US2551696A - Transformer - Google Patents

Description

Patented May 8, 1951 TRANSFORMER Georges Ogurkowski, Zug, Switzerland, assignor to Landis & Gyr, A. G., a body corporate of Switzerland Application July .2, 1946, Serial No. 680,959 In Switzerland July 6, 1945 4 Claims.

This invention relates generally to circuit arrangements for use in combined powerandaudiofrequency network installations having a remote control feature using a single or one control frequency in the audio range for the purpose of obtainingsufiicient stability in the audio-frequency control voltage for actuating various relays such as receiving relays; and more specifically the invention is concerned with a decoupling or acceptor circuit or circuits in the above network supplied with either single or polyphase power, the respective circuits being adaptable for creating varied ranges of resistance therein at any suitable predetermined control frequency depending upon the ultimate amount of decoupling desired.

In remote-control installations with audio-frequency currents superimposed on the network current and in which the transmission of the control impulses takes place at only one frequency it is necessary that, throughout the network to be controlled, the voltage of the superimposed audio-frequency currents should be kept as uniform as possible. This is of particular importance in connection with the satisfactory functioning of the receivers, which require a definite minimum voltage for their actuation. Lowering of the audio-frequency voltage to any considerable degree must therefore be avoided. Raising of the voltage is equally undesirable. Such fluctuat ions of the voltage very soon give rise to an increased transmission load in individual portions of the network. Normally this again causes voltage drop in adjacent portions of the network, which for the reasons above mentioned is undesirable. Control-frequency voltages exceeding about 12% of the network voltage cause fluctuations of the light, which are especially unpleasant when the transmission of the control impulses is effected by impulses produced by means of keys. From this it follows that the ideal condition is to have a control voltage that is as constant as possible, can be set at the outset and is uniformly distributed throughout the entire network.

Swith components which are liable to cause increases in the audio-frequency voltage in heavy-current supply networks, include in particular, heavy-current condensers serving for phase improvement. These are partly concentratedattached directly to the terminals of the local transformersand, on the other hand, are very often decentralized, in large numbers, among consumers having inductive loads (motors, etc.) distributed over a large network.

These, in conjunction with series reactances, which are inevitable, being always present in the network, set up the aforesaid increased voltages. These are fairly high, especially when the network concerned is under a low load. The series reactances in question, alone and associated with the condensers, are the transformers and long overhead lines. 7

Therefore, the primary object of this invention is to provide circuit means to overcome all of the above problems. v

Another object of the invention is to provide decoupling circuits for the elimination of undesirable voltage fluctuations and transients due toremote control switching in a combined audiofrequency and power network.

I A further object of the invention is to provide decoupling circuits with its special apparatus components to substantially block the audio-signal control voltage of an electrical network having impulses of intelligence superposed thereon within a limited and predetermined circuit branch or branches depending on the number of decoupling circuits;

A still further object of the invention is to provide at least one decoupling circuit for each phase of a polyphase power circuit adapted to convey intelligence communications over an extensive network by remote control means without failure of relays incident thereto and without creatin voltage rises at undesired points in the network. v

Another object of the invention is to provide a circuit arrangement or arrangements for a combined communications and power network under the influence of a remotely controlled predetermined unvariable frequency signal for the purpose of facilitating unfailing operation of communication type relays or receivers.

Generally. speaking, this. invention contemplates stabilizing the voltages of a combined service network carrying both audio-frequency and power signals at points selected for control relays and receivers such as audio receivers or meters in a remotely controlled system without interfering either with the power demands upon such a network or creating voltage fluctuations in the pure power circuits and also so that these receivers are reliably operated without possibility of damage thereto under unusual or heavy sub,- scriber usages, the remotely controlled feature being limited to a single frequency in the audio range. This is accomplished by placing at such receiver installation points a specially characterized low-loss transformer paralleled with a condenser and paralleling this combination in parallel with the receiver and with the further limitation that the combined transformer and condenser be in series with a power consuming device or other voltage affecting devices, such as a motor in the power circuit or a pure condenser arrangement in the latter instance to be pro tected. In this invention the energizing reactance of the transformer forms the inductance of a parallel resonance circuit made up of this transformer and condenser. These elements are so chosen that the named circuit is tunable to the audio control frequency and hence any resonant resistance desired can be obtained by the proper selection of reactance values for these elements as will be shown hereinafter.

In cases where the part of the network which raises the network voltage is organized for com. plete decoupling, if desired, the resonant re= sistance is adjusted to such a high value that full decoupling is effected. The above resonant ciredit for convenience is called a decouplingcircuit and is also known as an acceptor circuit. Several additional problems present themselves in this network. Since 60 cycle energy must be transmitted over this network, the values of inductive resistance in the various decoupling circuits must be also as low as possible at this frequency.- Fur thermore, if the portion in question of the network has also to be controlled, the value of the resonant resistance must be adjusted at a lower value so that only a damping effect is produced in contrast to a substantially complete stop-off of the voltage associated with the remote control signal. Thus, in the latter instance the voltage fluctuations to the power consuming devices are not rapid and discernible while the voltage upon the concerned relay or receiver has been main tained within proper limits.

It is realized at this place in the subject gener= aliz'ation of the invention that the discussed decoupling circuit cannot be used directly in this simple form. Hence, in adapting the inventive concept to commercial condensers and transformers certain precautions must be taken as for instance making certain that the condenser demand is not too large. This problem can be oven collie by placing the condenser in parallel with the transformer on its high secondary sideand thereby also accomplishing a higher reflected combined condenser and secondary side trans former impedance at resonance at the primary side of the transformer which is in series with the load to be protected. Recognitionshould be made of the fact that the energizing reactance of the. transformer forms the inductance of the parallel circuit in the decoupling circuit. By a suitable selection of the transformation ratio, the size of the condenser and the: number of turns in the transformer windings, the resonant resistance can be varied within wide limits.

By this means, the. decoupling or acceptor cir= cuit can be adapted to suit any desired purpose. The transformer in question must have an iron core formed as herein described and separate primary and secondary windings. It must satisfy certain requirements in particular the audio frequency loss must be extremely small, the in evitable stray-field reactance-s must be kept down as low as possible and in addition a linear mag netization curve obtained. For the passage of the 60'- network current the lowest possible induct mice is desirable The maximum voltage drop should be not more than. 2% of the network voltage. This result isxobtained by reduction of the inductive losses. Moreover, the inductive voltage drop in decoupling generates at 60-, a voltage increase at the condenser. Since the condensers are extremely sensitive to increase of voltage, this value should be kept as low as possible.

In the accompanying drawing:

Figure 1 shows a normal parallel-resonance circuit;

Figure 2 shows a decoupling or acceptor circuit according to the invention;

Figure 3 shows a substitute circuit thereto;

Figure 4 shows a typical embodiment applied to an installation;

Figure 5 shows a typical embodiment of decoupling or acceptor circuit for a condenser battery; and

Figure 6 shows a typical embodiment of the decoupling or acceptor circuit transformer.

In order to fully comprehend the present invention certain mathematical analysis of the problem is required. Therefore, reference is first made to Figure l which shows a parallel circuit consisting of an inductance L and a capacity C whose values to produce resonance at a predeter mined frequency and having a certain combined resonant resistance are now to be determined.

At the resonant control frequency, the resonant.

resistance of this circuit is determined by the formula where ws'i zirfst and in denotes the control frequency'. It is thus evident that for a constant product L.C, the values L and C can themselves beselected as desired. s

The resonance resistance works out to:

is. thereby determined. From these, the values of- L and C themselves can be determined.

The above description is concerned with a single decoupling circuit per se and hence at. this point it is desirable to show how such a circuit or circuits are used in a network, installation by means of the representationin Figure 4.

In this installation several motors M1, M2 andv M3 in a decentralized arrangement containing several condenser groups such as K1, K2 and K3 respectively across the terminals of these motors, possibly for power factor improvement of the respective loads are wired to the three bus bars S2 which in turn are supplied with polyphase power from any suitable banks of transformers suchv as transformers Ti and T2. The trans,- foriners are shown directly connected to an ad= ditional 3-wire bus bar Si because somewhere between bus bars Si and S2, at least one receiver.

or any relay on each line is desired and since this calls for a one frequency remotely controlled relay of the audio-frequency range to be. associated with each receiver or meter, a decoupling circuit is necessary for each relay for the reasons advanced heretofore. In this particular installation decoupling circuits 2I are inserted in the three phases of the power network between bars S1 and S2 and the primary side 8 of each decoupling circuit is in parallel with a relay 22 or other audio-frequency device to be remotely operated. This installation is susceptible to a high rise in the control voltage at undesirable points including the locations for the receivers or relays 22 because the stray field reactance of the transformers T1 and T2 may be high enough to cause series resonance between the impedance ofthe transformers and the capacitance of the load on the network. Therefore, since also in this selected case the load condensers K1, K2 and K3 must be controlled, the resonant resistance of each of the decoupling circuits 21 should be made to have a relatively small value. It is to be understood that the inventive concept is not to be limited by the above disclosure in matters such as types of power loads and their distribution, numbers of phases of power and whether the respective phases are balanced, whether input transformers T1 and T2 are Y-Y connected, delta-Y connected or Y-delta connected, and number of relays.

In order to show an example in which a decoupling circuit is not necessary for each phase in a three phase power network incorporating the audio-frequency remote control feature, an installation showing a battery of condensers K as the power load is given in Figure 5. These condensers K are energized from the three phase power lines R, S and T upon the closing of a suitable switch S. With this type of loading the resonant resistance of the decoupling circuits 2I may be made to have a relatively high resistance so as to virtually block off the control voltage within the relay circuits 22, and relays may be inserted in only two phases between the switch S and the condenser groups K because the amplitude of the currents flowin through these decoupling circuits is the same since the characteristics of the load has been changed only in respect to phase. However, this phase unbalance can be disregarded since the decoupling effect is great or nearly complete and thus the resulting voltage in the re spective individual condensers due to the control current is extremely small. Hence, no sensible or observable voltage unbalance occurs in the complete 3-phases of the power network due to control operations on the communication end of the network.

The above described decoupling or acceptor circuit enables parts of the installation which disturb the stability of the voltage to be damped or stopped Off, a constant control voltage being thereby obtained throughout the network. This leads to a very considerable economy of energy in transmission and nevertheless ensures reliable operation of the receiving relay. Slight fluctuations are also obviated. A further indirect advantag consists in the suppression of disturbing harmonics in the vicinity of the control frequency. By using an iron core, the whole arrangement is made extremely compact, so that it can easily be incorporated with the mains of 'existing installations. The possibility of adaptation to all conditions of the network likely to occur (i. e. by a suitable selection of the windings, and of the condenser) is also accompanied by low cost of construction, an important point in favor of its general use in audio-frequency control installations.

In order that the transformer may answer the rigid requirements of its usage in the described resonant circuit called a decoupling circuit 2I, it must be designed for extremely small power losses, its flux density kept low and substantial saturation must not be reached as the latter would produce modulation of the audi-frequency under 60- energizing of the transformer, thereby reducing the decoupling effect and creating undesirable secondary phenomena caused by harmonics and the like. In order to keep the losses low, the total air gap must the distributed among numerous small gaps for the reason that when there are few air gaps each of large size, the lines of force issuing laterally from the ordinary sheet metal laminations produce eddy current losses. Subdividingthe air gap into many air gaps marked I2 in Figure 6 overcomes this difficulty. Another consideration in this transformer is the distribution of the reluctance therein as uniformly as possible. This calls for proportioning the yokes I3 to that of the cores II as shown in Figure 6. stray field also plays an important part in this special transformer it is maintained sufficiently small by winding the primary 8 and secondary I0 very close together on the left side of the core II with insulation IT in the form of a cylinder separating the primary 8 from the core and insulation I9 between the respective windings. In order to reduce the supplementary eddy-current losses, the parts such as fastening bolts I6 and clamping plates I4 and I5 and any other necessary structural members exposed to the audiofrequency field, must be of non-ferromagnetic material. Referring again to Figure 6, it is seen that the righthand portion of the core I I is composed of a plurality of stacked laminations labeled II and each stack is held as a unit separated from its adjacent one with a small air gap by means of vertical clamping plates I4 and bolts I6 threaded into or otherwise fastened to each stack II. It will be noted that the cross-section of each yoke I3 is similar to that of the cores II. The whole transformer arrangement being virtually a closed magnetic circuit with interruption of same from a dimensional standpoint only taking place at predetermined substantially short distance intervals on one side of the core, the right side, the magnetic reluctance of th circuit is remarkably low and stable.

Since many changes could be made in the above construction and many widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustration and not in a limiting sense.

What is claimed is:

1. In a decoupling circuit the subcombination of a transformer comprising two magnetic yokes, a right-hand magnetic core longitudinally interrupted at a plurality of substantially small uniform distances, a left-hand uninterrupted magnetic core, primary and secondary windings wound on said left core, said yokes and cores being interconnected to form a substantially closed magnetic circuit and having cross-sections of such proportion that 60 cycle current passed through said windings produces ampere turns associated with only slight saturation of said Since the cores, and said interruption of said right-hand: core producing air gaps conducive to linear uti-- lization of the whole magnetization curve.

2. In a decoupling circuit the subcombination of a transformer comprising at least two magnetic yokes, a first iron core including a plurality of stacked laminated material forming an air gap arrangement of numerous small air gaps uniformly distributed through and across said core, a second continuous iron core, means interconnecting said cores and yokes to form a substantially closed magnetic circuit, a primary winding and a secondary winding each being wound on said second core, the cross-section of any portion of the magnetic circuit being of such proportion that 60 cycle current passed through said windings produces ampere turns associated with only slight saturation of said magnetic circuit, whereby the leakage reactance of said transformer is minimized and controlled.

3. A transformer as claimed in claim 2 wherein the cross section of the yokes of said transformer are such that the yoke reluctance at GEORGES OGURKOWSKI.

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

UNITED STATES PATENTS Number Name Date 1,467,771 Alden Sept. 11, 1923 2,300,940 Lenehan Nov. 3, 1942 2,336,258 Kenefake Dec. 7, 1943 2,385,673 Woodworth Sept. 25, 1945 2,431,867 Galla Dec. 2, 1947 OTHER REFERENCES Boddie, Journal A. I. E. E., Jan. 1929, High- Frequency Currents, page 40.

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