US2412609A

US2412609A - High-voltage transformer

Info

Publication number: US2412609A
Application number: US518363A
Authority: US
Inventors: Albert G Ganz
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1944-01-15
Filing date: 1944-01-15
Publication date: 1946-12-17
Anticipated expiration: 1963-12-17

Description

Dec. 17, 1946. A. G. GANZ 2,412,609

HIGH VOLTAGE TRANSFORMER Filed Jan. 15, 1944 FIG.

76. 2 FIG. a FIG; 4

muszmummj mumwf inumumm FIGS INVENTOR A. ,6- GANZ A TTORNEY Patented Dec. 17, 1946 UNITED STATES PATENT OFFICE HIGH-VOLTAGE TRANSFORMER Albert G. Ganz, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application January 15, 1944, Serial No. 518,363

7 Claims. 1

This invention relates to transformers and particularly to transformers subjected to high voltages.

In high voltage transformers the insulation between windings is of considerable importance in insuring against transformer failure in service. Increasing th amount of insulation between the windings is one way of obtaining a high safety factor, but increasing the insulation increases transformer size and cost and reduces the transformer efficiency, particularly where a wide band of frequencies is transmitted. Where space is limited and weight must be a minimum, as for example in airplanes, means for increasing the effectiveness of insulation is especially valuable since it reduces the amount that would be required.

An object of the present invention is a high voltage transformer in which the thickness of insulation between windings is reduced while still retaining a high safety factor.

Another object of the invention is a high voltage transformer having a high efficiency and which is of small size and low weight in relation to the voltage and power involved.

A further object of the invention is to increase the uniformity of the potential gradient across the insulation between the windings of a high voltage transformer.

In one embodiment, this invention comprises a single layer auxiliary winding between a single layer secondary winding and a single layer primary winding of the transformer. This auxiliary winding is open-circuited. When the primary winding is subjected to a voltage, there is induced in the auxiliary winding a voltage dependent upon the number of turns of the auxiliary winding. If the auxiliary winding is located between the secondary winding and the primary winding at a proper position determined by the number of turns therein, the insulation is effectively divided into two sections, each of which is subjected to only a fraction'of the original voltage. The potential gradients throughout the insulation will, therefore, be maintained more nearly uniform.

Th invention will be better understood from the following description in connection with the attached drawing, in which:

Fig. 1 is a partial section of a simplified form of transformer embodying the invention;

Fig. 2 is a schematic circuit of the transformer of Fig. 1;

Fig. 3 is a schematic circuit of a transformer in which two auxiliary windings are used;

Fig. 4 is a schematic circuit of a transformer showing the arrangement when a grounded shield and one auxiliary winding are used; and

Fig. 5 is a schematic circuit of a transformer showing the arrangement when a grounded shield and two auxiliary windings are used like parts in the different figures having like indicia.

The simplified form of th invention shown in Fig. 1 shows a part of the core Hi which may be of any magnetic or non-magnetic material and the core form may be of any type. Insulation H is placed on core [El and single layer primary winding I2 of Np turns is wound thereon. Insulation i3 is placed on winding I2 and single layer auxiliary winding l6 of Na turns is wound thereon. Additional insulation of thickness equal to 13 is placed on auxiliary winding l6 and single layer secondary windin ll of N5 turns is wound thereon, over which is placed insulation 18. The auxiliary winding I6 is thus located half way between windings I 2 and I l. The left ends of the. windings are at ground potential.

When a voltage is applied to primary winding 12 there are induced in auxiliary winding l5 and. secondary winding l1 voltages dependent upon the voltage of winding 12 and the ratio of turns between winding l2 and the respective windings.

If the number of turns of winding I6 is equal to (NS+N,,), the voltage induced in winding IE will be the average Of that in winding l2 and that induced in winding [1. Furthermore, each turn of winding it will then have a potential equal to the average of that in the nearest primary and secondary turns. These potentials are the same as would exist theoretically at the location of the auxiliary winding turns in an absolutely uniform dielectric without any auxiliary winding. Since dielectric materials in practice are not uniform, the potentials at these points would ordinarily depart from the ideal values, resulting in excessive gradients in portions of the insulation. Thus the auxiliary winding by maintaining the mid-section of the insulation at the proper potentials provides more nearly uniform potential gradients throughout the insulation. This increases the effectiveness of the insulation and permits a substantial reduction in its thickness without decreasing the safety factor.

More than one auxiliary winding may be used if desired. If two auxiliary windings are used and are spaced at equal intervals between the primary winding having Np turns and the secondary winding having NS turns, then the number of turns in that winding which is nearer the primary winding should be equal to %(2N +N=) .with one and the number of turns in the auxiliary winding nearer the secondary winding should be equal to /3(N -l-2Ns). In this way the potential gradient will be maintained substantially uniform throughout the insulation.

A transformer having two auxiliary windings is illustrated schematically in Fig. 3. In this case the number of turns in auxiliary winding 25 may be equal to /3(2.Np+1vs) and be spaced from winding l2 one-third the distance between windings l2 and l'i, while the number of turns in auxiliary winding 2i may be equal to /3(N l-2Ns) and be spaced. from winding l2 two-thirds of the distance between windings l2 and ll.

In Fig. 4 there is illustrated the arrangement when an electrostatic shield is used. As is usual in such cases, shield 22 is shown grounded at 23. Since the shield is at ground potential and the primary winding 5 is the low potential winding, the potential t between winding :2 and or importance. Auxiliary shield 22 is not 0. winding is, therelore, positioned with ref r ence to the shield 22 and high voltag wind i? and should have c e half the number of turns of wi ding i'l if 5 mod from shield the distance between shield "I: and winding ii.

If two auxiliary windings and a shield are used,

the distance between the shield and the high voltage winding controls and the auxiliary windings may be spaced at equal intervals between the shield and the high voltage winding. The auxiliary winding nearer the shield should have one-third and the other auxiliary winding twothirds the number of turns of the high voltage winding.

Fig. 5 is a schematic of a transformer having an electrostatic shield 22 and two an ary windlug 25 and located between primary winding l2 and secondary winding il Auxiliary winding 25 should have one-third the number of turns of secondary winding H and be spaced from shield 22 on.ethird the distance between the shield and winding ll while auxiliary wind should have two-thirds the number of turns of winding 9! be spaced from shi ld 22 twothirds the distance between the shield and winding ll.

the dra il'lg l of the windings are shown connected. to ground. The grounded termi--al for the primary and secondary windings is not essential and may be omitted if desired. However, the connection to ground of one terminal of the auxiliary winding or win ings is preferable to insure that the auxiliary winding does not float.

The inventi may also be applied to configurations other than cylindrical windings. The turns of the auxiliary winding or windings be embedded in the insulation of a coil of any structure to fix the potentials at particular points within the body of the insulation to predetermined values. these means the potential gradients may be controlled so to avoid excessive values.

The present invention is of particular value where the voltage developed across the secondary winding is of the order or" 10,0520 volts. or higher.

It is desired to point out also that the potential gradient be controlled to give any desired values. If for any reason it is desired that the potential gradient be other than uniform, the position and number of turns of the auxiliary windings may be arranged accordingly.

The invention may be carried out in other specificways than those herein set forth without one-halt 4 departing from the spirit and essential characteristics of the invention and the present embodiment is, therefore, to be considered in all respects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are to be embraced therein.

What is claimed is: V

1. A high voltage electrical transformer comprising a primary winding, a secondary winding,

insulation separating said windings, and means for insuring a substantially uniform potential gradient between said windings, said means comprising an open circuited auxiliary winding placed between said primary and secondary windings and insulated therefrom, the number of turns in said auxiliary winding being such as to cause to be induced in each elementary portion of said auxiliary winding a potential which is substantially the same as would exist at the relative location of said portion in an absolutely uniform dielectric in the absence of said auxiliary winding.

2. A high voltage electrical transformer comprising a primary winding, a secondary winding, insulation separating said windings, and means for insuring a substantially uniform potential gradient in said insulation, said means comprising an open circuited auxiliary winding located between said primary and secondary windings, the relation of the number of turns in said auxiliary winding to the number of turns insaid other windings determining the distance between said auxiliary winding and said other windings.

3. A high voltage electrical transformer comprising a primary winding, a secondary Winding adapted to have developed across its terminals an alternating current voltage at least of the order of 10,000 volts, insulation separating said windings, and an open-circuited auxiliary winding located substantially half way between said primary and secondary windings, the number of turns in said auxiliary winding being substantially equal to one-half the sum of the number of turns in said primary and secondary windings.

4. A high voltage electrical transformer comprising a primary winding, a secondary winding, insulation separating said windings, and a plurality of open-circuited auxiliary windings between said primary and secondary windings, said auxiliary windings having different numbers of turns, the auxiliary winding having the larger number of turns being positioned nearer said secondary winding.

5. A high voltage electrical transformer comprising a primary winding, a secondary winding, a grounded electrostatic shield therebetween, an open-circuited auxiliary winding and insulation separating said shield and windings, said auxiliary winding having about one-half the number of turns of said secondary winding and being positioned about half-way between said shield and said secondary winding.

6; A high voltage electrical transformer comprising a primary winding, a secondary winding, insulation separating said windings, and a plurality of open circuited auxiliary windings between said primary and secondary windings, the number of turns of said auxiliary windings and their location in reference to said primary and secondary windings being determined by the potentials which would exist in an absolutely uniform dielectric at the positions of said auxiliary windings.

'7. A high voltage electrical transformer com- 5 prising a single layer primary winding, a single layer secondary winding surrounding said primary winding and spaced therefrom, insulation between said windings, and means for insuring a substantially uniform potential gradient between said windings, said means comprising an open-circuited single layer auxiliary winding spaced between said primary and said secondary windings and insulated therefrom, one end of said 6 auxiliary winding being substantially at ground potential, the number of turns in said auxiliary winding being such as to cause to be induced in an elementary portion of said auxiliary winding a potential which is substantially the same as would exist at the relative location of said portion in an absolutely uniform dielectric in the absence of said auxiliary winding.

ALBERT G. GANZ.