US3832660A

US3832660A - Transformer having an electrically symmetrical tapped winding

Info

Publication number: US3832660A
Application number: US00389611A
Authority: US
Inventors: R Sinha
Original assignee: Westinghouse Electric Corp
Current assignee: ABB Inc USA
Priority date: 1973-08-20
Filing date: 1973-08-20
Publication date: 1974-08-27
Anticipated expiration: 1991-08-27

Abstract

A transformer having a winding which may be tapped without axially moving the electrical center of the winding. The winding includes at least four coil sections, with two of the sections having the same number of turns and the other two sections each having three times that number of turns. The coil sections are arranged in axially adjacent pairs with the lower end of the smaller section directly connected to the lower end of the larger section in a pair of coil sections. Tap leads are connected to ends of the coil sections and across one-third of the turns in the larger coil sections. Tap changing is accomplished by interconnecting the tap leads to tap out equal portions of the winding on both sides of the electrical center line.

Description

[45] Aug. 27, 1974 Primary Examiner-Thomas J. Kozma Attorney, Agent, or Firm-.1. R. Hanway ABSTRACT A transformer having a winding which may be tapped without axially moving the electrical center of the winding. The winding includes at least four coil sections, with two of the sections having the same number of turns and the other two sections each having three times that number of turns. The coil sections are arranged in axially adjacent pairs with the lower end of the smaller section directly connected to the lower end of the larger section in a pair of coil sections. Tap leads are connected to ends of the coil sections and across one-third of the turns in the larger coil sections. Tap changing is accomplished by interconnecting the tap leads to tap out equal portions of the winding on both sides of the electrical center line.

7 Claims, 6 Drawing Figures @000 5& an?) 7 ELECTRICALLY SYMMETRICAL TAPPED WINDING [75] Inventor: Ram R. P. Sinha, Athens, Ga.

Pittsburgh, Pa.

Filed: Aug. 20, 1973 Appl. No.: 389,611

us. 336/150; 323/435 [51] Int. H01f 21/12 Field of 336/l5 0;'323/43.5

References Cited UNITED STATES PATENTS 4/1967 Russell......... 336/150 X United States Patent Sinha TRANSFORMER HAVING AN [73] Assignee: Westinghouse Electric Corporation,

8 ,ooo ooocooo 000 9 4 A 9 QOOOOOOOO OOOOOOO BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates, in general, to electrical inductive apparatus and, more specifically, to transformers having a tapped winding.

2. Description of the Prior Art Coaxially positioned high-voltage and low-voltage windings are used in many power transformers. It is desirable to construct the windings in such a manner that their electrical centers will be at substantially the same axial position. If the electrical centers are not so aligned, forces acting between the windings when under high stress conditions, such as during a shortcircuit condition, tend to make the windings telescope with respect to each other.

In non-tapped windings, it is sometimes difiicult to place the electrical centers at the proper position due to the manufacturing variations. In tapped windings, the winding arrangement is such that, during. certain positions of the tap changer, the electrical center of the tapped winding is moved from the desired axial electrical center. This occurs since unequal positions of the tapped winding are energized on each side of the desired electrical center position.

Constructing tapped transformers which exhibit unbalanced electrical centers in certain tap positionsinvolves the necessity of providing additional winding braces to prevent telescoping of the winding. Therefore, it is desirable, and it is an object of this invention, to provide a transformer having a tapped winding which does not substantially change its electrical center in different tap positions.

SUMMARY OF THE INVENTION There is disclosed herein a new and useful transformer having a winding arrangement which provides a tapped winding that maintains its axial electrical cen ter throughout the tapping range. The tapped winding includes at least four coil sections to which tap leads are connected. The individual coil sections of each pair of coil sections are located at the same radial position as the other section in the pair. The two pairs of coil sections are located coaxially with respect to each other. One of the coil sections in each pair has three times the number of turns as its axially adjacent coil section in the pair and is tapped across one-third of its turns. The lower ends of each coil section in the pair are substantially non-inductively connected to each other. Tap leads from the coil sections are connected to a tap changerwhich connects together predetermined pairs of the tap leads to provide the desired winding rating. In each tap position, an equal amount of the coil sections in each pair is tapped out above and below the center of the winding to maintain electrical balance in the tapped winding.

BRIEF DESCRIPTION OF THE DRAWING Further advantages and uses of this invention will be-,

come more apparent when considered in view of the following detailed description and drawing, in which:

FIG. lis a view of a transformer having a tapped winding;

FIG. 2 is a schematic view of a tapped winding con-' structed according to the prior art;

FIG. 3 is a force diagram'for a tapped winding constructed as illustrated in FIG. 2;

FIG. 4 is a schematic view of a tapped winding, constructed according to this invention and taken generally along the lines IV-IV of FIG. 1;

FIG. 5 is a force diagram for a tapped winding constructed as illustrated in FIG. 4; and

FIG. 6 is a table which illustrates the electrical symmetry of the winding shown in FIG. 4 when in different tap positions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description, similar reference characters refer to similar elements or members in all of the figures of the drawing.

Referring now to the drawing, and to FIG. 1 in particular, there is shown a transformer assembly having a wound magnetic core 10 mounted within the frame 12. A winding structure 14 is positioned through windows in the two sections of the magnetic core 10. The low voltage leads 16 and the high-voltage leads 18 extend from the winding structure 14 for connection to the appropriate associated apparatus or cables. The tap leads 20 extend from the winding structure 14 and connect to the no-load tap changer 22 which is mounted to the frame member 24. The tap changer 22 may be set in different positions to change the rating of the highvoltage winding. The tap changer illustrated in this specific embodiment is capable of providing five different high-voltage winding ratings and is described, in detail, in US. Pat. No. 3,467,794, which is assigned to the assignee of this invention.

The high-voltage winding is wound coaxially'with respect to the low-voltage winding and comprises a plurality of conductor layers each having one or more coil sections which have a plurality of conductor turns. FIG. 2 represents, in a partially'schematic view, an arrangement of a high-voltage winding 26 as constructed according to the prior art. FIG. 2 is generally representative of a cross-section taken along the line IV-IV of F IG. 1, assuming that the transformer shown in FIG. 1 would have been constructed according to the prior art. 1

In FIG. 2, the layers 28 of insulation separate the layers of conductors. Each conductor layer includes a coil section, such as the coil section 30. Each coil section includes a plurality of conductor turns, such as the conductor turn 32 of the coil section 30. The conductor turns are provided by an insulated electrical conductor spirally wound or disposed around the winding axis. Therefore, the coil section 30 is formed from a conductor which progresses axially from the conductor turn 32' to the conductor turn 32". The coil section 34 is formed from the same or another conductor which progresses axially from the conductor turn 36 to the conductor turn 36. The direction of progression is basically a function of the method used in winding the coil section, and is not necessarily a requirement for the proper operation of the winding. However, all of the conductors must be wound tangentially, with respect to the winding axis, in the same direction to permit'the proper phase relationship between interconnected coil sections.

One of the major disadvantages of the winding arrangement shown in FIG. 2 is that relatively large axial stresses may develop when the windings are subjected to high currents, such as exist during a short-circuit condition. The magnitude of the stresses depends on the position of the tap changer, since certain tap changing positions produce displaced electrical winding centers between the high-voltage and low-voltage windings.

Normally, the low-voltage winding is divided into two portions which are coaxially located on each side of the high-voltage winding. Since the low-voltage winding is not tapped, the electrical center thereof is fixed at or near the mechanical center of the windings as indicated by the line 38. When the high-voltage winding 26 is tapped below maximum rating, such as provided schematically by the interconnection 40, the electrical center of the high-voltage winding 26 is shifted to a position below the line 38.

FIG. 3 is a force diagram of a transformer wherein the electrical center 48 of the high-voltage winding 26 is below the

electrical centers

50 and 52 of the

lowvoltage winding portions

54 and 56, respectively. The resultant forces generated by the short-circuit stresses in the windings are represented by the

vectors

58 and 60 which act through the electrical centers. The component vectors indicate that the vertical component forces add together. The physical result is that the highvoltage winding 26 tends to telescope, or move axially, with respect to the low-

voltage winding portions

54 and 56. This is undesirable since strong supporting structures must be used to maintain winding integrity during high stress conditions.

FIG. 4 is generally representative of a partial crosssection of a portion of a high-voltage winding 64 taken along the line IVIV of FIG. 1. The conductor layers which are not tapped, such as the conductor layer 66, are constructed substantially similar to the untapped conductor layers illustrated in FlG. 2. The conductor layer 68 contains the

coil sections

74 and 76, and the conductor layer 70 contains the coil sections 80 and 82. The conductor turns of the coil section 74 are formed by successive turns of an electrical conductor which progresses in the same tangential direction as the conductors which form the other conductor turns of the winding 64. All adjacent conductor turns are formed by an additional turn of the same conductor with the exception of the conductor turns 86 and 88, and the conductor turns 90 and 92. The insulation 94 is positioned between these conductor turns since more than a single turn of voltage exists between these conductor turns.

The conductor turn 86 is substantially noninductively connected to the conductor turn 96 by the interconnection 98. The primary purpose of the interconnection 98 is to provide direct electrical contact between the conductor turns 86 and 96 without inducing a significant voltage between them, such as would be the case if the conductor turns were electrically connected by one or more turns of the conductor. In other words, the conductor turns 86 and 88 are not substantially non-inductively connected to each other since their electrical connection traverses the coil section 74. A similar connection is provided to the conductor turns 90 and 100 by the interconnection 102.

The coil sections 76 and 82 contain the same number of conductor turns. Similarly, the

coil sections

74 and 80 contain the same number of conductors turns. The

coil sections

74 and 80 each contain three times the number of conductor turns as in the coil sections 76 and 82, respectively. The coil section 80 contains approximately two times the number of conductor turns above the tap lead 78 as below the tap lead 78. Similarly, the coil section 74 contains approximately two times the-number of conductor turns above the tap lead 72 as below the tap lead 72. Although the tapped

coil sections

74 and 80 are continuously wound with the same conductor, it is within the contemplation of this invention that separate portions of the coil sections could be wound separately and connected together to provide the same electrical characteristics.

More than two coil sections per conductor layer may be used within the contemplation of this invention to obtain more tap positions as long as the coil sections have taps which are symmetrical about the winding center 104. In addition, the number of conductor turns may be changed, without destroying conductor turn symmetry, to provide different tapping increments.

Tap leads are connected to the tap terminals A, B, C, D, E and F which would normally be a part of the tap changer 22. Depending on which tap terminals are interconnected by the tap changer, certain coil sections are electrically removed from the high voltage winding 64. However, with the proper interconnections, the tap changing can be accomplished without disturbing the symmetry of the high-voltage winding 64, thus its electrical center remains in line with the electrical centers of the low-voltage winding portions.

FIG. 5 is a force diagram applicable to the transformer shown in FIG. 1 and constructed according to this invention, as shown in FIG. 4. The diagram is applicable to all tap positions. Since the electrical center 108 of the high-voltage winding 64 is in line with the

electrical centers

110 and 112 of the low-

voltage winding portions

114 and 116, respectively, the resultant forces do not contain any vertical components. Thus, there is not any tendency for the coils to telescope under high stress conditions.

FIG. 6 illustrates how the electrical symmetry is maintained with the various tap positions. By referring to both FIGS. 4 and 6, itcan be seen that when the tap terminals C and D are connected to each other by the tap changer, every coil section of the conductor layers 68 and is included in the high-voltage winding. Thus, the symmetry about the center line 104 is maintained and the maximum rating exists for the highvoltage winding 64.

The tap terminals C and E are connected together to lower the voltage rating by one tapping increment, or the voltage developed across the coil section which is located above the position where the tap lead 78 is attached. Since an equal portion of the coil section 80 is tapped out on both sides of the center line 104, the symmetry is maintained.

The tap terminals B and E are connected together to lower the voltage from the full rating by two tapping increments. In this position, the upper portions of the

coil sections

74 and 80 are tapped out or removed from the circuit. However, the symmetry is still maintained. The tap terminals B and F are connected together to lower the voltage from the full rating by three tapping increments. In this position, the coil sections 80 and 82 and the upper portion of coil section 74 are removed from the circuit without changing the symmetry of the winding. The tap terminals A and F are connected together to lower the voltage from the full rating by four tapping increments. All of the coil sections in the tapped contion without changing the symmetry.

The novel arrangement disclosed herein permits tap changing in equal increments without changing the electrical symmetry of the tapped winding. Since numerous changes may be made in the above-described apparatus, and since different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in the foregoing description, or shown in the accompanying drawing, shall be interpreted as illustrative rather than limiting.

I claim as my invention:

1. A tapped transformer comprising:

a magnetic core;

a first winding inductively coupled to said magnetic core;

a tapped second winding having a plurality of coil sections which are inductively coupled to said magnetic core;

a first of said coil sections having a first tap lead connected to the first end thereof and a second tap lead connected at a position located between the first and second ends thereof;

a second of said coil sections being disposed at the same radial position as said first coil section, with the first end of said second coil section being substantially non-inductively connected to'the end of said first coil section which is located opposite to the end which is adjacent to said second coil section;

a third of said coil sections being disposed at a different radial position than said first coil section, with a third tap lead connected to the first end thereof and a fourth tap lead connected at a position located between the first and second ends thereof; and

a fourth of said coil sections being disposed at the same radial position as said third coil section, with the first end of said fourth coil section being substantially non-inductively connected to the end of said third coil section which is located opposite to the end which is adjacent to said fourth coil section.

2. The tapped transformer of claim 1 wherein the second tap lead is connected to the first coil section at a position which provides two-thirds of the total turns of the first coil section between the tap position and the first end of the first coil section, and one-third of the total turns of the first coil section between the tap position and the second end of the first coil section.

3. The tapped transformer of claim 1 wherein the fourth tap lead is connected to the third coil section at a position which provides two-thirds of the total turns of the third coil section between the tap position and the first end of the third coil section, and one-third of the total turns of the third coil section between the tap position and the second end of the third coil section.

4. The tapped transformer of claim 1 wherein the first end of the second coil section is positioned adjacent to the first end of the first coil section, and the first end of the fourth coil section is positioned adjacent to the first end of the third coil section.

5. The tapped transformer of claim 1 wherein the first and third coil sections are disposed substantially at the same axial position, and the second and fourth coil sections are disposed substantially at the same axial position.

6. The tapped transformer of claim 1 wherein the conductors which form the first, second, third and fourth coil sections all spiral around the winding axis in the same tangential direction.

7. A tapped transformer comprising:

a magnetic core;

a first winding inductively coupled to said magnetic core;

a first of said coil sections having a predetermined number of turns, with a first tap lead connected to the first end of said first coil section, a second tap lead connected to said first coil section at a position which provides two-thirds of the predetermined number of turns between the second tap lead and the first end of said first coil section;

a .second of said coil sections having one-third the predetermined number of turns with a fifth tap lead connected to the second end of said second coil section, the first end of said second coil section being substantially non-inductively connected to the second end of said first coil section, the first and second coil sections being disposed at the same radial position with the first end of said second coil section located adjacent to the first end of said first coil section;

a third of said coil sections being disposed at a different radial position and at the same axial position as said first coil section, said third coil section having said predetermined number of turns with a third tap lead connected to the first end of said third coil section, a fourth tap lead connected to the third coil section at a position which provides two-thirds of said predetermined number of turns between the fourth tap lead and the first end of said third coil section;

a fourth of said coil sections having one-third said predetermined number of turns with a sixth tap lead connected to the second end of said fourth coil section, the first end of said fourth coil section being substantially non-inductively connected to the second end of said third coil section, said third and fourth coil sections being disposed at the same radial position with the first end of said fourth coil section located adjacent to the first end of said third coil section; and

the conductors which form said first, second, third andfourth coil sections all being disposed to spiral around the winding axis in the same tangential direction.

Claims

1. A tapped transformer comprising: a magnetic core; a first winding inductively coupled to said magnetic core; a tapped second winding having a plurality of coil sections which are inductively coupled to said magnetic core; a first of said coil sections having a first tap lead connected to the first end thereof and a second tap lead connected at a position located between the first and second ends thereof; a second of said coil sections being disposed at the same radial position as said first coil section, with the first end of said second coil section being substantially non-inductively connected to the end of said first coil section which is located opposite to the end which is adjacent to said second coil section; a third of said coil sections being diSposed at a different radial position than said first coil section, with a third tap lead connected to the first end thereof and a fourth tap lead connected at a position located between the first and second ends thereof; and a fourth of said coil sections being disposed at the same radial position as said third coil section, with the first end of said fourth coil section being substantially non-inductively connected to the end of said third coil section which is located opposite to the end which is adjacent to said fourth coil section.

7. A tapped transformer comprising: a magnetic core; a first winding inductively coupled to said magnetic core; a tapped second winding having a plurality of coil sections which are inductively coupled to said magnetic core; a first of said coil sections having a predetermined number of turns, with a first tap lead connected to the first end of said first coil section, a second tap lead connected to said first coil section at a position which provides two-thirds of the predetermined number of turns between the second tap lead and the first end of said first coil section; a second of said coil sections having one-third the predetermined number of turns with a fifth tap lead connected to the second end of said second coil section, the first end of said second coil section being substantially non-inductively connected to the second end of said first coil section, the first and second coil sections being disposed at the same radial position with the first end of said second coil section located adjacent to the first end of said first coil section; a third of said coil sections being disposed at a different radial position and at the same axial position as said first coil section, said third coil section having said predetermined number of turns with a third tap lead connected to the first end of said third coil section, a fourth tap lead connected to the third coil section at a position which provides two-thirds of said predetermined number of turns between the fourth tap lead and the first end of said third coil section; a fourth of said coil sections having one-third said predetermined number of turns with a sixth tap lead connected to the second end of said fourth coil section, the first end of said fourth coil section being substantially non-inductively connected to the second end of said third coil section, said third and fourth coil sections being disposed at the same radial position with the first end of said fourth coil section located adjacent to The first end of said third coil section; and the conductors which form said first, second, third and fourth coil sections all being disposed to spiral around the winding axis in the same tangential direction.