US2519224A - Electrical transformer - Google Patents

Description

Patented Aug. 15, 1950 ELECTRICAL 'rasnsroamm John H. Chiles, Jr., Sharon, Pa}, and Homer 0.

Hood, Brookfield, Ohio, ass znors to Westinghouse Electric Corporation, East Pittsburgh. Pa., a corporation of Pennsylvania Application May 28, 1947, Serial No. 150,948

Claims. (Cl. 171-119) Our invention relates to electrical transform- K ers. In certain types of transformers, such as are suitable for use in certain types of protective systems for operating relays for the protection of transmission lines in the event of a transmission line fault, the current from the transformer secondary winding for operating the pro- I tective relay flows upon an unbalance in the current flowing in the two halves of a, primary winding, having its midpoint grounded. Such a system is disclosed in U. S. Patent No. 2,183,646 to E. L. Harder for Relaying Apparatus, issued December 19, 1939, and assigned to the same assignee as this application. Such transformers are shown in the Harder patent as insulating transformers located at the opposite ends'of the pilot-wires connecting tripping relay stations located at different points along the transmission line to be protected. In such insulating transformers it is desirable that substantially no current will flow in the secondary circuit of the transformers when the voltage between each primary winding terminal to the grounded midpoint of the winding are alike.

It has been customary in transformers of this type to closely couple the two halves of the primary winding by winding two conductors together side-by-side so that the conductors are closely coupled throughout the entire winding lengths. One of these two conductors is used as one of the two primary winding coils, and the other, as the other primary winding coil, constituting the two halves of the primary winding.

The insulation between the two halves of the primary winding is then only the conductor insulation, which is not altogether satisfactory, since the voltage between adjacent conductors may, under certain conditions, become quite large and cause failure of the transformer insulation. 0n the other hand, if the two halves of the primary winding are separated mechanically, it is very difiicult to assemble them so that the two halves will'be sufficiently symmetrical in their coupling to the secondary winding to provide It is a more specific object of the-invention to provide a transformer of the above-indicated character having magnetic shields between the primary and secondary windings for so guiding the primary leakage flux as to prevent or greatly reduce the amount of this leakagefiux that links turns of the secondary winding.

Other objects and advantages of the invention will be apparent from the following description of certain preferred embodiments of the invention, reference being had to the accompanying drawing,inwhich:

Figure l is an elevational view, partly in section, of a conventional transformer core and coil assembly; Fig. 2 is an elevational view, party in section, of a transformer core and coil assembly arranged in accordance with one preferred embodiment of the invention; I

Fig. 3 is a, diagram illustrating the connections of the primary and secondary circuits of the transformer core and coil assemblies illustrated inFigs. l and 2;

Fig. 4 is an elevational view, partly in section, of a core and coil assembly arranged in accordance with another preferred embodiment of the invention;

Fig. 5 is an elevational view, partly in section, of a core and coil assembly arranged in accordance with still another preferred embodiment of the invention, and

Fig. 6 is a diagram illustrating the connections of the primary and secondary windings of the embodiments of the invention illustrated in Figsand 5.

Referring to the drawing and, particularly, to Figs. 1, 2 and 3 thereof, a transformer core structure 1 formed of magnetic material is provided, including a winding leg 2 and two outer legs 3 and 4, respectively, connected together at their upper and lower ends by the yoke portions 5 and 6, respectively. The core structure provides two rectangular windows 1 and 8 on opposite sides of the winding leg 2 through which the windings are positioned about the winding leg 2. The primary winding ll comprises two similar coils or half windings l2 and I3, having their outer terminal conductors l4 and I5 connected to the primary circuit of the transformer and their inner terminal conductors I 6 and I1 connected together and through a common conductor [8 to ground at l9, as shown in Fig. 3. The secondary winding 2| is shown about the winding leg 2 within the primary winding ll and is provided with terminal conductors 22 3 a. .i 23 connected to the secondary winding circuit. The two primary winding coils l2 and II are similar in construction and extend about ,difierent portions of the winding leg 2, while the secondary winding 2! extends about the winding leg 2 over the portions thereof surrounded by both primary winding coils l2 and It. The structure shown in Fig. 1 is a conventional prior art structure. If the two primary coils l2 and I3 are positioned end-to-end (as shown), either-over or inside of the secondary winding 2|, and are perfectly centered with respect to the winding leg of the core and to the secondary winding, each primary coil will neutralize the effect of the other on the secondary winding when equal currents are flowing between each primary terminal through the two primary winding coils to ground. This condition is very diflicult to obtainin commercial production. It the two primary coils and the secondary are not exactly symmetrical, certain current will flow in the secondary due to this lack of symmetry, which is undesirable, since the secondary current which is intended to flow upon unbalance between the two primary'coils for operating the protective relay will then be indeterminate in value and may cause operation of the relay under conditions not intended.

The major portion of the magnetic flux produced by the flow of current in the primary coils i2 and I3 flows through the winding leg 2 and through a magnetic circuit including either the outer leg 3 or the outer leg 4, thus completing a magnetic circuit path within the core. A certain portion of flux, primary leakage flux, will flow about the primary winding coils l2 and i3 along lines represented generally by the dotted lines.

24 and 25 which will, to a greater or lesser extent, cut the winding turns of the secondary winding 2i. If the leakage flux from the coil i2 and the leakage fiux from the coil i3 are equal and opposite in direction in the winding turns of the secondary winding 2|, their eflect will be neutralized, and this is the desired condition. As above explained, this condition is difficult to maintain in practice.

In accordance with one embodiment of the invention shown in Fig. 2, magnetic shields 26 and 21, comprising a plurality of layers of magvent or greatly reduce the primary leakage flux linking with the turns of the secondary winding, since the leakage flux will pass between the primary winding coils and the secondary winding following the lower reluctance path through the shield and back to the core, without linking the secondary winding turns, as shown by the dotted line paths 24 and 25 in Fig. 2.

In accordance with the embodiment of the invention illustrated in Fig. 4, both the primary winding and the secondary winding are formed in two coils or two half portions assembled endto-end about the winding leg 2 of the core structure. The primary winding coils may be placed either inside or outside of the secondary winding coils and are connected in series circuit relation with respect to each other with the connection between them grounded ati |9,,as shown in with'respect to the structure illustrated in Figs. 1 and 2.

The secondary coils 3| and 32, which together comprise the secondary winding, extend about portions of the winding leg 2 corresponding to the winding leg surrounded by the primary winding coils l2 and I3, respectively. As shown in Figs. 4 and 5, the terminal conductors 33 and 34 of the secondary coil 3| and the terminal conductors 35 and 36 of the secondary winding coil 32 are connected, respectively, to junction points 31 and 38 that in turn ar connected to the secondary circuit conductors 22 and 23, respectively, thus connecting the secondary coils 3| and 32 in parallel circuit relation with respect to each other.

.a corresponding descrease in the voltage appearing across the secondary coils when applied tothe secondary circuit conductors 22 and 23, reducing this voltage to a negligible value.

In the embodiment of the invention illustrated in Fig. 5, the circuit arrangements of the primary and secondary windings corresponds to that shown in Figs. 4 and 6. Magnetic shields 6i and 42 corresponding to those shown in Fig. 2

have been added and positioned between the primary and secondary winding coils to provide equal air gaps at 23 and 29 between their opposite ends and the adjacent yoke portions 5 and 6, respectively, of the core structure. The arrangement of the magnetic shields shown in Fig. 5, together with the parallel connected secondary coils, gives even better results than either the structural arrangements shown in either Fig. 2 or 4 in that it combines the efl'ect of the magnetic shields in reducing the primary leakage flux thatcuts the windings of the secondary circuit conductors with the use of the circulating current in the two secondary coils resulting from any remaining primary leakage flux cutting the secondary coils to further reduce the eiiectiveness of this flux by the flow of circulating current in the local circuit including the two secondary coils 3| and 32.

It will be apparent from the above description of the invention that modifications may be made in the circuits and apparatus illustrated without departing from the spirit of the invention, and

we do not wish to be limited otherwise than by the scope of the appended claims.

We claim as our invention:

1. In a transformer, in combination, a core structure of magnetic material comprising a winding leg portion and two outer leg portions, and yoke portions connecting the corresponding ends of the three leg portions together to form two continuous magnetic circuit paths for the flow of magnetic flux from the winding leg, a low-voltage winding about the winding leg and a high-voltage winding about the low-voltage winding, the high-voltage winding comprising two similar coils each extending along substantially half of the length of the winding leg, the two coils being connected together and to ground at their Fisn e a mann s Shown in 8- 3 76 adjacent ends and to the circuit conductors of a common circuit at the ends remote from each other, and means for maintaining the effective coupling between one half of the high-voltage winding and the low-voltage winding susbtantially the same as the effective coupling between the other half of the high-voltage winding and the lowvoltage winding comprising magnetic material extending between the high-voltage and lowvoltage windings to completely shield the lowvoltage winding and reduce the primary leakage magnetic fiux linking the low-voltage winding, said magnetic shield having similar air gaps at its opposite ends.

2. In a transformer, in combination, a core structure of magnetic material comprising a winding leg portion, two outer leg portions, and yoke portions connecting the corresponding ends of the leg portions to form two core windows on opposite sides of the winding leg, 9, primary winding and a secondary extcnding through the core windows about the winding leg of the core, each winding comprising two similiar coils positioned end-to-end about different portions of the winding leg, each one of the primary winding coils and a corresponding one of the secondary winding coils being of the same length and positioned about a corresponding portion of the winding leg,

the two coils constituting the primary winding being connected in series circuit relation and the two coils constituting the secondary winding being connected in parallel circuit relation, and means for preventing or greatly reducing the primary leakage magnetic flux linking the secondary winding turns, comprising a shield of magnetic material extending between the primary and secondary windings, the ends of the shield being spaced from the yoke portions of the core to provide similar air gaps between the opposite ends of the shield and the adjacent yoke portions.

3. In a transformer, in combination, a core structure of magnetic material comprising a winding leg portion and an outer leg portion, and yoke portions connecting the corresponding ends of the leg portions together to form a continuous magnetic circuit path for the flow of magnetic flux from the winding leg, a low-voltage winding and a high-voltage winding about the winding leg, the high-voltage winding comprising two similar coils each extending along substantially half of the length of the winding leg, the two coils being connected together and to ground at their adjacent ends and to the circuit conductors of a common circuit at the ends remote from each other, and means for maintaining the effective coupling between one half of the high-voltage winding and the low-voltage winding substantially the same as the efiective coupling between the other half of the high-voltage winding-and the low-voltage winding comprising magnetic material extending between the high-voltage and lowvoltage windings to completely shield the lowvoltage winding and reduce the primary leakage magnetic flux linking the low-voltage winding, said magnetic shield having similar air gaps at its opposite ends.

4. In a transformer, in combination, a core structure of magnetic material comprising a winding leg portion and two outer leg portions and yoke portions connecting the corresponding ends of the three leg portions together to form two continuous magnetic circuit paths for the flow of magnetic flux from the winding leg, 9. lowvoltage winding and a high-voltage winding about the winding leg, the high-voltage winding comprising two similar coils each extending along substantially half of the length of the winding leg, the two coils being connected together and to ground at their adjacent ends and to the circuit conductors of a common circuit at the ends remote from each other, and means for maintaining the efiective coupling between one half of the high-voltage winding and the low-voltage winding substantially the same as the effective coupling between the other half of the high-voltage winding and the low-voltage winding comprising magnetic material extending between the highvoltage and low-voltage windings to completely shield the low-voltage winding and reduce the primary leakage magnetic flux linking the lowvoltage winding, said magnetic shield having sim-' ilar air gaps at its opposite ends.

5. In a transformer, in combination, a core structure of magnetic material comprising a winding leg portion and an outer leg portion, and yoke portions connecting the corresponding ends of the leg portions to form a core window, a primary winding and a secondary winding extending through the core window about the winding leg of the core, each winding comprising two similar coils positioned endto-end about different portions of the winding leg, each one of the primary winding coils and a corresponding one of the secondary winding coils being of the same length and positioned about a corresponding portion of the winding leg, the two coils constituting the primary winding being connected in series circuit relation and the two coils constituting the secondary winding being connected in parallel circuit relation, and means for preventing or greatly reducing the primary leakage magnetic flux linking the secondary winding turns, comprising a shield of magnetic material extending between the primary and secondary windings, the ends of the shield being spaced from the yoke portions of the core to provide similar air gaps between the opposite ends of the shield and the adjacent yoke portions.

JOHN CHIIES, JR. HOMER C. HOOD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS neuter Apr. 8, 1933

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