CA1160702A - Electrostatic shielding of non-sequential disc windings in transformers - Google Patents

Abstract

ELECTROSTATIC SHIELDING OF NON
SEQUENTIAL DISC WINDINGS IN TRANSFORMERS

ABSTRACT OF THE DISCLOSURE

Transformer coils wound with disk winding sections nonsequentially arranged are provided with shields between the turns of mechanical adjacent sections to increase the series capacitance of the winding. The increased series capacitance of the winding allows a reduction in insulation between the individual winding turns and between the winding discs.

Description

,'02 l 5D-5776 ELECTROSTATIC SHIELDING OF NON
SEQUENTIAL DISC WINDINGS IN TRANSFORMERS
This application is a divisional of Canadian Application Serial No. 348,735, filed March 28, 1980.
The initial impulse distribution of a transformer winding grounded at one end is given by the well known relation V-VO sinh a (1 - x)/sinh a, where X = percent distance along the winding from the line end, a = (Cg/Cs) where Cg = the total capacitance between the winding and ground and Cs= the total series capacitance of the winding.
The initial impulse distribution along the winding provides a voltage stress at the impulsed end of the coil greater than the stress caused by the steady state voltage distribution within the winding. The ratio of the impulse voltage stress to the operating voltage stress is equal to a . The impulse (initial) stress can be reduced by increasing Cg causing a to decrease. The effective series capacitance in a disc wound transformer winding is composed of the turn-to-turn capacitance between the electrical conductors making up the winding and the section-to-section capacitance between the sections along the disc winding. Various attemps have been employed to increase the effect of both the turn-to-turn and section-to-section capacitance of the winding upon the effective series capacitance of a disk winding section. One method for increasing the use of 116~02 the turn-to-turn capacitance consists in the employment of electrostatic shields between the turn conductors.
U.S. Patent No. 3,691,494 - dated September 12, 1972 to Okuyama and U.S. Patent No. 4,042,900 - Hinton et al dated August 16, 1977 teach various configurations of inter section electrostatic shields for increasing the series capacitance in disk windings. The aforementioned U.S.
Patents teach the insertion of shields in disk winding arrangements that are continuously connected in mechanical and electrical series. A second method of configuring disk winding sections makes more effective use of the section-to-section capacitance is taught in French Patent No. 1,147,282. This shows that an increase in series capacitance can be achieved by connecting the sections nonsequentially. A third method which maximizes the use of the turn-to-turn series capacitance in the winding is to interlace the turns so that the electrically sequential turns are not physically adjacent.
The purpose of this invention is to provide an electro-static shielding arrangement for nonsequential disk windings wherein the effective series capacitance of the winding is the highest heretofore obtained in a disk winding configuration.
In accordance with a broad aspect of the present invention there is provided a disc coil winding arrangement for a transformer comprising:
a plurality of turns of insulated electrical conductors radially disposed around a winding form in a disc winding configuration:
a plurality of winding sections of said radially disposed conductors linearly arranged along said winding form;
an electrostatic ring shield adjacent one of said winding sections and electrically connected with another of said winding sections;

1 ~ 6~2 said winding sections being electrically inter-connected in a nonsequential arrangement wherein a first one of said winding sections is electrically connected with a second one of said winding sections and a third one of said winding section is electrically connected with a fourth one of said winding sections, said first and said fourth winding sections being electrically connected together, said second section being electrically connected to the electrostatic ring shield and said third winding section being adapted for connection to a terminal of the transformer.
at least one electrostatic shield within said first winding section electrically connected with at least one electrostatic shield in said second section; and at least one electrostatic shield in the third winding section being electrically connected with at least one electrostatic shield in said fourth winding section.
FIGURE 1 is a side sectional view of a shielded nonsequential winding arrangement with shields along the outside of the winding according to the invention;
FIGURE 2 is a side sectional view of a shielded nonsequential coil arrangement according to the invention with shields along the inside of the winding;
FIGURE 3 is a side sectional view of a shielded nonsequential winding according to the invention with shields along both the inside and outside of the winding;
FIGURE 4 is a side sectional view O:e an alternative arrangement of the embodiment of FIGURE l;
FIGURE 5 is a side sectional view of an alternative arrangement of the embodiment of FIGURE 4;
FIGURE 6 is a graphic representation of the normalized effective series capacitance for various winding configurations;
FIGURE 7 is a graphic representation of the effective series capacitance as a function of the number of shields for various windings configurations, and ~ ~ B~ ~2 FIGURE 8 is a graphic representation of the per cent voltage variable as a function of distance along the coil for various winding configurations.
The series capacitance of a disc winding section pair wound as a continuous disk is given by the expression Cl = C ( n + n-2) ak) where n = the number of turns in the section pair, C
= the capacitance from a single turn to the equal potential plane above or below the section, ak = the ratio of Cw to Cx where C is the capacitance between turns of a section. The increased series capacitance of a disk winding section pair connected as nonsequential discs is given by the relationship 15C2 = Cx ( + ~ ~) ak ) The series capacitance of disk winding section pairs connected as continuous disks and containing internal shields a8 taught by the aforemention U.S. Patents is given by the expression 20C C (n + 0 8a (n2 _ 3 n+l~

for a section pair with each section containing a single 8hield.
The series capacitance of a section pair with each section containing two shields is given by the expression 25C4 = C (n + ~ 8ak ~ n - lln+l ~

and the series capacitance of a sectioned pair with each section containing three shields is given by the expression ' 0 2 C5 = Cx ~ + .8 ak ~n2 _ 22n ~ 44. ~

The series capacitance of a section connected as an interlaced disk winding is given by C6 = Cx C 818n + ~n-4 ) ak ) It can be seen from the above expressions (C3 - C5) that as the number of shields within each section are increased the effective series capacitance of a continuous disk containing shields also increases. It can also be seen that the connection of a disk section as an inter-laced disc winding provides a series capacitance (C6) greater than the series capacitance connection (C5) including as many as three shields. In order to determine quantitative values for the various winding configurations, examples one and two are given having the dimensions listed in Table I.
The calculated series capacitance for the afore-mentioned examples are given in TABLE III and it can be seen that the interlaced winding series capacitance (C6) is sub8tantially higher for both examples than either the 8ection pair connected as a non~equential diSC (C2~ or With the inclusion of internal shields within a continuous diSk winding arrangement (C3 to C5).
The use of the interlaced winding configuration i5 limited by the difficulties involved in winding large cross section conductors into the interlaced configuration.

, r~ ~3 2 SD_5776 -- 6 ~
TABLE I
Example 1 Example 2 R = average radius to center av line of section 21. 34" 35. 00"
n = number of turns in section pair 42 30 w = radial build of conductor .115" .125~' t = turn insulation (both sides) . 072" .144"
h = axial height of c conductor . 44011 . 350~
d = axial duct dimension . 225" . 22511 Rb = radial build of section 3. 92711 4 . 03511 C = turn to turn 1 10 w capacitance 5. 71X10- f 3. 73X10~ f 15 C = turn to epp -11 -10 x capacitance 9. 57X10 f 1. 89X10 f ak CW/CX 5 . 96 1 . 97 Serles CaPacltance Example 1 Example 2 C1 7 . 14 CX 5 . 06 CX
20 C2 14 . 14 CX 10. 06 CX
C3 11 . 43 CX 6 . 44 CX
C4 15 . 33 CX 7 . 64 CX
C5 18 . 93 CX 8 . 71 CX
C6 68. 46 CX 21. 45 CX
25 C7 18.43 CX 13.04 CX
C8 31. 84 CX 15 . 83 CX
C9 40. 06 CX 18 . 42 CX

Increased series capacitance, attained by including a plurality of electrostatic shields within transformer disk windlngs arranged in a nonsequential connection and containinq a single shield as shown 1 ~ 6~702 in FIGURE l, follows the expression:

C7 = C ~ ( 2 ) ) The series capacitance of a section pair connected in a nonsequential arrangement and containing two shields per section is given by the expression:
C8 = Cx ~ + .8 k ~ 2 ~ J

Quantitative values for the aforementioned nonsequential winding sections containing three shields in one of the sections is given by the expression:
9 Cx Cn3 + 8 ak ~ n ~ 22n + 44~5 ~

Quantitative values for the aforementioned nonsequential winding section8 containing from one to three shields for the examples I and II of TABLE I are given in TABLE
II. It can be ~een by comparision that the combination of eleCtrostatiC shield8 within nonsequential di8c winding 8ections provides a serie9 capacitance in excess of 8eries connected disk winding section having an equivalent number of electrostatic shields.
The nonsequential winding arrangement of the invention with one pair of electrostatic shields is shown in FIGURE
1 wherein the winding 10 consisting of a plurality of turns of a conductor 11 containing an insulating coating 12 is radially arranged around a winding form 13 in at least a first section 14 second section 15, third 16 and a fourth section 17. Alt~ough four sections are shown in the disk winding configuration depicted in FIGURE 1 this is for purposes of example only since any number of sections can be employed depending upon the transformer design. The sections are interconnected in nonsequntial winding arrangement wherein an electrostatic ring shield 18 t 1 6 ~ ~ 0 2 is electrically connected by means of conductor l9 to the second section and the first section is connected to the fourth section by means of electrical conductor 20. To complete the nonsequential arrangement the first section is electrically connected to the second section by means of conductor 22 and the third section is electrically connected to the fourth section by connector conductor 23.
An electrostatic shield 24 in the first section is electrically connected to a corresponding electrostatic shield 24 in the second section by means of conductor 25.
An electrostatic shield 24 in the third section is electrically connected by means of conductor 26 to a corresponding electrostatic shield 24 located in the fourth section. The arrangement of electrostatic shields 24 in the winding 10 of FIGURE 1 is such that the shields are located between the outermost conductors of the section, that is, at the end of the section furthest from the winding form 13. Electrical connection with the winding is made by means of electrical conductor 21. The series capacitance value for this single shield configuration is given by the mathematical expression for C7 given earlier for the examples listed in Table I and has the calculated capacitance values listed in Table II.
~ further embodiment of a nonsequential disk winding containing electrostatic shields is shown in FIGURE 2 wherein the sections 14, 15, 16 and 17 are radially arranged around winding form 13 in the same manner as described for the embodiment of FIGURE 1 so that like reference numerals will employed to designate similar elements. In the embodiment now depicted, an electrostatic shield 24 is located in the first section between the two most inner turns or strands, that is, the end of the section closest to the winding form. The shield in the first section is electrically connected to the electrostatic ring shield 18 by means of electrical conductor 27. A
pair of shields is inserted within the inner end of the 1 1 6~ ~'0 2 _ g _ second and third sections and are electrically interconnected by means of electrical conductor 28. The effective series capacitance of the configuration depicted in FIGURE 2, where the electrostatic shields are located at the inner end of the winding sections is given also by the expression for C7. The values for the parameters of examples l and 2 in Table I result in the calculated capacitances given in Table II.
FIGURE 3 contains an embodiment of the nonsequential winding arrangement 10 wherein a pair of electrostatic shields 24 are employed in each winding section and wherein one shield is situated in the outer end of the 8ection and one shield is situated in the inner end of the 8ection. The embodiment of FIGURE 3 is similar to the earlier embodiments of FIGURES 1 and 2 and similar reference numbers will be used to depict similar elements.
The 8erie8 capacitance of the two 8hield relationship is 81ightly larger than that given by the expression for C8.
A 8implified non8equential winding arrangement according to the invention employing a single pair of 8hields i8 8hown in FIGURE 4 wherein the non8equential winding lO contains a shield 24 in the second section and a 8hield 24 in the third 8ection electrically connected together by mean8 of conductor 30. The effective 8erie8 capacitance value for this arrangement is given by the following expreSsion:

n ~ 3 k C n ~) Although embodiments containing nonsequential windings whiCh include either a single shield or a pair of 8hields within each 8ection are disclosed, it is within the teachings of this invention to include as many shields as required to achieve the particula~ value of series capacitance desired for a particular transformer design.

~ g 6'~ 32 The relationship between the effective series capacitance for various winding configurations as a function of the number of winding turns per section is given in FIGURE 6.
A nonsequential disk winding arrangement similar to FIGURE 5 containing four shields on the outside of each winding section is shown at A. The series capacitance for an interlaced winding arrangement is shown at B for comparison purposes. It is to be noted that the normalized effective series capacitance for nonsequential disk winding arrangement A is very large for coils having a relatively few number of turns per section. The effective series capacitance for a nonsequential winding arrangement similar to FIGURE 5 containing a single shield at the outside of each winding section is shown at C. A non-sequential winding arrangement having a single shield inthe outer end as shown in FIGURE 1 wherein one shield in the first section is electrically connected to one shield in the 8econd section, and one shield in the third section is connected to a single shield in the fourth section, is shown at D. The normalized series capacitance for a nonsequential winding arrangement not containing any electro~tatic shield is shown at E. The normalized effective series capacitance of a continuous winding arrangement containing one shield per section is shown at F for comparision purposes.
The variation in the effective series capacitance as a function of the number of shields employed per winding section i~ shown in FIGURE 7. Curve A i8 the effective 8eries capacitance for a given section geometry as the number of shields per section is increased from zero (i.e. a plane continuous disk) to some integer value.
Curve B is the effective series capacitance for a given section geometry wound as a nonsequential disk as the number of shields per section is increa~ed from zero to some integer value. The nonsequential configuration used for obtaining the data in Table II is the embodiment shown 1 1 ~Or.J~2 in FIGURE 5.
The initial voltage distribution after an impulse voltage is applied is shown for various winding configurations in FIGURE 8. The greatest variation in per cent voltage along the winding occurs at G which represents a continuous winding with one shield per section. The next greatest variation occurs at E which represents a nonsequential winding arrangement without electrostatic shields. The voltage variation for an interlaced winding arrangement is shown at B to be less distorted than either a continuous winding arrangement with a shield or a nonsequential winding without electrostatic shields. A more nearly linear distribution along the coil occurs at A for a nonsequential winding arrangement containing internal shields in accordance with the teachings of this invention.
Electrostatic shields within nonsequential disk windings are disclosed for power transformer operation.
Thi8 i~ for purposes of example only since the inclusion of electrostatic shields within nonsequential winding arrangements finds application in any inductive device where hlgh effective series capacitance i~ de~ired.

Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A disc coil winding arrangement for a transformed comprising:
a plurality of turns of insulated electrical conductors radially disposed around a winding form in a disc winding configuration;
a plurality of winding sections of said radially disposed conductors linearly arranged along said winding form;
an electrostatic ring shield adjacent one of said winding sections and electrically connected with another of said winding sections;
said winding sections being electrically interconnected in a nonsequential manner wherein a first one of said winding sections is electrically connected with a second one of said winding sections and a third one of said winding sections and a third one of said winding sections is electrically connected with a fourth one of said winding sections, said first and said fourth winding sections being electrically connected together, said second winding section being electrically connected to the electrostatic ring shield and said third winding section being adapted for connection to a terminal on the transformer;
at least one electrostatic shield within said first winding section electrically connected to the electrostatic ring shield;
at least one electrostatic shield within said second winding section electrically connected with at least one electrostatic shield in said third winding section; and an electrostatic shield in said fourth section adapted for connection with a terminal on the transformer.
, 2. The winding arrangement of claim 1

Claim 2 (continued) wherein the electrostatic shields in said first, second, third, and fourth winding sections are located proximate said winding form.