US3222590A - High-voltage instrument transformer - Google Patents

Description

Dec. 7, 1965 H. RITZ HIGH-VOLTAGE INSTRUMENT TRANSFORMER Filed Feb. 13, 1962 United States Patent 3,222,590 HIGH-VOLTAGE INSTRUMENT TRANSFORMER Hans Ritz, 72 Alsterkrugchaussee, Hamburg, Germany Filed Feb. 13, 1962, Ser. No. 173,048 8 Claims. (Cl. 323-48) The invention relates to a high-voltage instrument transformer in the form of a current transformer or a combined current and voltage transformer.

It is known to provide high-voltage instrument transformers of this type with two or more current transformer cores through which there passes a common primary winding. Each of the cores has a secondary winding which forms part of a separate secondary circuit. These secondary circuits are more especially for protective purposes and for measuring purposes.

Difficulties have been encountered in developing highvoltage instrument transformers of the cascade type, as opposed to the single-stage type, comprising a number of separate secondary circuit-s, which operate with similar reliability and measuring accuracy. If there is connected in series with the primary winding of the lower cascade stage, which extends through the cores of the current transformer and the secondary windings of which are intended for the connection of the protective circuits and of the measuring or metering circuits, an additional current transformer system forming an upper cascade stage, of which the primary winding is connected to the highvoltage line, it is found that when one secondary circuit remains open for some time a considerable falsification of the current values in another secondary circuit may occur. In addition to such deficiencies with respect to measurement, there are dangers of breakdown in such a transformer (voltage rises, glow discharge effects, oil decomposition, excess heating) due to connection faults. If, in order to obviate these disadvantages, completely separate current transformer systems were provided in all the cascade stages, i.e., if separate cores having separate coverings of solid insulating material also enclosing the secondary conductors were provided in each instance within the housing containing the insulating liquid, a complicated and heavy construction of the transformer with large overall widths would be obtained.

According to the present invention there is provided a high-voltage instrument transformer comprising a columnlike insulating housing. Two ring cores of a current transformer system are within the housing. Secondary windings of the current transformer system are provided for the cores. Conductors extend from the secondary windings for connection to external circuits. A body of solid insulating material encases the two cores, the secondary windings and the conductors. Portions of the body define a first passage therethrough having an opening in one of the two cores between its two ends. Further portions of the body define a second passage therethrough having an opening in the other of the two cores between its two ends, so that two different primary conductors can be passed through the body, each through one only of the two cores. Further insulating material. of a kind which is liquid at least at elevated temperatures, is around the body and substantially fills the housing.

Fora better understanding of the invention and to show by example and not limitation, how the same may be carried into effect, reference will now be made to the accompanying drawings in which:

FIGURES 1 and 2 illustrate diagrammatically, and partly in section, two embodiments of a high-voltage instrument cascade transformer;

ice

FIGURE 3 illustrates a further embodiment of a highvoltage instrument cascade transformer; and

FIGURE 4 illustrates a portion of another embodiment:

FIGURE 5 is an enlarged section through an insulating body of the transformers taken in a portion of the body including rings 17 and 17'. It should be noted that the same reference characters will be used for similar elements in each of the figures.

The illustrated high-voltage instrument transformers consist of component sets each of which forms a cascade stage 1, 2 and constitutes an independent unit sealed in air-tight fashion filled with an insulating medium introduced in liquid form. These stages are then mounted one above the other at the place of use. A housing or insulating medium container of each cascade stage 1, 2 com prises a tubular ceramic insulator 32, 32, sealed at both ends. Insulator 31, 32 is indicated in the drawing by chain lines.

A current transformer head 3 is provided with external connecting pins 4, 5 in FIGURE 1, and with a primary conductor pin 6 extending transversely through the head 3 in FIGURE 2. Resilient expansion vessels 7 are provided for allowing for the temperature expansion of the insulating medium filling, which are separately provided for each self-contained cascade stage. The cascade instrument transformers according to FIGURES 1 and 2 are constructed as combined instrument transformers (current and voltage transformers), however the invention also contemplates their application to simple, uncombined instrument transformers.

In each lower cascade stage such as cascade 2 of FIG. 1, current transformer systems which are completely electrically and magnetically separate have separate primary windings 8, 9 which are provided for protective purposes and for measuring purposes. Primary winding 8 is about core 10 and primary winding 9 is about core 11. Separate current transformer ring cores 12, 13 are also provided in each upper stage 1. In the embodiment according to FIGURE 1, the cores 12 and 13 of the upper stage 1 are energised by a common primary Winding 14. The ends of the primary winding 14 are connected to external connecting pins 4, 5. Each current transformer core 12, 13 in each cascade stage carries a secondary winding. Core 12 has a secondary winding 40a, and core 13 has a secondary winding 40b. Core 10 has a secondary winding 41a and core 11 a secondary winding 41b. The cores 10 and 11, the winding 41 and the conductors are shown in dotted lines to indicate they are embedded in insulation.

The current transformer ring cores 12 and 13 for protective purposes and for measuring purposes which are disposed within each cascade stage, as well as their secondary windings and their connecting conductors, have a common insulating covering 15, as seen in FIGURES 1 and 2 consisting of a material of high mechanical and dielectric strength (oil paper wrapping or cast resin covering). Conductive coatings or inserts 18, 18 (FIG. 5) are provided in the covering 15 to serve for voltage control. In the current transformer system of the lower cascade stage of FIGURE 1 and all the current transformer systems of the remaining figures, the ring cores 10 and 11 are so arranged and enclosed by the insulating covering 15 that the core passages 33 and 34 are each separately accessible through separate apertures 35 and 36 in the common insulating covering body 15 for the purpose of passing therethrough the leads 37 and 3'8 of primary windings 8 and 9 respectively. The passage and apertures are best seen in FIG. 4. There are provided in each current transformer system two ring cores which in FIGURES 2 and 3 are disposed one above the other in each instance, the two ring cores being disposed in one plane in FIGURE 2, and in separate, parallel planes in FIGURE 3, while in FIGURE 4 they are juxtaposed in an inclined position.

The conductive inserts 18, 18' (FIGURE 5) which are provided within the insulating covering body 15 of each current transformer system are foil shaped and completely surround the cores and 11, the secondary windings 8 and 9 wound thereon together with the lead-in conductors 19c and 19d therefore, in the manner of onion skins. They terminate in rings, 17 distributed along the leadout ends (winding lobes). Rings 17 are also covered by material of high dielectric strength. Thus, only a few conductive inserts are necessary for the voltage control even with high voltages. The conductive inserts 18,18 are connected to rings 17, 17', of body 15. Inserts 18, 18' provide a uniform distribution of voltage within the insulating body 15. Each point of such an insert assumes automatically the same potential or voltage, and the potential of an inner insert 18 will be greater than that of an outer insert 18. In the insulating material between the inserts and outside thereof each point assumes a higher or lower corresponding potential so that there are equipotential surfaces whose shape conforms or adapts to the shape of the inserts 13, 18 and the rings 17, '17. Sharp edges at the ends of the inserts 13, 18 are avoided by the rings 17, 17 which are covered by insulating material 15, so that no arcing can arise there in A consequence of high electrical voltage. The insulating medium filling the column-like insulating vessel of each individual cascade stage may be a high-grade liquid insulating medium. Alternatively, a cast resin filling may be provided.

A voltage transformer part 20 having an iron core 21 with secondary windings for protective and measuring or metering purposes, may also be provided within each cascade stage. Instead of this arrangement, there may be provided in each of the cascade stages 1, 2 a voltage transformer core provided with a secondary winding, for protective purposes and a similar core for measuring or metering purposes.

In the instrument transformer shown in FIGURE 2, iron cores 22, 23 having a closed magnetic circuit are arranged as short-circuit dissipators on the primary-conductor or connecting pin 6 or pins extending entirely through the head 3 of the instrument transformer. Each of these cores 22 and 23 forms in combination with pin 6 a bar choke having a relatively high impedance with normal primary current passing through the primary conductor, so that the current flows to the current transformer primary windings 24, 25. For high primary currents or short-circuits, the impedance of the bar chokes decreases to such an extent, due to the saturation of the iron of the chokes, that the current flows primarily directly through the primary conductor pin 6 and not through the windings 24 and 25 and cannot damage the primary Windings of the current transformer. In some cases, the primary winding of the current transformer may be connected to the pin in accordance with the principles of an auto-transformer.

In order that the branch currents from both sides of each of the bar chokes may be separately fed to the current transformer systems, i.e. in order that the current transformer cores of the uppermost cascade stage which carry the low voltage may be separately provided with primary windings carrying high voltage, the iron cores separately provided for protective purposes and for measuring or metering purposes in the upper cascade stage in the transformer shown in FIGURE 2, as well as those in the lower cascade stages in the current transformer systems illustrated in FIGURES 1, 2 and 3, are so arranged that separate primary windings may be passed through their core passages. In this case, the two cores,

including their secondary windings, which carry low voltage, are commonly enclosed by oil paper wrappings or cast resin layers and conductive inserts disposed one within the other in the manner of onion skins, so that apertures remain free in the core apertures for the passage therethrough of the respective primary windings carrying high voltage.

In the arrangement according to FIGURE 2, there are provided in the lowermost current transformer cascade stage supplementary auto- transformers 26, 27 for voltage limiting in the event of the secondary circuit being opened.

I claim:

1. A transformer adapted to be coupled to conductors of a single phase electrical system comprising a hollow insulating housing, two ring-like cores in said housing each having a central opening, said cores being disposed adjacent one another in the same plane, separate secondary windings each around one of said cores, conductors extending from said separate secondary windings and adapted to be connected to electrical circuits, a common body of rigid insulating material encasing both said cores, said secondary windings and portions of said conductors, said body having a first aperture located within the opening of one of said ring-like cores, said body having a second aperture located within the opening of the other of said ring-like cores, a first primary winding passing through said first aperture and a second primary winding passing through said second aperture, said first and second primary windings being adapted for connection to conductors of a single phase electrical system, and a liquid insulator filling said housing and encasing said body and said primary windings.

2. The transformer according to claim 1 further comprising spaced conductive foil shaped inserts each enclosing both said cores and said conductors in said body for controlling the potential distribution therein, conductive rings connected to said conductive inserts, said rings being disposed along the said body and solid insulating material covering said rings to control the potential distribution in the environment of and along said body.

3. The transformer according to claim 1, wherein said 1ring-like cores are juxtaposed at substantially the same evel.

4. The transformer according to claim 1, wherein said ring-like cores are disposed in parallel planes.

5. The transformer of claim 1 further including a resilient expansion chamber operatively connected to said housing.

6. The transformer of claim 1 further including a second transformer comprising first and second separate transformer cores, first and second separate secondary wlndings each about one of said transformer cores, an input primary winding adapted to be connected to the conductors of said single phase electrical system, means for connecting said first separate secondary winding to said first primary Winding, and means for connecting said second separate secondary winding to said second primary winding.

7. The transformer of claim 1 further including a second transformer comprising first and second separate transformer cores, first and second separate secondary windings each about one of said separate trans-former cores, means for connecting said first separate secondary winding to said first primary winding, means for connecting said second separate secondary winding to said second primary winding, first and second input primary windings each about one of said separate transformer cores, a first saturabl choke connected in parallel with said first input primary winding, a second saturable choke connected in parallel with said second input primary winding, and means adapted for connecting said first and second input primary windings to the conductors of a single phase electrical system.

S. The transformer of claim 1 further including first 5 6 and second auto-transformers respectively connected to 2,804,577 8/1957 Roth 336-174 X said first and sec-0nd separate secondary windings. 3,024,434 3/ 1962 Carson 336-174 References Cited by the Examiner FOREIGN PATENTS UNITED STATES PATENTS 5 244,927 6/1947 Switzerland.

1,790,981 2/1931 Fischer 33694 X 2,113,421 4/1938 Camill-i et a1. 336-94 x JOHN BURNS Prlmary Exammer- 2,312,073 2/ 1943 Camilli 33694 E. JAMES SAX, Examiner.

Claims (1)

1. A TRANSFORMER ADAPTED TO BE COUPLED TO CONDUCTORS OF A SINGLE PHASE ELECTRICAL SYSTEM COMPRISING A HOLLOW INSULATING HOUSING, TWO RING-LIKE CORES IN SAID HOUSING EACH HAVING A CENTRAL OPENING, SAID CORES BEING DISPOSED ADJACENT ONE ANOTHER IN THE SAME PLANE, SEPARATE SECONDARY WINDINGS EACH AROUND ONE OF SAID CORES, CONDUCTORS EXTENDING FROM SAID SEPARATE SECONDARY WINDINGS AND ADAPTED TO BE CONNECTED TO ELECTRICAL CIRCUITS, A COMMON BODY OF RIGID INSULATING MATERIAL ENCASING BOTH SAID CORES, SAID SECONDARY WINDINGS AND PORTIONS OF SAID CONDUCTORS, SAID BODY HAVING A FIRST APERTURE LOCATED WITHIN THE OPENING OF ONE OF SAID RING-LIKE CORES, SAID BODY HAVING A SECOND APERTURE LOCATED WITHIN THE OPENING OF THE OTHER OF SAID RING-LIKE CORES, A FIRST PRIMARY WINDING PASSING THROUGH SAID FIRST APERTURE AND A SECOND PRIMARY WINDING PASSING THROUGH SAID SECOND APERTURE, SAID FIRST AND SECOND PRIMARY WINDINGS BEING ADAPTED FOR CONNECTION TO CONDUCTORS OF A SINGLE PHASE ELECTRICAL SYSTEM, AND A LIQUID INSULATOR FILLING SAID HOUSING AND ENCASING SAID BODY AND SAID PRIMARY WINDINGS.

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