US2363891A - Electric circuit - Google Patents

Description

Nov. 28, 1944. s. MINNECI ELECTRIC CIRCUIT Filed Dec. 14, 1942 SOURCE Inventor: Salvatore Minneci,

His Attorney.

TO LOAD Patented Nov. 28, 1944 ELECTRIC CIRCUIT Salvatore Minneci, Pittsfield, Mass, assignor to General Electric Com New York pany, a corporation of Application December 14, 1942, Serial No. 468,940

6 Claims.

This invention relates to electric circuits and more particularly to improvements in voltage control for selectively interconnected power circuits.

,When a number of automatically-controlled voltage regulating transformers are operated in parallel, one or more of them is sometimes removed from service to save transformer losses during light load periods. At such times it is also customary to render the automatic voltage regulating means inactive so as further to decrease the losses and prevent unnecessary regulator operation. The result is that when such transformer is reconnected to the others its voltage may be suificiently different from that of the others to cause an excessive or objectionable circulating current to flow.

In accordance with this invention I provide a novel and simple time-controlled interlocksystem for insuring that the voltage of the incoming transformer is equalized with. that of the circuit to which it is to be connected before such reconnection can occur.

If the'volta'ge regulating transformers are automatically controlled through. individual line drop compensators, as for example in the circuits forming the subject matter of an application Serial No. 444 999, filed. May 2.9, 1.942, in the name of '1. 0. Lemma: (now Patent No. 2,323,716) and assigned to the assignee of the present application, and the power circuits of the regulating transformers are paralleled on their load side, the removal of one or" more units from service will cause a larger portion of the remaining load current to pass throughthe line drop compensators on the units left in service. Because the numerical value of the impedance between the regulating transformers and the load center on the power line to which the regulating transformers are connected in parallel does not change, the increased value of load current passing through the line drop compensators left in service will cause the regulating transformers to hold 5, volt age which is higher than it should be. This can be corrected by the energization of all the line drop compensat'ors to be independent of the number of units in service. One way to do this is characterized by special interconnections between the control circuits whereby any excess current tending to flow in the line drop compensators' in service is diverted therefrom through an auxiliary circuit which includes the line drop compensators not in service and it forms the subject matter of my application Serial No. 444,523, filed May 26,

1942 (now Patent No. 2,322,249) and assigned to the-assicnee of the present application.

- The present invention is especially well suited for use with my above-referred-to system because a continuous and proper energization of the line drop compensator oi the inactive unit or units makes unnecessary the direct measurement of the voltage of the circuit to which an unconnected unit is to be connected.

Not all systems involving a plurality of power circuits which supply a common load and in which at least one unit is sometimes removed from service during load conditions comprise parallel-connected power circuits. For example, three such circuits may comprise three single-phase load ratio control power transformers which are normally delta-connected. but which may be operated open-delta or V-connectedi by the removal of one transformer from service. Furthermore, voltage regulating transformers may be of many-different types, such as load ratio control power transformers whose power ratings are equal to the ratings of the circuits in which they are connected, load ratio control step voltage regulators which are usually autotransformers and whose power ratings are usually proportional to the range of. voltage regulation they produce, and induction' voltage regulators. In addition, there are generator Voltage regulators in cases where the power circuits are fed by individual dynamo-electric generators. My invention-is applicable to systems employing all such variations in interconnections and variations in vol-taee regulated translating devices.

An object of the invention. is to provide a new and improved electric circuit.

Another object of the invention is to provide an improved control system for interconnected power circuits having individual automatic voltage regulators.

A further object of the invention is to provide .anew and. improved system for equalizing the voltage of a circuit and a translating device prior to connecting them together.

The invention will be better understood. from the following description taken in connection with the accompanying drawing and its scope will be pointed out in. the appended. claims.

Referring now to the single figure of the accompanying drawing, which illustrates diagrammatically a preferred embodiment of the invention, I show therein a power system comprising three power circuits l, l and I. These circuits them are substantial duplicates so that the same reference numerals will be used to describe similar elements in the three circuits and they will be distinguished by prime and double-prime marks for identifying them with their associated circuits. These circuits are connected in parallel as by connecting them between a source or supply bus 2 and a'load bus 3. To the latter is connected a into a potential circuit which is energized by a potential transformer 8 connected across its associated power circuit and a current circuit which is energized by a main current transformer 9 connected in its associated power circuit.

' Included in each potential circuit is a main or primary control winding H] which is connected by any suitable and well known electromechanical system, shown as a reversible servo motor H, to control the operation of the voltage regulating means for its associated main circuit. Thus an increase in voltage across winding l causes the regulating transformer to decrease its voltage output and a decrease in voltage across the winding I0 causes the regulating transformer to increase its output voltage with the result that the automatic regulating system acts to maintain constant voltage.

For insuring stable operation of the regulators each one is provided with a so-called circulating current compensator in the form of a reactance transformer l3 whose secondary winding is connected in the potential circuit. This reactance transformer is characterized by having its core worked over a linear portion of its magnetization characteristic throughout the normal operation of the circuit. This is usually accomplished by providing the core with an air gap which also has the effect of greatly increasing the magnetizing current of its primary winding. The device isessentially a high magnetizing current reactor with respect to its primary circuit, and its secondary winding, therefore, has voltage which is directly proportional to the voltage drop in the reactor which constitutes its primary winding so that, in other words, the voltage of the secondary winding is substantially in quadrature with the current in its primary winding. v

By stable operation of the automatic regulater is meant operation which does not result in the regulators running to their extreme limits of operation except when main circuit voltage conditions require it. The reason that this might otherwise occur is that if the voltages of the transformers should for any reason become even slightly unequal, the higher voltage transformer will cause a circulating current to flow through the power circuits. This current is lagging with respect to the voltage of the high voltage circuit and leading with respect to the voltage of the low voltage circuit or circuits with the'result that the reactance voltage drop in the inductive portions of the circuits will tend to lower the voltage of the high voltage circuit and raise the voltage of the low voltage circuits in the'inherent action of the circuits to equalize their voltages. However, this inherent action is interfered with by the action of the automatic regulators, which will respond to the decrease in voltage caused by the circulating current in the high voltage circuit to raise its voltage still higher, whereas the automatic regulators in the lower voltage circuits will respond to the rise in voltage to cause the voltages of these circuits to be still further decreased. The result is that the regulators tend to get further and further apart thereby increasing still further the circulating current until the high voltage regulator has been run to its maximum voltage raising position and the low voltage regulators have been run to their maximum voltage lowering positions. Actually, under such conditions the circulating currents would be so high as to cause damage to the circuits and regulating transformers. However, by

- passing currents through the primary windings of the circulating current compensators which are proportional to the circulating currents in their associated power circuits, the circulating current compensators can be made to raise the voltage applied to the main control coil of the circuit whose regulator voltage is too high, thereby to cause this regulator to lower its voltage, and the opposite effect will be produced in the circuits having too low voltage with the result that the compensators automatically act to bring the regulators together, so to speak.

Also connected in each potential circuit is a line drop compensator l4 consisting of a reactance transformer similar in construction to the circulating current compensator and a rheostat, the secondary winding of the transformer and the resistance element of the rheostat being connected in series in the potential circuit. The purpose of this device is to compensate for the voltage drop in the load line 4 between each regulator and the load or load center on the circuit 4. The line has both reactance and resistance so that its line drop has both reactance and resistance components and the reactance and resistance elements of the line dropcompensator are so adjusted that they produce voltages in the potential circuit which are proportional to the reactance and resistance components of the line drop.

The current circuits of each regulator have a common conductor l5 to which a corresponding terminal of each of the main current transformers is connected. For separating the output current of each current transformer into its circulating and load components there are provided auxiliary current transformers I6 whose primary windings are connected respectively between the remaining terminal of each main current transformer and its associated line drop compensator. A terminal of each circulating current compensator I3 is connected to the terminal of the main current transformer of its associated power circuit which is also connected to the primary winding of the auxiliary current transformer l6 and all of the secondary windings of the auxiliary current transformers l6 are normally connected in series through conductors [1, the series circuit being completed through the common conductor The normal ratio or distribution of currents in the parallel power circuits may be anything desired. If they are equal, the main current transformers can haveequal ratios, whereas if they are unequal the ratios of the current transformers may be made such that with normal current distribution the secondary currents of all of the current transformers are equal. For

aecaser the sake" of simplicity it will be assumedthat the currents in the" three parallel circuits aremor it flows through their associated circulating-current compensators. However, as soon as any circulating currents come into existence they will add to the output current of'themain current transformer in one or more of the circuits and will subtract" from the load current in the remaining circuits with'the'result that the-total or average current in all' of the circuits remains unchanged. Consequently; the dilference' between the' load current in each circuit and the actual current therein will be equal to the circulatingcurrent. Whenithis. is a current excess it will be prevented :lromv flowing through the line drop compensator by the auxiliary current transformer 16 so it must pass through the circulating' current compensator for that particular circuit having an excess current. Allof the circulating' currentv compensators are joined by a common connection. 18 so that this. excess current. will flow through the common conductor I8 and will distribute. itself among the circulating current compensatorsassociated with the power circuits in which the total current is less. than thenorm'al current; that is to say, among the compensators forv the circuits in which the circulating current subtracts from the load current and willi'then return to the main current transformers for these circuits.

For providing additionalprotection againstcircula'tingicurrents a winding is. is connected in series with each circulating current compensator i1 so that it carries a current which is proportional to the circulating current in its associated circuit. This winding may be caused to operate any suitable auxiliary protective means, such as an alarm or auxiliary contacts for incapacitating the regu lators so that upon the occurrence of a predetermined maximum safe value of circulatin current the regulators will be positively prevented from going farther apart.

For insuring that each line drop compensator carries the same value of current regardless of the number of parallel circuits which are active or in service, each current. circuit is provided with a second auxiliary current transformer 20 whose primary winding is connected in series with the auxiliary current transformer. l6. These trans formers preferably have the same ratio as the transformer l6, namelya 1:1. ratio, and their second'ary windings are connected in series by means 'of conductors 2.], the series circuit being comits-secondary winding and likewise each auxiliary current transformer 20 i i'sprovided with a switch 25" for short-circuiting its secondary winding. In addition; switches 26 are provided for making andbreaking theenergizing circuits for the circuleti'ng' current-compensatorsa The circuit breaker S-is provided with aspring 21 for biasing it t'oward itsopen position and it is held in its closed position by alatch 28 operated by a1. tripping coil- 29. It is closed by a closing coil" 30': The-energization of the tripping coil 29 is underthe control of an opening or tripping switch 3 which maybe-manually'or automaticallyoperat'ed; and. similarly the primary control ofthe closing coil 30: is under the control of a closing switch 32 which may either be manually or automatically operated.

In order to; prevent closure of the. circuit breaker't before the regulating means has had a chance to make the voltage of thecircuit I: ubstantially equal t'othe voltage'of thecircuit 3; an auxi1iary-relay33 and a time-controlledclosin'g rel'ay 34 are interposed'between the closing switch 32 and the closing coil 30; The relay 33 is provided with-a normall'y openset of'seal-in contacts 3fi 'and with a set of normallyopen contacts 36 which when: closed provide the automaticvoltage regulating means IO- I I with control energy so that it may operate as intended: The time delay relay 34 base, set of delayed closing contacts 31 which control directly: the energization of. the closing coil 30 forthe circuit breaker 6'.

The circuit breaker 6 isalso provided with a set ofnormally open back contacts 38 and a set of normally closed back contacts- 39; the former being connected in the energizing circuit for the relays- 3'3 and 34 and the latter being connected in parallel with the contacts 36 of the relay 33;

The operation of" the illustrated embodi'mentof the invention is as follows: Assume that under a given load condition each of the parallel-connected' circuits carr es one unit of load current when all three of them are active or in service and that circuit l has-just been rendered inactive by the opening of its'ci'rcuit breaker 6. Under these conditions the various switches should be in the positions shown in the drawing in which switch 26 is open, switches-=26" and 26" are closed, switch 24 is closed, switches 24 and 24" are open, and switches 23, 23 and 23 are all closed. The operation can best be understood by follow:- ing the arrows, of which each long arrow'represents one-unit of load current and each short arrow represents one-half unit of load: current. As the total load current remains the same, it will now be redistributed so that 1 units flow through the secondary winding of each main current transformer 9 and 9". It is assumed for the time being that the voltages of circuits I and I are equal so that no circulating current flows in them. The 1% units of load current flowing mthe' secondary winding of each ofthe current transformers 9" and 9" must flow through the primary windings of the auxiliary current transformers l6 and "5-" respectively. This induces an equal 1- /2 units of current in the secondary winding of each of the auxiliary current transformer f6 and I6 and as these secondary windings are connected in series in a closed circuitwhich excludes the secondary winding of current transformer l6, because the closed switch 2'4 short-circuits it, these 1%; units merely circulate through the conductors IT and the common return" conductor [5; However, all of the 1 units of current cannot flow through the primary windings of the current transformers 20 and 20". This is because the secondary winding of the current transformer 20 is connected in series with the secondary windings of the current transformers 20' and 20". Thus if more than one unit of current tends to flow in the primary windings of the current transformers 20 or 20" the ame excess over one unit of current will flow in all of the series-connected secondary windings of the current transformers 20, 20 and 20", thus inducing an equal current in the primary winding of the current transformer 20 and this current can only return by flowing through the line drop compensator M or the secondary Winding of the main current transformer 9. Ordinarily, the impedance of the line drop compensator will be less than the impedance of the secondary winding of the current transformer 9 whose primary circuit is of course open-circuited, so that practically all of such excess current over unity would tend to flow through the line drop compensator, but the impedance of this device reflected through the current transformer 20 into the series connection of the secondary windings of the current transformers 20 and 20 is such as to cause some of the 1 /2 units of current to flow through the closed switches 23 and 23" and through the equalizer bus 22 and through the closed switch 23 and thence through the primary winding of the current transformer 20 and the line drop compensator l4. By reason of the 1:1 ratios of all of the auxiliary current transformers an exact balance will be attained when unit of current flows through each of the switches 23 and 23 and the remaining single unit of current flows on through the secondary windings of the current transformers 20 and 2 This is because the two /2 units of current through the switches 23 and 23" combine to form one unit of current which flows through the closed switch 23 and then through the primary winding of the current transformer and the line drop compensator I4. Consequently, it will be seen that the one unit of current which is induced in each of the secondary windings of the current transformers 20 and 20" can now flow through the series connection including the secondary winding of the current transformer 20 because its primary winding already carries one unit of current so that all of the windings of the auxiliary transformers 20 will now have the same single unit of current flow therein.

In tracing the arrows around through their circuits the 1 /2 units of current from the secondary windings of the current transformers I6 and the one unit of current from the secondary windings of the current transformers 20 combine to form 2%; units of current which flow from left to right beginning at the left-hand end of the common conductor I5. After the line drop compensator I4 is passed, the current becomes 3 /2 units because to the one unit of current from the line drop compensator I4 is added the 2% units of current already in the conductor I5. After the connection to the current transformer 9' is passed the /2 unit of current which flowed away from the current transformer 9' through the switch 23 is returned to it so that three units of current continue on toward the right but one unit of cur rent flows in the opposite direction from right to left between the line drop compensator I4 and the current transformer 9' so that a net current of two units fiows in this part of the return conductor. After the line drop compensator is passed the three units of current continue on until f iliary current transformer l6.

the connection to the current transformer 9" is reached. At this point the unit of current which left the current transformer 9" through the switch 23" is returned to the current transformer so that 2 /2 units of current continue on to the right but as one unit of current flows to the left from the line drop compensator I4 to the main current transformer 9", the net current in this part of the common conductor is 1 /2 units of current. After the line drop compensator I4" is passed the 2 units of current return and one unit flows into the secondary winding of the current transformer 20" and the remaining 1 /2 units flow in the secondary winding of the aux- It will thus be seen that the current in the line drop compensators is unchanged as a result of the elimination of the circuit I.

By reason of the exact balance of currents in the windings of all of the auxiliary current transformers, any circulating current which might exist in the circuits, I and I" could not flow through the auxiliary current transformers as this would disturb the balance of their currents so that all such circulating current would be forced through the switches 26 and 26" and through their associated circulating current compensators.

Although only three parallel circuits have been shown it should, of course, be understood that any greater number can be used, the connections being similar to the connections of the circuit I" with respect to the others; that is to say, as many additional units as desired may be con.- nected in between the end units I and I". Thus, if there were 71 units or circuits, at of which were interconnected or connected in parallel, there would need to be at least (n+ac) auxiliary current transformers. Thus, there would need to be 21: auxiliary current transformers for the a: parallel units as each of the parallel units would need two current transformers whereas the remaining (n-x) auxiliary current transformers would be distributed one to each of the inactive circuits. If unit current flowed in each of the circuits when m equalled n, then the current in each circuit would be proportional to and the excess current in each of the a: circuits over unity would be If now it becomes desirable or necessary to close the circuit I so as to connect the regulating transformer 5 in parallel with the other regulating transformers the closing switch 32 is m0- mentarily closed. This energizes the relays 33 and 34. The relay 33 immediately picks up and seals in through its contacts 35 and these contacts also serve to seal in the time delay relay 34. The immediate closure of the contacts 36 completes an energizing circuit for the servo motor I I which is under the control of the primary voltage sensitive relay I0. Consequently, the automatic voltage regulating means will immediately act to bring the voltage of the circuit I into substantial equality with the voltage of the circuits I' and I. This is because the line drop compensator 14 carries the same current as that carried by the 'line'drop compensators l4 and l4-'so that the'voltage relay I is effected by thesame-line drop compensator voltage as are therelays L0 and lll'f for the other two circuits. As it is possible that the regulating means for transformer 5 might be at one extreme limit of its travel and the regulators for the transformers 5' and 5" might be at the opposite extreme limits of their travel at the time the closing switch 32 is actuated, the time delay relay 34 delays the closing of its contacts 31 for a time at least equal to the time required for the regulating means to go from one extreme limit to the other. On the expiration of this time the contacts 31 close, thereby completing an energizing circuit for the closing winding 30 and causing the main circuit breaker 6 to be closed whereupon it latches in the usual manner. This causes the contacts 38 to open, thereby deenergizing the relays 33 and 34 and therefore deenergizing the closing winding 30. open by reason of the dropping out of the auxiliary relay 33 the contacts 39 on the circuit breaker 6 close, thereby continuing the energization of the regulator.

When it is desired to operate the illustrated circuit with all of the units in parallel, all of the switches 26 will be closed because circulating current can then flow in all of the units and therefore it is desirable and necessary to have their circulating current compensators all connected so that the sum of these circulating currents can add up to zero. All of the other switches 23, 24, and 25 are preferably left open, under which conditions the secondary windings of all of the transformers I6 will be connected in series and the secondary windings of all of the transformers will be connected in series and unit current will flow in all of them.

If it is desired to operate any one circuit alone and to render the other two inactive or opencircuited, the switches 23 and 26 of the unit which is to be operated alone are opened, its switches 24 and 25 are closed and all of the other switches remain in the positions for normal parallel operation.- With this connection it will be seen that the auxiliary current transformers of the single unit to be in service are short-circuited andthe circulating current compensator is open-circuited as of course there can be no circulating current when a single circuit is in operation. Consequently, all of the output current of the main current transformer can flow through the line drop compensator as all of th circuit current will be load current.

While there has been shown and described a particular embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and therefore it is aimed in the appended claims to cover all such changes and modifications 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, In combination, an energized electric power circuit, an electric translating device, automatic voltage regulating means for said device connected to be responsive to the voltage of said circuit, a circuit maker and breaker for selectively connecting said device to said circuit and disconnecting it therefrom, means controlled by the opening of said circuit maker and breaker for immediately incapacitating said voltage regu- At the same time that the contacts 36 latlngmeanaand timing means for energizing said voltage regulating means for a predetermined time prior to the closing of said circuit maker and breaker.

2. In combination, a normally energized electric power circuit, an electric translating device, automatic voltage regulating meansfor said device continuously responsive to the voltage of a point on said circuit, a circuit maker and breaker for selectively connecting said device to said circuit and disconnecting it therefrom, said circuit maker and breaker whenit is open rendering said voltage regulating means inoperative, means for initiating the closing of said circuit maker and breaker and for energizing said voltage regulating means, and timing means for delaying the closing of said circuit maker and breaker until said regulating means has had time substantially to equalise the voltage on both sides of said circuit maker and breaker.

3. In combination, a normally energized load circuit, an electric translating device, a circuit maker and breaker for selectively connecting said device to said circuit and disconnecting it therefrom, automatic voltage regulating means for said device which is continuously effectively responsive to the voltage of a point on said circuit, means for rendering said voltage regulating means inoperative when said circuit maker and breaker disconnects said device from said circuit, means for rendering said regulating means operative when said circuit and translating device are disconnected by said circuit maker and breaker, and means for preventing said circuit maker and breaker from connecting said device to said circuit until after said regulating means has been operative for a predetermined time.

4.111 combination, a load circuit, a plurality of translating devices, separate switches for connectin said devices to said circuit for parallel operation, separate automatic voltage regulators for said devices, separate line drop compensators for said regulators, means for continuously energizing all of said line drop compensators with the same percentage of the power current of said load circuit, means controlled by the opening of each of said switches for inactivating the regulator of the translating device it disconnects, means for activating any inactivated regulator, and means for preventing closure of any of said switches until the regulator of its associated translating device has been activated for a predetermined length of time.

5. In combination, a load circuit, a plurality of translating devices, separate switches for connecting said devices to said circuit for parallel operation, separate automatic voltage regulators for said devices, separate line drop compensators for said regulators, means for continuously energizing all of said line drop compensators with the same percentage of the power current of said load circuit, means controlled by the opening of each of said switches for inactivating the regulator of the translating device it disconnects,

means for activating any inactivated regulator,

and means for preventing closure of any of said switches until the regulator of its associated translating device has had time to complete any regulating action it may have started.

6. In combination, a plurality of supply circuits. for supplying power to a common load circuit in parallel, separate automatically controlled voltage regulating transformers in each of said supply circuits, separate switches for respectively opening and closing each of said supply circuits,

one of said switches is closed, means for rendering operative the voltage regulating action of each transformer before the switch in its circuit is closed, and means for delaying the closing 01' each switch until after the voltage regulating action of the transformer in its circuit has been rendered active.

SALVATORE MINNECI.

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