US2398390A - System of mixing signal and power frequencies - Google Patents

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. April 16, 1946.

G. OGURKOWSKI SYSTEM OF MIXING SIGN AL AND POWER F REQUENCIES Filed Dec. 27, 1943 IN VEN TOR.

HTTORNE) "quency. large and costly condenser groups.

Patented Apr. 16, 1946 SYSTEM OF MIXING SIGNAL AND POWER FREQUENCIES Georges Ogurkowski, Zug, Switzerland, assignor toLandis&GyrA.G

Switlerland a body corporate of a Application December 21,1943, Serial a. 515,688

In Swltnerland December 3, 1942 4 Claims. (Cl. 172-281) Beat arrangement for foreign alternating currents by two synchronously. driven double-fed indilation-machines The superposition of signal alternating currents on power-current networks generally takes place by beat transformers, i. e. by transformers whose primary windings are connected in series to the line (current transformers). On the secondary winding the signal frequency is superposed, thus re-acting via the magnetic field upon the primary winding. This method is referred to as the so-called series-overlap. It is thereby essential that the large input to the distribution network does not re-act across the beat transformer upon the current source of the signal fre quency. This is brought about in its essentials by adiusting the coupling between the primary and secondary winding for the network frequency, whereas the signal frequencywhich as a rule is considerably higher-.-gets generally better transmitted, so that in the primary winding a tion of both frequencies takes place. It can be readily understood that thereby a compromise between the two requirements must be looked for, which is not always easy to find. A

' further objection appears in that this method involves big beat transformers. inasmuch as the superposition ought to occur centrally and that the method does not suit every remote control system.

Analogous to this method there exists a parallel overlap method. in which series resonance circuits are used, each phase thereof consisting of an inductance and a capacity in series-connection. Also in this case care must be taken to avoid the interaction of the power-current voltage upon the current source of the signal frequency. This is accomplished by bringing the series-resonance circuits properly in tune to the signal frequency. Nevertheless in this event, too,

there exists. on the one hand, a compromise of the-comparatively big share of the passingthrough-line-frequency energy and, on the other, the considerable resistance to the signal fre- In addition, the arrangement implies The invention relates to a, coupling method in which the aforementioned dr'awbdcks are no longer present. I

This is achieved in that two rigidly coupled induction machines of equal pole pair numbersdriven as to their synchronous speed by signal current, and having their rotor windings eiectricalb connected-are, at the stator end, each put on the power-current network to be superposed and to the current source of the signal frequency in' such a way, that the E. M. F. induced from the power current system into the first rotor due to its synchronous speed, is equal to zero,- that, on the other hand, the rotatin iield of signal frequency impressed on the second stator turns asynchronously with respect to the rotor, hence generating an E. M. F. of slip frequency, whose currents in turn re-act upon the first stator, thus inducing in the power-current system likewise an additional signal frequency.

The accompanying drawing shows two fundamental embodiments of the invention in diagrammatic representation.

Fig. 1 is a fundamental form of embodiment according to the parallel-overlap-method and Fig. 2 a fundamental form of embodiment according to the series-overlap method.

Referring to Fig. 1, the ordinal i represents a synchronous motor which, via shaft 4, mechanically drives the two asynchronous machines .2 and 3. For energizing the synchronous motor, the exciter arrangement I for this motor takes up the requisite D. C. line from the D. C. system 6 and carries it via suitable means I on to the synchronous motor. The stators of the synchronous motor and of the asynchronous machine 2 are on the power-current system with the ire quency 1, whereas the rotors of both asynchronous machines 2 and I are interconnected across slip rings 9, i0 and the electric. junction line H. The stator of the asynchronous machine 3 lies on network I! with the superposed frequency is. In Fig. 2 'the asynchronous machine 2 exhibits a three-phase winding in lieu of a standard staror mesh-connection, with the three phases separately branched off, i. e. led out.

Let it be assumed that all the machines are provided with an even number of pole pairs.

The action of the arrangement is then as follows: The aggregate is driven'by the synchronous motor I via a common shaft 4 and attains a number of revolutions which is given by resp. on

In the stator winding of the asynchronous machine 2, which is likewise connected up to the line or network 8 with the frequency h, a. rotary field is set up which is to turn in the same rotary direction of the rotor of the asynchronous machine 2. As in this case between rotor and rotating field no relative speed is present, there exists consequently no E. M. F. induced by this rotating field and the rotor is currentirec with respect to the frequency 11. Conversely, the superposed frequency In is impressed upon the stator of the asynchronous machine 1, whereby an electromagnetic field is established here rotating at inn ngs.

p p p (f2 Ill The thus obtained E. M. F. with the frequency It produces then in turn a rotating field in the rotor of the asynchronous machine 2 which relatively to the. rotor of this machine-rotates at the angular speed on. But as the rotor itself moves at the mechanical angular speed am, we obtain, by admitting a further identical direction of rotation between rotor and rotary field, an E. M. 1''. induced in the stator of the asynchronous machine I. which E. M. F. has a frequency In or an angular velocity mt (respectively) which is equal to at I @z= 2'+ ;(f: f1).+ i i= i that is to say, the E. M. 1". induced in the stator of the asynchronous machine 2 has the same frequency as that of the network I2.

Obviously, it is not absolutely necessary that the superposed frequency is precisely occurs in the line 8. Again, a frequency conversion may rather be provided in such a way, that in the line I a frequency different from f: occurs. This is accomplished in that the direction of the rotary field in the asynchronous machine I is so chosen, that the electromagnetic field turns contrariwise with respect to the rotary direction of the rotor. Thereby an increase in frequency already takes place which, then, is also transmitted via rotor and stator of the asynchronous machine 2. In the asynchronous machine I as well another frequency conversion may (once more) be brought about in the same way.

In Fig. 2 the invention is designed as seriesoverlap method. The arrangement of the aggreate and its drive remains in their essentials the same as that in .Pig. 1 with the sole exception that now in lieu of the standard staror meshconnection of the stator of the asynchronous machine 2, a three-phase winding is provided, whose phases are separately led out. These three phases are then suitably connected in series to the line and represent, so to say, the primary windings of the beat transformer.

It is understood that this winding must be proportloned to the flowing-through current of the line frequency, just as in Fig. 1 the stator winding must be dimensioned for the line voltage of the frequensy 11.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. A signal and'power frequency mixing system comprising a power frequency transmission line, a signal frequency circuit, a pair of similar, rigidly coupled frequency changers, said changers having wound rotors and wound stators, means for driving said coupled rotors at a speed synchronous with the power frequency,'means for impressing power frequency currents on the stator of one frequency changer, means for impressing signal frequency currents on the stator of the other frequency changer, and electrical connections between the rotors of the changers, the stator windings of said one frequency changer having the field rotating in the same direction as the rotor in synchronism therewith so that no power frequency currents are generated in the rotor, whereby currents are generated in the rotor of the other frequency changer, said cur-- rents being at a frequency different than the power or signal frequency with such currents being fed back to the rotor of the one frequency changer so that the stator of the one frequency changer has generated therein currents at a frequency different than the power frequency.

2. The system of claim 1 wherein the stator field of the other frequency changer is so connected that the field due to signal frequency currents rotates in the same direction as the rotor so that signal frequencies are impressed on the p wer line. i

3. The system of claim 1 wherein the stator windings of said one frequency changer are connected in series with the transmission line so that all power currents pass through the wind- 118s.

4. The system of claim 1 wherein the stator windings of said one frequency changer are con nected across the transmission line.

GEORGES OGURKOWSKI.

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