operational experience with latest gt26 upgrade

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POWER

Operational Experiencewith latest GT26 upgrade

Conference Paper



Operational Experience with latest GT26 upgrade

PowerGen Europe 2013 4-6 June 2013 in Vienna, Austria

© ALSTOM 2013. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it iscomplete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject tochange without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited.


Frank Hummel, Ralf Jakoby, Mark Stevens

Alstom Power, Baden, Switzerland

1 Abstract .............................................................................................................................. 3

2 Introduction ........................................................................................................................ 3

3 GT26/GT24 Development Evolution ................................................................................... 4

4 Units in Operation and Operational Experience ................................................................... 6

5

Operational Flexibility - Experience from Alstom GT26 Power Plant ................................... 9

6 Summary .......................................................................................................................... 19

7 Bibliography ..................................................................................................................... 20

Paper presented at PowerGen Europe in Vienna, Austria, 4-6 June 2013






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1 AbstractThis paper looks at both the increased operational flexibility features brought about by the sequential

combustion system of the latest GT26 (50 Hz) and GT24 (60 Hz) upgrades launched in 2011, as well as giving

an update on the operational capabilities validated at Alstom’s power plant in Birr, Switzerland. In particular,

this paper looks at the improved fuel flexibility, the newly introduced flexible operation modes, and the unique

low load operation capability – all made possible thanks to the sequential combustion system of the

GT26/GT24.

2 IntroductionPower markets around the world are facing new challenges: Building new power generation plants to meet

growing demand means also having to take into consideration more stringent global environmental standards.

Increasing all-round efficiency is one of the main market drivers for gas turbine and combined cycle

development and at same time produce power with lower emissions (NOx, CO, CO2 etc.), with the target of

reducing the net cost of electricity for the power companies.

Combined Cycle Power Plants (CCPP’s) are being required to operate and cater for an ever-increasing range of

operational duties and are being expected to meet challenging operating regimes ranging from base-load to

frequent (daily) stop-starts, which have the greatest impact on the plant components, especially thosecomponents exposed to the greatest thermal stresses during start-up / shut-down - namely the GT, ST, HRSG

and water-steam piping.

Operational flexibility as a key market requirement is becoming therefore increasingly more important in the

gas-fired power industry. OEM’s and Operators alike are re-defining the way combined cycle power plants

should be designed and the load-regimes that have to be supported today and in the future. The emergence

and growth of renewable power, in particular wind-farms, also brings new challenges and opportunities for

power companies and grid operators. The increasing installation of renewable power generation systems calls

for an increasing need for the reliable and rapidly available gas-fired CCPP power resources to be available as

back-up to cover periods of renewables-supply shortage, peak demands or simply following the automated

generation control over a wide range of relative load. As a result, the efficiency of CCPP’s under base-load and

part-load operation is becoming ever more important.

Additionally, today’s gas turbine equipment requires increased flexibility in terms of the degree of variation in

composition of natural gas as an increasing number of markets become more and more dependent on

imported LNG from varying sources. Market forecasts predict an increasing variation in the fuel gas

composition in the future. Already today, pipeline gases are seeing a higher fluctuation as they may consist of

combinations of multiple well-supplies that are blended and thus result in varying properties, and moreover,

power plants might be supplied directly with gas from LNG terminals. Flexibility regarding the fuel gases used

for gas turbines is therefore becoming more critical as this can greatly impact availability. A pre-condition for

this fuel flexibility is a robust combustion system that does not need additional measures like hardware change





© ALSTOM 2013. All rights reserved. Information contained in this document is indicative only. No representation or warranty is given or should be relied on that it iscomplete or correct or will apply to any particular project. This will depend on the technical and commercial circumstances. It is provided without liability and is subject tochange without notice. Reproduction, use or disclosure to third parties, without express written authority, is strictly prohibited..

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or re-tuning or fuel preheating, which either result in additional downtime for changing hardware or whichmight have an impact on the efficiency of the power plant.

Alstom’s latest GT26/GT24 gas turbines, with more than 15 years of operational experience behind it, offer

significant improvements in both performance and operational flexibility, whilst meeting low emission limits.

This paper will look in more detail at the following key operational flexibility features of the latest GT26

upgrade that is made possible thanks to sequential combustion and which have been validated at Alstom’s

power plant in Birr, Switzerland:

1) improved high fuel flexibility;

2) newly introduced flexible operation modes; and

3) unique Low Load Operation (LLO) capability

4) flexible start-up capability

3 GT26/GT24 Development EvolutionThe latest GT26/GT24 represents the fourth product-upgrade since their initial launch in the mid 1990’s.The

original platform has remained virtually unchanged throughout this time, but of course the GT26/GT24 have

reaped the benefits of operational (fleet) experience & feedback, as well as enhancements and improvements in

the aerodynamics and in-turn efficiency of the compressor, combustors and turbine. Figure 1 shows the

performance and flexibility evolution of the GT26/GT24 until today.

Figure 1: GT26/GT24 Performance and Flexibility evolution

The GT26/GT24 gas turbines from Alstom remain still the only “advanced-class” gas turbines featuring

Sequential (2-stage) Combustion, which has proven to deliver exceptionally high all-round performance as well

P E R F O R M A N C E *

Standard EV-burner +LP-Turbine Upgrade

• High Part-Load Efficiency

• Start up <60 min

• High fuel flexibility

Compressor Upgrade +Exhaust Housing

Upgrade

1999 features plus …

• Increased mass flow

• Improved all-round

performance (base-load and

part-load)

Compressor +

Turbine + CombustorUpgrade +

Staged EV-combustion



• Improved cooling and

leakage

• Start-up optimization

• Lower Emissions

• Low Load Operation option

• Fast Hot Start (< 30 min)

option

P E R F O R M A N C E

F L E

X I B I L I T Y

Compressor +SEV Burner +

LP-Turbine Upgrade



• Improved cooling and leakage

• Improved fuel flexibility

• High all-round performance

• Unprecedented part-load

efficiency (virtually constant

from 100% to 80% load)

• Flexible Operation Modes

(PO and MCO)

2002

2006

2011

1999

Higher Efficiency – Lower Relative CO2 Production






5

as outstanding operational and fuel flexibility. This unique combustion system allow the GT26/GT24 to deliverexceptionally high CCPP performance not just at base-load but also under part-load conditions, whilst at the

same time producing low NOx and CO emissions; and enabling the associated KA26/KA24 combined cycle

products from Alstom to be able to stay fully on-line to provide full stand-by spinning reserve at CCPP loads

down to 20% and even lower. From this low load operation point, the KA26 combined cycle can ramp back-up

to deliver more than 350 MW for the KA26-1 (1-on-1) configuration or more than 700 MW for the KA26-2 (2-

on-1) configuration in less than 15 minutes and the KA24-2 can provide more than 500 MW within 10

minutes.

Before looking more closely at some of the key operational flexibility features made possible by the sequential

combustion system of the GT26/GT24, we shall quickly re-cap on the core aspects of the Alstom GT26/GT24sequential-combustion system.

The latest GT26/GT24 gas turbine upgrades were introduced in June 2011 [1]. These upgrades contain

evolutionary modifications to the following GT components:

• Compressor

• SEV (2nd

stage) combustor

• LP Turbine

Figure 2 shows the major areas of development that took place for the latest upgrade. The modified

Compressor allows an increase in mass-flow for higher engine performance at improved operational flexibility

and high efficiency.

The LP Turbine is optimized for high efficiency and allows for flexible operation at increased inspection intervals

up to 30%.

The SEV combustion system is improved for increased fuel flexibility at yet lower emissions. To accommodate

the evolutionary compressor upgrade, the surrounding structural parts are modified as well. Again, an

evolutionary approach was done for design modifications to these parts. Further details on the features of the

latest GT26 upgrade are described in [1].

Compressor:- Increased mass flow

- Optimised blade design

- Increased turn-down ratio

LP Turbine :- Airfoil profile optimisation

- Leakage reduction

- Enhanced cooling scheme

SEV Combustor:- Optimised SEV burner

- Improved sealing

- Leakage reduction

Figure 2: Overview of major areas of evolutionary design modifications






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4 Units in Operation and Operational ExperienceAlstom designed the latest improved LP-Turbine for its latest GT26 engine upgrade to be retrofitable into

previous upgrades of GT26. It is available as an upgrade package for implementation within a regular

scheduled exchange of hot gas parts. To-date, three units in the GT24/26 fleet are in commercial operation

with the upgrade LP-Turbine. The front-runner GT26 unit has been operating with this latest LP-Turbine since

2009.

The complete GT26 upgrade has been in operation at Alstom’s own Birr Power Plant since April 2011. Two

further Units have been sold for a CCPP project in Thailand and are scheduled to enter commercial operation in

2015.

In the following sub-chapters the operational experience with the Units equipped with upgrade LP-Turbine, as

well as the Alstom Birr Power Plant will be shown. For the Alstom Birr Power Plant a short introduction with

respect to plant set-up and special instrumentation will be given.

4.1 Low Pressure Turbine Front-Runner

The first upgrade LP-Turbine has been running in a commercial field-engine in a KA26-1 CCPP in Spain since

2009. This front-runner has seen up to now two scheduled inspections. The first A-type (visual) inspection

undertaken after more than 5’000 OH, 45 starts showed the LP-Turbine to be in excellent condition. Picturesfrom the inspection were shown in [1]. The second scheduled B-type (visual) inspection was undertaken after

more than 10’000 OH, 173 starts in 2012. Again the LP-Turbine was found to be in excellent condition. Figure

3 shows pictures from this inspection.

As of March 2013 the front-runner has accumulated more than 11’000 OH and more than 210 starts. Since

the first implementation of the LP-Turbine front-runner two further retrofit upgrades have been implemented,

one in another GT26 unit in Europe and one in a GT24 unit in North America. These units have since their

retrofits accumulated more than 3’600 OH and 3’300 OH respectively.

Blade row 1Blade row 2






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Vane row 1 Vane row 2

Figure 3: Low Pressure Turbine front-runner B-type inspection pictures

4.2 Alstom GT26 Power Plant (Birr, Switzerland)

4.2.1 Plant Setup

The full 2011 package upgrade has been implemented in the ALSTOM GT26 Power Plant in Birr, Switzerland.

The Power Plant configuration is a simple-cycle with Once Through Coolers (OTC`s) connected to a water-steam cycle. The unit has been in operation since April 2011. It is connected to the local Swiss gas and

electricity networks. The electricity generated is sold to the Swiss power grid. The Birr power plant is also

equipped with a back-up fuel-oil system supporting base-load operation on oil and allowing high-load fuel

switchover. The unit is also equipped with an air-inlet pre-heater to enable engine operation simulation of high

ambient conditions. Figure 4 shows the power plant and the GT rotor during assembly.

Figure 4: Alstom GT26 Power Plant (Birr, Switzerland)






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4.2.2 Validation Instrumentation

The Alstom GT26 Birr Power Plant is equipped with more than 4000 special engine performance-monitoring

and validation instrumentation measurement locations. The data is used to validate and calibrate the

performance and lifetime prediction tools. In addition, the condition and health of the engine is monitored

online with the validation instrumentation during operation, including the operation of the unit beyond the

standard operating limits during special validation-runs.

The measurement data contains thermocouples, pressure taps, hot-gas rakes, exhaust rakes, strain gauges,

optical and capacitive clearance probes, pulsation and vibration sensors as well as an emission monitoring

system. The rotating system is monitored via two telemetry systems on both the hot- and cold-end of the GTrotor.

Around 10% of the instrumentation locations are equipped with high time resolution sensors to capture

dynamic effects. With this validation instrumentation the thermodynamic state, the aerodynamic flow

situation, hot gas temperature, the thermal state of structural parts and blades, blade vibration behaviour,

combustor stability and emissions can be monitored at all operating conditions.

Figure 5 shows the wiring for the hot end telemetry system and the instrumentation cable routing on the GT

rotor within the compressor blading.

Figure 5: Alstom GT26 Power Plant, instrumentation application on the GT rotor

Figure 6 shows instrumentation applied to a variable vane in the front part of the compressor to measure the

aerodynamic flow-condition.






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Figure 6: Alstom GT26 Power Plant, Compressor Variable Vane instrumentation

In the following chapter the operational experience in the Alstom GT26 Power Plant with respect to operational

flexibility will be presented.

5 Operational Flexibility - Experience from Alstom GT26 PowerPlant

The enhancement of the operational flexibility of the GT26/GT24 belongs to the key development targets. This

covers topics like

• Flexible Operation Modes

Optimisation of power output, efficiency and lifetime through adaptation of firing temperatures and

cooling air supply. The GT26/GT24 operation concept includes the possibility for on-line switching

between ‘Performance Optimised’ (PO) and ‘Maintenance-Cost Optimised’ (MCO) mode of operation.

• Fuel Switch-Over Flexibility

The GT26/GT24 units are capable of switching online between the main fuel (fuel gas) and the back-up

fuel (fuel oil) within a wide load range up to close to base-load.

• Low Load Operation

The entire KA26/KA24 CCPP can be “parked” fully on-line at very low plant loads (down to ≈ 15%)

during times of low electricity demand. The fast loading capability of the GT26/GT24 units allow the

KA26/KA24 plants to quickly react to short-term demand changes, thereby offering very fast acting

spinning reserve.






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• Fast GT and CCPP start-up

The start-up concept has been optimised to reduce the start-up time depending on the thermal

condition of the GT. A fast hot start takes 30 minutes from ignition to GT base load. Even shorter start-

up times are available as option. Start-up concepts for 10 minutes non-spinning reserve have been

demonstrated in the Alstom Power Plant Birr (Switzerland), where up to 60% GT load has been reached

within 10 minutes from push-button.

• Grid-Code Compliance

The current energy market with increasing share of renewables requires that gas turbines and

combined cycles to react faster and more flexible to fluctuations and disturbances of the grid frequency

than in the past. This is reflected in the grid codes of many countries, which become more and morechallenging for gas turbine operation. The GT26/GT24 are designed to provide the flexibility required by

today’s most demanding grid codes. Their features and limitations (e.g. compressor surge line for

under-frequency operation) have been thoroughly validated in the Alstom Power Plant Birr

(Switzerland).

5.1 Flexible Operation Modes

The flexible operation modes of the latest GT26/GT24 are outlined in Figure 7, where the Turbine InletTemperature of the EV-combustor (TIT1), the Turbine Inlet Temperature of the SEV-combustor (TIT2) and the

position of the Variable Inlet Guide Vane (VIGV) are shown vs. the relative load of the GT. The TIT1 and TIT2

lines represent the difference to the TIT2 base load value.

Two different operation modes are available. The plant operator can choose and switch fully on-line between a

‘Performance Optimised’ (PO) mode and a ‘Maintenance-Cost Optimised’ (MCO) operation mode.

The Maximum Continuous Load (MCL) is reached in the PO-mode with the standard GT26/GT24 inspection

intervals, whereas in the Maintenance-Cost Optimised operation-mode the plant sees a marginal reduction in

performance, but the GT26/GT24 inspection intervals is increased by up to 30%, resulting in reduced specificmaintenance-costs and higher availability.






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Figure 7: Loading Diagram for the latest GT26/GT24 upgrades

The TIT1 and TIT2 settings of the latest GT26/GT24 upgrades have been defined to achieve an optimumbalance between performance, lifetime of the hot gas path parts and engine emissions. TIT2 is kept at a high

level in the upper load range to maximise the combined cycle efficiency. In the lower load range with reduced

TIT2, the engine operates with increased TIT1 level in order to achieve low CO emissions.

In today’s dynamic markets this feature offers plant operators the ability to be able to vary on-line at any time

the plants’ operational setting to meet the power-market’s needs. During for instance peak-demand periods or

if the fuel price demands highest efficiency, the KA26/KA24 plants can be run in the PO-mode to deliver the

maximum power output with the highest efficiency, with the standard (normal) inspection intervals. During

lower demand periods or if fuel price does not dictate need for highest efficiency under all conditions, then the

MCO-mode with the 30% increased inspection intervals but with reduced performance could be more optimal.

The latest GT26/GT24 units are equipped with an active (closed loop) control of the cooling-supply conditions

from compressor bleeds 2 and 3 with control valves. Thus, a further degree of freedom for the optimisation of

the operation concept settings is achieved. The cooling-air is throttled when the compressor bleed pressures

are higher as in the design point (e.g. hot day conditions), which leads to a performance improvement. On the

other hand, the lifetime consumption of the hot gas path parts is reduced by opening of the control valves

when the bleed pressures are low (e.g. during oil operation). Furthermore, the commissioning time is reduced

since an adjustment of the cooling air systems is no longer needed.






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The operating conditions and the calculation models for the GT26/GT24 have been validated within a widerange in the Alstom Power Plant in Birr (Switzerland). Engine testing was done for the following conditions:

• Air intake temperatures: 0 to +35°C (including pre-heater operation)

• Load ranges: 0 – 110% (with peak-load)

• Fuel Gas and Fuel Oil operation

5.2 Improved Fuel Switch-Over Flexibility

The GT26/GT24 fuel switchover flexibility between fuel gas and fuel oil has been further improved so as to

allow switch-over even at high load without the need for de-loading. The switching can be done either in EV-

only mode or with both combustors in operation.

A typical fuel switch-over sequence as recorded in the Alstom Power Plant Birr (Switzerland) is shown in

Figure 8. The fuel switch-over was done at base-load from fuel gas (FG) to fuel oil (FO) and back again. The

active power output is indicated by the blue line in Figure 8. The green and the brown lines represent the ratio

of fuel gas to fuel oil for the EV and the SEV combustor.

Figure 8: High Load Fuel Switch-Over (as recorded in the Alstom Power Plant Birr, Switzerland)






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The fuel switch-over from gas to oil is initiated by filling of the fuel distribution system (FDS) with fuel oil. The

next step is the fuel transfer, which is done first on the EV and then on the SEV combustor. The fuel gas flow is

reduced while at the same time the fuel oil mass flow has to be increased such that the overall power output

remains constant. When the fuel transfer is completed, the fuel gas lines are purged first with N2 and then

blocked with air in order to avoid that fuel residues ignite in the gas system. The switching back from fuel oil to

fuel gas is done in reversed order. The fuel oil lances are finally purged with water, once the fuel transfer from

oil to gas is completed.

In this case, the switch-over from gas to oil was done in approximately six minutes. The switch back took less

than five minutes.

5.3 Low load Operation

The low load operation is a unique feature of the KA26/KA24 plants, which allows to park the entire plant in

full combined cycle operation at very low load (≈15% relative plant load) during times of low electricity

demand. This option can be more favourable than a shut-down of the plant when only a few hours have to be

bridged and/or a fast ramp up of the power output is needed afterwards. This can be done very fast with the

KA26/KA24 because the GT(s) and the Water-Steam Cycle are all still in operation.

The requirements and drivers for low load operation are:

• Minimising fuel consumption

• Minimising the plant power output

• Maintaining sufficient GT exhaust temperature level to keep the water steam cycle alive.

• Maintaining compliance with emissions limits.

• Enable fast de- and re-loading

• Offering an alternative to a stop/start event or operation at the more typical higher minimum load

points

These targets are achieved by operating with lowest possible compressor inlet mass-flow; thus the fuel

consumption is minimised. At the same time this results in a high exhaust temperature level, as the pressure

ratio and the expansion over the LP turbine are low.

The engine operates in EV-only mode, where the second (SEV) combustor is switched off. The EV firing

temperature is sufficiently high to ensure low emissions.






14

Also the de- and re-loading gradients have been modified in order to offer a high degree of flexibility to the

customer. An “accelerated” gradient has been defined for the loading to and from low load operation, which is

twice the normal load gradient. This is achieved without any penalty on lifetime factors, because the engine is

already ‘hot’ when low load operation is selected. A typical scenario would be normal electricity production

during the peak day-time periods and low load operation during the low demand periods of the day, including

possible overnight. In the Low Load mode the plant remains in a condition to load up very fast in order to cover

the morning peak. From the low load operation point:

• the KA26 combined cycle can ramp back-up to deliver more than 350 MW for the KA26-1 (1-on-1)

configuration or more than 700 MW for the KA26-2 (2-on-1) configuration in less than 15 minutes,and

• the KA24-2 can ramp back-up to deliver more than 500 MW within 10 minutes.

In the low load mode the CCPP gas turbine(s) consume approximately one quarter the fuel consumption of the

GT when running at base-load.

The low load operation feature including the transient operation to and from low load has been thoroughly

validated in the Alstom Power Plant Birr (Switzerland). Even higher gradients than the accelerated load

gradient have been tested, because one of the development targets is to be able to offer the ability of the plantto load-up from the low load parking-point to combined cycle base-load within just a few minutes. The super-

fast ramping of the gas turbine to allow this was demonstrated successfully at the Alstom Birr Power Plant.

An example of such a test is given in Figure 9, where the relative GT power and relative GT exhaust

temperature are shown for low load operation with subsequent super-fast loading. The first loading sequence

was done up to 70% GT load, whereas the second sequence went from low load to base load within two

minutes. The GT exhaust temperature is kept at a rather high level throughout the whole load range. The

maximum temperatures occur during part load, where the engine operates in exhaust temperature control.






15

Figure 9: Low load operation with super-fast loading

(as recorded in the Alstom Power Plant Birr, Switzerland)

5.4 Fast GT and Plant start-up

The start-up concepts of the GT26/GT24 and associated KA26/KA24 CCPP products have been optimised

towards a greater operational flexibility. This includes an adjustment of the loading gradients such that the

start-up time is reduced where this is possible without impacting the cyclic lifetime of the GT and Plant

components. The main driver is the thermal condition of the plant. A cold start requires more time than a

warm or hot start, because the thermal stresses during start-up and loading are generally higher. Therefore,

the normal loading gradient is selected for a cold engine. A warm or hot plant can start faster, as the thermal

stresses are much lower than for the cold start case.

For hot and warm starts the GT26/GT24 can be loaded with a gradient which is twice the normal loading

gradient without impacting the cyclic lifetime of the engine. The settings for the warm and hot start are definedsuch that GT base load can be reached within 30 minutes from ignition.

A further reduction of the start-up time can be achieved via “purge-credit”, which requires the modification of

the fuel system according to the NFPA85 requirements. The boiler purging during the GT start-up can be

omitted with this feature. It is available as option for the GT26/GT24.

Even shorter start-up times can be provided by the GT26/GT24, such as the “10-minute non-spinning reserve”

option. With this optional feature, it is possible for the GT26/GT24 to run up to 60% load within 10 minutes. At

this point, the water steam cycle can be started or further operation of the GT in simple cycle mode can be






16

chosen (including load-up to GT base-load). Among many other start-up options, the 10 minute non-spinningreserve feature has also been demonstrated on the GT26 unit at the Alstom Power Plant Birr (Switzerland).

The results are summarised in Figure 10, where the non-dimensional rotor speed and active power are plotted

versus the time. The total time from start initiation to 60% GT load was 13.5 minutes. The purge-time of 5

minutes has to be subtracted in order to get the net start-up time with purge credit, which is 8.5 minutes in

this case.

Figure 10: 10-minute non-spinning reserve start-up

(as recorded in the Alstom Power Plant Birr, Switzerland)

5.5 Grid-Code Compliance

The compliance of the GT26 with the most important grid code requirements in the 50 Hz market has been

tested and demonstrated in the Alstom Power Plant Birr (Switzerland) as far as this was possible within the

confines of the Swiss grid. The exploration of the limits of the engine was in the focus of these activities.Examples are fast transient operation with high loading gradients as required for primary response, peak-firing

to comply with CC.6.3.3 of the UK grid code, under-frequency operation and load rejection.

A key item for grid code compliance is the ability of the compressor to operate at low aerodynamic speeds. The

limit should be as low as possible. However, a sufficient margin to the surge limit must still be available under

all operating conditions in order to avoid damage to the engine in case of frequency drops especially at high

ambient temperatures. The knowledge of the surge limit is therefore essential for adequate protection of the

engine.






17

Figure 11: Under-frequency operation (as recorded in the Alstom Power Plant Birr, Switzerland)

The surge limit of the GT26 has been confirmed in Birr via surge approach tests in idle operation. An example is

given in Figure 11, where the relative rotor speed and the engine pressure ratio are shown for differentcompressor inlet mass flows, which are close to the base load flow. The validity of the model predictions as

well as the compliance with grid requirements for under-frequency operation could be confirmed with these

tests.

A further challenge for a heavy duty gas turbine is to stay in operation, when a disturbance leads to an opening

of the generator breaker and subsequent load rejection. The fuel flow and the compressor flow have to be

reduced fast enough to avoid a trip of the engine by the over-speed protection. At the same time a stable

combustion within this highly transient manoeuvre has to be ensured, because burner extinction would also

result in an engine trip.






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Figure 12: Load rejection from base load (as recorded in the Alstom Power Plant Birr (Switzerland))

The load rejection capability of the GT26 has also been demonstrated and optimised in the Alstom Power Plant

in Birr (Switzerland). Figure 12 shows the recordings of a load rejection from base load, where the relativepower output and the relative speed are plotted over time. The rotational speed of the engine starts to increase

once the generator breaker is open, because the surplus energy cannot be converted in the generator anymore,

but instead accelerates the rotor. The combustion system stays in operation, the engine is stabilised under idle

conditions.






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6 Summary

The latest GT26/GT24 engines from Alstom build on the long established and well proven operational

experience of the GT26/GT24 fleet with their unique sequential-combustion to offer the 50 Hz and 60 Hz

power markets large advanced-class gas turbines that …

• deliver high base-load performance, both in terms of power output and efficiency. The GT26 for

instance in an optimised CCPP cycle is able to deliver more than 60% efficiency;

•

maintain high part-load efficiency over a wide load range;

• can switch on-line between a ‘Performance-Optimised’ and a ‘Maintenance-Cost Optimised’ mode of

operation, depending on market drivers, so as to allow plant operators the choice between either

maximum performance with normal inspection intervals or extended inspection intervals with higher

availability with a marginal reduction in performance;

• can handle a wide range of fuel gas compositions with the standard combustion hardware, offering a

capability to handle fuel gases with a Wobbe index difference of more than ±15%, three times the

industry norm;

• is able to switch-over from fuel gas to fuel oil or vice-versa without need for load reductions at high GT

loads;

• allow the complete combined cycle to be de-loaded and parked at very low loads. When in the low load

mode the CCPP gas turbine(s) consume approximately one quarter the fuel consumption of the GT

when running at base-load with a plant load parking down to approximately 15%;

• offer improved ramping rates and starting concepts, so as to offer 30 minutes hot start capability for

the CCPP as well as the ability to deliver more than 60% GT load within 10 minutes; and

• are better able to meeting the requirements of most stringent grid codes.

The hot gas path components of the latest GT26/GT24 have been operating successfully in three commercial

field engines, with the front-running unit now having more than 11’000 running hours and having undergone

two scheduled visual inspections, showing excellent findings. In addition, the latest GT26/GT24 engine

hardware has been validated via extensive operational tests under real operational conditions by way of the

Birr Power Plant in Switzerland, where Alstom have installed a GT26 simple-cycle unit supplying power to the

Swiss grid. Through dedicated validation test campaigns and with high degree of special instrumentation

installed on the Birr unit, Alstom has been able to accumulate a full and comprehensive level of data to allow

us to validate and calibrate the design, performance and lifetime prediction tools.






20

7 Bibliography

[1] The Next Generation GT26 – The Pioneer of Operational Flexibility

Matthias Hiddemann, Frank Hummel, Michael Ladwig (Alstom)

Paper presented at PowerGen Europe 2011

[2] Superior fuel flexibility for today’s and future market requirements

Douglas Pennell, Matthias Hiddemann, Peter Flohr (Alstom)

Paper presented at PowerGen Europe 2010

[3] A further uprate for Alstom’s Sequential Combustion GT26 Gas Turbine

Stephen Philipson, Michael Ladwig, Karin Lindvall, Jürg Schmidli (Alstom)

[4] Combined Cycle Power Plants as ideal solution to balance grid fluctuations

– Fast Start Capabilities

Christoph Ruchti, Hamid Olia, Peter Marx, Andreas Ehrsam, Wesley Bauver (Alstom)

Paper presented at VGB Power Tech 20




PowerGen Europe 2013 4-6 June 2013 in Vienna Austria

Alstom Power

© ALSTOM 2012. All rights reserved. Informationcontained in this document is indicative only. Norepresentation or warranty is given or should berelied on that it is complete or correct or will apply toany particular project. This will depend on thetechnical and commercial circumstances. It isprovided without liability and is subject to changewithout notice. Reproduction, use or disclosure tothird parties, without express written authority, isstrictly prohibited.

Photo credit:

www.alstom.com/power

operational experience with latest gt26 upgrade

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