US2597185A

US2597185A - Self-protected distribution transformer

Info

Publication number: US2597185A
Application number: US137702A
Authority: US
Inventors: Fred C Roeding; Gerhard M Stein
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1950-01-10
Filing date: 1950-01-10
Publication date: 1952-05-20
Anticipated expiration: 1969-05-20

Description

May 20, 1952 F. c. ROSEDING ETAVL- 2,597,185

SELF-PROTECTED DISTRIBUTION TRANSFORMER Filed Jan. 10, 1950 v s Sheets-Sheet 1 9 Fig.l. V H Insulohon & Insulation 8 III IITI/II/I/I/IIIIIIU Insulation Insulation Fig.2.

9 II F 1 TA WITNESSES: INVENTORS Fred CQRoeding 0nd ATTORNEY GerhordMSfein. 77M 4. W

May 20, 1952 F. c. ROEDING ETAL 2,597,185

SELF-PROTECTED DISTRIBUTION TRANSFORMER Filed Jan. 10, 1950 :5 Sheets-Shqet 2 I PhoseA PhoseC Phase A I 4 up) my IOI as I4 I48 I us 49 us WITNESSES: INVENTORS .4 v Fred C. Roeding and i W $erhard M.Stein.

ATTORNEY Patented May 20, 1952 SELF-PROTECTED DISTRIBUTION. TRANSFORMER Fred C. Roeding and Gerhard M. Stein, Sharon,

Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 10, 1950, Serial No. 137,702

11 Claims. 1

Our invention relates to distribution transformers and more particularly to means for protecting such transformers from damage caused by too great overloads sustained for too long a period of time.

In many distribution transformers connected between a high voltage supply feeder circuit and a low voltage distribution circuit, circuit breakers are provided within the transformers for disconnecting the transformer from the distribution circuit upon predetermined load conditions on the transformer. In transformers operating in a cooling insulating liquid such as oil, a temperature-respOnsive element or a number of such elements may be employed for operating the circuit breaker to protect the transformer from damage resulting from overheating caused by overloading the transformer. Bimetal elements may be used for this purpose and so located that they are immersed in the insulating liquid and heated both in accordance with the temperature of the insulating liquid and in accordance with the current flowing in the transformer secondary circuit. The insulating liquid temperature is a function of the heating of the transformer core and coils over a considerable period of time and the current flowing at any particular time is a function of the heating of the transformer taking place at this time. By properly coordinating the relative effects of the long-time loads as indicated by the liquid temperature and the short time loads as indicated by instantaneous current flowing in the secondary winding of the transformer, the temperature-responsive elements or bimetals are made responsive to the copper temperature of the transformer in a well-known manner.

It is an object of the invention to provide a self-protected transformer having a circuit breaker for interrupting the secondary or distribution circuit therefrom, the circuit breaker being actuated by thermally responsive means heated in accordance with the heating of the transformer structure and in which the secondary current is divided by the winding circuits of the transformer in such a manner that a fraction only of the total secondary current flows through the thermally responsive elements, and in which the contacts of the circuit breaker are so located in the secondary circuit they they will interrupt the total current instead of only the fraction flowing through the thermally responsive element.

It is a further object of the invention to provide a self-protected transformer of the aboveindicated character in which parallel circuit paths including secondary winding coils are provided between transformer terminals in single phase and three phase transformers in order to reduce the current flowing in the bimetal or equivalent thermal responsive elements for operating the circuit breaker, thus reducing the size of the bimetal element necessary for controlling the circuit breaker and the number of bimetal elements required to protect the transformer.

Other objects and. advantages of the invention will appear from the following description of certain preferred embodiments thereof, reference being made to the accompanying drawings in which Figure 1 is a diagrammatic view of circuits and apparatus comp-rising a single phase transformer unit organized in accordance with one embodiment of the invention;

Fig. 2 is a somewhat more simplified view of the subject matter ShOWn in Fig. 1;

Fig. 3 is a diagrammatic view of circuits and apparatus comprising a single phase transformer arranged in accordance with another embodiment of the invention in which the transformer connections shown in Fig. 2 are rearranged for operation on half voltage with all four secondary winding coils connected in parallel circuit relation;

Fig. 4 is a diagrammatic view of circuits and apparatus comprising a three phase transformer having two secondary winding coils per phase connected in series circuit relation;

Fig. 5 is a simplified diagram of the circuit shown in Fig. 4;

Fig. 6 is a diagrammatic view of circuits and apparatus generally similar to that shown in Fig. 4, except arranged for parallel connection of the phase coils and comprises a three phase transformer having twp secondary winding coils per phase connected in two separate delta circuits which are connected in parallel relation;

Fig. 7 is a simplified diagrammatic view of the subject matter shown in Fig. 6;

Fig. 8 is a diagrammatic view of another modification of the invention as applied to a three phase transformer having two secondary winding coils per phase connected in series circuit relation;

Fig. 9 is a diagrammatic view of circuits and apparatus modifying the circuits shown in Fig. 8 to provide a parallel delta relation in the secondary winding coil circuits; and

Fig. is a simplified diagrammatic view of the subject matter shown in Fig. 9.

Referring to the drawings and particularly to Figs. 1 and 2 thereof, a transformer is provided having a tank or casing l enclosing a primary winding 2 and a secondary winding shown as having four

coils

3, 4, 5 and 5. The primary winding is connected through bushings l and 3 to a source of electrical energy represented by the supply conductors 9 and ii. The transformer is provided with a plurality of secondary winding transformer terminals l2, l3 and i i from which conductors extend through insulating bushings l5, l6 and 11, respectively, to diotribution circuit conductors 2!, 22 and 23. conductor 24 extends from the secondary winding terminal E3 to a junction point 25 that is connected to one end of each of the two secondary winding coils 3 and 4, and a similar conductor 26 extends from the terminal 13 to a junction point 2? connecting one end of the

secondary winding coils

5 and 6 together. The terminal [3 is a neutral or ground terminal.

A circuit breaker shown generally at it. is provided within the transformer casing having a two-pole switch represented by the circuit terrupting contact members 223 and 29 that are mechanically connected to operate together. Thermally responsive elements shor as

bimetals

30 and 3| are provided for ailecting actuation of the circuit breaker.

A conductor 32 is shown for connecting the end of the secondary winding coils 3 remote from the junction point 25 to ajunction point 33 be tween the switch contact members 28 and the bimetal 30 and the corresponding end of the secondary winding coil 4 is connected by means of conductor 34 to the bimetal 38 so that the current from this coil 4 will pass through the bimetal, the switch contact members 28 and conductor 35 to the terminal I2. The end of the winding coil 5 remote from the junction point 21 is connected by means of a conductor 35 to a junction point 37 between the bimetal 31 and the switch contact members 29. The corresponding end of the coil 6 is connected by a conduct-or 38 to the bimetal 3| and through the bimetal and the. switch contact m mbers 25 and conductor 39 to the terminal He. The bi-- metal elements 31' and 31 are positioned in. the transformer casing below the level of the cooling and insulating liquid and constitute thermally actuated load responsive elements for initiating the operation of the circuit breaker 8 to disconnect the transformer secondary winding from the distribution circuit conductors.

The

bimetal elements

30 and 31 are mounted on suitable abutments 4| and 42, respectively, and are provided with latches 43 carried by the outer or moving ends thereof that are adapted to disengage

tripping members

44 and 45 that are pivotally mounted on pins 46 and 4?, respectively, and are biased by

springs

48 and 49, respectively. The ends of the tripping

members

44 and 45 that are remote from the latches 43 are positioned adjacent to an operating member 5! attached to a latch rod 52 that is normally biased by the spring 53 to its illustrated position to engage a projection 54 for maintaining the switch

operating contact members

23 and 29 in circuit closing position. Upon movement of the bimetal member 33 sufiiciently to the left as shown in Fig. 1 to release the latch 43, the tripping member 44 will operate under the force of the spring 48 to move the operating member 5i and latch rod 52 downwardly to disengage the projection 54 causing the switch operating mem ber 55 to be moved to the right as operated by a toggle mechanism 56 actuated by a spring 51 which moves the

contact members

28 and 29 of the circuit breaker to their circuit interrupting positions. Likewise, movement of the bimetal element 31 to the right as shown in Fig. 1 sufficiently to unlatch the tripping member 45 causes a similar operation of the operating member 5! and latch rod 52 to cause movement of the circuit breaker to its circuit interrupting position.

The circuit breaker i8 is so mounted as to operate under the oil or cooling liquid in which the transformer is immersed so that the bimetal elements 30 and 3i are responsive both to the temperature of the transformer oil and also to the current flowing in the transformer secondary circuit. Either

bimetal

30 or 3| is effective to trip the breaker which, when it operates, interrupts the current flow through both poles of the breaker to completely disconnect the secondary circuit from the distribution circuit supplied from the transformers.

The modification of the invention shown in Fig. 3 is generally similar to that shown in Figs. 1 and 2 except that no neutral conductor corresponding to the conductor 22 of Figs. 1 and 2 is provided as the transformer secondary winding terminals i3 and [4 are connected to two distribution circuit conductors 6| and 62, respectively. The junction point 25 is connected by conductor 63 to the terminal (4 and the remaining circuits are similar to those shown in Figs. 1 and 2. Thus, the right-hand ends of the four

secondary winding coils

3, 4, 5 and 6 are all connected to the secondary winding terminal 14 and the left-hand ends of these four winding coils are all connected to the secondary winding terminal l3. Thus, the

bimetal elements

30 and 31 each carry one-fourth of the total secondary winding current if we assume that each of the

coils

3, 4, 5 and 6 carry the same current. In Fig. 3 as in Figs. 1 and 2, the bimetal 30 carries one-half of the current carried by the coils 3 and 4 and the bimetal 3| carries one-half of the current carried by the

coils

5 and 6. In the structure shown in Figs. 1 and 2 this is one-half of the secondary current while in the arrangement shown in Fig. 3 it is one-fourth the secondary current.

Referring to Figs. 4, 5, 6 and 7, the invention is applied to a three phase transformer having three primary winding coils and six secondary winding coils. In the arrangement shown in Figs. 4 and 5, the two secondary winding coils of' each phase are connected in series, the three phases being connected together in delta. relation, while in the circuit connections shown in Figs. 6 and '7, the two secondary winding coils of each phase are connected in parallel circuit relation forming two parallel connected delta circuits, as shown in Fig. 7.

Referring to Fig. 4, the broken line 8!! outlines the transformer casing containing the three primary windings H, 12 and 13 associated respectively with phase A, phase B and phase C of the transformer. Secondary winding coils 14' and 15 are provided inductively related, to the primary winding 1!, secondary winding coils 16 and 'l! are provided inductively related to the primary winding 72, and secondary winding coils 18 and 19 are provided inductively related to the primary winding I3. The letters A and B are used to indicate the terminals of the three secondary

phase winding coils

14, 16 and 18 so as to more readily show the relation of the windings in the simplified circuit diagrams of Figs. 5, '1 and and the letters C and D are used to designate that the terminals of the remaining three secondary winding coils 15, 11 and 19 for the same reason.

Two panel boards BI and 82 are shown, the panel board 8| having eight studs, 83, 84, 85, 86, '81, 88, 89 and 90 and the terminal board 82 having studs 9i to 98, inclusive, for use in making the desired circuit connections for the secondary winding coils in the secondary circuit. As shown in Fig. 4, the terminal A of the coil 14 is connected by conductor IOI to the stud 83, the terminal B of the coil 14 is connected by conductor I02 to the stud 89, the terminal 0 of coil 15 is connected to the stud 85 by conductor I03, the terminal D of coil 15 is connected by conductor I64 to the stud 95 and also to a junction point I05 to the middle one of three bimetals I06 of a three-pole circuit breaker I01. The terminal A of the coil 16 is connected by conductor I08 to the stud 90 and theterminal B of coil 16 is connected by conductor I09 to the stud 92. The terminal C of the coil 11 is connected by conductor I I I to the stud 9I and the terminal D of the coil 11 is connected by conductor I I2 and the junction point II 3 to the stud 94, and to a bimetal II4 associated with one of the three poles of the circuit breaker I01. The terminal A of the coil 18 is connected by conductor II5 to the stud 93, and the terminal B of the coil 18 is connected by conductor II6 to the stud 91. The terminal G of coil 19 is connected by conductor II1 to the stud 98 and the terminal D of the coil 91 is connected by conductor II8 to a junction point H9 and by conductor I2I to the stud 84 and to the third bimetal I22 of the threepole switch I01. As shown in Fig. 4, a jumper I23 connects the

studs

83 and 84 of the terminal board 8I, a jumper I24 connects the

studs

85 and 89, a jumper I25 connects the stud 90 of the terminal board 8| to the stud 95 of the terminal board 82, a jumper I26 connects the studs BI and 92, a jumper I21 connects the

studs

93 and 94 and a jumper I28 connects the

studs

91 and 98. The remaining studs are not connected in the circuit arrangement shown in Fig. 4. The threepole circuit breaker I01 is provided with sets of switches I3I, I32 and I33, one set for each pole of the circuit breaker. The three junction points II9, I05 and H3 referred to above are connected, respectively, through three bimetal elements I22, I06 and H4 and their associated pole switches I3I, I32, and I33 to three transformer secondary terminals XI, X2 and X3 and from them respectively to three distribution circuit conductors I34, I95 and I36.

The circuit shown in Fig. 4 is more readily understandable by reference to Fig. 5 in which the elements of the secondary circuit are shown in a simplified diagram. It will be noted that the two secondary windings of each phase are connected in series and the three phases connected together in delta with the three pole circuit breaker having a pole connected between each point of the delta circuit and its associated secondary transformer terminal.

Referring to Fig. 6, the general arrangement of the transformer windings, the terminal boards BI and 82 and the arrangement of the studs in the terminal boards, together with the connections of the several secondary winding coils to the studs correspond to the subject matter shown in Fig. 4. The several connecting jumpers I23,

I24, I25, I26, I21 and I28 shown in Fig. 4 are not used in Fig. 6, but other jumpers to be presently described are used. In Fig. 6, a jumper MI is shown connecting the stud 83 to the stud 81 and a conductor I42 is shown connecting the stud 81 to a junction point I43 between the bimetal I22 and contact members of the switch I3I of the first one of the three poles of the breaker I01. A jumper I44 is connected between the

studs

81 and 88 and a conductor I45 is shown connecting the stud 88 with the stud 91. A jumper I46 connects the

studs

84 and 85. A jumper I41 connects the

studs

89 and 90 and a jumper I48 connects the

studs

90 and 86 and a conductor I49 connects the studs 86 to a junction point I50 between the bimetal I06 and the switch contact members I32 of the second pole of the circuit breaker I01.

A jumper I5I connects the studs 9I and 95, a jumper I52 connects the

studs

92 and 96, a jumper I53 connects the

studs

93 and 92, a, jumper I54 connects the

studs

94 and 98, a conductor I55 connects the stud 96 with a junction point I56 that is connected between the bimetal H4 and the contact members of the switch I33 of the third pole of the circuit breaker I01. The circuit resulting from the arrangement of the various circuit conducting members illustrated in Fig. 6 is more clearly shown in Fig. 7 and comprises two parallel connected delta circuits connected together at their respective corners with a bimetal between each of the two corresponding corners of the delta and switch contact members between the outer corners of the delta and the secondary terminals so that the current flowing through the three bimetal elements I22, I06 and H4 will be only the current flowing through the windings of the inner delta as shown in Fig. '1 or half of the total current of the two delta connected winding circuits, while the current interrupted by the three-pole switch I01 will be the entire current from the two parallel connected delta circuits of the secondary windings.

Referring to Figs. 8, 9 and 10, a three phase transformer is shown having three primary Windings, six secondary winding coils, two terminal blocks, each having eight terminal studs, and a three-pole circuit breaker generally similar to those shown in Figs. 4 and 6. The particular crcuit connections are, however, difierent from the previously described figures in a manner to be presently explained. The circuit connections shown in Fig. 8 result in a series delta relation of the secondary winding coils similar to that shown in Fig. 5 and the circuit connections shown in Fig. 9 comprise a double delta or two parallel delta circuits shown in a simplified diagram in Fig. 10.

In Fig. 8, the secondary circuit from the transformer secondary terminal XI to the transformer secondary terminal X2 extends from the terminal XI through the contact members of the circuit breaker I3I of the first pole of the three phase circuit breaker I01, through the bimetal I22, conductor I6I to the junction point I62 and from there to the terminal A of the secondary winding coil 14, through the coil 14 to the terminal B, through conductor I63 to the stud 9|, through the jumper I64 to the stud 92 and conductor I65 to the terminal C of the secondary winding coil 15, through the coil 15 to the terminal D thereof and through conductor I66 including the junction point I 61 to the bimetal I06, through the bimetal I06 and switch conductor members I32 of the second pole of the switch I01 to the transformer secondary terminal X2.

The circuit from the transformer secondary terminal X2 to the transformer secondary terniinal X3 extends from the terminal X2 through the circuit breaker contact members I32 and the bimetal IfiB of the second pole of the circuit breaker I07, through conductor I65 to the junction point I6! and to the terminal A of the secondary winding coil I6, through the coil IE to the terminal B thereof, through conductor IT! to the stud 85 through jumper I12 to the stud 86, through conductor I73 to the terminal C of the secondary winding coil ll, through the coil 77 to the terminal D thereof to the junction point 134 and through conductor I15 to the bimetal I M and switch contact members I33 of the third pole of the circuit breaker III! to the secondary terminal X3.

The circuit from the transformer secondary terminal X3 to the transformer secondary termina XI may be traced from the terminal XI through the switch contact members I3I and bimetal I22, conductor lSI to the junction point I62, conductor I'IS to the terminal D of the secondary winding coil 15, through the coil 79 to the terminal C thereof through conductor ITI to the stud 94, through jumper I18 to the stud 9-3, through conductor I79 to the terminal B of the secondary whirling coil 78 through the coil F8 to the terminal A thereof and to the junction point ill, through conductor I75, bimetal H4 and circuit contact members I33 to the secondary winding terminal X3. As will be seen by following the above traced circuit-s, the embodiment illustrated in Fig. 8 uses fewer jumpers on the terminal boards SI and 82 than shown in Fig. 4, but arrives at the same general arrangement of the six secondary winding coils, namely, the two coils of each phase are in series circuit relation with each other forming a single delta connected secondary winding as shown in the simplified dia- 1 gram in Fig. 5.

In the embodiment of the invention illustrated in Fig. 9, the connections of the terminals of the several secondary winding coils I4 to I5, inclusive, to the several studs on the terminal boards 8! and 82 are similar to the connections shown in Fig. 8 and the connections of the several junction points I62, 56'! and I74 to the several poles of the three phase circuit breaker I"! and the transformer secondary winding terminals XI, X2

and X are also similar to the connections shown in Fig. 8. The same transformer unit may be connected as shown in Fig. 8 for series operation of the secondary phase winding coils or as shown in Fig. 9 for parallel operation of the secondary winding coils.

In Fig. 9, the circuits are changed from those shown in Fig. 8 by removing the three jumpers I72, I54 and I18 shown in Fig. 8 and adding jumpers I3I, I82, I83, I84, I85, I83 and a conductor I87. In addition, a conductor ifll is connected between the junction point {92 that is between the bimetal I22 and the switch cont ct members 53! of the first pole of the three phase circuit breaker to the stud '97, a conductor I93 is connected between a junction point I94 that is between the bimetal I86 and the contact mem bers of the switch I32 of the second pole of the three phase circuit breaker to the stud 95, and a conductor I95 is connected between a junction point I95 that is between the bimetal II4 and the contact members of the switch I33 of the third pole of the three phase circuit breaker to the stud 89.

The jumpers I8I to I86 and the conductor I81 8 are as shown in Fig. 9 connected as follows. The jumper I81 connects the stud 84 to the stud 85, the jumper I82 connects the stud to the stud 89, the jum er I83 connects the stud 86 to the stud SI, the jumper I84 connects the stud SI to the stud 95, the jumper I85 connects the stud 92 to the stud 93, the jumper I86 connects the stud 93 to the stud 91 and conductor I81 connects th stud S4 to the stud 84.

The circuit of Fig. 9 is more clearly shown in the simplified diagram of Fig. 10. It will be noticed by reference to Fig. 10, that any circuit from any transformer secondary terminal XI, X2 or X3 to any other one of the three terminals extends through two parallel branches between junction points inside the circuit breaker contact members and includes one of the three bimetals I06, I I I or I22 and two of the three circuit breaker pole switches I3I, I32 and I33. For example, from the transformer secondary terminal X2 to the transformer secondary terminal X3, the circuit includes both pole switches I32 and I33. The circuits divide between the junction points Ie and IE3, one circuit path including the conductor I93 to junction point 9|, the secondary winding coil 'II, junction point IIA conductor I I2 and the bimetal II4 to the junction point I96, and the other parallel path between the junction points I94 and I96 including the bimetal IE5, conductor I58 to the junction point I 67, secondary winding coil I6 and conductor I95 to the junction point I96. Likewise, in tracing the circuit from the terminal conductor X2 to the terminal conductor XI, or from the terminal conductor XI to the terminal conductor X3, the circuit in each case will pass through two poles of the three pole switch and through two parallel circuits including the two secondary winding coils of one phase of the three phase secondary of the transformer and including one of the bimetal elements.

There ar certain advantages in the circuit arrangements shown in Figs. 9 and 10 over that shown in Figs. 6 and 7. The circuit arrangements shown in Figs. 6 and 7 work properly, providing the current divides properly between the two complete delta circuits shown. It will be noted, by reference to Fig. 7, however, that the outer delta does not include any bimetal elements. The bimetal elements of Fig. '7 are between the corners of the inner delta and the corners of the outer delta as shown in Fig. 'I. If one of the circuits of the inner delta becomes interrupted for one reason or another, the entire current in that phase will necessarily flow through the coil connected in the outer delta of the diagram and will not include a bimetal element. This is impossible in the connection shown in Figs. 9 and 10, since each one of the two parallel paths per phase includes one thermal element which protects all six of the secondary winding coils independently of the difference of load between them.

It will be apparent from those skilled in the art that modifications may be made from the particular circuit arrangement shown Within the scope of the invention and we do not wish to be otherwise limited than by the scope of the appended claims.

We claim as our invention:

1. In combination, a single phase electrical transformer comprising a casing, a primary winding and a secondary winding within the casing, the secondary winding comprising a pair of groups of secondary winding coils, a pair or secondary winding transformer terminals, a pair of junction points connected to the pair of secondary winding transformer terminals, a two pole circuit breaker within the transformer casing, the two poles of said circuit breaker being connected respectively between one secondary winding terminal and its associated junction point, the secondary winding coils of each group being connected in a plurality of similar parallelconnected circuit paths between the pair of junction points, and temperature responsive means for operating the circuit breaker to interrupt the transformer secondary circuit comprising a pair of temperature responsive elements for tripping the circuit breaker, one temperature responsive element being associated with each junction point and responsive to the current flowing through one of the secondary winding coils only of the parallel-connected circuit paths.

connected to that junction point and responsive to a portion only of the current flowing through the junction point and the associated breaker pole to the associated secondary winding terminal.

three poles of said circuit breaker being connected respectively between one secondary winding terminal and its associated junction point,

the secondary winding coils of each group being connected in a plurality of similar parallel-connected circuit paths between each pair of said three junction points, and temperature responsive means for operating the circuit breaker to interrupt the transformer secondary circuit comprising three temperature responsive elements for tripping the circuit breaker, one temperature responsive element being associated with each junction point and responsive to the current flowing through one of the secondarywinding coils only of the parallel-connected circuit paths connected to that junction point and responsive to a portion only of the current flowing through the junction point and the associated breaker pole to the associated secondary winding terminal.

3. In combination, a three phase electrical transformer comprising a casing, a primary winding and a secondary Winding within the casing, the secondary winding comprising a plurality of winding coils for each of the three phases of the transformer, the secondary winding coils being connected to provide a plurality of delta connected phase Winding circuits providing junction points at the union between the adjacent coils in each delta connection, a three pole circuit breaker in said delta casing, three secondary transformer terminals, secondary circuit paths between corresponding junction points of the delta connected phase winding coils connecting the several delta connected groups of winding coils in parallel circuit relation, the circuit interrupting poles of the three pole circuit breaker being connected respectively between the three secondary transformer terminals and the secondary circuit paths connecting the several delta connected phase windings to the terminals, and three temperature responsive means each responsive to the current flowing in one of said circuit paths between corresponding junction points of the several delta connected groups of secondary winding coils for operating the circuit breaker to interrupt the secondary circuit upon predetermined load conditions between any of the three secondary transformer junction points connected thereto.

4. In combination, a three phase electrical transformer comprising a casing, a primary winding and a secondary winding within the casing, the secondary winding comprising a plurality of winding coils for each phase of the transformer, three secondary winding transformer terminals, the secondary winding coils being connected in a plurality of delta connected groups, each group including three phase winding coils, the several groups of delta connected phase winding coils being connected together through circuit connections between corresponding junction ,points of the several delta connected groups, a three pole circuit breaker within the casing, the three poles of the breaker being connected respectively between the three circuit connections joining the groups of delta connected phase winding coils and the three sec ondary winding transformer terminals for interrupting the secondary circuit from the transformer, and three temperature responsive elements for operating the circuit breaker to interrupt the transformer secondary circuit, the three temperature responsive elements being connected respectively between the three transformer terminals and one delta connected group only of the several groups of delta connected secondary phase Winding coils so as to be directly responsive to a portion only of the current flowing through the associated secondary winding terminal.

5. In a three-phase electrical transformer, a casing, a primary winding and a secondary winding within the casing, the secondary winding comprising a plurality of secondary winding coils for each phase, three secondary winding transformer terminals, phase winding coils associated with each of two phases of the transformer uniting to form a delta-connected group having junction points adjacent each one of the three secondary winding transformer terminals, addi tional phase winding coils associated respectively with each of the same two phases of the transformer uniting to form a similar delta-com nected group having junction points adjacent each 10f the three secondary winding transformer terminals, corresponding junction points of the two deltas being connected to a corresponding common junction point, a three-pole circuit breaker in the transformer casing, each of the three poles of the circuit breaker being connected respectively between the three secondary winding transformer terminals and the adjacent common junction points associated therewith for interrupting the transformer secondary current between the secondary winding coils and the three phase secondary terminals, and three thermal elements each responsive to the current flowing between one of the secondary terminals and an associated junction point of one of the delta-connected groups only adjacent thereto for initiating the operation of the circuit breaker.

6. In combination, an electrical transformer comprising a casing, a primary winding and a secondary winding within the casing, the secondary winding comprising a plurality of groups of winding coils, each group comprising at least a pair of the winding coils connected in parallel circuit relation and terminating in a junction point, a circuit breaker in the casing, a secondary circuit path from each of the junction points to a transformer terminal including circuit breaker contact members for interrupting the flow of current from the transformer, and temperature responsive means responsive to the current flowing in one of the winding coils of a group only disposed for operating the circuit breaker to interrupt the secondary circuit.

7. In combination, an electrical transformer comprising a casing, a primary winding and a secondary winding within the casing, the secondary winding comprising a plurality of groups of winding coils, each group comprising at least a pair or the winding coils connected in parallel circuit relation and terminating in a junction point, a circuit breaker in the casing, a secondary circuit path from each of the junction points to a transformer terminal including circuit breaker contact members for interrupting the flow of current from the transformer, and temperature responsive means connected in series circuit relation between one of the winding coils of a group and the junction point associated therewith and responsive to the current flowing in said one of the winding coils of the group only disposed to operate the circuit breaker to interrupt the secondary circuit.

8. In combination, an electrical transformer comprising a casing, a primary winding and a secondary winding within the casing, the second ary winding comprising a plurality of groups of winding coils, each group comprising at least a pair of the winding coils connected in parallel circuit relation and terminating in a junction point, a crcuit breaker in the casing, a secondary circuit path from each of the junction points to a transformer terminal includin circuit breaker contact members for interrupting the flow of current from the transformer, and a temperature responsive means for each of the groups of winding coils, each of the temperature responsive means being connected in series circuit relation between one of the winding coils and the junction point of the group with which it is associated to be responsive to the current flowing in said one of the winding coils of the associated group only for operating the circuit breaker to interrupt the secondary circuit.

9. In combination, an electrical transformer comprising a casing, a primary winding and a secondary winding within the casing, the secondary winding comprising a plurality of groups of winding coils, a plurality of secondary winding transformer terminals, each group of winding coils comprising at least a pair of the winding coils connected in parallel circuit relation and terminating in a junction point, a circuit breaker having a plurality of circuit interrupting poles disposed within the casing, the several poles of the circuit breaker being so disposed that each pole is connected between one of the secondary winding terminals and a junction point associated therewith for interrupting the flow of current from the transformer, and temperature responsive means comprising a plurality of temperature responsive elements each of which is operative to trip the circuit breaker, one of the temperature responsive elements being connected in series circuit relation between one of the winding coils of a group and the junction point associated therewith to be responsive to the current flowing in said one of the winding coils of the group only and to a portion only of the current flowing through junction point and associated breaker pole.

10. In combination, a single phase electrical transformer comprising a casing, a primary Winding and a secondary winding within the casing, the secondary winding comprising a plurality of groups of winding coils, each group comprising a plurality of the winding coils connected in parallel circuit relation and terminating in a junction point, a two-pole circuit breaker within the casing, a secondary transformer terminal for each of said junction points, a secondary circuit path from each of the junction points to the associated secondary transformer terminal and including one pole of the circuit breaker disposed for operation to interrupt the flow of current from the transformer, and temperature responsive means connected to be responsive to the current flowing in only one of the parallel-connected winding coils of a group disposed to operate the circuit breaker to interrupt the secondary circuit.

11. In combination, a single phase electrical transformer comprising a casing, a primary winding and a secondary winding within the casing, the secondary winding comprising a pair of groups of winding coils, each group comprising a plurality of the winding coils connected in parallel circuit relation and terminating in a junction point, a two-pole circuit breaker within the casing, a secondary transformer terminal for each of said junction points, a secondary circuit path from each of the junction points to the associated secondary transformer terminal and including one pole of the circuit breaker disposed for operation to interrupt the flow of current from the transformer, and temperature responsive means comprising a temperature responsive element for each group of the pair of groups of winding coils, each of the temperature responsive elements being connected in series circuit relation between one of the winding coils of the group associated therewith and the junction point of the group to be responsive to the current flowing in said one of the winding coils only to operate the circuit breaker to interrupt the second ary circuit.

FRED C. ROEDING. GERHARD M. STEIN.

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

UNITED STATES PATENTS Number Name Date 2,066,935 Hodnette Jan. 5, 1937 2,089,860 Rypinski Aug. 10, 1937 2,298,229 Putman et al Oct. 6, 1942 2,340,057 Hodnette Jan. 25, 1944 2,374,029 Maslin Apr. 17, 1945