PLANT FOR AC POWER SUPPLY TO A DEVICE MOVABLE ALONG A TRACK
United States Patent 3660621
For AC power supply to a device movable along a track, such as an electrically powered crane, the invention provides a compensated conductor system for each phase by placing, close to each contact rail, additional conductors of other phases are provided extending along the track in close but insulated relation to said contact and rail electrically connected to the remaining rails of said other phases at intervals along the track, whereby voltage drops are minimized and the power factor is improved. For each rail with adjacent conductors and appurtenant insulation, composite section units are provided.
US Patent References:
Electrical trolley systems, low reactance type
Shaw et al. - July 1961 - 2991336
Balancing a three-phase power transmission system for an electric arc furnace
Watterson - January 1968 - 3366725
Electric traction
Guignard - May 1935 - 2001357
Electrical trolley systems, low reactance type
Shaw et al. - July 1961 - 2991336
Balancing a three-phase power transmission system for an electric arc furnace
Watterson - January 1968 - 3366725
Electric traction
Guignard - May 1935 - 2001357
Application Number:
05/021753
Publication Date:
05/02/1972
Filing Date:
03/23/1970
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
307/147, 191/22R
International Classes:
B60L5/36; B60M3/02; B60L5/00; B60M3/00; B60M1/00
Field of Search:
307/147,148 191/22R,33R,30 174/34 191/2
Primary Examiner:
La Point, Arthur L.
Assistant Examiner:
Libman, George H.
Claims:
What I claim is
1. In an AC power supply system for a tracked electrically operated carriage having current collectors for receiving power supply as the carriage moves, a system comprising: a plurality of spaced electrically conductive contact rails for supplying power to the carriage; additional elongated conductors closely extending along and electrically insulated and associated with each of said contact rails in a number equal to the total number of contact rails less one, the additional conductors each having substantially the same electrical resistance per unit length as the contact rail; and connected means electrically connecting each of said additional conductors with one each of said contact rails other than with which said additional conductors are associated, so that current drawn by the electrically operated carriage through said collectors is shared substantially equally by each contact rail and said additional conductors which are electrically connected thereto, whereby because of the closeness of the additional conductors and an associated contact-rail, the reactance of the system is reduced.
2. A system as claimed in claim 1 in which said plurality of spaced rails are arranged in longitudinal sections with electrical continuity between sections, and said connecting means are connected in regions between said sections.
3. A system as claimed in claim 2 in which each contact rail is bunched with its said associated additional elongated conductors in insulated relation.
4. A system as in claim 3 which includes insulation partly surrounding each contact rail exposing a longitudinal contact-strip surface, and substantially completely surrounding said additional elongated conductors.
1. In an AC power supply system for a tracked electrically operated carriage having current collectors for receiving power supply as the carriage moves, a system comprising: a plurality of spaced electrically conductive contact rails for supplying power to the carriage; additional elongated conductors closely extending along and electrically insulated and associated with each of said contact rails in a number equal to the total number of contact rails less one, the additional conductors each having substantially the same electrical resistance per unit length as the contact rail; and connected means electrically connecting each of said additional conductors with one each of said contact rails other than with which said additional conductors are associated, so that current drawn by the electrically operated carriage through said collectors is shared substantially equally by each contact rail and said additional conductors which are electrically connected thereto, whereby because of the closeness of the additional conductors and an associated contact-rail, the reactance of the system is reduced.
2. A system as claimed in claim 1 in which said plurality of spaced rails are arranged in longitudinal sections with electrical continuity between sections, and said connecting means are connected in regions between said sections.
3. A system as claimed in claim 2 in which each contact rail is bunched with its said associated additional elongated conductors in insulated relation.
4. A system as in claim 3 which includes insulation partly surrounding each contact rail exposing a longitudinal contact-strip surface, and substantially completely surrounding said additional elongated conductors.
Description:
BACKGROUND OF THE INVENTION
The present invention relates to systems for electric power supply to a device moving along a track, for example an electrically powered crane.
Usually, the power supply to such devices is effected through rails mounted along the track and a corresponding number of current collectors with spring-loaded slide contacts are mounted on the device. Each of the conductor rails has an uninsulated contact face affording electric contact with the collector sliding along the rail.
Such tracks may be very long, up to several hundred meters, and the contact rails are mostly divided into longitudinal sections, usually about 7 to 14 meters long. As few joints as possible are desired, but on the other hand, for convenient handling the sections ought not to be too long. Provision must be made for a thermal expansion and contraction of the rails, and it is therefore usual to provide several expansion joints in these.
In plants of this kind it is mostly necessary for practical reasons to mount the contact rails with a relative large spacing, usually about 0.20 to 0.40 meters. In AC plants for long tracks this results in a high reactance of the rail system. Since large currents, for example of 2,000 ampere or more, may be involved, this results in considerable voltage drop along the line to the load. For reducing the voltage drop to acceptable values it is necessary to use relatively large conductor cross sections, and several rails are therefore often connected in parallel, and it is mostly necessary to provide for feeding at several points along the rail system.
SUMMARY OF THE INVENTION
The present invention has for an object to overcome this drawback and primarily consists in providing a so-called compensated conductor system for the individual contact rails by closely placing along each contact rail additional phase conductors substantially of largely equivalent cross section and in a number corresponding to the number of the remaining phase contact rails and each conductively connected to one of the remaining phase contact rails at points distributed along the track.
In this manner it is possible to make the reactance of the contact rail plant ignorable. This, of course, applies irrespective of the number of phases and hence of contact rails.
The necessary transverse connections may most conveniently be provided at the locations of the joints in the contact rails, where the conductors may be accessible. The additional conductors may be laid in insulated relation with respect to each other and to the adjacent contact rail in any suitable manner, but for rational manufacture it is preferred to arrange them in joined and insulated relation to the respective adjacent contact rails.
Hence, in addition to having the novel features specified, the system of the invention also provides a composite conductor section adapted to be used in such a plant, and characterized in that it consists of a contact rail partly surrounded by insulation and one or more additional conductors of substantially equivalent cross section and entirely surrounded by the insulation.
In the accompanying drawings the invention is diagrammatically illustrated for the case of a three-phase system, since a three-phase current supply is mostly used in system of the kind referred to.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic cross-sectional view of the conductor rail system with cross-connections added; and
FIG. 2 is a circuit diagram of the system of the invention.
As a consumer unit on the movable device (the crane) only a motor M connected to the current collectors 15 to 17 has been indicated in the drawings.
Along each of the contact rails 1, 2 and 3 of the phases R, S and T, respectively, and at a short distance therefrom there are placed groups of two conductors 4 and 5, 6 and 7, 8 and 9, respectively. Each of the two conductors extending adjacent one contact rail is connected to one of the two remaining phases of the three-phase system. Thus, each rail unit comprises the three phases R, S and T of a three-phase system, but the phases are cyclically interchanged in the three rail units. At certain intervals along the rail plant the three conductors of each phase are interconnected by transverse connections designated by 10, 11 and 12 in FIG. 1. The insulation of each rail unit is composed of an insulating compound cast around it as indicated at 13, 14 and 15, respectively, in FIG. 1. With this rail arrangement the spacing a (FIG. 1) of the contact rails is irrelevant from an electrical viewpoint, but may be as usual, that is for example 0.20 to 0.40 meters. Likewise, the length b of the rail sections may be as usual, that is about 7 to 14 meters, and the cross-connections may be located at the joints.
Provided that all conductors 1 to 9 inclusive have equivalent conducting cross sections, i.e., they have the same electrical resistance per unit length, the currents will be distributed on the three conductors of the same phase, due to the fact that currents will flow in the cross-connections in the proximity of the collection point as indicated in the diagram of FIG. 2. Throughout nearly the whole stretch between the feed point A and the collection point B the currents in each rail unit I R /3, I S /3 and I T /3, respectively, will be balanced. Therefore, as a result there will exist three three-phase conductor systems extending to the collection point, each with an ignorable reactance.
Since practically only resistive voltage drops will occur in this system, one single feed point will be sufficient for covering several hundred meters of contact rails.
For economic reasons aluminum is preferred as conductor material for the additional conductors 4 to 9. However, aluminum is not suited for forming a contact face engaged by the slide contacts, and therefore the contact rails 1, 2 and 3 ought at least to have a contact surface of a different material, such as copper or stainless steel. In the part of the cross section not engaged by the sliding collector it is, of course, also possible to use aluminum.
In addition to an efficient utilization of the conductor cross sections the power supply plant according to the invention will result in an improved power factor as compared with previously known contact rail plants for the same purpose.
In a single phase system the power supply system will comprise two contact rails, each with one conductor at a short distance from the rail and connected to the other phase of the system. Like in a three-phase system the conductors of the same phase are interconnected by a number of cross-connections, likewise at intervals of about 7 to 14 meters.
Although in the present specification it is said that adjacent each contact rail there shall be placed one conductor for each of the remaining phases of the system, it will, of course, be understood that each such additional conductor may be composed of a plurality of parallel-connected conductor strands.
The present invention relates to systems for electric power supply to a device moving along a track, for example an electrically powered crane.
Usually, the power supply to such devices is effected through rails mounted along the track and a corresponding number of current collectors with spring-loaded slide contacts are mounted on the device. Each of the conductor rails has an uninsulated contact face affording electric contact with the collector sliding along the rail.
Such tracks may be very long, up to several hundred meters, and the contact rails are mostly divided into longitudinal sections, usually about 7 to 14 meters long. As few joints as possible are desired, but on the other hand, for convenient handling the sections ought not to be too long. Provision must be made for a thermal expansion and contraction of the rails, and it is therefore usual to provide several expansion joints in these.
In plants of this kind it is mostly necessary for practical reasons to mount the contact rails with a relative large spacing, usually about 0.20 to 0.40 meters. In AC plants for long tracks this results in a high reactance of the rail system. Since large currents, for example of 2,000 ampere or more, may be involved, this results in considerable voltage drop along the line to the load. For reducing the voltage drop to acceptable values it is necessary to use relatively large conductor cross sections, and several rails are therefore often connected in parallel, and it is mostly necessary to provide for feeding at several points along the rail system.
SUMMARY OF THE INVENTION
The present invention has for an object to overcome this drawback and primarily consists in providing a so-called compensated conductor system for the individual contact rails by closely placing along each contact rail additional phase conductors substantially of largely equivalent cross section and in a number corresponding to the number of the remaining phase contact rails and each conductively connected to one of the remaining phase contact rails at points distributed along the track.
In this manner it is possible to make the reactance of the contact rail plant ignorable. This, of course, applies irrespective of the number of phases and hence of contact rails.
The necessary transverse connections may most conveniently be provided at the locations of the joints in the contact rails, where the conductors may be accessible. The additional conductors may be laid in insulated relation with respect to each other and to the adjacent contact rail in any suitable manner, but for rational manufacture it is preferred to arrange them in joined and insulated relation to the respective adjacent contact rails.
Hence, in addition to having the novel features specified, the system of the invention also provides a composite conductor section adapted to be used in such a plant, and characterized in that it consists of a contact rail partly surrounded by insulation and one or more additional conductors of substantially equivalent cross section and entirely surrounded by the insulation.
In the accompanying drawings the invention is diagrammatically illustrated for the case of a three-phase system, since a three-phase current supply is mostly used in system of the kind referred to.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic cross-sectional view of the conductor rail system with cross-connections added; and
FIG. 2 is a circuit diagram of the system of the invention.
As a consumer unit on the movable device (the crane) only a motor M connected to the current collectors 15 to 17 has been indicated in the drawings.
Along each of the contact rails 1, 2 and 3 of the phases R, S and T, respectively, and at a short distance therefrom there are placed groups of two conductors 4 and 5, 6 and 7, 8 and 9, respectively. Each of the two conductors extending adjacent one contact rail is connected to one of the two remaining phases of the three-phase system. Thus, each rail unit comprises the three phases R, S and T of a three-phase system, but the phases are cyclically interchanged in the three rail units. At certain intervals along the rail plant the three conductors of each phase are interconnected by transverse connections designated by 10, 11 and 12 in FIG. 1. The insulation of each rail unit is composed of an insulating compound cast around it as indicated at 13, 14 and 15, respectively, in FIG. 1. With this rail arrangement the spacing a (FIG. 1) of the contact rails is irrelevant from an electrical viewpoint, but may be as usual, that is for example 0.20 to 0.40 meters. Likewise, the length b of the rail sections may be as usual, that is about 7 to 14 meters, and the cross-connections may be located at the joints.
Provided that all conductors 1 to 9 inclusive have equivalent conducting cross sections, i.e., they have the same electrical resistance per unit length, the currents will be distributed on the three conductors of the same phase, due to the fact that currents will flow in the cross-connections in the proximity of the collection point as indicated in the diagram of FIG. 2. Throughout nearly the whole stretch between the feed point A and the collection point B the currents in each rail unit I R /3, I S /3 and I T /3, respectively, will be balanced. Therefore, as a result there will exist three three-phase conductor systems extending to the collection point, each with an ignorable reactance.
Since practically only resistive voltage drops will occur in this system, one single feed point will be sufficient for covering several hundred meters of contact rails.
For economic reasons aluminum is preferred as conductor material for the additional conductors 4 to 9. However, aluminum is not suited for forming a contact face engaged by the slide contacts, and therefore the contact rails 1, 2 and 3 ought at least to have a contact surface of a different material, such as copper or stainless steel. In the part of the cross section not engaged by the sliding collector it is, of course, also possible to use aluminum.
In addition to an efficient utilization of the conductor cross sections the power supply plant according to the invention will result in an improved power factor as compared with previously known contact rail plants for the same purpose.
In a single phase system the power supply system will comprise two contact rails, each with one conductor at a short distance from the rail and connected to the other phase of the system. Like in a three-phase system the conductors of the same phase are interconnected by a number of cross-connections, likewise at intervals of about 7 to 14 meters.
Although in the present specification it is said that adjacent each contact rail there shall be placed one conductor for each of the remaining phases of the system, it will, of course, be understood that each such additional conductor may be composed of a plurality of parallel-connected conductor strands.