions of the control systems in wind turbines is close to the concept of condition monitoring. For large wind system is a module of the security system and is one of the most sensitive of a wind turbine. One of effective methods for monitoring the state is the visual inspection machines, but it is limited to fixed equipment.

Two techniques for monitoring the state explained in this study are

1. Vibration analysis and

2. Oil analysis.

1. Vibration Analysis

The vibration analysis is the main technique used for condition monitoring, particularly for rotating equipment, turbines in the wheels and bearings in the box of gears, bearings of the generator and level can be controlled adequately. Vibration analysis is not new. In the early 80 years, the instrumentation and systematic skills required for noise or vibration-based monitoring have been developed.

Having provided the wind is indicated by the noise; higher rotation per minute (rpm) and more stress to wear the rotation soon. A few years ago computer based equipment to measure noise and to assess the impact of state was available, it does not need a person going into the wind and climb the tower to hear the bearings.

There were no products on the market for monitoring the levels that have been adapted for wind turbines in early 2000. But later, nine vibration sensors were collected to monitor the bearings on the main axis, gearbox and generator on the turbine Elida Risholmen in the archipelago Gothenburg. This system is called the management system of the SKF WindCon.

This analysis is based on two elements, they are;

• All failure modes are different frequency components of vibration that can be identified and isolated and
• The amplitude the frequency remains constant, unless there is a change in the dynamic operation of the machine.

Vibration and noise is normal in the machinery, it is important to remember that:

• Each machine will have a normal level of vibration and noise.
• Malfunction is usually the result of increased noise and vibration.
• Possess a unique way of vibration and noise is generated each malfunction.

The benefits, if the problem can be detected and analyzed at the beginning, are as follows:

• Practice of stopping time of repair systems may be considered.
• Damage is minimized.
• Work schedule, the requirements of manpower, tools and replacement parts can be fitted before closing.
• Reduce machine downtime.

Periodic monitoring is not suitable for high performance machines. For these machines, online continuous, automatic control is required using vibration sensors located at critical points on the machine where the vibration is higher to pre-set levels, an alarm or shut the machine unintentionally.

Techniques used in the analysis of vibration Machine Condition Monitoring

Here are some of the machine conditioning monitoring,

1. Analysis of waveform

2. Indices

3. Synchronous average

4. Orbit

5. Statistical analysis

6. Digital fast Fourier analysis.

Waveform analysis of records of the time history of events on an oscilloscope or a real time analyzer and wind energy. It is easy to identify damage in gears and bearings, such as broken teeth and cracks.

Indices used to quantify the time signals using the peak level and the RMS (Root Mean Square) level is not reliable in detecting damages continuous operating systems.

Synchronous is useful in the average speed of vibration diagnosis where several trees are present, it not only removes noise, but also periodic events not synchronous with the machine being monitored. Bearing wear, misalignment of shaft, tree of difference, the lubrication of hydrodynamic instabilities in the bearings and shaft friction are indicated by Orbit.

The analysis statistical curves of drift of vibration signals of machinery which may be used in machine condition monitoring. Digital fast Fourier analysis is derived from frequency signal and the signature of the spectrum obtained can not afford important information regarding the status of the machine.

2. Oil Analysis

Oil failure of wind energy is not detected and it is too late when it is detected. The measure is needed to find defects in the oil. Oil analysis is used to determine the status and condition lubricants used in the turbines and equipment. The design and operation of the dynamic range of lubrication and support structure of the rotor of the machine is commonly referred to as tripology. Analysis of lubricating oil is one of tribology technique used in surveillance, it assesses the condition of lubricating oil in the mechanical and electrical equipment. Comparison of trace metals in oil samples shows the pattern of the oil wetted parts which provide an indication of the likelihood of machine failure. Systems based on microprocessors are available for analysis oil lubrication.

Oil analysis examines the oil and the elements of the chemical composition of debris. The main elements present in samples of oil are the penetration of foreign matter such as dust and oil with its additives.

Atomic absorption, infrared spectral analysis, atomic emission, plasma, X-ray fluorescence and energy dispersive X-ray analysis are examples of oil analysis. Atomic absorption analysis is the analysis of wear debris, spectral analysis Infrared detects and measures the compounds molecular and atomic emission is used for the analysis of debris. Coupled plasma and fluorescence X-rays are used to analyze the wear debris and oil components and energy dispersive X-ray analysis is used for the analysis of wear debris drought.

Gearbox

Monitoring boxes speed is quite difficult because they include many interior components. The wind turbines have three stages, which have several gearboxes and bearings gear wheels, it is difficult to find the source of the failure. Gearbox is controlled by sensors and four or six accelerometers. Since, he works in a changing environment, May pity not be detected until the future. Gearbox wear and failure is due to the cost of items such as shafts, gears and bearings. Cracks on the surface of these parts are due to contact between the metal and the ring during the loading operation and what ultimately leads to failure.

Survey analysis of vibration of the box speeds of vibration, and is divided into two categories: spectral analysis and functionality. Includes spectral analysis Fast Fourier Transform (FFT), which plots amplitude of the vibration signal as a function of frequency.

Reliability Centered Maintenance (RCM)

Reliability Centered Maintenance (RCM) is the structured approach to find the balance between corrective maintenance and preventive maintenance and to determine plans focusing on the reliability. It determines the maintenance plan, for example, in order of priority of the critical and the choice of preventive maintenance tasks right and choose the maintenance activities for the right component at the right time to achieve the best cost control solution. Civil aviation industry is place of origin for the interview focused on the reliability (RCM) and the first came in the description and Nowlan 1978 by the introduction of energy Nuclear power is coming in 1980 and hydro-electricity in 1990. RCM is characterized by:

1. Operating system maintenance.

2. Failure mode of identification

3. According to priority

4. Choosing effective maintenance

The descriptions of the process definition of a plan MRC,

1. Seven stages of Smith, 1993

2. The first stages of a plan RCM – Nowlan

3. Seven of Moubray question.

Seven of the measures of Smith

Theoretical models and analysis of tree decision is the basis of the method smith. The seven steps of the blacksmith are

1. Collecting information and the choice of

2. Limits of system

3. System description and function block diagram

4. System functions and loss of function

5. Effect of failure and the Analysis (FMEA)

6. The analysis of the decision tree

7. Maintenance position estimation.

Effect of failure and analysis function

In reliability analysis, the lack of effect and FMEA analysis function is used and can determine the possible link between the failure modes for construction and failure effects. Manufacturer Boeing has introduced this method in 1957. To find all the means by which a product can fail is the purpose of this method. The three questions are answered,

1. What failures / events could occur?

2. What are the effects of failures and events?

3. What are the causes of failures / events?

With the responses of these three failure frequency is given by a number between 1 and 10 for example. These figures show the seriousness of the consequence and the probability of discovery. These figures are multiplied in a combined index, for which a higher value indicates a deterioration of failure and it is called risk priority. Using the size of the priority risk estimating the severity of the failure can be determined and a measure can be formulated.

Stages of a first RCM – Nowlan

1. Identify areas which require study by the partitioning of material into categories of objects.

2. Identify the elements that have essential safety or economic consequences.

3. Identify functions Hidden in need of maintenance.

4. Choose only the tasks that meet the maintenance requirements through the evaluation of maintenance requirement for each important and hidden functions as the consequences of failure.

5. Identify items for which there is not applicable or effective work can be found.

6. For each of the tasks included, conservative and select the initial group of intervals maintenance tasks of the application

7. To provide factual information necessary to review the initial decisions on a exploration program of age.

Moubray Sept issue of RCM II

Identify the system points that should be analyzed is the first step to analyze the maintenance of a system. After that, according to Moubray we meet seven questions,

1. What are the functions and performance required?

2. How each function can fail?

3. What causes each malfunction?

4. What are the effects of each failure?

5. What are the consequences of each failure?

6. How can be avoided each failure?

7. How can we proceed if no activity is prevention possible?

Functions are the major asset is to be carried out and where the function is specified, it is important to indicate a certain level that the unit must comply. There are two functions of primary and secondary, primary function is the main objective of the active and secondary is a function additional features of the asset must meet. The cause of failure is then described and the consequences of failure are divided into three categories,

1. Safety and Environment

2. Operational

3. Non-operational

If the failure cause environmental law to be broken, it is classified as safety and environmental consequences. The environmental and operational consequences have an effect on the relative costs of production and operation and not only the provides operational cost in the form of operations. The decision tree that determines the maintenance should be carried out according to the consequence of failure.

Benefits of RCM   

1. The amount of maintenance those can often be reduced or replaced by the corrective maintenance of prudent analysis of failures

2. Decrease alternative transport Parts

3. At an early stage of poor construction methods are revealed.

Asset management focuses on the reliability (CAMR)

This method is developed from RCM principle to try to connect the preventive maintenance of all maintenance costs and system reliability. To see the effect on a component level of preventive maintenance on reliability of the system, quantitative methods, is the purpose of this technique. In this method, the critical elements identified for system reliability are studied and the relationship between reliability and maintenance was established by the relative effect of preventive maintenance on the causes of failures for the part being evaluated. Main stages of RACM approach

1. System reliability analysis

2. Reliability Component modeling

3. System reliability and cost / benefit analysis.

Vattenfall Vattenkraft RCM (VVK RCM) in hydro-electricity

Vattenfall Vattenkraft developed and implemented a model for its hydroelectric RCM, it is similar to the MRC Moubray II in many aspects. This model follows the same steps in the RCM Moubray II, but differs in the maintenance strategy.

1. Define the functions

2. Determine the function of failure

3. Determine failure modes

4. The analysis Risk Performance

5. Determine the possible maintenance tasks

6. To analyze and decide on strategies maintenance

Each function of the standard is under review and analysis of functional failures are added or removed if necessary. Use analysis of standard reference in case of failure all the causes of each failure are listed.

Eight different categories of consequences for each failure,

1. The costs incurred due to break

2. Global costs

3. Environment where the work takes place

4. Dam flow

5. The damages took place in the environment

6. Have personal need

7. Cessation of production

8. Effectiveness

Risk analysis is performed for each failure mode and the frequency of failure is approximately estimated. Using risk matrix, we can obtain a number between 0 and 5, which describes the risk of failure, if the number is three or more, preventive maintenance could be used, or corrective maintenance should be used.

The data, such as staff costs to perform maintenance, stop time and costs due to lost production, the cost of new parts for damaged equipment and other costs related to maintenance tasks and failures are necessary to determine the economic nature of the interview to be used.

The main difference between VVK RCM and RCM II is, VVK RCM II with a cost analysis and risk the best maintenance strategy is taken, but RCM II has a diagram where the decision of some maintenance strategies are preferred and if possible, they are selected.

Conclusion

  Planning for an interview with MCM as a system that collects data is required for wind turbines industry.RCM combined with CMS allows the wind industry monitoring equipment that can be regularly checked manually. For any industry, not only the maintenance but the reliability is also an important factor. MRC provides better maintenance management system to increase the reliability of wind turbines. MRC provides the amount of preventive maintenance which can often be reduced or replaced by the corrective maintenance of prudent analysis of failures. Cooperation among farmers wind, the owners and original equipment manufacturers (OEM) is very important to the maintenance process based on the retention of experience in wind energy industry.

About the Author:

Malarvizhi.G, a BA in Electronic Engineering and Communication and Master of Business Administration. It has completed projects in electronics and the marketing of his university degree and post graduate programs. It focuses on marketing research. She can be contacted at – gmalar85@gmail.com

Article Source: ArticlesBase.com – Centered Maintenance Combined with the state systems monitoring of wind energy systems "> Reliability Centered Maintenance Combined with the condition monitoring systems of wind energy systems

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