US2478257A - Compensatory electrical control circuit - Google Patents

Description

COMPENSAT ORY ELECTRICAL CONTROL CIRCUIT Filed Nov. 5, 1947 T0 Oil/1? SECTIONS FRoM Sauna:

I FEEDER- ifi COHPE VSATOKY CONT/70L 5U5- TOLOAD INVENTOR.

Haw/4K0 mew) Patented Aug. 9, 1949 coMrENsAroRY ELEo'rnIoA ooN'rno CIRCUIT Howard Farley, East Orange, N. J

Application November 5, 1947, Serial No. 784,136

2 la ms- This invention relates toelectrlcal control circuits and more; particularly tocircuits to be employed where automatic potential regulators are used upon a plurality of feeder circuits which are arranged to ultimately feed acommon load.

Circuit arrangements of this general type are often encountered, in networkpower distribution systems. Due to fluctuations, ofathe; load distribution, or sometimesv to accidental interruption of some one or more feeder; circuits, the current flow through'various, portions of thesystem is altered in value: thus cau ing; a corresponding change of potential values; at various points of the-network. V

The employment of; automatic potential regu lators located at a, Pluralityof; points, usually where branch feeders-depart fromthemain feeder lines, is familiar in theart. However; difficulties have arisen fromthispractice,,especlally under conditions, where two or more; such feeder circuits, each provided with. an individual and independent potentiahreglliator, are interconnected via a common load, circuit, which; latter capable of receiving energy simultaneously from all of such feeder circuits-., These difficulties owe their origin to, the fact thatv the interconnection just referred. to unavoidably sets up a circuit of the type known. as a loop circuit, through, which latter there may flowcirculatory currents havingrelatively great magnitudes. owing to the. fact that the interconnection conductors comprising the loop circuit arealmost, invariably of; relatively low impedance, whereby an unbalance of even relatively small, magnitude in the potentials appearing at differentpoi-nts; of the loop circuit will cause the flow of circulatory currents having such high values as to represent the loss of a very con side'rable amount oiiene t y, as w ll as. tending t negate the desired resultto, be obtained by the system, nam'el'y, a uniformpotential at various points thereof, since. the IR drops of potential caused by the circulatory. currents act. in oppfosition to the desired regulatory action.

The particular fault-Just described is further complicated by the manner in which the auto.- matic potential compensators react to the circu-v latory currents. These. last devices are well known in the art and include, as an integral part of their actuating mechanisms, relay type devices which are sensitive to the quantity of current flowing through the feeders. Such regulators are designed, not tokeep the potential constant at the exactipoint where they are situated, but rather at some point nearer the ultimate load, usually termed the centre of distribution, in order that the average potential, of the entire network may be kept as constant, as practicable. In order to accomplish this particular result, the compensators are deliberately arranged, to afford arising characteristic to the regulatory action, in such fashion that an increase of, load current will boost the potential at the. feeders, in order tocompensate for the increased line potential losses between the feeder and the load, due to increased current flow therebetween. Itis this particular element of the regulatory mechanism which is the worst sufferer from the presence of these circulatory currents, which may conveniently be termed parasitic currents, since the. mere presence of such parasitic current causes the regulator to boost the potential, there being ordinarily incorporated in the regulator no elements which are able to discriminate between the true load current and the parasitic current. Therefore the boosting of potential; will in turn again increase the parasitic current flow, and this last will react to cause further boost or potential, until extreme ly abnormal potential values, predicated upon purely fictitious load values are ultimately reached. There likewise flows from this sequence of reactions, the additional disadvantage that the various portions of the network no longer divide the load uniformly, but certain sections, in which the potential has been raised above the average by the hyper-compensatory action just described, will carry more than their share of load, and there may even result the triggering of one or more safety devices, such as circuit breakers or fuses, which last will make matters still worse by throwing the entire load upon the still connected portions of the feeding system. These latter may then repeat the self-propagating cycle of erroneous control, thereby leading to the cutting off of still other feeders and to still greate": overloading until eventually the entire system may fail.

Various remedies to prevent the occurrence of the above described undesired sesuence have been proposed. In one such proposed device, the portion of the regulator which responds to current flow has been endowed with discriminatory characteristics, so that it will respond only to the true load current, and not to the fictitious circulatory currents. However, this solution has not been satisfactory for many reasons. In this system, it is immediately found necessary to provide additional interconnecting circuits to comprise a so-called circulating compensatory network. Not only does this add greatly to the complexity of the system, and the cost thereof, but in turn this new interconnecting circuit becomes subject to malfunctioning, due to secondary causes, concerning which it is unnecessary here to amplify.

An amplification of the system just mentioned employs still more regulatory apparatus in order to minimize these last second magnitude defects, by which time the complexity and cost of the regulatory system have been excessively increased, and the possible sources of functional faults have been multiplied to an entirely disproportionate degree.

The present invention secures uniform potential control of network of the character specified, while at the same time keeping parasitic current flow at a minimum, without the need of the elaborate cross-regulatory circuits and apparatus demanded by the proposed systems just described. By the use of this invention it has been found possible to reduce the multiplicity of transformers, switches, and other elements of the hitherto proposed systems to a single metallic conductor, with the optional use of a single simple switch to remove the. regulatory device from the circuit, as is often highly desirable when manual switching of the network is to be performed, or when some portion thereof is subject to failure.

One object of this. invention is to provide a regulatory circuit of the type described, which shall be extremely simple, inexpensive and subject to substantially no operative troubles, since a single stationary conductor, carrying only a fractional percentage of the true load current, performs the entire regulatory'action.

, Another object of this inveition is to provide a new and improved regulatory system for interconnected power circuits having a multiplicity of potential regulators, in which "runaway cumulative over-regulation is completely avoided, and energy loss due to parasitic current flow is reduced to a negligible amount.

Still another purpose of thi invention is to provide a simple interconnection system for use with potential regulated networks, wherein an ancillary bus bar type of connection afiords complete equalization of potential control throughout the network, and entirely avoids the difficulties and dangers of over-regulation, or false regulation, at any point of the network.

Other purposes and advantages of this invention will be apparent to those skilled in the art from the. following description, and from the drawing annexed thereto.

The drawing is of a schematic nature and for simplicity and a clearer showing of the invention proper, certain elements which are well known in the regulator art are indicated diagrammatically, ince the physical construction thereof bears no essential relationship to the operation of thi invention. 7 f V The drawing shows a single phase main feeder line, supplyinga common load via three interconnecting feeder lines. It is to be understood that this is merely an isolated section of a typical network, wherein many more interconnecting lines may be used, without in any way changing the operation of this invention. Likewise it is to be understood that in the case of a polyphase distribution system, all the element of this invention are to be duplicated upon each phase of the system.

By actual operation of the system of this invention over an-extended period of time under various conditions, upon typical power networks, it has been found that it may be adapted for use upon any potential, frequency or number of phase commonly employed for power distribution. However for best operative characteristics, it has been found desirable that the total impedance of the feeder line, from the automatic regulator to the point where it is tied into the load line. should not be materially less than 5%. As far as known, this is the only limitation of the field of use of the'present invention. v

Reference is now made to the left hand one of the three distributing circuits shown in the drawing as transferring power from a main feeder line I to a single line 2, from which the load is tapped off, as indicated at 3. It is to be understood that the particular number of branch circuits shown is purely by way of example, and that a lesser or a greater number may be used without altering the functioning of the system.

A transformer 4, of the variable tap secondary type, is bridged across feeders I. One side of this transformer is shown as grounded, but it is to be understood that such grounding, while customary, is not essential to the operation of the invention. A motor 5, of the reversing type, is mechanically coupled, as indicated by dotted line 6, to the tap changer of transformer 4. The two windings i and 8 are to indicate in a schematic manner the two directions of'motor rotation, it being understood that the motor is stationary when neither winding is excited, and moves the tap changer to the left, for example, when winding 8 is excited, and to the right whenwinding 1 is excited. Motors of this type are commonly employed in potential regulators, and detailed description thereof is accordingly thought superfluous. Energy for the operation of the motor i derived from transformer 9, bridged across secondary leads It of transformer 4. The secondary of transformer 9 has one terminal connected to a control switch II, which allows the automatic-control action'to be suspended when desired, as for the reason previously mentioned. The other secondary terminal is connected to the common junction point of windings I and 8.- From switch I I the circuit proceeds to movable relay armature I3, which a1ter-' natively makes contact with stationary contact is or I4, thereby determining which one of windings I or 8 shall be excited, and consequently determining the direction of rotation of motor 5. The means to operate armature I 3 is diagrammatically indicated by a winding I6. It will be seen that when winding I6 is excited with energy sufficient to hold armature I3 in the position shown, against the retractile action of spring II, regulatory mo-.

tor 5 will remain quiescent. If the current through winding I6 be decreased, the armature. will be pulled to the left by the spring, and cause the motor to rotate in one direction, while if the winding current be increased the armature will travel to the right, thereby determining rotation of the motor in the opposite direction.

Power for operation of the relay assembly constituted by elements I3, I4, I5, I6 and I1, is derived from a plurality ofsources, in order to secure the desired combination of determinant factors to bring about the desired regulation. The determinant representing purely the potential of the secondary of transformer 4 is derived from a potential transformer I8, of which the primary winding I 9 is shunted directly across leads I 0. The primary and the secondary windings of transformer I8 are interconnected at one end of each winding, the grounded side, if a ground is used, and the unconnected end of the secondary 20 is connected to winding I6. of the relay. The

retumcircuitfrointhe' other endof "secondary to the other endofwinding t6 is made via a correnttransformer 21', of "which one terminal is c'onnc'ctedto the common point of interconnection 'ofthe-primaryand secondary windings of transformer l8. From the other'end ofourrent transformer '2!- the 'circuit passes through the portion of a substantially non-inductive winding 22, defined by the position-upon this last winding of a slider-'23. From the point of contact of-slider23 aparallel-current path through the lower portion of resistance 22 and the lowerportion of an inductive winding 24, up to'thepoint of-contact of another'slider 2 5, upon this last winding, and then backto thepoint'ofcommon interconnection of transformers l8 "and 21, is provided. *By this means'the lowrportions of both the resistive and the inductive windings are placed in series with one another, between the two secondary terminals of'transformer 2!. The potential which is available to operate the motor relay winding [6 is then determined not merelyby the potential of transformer l8, but by a potential which is a combination of this last mentioned potential and the potential available from" transformer? I, as modified by the combination inductive and noninductive shunt existing thereacross. In opera tion, the positions of sliders 23 and 25 are adjusted in accordance with the characteristics of the load connected to leads [0, as Well known in the art, until the net effect of current flow through the leg of leads ID constituting the primary of transformer 2| and the secondary winding characteristics, as modified by the shunt established, yield the desired potential boosting effect at a chosen distant point, as previously described.

Up to this point, all the elements described are well known in the art and are connected in a conventional fashion. As so connected they are subject to the difficulties already described, whereby currents circulate in parasitic fashion from one such potential control unit to another unit in the system, and thereby give false alterations of the net potential supplied to winding It, so that the potential of a feeder is raised above the correct value, usually in a cumulative fashion.

The elements of this invention proper are now described. From slider 23 a connection is made, preferably via a simple switch 26, to a compensatory control bus 21. Reference is now additionally made to the other branch feeder circuits of the drawing. Each of these units is substantially identical with the one just described, and similar reference numerals are employed to identify similar elements thereof. In each branch feeder circuit, the sliders 23, 23' and 23" are interconnected via the bus 21, the individual switches being used only when it is desired to shift load, add or remove a feeder circuit, or the like, or when for any other reason it is desired to suspend the compensatory action of this invention in an individual branch.

In the operation of this invention each potential regulator will respond exactly as before the addition of the compensatory bus, insofar as the potential derived from transformers I8, I8 and H! are concerned. However it is no longer possible for any one current transformer, as for example transformer 2|, to supply to the motor relay a current component differing from that supplied by any other similar current transformer in the system. This also brings about the result that instead of heavy parasitic currents circulating through the main feeders of the system and causing upsetting false responses of the individual regulators, by fictitious determinative potentials being induced in the secondary windingsof the various current transformers used to actuate the regulators, all the potentials thus derived will'be equalized by current flow along the compensatory bus bar 2?. It might seem that thislastcurrent flow would itself be a parasitic circulatory current, but upon analysis it can be seen that it differs from the parasitic current flow previously described in at least two important respects. In-the first place, the value of this current flow is so very low, it usually being only a small fraction of one per cent of the current flowing in the main power leads, that little power is wasted thereby, especially since the potentials found in the regulatory circuits are comparatively low, while the main feeders, and branch circuits may be of several thousand volts. Furthermore, this circulatory current is kept completely away from the main feeders, so that it can in no wise interfere with power passing through these latter.

Finally there is to be noted the extremely important distinction between the circulatory currents of 'this'system and those of prior art systems, that While circulatory current flow of the prior art exerted a vicious effect upon the desired regulatory action, in addition to being extremely wasteful of power, the cross-currents of the system of this invention perform the highly useful function of contributing to the desired regulatory action. For these reasons it is hardly possible truthfully to label the compensatory currents of this invention as parasitic, since they perform an extremely useful function and since the energy dissipated by such currents is of such a low order of magnitude that it does not ordinarily exceed such values as are considered reasonable and allowable for purposes of system potential control.

It has been found in practice that the degree of intercontrol afforded by the circuits of this invention is so nearly ideal that it is usually possible to switch into the system additional feeder circuits, provided with potential regulators, without the need of making extremely close manual adjustments of the potentials thereof, or of the positions of the sliders upon the compensating winding-s, as the compensatory bus currents of this invention will very quickly equalize conditions throughout the entire system, without permitting excessive current flow, which might actuate safety ancillaries connected thereto, such as circuit breakers or the like.

While there have been shown and described certain embodiments of the instant invention, it is to be understood that such are by way of example and not of limitation. Many modifications and extensions of the circuits here shown will be apparent to those skilled in the art, and the scope of this patent is accordingly limited only by the hereunto annexed claims.

Having fully described and set forth this invention, what is claimed and is desired to be secured by Letters Patent of the United States is:

1. An electrical network including a common load, a plurality of feeders supplying said load, a plurality of variable ratio transformers, one supplying each of said feeder-s, a potential and a current transformer for each feeder, and. responsive to both the potential developed by and the current flowing out of said transformer, a potential-regulatory relay actuated by the seriesconnected output of said potential and current transformers, said two transformers having directly and conductively series-connected secondaries; via a substantially resistive path to said potential-regulatory relay, and additional means for causing all said ratio varying means responsive to the current flowing out of said transformer to be actuated in accordance with the average current flowing in all said feeders, said last means comprising a single compensatory control bus conductively and directly connected to the terminal of each current transformer which feeds a respective relay via said resistive path, whereby current flow through said control bus causes actuation of all the relays according to the average current flow in all the plurality of feeder circuits.

2. An electrical distribution system including a plurality of alternating current power circuits, separate potential regulators, one in each circuit, for automatically maintaining the potential of all said circuits substantially uniform, said circuits being all connected to a common load so that inequality in the respective potentials causes a circulating current to flow in the system, a separate line drop compensator located in each circuit and connected to the corresponding potential regulator thereof, and means for energizing each line drop compensator by a current representing the average current in all said plurality of circuits, said means including in each circuit a potential and a current transformer and a potential-regulatory relay, said two transformers having directly and conductively seriesconnected secondaries, via a substantially resistive path to said potential-regulatory relay, and a single compensatory control bus conduc tively and directly connected to the terminal of each current transformer which feeds a respective relay via said resistive path, whereby current flow through said control bus causes actuation of all the relays according to the average current flow in all the plurality of feeder circuits.

HOWARD FARLEY.

REFERENCES CITED UNITED STATES PATENTS Name Date Minnecl June 22, 1943 Number

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