Method and apparatus for providing selectable output voltages
A transformer is provided along with a combination of bridging tap-changers to provide a wide range of selectable output voltages in discrete, relatively small voltage steps where the highest voltage is more than double the lowest output voltage. Relatively inexpensive, off-the-shelf, bridging tap-changers are utilized in conjunction with transformer winding schemes to provide a low winding loss ratio.
The present invention claims the benefit of the filing date of provisional application, U.S. Serial No. 60/175,647, filed on Jan. 12, 2000.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to electrical power distribution equipment and more particularly to electrical transformers and switching means therefor.
2. Description of the Prior Art
In some electrical power distribution systems it is desirable to provide a plurality of selectable, often incrementally different, voltage outputs from system transformers. A range of such selectable voltage outputs from a single transformer may be achieved through the use of transformers having a number of isolated multiple tap primary and/or secondary windings interconnected to appropriate switching mechanisms. Commonly used in such applications are bridging tap changers and series-parallel-series (S-P-S) switches.
Bridging tap changers may take the form of several stationary electrical contacts arranged in an arcuate array with a movable contact mounted on an insulating rotor. Rotation of the rotor brings the movable contact into bridging contact with any selected pair of adjacent stationary contacts. Bridging tap changers may be connected to provide selectable voltage outputs by interconnecting the ends and/or taps of transformer windings so as to bypass any or all selected portions (turn groups) of windings.
Two-position series-parallel (S-P) switches and multiple position S-P-S switches are used to connect multiple transformer windings, some of which may be tapped, into various series-parallel-series configurations as well as full series or full parallel configurations. S-P and S-P-S switches characteristically are ganged switch pairs where each switch of each pair has a common terminal.
Bridging tap changers having six stationary contacts (five positions) or eight stationary contacts (seven positions) are the most commonly used in the industry. For this reason, five and seven-position bridging tap changers are easily obtainable as “off-the-shelf” items and are relatively inexpensive. Bridging tap changers with a greater number of positions are usually made to order and therefore are more expensive and have longer delivery times.
It is at times expedient to interconnect bridging tap changers in a manner to provide a common terminal. Such a configuration is achieved in the prior art by “jumper wiring” every other stationary contact of a bridging tap changer in common. Thus, the rotary contact becomes, in effect, the common terminal since in every position of the changer it is in contact with one of the “jumped” stationary contacts. When so wired, a five-position bridging tap changer becomes, in effect, a three-position device and a seven-position bridging tap changer becomes a four-position device, each with a common terminal.
In constructing tap changing selectable output transformers it is desirable to provide a wide range of output voltages available in discrete, relatively small voltage steps. Among the design factors to be considered are cost and ready availability of material or parts, such as switches. Also to be considered, are the winding losses and in particular the winding losses of the highest loss configuration relative to the losses of the lowest loss configuration.
SUMMARY OF THE INVENTIONIt is therefore one object of the present invention to provide a method and apparatus that will provide output voltages in small increments between the highest and lowest output voltage in multiple-tap power transformers.
It is another object of the present invention to provide a method and apparatus that will provide a wide range of output voltages in multiple tap power transformers where the highest voltage output is greater than twice the lowest voltage output and the winding loss factor is low.
The foregoing objects are achieved as is now described. In the illustrated embodiments of the present invention, there are provided a series of switched, multiple tap power transformers offering a wide range of selectable output voltages in discrete, relatively small voltage steps wherein the highest voltage is more than double the lowest output voltage. Further, the highest to lowest loss ratio is less than most comparable prior art systems. The present invention uses “off-the-shelf,” relatively inexpensive, and readily available switches in conjunction with less elaborate and thus less expensive transformer winding schemes than comparable prior art systems.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.
The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:
Referring to
In the prior art arrangement shown in
A design such as that of
The secondary winding losses asserted herein are calculated using the following assumptions: constant power frequency, constant applied sinusoidal voltage, constant kVA load, equal resistance in each turn and equal impedance in each turn. Core loss, primary winding loss, lead loss, stray loss and eddy current loss are ignored. The relative value of the various tapping schemes are thus compared on a consistent basis.
The prior art shown schematically in
Prior art systems similar to that shown in
The present invention combines three, five, and/or seven-position tap changers, which are off the shelf, relatively inexpensive switches and are readily available with unique but inexpensive tapped winding transformers.
In the first embodiment of the present invention, shown in
Leads 16 through 21 are interconnected through a pair of ganged five-position bridging tap changers 25 and 26 and wired as a three-position series-parallel-series switch. Leads 21 through 24 are interconnected through a three-position bridging tap changer 27. Both three-position and five-position bridging tap changers are relatively inexpensive, off-the-shelf switches.
According to the invention, the system of
In the transformer system schematically depicted in
Referring to
In the system of
In the embodiment schematically illustrated in
The system of
In the sixth embodiment of the present invention shown in
With the leads of windings 52″ and 53″ connected by series-parallel-series switch, ganged switches 68″ and 69″, as in the previous embodiments, and the leads of windings 54″ and 55″ are interconnected through a seven-position bridging switch 70″, as shown, the system of
It will be apparent to those familiar with the art that the fixed connection between terminal 63″ of winding 53″ and terminal 70″ of winding 54″ can be a internal coil connection as well as an external connection. An internal connection essentially makes winding 53″ and 54″ one continuous winding. This alternative construction may be adapted to any of the embodiments depicted in
Referring now to
The process then proceeds to step 1006, which depicts connecting selected winding points on the secondary winding with selected contacts on the two stage, ganged bridging tap-changers. The process next passes to step 1008, which depicts connecting windings via various switch positions of the two stage bridging tap-changer and single stage bridging tap-changer combination. If the switch is moved to a first position, the process proceeds to step 1010, which illustrates corresponding windings being connected in parallel. The process continues to step 1016. If the switch is moved to a second switch position, the process passes to step 1012, which depicts connecting corresponding windings being connected in series. The process then continues to step 1016. If the switch is moved to any other position, the process instead passes to step 1014, which illustrates connecting a portion of the corresponding windings in parallel and in addition, a portion of the windings in series.
Corresponding windings include those winding turns from one selected winding tap to another selected winding tap, and all the windings in between, physically connected to a particular switch, including a ganged switch. With reference to the figures, a corresponding winding includes a pair of taps from a winding with one end having a polarity opposite that of the other end and including all the taps between the pair.
The process continues from step 1014, step 1012 or step 1010 to step 1016, which depicts a single stage bridging tap-changer interconnected to the first switch. If the second switch is moved into a first switch position, the process passes to step 1018, which illustrates corresponding windings being fully bypassed. If the tap-changer is in a second switch position, the process moves to step 1020, which depicts the corresponding windings being connected in series. If the tap changer is in any other position, the process passes to step 1022, which illustrates a portion of the corresponding windings being series connected.
The present invention achieves voltage steps of 1/48th of a fully series connected winding utilizing off the shelf seven position bridging tap-changers. The prior art of
While the designations “primary” or “input” and “secondary” or “output” windings have been used herein, arbitrarily, to designate various windings of the embodiments disclosed, it is well recognized by those skilled in the art that the switches and tapped winding arrangements may be used in the primary or input windings and the other windings used as secondary or output windings. It will be recognized as well that any of the systems of the present invention may be used in multiples on polyphase electrical systems.
Thus, there has been disclosed a new transformer topology that may inspire others to make changes and modifications still within the spirit and scope of the invention. The above detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.
Claims
1. A transformer comprising:
- a primary winding having terminals for conveying input power;
- a plurality of secondary windings having output terminals for conveying output power, said secondary windings including a first pair of isolated center tapped windings and a second pair of isolated windings;
- a plurality of switches electrically coupling leads of said plurality of secondary windings providing a selection of n distinct output voltages at said output terminals ranging from x voltage units to y voltage units, wherein y is greater than 2x.
2. The transformer of claim 1, wherein incremental steps of said n distinct output voltages are equal.
3. The transformer of claim 1, wherein said plurality of switches includes a pair of ganged five-position bridging tap changers, wired as a three-position series-parallel-series switch interconnecting said first pair of isolated center tapped windings.
4. The transformer of claim 3, wherein said plurality of switches further includes a three-position bridging tap changer interconnecting said second pair of isolated windings.
5. The transformer of claim 4, wherein n is equal to 9, x is equal to 6, and y is equal to 14.
6. The transformer of claim 3, wherein each winding of said second pair of isolated windings is center tapped and interconnected via a five-position bridging tap changer.
7. The transformer of claim 6, wherein n is equal to 15, x is equal to 10, and y is equal to 24.
8. The transformer of claim 3, wherein each winding of said second pair of isolated windings is divided into thirds by two winding taps dividing said windings and wherein said second pair of windings is interconnected via a seven-position bridging tap changer.
9. The transformer of claim 8, wherein n is equal to 21, x is equal to 14, and y is equal to 34.
10. The transformer of claim 1, wherein a fixed connection between an end lead of one winding of said first pair and an end lead of one winding of said second pair is provided via an external coil connection.
11. The transformer of claim 1, wherein a fixed connection between an end of one winding of said first pair and an end of one winding of said second pair is provided via an internal coil connection.
12. The transformer of claim 1, wherein a ratio of maximum secondary winding loss to minimum secondary winding loss is less than 1.35.
13. A transformer comprising:
- a primary winding having terminals for conveying input power;
- a plurality of secondary windings having output terminals for conveying output power, said secondary windings including a first pair of isolated windings tapped at thirds and a second pair of isolated windings;
- a plurality of switches electrically coupling leads of said plurality of secondary windings providing a selection of n distinct output voltages at said output terminals ranging from x voltage units to y voltage units, wherein y is greater than 2x.
14. The transformer of claim 13, wherein the incremental steps of said n distinct output voltages are equal.
15. The transformer of claim 13, wherein leads of said first pair of isolated windings are interconnected via a pair of ganged seven-position bridging tap changers connected as four-position series-parallel-series switches.
16. The transformer of claim 13, wherein leads of said second pair of isolated secondary windings are interconnected to a three-position bridging tap changer.
17. The transformer of claim 13, wherein:
- each of said second pair of isolated windings is center tapped with leads interconnected via a five-position tap changer; and
- each of said second pair comprises k turns each divided into two groups of m turns, and each of said first pair comprises p turns each divided into three groups of q turns where k is equal to 2m, q is equal to 2k+m, and p is equal to 3q.
18. The transformer of claim 17, wherein n is equal to 20, x is equal to 15, and y is equal to 34.
19. The transformer of claim 13, wherein:
- each of said second pair of isolated secondary windings is tapped at thirds with leads interconnected via a seven-position bridging switch; and
- each of said second pair comprises k turns each divided into three groups of m turns and each of said first pair comprises p turns each divided into three groups of q turns where k is equal to 3m, q is equal to 2k+m, and p is equal to 3q.
20. The transformer of claim 19, wherein n is equal to 28, x is equal to 21, and y is equal to 48.
21. The transformer of claim 13, wherein a fixed connection between an end lead of one winding of said first pair and an end lead of one winding of said second pair is provided via an external coil connection.
22. The transformer of claim 13, wherein a fixed connection between an end of one winding of said first pair and an end of one winding of said second pair is provided via an internal coil connection.
23. The transformer of claim 13, wherein a ratio of maximum secondary winding loss to minimum secondary winding loss is less than 1.29.
24. A method for providing incrementally selectable electrical power outputs from a transformer, said method comprising:
- providing a primary winding and a plurality of secondary windings including a first set of secondary windings and a second set of secondary windings;
- providing at least a first switch and a second switch for interconnecting leads of said plurality of secondary windings, said first switch being independently operable and comprising a ganged pair of bridging tap-changers and said second switch comprising a single bridging tap-changer;
- creating a plurality of sub-windings by electrically connecting taps to selected points on said secondary windings to stationary terminals of said first and second switch; and
- connecting end leads of said secondary windings and tap leads of said sub-windings with said first and second switch such that said secondary windings and associated sub-windings are configurable in parallel, series, and series-parallel combinations that provide n distinct output voltages ranging from x voltage units to y voltage units, wherein y is greater than 2x.
25. The method of claim 24, wherein said connecting step further comprises:
- interconnecting said first set of secondary windings utilizing said first switch, wherein one switch position of said first switch connects said first set of windings in parallel; another switch position connects said first set of windings in series and all other positions of said first switch connects only portions of said first set of windings in parallel and connects a remainder of said first set of windings in series.
26. The method of claim 24, wherein said connecting step further comprises:
- interconnecting said second set of secondary windings utilizing said second switch, wherein one switch position of said second switch fully bypasses said second set of windings; another switch position fully series connects said second set of windings, and all other switch positions of said second switch connects only a portion of said second set of windings in series and bypasses a remainder of said second set of windings.
27. The method of claim 24, further comprising providing a three-position bridging tap changer as said second switch.
28. The method of claim 24, wherein said creating a plurality of sub-windings is accomplished by center-tapping each of said second set of secondary windings, said method further comprising providing a five position bridging tap changer as said second switch.
29. The method of claim 24, wherein said creating a plurality of sub-windings is accomplished by tapping each of said second set of secondary windings at thirds, said method further comprising providing a seven position bridging tap changer as said second switch.
30. A transformer comprising:
- a primary winding;
- a plurality of secondary windings having a plurality of sub-windings created by taps at selected points on selected ones of said plurality of secondary windings;
- a first switch and a second switch having terminals that connect end leads of said secondary windings and tap leads of said sub-windings, said first switch being independently operable and comprising a ganged pair of bridging tap-changers, and said second switch comprising a single bridging tap-changer, wherein said secondary windings and associated sub-windings are configurable in parallel, series and series-parallel-series combinations to yield n distinct voltage outputs ranging from x voltage units to y voltage units, wherein y is greater than 2x, and wherein a substantially low maximum to minimum winding loss is achieved.
31. The transformer of claim 30, wherein said first switch is interconnected between corresponding windings of a first set of secondary windings, wherein at least one switch position of said first switch connects said corresponding windings in parallel, at least one other switch position connects said corresponding windings in series, and other positions of said first switch connect only a portion of said corresponding windings in parallel and connect a remainder of said corresponding windings in series.
32. The transformer of claim 30, wherein said second switch is interconnected between corresponding windings of a second set of secondary windings, wherein one switch position of said second switch fully bypasses said corresponding windings; another switch position fully connects in series said corresponding windings, and all other switch positions of said second switch connects in series only a portion of said corresponding windings and bypasses the remainder of said corresponding windings.
33. The transformer of claim 30, wherein said second switch comprises a three position bridging tap changer.
34. The transformer of claim 30, wherein said second switch comprises a five position bridging tap changer.
35. The transformer of claim 30, wherein said second switch comprises a seven position bridging tap changer.
Type: Grant
Filed: May 19, 2009
Date of Patent: Oct 12, 2010
Assignee: TAPS Technology, Inc. (Plano, TX)
Inventor: Donald W. Owen (Plano, TX)
Primary Examiner: Shawn Riley
Attorney: Dillon & Yudell LLP
Application Number: 12/468,599
International Classification: H01F 21/12 (20060101);