Alstom Vailbility Assessment

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ALSTOM GT26 AN AVAILABILITY AND RELIABILITY ASSESSMENT Robert F. Steele Kevin P. Licata Director Engineering Manager - Customer Service Strategic Power Systems, Inc. Strategic Power Systems, Inc.

Salvatore A. DellaVilla President

Strategic Power Systems, Inc. Abstract

The global energy market continues to drive and motivate significant change, both structurally

and technologically. Structural change is the result of the markets move toward deregulation,

while technological change is driven by the need for new generating alternatives with improved

efficiency, higher output, and increased environmental friendliness. In one sense the markets

motivation for structural and technological change has provided both the catalyst and the

incentive for the evolution of advanced gas turbine designs (also known as F class), made

available to the market by several original equipment manufacturers (OEMs). And as these gas

turbine lines have evolved in capacity, output, and performance, market expectations for

availability and reliability, set by pro forma requirements remain high. Availability and

reliability is tied to the owner/operators pro forma profitability objectives for the plant.

Normally, the success of product design evolution and advancement is achieved in time through

active and effective engineering improvement efforts typically focused on the commitment to

reliability growth. Certainly, the characteristic curve of reliability growth is applicable to and

evidenced by the actual performance of these F class gas turbine machines, across all

manufacturers, as they have been introduced in the field over the past fifteen years. This paper

focuses on the use of Strategic Power System, Inc.s (SPS) ORAP (Operational Reliability

Analysis Program) Program for accurate analysis and measurement of reliability and availability

growth. To demonstrate this, ALSTOMs GT26, a 50-Hertz gas turbine fleet was selected as a

case study, as it had introductory issues, which required engineering efforts, and measurement of

reliability growth was feasible. ORAP tracks and reports reliability and availability performance

characteristics of several gas turbine designs across various MW size ranges, manufacturers,

ORAP and SPS are registered 2 Trademarks of Strategic Power Systems, Inc. COPYRIGHT 2004 Strategic Power Systems, Inc. - All Rights Reserved

applications, and duty cycles. The paper presents and discusses the engineering effort made by

ALSTOM to strengthen the operational capability of the GT26 fleet to achieve and maintain the

necessarily high levels of reliability and availability performance that are expected from this

dynamic and challenging market. A detailed review of the current performance of the GT26 gas

turbine, as compared with the industry is provided.

The data on the GT26 fleet and the F class gas turbines in general, was utilized from the

ORAP program to accurately and impartially present current performance, to assess and

determine the impact of reliability growth. The recorded improvement observed in the GT26

fleet ORAP data, reported from a large number of operating plants, demonstrates that the GT26

has achieved reliability growth that is consistent with market expectations for the performance of

F class gas turbine and is consistent with other OEMs F- class gas turbines.

Introduction and Background

Market Expectations Reliability and Availability

Reliability and availability expectations are set by the market place based on an understanding of

the performance of mature gas turbine technology. This was and is clearly the case as the various

advanced class F-class product lines, both, for 50Hz and 60Hz market, across all manufacturers,

were introduced for commercial operation in the late 1980s and into the 1990s. Pro forma

expectations for the achievable level of reliability and availability required operational

performance consistent with the current technology at that time. Mature gas turbine design units

in the size range between 70 and 125 MW were expected to achieve 98% reliability and 93%

availability. These numbers, for this more mature class of gas turbines, were used to set market

expectations as the first of the F class fleet of gas turbines were deployed and went into

commercial operation.

In fact, the values are consistent with expectations set by EPRI (the Electric Power Research

Institute) during the Design of High-Reliability Gas Turbine Controls and Accessories

program of the early 1980s. This is also consistent with the goals for the U.S. Department of

Energys Advanced Turbine System (ATS) Program.


To achieve this high level of reliability and availability on a continuing unit year basis requires

that out of a total of 613 hours of downtime (both forced and scheduled outages), no more than

133 hours (~22%) should be classified as forced outage. ORAP data suggests that these values

are and have been sustainable, and in fact are representative of mature gas turbine designs in the

70 to 125 MW class range aggregated across all manufacturers.

The scope of equipment covered by this performance expectation covers the simple cycle plant -

gas turbine, controls and ancillary systems, generator, and related balance of plant systems

(Refer to Appendix A for details on scope). Clearly, the gas turbine is the prime mover in a

combined cycle plant arrangement (both single and multi shaft), and has a significant

contribution to the performance and operating flexibility of the plant. Consequently, the

technology advancement associated with the gas turbine has been the focus of the market relative

to establishing reliability and availability expectations. That is the reason EPRI set reliability

and availability goals during the High Reliability Controls and Accessories program of the

early 1980 at the simple cycle plant level. Hence, the focus of this paper is an assessment of the

simple cycle plant comprising the GT26 gas turbine as compared to all other F class gas

turbines across all other manufacturers.

Reliability98.0%

Availability93.0%

0%

20%

40%

60%

80%

100%

Historical ORAP Data For Mature Units and Initial Market Expectations for F-Class Units

Figure 1


These initial expectations for the F-class did not consider the pattern of reliability growth

typically associated with a new product introduction. Especially with the advanced class gas

turbines such as the F-class, that incorporated more complex technologies, including higher

temperatures, more sophisticated materials and cooling methodologies, with a major constraint

being the environmental requirement for low NOx emission levels. However, they did reflect the

market perception and requirement for achieving high reliability and availability levels, across

all operating duty cycles, as they directly influence the profitability of the plant and the

owner/operator. Consequently, as key indicators of performance, the market expects that

reliability and availability will influence and be treated as essential design criteria that must be

considered as alternatives and trade-offs are made.

There was no consideration for reliability growth, as stated earlier, only that the F class gas

turbines would achieve current levels of performance as already seen in mature gas turbine

designs. The fact is that reliability growth was necessary to achieve and sustain these market

expectations.

However, it is important to recognize, that the markets perception and expectations for pro

forma reliability and availability rarely reflect the actual pattern of reliability growth that is

experienced in the field. Reliability performance is a function of both the inherent designed in

reliability or capability of a product, as well as the specific operating and maintenance profile

that must be met. Whether performance is acceptable or not is determined by the market, against

the existing perception. Relative to market acceptance, when a product under-performs

expectations, reliability growth must be achieved. And reliability growth is driven by how

quickly and completely operating experiences (i.e. issues, problems, forced outages, pre-mature

maintenance) can be defined, resolved, and implemented across the operating fleet.

F class operating units, in general, have demonstrated the typical pattern of reliability growth

from the late 1980s to the present. Note that, F- class gas turbines were launched for both 50Hz

and 60Hz market. Given the actual field experience, perhaps expectations for the initial

performance of F class technology should have been lower to allow for the introductory

reliability growth period associated with a new product introduction. Nonetheless, on average,


the achieved reliability and availability of F class technology today, across all manufacturers,

is 96% and 88% respectively. The availability of 88% has improved over time from the low

80s, indicating the initial introductory issues of all F-class gas turbine technology.

These reliability and availability values must be considered as the markets current requirement

for the performance of F class technology plants. Whether the units are in simple or combined

cycle, or whether they operate in a baseload, cyclic, or peaking duty, the performance

expectations are consistent.

ORAP Process and Methodology

In order to accurately measure RAM performance relative to goals and market expectations, a

source of accurate and unbiased data is required. The independent and unbiased source of

reliability and availability statistics used to support the market in establishing realistic

expectations for achieving and sustaining acceptable reliability and availability performance

levels is an extremely important consideration. Strategic Power Systems, Inc. (SPS), a global energy sector business, is uniquely focused on this important issue, and is able to provide the

market with meaningful and accurate reliability and availability information through ORAP

(the Operational Reliability Analysis Program). ORAP is the largest most comprehensive

reliability database in the energy market focused on gas turbines in both simple and combined

cycle operation. The data reflects the operating experience of over 1,700 gas and steam turbines

worldwide, across all manufacturers, product lines, and duty cycles. Further, the data represents

the performance capability of both mature and advanced technologies.

ORAP is an automated system for monitoring the Reliability, Availability, and Maintainability

(RAM) of both combustion (gas) and steam turbine driven plants, with the emphasis on the total

plant, including condensate and feed water systems, power distribution, heat recovery steam

generators, electrical generators, driven equipment, and all mechanical and electrical balance of

plant systems. Standard Equipment Codes, developed by SPS under an EPRI contract, are the

basis for the uniform reporting system across all product lines and OEMs. These codes provide

reporting uniformity across all equipment types, providing a basis for combining or segmenting


data at a component level across equipment manufacturers, size ranges, or other valid criteria.

Additionally, ORAP is capable of obtaining data using the European KKS standard.

This product breakdown structure or equipment taxonomy is essential for recording event data

(either/or forced or planned outages at the component level). Further, SPS ensures that the

ORAP system adheres to industry measurement standards of RAM (i.e. IEEE 762 and ISO 3977-

9), please see Appendix B for applicable definitions from ORAP. The information available in

ORAP covers various applications, duty cycles, and plant arrangements for both simple and

combined cycles.

Data from participating plants is submitted to SPS on a monthly basis, or in some cases on a

real time basis, for engineering review and data validation, data acceptance according to

relevant industry standards, and incorporation in the ORAP database. This process is illustrated

in Figure 2.

Issue Electronic Reports

Web Enabled Reporting

Participating Plants

ORAP

Reliability Database Operating Data Time, Capacity & Events Outage Events to Component Level Maintenance Events Others

Data Edit & Verification Preparation for Reporting

ORAP Information Flow

Quarterly Reports Fleet & Industry

Participating Plants vs. Fleet Benchmarking

Component Detail

Submit Monthly Data

Total Plant Simple and Combined Cycle

Standard Equipment Codes Component Level

Figure 2


An important aspect of the data collection process is to obtain event data (forced and scheduled

outages) at the right level of detail to support an understanding of the causes of

unavailability/unreliability. Standard event types, based on IEEE Std. 762, were created and used

by ORAP. ORAP data is collected and reported from the "bottom-up". In other words, ORAP

allows the engineer to see the impact of a component failure including shared equipment, up to

the system, up to the plant. This level of detail is essential for effective reliability analyses.

The ORAP information system then converts the data into RAM statistics such as: detailed

system and component outage factors, failure rates, starting unreliability, service factors, time to

repair, and other outage factor information. Additionally, ORAP provides outage description

details, outage causes, failure modes, and corrective actions taken (as supplied by the plant

operator). This information provides the basis for assessing plant, system, and component RAM

performance, as well as, for developing RAM values to assess improvement. It should be noted

that the data reported to the SPS ORAP system from various utility and co-generator participants

is reviewed for accuracy, verification, and then entered into the database. The information is not

modified by SPS unless the participating customer concurs with and accepts the recommended

change. SPS engineers work with each participant to ensure data accuracy and completeness.

This ensures that SPS ORAP data reflects the specific operational, failure, and maintenance

history for each component in the database, and therefore, the availability and reliability

performance measurements are valid indicators of unit experience and capability.

A proprietary and non-disclosure relationship establishes the basic rules for how SPS will

process unit and site specific data for each participant, as well as combining like data together

to develop fleet level performance. Participation in ORAP provides members with quarterly

reports of statistical comparisons of their equipment with units in similar applications and MW

range for industry assessment, fleet benchmarking, and up-to-date operational information.

Moreover, the ORAP data is used to perform reliability assessments that can effectively measure

and demonstrate reliability performance. As an example of an assessment, the RAM performance

of the ALSTOM GT26 is presented here.


GT24/GT26 Technology Review

The GT24 (60 Hz) and the GT26 (50 Hz) product lines are unique in the gas turbine industry in

that they utilize sequential combustion to provide a method for achieving high cycle efficiency

with increased power output, without significantly increasing the firing temperature above

current available technology. The engine was developed in the early 1990s and combines two

features used in other ALSTOM engines: the EV burner in annular combustion and the

sequential combustion technology (see figure 3). Sequential combustion had already been

applied to earlier (Brown Boveri) gas turbines, but using two side mounted silo combustors.

The design philosophy focused on the use of an annular combustion process, capitalizing on the

design approach and operating experience associated with the GT13E2 and GT8C2 product

lines. This sequential combustion design utilized ALSTOMs Environmental (EV) and

Sequential Environmental (SEV) burners in tandem to maintain cycle temperature at current

levels, while achieving a higher output and improved efficiency, especially at part load

conditions. The high power density is apparent with the GT26 having the same basic footprint as

the GT13E2 but developing some 100 MW more power.

A further, yet important benefit of the sequential combustion approach relates to the ability to

attain low NOx emission levels. The simple design of the EV burner leading to complete air /fuel

mixing before ignition and the lower oxygen levels and less heating required to reach flame

temperature in the SEV combustor both go towards NOx emission levels well below the current

statutory limits of 25 ppm.


Compressorwith 3 VGV rows

EV Fuel Distribution System

SEV Fuel Distribution System

High Pressure Turbine

Low Pressure Turbine

Maintenance-free welded rotor

Figure 3: Main Features of the GT26 gas turbine (courtesy ALSTOM)

The high-pressure turbine comprises a single stage of rotating blades downstream of the EV

combustor. The exhaust from this stage passes to the SEV combustor where additional fuel is

introduced before expanding through a four-stage low-pressure turbine. The turbine components

make use of advanced materials such as single crystal and directionally solidified castings as

well as thermal barrier coatings.

The cooling circuit/flow was designed to provide required and adequate cooling through an

external once through heat exchanger. Air extracted from the compressor is cooled in both a

high and low-pressure heat exchangers (once through cooler) and then used to cool the various

turbine stages. By integrating these coolers into the water/steam cycle, the heat removed from the

GT cooling air is not lost but used to maximise both power output and efficiency of the overall

combined cycle. From a reliability engineering perspective, the integration of the compressor,

combustion, turbine, and cooling systems, that drive the gains in operating efficiency and output,

have a strong influence on the operational reliability and availability of this advanced product.

GT26 Product Evolution

In 1999, the first B configuration versions of the GT24/GT26 engine went into operation (the

earlier GT24/GT26 engines being subsequently designated as A configuration engines). These

improved versions incorporated not only performance improvements based on ongoing

development but also included changes that would provide improved reliability and availability.


LPT Blade 2

LPT Blade 1

19991999 20002000 20012001 20022002 20032003

Introduction of the GT24/GT26 B-Configuration

LPT Row 2 shroud

LPT Blade 1

The objective was to ensure reliability growth, as well as to achieve the performance and

operating requirements of the plant. Following were the changes made:

The EV burner was modified to a cast as opposed to a welded design for improved performance. Additionally, the burner went from a fixed design to a retractable

design so improving maintainability. At the same time, the burner size could be

standardized for both the GT24 and GT26 and the number of burners could also be

reduced (on the GT26, reduced from 30 to 24)

Improved turbine cooling: changes involved further use of thermal barrier coating, adjustments to cooling holes patters.

Improved seal designs to reduce losses.

1999 1999 2000 2000 2001 2001 2002 2002 2003 2003 20042004

Fleet Operation

Reliability Assurance Plant

(Inlet cooling and cycle optimization)

Upgrade Compressor

Figure 4: GT26 gas turbine Evolution over time (courtesy ALSTOM)

Figure 4 provides an overview of the reliability assurance and engineering improvement program

followed by ALSTOM that resulted in the B configuration of the GT26.

Furthermore, during the introductory phase on the B configuration operation, several issues came

to light that required modifications. The two items that are of interest in the time period studied

are:


Shroud deformation on the 2nd stage low-pressure turbine blade was resolved by modifying the stator heat shield to improve shroud cooling. In addition, improvements

were made to the blade airfoil comprising of additional thermal barrier coatings and by

cutting back the blade to reduce trailing edge stresses, as well as providing improved

temperature resistance.

1st stage low-pressure turbine blade exhibited cracking at a particular row of cooling air holes. The solution was straight forward in that it proved possible to omit these cooling

holes in subsequent production. While there were no cases of actual blade failure, engine

monitoring was necessary which had a corresponding impact on engine availability

Of the current fleet of GT26 operating units in the field, approximately 50% (11 units) were

either shipped with or modified in the field during the commissioning phase to include the two

issues noted above. This provides an important source of information specifically related to

monitoring these units from a reliability growth perspective. In addition, all of the enhancements

(except for retractable EV burners which are not available for A configuration engines) were also

made to the remainder of the GT26 fleet prior to July 2002. Consequently, the GT26 fleet after

July 2002 included all the above enhancements, and the operational reliability performance can

be assessed to quantify the reliability improvement and growth.

GT26 Current Performance and Reliability Growth

The GT24/GT26 fleet consisting of 74 units in commercial operation has crossed one million

fired hours. More than 700,000 operating hours have been accumulated since mid 2002 when

most of the units started operating commercially. During the period measured, the fleet of GT26

gas turbines includes 23 units in commercial operation that have accumulated over 425,000

operating hours. Three quarters of the total operating hours were accumulated in the period of

mid 2002 till May 2004. From this perspective, it is important to review the period when the gas

turbine is considered stable and has accumulated major operating experience. Moreover, it is the

period, as stated earlier, when most of the reliability assurance enhancements were completed.


As stated previously, the market expectations for reliability and availability are based on simple

cycle plant scope. In other words, the unreliability/unavailability (that ultimately set the goals)

are based on a scope of plant equipment that includes; gas turbine, control and ancillary systems,

generator, fuel supply, power distribution, and other related balance of plant systems. This is an

important consideration that characterizes the performance indicators and comparisons on a

uniform basis across the ORAP F class fleet.

With these points in mind, SPS performed an independent technical reliability engineering

review of the data available in ORAP to determine if reliability growth has been experienced and

achieved by the GT26 gas turbine fleet. It is important to describe the technical approach that

SPS followed to derive meaningful and accurate results using the ORAP system. ORAP data for

the period July 2002 to May 2004 was reviewed. This period, as previously stated, represents

the point in time where all GT26 units included most of the engineering improvements along

with high operating experience. Consequently, the reliability and availability performance of the

GT26 during this period should be indicative of the effectiveness of the improvement program,

hence an indicator of reliability growth. Further since the other F- class machines were

introduced earlier than the GT26 this period should be indicative of their current performance.

Sample selection is an important consideration when performing an assessment of reliability. If

care is not taken when defining samples, results and conclusions can be distorted. In addition the

following describes the major considerations that went into the definition of the samples utilized

in this assessment.

14 of the 23 GT26 units (~60%) participate on the ORAP program. This sample size can be considered as random and therefore provides a sound base from which measures of

central tendency can be developed with strong statistical significance and inference.

To be considered an ORAP participant, data must be continuous i.e. with no gaps in the data. Therefore the data represents all operating experience on the units since participation

in ORAP began. Further, SPS does not modify the data reported from the operating plant.

If there is a question on the data submitted, the SPS personnel will contact the site to ensure


that the data accurately reflects site experience. The data is not changed unless the site

concurs with the changes. This ensures that RAM performance is accurately represented.

All comparisons made in the assessment between the GT26 and the rest of the F Class fleet in general is made on a simple cycle plant basis. The units that make up the fleet are

in different configurations, whether in simple or combined cycle. The Simple Cycle Plant

represents the largest common denominator of plant equipment. By performing the

comparisons on this basis, it ensures that similar equipment is being compared from plant

to plant. Steam cycle design differences such as the ability to bypass the steam cycle, or

the possibility to operate at partial plant output in a multi-shaft arrangement do not impact

the assessment. The assessment is therefore focused on the gas turbine plant equipment in

order to ensure consistent comparisons.

The GT26 units reporting to ORAP during July 2002 to May 2004 accumulated approximately 160,000 period hours, with approximately 126,000 operating hours

accumulated during this period. In general this is indicative of a high service factor

(~78%). Even though the period since the engineering changes have been made is

relatively short, the GT26 Fleet has gained a significant amount of operating experience in

that time. Therefore, the effect of the engineering improvements can be seen relative to the

impact on the operational capability of these units.

Statistically, the greater the operating time accumulated, the tighter the confidence limits on the sample. Estimating the 95% confidence bounds on the reliability, based upon the

standard error of the mean, results in a range of approximately +/-1.5%. This is an

indication that, the confidence bounds around the sample are fairly tight.

When utilizing any particular period of time to perform comparisons, it is important to understand that since major maintenance activities are performed on an operating time

basis, and could possibly be excluded in such a time sample. When reviewing the GT26

data from July 2002, it is clear that this is not the case. During this period, all units had the

A & B visual inspection and some had C Inspections (Hot Gas Path Inspections). Since


some of these inspections were also extended to perform compressor upgrades, the impact

of this maintenance would tend to decrease the availability (as opposed to the availability

being increased if the sample included no maintenance), making comparisons somewhat

conservative from a maintenance perspective. In addition, given any sample, units will be

at different points in their maintenance cycles, so some units will have maintenance

activities included and some will not. The percentage of Hot Gas Path inspections that

GT26 went through in this period can be considered to be consistent with the percentage of

units in the other F-class. Therefore, as with the other F-class sample, this can be

considered to provide an indication of average performance over time.

All GT26 units reporting to ORAP are operating in a combined cycle with various modes of operation; daily start/stop, baseload/continuous, and cycling/intermediate.

Consequently, this provides the opportunity to assess the impact of the engineering

improvements across a variety of operating regimes.

Reliability and Availability -

Figure 5 provides a review of the reliability and availability of the GT26 ORAP fleet as

compared with the other F class ORAP fleet for the period of July 2002 to May 2004 (on a

cumulative basis). This figure shows that the GT26 has achieved both reliability (98.3%) and

availability (91.8%) levels that are consistent with the market expectations relative to F class

performance (described in a previous section of the paper).


98.3% 97.9% 98.0%

91.8% 91.8%93.0%

75%

80%

85%

90%

95%

100%

Reliability Availability

Simple Cycle Plant Availability & ReliabilityJuly 2002 through May 2004GT26 Units and F Class Units

GT26 F Class Units Market Expectations

Figure 5

The ORAP data demonstrates that the engineering improvement program and implementation

efforts along with the reliability assurance program for GT26 have been effective and have

resulted in reliability growth that is consistent with market perceptions and expectations.

Figure 6 provides a review of the ORAP data on a rolling 12-month basis. A rolling 12-month

average is important to demonstrate that fluctuation in the monthly levels of availability and

reliability, and the ability to sustain a required level of performance and reliability growth. It

shows a pattern of growth beginning in July 2002 and increasing over time to the levels required

by the market. Also, the chart shows that reliability has achieved a sustainable level of ~97.3%

since January 2003.


Simple Cycle Plant Availabilty & ReliabilityGT26 Units - Rolling 12 Month Average

75%

80%

85%

90%

95%

100%

Jul-02 Sep-02 Nov-02 Jan-03 Mar-03 May-03 Jul-03 Sep-03 Nov-03 Jan-04 Mar-04 May-04

12 Month Period Ending

Reliability Availabilty

Figure 6

NOTE: It is important to note that the rolling 12-month averages for the periods prior to June

2003, contain data prior to the implementation of all engineering improvements.

To provide a more detailed example of the reliability growth of GT26, Figure 7 and 8 provides a

review of the ORAP data on a rolling 12-month basis for the GT26 and other F class units in

baseload/continuous duty operation over the past 12 month period.


F Class & GT26 Baseload/Continuous DutySimple Cycle Plant Reliability

Rolling 12 Month - July 2002 to May 2004

85%

88%

91%

94%

97%

100%

Jun-03 Jul-03 Aug-03 Sep-03 Oct-03 Nov-03 Dec-03 Jan-04 Feb-04 Mar-04 Apr-04 May-04

Rel F Class 97.8% 97.9% 98.0% 98.0% 98.1% 97.6% 97.3% 97.3% 97.6% 97.8% 98.0% 98.0%

Rel GT26 98.2% 98.2% 98.4% 98.3% 98.3% 98.3% 98.3% 98.4% 98.4% 99.0% 98.8% 98.9%


Figure 7

F Class & GT26 Baseload/ContinuousSimple Cycle Plant Availability

Rolling 12 Month - July 2002 to May 2004

85%

88%

91%

94%

97%

100%


Avail F Class 92.8% 93.2% 93.2% 93.1% 93.1% 92.2% 91.5% 91.0% 91.6% 92.4% 93.1% 93.3%

Avail GT26 89.3% 89.1% 87.8% 88.9% 89.6% 90.1% 90.7% 92.0% 92.1% 92.6% 92.9% 94.8%


Figure 8

As in the previous charts, a pattern of reliability growth beginning in 2002 and steadily

increasing over time is evident in these charts. Specifically, the reliability chart indicates that the


GT26 gas turbine achieved, and has sustained a level that meets and exceeds market expectations

(greater than 98%).

The following can be concluded for Reliability and Availability:

The GT26 is equal to other F class engines.

The GT26 has shown steady and sustained improvement over the past 2 years indicating the effectiveness of the engineering efforts.

Service Factor

A review of the service factor experienced during this period of July 2002 to May 2004 (on a

cumulative basis) is shown in Figure 9. The data shows that the GT26 units operated ~78.5% of

the time (on average 6,877 hours per year).

78.5%

55.1%

68.5%

0%

20%

40%

60%

80%

100%

Service Factor

Simple Cycle Plant Service FactorJuly 2002 through May 2004GT26 Units and F Class Units

GT26 F Class Units Market Expectations

Figure 9

Figure 10 represents a plot of the service factor versus the service hours per start ratio, by unit

for the period July 2002 through May 2004. It demonstrates the operating profiles of the GT26


compared with other F Class fleet in general. This clearly illustrates that while the GT26 units

are operating in all duty cycle modes there is a large number of units in the F Class that are

operating in peaking duty, with very low service factors and service hours per start ratios.

Because the GT26 units are operating with high service factors, there is not a significant period

of reserve time that influences the availability, therefore, the availability figure of GT26 (91.8%)

presented in the earlier chapter could be considered to be rather conservative.

Service Factor v. Service Hours per StartJuly 2002 through May 2004

GT26 Units and F Class Units

0

300

600

900

1,200

1,500

0% 20% 40% 60% 80% 100%Service Factor (%)

Serv

ice

Hou

rs p

er S

tart

GT26 Units F Class Units

Figure 10 Unavailability Assessment

The sources of equipment unavailability are recorded as forced outages, unscheduled

maintenance, and scheduled maintenance. From the reliability and availability data presented

above, Table 1 below shows the outage factors for the GT26 and the other F class units in

general for the cumulative period, July 2002 through May 2004.


Simple Cycle Plant Unavailability July 2002 through May 2004

GT26 Units and F Class Units GT26 Units F Class Units Forced Outage Factor (%) 1.70 2.10 Unscheduled Maintenance Factor (%) 0.52 0.97 Schedule Maintenance Factor (%) 5.95 5.13 Total Unavailability (%) 8.20 8.20

Table 1 This data suggests that the majority of downtime for both the GT26 and the F class units in

general is related to scheduled maintenance. In fact, scheduled maintenance represents more

than 60% of the total downtime experienced by these units.

As a note, when comparing these values of scheduled outage factor with mature technology there

is a significant increase in the downtime contributed by scheduled maintenance for all F class

advanced technology.

To assess the reliability growth, it is important to review forced outages, from both a frequency

and duration standpoint. This assessment should focus on the units ability to meet its required

operating profile. In this case measured by the frequency of forced outages from a state

operation) or Mean Time Between Failure (MTBF) and the time to restore the unit to a state of

operational readiness or Mean Time To Repair (MTTR). Figure 11 provides the Mean Time

between Failures for the GT26 units based upon a rolling 12-month average. The increased

service time between forced outages can be clearly seen from the trend in this figure. In

addition, since the end of 2003, the average service time between trips for the GT26 has

remained at or above ~1,000 hours, consistent F class units and with availability requirements.

Figure 12 provides the rolling 12-month average for the Mean Time to Repair. Both, MTTR and

MTBF are consistent with the other F class data.


0

250

500

750

1,000

1,250

Ho

urs

Jun-03

Jul-03

Aug-03

Sep-03

Oct-03

Nov-03

Dec-03

Jan-04

Feb-04

Mar-04

Apr-04

May-04


Simple Cycle Plant - Mean Time Between Forced OutagesGT26 Units - Rolling 12 Month Average

0

10

20

30

40

50

Ho

urs

Jun-03

Jul-03

Aug-03

Sep-03

Oct-03

Nov-03

Dec-03

Jan-04

Feb-04

Mar-04

Apr-04

May-04


Simple Cycle Plant - Mean Time To Repair Forced OutagesGT26 Units - Rolling 12 Month Average

Figure 11 Figure 12

Note: MTBF is the mathematical inverse of the failure rate. Therefore an increase in MTBF

indicates a decreasing failure rate, which in turn indicates a reduction in trips from a state of

operation.

Starting Reliability

An important issue in the market, especially for gas turbines that must meet either a peaking duty

or a daily start/stop mission profile is starting reliability. Relative to the effectiveness of the

engineering improvement effort described earlier and as an additional measure of the units

ability to meet its operating profile, the ability of the GT26 to successfully start and achieve a

preset load is an important factor that must be considered. ORAP data for the F- class and

GT26 fleets shows a starting reliability for both samples that is approximately 96%.

Operational Flexibility

The GT26 units participating in the ORAP database as described earlier are all operating in

combined cycle plant configurations. There are no simple cycle units included in this data set.

When the duty cycle of these operating plants is considered on a service hours per year and

service hours per start basis, it is clear that the GT26 ORAP fleet can be considered from the

following operating perspectives;


(1) Cycling/Intermediate Duty - high service hours (~6,300 hours/year) and high starts (~70

starts/year)

(2) Baseload/Continuous Duty high service hours (~7,300 hours/year) and fewer starts (25

starts/year)

(3) Daily Start Stop operation low service hours (~4,000 hours/year) and very high starts

(~270 starts/year)

These statistics demonstrate the capability of the complete combined cycle plant to meet the

economic dispatch profile of the owner/operator. When the total plant statistics are reviewed, the

steam cycle (HRSG, steam turbine, condensate and feed-water, etc.) does not contribute a

significant level of unreliability during these operating periods. These results support findings

developed by the Electric Power Research Institute (EPRI) in High Reliability Combined Cycle

Power Plant study.

A review of the reliability and availability trends stratified by duty cycle using ORAP data would

demonstrate a similar trend of growth that is consistent with the GT26 sample (including all duty

cycles) that has been presented here. The effect of these strenuous duty cycles must be

considered relative to the operational flexibility of the GT26 gas turbine. This is an important

consideration as operating requirements for cycling, daily start/stop operation, and baseload

requirements in todays operating environment are driving the economic viability of the

operating plant.

Upgrade Opportunity

As the design changes were made and completed, prior to July of 2002, opportunity for uprating

the GT26B configuration allowed ALSTOM to take advantage of available margin in the design,

resulting in a higher output and improved efficiency. As part of this product development, a

compressor upgrade program was made available with the target of providing higher output. The

compressor has been modified to achieve an approximately, 5% higher mass flow. This was


achieved by optimized aerofoil design and restaging of the blades. There has not been any

degradation in reliability growth due to the introduction of this compressor upgrade.

From an availability perspective, the changes that were made and introduced took place during

periods of scheduled maintenance. ORAP data does not show any issues and initial operating

constraints that resulted in significant forced outage downtime. Rather, limitations in

performance and output resulted in design change that required scheduled downtime to introduce

the improvement to the operating plant. In fact, the additional time required to perform the

compressor upgrade as observed in ORAP data, typically extended the scheduled maintenance

over the normal period. From an assessment of the data, the outage extensions represented

approximately 0.4% of additional unavailability. Consequently, the achievable level of

availability is expected to be in the range of 92% and continues to be consistent with market

expectations. In fact, the GT26 value (91.8%) expressed earlier is conservative, as the percentage

of additional unavailability due to compressor upgrade program is included in the statistics.

Summary and Conclusion

Today the global market continues to evolve as new challenges and constraints place an ever-

increasing focus on the value of reliability and availability. Expectations for reliability and

availability performance at the right level, as set in the pro forma, have a tremendous impact

on the profitability of the operating asset. Consequently, the financial implication of not

achieving performance requirements is a significant risk a risk that can be typically mitigated

through contractual service arrangements. The owner/operator and the OEM are now uniquely

committed to the same objective financial reward as a function of equipment capability and

performance. The gap between equipment design and serviceability (operations and

maintenance practice) has been closed due to the value proposition and shared risk associated

with high reliability and availability.

This paper has described the ORAP process and demonstrated the effect of its usage rightly to

measure quantitatively from its database on the engineering efforts put forth by ALSTOM to


provide a substantial level of reliability growth associated with the performance of the GT26,

to specifically meet market expectations in a manner that is sustainable.

As can be seen from the information presented here, ORAP provides a strong basis for assessing

the RAM performance of gas turbines plants. Further, because of the level of detail available

from ORAP, detailed Reliability Engineering assessments are feasible.

Conclusions that are developed from a review of the ORAP data are:

A reliability of 98% and an availability of 92% are achievable and sustainable by GT26 and other F-Class fleet across all manufactures.

The GT26 recorded and achieved substantial improvement and sustainable reliability growth in a relatively short period of time (just less than 2 years) indicative of the

effectiveness of focused engineering efforts.

In general, the fleet of GT26 units have a significantly high economic demand profile (relative to the market in general) these economic dispatch requirements are

supported by reliability growth as seen through a reduction in forced outage trips, and

an improved mean time between failure.

Reliability growth is necessary for any product line to achieve the reliability and availability targets. This assessment of GT26 fleet demonstrated that with appropriate

engineering focus, these targets could be achieved.

In general, the fleet of GT26 units demonstrates a relatively high operational flexibility, with a high level of starting reliability (96%), at varying load profiles and

operating regimes.

The steam cycle equipment (HRSG, Steam Turbine, Condensate, Feed-water and associated balance of plant equipment) has negligible impact on the reliability

performance of the GT26 units. This is significant because all of the GT26 are in

combined-cycle.


The design evolution of the GT26 technology has proceeded in a manner consistent with the markets expectations for F class gas turbines. Specifically, the increased

output and improved efficiency attributes, obtained through the engineering

improvements and the compressor upgrade opportunity, have resulted in a product

that effectively meets the demands of the market.

The reliability growth of GT26 gas turbine and current levels of reliability and availability

achieved, as demonstrated by the ORAP data, fully meet the performance expectations of the

market, and are consistent with the reliability and availability of the fleet of F class gas

turbines across all equipment manufacturers. The results of the reliability assurance efforts (the

engineering improvements) clearly demonstrate a commitment to the market through a focus on

reliability growth.


Bibliography - [1] Electric Power Research Institute, High-Reliability Gas Turbine Combined-Cycle Development Program, EPRI AP-1681-SY, January 1981

[2] Electric Power Research Institute, Design of High-Reliability Gas Turbine Controls and Accessories, EPRI AP-5823, June 1988. [3] Von Rappard, A.W., Della Villa, S.A., 2001, Gas Turbine Performance of Mature, F- and Advanced Technologies 2000, ASME 2001-GT-394. [4] Lloyd, Jonathan, 2003, ALSTOMs GT24 and GT26: A High-Performance Workhorse. [5] ANSI/IEEE Std 762-1987, IEEE Standard Definitions for Use in Reporting Electric Generating Unit Reliability, Availability, and Productivity. [6] International Standard ISO 3977-9:1999, Gas Turbines Procurement, Part 9: Reliability, availability, maintainability and safety. [7] Philipson, Stephen, Sudland, Martin, and Raza, Mohammad, 2004, The GT24/GT26 Fleet: A Review as the Fleet Approaches 1 Million Hours of Operation. [8] Della Villa, S.A., Electric Power 2004, Optimizing Product Performance Using Reliability & Information Technology to Improve Productivity and Drive Profitability. [9] ALSTOMs GT24 and GT26: Building on Experience Brochure [10] ORAP RAM definitions and unavailability Event types. [11] ORAP Data from different Power Plants with gas turbines from different manufacturers


Appendix A Simple Cycle Plant, Equipment Scope

System Description

Gas Turbine Station Equipment (Balance of Plant) Electric Generator Atomizing Air Plant Service Air Bearings Accessory Drive Plant Instrument Air Cooling Air Air Inlet Cycle Chemical Feed Control and Protection Auxiliary Power Cranes Excitation Bearing Lift Oil Distributed Control System Hydrogen Cooling Bearings Emissions Monitoring Lubrication Cooling and Extraction Air Plant Fire Protection Generator Combustion Fuel Gas Supply Seal Oil High Pressure Compressor Engine Auxiliary Cooling Water Closed Compressor Liquid Fuel Unloading Auxiliary Power Controls Liquid Fuel Storage Load Couplings Cooling Water Closed Liquid Fuel Treatment Load Gear Enclosures Nitrogen Lubrication Exhaust Non-Component Chargeable Event Power Distribution Liquid Fuel Forwarding Plant Process Steam Fire Protection Power Distribution Gas Fuel Auxiliary Steam Supply Hydraulic Control Exhaust Stack Heating and Vent. Combined Cycle Steam Supply Instrument Air Raw Cooling Water Ignition Gas Water Cooling Tower Liquid Fuel Auxiliary Cooling Lubrication Circulating Chemical Feed Fuel Purge Cycle Water Makeup & Storage Regenerators Cycle Makeup Water Steam Injection Waste Supports Starting Turbine High Pressure Turbine Low Pressure Turbine Water Injection Water Wash


Appendix B - Standard Terms and Definitions

Availability: The percentage of time that a unit is available to operate without a maintenance

repair or a failure of an equipment system or component. Availability includes the effects of

both maintenance and forced outages. This is a statistical measurement represented in the

following equation:

( ) 100100(%)

+=PH

FOHMHtyAvailabili

Where Maintenance Hours (MH) = Scheduled + Unscheduled Maintenance Hours FOH = Forced Outage hours PH = Period hours

Reliability: The percentage of time that a unit is available to operate without a failed equipment

system or component causing a forced shutdown. This is a statistical measurement represented

in the following equation:

Reliability (%) = 100100 HoursPeriod

HoursOutageForced

Forced Outage Factor: Represents the ratio of Forced Outage Hours and Period Hours. This is a

statistical measurement represented in the following equation:

100(%)

=

hoursPeriodHoursOutageForcedFactorOutageForced

Scheduled Maintenance Factor: Represents the ratio of Scheduled Maintenance Hours and

Period Hours. This is a statistical measurement represented in the following equation:

Scheduled Maintenance Factor (%) = 100PH

SMH

SMH = Scheduled Maintenance Hours PH = Period Hours

Unscheduled Maintenance Factor: Represents the ratio of Unscheduled Maintenance Hours and

Period Hours. This is a statistical measurement represented in the following equation:

Unscheduled Maintenance Factor (%) 100

=PH

UMH

UMH = Unscheduled Maintenance Hours PH = Period Hours


Mean Time Between Failure (MTBF): An average measure of the number of operating hours that

a piece of equipment accumulates before incurring a forced outage. This statistic can be utilized

to represent the average mean time failure based on any failure type, but is traditionally utilized

for forced outage trip events. This is a statistic is represented in the following equation:

EventsTripOutageForcedofNumber

HoursServiceHoursMTBF =)(

Mean Time to Repair (MTTR): The average time required to restore a piece of equipment to

service following an event. This statistic can be utilized to represent the average time to repair

based on any failure type, but is traditionally utilized for forced outage trip events. This is a

statistic is represented in the following equation:

EventsTripOutageForcedofNumber

EventsTripOutageForcedofSumHoursMTTR =)(

Service Factor: Represents the percentage of time the unit was in operation during a given time

period. This is a statistical measurement represented in the following equation:

100(%)

=

HoursPeriodHoursServiceFactorService

Service Hours per Start: Represents the ratio of Service Hours and Successful Starts. This is an

average value of how long a unit will operate after each start. This is a statistical measurement

represented in the following equation:

=

StartsSuccessfulHoursServiceHoursStartperHoursService )(

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Alstom Vailbility Assessment

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