ROLE OF MAINTENANCE IN COMPONENT AND …jed3/Theses/Haider-MEngReport-UofA-2007.pdf... predictive...

TTHHEE UUNNIIVVEERRSSIITTYY OOFF AALLBBEERRTTAA

RROOLLEE OOFF MMAAIINNTTEENNAANNCCEE IINN CCOOMMPPOONNEENNTT

AANNDD SSYYSSTTEEMM RREELLIIAABBIILLIITTYY:: A Diesel Power Generation Case Study

By

SYED JEHANZEB ADEEL HAIDER ID: 1135539

A Project Report

Presented to,

FACULTY OF GRADUATE STUDIES AND RESEARCH IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

MASTERS OF ENGINEERING

DEPARTMENT OF MECHANICAL ENGINEERING UNIVERSITY OF ALBERTA

EDMONTON, ALBERTA T6G2V4

WWiinntteerr--22000077

AACCKKNNOOWWLLEEDDGGEEMMEENNTT

First of all the author wishes to thank his mother for all her prayers and support because of whom he is at this

stage of completing his M.ENG Program, and to his family for the love and support they have always provided.

Dr. John Doucette provided continuous encouragement, knowledge, advice, optimism, and uplifting

supervision throughout the duration of the project. The author would like to sincerely thank and express

appreciation for the supervisor role in this effort.

Many individuals have contributed to this report by giving their time, knowledge, expertise, and experience.

Their contributions are mainly in the form of ideas, concepts, approaches, guidelines, recommendations, and

reviews. The authors extend their thanks and appreciation to the contributors

As well, thanks to Dr. David Checkel and Mr. Zhigang Tian, whose instructions in the courses, “Combustion

Engines” and “Reliability for Design”, played a vital role in this report. Thanks to the faculty staff, librarians, and

other colleagues for providing assistance, technical support, comments, and social atmosphere throughout the

project report.

M.Eng. Project Report, Winter 2007

Role of Maintenance in Component and System Reliability Syed J A Haider

1

CCOONNTTEENNTTSS EEXXEECCUUTTIIVVEE SSUUMMMMAARRYY..............................................................................................................................................................................................................................................................................................22

11.. IINNTTRROODDUUCCTTIIOONN ..............................................................................................................................................................................................................................................................................................................33

22.. MMAAIINNTTEENNAANNCCEE SSTTRRAATTEEGGIIEESS ................................................................................................................................................................................................................................................................44

2.1. CORRECTIVE MAINTENANCE (CM) ...............................................................................................................4 2.2. PREVENTIVE MAINTENANCE (PM) ................................................................................................................5

2.2.1. SCHEDULED MAINTENANCE............................................................................................................................5 2.2.2. PREDICTIVE MAINTENANCE (PdM) .................................................................................................................5 2.2.3. RELIABILITY CENTERED MAINTENANCE ...........................................................................................................6

2.3. COMPARISON OF MAINTENANCE METHODS ..............................................................................................8 2.4. CONDITION MONITORING SYSTEMS (CMS) .................................................................................................9

2.4.2. WHAT IS POSSIBLE TO BE MEASURED? ............................................................................................................9 2.5. DESIGN IMPROVEMENT TO MINIMIZE THE MAINTENANCE .....................................................................10

33.. RREELLIIAABBIILLIITTYY TTHHEEOORRYY......................................................................................................................................................................................................................................................................................1111

3.1. RELIABILITY....................................................................................................................................................11 3.1.1. SYSTEM RELIABILITY ...................................................................................................................................12

3.1.1.1. System Reliability Analysis ...............................................................................................................12 (a) Reliability Block Diagrams....................................................................................................................12 (b) Fault Tree Analysis ..............................................................................................................................13 (c) Failure Mode and Effect Analysis .........................................................................................................13

3.1.1.2. Binary Reliability Analysis .................................................................................................................13 3.1.1.3. Typical System Reliability Models.....................................................................................................14

(a) Series Systems ....................................................................................................................................14 (b) Parallel Systems ..................................................................................................................................14 (c) Series-Parallel Systems .......................................................................................................................15 (d) Parallel-Series Systems .......................................................................................................................15 (e) Mixed Series-Parallel Systems ............................................................................................................15 (f) k-out-of-n Configuration ........................................................................................................................16 (g) Complex Systems / Bridge Structures .................................................................................................16

3.2. AVAILABILITY..................................................................................................................................................17 3.2.1. UNAVAILABILITY ..........................................................................................................................................18

3.3. MAINTAINABILITY...........................................................................................................................................18 3.4. BATHTUB CURVE...........................................................................................................................................19 3.5. RELIABILITY, AVAILABILITY, AND MAINTAINABILITY .................................................................................19

44.. EEQQUUIIPPMMEENNTT LLIIFFEE AANNDD IIMMPPAACCTT OOFF MMAAIINNTTEENNAANNCCEE ..................................................................................................................................................................................2211

4.1. FAILURE MODELS..........................................................................................................................................21 4.2. THE IMPACT OF MAINTENANCE ..................................................................................................................21

4.2.1. AN EXAMPLE OF IMPACT OF MAINTENANCE ON EQUIPMENT LIFE .....................................................................22

55.. AANN OOVVEERRVVIIEEWW OOFF DDIIEESSEELL EENNGGIINNEESS ..................................................................................................................................................................................................................................2244

5.1. HOW DIESEL ENGINES WORK .....................................................................................................................24 5.2. WHY DIESEL? .................................................................................................................................................27 5.3. ADVANTAGES OF A DIESEL ENGINE...........................................................................................................27 5.4. DIESEL POWER GENERATORS....................................................................................................................28 5.5. TODAY'S DIESEL GENERATION ...................................................................................................................28

66.. CCAASSEE SSTTUUDDYY:: PPOOWWEERR GGEENNEERRAATTIIOONN TTHHRROOUUGGHH DDIIEESSEELL GGEENNEERRAATTOORRSS ........................................................................................................2299

6.1. SITE OVERVIEW.............................................................................................................................................29 6.2. COMPOSITION OF THE POWER GENERATION SYSTEM ..........................................................................29 6.3. RELIABILITY ANALYSIS OF THE SYSTEM ...................................................................................................30 6.6. PROBLEMS FACED ........................................................................................................................................34

77.. CCOONNCCLLUUSSIIOONNSS ............................................................................................................................................................................................................................................................................................................4400

RREEFFEERREENNCCEESS ........................................................................................................................................................................................................................................................................................................................4422

Appendix A: Specifications of Cummins NT855 Set Used for Case Study



2

EEXXEECCUUTTIIVVEE SSUUMMMMAARRYY This report explains different types of maintenance strategies which are frequently observed in mechanical

engineering industry, how they are carried out, their advantages and disadvantages, how they differ from each

other, how they are related to one another, and above all these, how they can affect reliability of components

as well as of the system. As we all know that reliability of a new component is higher than a used one,

similarly, proper and timely maintenance of a component results in improved reliability of that component and

of the system of which this component is a part. This report also throws light on this aspect of maintenance. In

relation to the project title, this report will also present a case study which includes personal experience and

actual data analysis of Power Generation System through Diesel Generator Sets. This report explains what a

diesel engine is and how it works. Following this introduction, the report explains actual problems faced by our

company, and remedial steps regarding maintenance, reliability, and cost. We also discuss some of the steps

which were actually taken by management, their impact, positive and negative, and if negative, then what were

the causes. We conclude with some suggestions which could have helped resolve the problem regarding

system reliability and maintenance.



3

11.. IINNTTRROODDUUCCTTIIOONN What is maintenance and why is it performed? Past and current maintenance practices would imply that

maintenance is the set of actions associated with equipment repair. The Merriam-Webster’s Collegiate

Dictionary defines maintenance as follows: “the work of keeping something in proper condition; upkeep.” [23].

This means that maintenance is the action or a series of actions that are taken to prevent a component, a

device, or a system from failure or to repair regular degradation that a component or a system experience with

the normal operation to keep it functioning properly. It is unfortunate that the data available in many recent

studies shows that proper measures of equipment maintenance are not taken to keep it in good running

condition. Rather, they wait for component and system failures and then take necessary actions to repair or

replace the component or the system as needed. We know that every equipment and system has a predefined

operational life and there is no such system or component that lasts forever. For instance, a system may be

designed to work at full design load for 3,000 hours and to bear 10,000 start and stop cycles.

Maintenance is required to reach the design life and to make the most of any particular system or equipment.

For example, belts need adjustment, alignment needs to be maintained, rotating equipment requires proper

lubrication, etc. Sometimes, replacement of certain components is required, e.g., a motor vehicle’s wheel

bearing, to ensure the main system, in this case a car, lasts for its design life. Anytime we fail to perform

equipment’s or system’s maintenance as recommended by the designer/manufacturer, we cut down the life of

the system or equipment. Over the last 30 years, different approaches of maintenance activities have been

developed to ensure equipment or system completes or goes beyond its design life. We can make the most of

any equipment or system by using preventive maintenance, predictive maintenance, or reliability centered

maintenance in addition to the corrective maintenance which is simply to wait for a system to fail [1].



4

22.. MMAAIINNTTEENNAANNCCEE SSTTRRAATTEEGGIIEESS

Two basic types of maintenance philosophies or strategies can be identified, namely corrective and preventive.

Preventive maintenance can be sub-divided into scheduled, predictive, and reliability centered maintenance.

Predictive maintenance is the most recent development. In practice, all these types are used in maintaining

engineering systems. The challenge is to optimize the balance between these types for maximum profitability.

In general, corrective maintenance is the least cost effective option when maintenance requirements are high.

As Rao stated in [2], “An ideal maintenance strategy meets the requirements of machine availability and

operational safety, at minimum cost.”

2.1. CORRECTIVE MAINTENANCE (CM)

Corrective maintenance is carried out when a defect in an item is recognized and is anticipated to put that item

into a state in which it can carry out its intended function. This type of maintenance is often called repair and is

carried out after the failure of a component. The purpose of the corrective maintenance is to bring the

component immediately back in to a running state, either by repairing or replacing the failed component. To

use only corrective maintenance is seldom a good solution. This means that you will run your system until a

breakdown occurs and in some literature this is referred to as a breakdown strategy. By choosing breakdown

strategy, the preventive maintenance can be reduced to a lowest and the system can function unless a major

breakdown of a component resulting in a system shutdown. This strategy is uncertain, as failures of relatively

small and dispensable components can lead to severe consequential damage. Another aspect of this strategy

is that most breakdowns are likely to occur during high load conditions when the system is at peak

performance and needed the most. One more drawback of this strategy is that when repair or replacement of

any component is needed the downtime can be extensive as logistics gets more complicated if things are not

Maintenance

Corrective Maintenance

Preventive Maintenance

Scheduled Maintenance (Time-based)

Predictive Maintenance

(Condition-based)

Reliability Centered

Maintenance

Figure 2.1: Types of Maintenance



5

planned in advance. Comparing with other strategies, corrective maintenance has some benefits too, such as

low maintenance cost during operation of the system and that the components of the system will be used for

maximum lifetime. The lifetime of the component cannot be predicted and true assessment of the cost and

lifetime can only be made once the component has failed [2].

2.2. PREVENTIVE MAINTENANCE (PM)

Preventive maintenance is carried out at fixed intervals or in accord with approved norms and intended to

reduce the likelihood of failure or the degradation of functioning of an item. Preventive maintenance is

performed regularly to postpone failures or to prevent failures from occurring. There are three different types of

preventive maintenance; scheduled maintenance or time-based maintenance, predictive or condition based

maintenance, and reliability centered maintenance. What differs between these three are the way of deciding

when to perform the preventive maintenance [2].

2.2.1. SCHEDULED MAINTENANCE

Scheduled or Time-Based maintenance is a type of preventive maintenance that is carried out in accordance

with an established time schedule or established number of units of usage. The schedule for the preventive

maintenance can be either clock-based or age-based maintenance. Clock-based maintenance means that the

preventive maintenance is carried out at specified calendar times and age-based maintenance means that the

maintenance is carried out when a component reach a certain age. The age does not need to be calendar

time, but measured for example, in revolutions or operational time, etc.

Scheduled maintenance should be designed to minimize the probability of failures. The cycle times of the

maintenance program should be harmonized with the system requirements. The system should be examined

and maintained periodically, see Figure 2.2. This maintenance approach implies that components showing

wear will be replaced on a regular basis even if they are not at the end of their lifetime. Scheduled

maintenance requires regular contact with the system and the supply for maintenance tools and workforce

shares a considerable cost for the maintenance. The advantage of preventive maintenance is that it can be

scheduled ahead of time and the management of logistics can be made simple [2], [3].

2.2.2. PREDICTIVE MAINTENANCE (PdM)

Predictive maintenance refers to an approach that deals with the actual condition of a component or a system.

This type of maintenance is not carried out according to periodic schedules but rather when a change is

observed in characteristics. Predictive maintenance is a type of preventive maintenance that is based on

equipment’s performance and/or condition monitoring and the consequent actions. In this type of preventive

maintenance, a designated monitoring device collects data of the system or component. The condition

monitoring could be scheduled, on request, or continuous. The collected data can forecast required

maintenance prior to predicted failure. Maintenance is carried out when a condition variable reaches or

exceeds a threshold value. The system components are operated to a predefined condition of wear and

fatigue. When this condition is reached, the component has to be maintained or replaced. Examples of such

condition variables are vibrations in a machine, temperature, measure of quality of the lube oil, etc.



6

Condition monitoring of components helps to plan the maintenance before failure and reduces downtime and

repair costs. The components are therefore used closer to their lifetimes and the coordination of spare parts is

easy. Another advantage of putting condition based system into practice is that trends and statistical data such

as mean time to failure can be made available. The statistical data from condition monitoring system provides

reliable data for remaining lifetime of components in the system [2], [3]. Figure 2.2 shows an example of

condition based maintenance along with corrective and scheduled maintenance.

Figure 2.2: Condition based / Predictive maintenance compared to scheduled and corrective maintenance [3]

2.2.3. RELIABILITY CENTERED MAINTENANCE

Reliability centered maintenance (RCM) is in fact establishing or improving a maintenance program in the most

cost-effective and technically feasible manner. This is a systematic, planned approach which is based on the

consequences of failure. It actually represents a shift away from scheduled or time-based maintenance and

puts emphasis on the functional significance of system components and their records of failures and

maintenance. RCM involves a methodical approach to the following three main matters.

1. Understanding failure

2. Consequences of failure - if consequence of failure is zero, one would choose “run to failure”.

3. Impact of preventive maintenance

The application of RCM results in a scheduled maintenance program that includes all scheduled tasks that are

required for safe and economical operations. There are two activity branches for RCM:

1. Operational

2. Analytical



7

Operational RCM is concerned with designing and implementing effective scheduled maintenance tasks and

procedures for performing them. Analytical RCM evaluates and applies inherent reliability characteristics to

optimize the scheduled maintenance program [13]. RCM measures consider the following key objectives of a

maintenance program:

• Minimise Costs

• Meet Safety and Environmental Goals

• Meet Operational Goals

The RCM process starts with a failure mode and effects analysis which spots the critical failure types in a

methodical and structured manner. The process then requires the assessment of each critical failure mode to

determine the best maintenance strategy to reduce the severity of every failure. Maintenance strategy that is

chosen, should consider cost, safety, environmental, and operational consequences. The results of

redundancy, spares costs, maintenance team costs, equipment aging and repair times must be taken into

account along with all other factors. Once most favourable maintenance procedures have been recorded the

RCM practice gives us predictions and costs of system performance. It also provides expected requirements of

spare parts and manpower requirements for maintenance.

RCM is in fact a method which relates reliability to maintenance. It is a qualitative approach to systematize

maintenance. It was first put into practice in 1960s by the aircraft industry when Boeing 747 series was

introduced, and the objective was to lower Preventive Maintenance (PM) costs in achieving a predefined

reliability level. This methodology was developed further after getting successful outcome. The key feature of

RCM is its emphasis on preserving system function where critical components for system reliability are

prioritized for PM measures. However, the method is generally not capable of showing the benefits of

maintenance for system reliability and costs [8].



8

2.3. COMPARISON OF MAINTENANCE METHODS In the light of above explanations of different maintenance approaches, Table 2.1 throws light on some merits

and demerits of these methodologies.

Table 2.1: Comparison of different maintenance methods

Method Advantages Disadvantages

Corrective Maintenance • Low maintenance costs during operation.

• Components will be used for a maximum lifetime.

• High risk in consequential damages resulting in extensive downtimes.

• No maintenance scheduling is possible.

• Spare parts logistics is complicated.

Preventive Maintenance (Scheduled/Time based)

• Expected downtime is low. • Maintenance can be scheduled. • Spare logistics is easy.

• Components will not be used for maximum lifetime.

• Maintenance costs are higher compared to corrective maintenance.

Predictive Maintenance (Condition based)

• Components will be used up to almost their full lifetimes.

• Expected downtime is low. • Maintenance activities can be

scheduled. • Spare part logistics is easy

because a failure can be detected early in time.

• Reliable information about the remaining lifetime of the components is required.

• High effort for condition monitoring hardware and software is required.

• Cost of another layer in the system. • Identification of appropriate condition

threshold-values is difficult.

Reliability Centered Maintenance

• Can be the most efficient maintenance program.

• Lower costs by eliminating unnecessary maintenance or overhauls.

• Minimize frequency of overhauls. • Reduced probability of sudden

equipment failures. • Able to focus maintenance

activities on critical components. • Increased component reliability. • Incorporates root cause analysis.

• Can have significant start-up cost, training, equipment, etc.

• Savings potential not readily seen by management.



9

2.4. CONDITION MONITORING SYSTEMS (CMS)

Is condition monitoring system (CMS) is a fine method of reducing the maintenance for any component or a

system? Actually, what is required is more acquaintance of how to monitor the system and information that

whether condition monitoring is applicable to the components of this system or not [4].

2.4.1. BENEFITS OF A CONDITION MONITORING SYSTEM

Methods to measure the condition of the components in any system are essential to put condition based

maintenance into practice, and this is achieved by using a condition monitoring system which continually

observes the system. The implementation of a CMS leads to some new advantages because of its

characteristics. Table 2.2 indicates some of the major characteristics, advantages, and benefits of CMS.

Table 2.2: Characteristics of Condition Monitoring Systems

Characteristics Advantages Benefits

Early warning • Avoid breakdowns. • Better planning of maintenance.

• Avoid repair costs. • Minimize downtime.

Identification of problem

• Right service at the right time. • Minimizing unnecessary

replacements.

• Prolonged lifetime. • Lowered maintenance costs.

Continuous monitoring • Constant information that the system is working.

• Security. Less stress.

The main characteristic of a CMS is its recognition of problems in the system in advance. An early warning can

provide the time to plan the repair work and to order required parts for replacement if necessary. The ability to

spot the trouble at an early stage is helpful to employ the right maintenance activity at the right time and the

ability to forecast where the problems rising from can assist in pointing out which parts need replacement and

also possible reasons and causes of the failure. As Davies stated in [4], “A condition monitoring programme

can minimize unscheduled breakdowns of all mechanical equipment in the plant, and ensure that repaired

equipment is in an acceptable mechanical condition. The programme can also identify machine train problems

before they become serious.”

2.4.2. WHAT IS POSSIBLE TO BE MEASURED?

When applying a condition monitoring system on a system mainly comprised of mechanical components such

as bearings, gearboxes, etc., there are different parameters to examine. These parameters may include

vibration, noise, debris and water in oil, alignment, pressure, temperature, stress, strain, erosion, corrosion,

etc.

Applying a condition monitoring system also includes applying new methods for maintenance planning. Davies

stated, “The output of a condition monitoring programme is data. Until action is taken to resolve the deviations

or problems revealed by the programme, plants performance cannot be improved. Therefore, a management

philosophy committed to plant improvement must exist before any meaningful benefit can be derived” [4].



10

2.5. DESIGN IMPROVEMENT TO MINIMIZE THE MAINTENANCE

Engineered modifications and design improvements in any system or component could result in minimizing the

requirement of its maintenance and even in elimination of several maintenance tasks. These changes and

improvements utilize the recorded data of previously employed procedures to design the need for

maintenance. We can use analogy of an automobile as an example. If we compare the modern automobile to

a 1970s era automobile, a significant drop in the maintenance requirements are quite obvious. One of the main

areas is engine tune ups. Automobiles of 1970s required tune ups every 30,000-to-40,000 miles. Today’s

automobiles require tune ups at 100,000 miles, with no degradation in performance. These improvements

were studied, re-engineered, and implemented. Same is the case for plant and facility equipment today.



11

33.. RREELLIIAABBIILLIITTYY TTHHEEOORRYY

“The main objective of a reliability study should always be to provide information as a basis for decision.” -

Rausand and Hoyland, 2004

The results provided by a reliability study will not tell us exactly what to do, but in what direction to look. For

example, a reliability study can be useful in areas of risk analysis, optimization of operations and maintenance.

The risk analysis is a way of identifying causes and consequences of failure events, and the optimization is a

way of telling how failures can be prevented and how to improve the availability of a system. One can see

reliability theory as a tool for analysing and improving the availability of the system [5].

3.1. RELIABILITY

The word reliability is vast in meaning. In common, reliability measures the capacity of a system to carry out its

assigned task successfully and takes into account the past experiences and behaviour to assess the upcoming

performance of the system. Another description that shows a different aspect of the concept is that reliability is

the probability that a component or a system is performing its role satisfactorily, for the intended period of time,

under the intended operating conditions. Reliability can be measured through the mathematical model of

probability by identifying the probability of successful performance with the degree of reliability. Normally, a

component or system is said to perform satisfactorily if it does not fail during the time of service. On the other

hand, many components are expected to experience failures, be repaired and then returned to working state

during their entire useful life. In this case a more suitable measure of reliability is the availability of the

component.

We can measure reliability in many ways depending on particular circumstances. The mean time to failure

(MTTF) is defined as the mean time between first operation of a component or a system and the first event of

a breakdown or malfunction. When a breakdown is observed, the system is repaired and put back into

operation and the system is then considered as fully functioning. The mean down time (MDT) is defined as the

average time that the system is not functioning when a component is being repaired, and is basically the time it

takes to repair a failure that is why it is also called mean time to repair (MTTR). The mean time between

failures (MTBF) takes into account the mean time to failure and the mean down time/mean time to repair. The

down time is usually much shorter than the time of operations, and if so, then the two measurements can be

viewed as MTTF ≈ MTBF [3].



12

Figure 3.1: Measurements of reliability [3]

3.1.1. SYSTEM RELIABILITY

A system is a collection of components arranged according to a certain structure. A large system may be

comprised of a number of smaller subsystems. Reliability modeling is actually analyzing components and their

relationships and relating components’ states (working or failed) to system state.

3.1.1.1. System Reliability Analysis

System reliability analysis involves evaluation of the system reliability based on the reliabilities of its

components. A number of methods can be applied to the system reliability analysis, such as:

(a) Reliability Block Diagrams

Designing a reliable system starts with the development of a model. A reliability block diagram (RBD) is a

logical model that gives a graphical presentation to evaluate the relation ship between different parts of a

system. Basic RBDs are built of series, parallel, or combinations of series and parallel components. Every

block symbolizes an event or purpose of a system component. If all components are required to operate

successfully for the system to operate successfully then these blocks are arranged in series. In contrast, if only

one component needs to operate successfully for the system to be functional then these blocks are arranged

in parallel. The main purpose of producing reliability assessments is to enable the user to:

(i) compare one product against another.

(ii) compare the virtues of different distribution systems.

(iii) compare the variation in the scale of the reliability evaluation between the different systems under

assessment.

The graphic representation of RBDs makes them easily understandable and hence readily checked. The

overall system reliability can be very easily calculated from the reliability of the blocks using the laws of

probability. Block diagrams can also be used for the evaluation of system availability

Some limitations of this method are that it cannot model systems in which the sequence of failures affects the

outcome and this method cannot model maintenance strategies also.



13

(b) Fault Tree Analysis

Fault tree analysis (FTA) is a conclusive, failure-based approach which helps us derive a conclusion based on

logical deduction. FTA begins with an unwanted event, such as a failure, and then deduces its causes using a

methodical logical process in backward direction. In order to determine the cause of failure, a fault tree (FT) is

constructed as a logical diagram of the events and their relationships that are necessary and sufficient to

cause an undesired event, which is the top event.

In fact FT does not consider all possible failures of any system or all the causes of the failures. It takes into

account any one particular failure which is the top event and include only those faults that contribute to this top

event. Further, only those faults are covered in FTA that are assessed and considered to be realistic. It is also

important to know that a fault tree is a qualitative model that can be analyzed quantitatively but it is not a

quantitative model in itself.

As stated in the NASA handbook [25]: "FTA provides critical information that can be used to prioritize the

importance of the contributors to the undesired event. The contributor importance provided by FTA vividly

shows the causes that are dominant and that should be the focus of any safety or reliability activity”.

(c) Failure Mode and Effect Analysis

A failure mode and effects analysis (FMEA) is a logical process of recognizing and avoiding any failures

associated with product, service, or the process before they actually occur. The center of attention of FMEA is

prevention (i.e., “fix it before it breaks”). The purpose of FMEA is to observe all of the means of failure of a

product or a process, analyze associated risks, and take action where necessary. General applications of

FMEA include prevention of defects, improvement of processes, identification of probable safety issues, and

increasing satisfaction of the client. FMEAs should be performed by organizations from initial product or

process design through the entire life of the product. Design FMEAs or process FMEAs are chosen by

organizations accordingly. Organizations can also get advantage by performing FMEAs on existing products or

processes for improvements [26].

As explained in [26], implementation of an FMEA can help

1. identify possible failures.

2. identify chances of cost reductions and quality improvement.

3. identify issues in advance that can reduce the cost of making changes.

4. exhibit an organization’s dedication to an inclusive quality system.

5. provide an outstanding preventive device for ISO 9001.

3.1.1.2. Binary Reliability Analysis

Let’s consider a system with n components. A component may only be in one of two possible states, working

or failed. Xi is used to indicate the state of component i.

0, if component i is failed by time t Xi =

1, if component i is working up to time t



14

Similarly, in a binary reliability analysis, a system can be in only one of two possible states, working or failed;

Φ(X) is used to denote the state of the system, i.e., structure function. The state of the system is completely

determined by the states of the components [12]. The component and system reliability can be stated as:

Ri = Pr(Xi = 1): reliability of component i

Fi = Pr(Xi = 0) = 1-Ri: failure probability or unreliability of component i

RS = Pr(Φ = 1): reliability of the system

FS = Pr(Φ = 0): 1-RS: failure probability or unreliability of the system

3.1.1.3. Typical System Reliability Models

(a) Series Systems: In a series system, if one component fails, the entire system fails. For instance, a car is

comprised of four basic subsystems: the engine, the transmission, the battery, and the wheels. These

subsystems are in a series combination and a failure of any of these four will result in a system failure. In other

words, all of the units in a series system must succeed for the system to succeed. Analytically, it is

represented as follows:

nxxxxxX .....)( 4321=Φ

nS RRRRR .....321=

)()......().().()( 321 tRtRtRtRtR nS =

(b) Parallel Systems: A parallel system is working if one component is working. In a simple parallel system, at

least one of the units must succeed for the system to succeed. Units in parallel are also referred to as

redundant units. Adding redundancy is one of a number of methods through which system reliability can be

improved. It is widely used in the aerospace industry and generally used in exceptionally critical systems. So in

a parallel system, all n units must fail for the system to fail.

)1).....(1).(1(1)( 21 nxxxX −−−−=Φ

nS FFFFF .....321=

∏=

=n

iiS tFtF

1

)()(

Here, SS FR −= 1

… 1 2 n

…

1

2

n

Figure 3.2: Series System

Figure 3.3: Parallel System



15

(c) Series-Parallel Systems: In a series-parallel system, the system requires at least one of the modules from

each column to be functioning in order to remain operational. It is represented as follows:

Figure 3.4: Series-Parallel System (d) Parallel-Series Systems: In a parallel-series system, the system requires that all the modules of at least

one row to be functioning in order to remain operational. It is represented as follows:

Figure 3.5: Parallel-Series System (e) Mixed Series-Parallel Systems: Most of the simple and smaller systems can be correctly presented by a

series or parallel arrangement, but there are many larger complicated systems that involve both series and

parallel composition of components in the entire system. Reliability of such systems can be evaluated by

calculating the reliabilities of the individual series and parallel segments and then combining them properly. An

example of mixed series-parallel systems is a computer-projector system which is quite common in our

classrooms, meeting rooms, and conference rooms in the offices:

Figure 3.6: An example of Mixed Series-Parallel System [12]

… …

1

2

n1

…

1

2

n2 …

1

2

nN

… 1 2 n1

… 1 2 n2

… 1 2 nN

Laptop Video cable Socket

USB

Internet Desktop PC

Power Cable Projector Screen



16

(f) k-out-of-n Configuration: The k-out-of-n configuration can be considered as a special type of parallel

configuration of components. This type of configuration requires minimum k components to work successfully

out of the total n parallel components for the system to be functional. For instance, consider an airplane that

has four engines. The plane is designed in a manner that at least two engines are required to operate for the

plane to remain in the air. This means that the engines are in a k-out-of-n configuration, where k = 2 and n = 4.

This example is elaborated in Figure 3.7:

Figure 3.7: An example of k out of n configuration

In this type of configuration, when the number of components required to keep the system running approaches

the total number of components in the system, the system's nature inclines to that of a series system. And

when k = n, the system is a series system. Mathematically,

)1,()1,1(),( −+−−= nkRFnkRRnkR nn

Boundary conditions; ,1),0( =nR ,0),( =nkR for kn <<0

(g) Complex Systems / Bridge Structures: In many cases, it is not easy to recognize which components are

in series and which are in parallel in a complex system. The network shown in Figure 3.8 is a good example of

such a complex system. Several methods exist for obtaining the reliability of a complex system including

decomposition method, event space method, and path-tracing method. We will here briefly discuss the

decomposition method.

Decomposition Method: The decomposition method is an application of the law of total probability. It involves

choosing a "key" component and then calculating the reliability of the system twice; once as if the key

component failed (R5 = 0) and once as if the key component succeeded (R5 = 1). These two probabilities are

then combined to obtain the reliability of the system, since at any given time the key component will be failed

or operating. Using probability theory, the equation is:

( ))(1)0|()()1|()( 5555 tRxtRtRxtRtR −⋅=+⋅==

The key component is 5 in the following complex system which is simplified by decomposing method [10], [12].

(a) System Working (b) System Failed



17

Figure 3.8: An example of decomposition of a Complex/Bridge Structure

3.2. AVAILABILITY

Availability is the probability that a component or a system is successfully operating at any point of time. For

instance, if a computer can be used for 18 hours in a day, the availability of the computer is said to be 18/24.

The most simple representation for availability is as a ratio of the expected value of the uptime of a system to

the sum of the expected values of up and down time, or

][][][

DowntimeEUptimeEUptimeEA+

=

If we define the status function X(t) as

1, sys functions at time t X(t)=

0, otherwise

therefore, the availability is represented by

A(t) = Pr[X(t) = 1]

A(t) = Pr[X(t) = 1] = E[X(t)], t > 0

The availability performance is defined as “The ability of an item to be in a state to perform a required function

under given conditions at a given instant of time or during a given time interval, assuming that the required

external resources are provided” – Maintenance terminology, SIS 2001 [2], [5].

A commonly used measurement of availability is the amount of operational time divided by the nominal time,

the nominal time or uptime is usually a period of one year and then the availability is presented as percentage

of operational time per year [12].

1 3

2 4

1 3

2 4

(a) When R5 = 1 (b) When R5 = 0

1 3

2 4

5



18

A common equation for measurement of availability is:

MTTRMTBFMTBFtyAvailabili

+=

+=

λµµ

when t → ∞

Here, µ = repair rate (following exponential distribution) and λ = failure rate (following exponential distribution)

3.2.1. UNAVAILABILITY

The term unavailability is the likelihood that a system is not available at a point of time when it is required.

Unavailability may be expressed mathematically,

Unavailability = 1 – Availability, or as the ratio,

MTTRMTTFMTTRU+

=+

=λµ

λ when t →∞ ,

where, µ = repair rate (following exponential distribution), λ = failure rate (following exponential distribution),

MTTR = mean time to repair, and MTTF = mean time to failure 3.3. MAINTAINABILITY

Maintainability is defined as the probability that the system is successfully restored after failure within a

specified time. It is in fact a measure that how conveniently and rapidly a system can be repaired and restored

to working state after a failure. It is an attribute of design and mechanism, workforce availability in the required

skill levels, sufficiency of maintenance methods and tools. Maintainability is generally expressed as the

probability that a system will be restored to running condition within a given time, when the maintenance is

carried out according to recommended procedures. e.g. 90% maintainability in an hour [20].

Maintainability Function, M(t), for a system with the repair times distributed exponentially is given by:

Where, µ = Repair rate and MTTR = mean time to repair

Maintainability represents the ease with which maintenance can be done to repair a system after a failure.

Maintainability addresses all scheduled and unscheduled events, which are performed to:

a. repair or replace a component that shows undesirable physical condition or performance degradation,

repair or replace a component that has failed, and verify the restoration of a component or system to

working state,

b. determine the running status of the system or a component, and

c. adjust, align, or service components.

MTTR

etM t

=

−= ⋅

µ

µ

11)(



19

3.4. BATHTUB CURVE

“Normal mechanical failure modes degrade at a speed directly proportional to their severity. Thus, if the

problem is detected early, major repairs can be prevented in most instances.” - Davies, 1998 [4].

Generally the chances of a component to fail are high in the early period of its lifetime. The component might

have hidden flaws which could lead it to instant failure at the very beginning of its life span. If the component

survived this early phases after its birth, the chances of failure reduces and it enters a stable phase where it

remains for a definite period unless it enters the final stages of its life where the probability of its failure starts

to raise again because of wear and tear. If this failure is plotted on a graph, the shape of the curve is similar to

that of a bathtub, for this reason it is known as bathtub-curve. Figure 4.9 shows the bathtub curve with the

three typical phases.

The initial phase is called burn-in period; the stable phase is called useful life period and the end phase is

called wear out period. In a Burn-in process, a component is checked before being used as a part of the

system and the motive is to detect those components that would fail as a result of infant mortality. The system

can be made more reliable and trustworthy especially for reduced early failures if the burn-in period is made

sufficiently long.

Figure 3.9: Typical Bathtub curve [3]

Figure 3.9 exemplify a possible shape of the failure function. There are some other shapes of failure function

curves as well, but the bathtub curve generally represents the failure rates for mechanical components. Since

majority of the mechanical components goes through wear and tear, the failure function curve shows a little

escalating trend during the useful life period, consequently their actual curves may vary to some extent from

the one shown in Figure 3.9 [3].

3.5. RELIABILITY, AVAILABILITY, AND MAINTAINABILITY

We’ve already discussed that, reliability of a component or a system is the probability that it will not fail and will

carry out its assigned function successfully. Maintainability is the probability the system is successfully

restored after failure. Availability is the probability that the system is successfully operating at any point of time,



20

and it depends on both reliability and the maintainability. For this reason, one must realize how vital the

probability theory is to understand the reliability, maintainability, and availability of the system [9]. The relation

between reliability, availability, and maintainability can be understood better from Figure 3.10.

Reliability Maintainability Availability

Constant Decreases Decreases

Constant Increases Increases

Increases Constant Increases

Decreases Constant Decreases

Figure 3.10: Relation between Availability, Reliability, and Maintainability [12]



21

44.. EEQQUUIIPPMMEENNTT LLIIFFEE AANNDD IIMMPPAACCTT OOFF MMAAIINNTTEENNAANNCCEE Here we will discuss some important aspects of maintenance, equipment lifetime, how failure can be avoided,

types of failures, and impact of maintenance on equipment life.

4.1. FAILURE MODELS

Failure is the termination of the ability of a device to perform a required function. In many applications,

component failures can be divided into two categories i.e. random failures and deterioration. In random

failures, the rate of failure is constant. In other words, the chance of a failure occurring in any future time-

interval is the same as it is now. This is a failure whose rate of occurrence (intensity) is constant, and

independent of the device’s condition. In deterioration, failures arise as a consequence of the component

aging or wearing out. This is a process by which the rate of failure increases due to loss of strength, the effects

of usage, environmental exposure or passage of time. Simple failure-repair processes in the two cases are

shown in Figure 4.1. The various state designations are explained in the legend of the figure. The deterioration

process is represented by a sequence of stages of increasing wear, finally leading to equipment failure [6].

Figure 4.1: State diagrams for (a) random failure and (b) deterioration failure. W: working state, F: failure state, D1, D2, …Dk: stages of deterioration [6]

4.2. THE IMPACT OF MAINTENANCE

According to the concepts available in [6], the prime intention of maintenance is to improve the mean time to

failure. One approach of including maintenance to the system models presented in Figure 4.1 is shown in

Figure 4.2. In Figure 4.2(b), it is supposed that maintenance will result in an improvement to the situation in the

previous stage of wear and tear (with least maintenance). This differs with many approaches explained in this

study, where maintenance involves replacement (i.e., a return to the “new” conditions). In the case of random

failures, Figure 4.2(a), the hypothesis of constant failure-rate explains that maintenance cannot make any

improvement, since the probability of a breakdown during any upcoming time span are the same with or

without maintenance. The situation is quite different for deterioration processes, where the times from the new

condition to failure are not exponentially distributed even if the times between subsequent stages of

deterioration are. In such a process the hazard function denoted by h(t), is increasing, and maintenance will

bring about improvement independently of the types of distributions between stages. Hazard function can be

defined as instantaneous failure rate at any point in time. For this reason, conditions cannot be improved by

maintenance for random failures, but maintenance has a major role to play when failures are the consequence

of aging.

W F D1 D2 Dk F

(a) (b)



22

In Fig. 4.2(b), the dotted-line transitions to and from state M1 indicate that maintenance out of D1 should really

not be performed because, as noted, it would be meaningless. State M1 could be indeed omitted if the

maintainer knew that at the time of next maintenance, the deterioration process would still be in its first stage

and, therefore, no maintenance would be needed. Otherwise, maintenance must be carried out regularly from

the beginning, and state M1 has to be part of the diagram. Note that deterioration processes are a subset of

the failure models where the hazard function h(t), is increasing with time. Maintenance is advantageous in all

such cases. If the failure is random, the hazard function is constant, and maintenance is of no use.

Figure 4.2: State diagrams including maintenance states for (a) random failure, (b) failure following a three-stage deterioration process [6].

4.2.1. AN EXAMPLE OF IMPACT OF MAINTENANCE ON EQUIPMENT LIFE

In order to understand the impact of maintenance on equipment life better, let us consider an example a

system assuming that without maintenance, the system would fail after exactly 10 years, the scheduled

maintenance time is 3 years and the effect of this maintenance is a 1-year improvement in life. This system is

shown in Figure 4.3(a) and the horizontal line represents as a scale of deterioration. It can be seen that the

time to failure is now extended to 14 years as a result of the four maintenances carried out in the interval.

Figure 4.3: Maintenance every 3 years, resulting in (a) 1-year improvement, (b) 3-year improvement if total wear is 6 years or more, otherwise as in (a).

M—maintenance MM—overhaul F—failure [6].

W F D1 D2 D3 F

(a) (b)

M1 M2 M3 M



23

It is not hard to understand that improvement in the system as a result of maintenance is less than the wear

and tear of the system between two consecutive maintenances, particularly in the early life of the system when

only small maintenances are carried out. After this initial phase, the effect of maintenance should be equivalent

or more than the wear and tear going on between maintenances. This can be done by planning overhauls

(major maintenances) before a given state of deterioration. Now considering the example of Figure 4.3(a), if

the overhaul is required after 6 years, and if the effect of this overhaul is a 3-year improvement in system life,

Figure 4.3(b) will be the correct represent of this scenario. An important point to notice here is that now the

expected time to failure is infinity; means that failure will never take place. This is a false conclusion and is

completely because of the hypothesis that all quantities involved have fixed values. If variables are used

instead of fixed values, the failure will occur sooner or later [6].



24

55.. AANN OOVVEERRVVIIEEWW OOFF DDIIEESSEELL EENNGGIINNEESS 5.1. HOW DIESEL ENGINES WORK

The Diesel cycle is a combustion process of a reciprocating internal combustion engine, in which fuel is ignited

by heat generated when air is compressed in the combustion chamber, into which fuel is injected. This is as

opposed to igniting it with a spark plug as in the Otto cycle (four-stroke/petrol) engine. Diesel engines (heat

engines using the Diesel cycle) are used in automobiles, power generation, diesel-electric locomotives, and

submarines. Invented by Rudolph Diesel in 1897, it was initially planned to work on Peanut oil. A Diesel engine

generates power (while continuously injecting fuel) to maintain the cylinder at constant pressure during its

power stroke.

We all know that if we compress any gas, its temperature will increase, and through this process, fuel is ignited

in diesel engines. The process starts when air is drawn into the cylinders and then compressed by the pistons

at compression ratios of about 25:1, which is quite higher than the compression ratios of 7:1 to 10:1 in the

spark-ignition Otto cycle engines. When the compression stroke is at or near to the end, diesel fuel is injected

into the combustion chamber through an injector. As the fuel comes into contact with air, it ignites. This is

because the air has been heated to a temperature of about 700–900 °C (1300–1650 °F) due to compression.

The combustion resulting from the fuel ignition causes a sudden rise in heat. This results in expansion in the

cylinder and moves the piston downward due to increased pressure. A connecting rod transmits this motion to

a crankshaft to convert linear motion to rotary motion. This rotary motion is used as power source in many

applications such as a diesel engine vehicle. Mechanical valves, present in the cylinder heads, generally

control the air intake. Most of today’s advance diesel engines are supplied with a turbocharger for increased

power output, and in some types, a supercharger is used to increase the amount of intake air [21]. A simple

piston-cylinder arrangement of a four stroke diesel engine is shown in Figure 5.1 [23].

Figure 5.1: Simple piston-cylinder arrangement of a four stroke diesel engine [23]



25

A four stroke Diesel Cycle Engine is discussed onwards in this study. The four-stroke operating principal

applied to a diesel engine is illustrated in Figure 5.2 [19]:

Figure 5.2: Four stroke operating principle applied to diesel engine [19]

In thermodynamic terms, in a diesel engine, air is compressed adiabatically in the cylinder. An adiabatic

process is one in which no heat is gained or lost by the system. As already mentioned above, this compression

of air increases the temperature and causes the fuel mixture to ignite. The ideal air-standard cycle is

considered as a reversible adiabatic compression followed by a constant pressure combustion process, then

an adiabatic expansion as a power stroke and a constant volume exhaust. At the end of exhaust, a fresh

amount of air is taken in as indicated in Figure 5.3. As the compression and power strokes of this idealized

cycle are adiabatic, the efficiency can be calculated from the constant pressure and constant volume

processes. The input and output energies and the efficiency can be calculated from the temperatures and

specific heats.

)(1 bcp TTCQ −= and )(2 dav TTCQ −=

1

21

QQQ

Efficiency+

==η

Here, Q1 = heat input, Q2 = heat Output, η = efficiency, Cp = Specific heat at constant pressure,

Cv = specific heat at constant volume, Ta = temperature at point a in diesel cycle,

Tb = temperature at point b, Tc = temperature at point c, and Td = temperature at point d



26

Figure 5.3: Air standard diesel engine cycle [23] According to the concepts in [20] and [23], it is a little hard to start diesel engines in cold weather as the low

metal temperature of the cylinder and head consume part of the heat generated in the cylinder during the

compression stroke, making it difficult for the fuel to ignite. This is why some of the diesel engines use little

electric heaters, called glow plugs, inside the cylinder to help ignition when starting.

An essential part of every diesel engine is a mechanical or electronic governor. The purpose of this governor is

to manage the engine speed by controlling the rate of fuel deliverance.

Figure 5.4: Cutaway view of an in-line overhead cam four-cylinder diesel engine [20]



27

For two reasons, diesel engines are heavier than Otto cycle or gasoline engines of the equal power. The first is

that diesel engines require a larger displacement of cylinders in each power stroke than a gasoline engine to

produce the same amount of power. The second reason for the greater weight of a diesel engine is it has to be

tough to endure the high combustion pressures required for ignition of the fuel, and also to bear the shock from

the detonation of the fuel mixture after ignition. Consequently, the weight of the piston and the connecting rod

are considerably heavier, and the cylinder and rest of the engine are also heavier in order to accelerate and to

decelerate these masses [21], [17], [18].

A diesel generator is basically a diesel engine that drives an alternator which converts the mechanical energy

into electrical energy. An alternator works by creating a magnetic field that rotates in such a manner that the

field passes through a set of coils. As the field passes through the coils, an electric current is induced on the

coils. This electric current is then regulated to become the electricity and is made available on the generator's

output. For very small generators, the magnetic field may be produced by permanent magnets, whereas for

larger generators, the field is generated by a set of coils.

5.2. WHY DIESEL? On account of growing demand and low supply, the prices of fuel are rising on a regular basis and therefore

we need a cost effective fuel to fulfil our requirements. The diesel engine has proved to be extremely efficient

and economical. The energy density of diesel is greater than gasoline, means that diesel fuel can provide

more energy as compared with the same amount of gasoline. For this reason, diesel engines can offer better

mileage in automobiles, and consequently the first choice for heavy-duty transportation and equipment. Diesel

engines draw larger interest today mainly because of higher efficiency and cost effectiveness [21], [22].

5.3. ADVANTAGES OF A DIESEL ENGINE

If studying in detail, there is a big list of advantages and distinct features of diesel engines over gasoline/petrol

engines. Briefly stating here, the diesel engine is more efficient and preferable as compared with gasoline

engine due to the following reasons [22]:

• Modern diesel engines have lower noise as well as lower maintenance costs. They need smaller

amount maintenance as compared with older models and gas engines of similar size.

• They are more rough and reliable.

• In a diesel engine, there is no sparking because of auto-ignition of fuel. Since there are no spark plugs

or spark wires, the maintenance cost is less.

• The cost of fuel consumed to produce one kilo-Watt power is 30% to 50% lower than that of gasoline

engines.

• A water-cooled 1800 rpm petrol engine normally runs 6000-10,000 hours before it needs maintenance

but an 1800 rpm water-cooled diesel engine runs 12,000 to 30,000 hours prior to any major servicing

is required.

• Petrol/Otto engines burn hotter than diesel engine, and therefore they have a considerably shorter life

compared with diesel engines.



28

5.4. DIESEL POWER GENERATORS

Diesel engines are generally used as mechanical engines, power generators and in mobile drives. They are

extensively utilized in automobiles, locomotives, construction equipment, and numerous other industrial

applications. Industrial diesel engines and diesel powered generators are widely used in construction, marine,

mining, hospital, forestry, telecommunications, underground, and agricultural applications. Power generation

for prime or standby backup power is a major application of today's diesel engines.

Diesel powered electrical generators are used in many industrial and commercial organizations. These

generators can be used in homes for small loads, as well as in hospitals, industrial plants, and commercial

buildings for big loads. They can be used both as a source of prime power or standby power back-up. They

are available in various specifications and sizes. Diesel generator sets rating 5-30KW are normally used in

simple home and personal applications. Industrial applications cover a wider range of power ratings (from 30

kW to 6 Megawatts) and are used in different industries all over the world. For home use, single-phase power

generators are sufficient. Three-phase power generators are mainly used for industrial purposes [22].

5.5. TODAY'S DIESEL GENERATION

Modern diesel generators are extremely powerful and advanced. They are designed to last longer and to give

reliable and durable source of power. Commercial businesses can depend on them when a storm arrives or a

crisis crop up with the local power network. A good, solid diesel generator can give any commercial business

a safe, secure backup power source that can save a possible loss of production. All important industries such

as construction, marine, manufacturing, forestry, and mining, to name a few, needs a reliable backup power in

cases of blackouts. With a diesel generator, commercial industries can continue functioning normally with little

to no downtime [22].



29

66.. CCAASSEE SSTTUUDDYY:: PPOOWWEERR GGEENNEERRAATTIIOONN TTHHRROOUUGGHH DDIIEESSEELL GGEENNEERRAATTOORRSS

-- Power Generation by a Reputable Multi-national Engineering Firm in Karachi, Pakistan

There are many aspects to consider in power generation system reliability. Here, we try to give a brief

overview of personal experiences at an unnamed industrial site in Karachi, Pakistan to show the impact of

effective maintenance on the performance and reliability of such a system.

6.1. SITE OVERVIEW

The objective was to supply continuous electric power to a commercial building through diesel generator sets

which acted as a source of prime power for the building. This is why the generators operated at prime working

cycle. The reason for using diesel power as the prime source is the unreliable local power supply in Karachi,

which include voltage problems, total blackouts, and long downtimes. Most of the firms use diesel power as a

backup source but some, like this site, use diesel power as their only source which is much more reliable than

local power.

This power generation site actually started up in June 2000, when our company installed the entire setup and

the client took over operation and maintenance (O&M) on its own. Due to the inability of the client to manage

the system prudently and not observing the desired results, O&M was also subsequently awarded to our

company. The Power Generation Department of our company took over the site in July 2002. The author was

employed by this firm as a mechanical engineer in the maintenance department from 2002 to 2004.

6.2. COMPOSITION OF THE POWER GENERATION SYSTEM

The power generation site discussed in this study had three diesel generator sets listed in Table 6.1:

Table 6.1: List of Diesel generators at site

DG No. kVA Rating Safe Load (kilo-Watt) Make/Model Working Cycle

1 300 kVA 180 kW Cummins NT 855 Prime

2 300 kVA 180 kW Cummins NT 855 Prime

3 70 kVA 42 kW Perkins UK 1004 TG Prime

The ratio of the actual power transmitted (“real power”) to the apparent power that could have been transmitted

if the same current were in phase and undistorted is known as the power factor (PF). It is always less than or

equal to 1 [28].

)()(.

kVAPowerApparentkWPowerealRPF =

DG-1 and DG-2 had apparent power of 300 kVA with power factor of 0.8 which gives 240 kilo-Watt of real

power transmission for each set. Safe working load of each set is 75% of the full load which was 180 kW for



30

DG-1 and DG-2. These two sets were synchronized (i.e., can share the load while working simultaneously)

and are used in the daytime. DG-3 was a 70 kVA set which gave 56 kW of real power and 42 kW of safe

working load, and worked nights and all day on Saturdays and Sundays (when the site required minimum

load). DG3 was not synchronized with DG1 and 2.

Synchronizing is the term given to electrically connecting two or more generators together. Paralleling means

electrically connecting a generator or set of generators to the electrical supply network. Both synchronizing

and paralleling add additional cost to a project but have significant advantages. Synchronizing can allow a

stepped approach to power supply using several generators that automatically switch in or out depending on

the required load. This means the generators are used in the most fuel efficient manner. It is sometimes

better to run three 500 kVA generators in a load stepped configuration than it is to run a 1500 kVA generator.

Running a generator lightly loaded for an extended period is inefficient and can cause a diesel engine to glaze

its bores. Having a synchronizing panel gives you the ability to add additional generating capability as required

without losing power to the building [14].

For detailed specifications and configuration of the Cummins C300-D5, Engine NT855 Diesel Generator Set,

refer to Appendix-A [24].

6.3. RELIABILITY ANALYSIS OF THE SYSTEM

The entire power generation setup of the site can be referred as a series system for around 10 hours of

daytime in weekdays. This was mainly due to the absence of a standby generator at site. This situation is

elaborated in the load distribution graph in Figure 6.3. These circumstances were quite alarming and required

client’s immediate attention. There was a 100 % chance of a complete blackout even if a single generator has

failed during the daytime, (i.e., entire system would have failed if one of its components has failed). The client

was well aware of the situation and was planning to install a standby generator to avoid any possible blackouts

as well as to improve reliability of the entire system. Our company was working on the feasibility of this project

to get the client’s approval until I left in May 2004. As indicated in the load curve in Figure 6.3, the maximum

load required by the site never exceeded 250 kW. We were dealing with this problem in such a manner that

whenever we faced problems with any of the generators during peak load hours, we requested the client to

turn off the air-conditioning system of the building. We had full support of the client in case of such a difficulty.

This trick reduced the building load to a level of less than 180 kW, which was well bearable for the only

available 300 kVA generator at that particular time. In the meantime, the broken generator set was attended

and fixed, and the system became functional again. As we already studied in Section 2.1, this is an example of

corrective maintenance.

Now we will briefly look into the reliability analysis of this entire power generation system. During the peak load

hours in the daytime, the system block diagram can be shown as in Figure 6.1.



31

Figure 6.1: RBD of the Power Generation System during daytime in weekdays

DG-3 is not included in the above diagram as it was not synchronized with DG-1 and DG-2 as mentioned

before. DG-1 & DG-2, both were 300 kVA Cummins NT855 models of 1998 and 2001 respectively. We do not

have the exact reliability figures of these generators, but here we try to make some logical assumptions for

their reliabilities for the study purpose, taking the generators’ condition, history, and year of manufacture into

account. By assuming R1 = 0.9 for DG-1 and R2 = 0.95 for DG-2, we can calculate the reliability of this system

during peak hours of daytime as explained in Section 3.1.1.3 (a):

855.0)95.0).(9.0(. 21 === RRRS

During the weekends, nights, and public holidays, the system reliability block diagram can be shown as in

Figure 6.2.

Figure 6.2: RBD of the Power Generation System during weekends and nights

Since during the minimum load hours, all the three generators of the site were available. DG-3 was 70 kVA

Perkins model of 1998, so we assume its reliability as R3 = 0.9. Now we can calculate the reliability of the

power generation system as it worked on weekends and nights as following:

9995.0)9.01).(95.01).(9.01(1)1).(1).(1(1 321 =−−−−=−−−−= RRRRS

We can see that the reliability of this parallel configuration at minimum load is 0.9995 which is considerably

higher than the reliability of series configuration at peak load hours in daytime, which is 0.855.

DG-1 180 kW

DG-2 180 kW

DG-3 42 kW

DG-2 180 kW

DG-1 180 kW



32

The load distribution shown in Table 6.2 is one of the daily observations recorded at site. These observations

were taken on August 01, 2002, a month after our company took over the site. This table gives a very clear

picture of site load conditions. It tells us the total load of the building, the power generated by the entire

system, and the load each generator was bearing at that time. The adverse affects of this type of loading,

when there is a big difference in generated load and consumed load, are discussed in upcoming section. The

load distribution curve in Figure 6.3 based on these observations gives a better understanding of site load

conditions.

Table 6.2: Load Distribution at Site observed on August 01, 2002

Time DG1 Load (kW)

DG2 Load (kW)

DG3 Load (kW)

Building Load (kW)

Available Load (kW)

7:00 90 0 0 90 180

8:00 130 0 0 130 180

9:00 100 100 0 200 360

10:00 110 110 0 220 360

11:00 110 110 0 220 360

12:00 120 120 0 240 360

13:00 120 120 0 240 360

14:00 120 120 0 240 360

15:00 120 120 0 240 360

16:00 120 120 0 240 360

17:00 120 120 0 240 360

18:00 120 120 0 240 360

19:00 90 90 0 180 360

20:00 0 110 0 110 180

21:00 0 100 0 100 180

22:00 0 90 0 90 180

23:00 0 90 0 90 180

0:00 0 0 40 40 42

1:00 0 0 30 30 42

2:00 0 0 30 30 42

3:00 0 0 30 30 42

4:00 0 0 25 25 42

5:00 0 0 25 25 42

6:00 0 0 25 25 42



33

Figure 6.3: Load Distribution Curve at Site observed on August 01, 2002

LOAD

CURV

E

90

130

200

220

220

240

240

240

240

240

240

240

180

110

100

9090

180

180

360

360

360

360

360

360

360

360

360

360

360

180

180

180

180

4242

4242

4242

42 2525

2530

3030

40

050100

150

200

250

300

350

400

7:00

8:00

9:00

10:00

11:00

12:00

13:00

14:00

15:00

16:00

17:00

18:00

19:00

20:00

21:00

22:00

23:00

0:00

1:00

2:00

3:00

4:00

5:00

6:00

TIME

L O A D -K W

Build

ing Lo

ad (k

W)Av

ailab

le Lo

ad (k

W)



34

6.6. PROBLEMS FACED

The load curve based on one of the daily observation charts dated August 01, 2002, is shown in Figure 6.3

and the data is available in Table 6.2. It shows that the total load of the building varied between 90 kW to 240

kW during daytime and between 25 kW to 45 kW on the weekends and nights. The major problems that we

faced when the site was handed over to us in July 2002 were:

1. Absence of standby generator: Absence of standby generator for peak hours in daytime as both 300

kVA generators (i.e., DG-1 and DG-2) were running simultaneously for around 10 ~ 11 hours without

any back up.

2. High Fuel Consumption: At this kind of load distribution, where both 300 kVA generators which can

bear 180 kW of load each, runs at 100 or 90 kW of load as indicated in the load curve in Figure 6.3,

the specific fuel consumption (SFC), which is the amount of fuel consumed to produce 1 kWh of

power, is at maximum. Another significant reason for higher fuel consumption was poor maintenance

of generators.

3. Lack of Maintenance: The preventive maintenance was very much neglected by the previous

management and all the generators needed immediate attention for maintenance. Due to this reason,

the site had a history of large downtimes and failures when it was handed over.

In response to the first problem, as we already mentioned, the client was planning to install a standby

generator and our company was working on the feasibility of this project to get the client’s approval.

For the remaining two problems, we will throw some light on the actions that were taken to solve these

problems and what was their outcome.

As specified in manufacturer’s maintenance procedures and recommendations, preventive maintenance

should be followed according to the schedule provided in Table 6.3.

Table 6.3: Schedule for preventive maintenance of generators

1. Changing Lube oil, Oil filter, Fuel filter and Air filter Every 250 running hours

2. Fuel injectors/Tappet Calibration Every 1500 running hours

3. Top Overhauling (Minor OH) Every 6000 running hours

4. Major Overhauling Every 10,000 running hours

When the site was taken over by our company in July 2002, it was revealed that the fuel injectors’ calibrations

of DG-1 and DG-2 have been delayed for more than 3500 running hours. As mentioned in Table 6.3, this

activity was supposed to be carried out at every 1500 running hours. We took a set of observation on August

01, 2002 before carrying out the injectors’ calibrations of both generators to examine the fuel consumption of

both generators without calibration. These observations are shown in Table 6.4. The capacity of the main

diesel tank at was 8,000 liters through which the fuel is supplied to all the three generators at site. Each

generator has its own fuel sump at the base of skid which is programmed to be automatically refilled when the

diesel level is reduced to half of its actual capacity. The fuel sump capacity of the 300 kVA Cummins generator

sets (i.e., DG-1 and DG-2) is 800 liter.



35

Table 6.4: Observation of fuel consumption of DG-1 and DG-2 before tappet calibration on August 01, 2002

Diesel Consumed

(Liters) Time Synchronizing Panel Meter Reading (kWh)

DG1 DG2

DG Set Fuel Sump Level

Laod DG1 (kW)

Laod DG2 (kW)

7:00 1019488 Full – 800 liters 100 100

8:00 - 100 100

9:00 - 105 110

10:00 - 90 95

11:00 - 95 100

12:00 1020160 400 400 Half – 400 liters 100 100

13:00 Re-filled – 800 liters 100 100

14:00 - 100 110

15:00 - 110 110

16:00 - 100 100

17:00 - 90 90

17:50 1021472 400 400 Half – 400 liters 90 100

For the above set of observation we can see in the ‘fuel sump level’ column that the amount of diesel

consumed by each generator during the observed time is 800 liters. Synchronizing panel has a meter installed

on it which tells us the cumulative power generated by the entire system. The difference in the synchronizing

panel’s meter reading at the start and end of observation is in fact the total power generated in kWh within the

observed time.

Synchronizing panel’s meter reading difference = 1021472 - 1019488 = 1984 kWh

SFC, as already defined, is the amount of diesel consumed to produce 1 kWh of power. Therefore, SFC of the

power generation system before injectors’ calibration is:

SFC = 8000 / 1984 = 0.403 liters / kWh

After conducting the fuel injectors’ calibrations of both generators, DG-1 and DG-2, on August 10, 2002, we

observed the fuel consumption of these generators again on August 18, 2002. These observations are shown

in Table 6.5.



36

Table 6.5: Observation of fuel consumption of DG-1 and DG-2 after tappet calibration on August 18, 2002

Diesel Consumed

(Liters) Time Synchronizing Panel Meter Reading (kWh)

DG1 DG2

DG Set Fuel Sump Level

Laod DG1 (kW)

Laod DG2 (kW)

7:00 1096384 Full – 800 liters 100 100

8:00 - 100 100

9:00 - 100 110

10:00 - 100 95

11:00 - 95 100

12:00 1097600 400 400 Half – 400 liters 100 95

13:00 Re-filled – 800 liters 100 100

14:00 - 100 110

15:00 - 110 100

16:00 - 100 110

17:00 - 95 90

17:50 1098848 400 400 Half – 400 liters 90 100

Here, we can see again that the fuel consumed by each generator is 800 liters for the observed time.

Synchronizing panel’s meter reading difference, which is the total power generated by the system in observed

time, is:

Synchronizing panel’s meter reading difference = 1098848 - 1096384 = 2464 kWh

Now the SFC after injectors’ calibration of both generators, DG-1 and DG-2, is:

SFC = 8000 / 2464 = 0.325 liters / kWh

This set of observation clearly shows a considerable improvement in SFC from 0.403 to 0.325 after we carried

out fuel injectors’ calibrations of DG-1 and DG-2. Although the ideal SFC for these generators as claimed by

the manufacturer is 0.25 liters/kWh, at this kind of minimum load of the building, as indicated in the load

distribution curve in Figure 6.3, each generator was running at extremely light load for an extended period of

time and therefore the SFC was exceedingly high. For this reason, there was still much room for improvement

of SFC at this site which could have only been achieved if the building load would have remained around the

maximum load these generators can bear, i.e., between 300 to 360 kWh. It was also observed that there was

a tremendous improvement in the engines’ sounds of DG-1 and DG-2 after the tappet calibrations were done.

In Table 6.6, we are listing the record of failures and downtimes at the site from June 2001 to June 2002,

before it was handed over to our company.



37

Table 6.6: Record of failures and downtimes from June 2001 to June 2002

Number of failures S.No Parts DG1 DG2 DG3

Downtime caused by

failures (hrs) A Engine 1 Flexible coupling and flywheel 0 0 0 0 2 Dry type air filter with clogged condition indicator 0 0 0 0 3 Cooling radiator 2 1 0 3 4 Fuel pump 0 1 1 4 5 Gasket 1 0 1 4 6 Electronic governor 0 1 0 0 7 Dual fuel filter with on line filter changing provision. 0 0 0 0 8 Lube oil pump, oil cooler and filter 1 0 1 0 9 Turbo charger 1 1 0 2 10 24V DC starter & battery charging alternator 0 0 0 0

11 Engine mounted microprocessor based control panel that displays engine and electrical parameters

a Lube oil pressure indicator and temperature gauge 1 0 0 0 b Tacho meter for speed indication with hour meter 0 0 0 0 c Battery charging Ammeter 0 0 0 0 d Starting switch with key 0 0 0 0 e Over speed stop switch with contacts 0 0 0 0 f Low lube oil pressure switch 0 0 0 0 g High water temperature alarm & trip 0 0 0 0

12 Stainless steel flexible for engine exhaust 0 0 0 0

13 Control cables from engine to AMF (Automatic Mains Fail) panel 0 0 0 0

14 Batteries 0 0 0 0 B Alternator 1 Continuous damper winding 0 0 0 0 2 RTDs (Resistance Temperature Detectors) 0 0 0 0 3 Anti condensation heaters 0 2 1 3 4 Pilot exciter 0 0 0 0 5 3-Phase sensing AVR (Auto Voltage Regulator) Card 2 0 1 4 TOTAL 8 6 5 20 hrs

Here, we can see that the total number of failures at site from June 2001 to June 2002, which is the sum of

failures occurred in each generator, (i.e., DG-1, DG-2, and DG-3), at site, is: Total number of failures at site from June 2001 to June 2002 = 8 + 6 + 5 = 19

The downtimes caused by these failures are also recorded in Table 6.6 which sums up to 20 hours for the

observed year. We can now calculate the total operating hours for the observed year:

Total operating hours from June 2001 to June 2002 = (365 x 24) - 20 = 8740 hours



38

Now, for the observed year, we can calculate the Estimated Failure Rate, which can be defined as the number

of failures in a particular span of time.

Estimated Failure Rate from June 2001 to June 2002 = Number of failures / Operating hours

= 19 / 8740 = 0.002174 failures / hour

Now we will list the record of failures and downtimes at the site from June 2002 to June 2003 in Table 6.7.

Taking you back, our company took over the site in July 2002 and these records are of one of the year when

our company managed the site.

Table 6.7: Record of failures and downtimes from June 2002 to June 2003

Number of failures S.No. Parts DG1 DG2 DG3

Downtime caused by

failures (hrs) A Engine 1 Flexible coupling and flywheel 0 0 0 0 2 Dry type air filter with clogged condition indicator 0 0 0 0 3 Cooling radiator 0 1 0 1 4 Fuel pump 0 0 1 1 5 Gasket 0 1 0 1 6 Electronic governor 0 0 0 0 7 Dual fuel filter with on line filter changing provision 0 0 0 0 8 Lube oil pump, oil cooler and filter 1 0 0 0 9 Turbo charger 0 1 0 0 10 24V DC starter & battery charging alternator 0 0 0 0

11 Engine mounted microprocessor based control panel that displays engine and electrical parameters

a Lube oil pressure indicator and temperature gauge 0 0 0 0 b Tacho meter for speed indication with hour meter 0 0 0 0 c Battery charging Ammeter 0 0 0 0 d Starting switch with key 0 0 0 0 e Over speed stop switch with contacts 0 0 0 0 f Low lube oil pressure switch 0 0 0 0 g High water temperature alarm & trip 0 0 0 0

12 Stainless steel flexible for engine exhaust 0 0 0 0

13 Control cables from engine to AMF (Automatic Mains Fail) panel 0 0 0 0

14 Batteries 0 0 0 0 B Alternator 1 Continuous damper winding 0 0 0 0 2 RTDs (Resistance Temperature Detectors) 0 0 0 0 3 Anti condensation heaters 0 0 1 0 4 Pilot exciter 0 0 0 0 5 3 Phase sensing AVR (Auto Voltage Regulator) Card 1 1 0 1 TOTAL 2 4 2 4 hrs



39

Here, we can sum the total number of failures at site from June 2002 to June 2003 as follows: Total number of failures at site from June 2002 to June 2003 = 2 + 4 + 2 = 8

The downtimes caused by these failures are recorded in Table 6.7 and these failures sums up to 4 hours for

this observed year, which is considerably less than the previous year’s downtime. Now calculating the total

operating hours for the observed year:

Total operating hours from June 2002 to June 2003 = (365 x 24) - 4 = 8756 hours

Estimated Failure Rate from June 2002 to June 2003 can be calculated as follows:

Estimated Failure Rate from June 2001 to June 2002 = Number of failures / Operating hours

= 4 / 8756 = 0.000914 failures / hour

It is can be clearly noticed by comparing Table 6.6 and Table 6.7 that the number of failures reduced 58%,

(i.e., from 19 to 8), Estimated Failure Rate also reduced 58%, (i.e., from .002174 to .000914 failures per hour,

as shown in Figure 6.4(a)), and the downtime was reduced to 80%, (i.e., from 20 hours to 4 hours, as shown in

Figure 6.4(b)), which is a huge difference. This difference was mainly because of negligence of preventive

maintenance by the previous management as already discussed, and because our company very strictly

followed the preventive and scheduled maintenance procedures after taking over the site as recommended by

the manufacturer.

0.002174

0.000914

0

0.0005

0.0010.0015

0.002

0.0025

Failure Rate

2001-2002 2002-2003

Year

Figure 6.4 (a): Estimated Failure Rate Comparison

20

4

0

5

10

15

20

Hours

2001-2002 2002-2003

Year

Figure 6.4 (b): Downtime Comparison



40

77.. CCOONNCCLLUUSSIIOONNSS Maintenance processes are meant to increase the mean time to failure of a component or system. As defined

earlier in this study, maintenance is a set of actions carried out to avoid a component or system failure or to

repair regular degradation that a system or component goes through with the passage of time to keep it in

proper working order.

The concept of corrective maintenance allows any system to work until it fails completely, only providing the

option of repair or replacement of defected component when evident problems arise. Recorded data and

studies show that operating cost in this style is maximum of all types of preventive maintenance. The benefits

of this method are that it works well if downtimes do not have an effect on production and if labour and material

costs do not matter.

The idea of preventive (scheduled/time-based) maintenance deals with the scheduling of maintenance actions

at planned time intervals, where broken component is fixed or replaced before any noticeable problem arises.

Studies show that the costs of operating a system in this manner are very less than corrective maintenance.

The concept of predictive maintenance involves planning of maintenance actions only if and when some

specific operational situations are observed such as increased vibration, temperature and/or lubrication

degradation, or any other detrimental trend through timely monitoring of the system. When any predefined

specific characteristic or parameter reaches a predetermined undesirable level, the system is shut off for

repairing or replacing broken components to prevent a more pricey failure from taking place in future. Studies

show that operating cost for this approach is even lesser than scheduled maintenance. Also, since

maintenance is only acted upon when it is needed, the production capacity is likely to improve.

Reliability centered maintenance approach involves all of the above mentioned methodologies of predictive

and preventive maintenance, in accordance with root cause failure analysis. This not only identifies exact

problems that occur, but also guarantees that highly developed repair and replacement procedures are

adopted, including possible modification of the system, and therefore assisting to stay away from problems or

keep them from taking place. Studies show that in this fashion, the operating cost is the least. This approach

works exceptionally well if the maintenance workforce if well aware, skilled, and knows the time to carry out all

of the required actions. In RCM approach, system maintenance works can be scheduled in an orderly manner

as with the predictive based method. Moreover, extra improvement efforts also can be taken on to minimize or

eliminate probable problems from happening again and again. It also gives opportunity to purchase materials

for necessary repairs ahead of time, hence reducing the requirement of huge inventory. Since maintenance

work is carried out only when needed, and additional efforts are put forward to comprehensively examine the

reason of the breakdown and determine the techniques to enhance system reliability, there can be a

considerable improvement in production capacity [1].

We know that while there have been dramatic technological advances in energy efficiencies that have resulted

in significant energy savings, (an example of which is discussed in Section 5.5 “Today’s Diesel Power

generation”) there is still room for improvement. In any power generation system (for instance the one

mentioned in the case study in Section 7), the most immediate opportunity to improve the reliability of the



41

system and save energy is taking the simple and relatively easy steps of preventive maintenance in a timely

manner to ensure that the system is maintained at peak efficiency and hence reducing failure rate and

downtimes.

According to a survey conducted in Karachi, Pakistan in 2004, over 90% of Commercial Diesel Generators

were under-performing due to one problem or another [29]. In many cases, the problem was as simple as a

dirty filter. In the commercial arena, up to 50% more energy would be saved through proper installation, sizing

and maintenance of Diesel Generators and related equipment [29]. Improving system efficiency by 10% to

20% is a conservative estimate of the impact of proper maintenance [29]. For systems that are seldom or

never serviced, the savings could reach 100% [29]. To achieve this efficiency, we would recommend to strictly

following the requirements for system maintenance timely and efficiently. Just like the system mentioned in the

case study, the results that have been compared for both scenarios (i.e. system conditions with maintenance

and without maintenance), clearly shows how much impact can be made on the system reliability and

availability by following proper preventive maintenance procedures.



42

RREEFFEERREENNCCEESS [1] Pro-Active Maintenance for Pumps, Archives, Piotrowski, J. April 2, 2001. [2] Underhall Terminology - Maintenance terminology, Svensk Standard SS-EN 13306, Stockholm: SIS Förlag AB 2001 [3] System Reliability Theory, M. Rausand, A. Hoyland, Hoboken: John Wiley & Sons 2004, ISBN 0-471-47133-X [4] Handbook of condition Monitoring, A. Davies, London: Chapman & Hall 1998, ISBN 0-412-61320-4 [5] Reliability Theory with Application - Preventive Maintenance, I. Gertsbakh, Berlin: Springer-Verlag 2000, ISBN 3450-67275-3 [6] S. H. Sim and J. Endrenyi, “Optimal preventive maintenance with repair,” IEEE Trans. Reliability, vol. 37, no. 1, pp. 92–96, Apr. 1988. [7] J. Endrenyi and S. H. Sim, “Availability optimization for continuously operating equipment with maintenance and repair,” in Proceedings of the Second PMAPS Symposium, September 1988, Nov. 1989, EPRI Publication EL-6555. [8] L. Bertling, “Reliability centred maintenance for electric power distribution systems,” Ph.D. dissertation, Dept. Elect. Power Engineering, KTH, Stockholm, Sweden, 2002. [9] Reliability, Availability, and Maintainability, “RAM”, website: www.answers.com/topic/reliability-availability-and-maintainability (accessed in March 2007) [10] System Reliability, Maintainability, and Avalability Analysis, “Overview”, website: http://www.weibull.com/basics/system_reliability.htm (accessed in March 2007) [11] Corrosion Maintenance, “The maintenance revolution”, website: http://www.corrosion-doctors.org/Inspection/Maintenance.htm (accessed in February 2007) [12] Lecture Notes for MecE 514 “Reliability for Design” Fall- 2006 by Zhigang Tian (University of Alberta) [13] What Analytical RCM is?, “Analytical RCM”, website: http://www.ca-advisors.com/quals/epri/a_rcm/ (accessed in April 2007) [14] Power Hire – about generators, “Synchronizing”, website: http://www.powerhire.co.nz/tools/faqs.html [15] The value of reliability in power systems - pricing operating reserves - José Fernando Prada, MIT-EL99-005 WP July 1999 [16] Perkins Engines Company – Industrial, “Engine Genetics”, website: http://www.perkins.com/cda/ (accessed in March 2007) [17] How Diesel Engine Works?, “ Diesel Fuel”, website: http://auto.howstuffworks.com/diesel.htm (accessed in February 2007) [18] Modern High-Speed Oil Engines Volume II by C. W. Chapman published by The Caxton Publishing Co. Ltd. reprinted in July 1949 [19] DP Chip Power, “Generat Diesel Information”, website: http://www.dpchip.com/pumpinfo.html (accessed in June 2007)



43

[20] Engine-AutoZone, “How engine works” website: http://www.procarcare.com/icarumba/resourcecenter/encyclopedia/icar_resourcecenter_encyclopedia_engine1.asp (accessed in March 2007) [21] Internal Combustion Engines Fundamentals – John B. Heywood [22] Industrial Diesel Generators and Engines, “Types and Applications”, website: http://www.dieselserviceandsupply.com/ (accessed in April 2007) [23] The Diesel Engine, “Diesel Engine Cycle”, website: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/diesel.html (accessed in March 2007) [24] Cummins N Series Generator Sets (200kVA ~ 450kVA), “Detailed Lead Description”, website: http://honny1992.en.alibaba.com/offerdetail/52720984/Sell_Cummins_N_Series_Generator_Set.html (accessed in April 2007) [25] PBMA-KMS, “What is FTA?”, website: http://pbma.nasa.gov/framework_content_cid_356 (accessed in June 2007) [26] CIRAS-FMEA, “What is FMEA?” website: http://www.ciras.iastate.edu/quality/fmea.asp (accessed in June 2007) [27] Understanding High Availability of IP and MPLS Networks, “Defining key terms – Unavailability” website: http://www.ciscopress.com/articles/article.asp?p=361409&seqNum=2&rl=1 (accessed in June 2007) [28] BC Hydro. Guides to Energy Management (GEM) Series: Power Factor. Vancouver, B.C. 1999. [29] Prospects of energy in Pakistan by Aamir Kabir, March 03, 2003, The Daily Dawn

AAPPPPEENNDDIIXX –– AA

Specifications of Cummins C-300 D5 Generator with NT- 855 Engine

Diesel PoweredGenerating SetsC300 D5

Standard Genset Features Generator Set Performance Generator Set OptionsCummins water cooled Diesel engine, Voltage Regulation Mechanical OptionsOil and fuel filter fitted, water separator,, Maintains voltage output to within ±1.0%. Compliance - CE Certification (Guarding)Lube-oil drain valve fitted At any power factor between 0.8 and 1.0Electric starter & Charge alternator 24 v D.C. At any variations from No load to Full load. Fuel sytem optionsElectronic governor At any variations from Cold to Hot. Low Fuel Level ShutdownNormal duty air filter At speed droop variations up to 4.5%.Single bearing alternator, class H/H , IP23 Frequency RegulationStandard voltage 400/230 volts 50 Hz Isochronous under varying loads from no Exhaust OptionsExciter/Voltage reg - Torque Match as std load to 100% full load when electronic Exhaust Silencer - Industrial (9 dB), In-Line PCC2100 without Bargraph governor is ?tted. Exhaust Silencer - Residential (25 dB), In-Line 3 pole MCCB Random Frequency Variation Flexible and fixing kit for Industrial silencerWelded steel base frame with A/V mounting, Random Frequency Variation Flexible and fixing kit for Residential silencerAnti Vibration Mounts Will not exceed ±0.25% of its mean value forSingle skin metal fuel tank constant loads – no load to full load.Tank capacity of min 8 hours operation at Waveform Warranty70% standby load Total harmonic distortion open circuit voltage Warranty - 5 Year Extended Standby ApplnLoose 9 dB(A) silencer waveform in the order of 1.8%. Three-phase Warranty - 2 Year Extended Prime ApplnSet mounted starting battery balanced load in the order of 5.0%.Engine Tractor Blue & Alternator Munsell Jade Green Telephone In?uence Factor (TIF) Voltage ConnectionsRadiator and Guarding black TIF better than 50. 277/480V, 3 PhasePacking under shrunk plastic film THF to BS 4999 Part 40 better than 2%. 254/440V, 3 PhaseOperation & Maintenance manual Alternator Temperature Rise 240/416V, 3 PhaseStandard set of labels Class H insulation. 230/400V, 3 Phase

220/380V, 3 PhaseRadio Interference 127/220V, 3 PhaseIn compliance with BS 800 and VDE levels 115/200V, 3 PhaseG and N. 110/190V, 3 Phase

Miscellaneous OptionsEngine Specification Alternator Specification Coolant heater -240/120VCummins NT855G6 Type Battery Charger 110-277V, 3AIn-line direct injection Brushless single bearing, revolving ?eld, PCC2100 with bargraph6-cylinder diesel engine. pole, drip proof, screen protected. Automatic Transfer SwitchesType Class H Insulation, IP23 Protection Packing - Export BoxWater cooled, four cycle IC 01 cooling system. Compliance StandardsTurbocharged Fully interconnected damper winding. To BS4999/5000 pt 99,Construction AC exciter and rotating recti?er unit. VDE 0530, UTE5100,Two valves per cylinder, forged steel Epoxy coated stator winding. NEMA MG1-22, CEMA,crankshaft and connecting rods, cast iron Rotor and exciter impregnated with tropical IEC 34, CSA A22.2,block. grade insulating oil and acid resisting AS1359, BSS 5514,Starting polyester resin. Dynamically balanced rotor ISO 3046 and ISO 852824 volt negative earth. Battery charging BS 5625 grade 2.5.alternator 35 amp on engine. Cranking Sealed for life bearings.current 640 amps at 0°C. Layer wound mechanically wedged rotor.Fuel System24 volt fail safe actuator. Spin-on paper Exciterelement fuel ?lters with Bosch fuel Triple dipped in moisture, oil and acidpump injection system with integral resisting polyester varnish and coated withElectronic governor. Dual ?exible fuel lines anti-tracking varnish.and connectors. Standard fuel waterseparator.Filters Output windings with 2/3 pitch for improvedAir cleaner with dry element and restriction harmonics and paralleling ability.indicator. Spin-on full ?ow lube oil ?lter. Close coupled engine/alternator for perfectCooling alignment.50°C radiator as std Oil cooler. Drain Tap

Model name

ESP PRP ESP PRP

C300 D5 300 275 240 220

Specifications may change without noticeC300 D5

kVA kWe

Technical Data

PRIME POWER (PRP)Prime power is available for an unlimited number of annual operating hours in variable load applications, in accordance with ISO8528-1.A 10% overload capability is available for a period of 1 hour within a 12-hour period of operation, in accordance with ISO 3046-1.STANDBY POWER RATING (ESP)

In installations served by unreliable utility sources (where outages last longer or occur more frequently), where operation is likely to exceed 200 hours per year, the prime power rating should be applied. The Standby Power rating is only applicable for emergency and standby applications where the generator set serves as the back up to the normal utility source. All ratings are based on the following reference conditions:- Ambient temperature – 27oC

Dimensions and Weights

Model Engine Length (mm) Width (mm)Height (mm) (50Deg Rad)

Set weight wet (Kg)

Set weight dry (Kg)Enclosed Weight

Wet (Kg)

C300 D5 NT855G6 3549 1100 2078 3360 3170 5005

06/2004 C300 D5

Model

Set output

C300 D5

380-440 V 50 Hz

Speed

Alternator voltage regulation

Prime Rating

Standby Rating

Engine Make

Engine Model

Starting/Min °C

Cylinders

Engine build

Standard Governor/Class

Aspiration and cooling

100 A/hrBattery capacity

Gross Engine output – Prime

Cummins

NT855G6

Six

In-line

Bore and stroke

Compression Ratio

Cubic capacity Air intake – engine (Prime)

220 kWe 275 kVA

240 kWe 300 kVA

280 kWm

Electronic/Class G2

Turbocharged

140 mm x152 mm

14:1

14 Litres

Unaided / 4°C

Alternator insulation class

Fuel consumption (Prime)

Exhaust gas flow – prime

Exhaust gas back pressure max

Pusher fan head (duct allowance)*

Heat radiated by eng (Prime)

Fuel consumption (Standby)

Lubrication system oil capacity

Base fuel tank capacity – open set

Coolant capacity

Exhaust temp – prime

Minimum air opening to room

Minimum discharge opening

Air flow – radiator*

1500 rpm

±1.0%

H

56 l/hr

62 l/hr

38.6 Litres

750 or 900 Litres

63.9 Litres

574°C

1071 l/s

76 mm Hg

4.92m3/s

361 Litre/s

2.10 sq m

1.39 sq m

13 mm Wg

- Altitude above sea level – 150 metres - Relative humidity – 60%

The Standby Power Rating is applicable for supplying emergency power for the duration of a utility power interruption. No overload, utility parallel or negotiated outage operation capability is available at this rating.

50 kWm310 kWmGross Engine output – Standby

Diesel Power Generator – Cummins NT855 [24]

Date post:	20-Mar-2018
Category:	Documents
Upload:	truonganh
View:	214 times
Download:	2 times

ROLE OF MAINTENANCE IN COMPONENT AND …jed3/Theses/Haider-MEngReport-UofA-2007.pdf... predictive...

Documents