GB2300884A

GB2300884A - Starting a gas turbine

Info

Publication number: GB2300884A
Application number: GB9609941A
Authority: GB
Inventors: Hermann Seelinger
Original assignee: ABB Patent GmbH
Current assignee: ABB Patent GmbH
Priority date: 1995-05-17
Filing date: 1996-05-13
Publication date: 1996-11-20
Also published as: GB9609941D0; DE19518093A1

Description

2300884 Method of and arrangement for starting a gas turbine

Description

The invention relates to a method of and an arrangement for starting a gas turbine of high output of P > 100 MW., in a combined-cycle power station, having a first steam boiler, heated by the waste heat from the gas turbine, for generating steam, a steam turbine to which the steam is admitted, and generators allocated in each case to and loaded by the gas turbine and the steam turbine and coupled to one another.

The development of the gas-turbine technology used in the power station sector has led in the recent past to a considerable improvement in the process parameters and has thus made possible the development and operation of gas turbines of high output, that in of at least 100 MW,,. In particular, the pressure ratio has been increased from 15 originally to about 30 now.

The inevitable consequence of this increase in output is that the starting output required for starting the relevant gas turbine is also higher. At the same time, it has to be taken into account that the gas turbine must have reached at least 60% of its rated speed before it is able to produce by itself the power required for further run-up.

in previous plants, the electric energy required for the starting output is provided from a connected high-voltage network or by so-called diesel generators, that is emergency power -generating units driven by diesel engines.

Frequency converters are used here, which convert the electric energy supplied so that the voltage and frequency delivered to the stator winding of the generator connected to the gas turbine are variable. The generator works an a synchronous motor during the starting operation.

In view of the considerable increase in the output of the gas turbine, the starting operation, instead of about 3.5 MW originally, now requires an almost five-fold increase in the starting output to about 15 MW, which technically can no longer be provided in a practical manner by means of diesel units. Feeding from a possibly connected high-voltage network should likewise be dispensed with in view of this power requirement in order to avoid the starting current inrush associated therewith and the reactions for the network resulting therefrom.

Starting from this prior art, the object of the invention in to specify a method of starting a gas is turbine of high output of P > 100 MW,, an well as a corresponding arrangement for carrying out the method.

Claims

This object in achieved according to the invention by the characterizing

features of Claims 1 and
2. The method according to the invention in accordingly characterized by the following method steps:

a) generation of starting steam for starting the steam turbine, admission of the starting steam to the steam turbine and run-up of the steam turbine, which likewise accelerates a generator coupled thereto, generation of electric energy at a voltage and frequency varying as a function of the rotational speed, feeding the electric energy at variable voltage and frequency into the generator allocated to the gas turbine and working in motor operation, run-up of the gas turbine by the allocated generator working in motor operation to at least 60% of the rated speed, and f) switching over to generator operation and synchron izing the generators.

The method according to the invention is distinguished in particular by the fact that, irrespective of the respective location of the power station plant in b)- c) d) e) c question, whether it is incorporated in a grid system which is fed from further power station plants or is in so-called isolated operation, the starting operation can be carried out in a technically practical manner with relatively little outlay but with great reliability and without disturbing reactions.

A not insignificant accompanying effect of the method according to the invention is the fact that the sequences of the method according to the invention, possibly with the exception of the generation of the starting steam for the steam turbine, take place with comparatively favourable efficiency, the outlay for the activation and monitoring of diesel generators required hitherto being dispensed with. This means a considerable simplification from a process point of view.

An arrangement for carrying out the method according to the Invention is characterized in that a second steam boiler of low a team- generating capacity (< 100 t.,../h) is additionally provided for generating starting steam for starting the steam turbine, in that the generator allocated to the gas turbine in used as a motor during the starting operation, In that the electric current generated during the starting operation by the generator loaded by the steam turbine feeds the generator coupled to the gas turbine, and in that the generator starts the gas turbine in motor operation.

An advantageous further development of the.Invention, instead of providing for a frequency converter for providing electric energy at varying frequency, provides for the electric current generated upon acceleration during the starting operation by the generator driven by the steam turbine to flow at increasing frequency to the generator allocated to the gas turbine and working in motor operation.

In a preferred embodiment of the invention, the two generators allocated to the steam turbine and the gas turbine respectively are electrically coupled.

The omission, first made possible by the invention, of the diesel generator and the frequency converter 4 - likewise no longer required results not only in substan tial savings in investment capital but also in oper ational advantages on account of the possible simplifica tion with regard to the switching and control devices required for controlling and monitoring the operation of the power station plant equipped with the arrangement according to the invention.

The invention, advantageous developments and improvements of the invention and special advantages of the invention are to be explained and described in more detail with reference to an exezaplary embodiment shown in the schematic drawing, wherein:

Fig. 1 shown a circuit arrangement for starting a gas turbine according to the prior art, and is Fig. 2 shown a circuit arrangement according to the invention. Fig. 1 shows a circuit arrangement for starting a gas-turbine group 10 consisting of a c=Wressor 12, a combustion chamber 14 and a gas turbine 16, which gas turbine group in coupled to a generator 20 via a shaf t 18.

The generator 20 is connected via a generator switch 22 to a transformer designated an the main trans former 24, which in turn in connected via a high-voltage switch 26 to a high-voltage network 28.

Arranged in parallel with the generator switch 22 is an electric starting circuit 30 having a so-called auxiliary service transformer 32 and two medium-voltage switches 34, 35 connected in series, between which an output which can be switched off by a further medium voltage switch 36 is connected to a so-called auxiliary service network 38.

The abovementioned electric starting circuit 30 arranged in parallel with the generator switch 22 is completed by a static starting apparatus 40 which adjoins the line between the generator 20 and the generator switch 22 via an isolating link 42.

The static starting apparatus 40, shown here as an individual component, serves to draw from the high- voltage. network 28 the electric energy required for feeding the generator 20 working in motor operation during starting and to provide it at an appropriately adapted voltage and frequency. In this case, as shown in Fig. 1, the generator switch 22 is open, while the remaining switches 26, 34 and 35 and the isolating link 42 are closed.

Shown in Fig. 2 is a circuit arrangement according to the invention in which a combined-cycle power station plant 50 has a gas-turbine group 52 and a steamturbine group 54, to which a generator 56 and 58 is allocated in each case.

The gas-turbine group comprises a gas turbine 60, a combustion chamber 62 arranged upstream and a com- pressor 64. Here, the gas turbine and the compressor are coupled via a common shaft 66 to the allocated generator 56.

The steam-turbine group 54, which in formed from a steam turbine coupled to the allocated generator 58, is supplied in normal operation with steam from a waste-heat boiler 70 heated by the exhaust gas from the gas turbine. Used for the starting operation in an additionally provided starting or auxiliary-steam boiler 72, that in boiler of low a teamgenerating capacity, for example 100 t., ../h, the efficiency of which in =re favourable than that of the waste- heat boiler 70 with regard to the steam quantity required for the starting operation.

A three-pole connecting line 74 which connects the two generators 56 and 58 to one another serves to electrically couple them as intended according to the invention.

The fact that a considerable outlay in required according to the prior art for the starting operation of the gas-turbine group 10, but at least a starting appar- atus which contains a frequency converter (not shown here in more detail) with corresponding switching devices, must not be overlooked.

In contrast, the circuit provided according to the invention needs considerably less outlay. Only the auxiliary or starting boiler 72 has to be additionally provided. Complicated switching devices with frequency converters and the like are just as unnecessary as diesel-operated auxiliary power -generating units likewise intended for use.

Patent Claims 1. Method of starting a gas turbine of high output of P > 100 MW., in a combined-cycle power station having a gas turbine allocated generators following steps:

a) generation of starting steam for starting the steam turbine r and a steam turbine with characterized by the is generators c) d) 0) b) admission of the starting steam to the steam turbine and run-up of the steam turbine J. which likewise accelerates a generator coupled there to, generation of electric energy at a voltage and frequency varying an a function of the rotational speed, feeding the electric energy at variable voltage and frequency into the generator gas turbine and working In =tor operation, allocated to the run-up'of the gas turbine by the allocated generator working in motor operation to at least 60% of the rated speed, and f) switching over to generator operation and synchronizing the generators 2. Arrangement for carrying out a method according to Claim 1 for starting a gas turbine of high output of P > 100 MW,, in a combined-cycle power station having a first steam boiler 0 heated by the waste heat from the gas turbine for generating steam, a steam turbine to which the steam in admitted, allocated in each case to and loaded by the gas turbine and the steam turbine and coupled to one another, and a frequency converter allocated to the generators characterized in that a second steam boiler of low stearn-generating capacity of < 100 tatclh in additionally provided for generating starting steam for starting the steam turbine, in that the generator allocated to the gas turbine is used an a motor during the starting operation, in that the electric current generated during the starting operation by the generator loaded by the steam turbine feeds the generator coupled to the gas turbine and in that the generator starts the gas turbine in =tor operation.
3. Arrangement according. to Claim 2, characterized in that, instead of a frequency converter for providing electric energy at varying frequency, the electric current generated upon acceleration during the starting operation by the generator driven by the steam turbine flown at increasing frequency to the gener- ator allocated to the gas turbine and working in =tor operation.
4. Arrangement according to Claim 2 or3, character ized In that the two generators allocated to the steam turbine and the gas turbine respectively is are electrically coupled.