In the course of the last decade gas turbines have emerged as a core component of modern power plants. Key for this development has been the structural change of important power markets along with the rapid progress in technology, i. In a combination with improved thermodynamic cycles, standardisation and optimised production processes, manufacturers succeeded in strongly upgrading efficiency, power output plus environmental compatibility on the one hand and, on the other hand, in drastically reducing installation costs. These trends have been followed by growing need for insurance of gas turbine power plants.

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In the course of the last decade gas turbines have emerged as a core component of modern power plants. Key for this development has been the structural change of important power markets along with the rapid progress in technology, i. In a combination with improved thermodynamic cycles, standardisation and optimised production processes, manufacturers succeeded in strongly upgrading efficiency, power output plus environmental compatibility on the one hand and, on the other hand, in drastically reducing installation costs.

These trends have been followed by growing need for insurance of gas turbine power plants. Most reflections concentrate on 50 Hz models.

Statistics and loss examples help to analyse the impact of the latest developments on typical loss mechanisms, their frequency and costs involved.

On this basis some proposals on loss prevention, underwriting considerations and also a depiction of future prospects are given. Market Situation. Gas Turbine Power Plants. Development in Technology. Compressor and Turbine Design. Combustion Systems. New Cycle Concepts. Loss Experience and Loss Mechanisms. Data Base. Loss Records. Loss Analysis: Causative Processes. Conclusion and Outlook. Underwriting Considerations and Conclusions.

Over the last decade the world-wide power plant markets have been characterised by the trend towards the opening and privatisation of important electricity markets. An increasing number of power plants are being ordered and operated by Independent Power Producers IPP's or as merchant plants.

Influenced by strong competition, capital spending decisions are mainly governed by cost criteria, e. As a consequence of this phenomenon and the progress in technology as well as the growing availability of natural gas, more and more power plants use gas turbines for electricity and heat generation.

When speaking of gas turbine power plants, both single cycle and combined cycle applications are meant. Since the begin of the nineties, continuous strong competition and overcapacities dropped the prices down by approx. In the meantime due to a gas turbine order boom from U. In parallel to this development, manufacturers were more and more forced to grant very comprehensive guarantees regarding efficiency, output, emissions and availability.

As a consequence of the economic environment, manufacturers reacted by continuously improving the technology of their range of products. The introduction of ever larger and more efficient units, the implementation of low-cost standard solutions and a logically consistent pursuit of homogeneous product families demonstrate this trend. A further reaction of the manufacturers is the permanent optimisation of their business processes.

This includes outsourcing development activities and the production of essential plant components as well as a constant adaptation of personnel to order situation. Contrary to the development process for aircraft engines, with large industrial gas turbines for cost and time reasons time-consuming prototype tests before release for series production were reduced or even rationalised away.

Completely new machines or components are frequently installed and tested for the first time with selected customers. In parallel, series production starts up, identical machines are manufactured, shipped and erected. This procedure, however, requires both overcoming expected starting problems with the prototype plant and the timely implementation of necessary corrective actions in all other machines of the fleet. During the last two years there has been a massive reorganisation of the big players.

Siemens took over Westinghouse, an immediate competitor. Mitsubishi, partner of Westinghouse so far, successfully proceeded in supplying gas turbines for the 50 and 60 Hz market.

ABB sold its power generation segment, gas turbines included, to Alstom and thereby disappeared from this market segment. Simultaneously Alstom's former activities in large gas turbines were transferred to their original license holder GE. So far, GE and their license holders have reached an average of approx. The next years will show, rather interestingly, the influence of the current restructuring processes on the market position of the manufacturers.

Altogether, the technical and commercial advantages of gas turbines, their flexibility and development potential will lead to a big share of the new power plant business in the near future relying on this technology. The insurance market had to follow the changing requirements of the insured's needs, resulting - for example - from the delivery contract.

Some trends within the insurance market have basically been driven by following forces. Since the end of the eighties, gas turbine technology has taken a tremendous step forward in development.

This section will describe some of the important technical progress regarding performance figures, development strategies and model development, the large 50 Hz industrial gas turbines being used as an example. Principally and according to the well-known basic rules of thermodynamics, the performance or efficiency of gas turbines is increased by raising the average turbine inlet temperature TIT and simultaneously optimising the pressure ratio.

In parallel, the pressure ratio has gone up from approx. This improvement of the gas turbine cycle parameters during the nineties was achieved on the one hand by the introduction of completely new gas turbine models and on the other hand by a continuous development of the existing series see fig. For instance, the presently largest gas turbines models, the so-called F class i.

GT26, V The technical achievements from prototype engines were also used to modernise the proven E-class models i. GT13E, V Even though this procedure offers undeniable advantages, questions came up regarding the risk involved and the logistic efforts required by this high speed of model development.

The logistic efforts for new models have been increased already by the fact that in order to resolve teething troubles, some components had to be touched up again and again. Sometimes it might even appear as if every machine is unique whilst having the same designation. Nowadays the majority of modern gas turbines are offered as part of a standard power plant configuration whereas hitherto the basic components of a power station have been optimised individually and tailored to the client's requirements.

The standardisation of the whole power plant allows, in addition to cost saving, a better comparison of experience and as a consequence, at least theoretically, a minimisation of risks. Nevertheless, the benefits of modern high-tech gas turbines in some cases contribute towards an application into individual plant concepts e.

The risks involved in such applications have to be analysed carefully. For example, the development of improved compressor blade profiles made it possible to simultaneously increase air inlet flow, compressor efficiency and pressure ratio.

Thus the new machines reach much higher pressure ratios, whereas the number of stages and main dimensions of the compressor remain practically unchanged. In conjunction with similar improvements to turbine aerodynamics, the realisation of minimised blade clearances and the use of more efficient sealing elements have contributed towards a significant increase of the gas turbine's efficiency. These computing tools also allow a widely computerised design of gas turbine components.

This means that time-consuming and expensive tests and thus development times could be reduced clearly over the last decade. So far, the admissible gas temperature at the turbine inlet is limited by the thermal load capacity of the hot gas components and particularly the technology of the first turbine stage. By introducing a whole package of measures it has been possible to raise this temperature drastically.

Simultaneously, thanks to the insulation effect, the application of thermal barrier coatings TBC on the surface of the blades made it possible to further increase the hot gas temperature by approx. A similar increase of the hot gas temperature could be reached by introducing modern cooling technologies derived from aircraft engine technology.

Modern turbine blades are rather complex systems and are made in a series of complicated manufacturing processes. The price of individual guide vanes and blades may easily reach the price of a middle class car. If, for reason of design optimisations, the casting form has to be changed, processing times of 2 years are common.

As very strong development tools are available with the modern three dimensional computer simulations, the knowledge about the stresses of blades in design conditions is excellent. Based on this, safety margins on new turbines could be reduced to a minimum. Currently the sensitivity of such turbine blades and vanes greatly requires an exact control of all operating parameters. Even small deviations, for example of flow conditions, cooling parameters or hot gas temperature, may lead — contrary to earlier systems — to severe problems or even failure of the component.

Moreover, issues such as lifetime or repair methods with directionally solidified or single crystal blades have not yet been completely resolved. During the last decade significant improvements have been made in the field of burner systems. The NO x - emissions formed in the combustion chamber have meanwhile decreased from several ppm to less than 10 ppm without additional water or steam injection.

The breakthrough was achieved by the end of the eighties, when instead of the standard diffusion type of burners, lean premix burners have been introduced. In principle these burners consist of a mixing zone, where the combustion air and the fuel are homogeneously premixed and a separate reaction zone where the flame is stabilised. The combustion process is controlled on such a way that so-called "cold" flames of approx.

It is nowadays necessary to have an almost airtight combustion chamber and to pass nearly all the combustor air to the burners to reach such low flame temperatures. Big silo combustors traditionally used by European manufacturers have been replaced by compact annular combustion chambers in order to minimise the cooling surface area and to smooth the temperature profile at the turbine inlet simultaneously.

The design and cooling concepts of the combustor. Mitsubishi and Siemens- Westinghouse, in turn, test closed steam cooling systems for their transition pieces see figure 4. Since the available theoretical models are not yet capable of calculating these complex processes and the lowest emissions are reached close to the lower stability limit of the burner, the burner systems turned out to be adjusted and optimised empirically in risky and long-lasting tests in the field.

The manufacturers are experimenting with systematic variations of fuel distribution, flow conditions as well as passive and active damping systems. In most cases the operational safety of the burner systems has to be monitored by means of additional instrumentation. Due to the increase of the turbine inlet temperature and through the permanent tightening of legal emission regulations, the technical success reached with combustion systems has in most cases been compensated immediately over the last decade.

A good deal of additional attention is required if liquid fuels or synthetic gases are burnt instead of natural gas. To overcome this dilemma, manufacturers are currently focusing their development efforts on improved gas turbine cycle concepts. The future gas turbine models of GE, Mitsubishi and Siemens-Westinghouse provide a partial substitution of the air cooling by closed steam cooling systems.

GE for example will cool both stator and rotating blades of the H-models by steam. Whereas the advantages of steam-cooled transition pieces, which are used in the current G-models of MHI and Siemens-Westinghouse, primarily focus on keeping the emissions low, the application of steam-cooled components in the turbine will at the same time make it possible to increase the gas turbine and the combined cycle efficiency. Provided a constant combustion chamber exhaust temperature, the firing temperature and thereby the efficiency rises, the more the turbine cooling air is saved or replaced by steam.

Figure 5 outlines this principle with the example of a steam-cooled turbine vane 1. The steam for cooling is usually taken from the heat recovery steam generator, led into the gas turbine casing or rotor and after being heated up in the elements to be cooled, fed back into the steam cycle.


Gas turbine

A gas turbine , also called a combustion turbine , is a type of continuous and internal combustion engine. The main elements common to all gas turbine engines are:. A fourth component is often used to increase efficiency on turboprops and turbofans , to convert power into mechanical or electric form on turboshafts and electric generators , or to achieve greater thrust-to-weight ratio on afterburning engines. The basic operation of the gas turbine is a Brayton cycle with air as the working fluid. Atmospheric air flows through the compressor that brings it to higher pressure.


Gasne Turbine i Kompresori


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