Dynamoelectrical generator

Abstract

A dynamoelectrical generator is cooled in its interior by a closed gas circuit, in particular an air circuit, which is connected via generator coolers arranged in the generator to an external cooling water circuit, in which a recooling device for cooling down the heated cooling water is arranged between the output and the input of the generator coolers. A refrigeration unit produces refrigeration and extracts further heat from the cooling water before it enters the generator coolers, and is disposed in the cooling circuit between the recooling device and the input to the generator coolers.

Description

BACKGROUND

A generator such as this is known, for example, from U.S. Pat. No. 5,883,448.

The power output from dynamoelectrical generators is dependent on the permissible internal heating of the components. So-called isolation classes limit the absolute value of the temperatures. They are normally used on the basis of Class B or F, which corresponds to a maximum permissible component temperature of 130 or 155° C., respectively. If the maximum permissible component temperatures are exceeded, this results in the components aging more quickly, and thus in reduced availability and a shorter life. By way of example, an air-cooled generator can suck in the surrounding air for cooling purposes (so-called open ventilation, OV), force it through its components, and emit it to the environment again after it has been heated. If the surrounding air is relatively cool, it is possible to obtain more electrical power from the machine by increasing the temperature range between the cooling air and the maximum permissible component temperature, without exceeding the maximum permissible component temperatures. The generator can thus follow a gas turbine power output in a desirable manner, which likewise increases with lower surrounding air.

In order to avoid dirt in the generator interior as well as blockage of air filters and in consequence restricted availability, a closed air circuit is frequently chosen in the generator interior, and the power losses are emitted via an air/water heat exchanger (generator cooler) to a separate cooling water circuit (Totally Enclosed Water-Air Cooling, TEWAC). The resultant temperature dependency between the terminal power (P) and the cooling water temperature (Tcw) is represented by so-called capability curves (see FIG. 1), in which the curves A (cooler) show the relationship between the cooling air inlet temperature and the cold water inlet temperature, and the curves B show the relationship between the generator output power and the cooling air inlet temperature, and in which the relationship between the generator output power and the cold water inlet temperature can be determined, by way of example, on the path marked by two arrows. The cooling water may, for example, itself be cooled down in a closed circuit with cooling towers.

It is not uncommon for the rating of already existing power stations to be increased by increasing the rating of the turbines (so-called uprating). Conventional uprating of turbines to a higher power level should be possible by additionally driving the generator. The expenditure for uprating should be as low as possible. In most cases, no cooler connecting temperature is available for the generator cooler. Conversion to a higher temperature class requires component replacements and is costly and time-consuming, as is the replacement of the entire generator. Derating of the generator from the start with the aim of subsequent rating adaptation is costly. This reveals one disadvantage of generators of the described type.

In new systems, it is possible for the required rating data just to require the use of a different type of generator with more complexity and more stringent safety requirements (for example internal generator cooling by means of hydrogen). The generator then results in a sudden cost rise and adversely affects the overall attractiveness of the power station.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a generator with cooling based in particular on the TEWAC principle, which avoids the disadvantages of known solutions and is distinguished in particular by an increased power output with comparatively little additional cost and great flexibility.

The present invention provides a dynamoelectrical generator which is cooled in its interior by a closed gas circuit, in particular an air circuit, which is connected via generator coolers which are arranged in the generator to an external cooling water circuit, characterized in that at least one refrigeration unit, which produces refrigeration, and extracts further heat from the cooling water before it enters the generator coolers, is provided in the cooling water circuit upstream of the input of the generator coolers. The present invention thus provides a refrigeration unit, which produces refrigeration and extracts heat from the cooling water before it enters the generator coolers, in the cooling water circuit upstream of the input of the generator coolers. The cooling water temperature is thus reduced by the upstream refrigeration unit. Existing systems are converted for adaptation to an increased turbine rating simply by inserting the refrigeration unit or a corresponding heat exchanger upstream of the water inlet to the generator coolers. No action is required on the generator itself.

Generators for new systems with the refrigeration unit installed as standard in advance can be designed to be more cost-effective overall. This results in advantages in terms of physical size and mechanical short-circuit torque on the shaft, with slightly reduced efficiency. Furthermore, a cost-effective type of cooling for the generator can be used to achieve higher ratings, thus having a positive effect on the generator price. The cooling can be provided by refrigeration systems operating in various ways, for example absorption or adsorption refrigeration systems as well as compression refrigeration systems. In this case, when electrically driven compression refrigeration systems are used, the increased requirement for electrical power is surprisingly several times less than the increased power produced at the generator terminals. In the case of large air-cooled generators in the rating class above 200 MW, for example, this results in a multiplication factor in the order of magnitude of 50 or more, by which the achievable additional power from the generator is greater than the electrical input power required for the refrigeration unit. This amazingly high multiplication factor is due to the inherently high efficiency of such generators, which is in the region of 99%.

One preferred refinement of the generator according to the invention, which is distinguished by particular simplicity, is characterized in that the refrigeration unit has a refrigeration producer which is operated by electrical power, in that the generator is part of a power station, and in that the electrical power which is required for operation of the refrigeration producer is taken from the power station's own power supply system.

According to a further preferred refinement to the invention, a bypass water circuit is provided for dissipation of the waste heat losses from the refrigeration unit, is tapped off from the cooling water circuit downstream from the recooling device and opens into the cooling water circuit again downstream from the cooling water outlet from the generator coolers. This further simplifies the design of the additional cooling system.

The arrangement according to the invention is particularly compact if, according to another refinement, a heat exchanger is arranged in the bypass water circuit in order to absorb the waste heat losses from the refrigeration unit, and if the bypass water circuit is physically integrated with the heat exchanger in the refrigeration unit.

Condensation in the generator can reliably be avoided if, according to a further refinement to the invention, the refrigeration unit is connected to a controller which switches on the refrigeration unit only when a predetermined threshold value is exceeded, in which case the generator power, a generator component temperature, the ambient temperature or the cold water temperature can be provided as a criterion.

It is also particularly advantageous for the refrigeration unit to be inserted into the cooling water circuit in such a way that failure of the refrigeration unit does not impede the cooling water circuit. This allows maintenance work to be carried out on the refrigeration unit, with the generator continuing to run with the “capability” which can be achieved without the refrigeration unit.

Furthermore, interruptions in operation which are related to the cooling are avoided if the refrigeration unit is in a redundant form.

If, according to another refinement to the invention, an antifreeze agent, in particular glycol, is mixed with the cooling water in the cooling water circuit, this results, in principle, in the capability to operate with the cooling water temperature at the outlet from the refrigeration unit in the negative temperature range, which, if required, can considerably extend the operating range.

Further embodiments can be found in the dependent claims.

BRIEF EXPLANATION OF THE DRAWINGS

The present invention is explained in more detail in the following text with reference to exemplary embodiments and in conjunction with the drawings, in which:

FIG. 1 shows capability curves of an example of a generator with TEWAC cooling; and

FIG. 2 shows a simplified circuit diagram of one preferred exemplary embodiment of a gas-cooled or air-cooled generator according to the invention.

DETAILED DESCRIPTION

FIG. 2 shows a simplified circuit diagram of one preferred exemplary embodiment of a gas-cooled or air-cooled generator according to the invention within a power station 10. The generator 11 is indicated, with its generator axis 28, only as a box. Air or some other suitable gas, for example hydrogen, circulates in one or more gas circuits 12, 12′ within the closed housing of the generator 11. The gas circuits 12, 12′ in this case normally pass through the rotor and stator of the generator 11. The gas which is heated by the thermal power losses in the interior of the generator 11 is cooled down in one or more generator coolers 13, . . . , 16. The generator coolers 13, . . . , 16 are in the form of gas/water heat exchangers and are part of an external cooling water circuit 17a, b. FIG. 2 shows the generator coolers 13, . . . , 16 connected in parallel. Other types of interconnection are, of course, also feasible, such as connection in series or a mixed form of series and parallel connection.

The heated cooling water coming from the generator coolers 13, . . . , 16 is pumped by means of a pump 18 through a recooling device 19, for example a cooling tower or the like, within the cooling water circuit 17a, b, where it is cooled down and is fed back into the generator coolers 13, . . . , 16. Now, according to the invention, a refrigeration unit 20 which produces refrigeration and extracts heat from the cooling water before it enters the generator coolers 13, . . . , 16, or cools down this cooling water, is inserted in the cooling water circuit 17a, b between the cooling water inlet 17a and the input to the generator coolers 13, . . . , 16. It is, however, also feasible and worthwhile for the refrigeration unit 20 to act on only selected flow elements of the cooling water circuit 17a, b which flow through the generator coolers 13, . . . , 16. Cooling down takes place, for example, via a refrigeration producer 22 which is provided in the refrigeration unit 20 and emits the coldness via a heat exchanger 24 to the cooling water in the cooling water circuit 17b, and emits the absorbed heat via a further heat exchanger 26 to a bypass water circuit 21, which is tapped off from the cooling water circuit 17a upstream of the refrigeration unit 20, and opens into the cooling water circuit 17b again downstream from the cooling water outlet from the generator coolers 13, . . . , 16. In order to design the refrigeration unit 20 in a redundant form, a further refrigeration producer 23 can be provided in addition to the first refrigeration producer 22, and emits coldness when required via a further heat exchanger 25 if the first refrigeration producer 22 fails. Alternatively, if required, two refrigeration producers can operate at the same time. The heat exchangers 24, 25 which are used in the refrigeration unit 20 allow the generator 11 to continue to operate at its original power output if the refrigeration unit 20 were to fail, because the water flow through the heat exchangers 24, 25 remains unaffected. However, an open cooling circuit (for example with flow water) can also be used in addition to the closed cooling water circuit 17a, b shown in FIG. 2.

In the illustrated exemplary embodiment, the refrigeration unit 20 is operated by electrical power 27, which is preferably taken from the power station's 10 own power supply system. The refrigeration unit 20 is advantageously controlled by a controller 29 which switches on the refrigeration unit 20 only when a predetermined threshold value is exceeded. In this case, a threshold value for the generator power or a threshold value for the ambient temperature may be provided as the threshold value. The refrigeration unit can in this case advantageously be controlled in such a way that the control system is matched to the operating state of the generator 11. The use of an adsorption or absorption cooling refrigeration is, of course, also possible, which is then operated predominantly by the input heat flow, instead of by electrical power. This may be taken, for example, from the hot gas part of the generator.

The cooling water temperature is reduced in the upstream refrigeration unit 20. Existing systems are converted for matching to increased turbine ratings simply by inserting the refrigeration unit 20 upstream of the water inlet to the generator coolers 13, . . . , 16. No action is required on the generator 11 itself.

Generators 11 for new systems with the refrigeration unit 20 installed in advance as standard may be designed more cost-effectively. This results in advantages in terms of the efficiency and the mechanical short-circuit torque on the shaft. Furthermore, a cost-effective type of cooling for the generator can be used to increase power levels, having a positive effect on the generator price.

As already mentioned, the additional requirement for electrical power for the refrigeration unit 20 which is operating as a compression refrigeration machine is, surprisingly, several times lower than the additional power achieved at the generator terminals (adsorption or absorption refrigeration systems may, on the other hand, be operated very cost-effectively by using waste heat).

This results in a multiplication factor in the order of magnitude of 50 or more, by which the achievable additional power of the generator 11 is greater than the required electrical power input for the refrigeration unit 20.

This amazingly high multiplication factor is due to the inherently high efficiency of the generator, which is in the region of 99%. The idea of the invention therefore has its remarkable advantages only in this described field of application for generators. Other energy converters whose efficiencies are poorer, such as turbines, cannot be dealt with by means of the described idea because the refrigeration unit would be much too large and uneconomic.

The following numerical example of an air-cooled 240 MW generator of the TEWAC type from the applicant reveals the following data:

without the refrigeration unit 20:

generator cold air: 40° C.

generator rating: 240 MW

cooling water requirement: 0.05 m³/s

total generator losses: 2960 kW

with the refrigeration unit 20 (compression refrigeration system):

refrigeration power: 1050 kW

reduction in the cold water inlet to the generator: −5 K

generator cold air: 35° C.

generator rating: 251 MW

total generator losses: 3050 kW

refrigeration power index: 5

electrical power consumption: 1050/5=210 kW

power emitted to the separate cooling circuit: 1050+210=1260 kW

example: bypass water flow rate: 0.005 m³/s

bypass circuit heating: +60 K (without any effect on the generator)

Claims

1. A dynamoelectrical generator comprising: a closed gas circuit configured to cool an interior of the generator; an external cooling circuit including a coolant; a plurality of generator coolers disposed in the interior of the generator and connecting the closed gas circuit to the external cooling circuit; at least one refrigeration unit disposed in the cooling circuit upstream from an input to the plurality of generator coolers, the at least one refrigeration unit producing refrigeration and extracting further heat from the coolant prior to the coolant entering the plurality of generator coolers.

2. The generator as recited in claim 1, wherein the closed gas circuit is an air circuit and the coolant is cooling water.

3. The generator as recited in claim 1, wherein the refrigeration unit includes a refrigeration producer operable using electrical power.

4. The generator as recited in claim 3, wherein the generator is part of a power station having a power supply system and wherein the electrical power for the refrigeration producer is taken from the power supply system.

5. The generator as recited in claim 1, wherein the refrigeration unit includes a refrigeration producer operable using waste heat based on adsorption or absorption.

6. The generator as recited in claim 1, further comprising a recooling device disposed in the cooling circuit and a bypass circuit configured to dissipate waste heat losses from the refrigeration unit, the bypass circuit being tapped off from the cooling circuit downstream from the recooling device.

7. The generator as recited in claim 6, wherein the bypass circuit opens into the cooling circuit downstream from a coolant outlet of the plurality of generator coolers.

8. The generator as recited in claim 6, further comprising a first heat exchanger disposed in the bypass circuit and configured to absorb the waste heat losses from the refrigeration unit, and wherein the bypass circuit is physically integrated with the first heat exchanger in the refrigeration unit.

9. The generator as recited in claim 1, further comprising a controller connected to the refrigeration unit and configured to switch on the refrigeration unit only when a predetermined threshold value is exceeded.

10. The generator as recited in claim 9, wherein a generator power is provided as a criterion for the threshold value.

11. The generator as recited in claim 9, wherein one of a generator component temperature, an ambient temperature, and a coolant temperature is provided as a criterion for the threshold value.

12. The generator as recited in claim 1, wherein the refrigeration unit and the cooling circuit interact in a manner that enables a flow of the coolant through the cooling circuit in the event of a failure of the refrigeration unit.

13. The generator as recited in claim 1, wherein the refrigeration unit includes at least two redundant refrigeration producers.

14. The generator as recited in claim 1, wherein the coolant includes an anti-freeze agent.

15. The generator as recited in claim 14, wherein the anti-freeze agent includes glycol.

16. The generator as recited in claim 1, wherein the closed gas circuit is a hydrogen circuit.

17. The generator as recited in claim 1, wherein the cooling circuit includes a plurality of flow elements of the coolant, each flow element flowing through one of the plurality of generator coolers, and wherein the at least one refrigeration unit acts only on selected ones of the flow elements.

18. The generator as recited in claim 1, wherein the cooling circuit is a closed cooling circuit.

19. The generator as recited in claim 1, wherein the cooling circuit is an open cooling circuit.

20. The generator as recited in claim 1, wherein the controller is configured to control the refrigeration unit as a function of an operating state of the generator.