GB2474056A

GB2474056A - Parallel single phase AC power supply arrangements

Info

Publication number: GB2474056A
Application number: GB0917310A
Authority: GB
Inventors: Davor Vujatovic
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-10-05
Filing date: 2009-10-05
Publication date: 2011-04-06
Also published as: GB0917310D0

Abstract

A Single phase AC power supply arrangement comprises a plurality of distributed single phase AC power sources 1A, 1B, 1C and a number of electrical loads 19. Circuit breakers 33 and interconnectors 22 may be provided for the operation of said power sources in parallel and in sufficient numbers so as to meet the electrical operating requirements of the electrical loads. Measurement units 21A, 21B, 21C and load balancing and voltage compensation units 20B, 20C may be provided to measure and regulate the voltage magnitude and phase angle and achieve conditions for parallel operation of as many of the power sources as are connected into the system. The power sources may comprise either grid interface transformers, used to step down a three phase high voltage grid supply to the network working voltage, or frequency regulated single phase AC voltage generation devices. The arrangement is particularly useful to supply power to an electric railway system to meet the requirements of the traction load.

Description

Sin2le Phase AC Power Supply Arrangements

Background of the Invention:

The background of a particular instantiation of this invention relates to the operation of electrical feed arrangements for the supply of power to an AC railway system or network. A typical prior art arrangement for this purpose is shown in Figure 1 with the numbered features described in the following text. Indicative switching and connecting devices [33] only are shown.

Description of Pnor Art:

Typically, prior art arrangements for the supply of AC electrical power to support railway traction requirements involve connection from a national or local utility company power supply grid [1A and 1B] to single phase traction transformers [2A and 2B] at supply points, typically designated Feeder Stations' [3A and 3B], distributed as required along the track network [4]. Each traction transformer [2A and 2B] is generally used to supply a single phase voltage to each section of track, typically designated Feeder Sections' [5A and 5B, SC and 5D], geographically extending away from the feeder station along branch lines as necessary. Feeder sections are electrically separated at each feeder station using insulators, typically designated Insulated Overlaps' [6A and 6B] in order to allow reconfiguration of the network in the event of traction transformer outages and to facilitate fault discrimination by any associated electrical supply protection systems in use. As the feeder sections [Examples 5A and 5B] either side of insulated overlaps [Example 6A] are normally fed from the same phase or phase pair (depending on the transformer connection configuration), the insulated overlap is necessarily designed to permit temporary bridging by the traction unit connecting device, typically a pantograph arrangement [7].

The feeder sections fed by each feeder station are also electrically separated from other adjacent feeder sections at points typically designated Sectioning Stations' [8]. Sectioning stations are generally geographically sited between feeder stations throughout the complete rail network. Electrical separation is achieved by the installation of an insulated break in the section continuity at each sectioning station. Typically, these insulated breaks are referred to as Neutral Breaks' or Neutral Sections' [9].

From the traction transformers [2A and 2B], typically, there is either a single or two pole connection to the network power connection arrangements, such as an overhead line [12], from which a voltage pick up contact arrangement, such as a pantograph [7], is used to make electrical connection to the traction load [10]; which can include the traction unit prime mover and any auxiliary systems. The return current path back to the traction transformer, typically, includes use of the wheels and track, an overhead line or a combination of both [11].

Typically, power supplies to the feeder station are taken directly from connection points on the grid [1A and 1B] as a single phase supply to the primary side of single phase traction transformer(s) [2A and 2B] sited at each feeder station [3A and 3B]. The traction transformer [2A and 2B] fransforms the voltage down to a working voltage which is fed as a single phase supply to the traction load via an AC busbar [13], the contact lines [12] and the connecting device [7].

The fraction load is mainly inductive in nature and variable in magnitude due to factors that include fraffic flow, traffic type and terrain conditions. As such, it is an electrically complex load, with active and reactive components. When imposed on a single phase or phase pair of the grid supply, the nature of the traction load causes varying imbalance in the loading of the grid supply.

In order to minimise the adverse effects of imbalance on the grid supply, different phase pairs are selected from the grid for the supply of different single phase traction transformers [2A and 2B] with the object of equalising the number of times each phase or phase pair is connected to, and thus loading, the grid. Additionally, load balancing techniques may also be used to minimise imbalance on the grid.

Generally, under normal operating conditions, different phases or phase pairs from the grid [1A and 1B] will be feeding adjacent feeder stations [3A and 3B]. There will also be a variation of traction load between adjacent feeder sections. Accordingly, feeder sections [SB and 5C] would normally be supplied from different feeder stations [respectively 3A and 3B].

Under this normal condition, the safety of the system must rely on the electrical separation provided by the neutral section [9] to avoid paralleling the two supplied AC voltages from the adjacent traction transformers [2A and 2B] as these voltages will be at variance in magnitude and phase. The transition of the traction unit [10] across the neutral section [9] requires close technical management in order to remove any risk of electrical bridging by the traction unit [10] connection, typically a pantograph arrangement [7], which would cause the connection of one phase or phase pair with another phase or phase pair. Any failure to safely manage a neutral section [9] could cause an inadvertent attempt to parallel two phases or phase pairs carrying voltages which would invariably be out of phase due to differing grid conditions and traction loading.

Under temporary operating conditions, for example caused by the failure of the power supply from a feeder station [3A or 3B], the network distribution system must be reconfigurable such that any feeder station can be used to supply an extension of its feeder sections up to a second and further neutral section along the network. In order to support such reconfiguration, the neutral section [9], typically sited at each sectioning station [8], is also capable of being configured to allow the electrical connection of the two feeder sections {5B and 5C] so that they can be fed from either of the adjoining feeder stations [3A and 3B].

Under these reconfiguration conditions, each feeder station [3A or 3B] may be required to supply up to four feeder sections [in the case of Feeder Station 3A this would be Feeder Sections 5A, 5B, SC and 5D], effectively doubling the potential traction load and causing an increased voltage drop along the railway traction distribution system and a commensurate increase in system power losses.

II is the primary objective of this present invention to overcome the problems of the aforesaid conditions that lead to variations in voltage magnitude and phase such that the contributing AC power sources can be operated in parallel for the purpose of supplying the system network as a whole and permit the elimination of the requirement for neutral sections.

Statement of Invention:

In its application to the supply of single phase AC power to a rail network, the present invention proposes to meet the primary objective stated above by creating the electrical conditions where two or more single phase AC power sources, generators or transformers, can be operated in parallel and used to support the entire network traction load at any demand level. The methodology for creating such conditions involves: 1. Providing a method of voltage regulation throughout the network system such that the AC power source voltage magnitude and phase outputs can be continuously controlled and synchronised to allow parallel operation of such power sources. Under the present invention, options to meet this requirement include matching either an actual reference level taken from another operational feeder station or a predetermined level which may be set locally at feeder stations for optimal network operation.

2. Where the voltage reference is taken from another feeder station, designating that feeder station as a Master feeder station and using it to provide voltage magnitude and phase reference values to other stations for the purpose of network voltage regulatory control; feeder stations under such control being designated as Slave feeder stations. Railway system operation in this mode being designated as Mode 1.

3. Where the operating voltage reference level is predetermined and set locally, providing a common time reference across the network to allow independent but synchronised regulation of voltage magnitude and phase. Railway system operation in this mode being designated as Mode 2. Reference levels may also be set to provide control of other electrical parameters, such as power factor, power or current magnitude to achieve the same objective of parallel operation.

4. Where network feeder stations are supplied by different phases or phase pairs from the grid, or where the same phases or phase pairs are used and local network load conditions make it necessary, providing a load balancing capability in order to make it electrically more feasible to run traction supply sources in parallel.

5. In Mode 1 operation, providing a control loop which is able to carry reference data from the Master to each Slave feeder station for the purposes of comparison and use in regulation at the Slave feeder stations. It is not strictly necessary to have any regulation at Master station.

6. Providing connection and control facilities which would enable and control the parallel operation of the optimal number of feeder stations needed to meet the traction load requirement in any synchronised mode of operation, including Mode 1, Mode 2 and any future modes made possible by other techniques, and under both normal and temporary operating configurations.

7. Where AC Generator sources are used to directly supply the rail network, the invention requires that such sources should have a frequency regulation facility that will maintain the frequency of supply at a constant level and matched to the grid frequency where necessary, regardless of electrical load.

introduction to Drawings:

Figure 1 is an illustration of a typical AC power supply arrangement for a rail network

occurring in prior art systems.

Figure 2 is a schematic diagram showing a typical embodiment of the invention system architecture using multiple generic AC power sources and multiple electrical loads in a Mode 1 operating configuration.

Figure 3 is a schematic diagram showing a typical embodiment of the invention system architecture using multiple generic AC power sources and multiple electrical loads in a Mode 2 operating configuration.

Figure 4 is a schematic diagram showing a typical embodiment of the invention at a feeder station using Static Synchronous Compensator and Voltage Source Tnverter technology in a Mode 1 rail network operating arrangement.

Figure 5 is a schematic diagram showing a typical embodiment of the invention at a feeder station using transformer on-load tap changer technology in a Mode 2 rail network operating arrangement. This embodiment of the invention assumes that load balancing is required and it is achieved using a static load balancer utilising single phase Static VAr Compensator technology.

Detailed Description:

In addition to the embodiments disclosed in this document, this invention is capable of other embodiments using alternative technologies, some of which are listed below, to meet the requirements of the primary objective above. The use of other technologies with similar functionality, features and advantages not listed below will occur to those skilled in the art but these are not excluded by the description disclosure of the illustrative embodiments and the accompanying drawings.

The following systems and devices, but not exclusively, have the functionality which would be appropriate for use in combination in implementing this invention.

Load Balancing and voltage regulating devices such as single phase or three phase Static VAr Compensators (SVCs).

Tap changeable transformers for the control of voltage magnitude and/or phase.

Static Synchronous Compensator (STATCOM) devices with the capability of load balancing and regulating voltage using Voltage Source Inverter (VSI) technology.

Static Synchronous Series Compensator (SSSC) technology for voltage regulation.

Unified Power Flow Controller (UPFC) devices comprising STATCOM and Static Synchronous Series Compensator (SSSC) technology for load balancing and voltage regulation.

Data communication and control systems, including landline, terrestrial and space propagated data link systems, that may be used for supporting the operation of distributed power generation or transformed power supply sources.

Universal time devices both internal and external to the rail network system, such as internal clocks, satellite time coding facilities etc. Moreover, the invention in various embodiments is also capable of being used to meet similar AC power supply requirements occurring in industries other than the rail industry.

Accordingly, the present invention is not limited in its implementation by the rail industry application, technologies, construction and arrangements of components described or illustrated in any preceding or following description or drawing in this document. This versatile capability is demonstrated by a generic embodiment of the invention which is used to illustrate the invention Mode 1 architecture at Figure 2 and Mode 2 architecture at Figure 3. For clarity, switching and connecting devices have been omitted from both figures and the numbered features are as described in the following text.

Mode 1 Operation: The generic Mode 1 embodiment, Figure 2, shows a distribution system comprising any number of three phase AC transformers [14A, 14B and 14C etc.] being used to down transform high voltage three phase grid supplies [1A, 1B, 1C etc.] to a single phase working voltage. The architecture provides for the paralleling of the single phase output from each transformer in the operation of the system as a fully connected network of power sources and loads by designating one transformer as a Master' [1 4A], for the supply of a reference for system voltage regulation purposes, and all other transformers [14B, 14C etc.] as Slaves'.

The Master [14A] is shown connected to one phase pair of the grid supply [15A] on the primary side and to a single phase busbar [16] on the secondary side of the transformer. The Slave transformers [14B and 14C] are shown connected to a three phase grid supply [15B and C] on the primary side and to three phase busbars [17] on the secondary side. At each transformer [14A, 14B and 14C] in the system, a single phase (or phase pair depending on the transformer design configuration) [18] is taken from a busbar [either 16 or 17] on the secondary side, and used to supply a section of contact line [23] which enables the distribution of power to any number of electrical loads [19] connected to the contact line [23] at any one time. Slave transformers are shown fitted with a Load Balancing and Voltage Compensation capability [20B, 20C etc] for balancing the electrical load presented to each transformer, by as many complex electrical loads [19] which may be connected at one time, and control of the magnitude and phase angle of the voltage supplied to the contact line [23], within designed working limits, to match the reference values received from the Master.

The real time voltage magnitude and phase angle output by the Master [14A], as measured by the Measurement Unit [21A], is used as a reference which is transmitted over a data link [24] facility to each Slave [14B, 14C etc.] to be brought into the operation of the system as a whole. At each Slave, the Master reference values received are compared [25] with the local voltage as measured by the local Measurement Units [21B, 21C etc]. The difference is used to generate a correcting input to the Load Balancer and Voltage Compensator Units [20B, 20C etc.] in order to rebalance the load as necessary and to bring the Slave output voltage into synchronisation with that of the Master. This state of synchronisation thus enables the Master and Slaves to be linked, for example through the Interconnectors [22] between each section of the contact line [23], and operated in parallel for the power supply of the system as defined by the system operational connectivity requirements in force at any time.

Mode 2 Operation: The generic Mode 2 embodiment, Figure 3, similarly shows a distribution system comprising any number of three phase AC transformers [14A, 14B and 14C etc.] being used to down transform high voltage three phase grid supplies [1A, 1B, 1C etc.] to a single phase working voltage. The architecture provides for the paralleling of the single phase output from each transformer in the operation of the system as a fully connected network of power sources and loads by allowing a common reference to be input locally at each transformer [34] for comparison [35] with the actual voltage output from each transformer as measured by the Measurement Units [21A, 21B and 21C].

All transformers [14A, 14B and 14C] are shown connected to a three phase grid supply [iSA, 1 SB and 15 C] on the primary side and to three phase busbars [17] on the secondary side. At each transformer [14A, 14B and 14C] in the system, a single phase (or phase pair depending on the transformer design configuration) [18] is taken from a busbar [either 16 or 17] on the secondary side, and used to supply a section of contact line [23] which enables the distribution of power to any number of electrical loads [19] connected to the contact line [23] at any one time. All transformers [14A, 14B and 14C] are shown fitted with a load balancing and voltage compensation capability [20A, 20B, 20C] for balancing the electrical load presented to each transformer, by as many complex electrical loads [19] which may be connected at one time, and control of the magnitude and phase angle of the voltage supplied to the contact line [23], within designed working limits, to match the reference value set locally.

A universal time facility [36] is used to synchronise the sampling of the transformer [14A, 14B and 14C] voltage outputs by the Measurement Units [21A, 21B and 21C] for comparison with the locally set reference [34]. The difference is used to generate a correcting input to the Load Balancer and Voltage Compensator Units [20A, 20B, 20C] in order to bring the actual output voltage into synchronisation with that of the local reference [34]. The states of synchronisation at each transformer are linked by virtue of the universal time device and this enables the transformers [14A, 14B and 14C] to be linked, for example through the Interconnectors [22] between each section of the contact line [23], and operated in parallel for the power supply of the system as defined by the system operational connectivity requirements in force at any time.

An example implementation of a load balancing and voltage regulation system to enable the parallel operation of single phase transformers in accordance with the present invention using STATCOM and VSI technology for the supply of a rail network power distribution system is shown in Figure 4. Indicative switching and connecting devices [33] only are shown and the numbered features are as described in the following text.

Figure 4 shows a typical three phase traction transformer [14B] at a feeder station with a star primary winding connected to a high voltage three phase grid busbar [1 5B] and a delta secondary winding connected to a three phase working voltage, traction busbar [17]. A single phase working voltage supply is taken from the traction busbar [17] via the secondary winding of the single phase series connected transformer [26], traction busbar [13] and circuit breakers [33] to the traction load [10] as presented by the rail network via contact lines [12].

The current return path [11] is shown through the wheels and track back to the fraction busbars [17] at the feeder station. The load balancing and voltage regulation system [27] has a parallel control interface to all three phases as supplied to the traction busbars [17] using a three phase transformer [28] which may also act as a commutating reactance. The load balancing and voltage regulation system [27] also has a control interface to the single phase traction power supply via the primary winding of the series connected transformer [26]. This system configuration enables control of the flow of both reactive and active power for load balancing and control of the voltage supplied to the rail network.

At the heart of the voltage regulation system [27] are the STATCOM [29] and the Series Compensator [30] devices, both of which employ VSI technology. Tn this configuration the STATCOM [ 29] is used as a load balancer, supplying compensatory reactive and active power as necessary. The Series Compensator [30] is used for fine control of the magnitude and phase angle of the output traction voltage by means of the series connected transformer [26]. This arrangement can also supply/accept active power to/from both the grid [15B] and the traction load [10] by means of the connecting energy storage device [31] which may be a DC capacitor, battery arrangement or combination of both. This regulation system ensures that a balanced load is presented to the grid supply source and facilitates the regulation of the voltage at the output of the feeder station in phase and magnitude. Tf the measured output voltage [21B], of such a feeder station is matched to the reference voltage [37], then it becomes feasible to parallel the sources of power at all feeder stations and operate the rail network under these conditions.

Figure 5 shows a typical three phase traction transformer [1 4B] at a feeder station with a star primary winding connected to a high voltage three phase grid busbar [1 5B] and a zig-zag secondary winding connected to a three phase working voltage traction busbar [17]. A single phase working voltage supply, in this instance phase A, is taken from the traction busbar [17] via the secondary winding of the single phase series connected transformer [26], traction busbar [13] and circuit breakers [33] to the traction load [10] as presented by the rail network via contact lines [12]. The current return path [11] is shown through the wheels and track back to the earthed neutral of the transformer [1 4B] zig-zag secondary winding at the feeder station. The load balancing and voltage regulation system [27] has a parallel control interface to all three phases as supplied to the traction busbars [17]. The load balancing and voltage regulation system [27] also has a control interface to the single phase traction power supply via the primary winding of the series connected transformer [26], which is in this instance connected between the phases B and C of the working voltage traction busbars [17] and is thus in quadrature with the phase A voltage. This system configuration enables control of the flow of both reactive and active power for load balancing and control of the magnitude and phase angle of the voltage supplied to the rail network.

At the heart of the voltage regulation system [27] are the SVC based load balancer [29] and the series connected transformer [26]. In Figure 5, the Load Balancer [29] is shown as three single phase SVCs connected between the three phase traction busbars [17] and earth. In this configuration it is also used to supply compensatory reactive power as necessary to fine tune the voltage magnitude; any large voltage magnitude adjustments, or voltage adjustments necessary to compensate variations in the grid supply voltage, could be done by automatic on-load tap changer action of the main three phase transformer [14B]. The phase angle of the output traction voltage is controlled by the on-load tap changer action of the series connected transformer [26]. This regulation system ensures that a balanced load is presented to the grid supply source and facilitates the regulation of the voltage at the output of the feeder station in phase and magnitude. If the measured output voltage [21B], of such a feeder station is matched to the reference voltage [37], then it becomes feasible to parallel the sources of power at all feeder stations and operate the rail network under these conditions.

Benefits Offered: The benefits attributable to this invention for implementation in power supply arrangements for a rail network include: Removal of the existing requirement for neutral sections and sectioning stations as parallel operating feeder stations will be the normal method of network operation and the paralleling risks occurring in the present distribution configuration will no longer be a factor for concern or a design constraint.

Reduction of the need for individual feeder stations to be rated with excess capacity as the traction load is distributed throughout the active feeder stations with, as necessary, all feeder stations being brought on line to meet peak demand.

Removal of the constraining system design requirement to balance the loading on the high voltage grid by selecting an equal number of the three phase pairs.

Reduction of the need for complex neutral section arrangements and procedures for transiting neutral breaks and enhances safe passage from one feeder section to another.

Simplification of the complex signalling arrangements around neutral sections.

Reduction in the size of the catenary system whilst improving the voltage profile and reducing system losses.

More effective power delivery leading to a reduction railway corridor requirements for both open routes and tunnels.

Recovery of regeneration energy will also be more viable.

Claims

Claims Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. Words, such as typically', generally', arrangement', include', comprise', may', any', system', conditions' or circumstances' and any derivatives of such words as used herein are to be interpreted broadly and comprehensively and are not limited to any physical embodiment, example, case, configuration or condition as used to disclose the invention. Moreover, any embodiments disclosed herein are not to be taken as the only possible embodiments and such possible embodiments include those which may be used to support applications of the invention to other industries with power supply requirements similar to those of the Rail industry. Other such embodiments will occur to those skilled in the art and these are still deemed within the following claims: 1. The continual operation of two or more single phase AC power sources in such a manner as to allow their operation in parallel to meet the power supply requirements of an electrical load.
2. Operation of single phase AC power sources according to Claim 1 using dynamic voltage regulation technologies to achieve synchronisation and parallel operation.
3. Operation of single phase AC power sources according to Claim 1 using load balancing and dynamic voltage regulation technologies to achieve synchronisation and parallel operation.
4. Operation of single phase AC power sources according to Claim 1, to supply a distributed and randomly changing electrical load which may be electrically complex in nature and may comprise dynamic, inductive or capacitive load components.
5. Operation of single phase AC power sources according to Claim 1, for use in the supply of power to an electric railway system to meet the requirements of the traction load.
6. Operation of single phase AC power sources according to Claim 1, for use in the supply of power to an electric railway system without the requirement to provide electrical separation, typically Neutral Breaks or Neutral Sections, between traction transformers.
7. Operation of single phase AC power sources according to Claim 1, with regulation of voltage magnitude and phase angle being controlled by a designated single phase AC power source.
8. Operation of single phase AC power sources according to Claim 1, with regulation of voltage magnitude and phase angle being individually controlled at each source by universal time sharing methods, or other appropriate reference and devices to achieve synchronisation.
9. Operation of single phase AC power sources according to Claim 1, with regulation of voltage magnitude and phase angle being individually controlled at each source by reference signals as appropriate to meet network operational requirements and such devices as required to achieve synchronisation.
10. Operation of single phase AC power sources according to Claim 1, using Static VAR Compensator technology to balance the electrical load.
11. Operation of single phase AC power sources according to Claim 1, using tap changeable transformers to control the system voltage magnitude and phase angle.
12. Operation of single phase AC power sources according to Claim 1, using Static Synchronous Compensator [STATCOM] devices and Voltage Source Inverter (VSI) technology to balance the load and control the system voltage magnitude and phase angle.
13. Operation of single phase AC power sources according to Claim 1, using Static Synchronous Series Compensator [SSSC] devices and VST technology to confrol the system voltage magnitude and phase angle.
14. Operation of single phase AC power sources according to Claim 1, using Unified Power Flow Controller (UPFC) devices comprising STATCOM and SSSC devices and VST technology to balance the load and control the system voltage magnitude and phase angle.
15. Operation of single phase AC power sources according to Claim 1, using Current Source Inverter (CSI) technology.
16. Operation of single phase AC power sources as a system according to Claim 1, using a data link to share the controlling data and to provide the functions needed to support the operation of the system.
17. Operation of single phase AC power sources as a system according to Claim 1, using a local reference data as needed to support the operation of the system.AMENDMENTS TO CLAIMS HAVE BEEN FILED AS FOLLOWSOperation of AC power sources for use in the supply of power to an electric railway system without the requirement to provide electrical separation, typically known as Neutral Breaks or Neutral Sections, between different supply points and feeder stations, this being made possible through: a. Application of dynamic load balancing thus removing the requirement for selection of different phases or phase pairs for the purposes of equalising the imbalance caused by connection of single phase loads to the three phase supply system b. Application of dynamic voltage magnitude regulation at feeder stations so that the voltages present on adjacent feeding sections supplying power to traction loads have the same or nearly the same magnitudes c. Application of dynamic voltage phase angle regulation at feeder stations so that the voltages present on adjacent feeding sections supplying power to traction loads have the same or nearly the same phase angles d. Application of common reference signals distributed to feeder stations for the Q purposes of dynamically adjusting voltage magnitude and phase angle regulation at feeder stations as appropriate to meet the requirements of equalising the voltages supplying adjacent feeding sections e. Tntegration of control systems and regulators so that a number of feeder stations operate together to achieve the common operation as appropriate to meet the requirements of equalising the voltages supplying adjacent feeding sections 2. Operation of AC power sources for use in the supply of power to an electric railway system without the Neutral Breaks or Neutral Sections therefore making possible the continual operation of said power sources in parallel with the effects of: a. Reduction of the rating of equipment in feeder stations as the traction load is supplied from multiple feeder stations so the maximum load demand of individual feeder stations is reduced.b. Removal of the constraining system design requirement to balance the loading on the high voltage grid by selecting different phases or phase pairs of the three phase system.c. Reduction of the need for complex system operation arrangements and procedures for transiting Neutral Breaks' or Neutral Sections' and enhancing safe passage from one feeder section to another.d. Simplification of the signalling arrangements around neutral sections.e. Reduction in the size and rating of the catenary system.f. Improvement of the catenary system voltage profile and reduction of system losses.g. More effective power delivery leading to a reduction in railway corridor requirements for both open routes and tunnels.h. More viable and efficient recovery of train regeneration energy.3. Claim 1 and Claim 2 are applicable to practically all designs and implementations of single phase AC power distribution systems supplying railways because: a. the invention addresses the design and operation of feeder stations in a way which is sufficiently independent of the traction power distribution system design and implementation Q b. the functionality and operability of the traction power distribution system is not restrictive to the application of the invention