US2853628A - Parallel operation of transformers - Google Patents

Description

Sept. 23, 1958 H. E. PINNEY PARALLEL OPERATION OF TRANSFORMERS Filed May 18, 1956 [II/677757 Harold P/Ime Qg 6W/Q 72% United States Patent PARALLEL OPERATION OF TRANSFORMERS Harold E. Pinney, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application May 18, 1956, Serial No. 585,667

11 Claims. (Cl. 30724) This invention relates to automatic parallel operation of alternating current power supply systems, and more in particular to means for interconnecting a plurality of independent alternating current power supply systems such as voltage regulating transformer systems or other voltage regulating systems.

When two or more automatically controlled voltage regulating transformers such as load tap changing trans- Y formers are parallel connected, circulating currents often flow in the circuit clue to unequal secondary voltages of the transformers. These circulating currents do no useful work, and cause wasteful losses in the system. Various interconnecting circuits have been employed for correcting this condition automatically to reduce or entirely eliminate the circulating currents. Typical circuits of this type are disclosed in U. S. Patent No. 2,322,249 issued on June 22, 1943 on an application of S. Minneci and assigned to the present assignee and also in U. S. Patent No. 2,323,716 issued on July 6, 1943 on an application of T. C. Lennox and also assigned to the present assignee.

When regulating transformers are interconnected under load conditions, it is desirable that the voltages of the individual transformers be substantially equalized prior to the interconnection in order to avoid excessive momentary circulating current flow. Previously, equalizing means have been provided for the case where the transformers have a common load, the provision of such means being disclosed in U. S. Patent No. 2,363,891, which issued on November 28, 1944 on an application of S. Minneci assigned to the present assignee. In this type of equalizing system, the voltage of any idle unit that is to be put in service may be readily equalized with the common load voltage, since' the line drop compensator of the idle unit may be previously set at the same compensation value as the units which are in service.

A different problem arises, however, in the case where several regulating transformers having independent load circuits are to be interconnected. In this case, the settings of the line drop compensators of the individual units may be diiferent, and thereby direct interconnection of the circuits would result in an unequal current distribution between the several interconnected units. The line drop compensators of the power circuits are set to maintain constant predetermined voltages at certain points (load centers) of the independent load circuits, and the load centers of the power systems are generally at different locations so that the direct interconnection of load centers is not feasible, and therefore it has been found to be necessary to equalize the voltages of the systems at points other than the load centers.

It is therefore an object of this invention to provide a control system for interconnecting electrical power circuits having individual automatic voltage regulators and independent load circuits.

A further object of this invention is to provide means for equalizing the voltages of a number of electrical power circuits having individual automatic voltage regulators and independent load circuits, the equalizing ice means enabling the interconnection of the power circuits with the desired division of load current between the systems and without momentary excessive circulating currents.

Briefly stated, in accordance with one aspect .of my invention, 1 provide a system for interconnecting a plurality of electrical power circuits, such as voltage regulating transformer circuits, having separate independent load circuits. Each of the electrical power circuits has a separate automatic voltage regulating means connected to be responsive to the voltage of its respective power circuit. Circuit making and breaking means are provided for selectively interconnecting the load circuits of the power circuits. Each of the automatic voltage regulating means has a first line drop compensating means set for independent operation of the respective power circuits, and the second line drop compensating means set for interconnected operation of the power circuits. Means are provided for interconnecting the regulating circuits, the interconnecting means preferably being relays. The relays are operatively connected to disconnect the first line drop compensating means from their respective automatic voltage regulating means, connecting the second line drop compensating means to the respective voltage regulating means, and for energizing means for providing a predetermined ratio of currents in the second line drop compensating means. Time delay means are operatively connected to energize the circuit making and breaking means for interconnecting the load circuits a predetermined time after the second line drop compensating means have been connected to their respective automatic voltage regulating means.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject mat ter which I regard as my invention, it is believed that the invention will be better understood from the following description taken in connection with the accompanying drawing.

The single figure of the drawing is a circuit diagram illustrating the preferred embodiment of my invention as it may be applied to the interconnection of two voltage regulating transformer circuits.

Referring now to the drawing, therein is illustrated a regulating transformer system comprising two power circuits (and their associated voltage regulating and control equipment) 10 and 10'. Since these circuits are substantially identical, in order to reduce confusion, the same reference numerals will be employed to denote similar elements in the two circuits, the elements of the circuit 10' being distinguished by having prime marks associated therewith. Accordingly, where the circuits are identical, the detailed description will refer to only one of the circuits.

The two power circuits 10 and 10' are supplied by a common source of supply 11 across which are connected the primary windings of the regulating transformers 12 and 12'. The two power circuits have separate load circuits 13 and 13 which are connected across the secondary windings of the regulating transformers by pairs of leads 14 and 14 and 15 and 15. The leads 15 and 15' are connected to the tapped ends of the secondary windings of the regulating transformers, and the taps of the secondary windings are changed by means of tap changing control systems 16 and 16' of any suitable type, such as reversible motors 17 and 17' mechanically coupled to the tap changing switches of the regulating transformers.

A potential proportional to the output voltage of the regulating transformer 12 is provided by means of potential transformer 18 having its primary winding connected across the leads 14 and 15. The secondary winding of the potential transformer 18 is serially connected with the coil 19 of voltage regulating relay 20 and line drop compensating network 21. The contact 22 of the voltage regulating relay 2% are connected so that the tap changing motor control 16 is actuated to make tap changes on the regulating transformer to maintain a substantially constant voltage across the coil 19 of the voltage regulating relay 2t).

In order to compensate for line voltage drop and thus provide a constant load voltage, a current transformer 23, coupled to the lead 15 and providing a current proportional to the regulating transformer current, is serially connected with a portion of the line drop compensator circuit 21 as will be described in more detail in the following paragraphs.

The line drop compensator circuit 21 is comprised of a reactor 24 having windings 25, 26, 27 and a reactor 28 having windings 29 and 30. The winding 26 and 29 are connected on one end by way of normally open contacts 31 and normally closed contacts 32 respectively of relay 33 to the coil 19 of voltage regulating relay 2G. The other ends of the windings 26 and 29 are connected by way of potentiometers 35 and 36 respectively to the secondary winding of the potential transformer 13. One end of the winding 27 is connected to one side of the current transformer 23, and the other ends of the windings 27 and 27' are connected together by way of nor mally open contacts 37 of a time delay relay 38. The end of the current transformer 23 connected to the winding 27 is also connected by way of a primary winding load current transformer 40 and compensating current transformer 41 to a variable arm on the winding 25. The end of the winding is connected by way of the primary winding of an isolating transformer 42 to a variable arm on the winding 33. The end of the winding is connected to the arm of potentiometer 36. The secondary winding of the isolating transformer 42 is connected between the arm and one end of potentiometer 35. The other end of the current transformer 23 is connected to the junction between the secondary winding of the potential transformer 18 and the potentiometers and 36.

The junction between the primary windings of the load current transformer 49 and compensating current transformer 41 is connected by way of normally open contacts d5 of relay 33 to the junction between the primary windings of load current transformer 4t) and compensating current transformer d-lt'. One end of. each of the secondary windings of load current transformers 4t} and 4 3' and compensating current transformers 61 and 4-1 are joined together. The secondary windings of the compensating current transformers 41 and 41 are short circuited by normally closed contacts 46 of relay 33, and the secondary windings of load current transformers it? and are short circuited by normally closed contacts 47 of time delay relay 33.

A circuit breaker St) is provided having contacts 51 joining the leads 14- and 14' and contact 52 joining the leads 15 and 15'. A circuit breaker opening circuit 53 mechanically connected to open the contacts of the circuit breaker 5G is energized by way of normally closed contacts 54 of relay 33. A circuit 55 for closing the contacts of circuit breaker 50 is energized by way of normally open contacts 56 of time delay relay 38. The coil 57 of relay 33 is connected by way of a normally open push switch 59 to a source of electrical power 60. Holding contacts 61 are provided on the relay 33 for maintaining energization of the coil 57 in the conventional manner and for initiating the energization of a coil as of time delay relay 38. A normally closed push switch 63 is provided in circuit interrupting arrangement in the circuits of the windings 57 and 62 of relays 33 and 38 respectively.

When the two power circuits operate independently of each other, i. e., when the contacts of the circuit breaker H formers 50 are open, the coil 29 of reactor 28 is connected to the coil 19 of voltage regulating relay 20 by way of contacts 32 of relay 33, the secondary windings of the load current transformers 4t) and the compensating current transformer 41 are short circuited so that their primary windings present very low impedance to the flow of current, and the connection between the junctions of primary windings of transformers 4t) and 41, and 40 and 41' is open. The connection between the windings 27 and 27' of the line drop compensating circuit reactors is also open. The winding 25 and potentiometer 36 may be set for the desired line drop compensation of the independent circuit 13. It is obviously not necessary that the line drop compensation be the same for the two load circuits 13 and 13'.

When it is desired to interconnect the two systems, do pressing of the switch 59 energizes the coil 57 of relay 32, and coil 57 remains energized by way of contacts 61.

Upon energizing of the relay 33, contacts 45 establish a connection between the junction of the primary windings of transformers 4t) and 41 and the junction of the primary windings of transformers 4t) and 41'. The contacts 46 are open to remove the short circuits on the secondary windings of the compensating current trans- 41 and 41. Normally open contacts 31 establish a connection between the winding 26 of reactor 24 and the coil 19 of voltage regulating relay 20, and opening of the contacts 31 removes the connection between the winding 29 of reactor 28 and the coil 19 of voltage regulating relay 20. Similarly closing of contacts 31' establishes connection between the winding 26 of reactor 24' and the coil 19 of voltage regulating relay 20 and opening of contacts 32 removes connection between the winding 29 of reactor 28 and the coil 19 of the voltage regulating relay 20. The contacts 54 of relay 33 open to remove power from the circuit breaker opening circuit 53, but the circuit breaker does not close at this time.

The windings 25 and 25' and the otentiometers 35 and 35 are set so that the same line drop compensation is provided for each of the load circuits 13 and 13' respectively. Due to the connection of the compensating current transformers 41 and 41' and the connection established between the junctions of the primary windings of the load current transformers and compensating current transformers, the same current or a predetermined ratio of currents is caused to flow in the line drop compensators of the two power circuits, and the tap changing control systems of the two power circuits will be energized to maintain substantially the same output voltage. If the currents in the line drop compensators are initially not equal, or of a predetermined ratio, a portion of the current of the circuit having excess current is forced by action of the compensating current transformers to flow through the lead joining the junctions of the load current transformers and circulating current transformers. The arrows illustrated on the drawing indicate instantaneous current flow in and between the systems at this time if the current flowing in the system 10' is excessive.

After a predetermined period of time, the time delay relay 38 closes its contacts 56 to energize the circuit breaker closing circuit 53, opens the contacts 47 to remove the short circuit of the secondary windings of the load compensating transformers 40 and 4i), and closes the contacts 37 to establish a connection between the ends of reactor windings 27 and 27. The contacts 56 are preferably actuated before the contacts 47 and 3'7, so that the circuit breaker 53- establishes connection between the load circuits 13 and 13 prior to actuation of contacts 37 and 47.

After the contacts of the circuit breaker have closed, the contacts 37 and 47 complete the setting up of the interconnected circuits in the manner disclosed in the above-mentioned Minneci and Lennox patents. The removing of the short circuit on the secondary windings formers in a delta or open delta connection.

of the load current transformers 40 and 40' prevents circulating current from passing through the reactor windings 2 5 and 25' in order to prevent erroneous tap changes resulting from circulating current, and the establishing of the connection between the reactor windings 27 and 27 completes a path for circulating current so that circulating current flOWing through thewindings 27 and 27' provides the correct compensating effect in the event of unbalance of voltages of the two regulating transformers.

Theclosing of the contacts 45 effectively establishes a parallel connection between the serially connected primary winding of transformer 41, winding 25, winding 30, and potentiometer 36 and the serially connected primary winding of transformer 41, winding 25, winding 3%, and potentiometer 36.

The operation of the interconnecting system of my invention, stated in another manner, provides voltage regulating means for the power circuits that are arranged to maintain constant predetermined voltages at the load centers of the different load circuits when the systems are independently connected, but are arranged to establish substantially the same voltage at the points of the load circuits to be interconnected prior to the actual interconnection of the load circuits. After the circuits are interconnected the line drop compensators serve to maintain a constant predetermined voltage at some point in each of the load circuits, although this point may not be the same as the load centers for independent operation.

While the previous disclosure and drawing are directedv to a parallel connection between the load circuits of a pair of voltage regulating transformers, it will be obvious that only slight modification is necessary in order to apply the interconnected system to three or more power circuits, and also that the interconnection need not be parallel connections. For example, the same arrangement may be employed to interconnect the trans- It is obvious that thevoltage regulating transformers may be of many different types, such as load tap changing power transformers, auto-transformers, and induction voltage regulators. The power circuits may also be supplied by separate power sources.

It is also obvious that the line drop compensators for each power circuit be combined on the same core with minor changes in the switching circuits.

Itwill be understood, of course, that, while the form of the invention herein shown and described constitutes a preferred embodiment of my invention, it is not intendedherein to illustrate all of the possible equivalent forms or ramifications thereof. It will also be understood that the words employed are words of description rather than of limitation, and that various changes may be made without departing from the spirit or scope of the invention herein disclosed, and it is aimed in the appended claims to cover all such changes as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States'is:

1. A system for interconnecting a plurality of electrical power circuits having separate independent load circuits, said system comprising separate automatic voltage regulating means connected to each of said power circuits and continually responsive to the voltage of their respective circuits, circuit making and breaking means connected between said load circuits for selectively interconnecting said load circuits, each of said automatic voltage regulating means having first line drop compensating means for independent operation of said load circuits and second line drop compensator means for interconnected operation of said load circuits, and means for interconnecting said automatic voltage regulating means for intercom nected operation of said load circuits.

- 2. A'system for interconnecting a plurality of electrical power circuits having separate independent load circuits, said system comprising separate automatic voltage regulating means connected to each of said power circuits and continually responsive to the voltage of their respective circuits, circuit making and breaking means connected between said load circuits for selectively interconnecting said load circuits, each of said automatic voltage regulating means having first line drop compensating means for independent operation of said load circuits and second line drop compensating means for interconnected operation of said load circuits, and means for interconnecting said automatic voltage regulating means comprising means providing a predetermined ratio of current in said second line drop compensating means and time delay means for energizing said circuit making and breaking means to interconnect said load circuits.

3. A system for interconnecting a plurality of electrical power circuits having separate independent load circuits, said system comprising separate automatic voltage regulating means connected to each of said power circuits and continually responsive to the voltage of their respective power circuits, circuit making and breaking means connected between said load circuits for selectively interconnecting said load circuits, each of said automatic voltage regulating means having first line drop compensating means for independent operation of said load circuits and second line drop compensating means for interconnective operation of said load circuits, and timing means for interconnecting said automatic voltage regulating means for a predetermined time prior to the closing of said circuit making and breaking means.

4. A system for interconnecting a plurality of electrical power circuits having separate independent load circuits, said system comprising separate automatic voltage regulating means connected to each of said power circuits and continually responsive to the voltage of their respective power circuits, circuit making and breaking means connected between said load circuits for selectively interconnecting said load-circuits, each of said voltage regulating means having alternately connected first and second line drop compensating means, circuit making and breaking means for selectively interconnecting said automatic voltage regulating means comprising means for connecting said second line drop compensating means in their respective voltage regulating means, means for providing a predetermined ratio of currents through the second line drop compensating means, and time delay means operatively connected to energize said circuit making and breaking means for interconnecting said power circuits a predetermined time after said connecting means has connected said second line drop compensating means in their respective voltage regulating means.

5. A system for interconnecting a plurality of electrical power circuits having separate independent load circuits,-said system comprising separate automatic voltage regulating means connected to each of said power circuits and responsive to the voltage of their respective power circuits, circuit making and breaking means connected between said load circuits for selectively interconnecting said power circuits, each of said voltage regulating means having first and second line drop compensating means connected thereto alternately during independent and interconnected operation of said power circuits respectively, and means for interconnecting said automatic voltage regulating means comprising means for removing said first line drop compensating means and connecting said second line drop compenssting means to their respective voltage regulating means, means for providing a predetermined ratio of current through said second line drop compensating means, and time delay means operatively connected to energize said circuit making and breaking means to interconnect said load circuits a predetermined time after said second line drop compensating means have been connected to their respective voltage regulating means.

6. A system for interconnecting a plurality of electrical power circuits having separate independent load circuits, said system comprising separate automatic voltage regulating means connected to each of said power circuits and responsive to the voltage of their respective power circuits, circuit making and breaking means connected between said load circuits for selectively interconnecting said power circuits, each of said voltage regulating means having first and second line drop compensating means connected thereto alternately during independent and interconnected operation of said power circuits respectively, each of said voltage regulating means having transformer means having first windings serially connected with the respective line drop compensating means and second windings arranged to be short circuited during independent operation of said power circuits, and means for interconnecting said automatic voltage regulating means comprising means for removing said first line drop compensating means and connecting said second line drop compensating means to their respective voltage regulating means, means for removing the short circuits on said second windings and serially connecting said second windings, and time delay means operatively connected to energize said circuit making and breaking means to interconnect said load circuits a predetermined time after said second line drop compensating means have been connected to their respective voltage regulating means.

7. A system for interconnecting a plurality of electrical power circuits having separate independent load circuits, said system comprising separate automatic voltage regulating means connected to each of said power circuits and responsive to the voltage of their respective power circuits, circuit making and breaking means connected between said load circuits for selectively interconnecting said power circuits, each of said voltage regulating means having first and second line drop compensating means connected thereto alternately during independent and interconnected operation of said power circuits respectively, each of said voltage regulating means having transformer means having first windings serially connected with the respective line drop compensating means and second windings arranged to be short circuited during independent operation of said power circuits, and means for interconnecting said automatic voltage regulating means comprising means for removing said first line drop compensating means and connecting said second line drop compensating means to their respective regulating means, means for providing a predetermined ratio of currents between said second line drop compensating means comprising means for removing the short circuits on said second windings, serially connecting said second windings, and parallel connecting said serially connected second line drop compensation means and first windings, and time delay means operatively connected to energize said circuit making and breaking means to interconnect said load circuits a predetermined time after said second line drop compensating means have been connected to their respective voltage regulating means.

8. A system for interconnecting a plurality of regulating transformer circuits having separate load circuits, said system comprising separate automatic voltage regulating means connected to each of said transformer circuits and responsive to the voltage of their respective transformer circuits, circuit making and breaking means connected between said load circuits for selectively interconnecting said load circuits, each of said voltage regulating means having first and second line drop compensating means connected thereto alternately during independent and interconnected operation respectively of said transformer circuits, and means for interconnecting said automatic voltage regulating means comprising means for removing said first line drop compensating means and connecting said second line drop compensation means to their respective voltage regulating means, means for providing a predetermined ratio of current through said second line drop compensating means, and time delay means operatively connected to energize said circuit making and breaking means to interconnect said load circuits a predetermined time after said second line drop compensating means have been connected to their respective voltage regulating means.

9. A system for interconnecting a plurality of regulating transformer circuits having separate load circuits, said system comprising separate automatic voltage regulating means connected to each of said transformer circuits and responsive to the voltage of their respective transformer circuits, circuit making and breaking means connected between said load circuits for selectively interconnecting said load circuits, each of said voltage regulating means having first and second line drop compensating means connected thereto alternately during independent and interconnected operation respectively of said transformer circuits, and means for interconnecting said automatic voltage regulating means comprising first relay means operatively connected to disconnect said first line drop compensating means from their respective voltage regulating means, to connect said second line drop compensating means to their respective voltage regulating means, and to operatively connect means for providing a predetermined ratio of current through said second line drop compensating means, and time delay means connected to energize said circuit making and breaking means to interconnect said load circuits a predetermined time after said second line drop compensating means have been connected to their respective voltage regulating means.

10. A system for interconnecting a plurality of electrical power circuits, said system having independent load circuits comprising separate automatic voltage regulating means connected to each of said power circuits and continually responsive to the voltages of their respective power circuits, circuit making and breaking means connected between said load circuits for selectively interconnecting first predetermined points of said load circuits, and second predetermined points in said lead circuits, each of said voltage regulating means having line drop compensating means arranged to maintain first predetermined voltages at said second points when said lead circuits are independently operated and to establish second substantially the same voltages at said second points prior to the interconnection of said load circuits.

11. A system for interconnecting a plurality of electrical power circuits, said system having independent load circuits comprising separate automatic voltage regulating means connected to each of said power circuits and continually responsive to the voltages of their respective power circuits, circuit making and breaking means connected between said load circuits for selectively interconnecting first predetermined points of said load circuits, first line drop compensating means in said voltage regulating means to maintain constant first predetermined voltages at second predetermined points in said load circuits when said load circuits are independently operated, second line drop compensating means in said voltage regulating means to establish substantially the same voltage at said first predetermined points, and means to sclectively connect said line drop compensating means in their respective voltage regulating means.

References Cited in the file of this patent UNITED STATES PATENTS 1,743,771 Hall Jan. 14, 1930 2,128,802 Crary Aug. 30, 1938 2,322,249 Minneci June 22, 1943 2,447,644 Frisch Aug. 24, 1948 2,753,467 Pinney July 3, 1956

Images