A three-phase high voltage (typically 70-220 kV) is in such plants usually converted into a one-phase high voltage, either to the contact line voltage (for example about 16 kV in Sweden) or to a higher voltage, for example about 130 kV, of a superior high voltage network for feeding to the contact line network through feeding stations comprising at least one transformer, in which the voltage is transformed down to the contact line voltage. This means among others reduced transmission losses.

The Swedish patent application No. 9702129-9 suggests also to prolong said direct voltage intermediate link so that it will extend along the contact line for convertion into a one-phase alternat- ing voltage having a lower level at points along the contact line for feeding electric power thereto, wherethrough the conducting losses be reduced even more, since only resistive conducting losses will then exist.

However, it would be desirable to increase the efficiency further in the entire chain from the generation to the contact line.

Moreover, some types of power generation as wind power ex- pose the electricity network to rapid and irregular fluctuations of the power generated, which may be very unfavourable for weak three-phase networks.

SUMMARY OF THE INVENTION The object of the present invention is to provide a plant of the type defined in the introduction, which fulfils said desire and to a large extent reduces the drawback just mentioned of the plants already known of this type.

This object is according to the invention obtained by connecting at least one generator of alternating voltage in such a plant through a converter to said intermediate link so as to feed elec- tric power to the public three-phase alternating voltage network and/or the one-phase alternating voltage network for railway ve- hicles.

By using the direct voltage intermediate link of such a plant in this way also for feeding in electric power through at least one generator a higher efficiency in the generation of the one-phase power may by achieved by the possibility to avoid the round- about through the public three-phase alternating voltage net- work. Furthermore, the plant will be more flexible since the electric power delivered by said generator to the direct voltage intermediate link may be used on one hand for feeding said contact line, should this be needed, and on the other, when there is a lower need of feeding power to the contact line, for feeding parts thereof into the public three-phase alternating voltage network for additional power thereto. Furthermore, the converter maintains the original function thereof to convert three-phase power to one-phase power should the power gene- rated not be sufficient or should it temporarily drop out entirely.

The existence of said generator makes it also possible to reduce the load on the three-phase alternating voltage network on high

load peaks of the one-phase line for feeding the railway, since at least a part of the electric power required thereby may be de- livered by the generator.

According to a preferred embodiment of the invention said ge- nerator is of the type allowing the number of revolutions thereof and by that the frequency of the alternating voltage generated thereby to vary according to the conditions prevailing so as to obtain an efficiency of the energy generation thereof being as high as possible under different conditions. Such a generator may thanks to said direct voltage intermediate link be used for delivering electric power to the three-phase network and/or the one-phase railway feed line. This enables an efficient utilisation of wind and water power, since generators having such a driving result in the best efficiency if the number of revolutions thereof is allowed to vary depending upon wind speeds and amounts of water/fall heights, respectively. Such generators will also deliver an electric power which may vary very much depending upon the conditions prevailing, and which may be difficult to manage for weak public three-phase alternating voltage networks in regions often having spare settlement where especially wind power is installed, while the electricity system of the railway, i. e. the one- phase railway feed line, is characterized by large and rapid load variations and therefor is designed to withstand them. Accord- ingly, the one-phase railway feed line may swallow at teast a part of the large power variations possibly occurring when feed- ing from said generators and in particular take peaks difficult to take by the public network. An additional advantage of this em- bodiment is that coordination wins are obtained by coordinating generation and conversion in this way.

According to another preferred embodiment of the invention a plurality of generators are connected to the intermediate link which forms a so-called direct voltage connecting bar in com- mon thereto. By connecting a plurality of such generators to one

and the same direct voltage intermediate link additional savings of costs may be done.

According to another preferred embodiment of the invention said intermediate link comprises a direct voltage transmission line extending in parallel with said contact line along a track for rail- way vehicles and adapted to transmit electric power to the con- tact line through conversion into alternating voltage on different points therealong. By designing the intermediate link in this way the losses resulting when feeding electric power to different places remotely located along a railway feeding line may be re- duced considerably, and it will also be possible to supply elec- tric power to the intermediate link through generators connected thereto through converters and located at comparatively great mutual distances, which enables an eminent utilisation of wind and/or water power possibly available. The number of conver- ters may at the same time be reduced in this way and by that costs are saved.

According to another preferred embodiment of the invention the plant comprises a transformer arranged between the second converter and the contact line for ensuring that the level of the one-phase alternating voltage produced by this converter is modified to a voltage level desired for said contact line. This is advantageous if another voltage level is more advantageous fQrç the intermediate link than the voltage level determined for the contact line.

According to another preferred embodiment of the invention the plant comprises a transformer adapted to transform the one- phase alternating voltage produced by the second converter into a level being considerably higher than the voltage level of the contact line and transmit this high alternating voltage to a high voltage transmission network adapted to transmit electric power to stations located along the contact line for transforming this high voltage to a level adapted for the voltage of said contact

line and feeding electric power thereto. The high voltage trans- mission line has then not to run directly along the railway. It is enough if it comes close to the railway at the feeding stations or that there are connecting lines thereto. By arranging such a high voltage transmission network, which in Sweden usually has a voltage of about 130 kV and in Central Europe 110 kV, the transmission losses may be reduced with respect to the case of conducting the electric power for the railway vehicles over longer distances through the contact line on a considerable lower level, for example 16 kV.

Further advantages as well as advantageous features of the in- vention will appear from the following description and the other dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a de- scription of preferred embodiments of the invention cited as ex- amples.

In the drawings : Fig 1 is a schematic, very simplified diagram illustrating a plant for transmitting electric power according a preferred embodi- ment of the invention, and Fig 2 is a view corresponding to Fig. 1 of a plant for transmitting electric power according another preferred embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION It is illustrated in Fig. 1 how a public (general) three-phase al- ternating voltage network 1, which may conduct an alternating

voltage of for example 130 kV having a frequency of 50 Hz, is through a transformer 2 connected to a first converter 3 of a converter unit 4 for converting the alternating voltage to a direct voltage of a direct voltage intermediate link 5 of the converter unit. A second converter 6 is connected to the direct voltage in- termediate link and adapted to convert the direct voltage into a one-phase alternating voltage, which is through a transformer 7 transferred to a high voltage transmission network 8, which car- ries a one-phase alternating voltage of for example 30 kV having a frequency of 16 2/3 Hz along a contact line 9 for railway ve- hicles 10 for transmitting electric power through transformer stations 11 at points therealong.

Three wind power generators 12-14 are also connected to the direct voltage intermediate link 5 through converters 15-17 for delivering electric power to the direct voltage intermediate link, in which this electric power may be fed to one of the railway feed line constituted by the contact line and the public alternat- ing voltage network 1 or be shared by them in desired propor- tions depending upon the load conditions prevailing in this line and this network.

The different converters 3,6, 15-17 are of conventional type having current valves including controllable power semicon- ductor devices, such as thyristors or IGBTs, which are controlled so that the alternating voltage side thereof is alternatingly connected to different levels of the direct voltage intermediate link during short periods of time for converting the direct voltage into an alternating voltage and conversely. The direct voltage intermediate link has in a conventional way at least one capacitor not shown for defining the direct voltage as well as an inductor for forming a LC-filter for eliminating harmonics gener- ated by the conversion and which could disturb primarily the public three-phase alternating voltage network.

A plant of this type has many advantages, which have been thoroughly penetrated in the introductory portion of the descrip- tion of the present disclosure, but they will nevertheless be sum- marised here. Wind power generators for one-phase alternating voltage and low frequency would be far to heavy, so that a direct generation without any direct voltage intermediate link would be disadvantageous. However, the number of revolutions of the generators is here allowed to vary and this may also mean a totally different frequency of the alternating voltage generated thereby than on the public alternating voltage network 1. Water power generators and wind power generators may in this way by the change of the number of revolutions better utilise varying wind speeds and amounts of water/fall heights, respectively.

The efficiency of the generation of the one-phase power through the wind power generators will be higher by avoiding the roundabout through the public three-phase network 1. The electricity system of the railway is characterized by large and rapid load variations and is as a consequence thereof con- structed to withstand such variations, so that it may also swal- low a generation having comparable variations of power, which may be difficult for weak public three-phase networks in regions often sparesly populated and in which wind power plants are in- stalle. Thus, the power generated by wind power generators and strongly varying as a consequence of the large variations of the wind speed may at least partially be absorbed by the one- phase railway feeding line. It may also be so that the public three-phase alternating voltage network is not able to receive the additional power generated by the wind power plant erected on a location covered by this network, but the connection of the wind power plants to the direct voltage intermediate link of said converter unit enables then the utilisation of the wind power en- ergy after all by letting the railway feeding line to take care thereof. By coordinating generation and conversion coordination profits saving costs are obtained. Finally, both wind energy and electric railway are associated with large environmental advan-

tages, so that a combination thereof is particularly advanta- geous.

The plant according to Fig. 2 differs from the one according to Fig. 1 by feeding the one-phase power from the second con- verter 6, instead of feeding the one-phase power on a separate high voltage system 8, or as also would be possible directly on a contact line system 9, on a so called auto-transformer system comprising a contact line 9 and a so called negative feeder 18 fed by an alternating voltage in the opposite phase position and which are connected to each other and the rail 19 along the railway by means of auto-connected transformers 20, so called auto-transformers. This makes an increased voltage between the negative feeder 18 and the contact line 9 possible, for example a double voltage between the negative feeder and the contact line when the negative feeder is fed by the same voltage rate as the conduct line, but opposite in phase. This reduces the transmission losses and increases the transmission capacity considerably and makes it accordingly possible to feed in a considerable power without any need of a separate high voltage system, such as the high voltage transmission network 8 according to Fig. 1.

The invention is of course not in any way restricted to the pre- ferred embodiment described above, but many possibilities to modifications thereof would be apparent to a man skilled in the art without departing from the basic idea of the invention.

The wind power generators could for example be exchanged by other generators, which are preferably of the type that may be driven better would the number of revolutions thereof be allowed to vary and deviate from the frequency of the public three-phase network, such as water power generators, but also other ge- nerators may be considered.

It would be well possible to omit the transformer 7, so that the second converter delivers a one-phase alternating voltage hav- ing a suitable level for the alternating voltage transmission net- work extending along the contact line, the transformer 11 and then also the network 8 may be omitted, so that the one-phase alternating voltage from the converter would after transformation in the transformer 7 be fed directly to the contact line, and it would also be possible to remove the two transformers 7,11 as well as the line 8 and let the converter feed electric power di- rectly to the contact line.

Any other voltage levels and frequencies whatsoever than those mentioned above are within the scope of the invention.

It is pointed out that the electric power in some cases may be fed in other directions than said above and electric power is for example fed from the vehicle 10 to the contact line 9 upon braking. Electric power may for example also be fed from the public alternating voltage network to a direct voltage interme- diate link as well as from the latter to the public alternating vol- tage network.