IL28655A - Method and apparatus for influencing the output voltages of current supply installations - Google Patents

Description

l'gmnn ΒΗΙιπι · ιπΐ"Ί ·Π PATENT ATTORNEYS · D'D ID . ' 31111 OR. REINHOLD COHN |Π3 Τ>ΙΠΙ"Ί 'Π DR. MICHAEL COHN | Π 3. 1H 3'D -m ISRAEL SHACHTER B.Sc. Bog g¾ J .D 3 T D 3 III "J N T EU * File C| 27212 PATENTS AND DESIGNS ORDINANCE SPECIFICATION Method and apparatus for influencin the output voltages of current supply installations DIT npsoa1? ntsiyD A.G. FUR INDUSTRIELLE BLEKSRONIK AGIS LOSONB B.LOCARNO, incorporated under the Laws of Switzerland, of Losone, Switzerland. do hereby declare the nature of this invention and in what manner the same is -to be performed, to be particularly described and ascertained in and by the following statement:- ABSTRACT OF THE DISCLOSURE A method and apparatus for influencing or controlling the vectors of output voltages from a direct-current supply device feeding a multiconductor alternating-current transmission system. The total voltage vector for each conductor is generated from two partial voltage vectors. Control of the magnitude of the total voltage vector is effected by phase-shifting the partial voltage vectors, each partial voltage vector being phase-shifted through the same angular magnitude but in opposite angular direction. In this manner, the total voltage vector for each conductor is maintained in a constant phase position even during automatic regulation and in the presence of an asymmetrical load.

BACKGROUND OF THE INVENTION The present invention relates to an improved method of and apparatus for influencing or controlling the vectors of output voltages from a current supply installation or device during the presence of an asymmetrical load such as caused by at least one load or consumer connected through a two-conductor or multi-conductor transmission system with the ourrent supply device. The basic current supply device referred to above essentially consists of a direct-current source, control devices and static inverters which receive ignition pulses from the control devices.

Loads drawing relatively high power preferably receive their current supply through a polyphase system, for example a three-conductor transmission system. Such a system has a predetermined voltage and a particular frequency. VJhen loads of different voltage or different frequency requirements are connected to an existing supply system, corresponding converting means must be attached to the load. Such converting means are likewise required when a permanent current supply to polyphase loads is to be provided, for example by means of a battery, in the event of failure of the normal supply system or in the event of any other disturbances therein such as harmonics, switching surges, etc. These converting means are either rotary converters consisting of a generator and a motor, or static converters consisting of a direct-current source or a rectifier arrangement and Inverters. Such converters operate satisfactorily if a symmetrical load is' connected within the multi-conductor system* However, if an asymmetrical' load is present within the multiconductor system, i.e. if a different load is connected or disconnected between each conductor, an asymmetry of the angles present between the vectors occurs in relation to the external loading because of the appreciable internal impedances of the inverters. If differential loads, for example those presented by a radar apparatus or electrical laboratory apparatus or large-scale data-processing installations, are connected to the multiconductor system, costly regulating precautions must be taken, because such loads depend upon a satisfactory current supply with constant values of the polyphase relations ' despite any asymmetrical loading.

Accordingly, it is a primary object of the present invention to provide an improved method and apparatus wherein the voltage vectors for the Individual conductors of a multiconductor supply are maintained constant in their phase position in relation to one another despite asymmetrical loading. This constant phase position Is to be maintained even in automatic regulation.

Additionally, it is desired to ensure that the current supply of the instant invention can be connected where necessary in parallel operation to existing alternating-voltage supply systems or to other circuit arrangements according to the invention, while the frequencies of the output alternating voltages may be adjustable as desired and according to choice, depending upon the load requirements.

SUMMARY OF THE INVENTION The principle of a current supply system consisting of rectifiers and inverters for feeding supply conductors, the inverters receiving controlled by ed in British Patent ApyjJofffinn No. ^nnff fn «ri wnTn-mhnn n, -ιοΑ , and in Austrian Patent No. 257»7½.

Proceeding from this principle, the present inventive method and apparatus fulfills the aforementioned requirements and objects in that the inventive method and apparatus are characterized by the features that, the ignition impulses which are transmitted from one control device to an associated inverter are displaced by the phase angle + ψ/2 , and the ignition impulses transmitted from another control device to another associated inverter are displaced by the phase angle - /2. Both phase-displaced inverter outputs are combined to produce an output voltage for associated conductors. In this manner, the voltage vectors between the conductors of a multi-conductor system may be adjusted to a fixed phase relation to one another. This is particularly importan because otherwise the phase relation between conductors would change during regulation as a result of asymmetrical loading.

It is advantageous to maintain this phase relatio constant by this technique in many applications, for example, in the current supply of radar equipment constituting an asymmetrical loading, and fed with alternating voltage at 00 c/s. The circuit ar- rangement and method of the instant invention are also suitable for the current supply in aircraft and for the current supply ©f ground stations for air traffic. For measurement purposes in laboratories, a current supply at any variable frequency is often desired.

Alternatively, in accordance with the subject invention, the voltage vectors may be arbitrarily changed, or controlled, in their mutual phase relations. This control is desirable when, for example, an elliptical rotating field is to be present in a threes-conductor system instead of a circular rotating field, for the pur-pose of carrying out particular tests on a load such as synchronous or asynchronous motors, for example.

Additionally, a fine-stage speed control of an asynchronous or synchronous motor may be effected by means of the circuit arrangement according to the invention.

BRIEF DISCRIPTIOU OF THE DRAWINGS In the following, two embodiments of the invention will be more fully explained with reference t© the drawings, in which: Figure 1 illustrates a part ©f the circuit a#rnge- ment mentioned in the above patentsand- patont appllooi iow; Figures la, lb and lc show the vector diagrams of the individual conductor voltages in a three-conductor transmission system Figure 2 illustrates a circuit arrangement aee©rdi¾g to the invention for carrying out the inventive method; Figures 2a, 2b and 2c depict the vector diagrams of the individual conductor voltages in a transmission system and Figure 3 illustrates a further circuit arrangement for carrying out the inventive method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawings, it will be recognized that in Figure 1 an oscillator 1 is arranged in a control device 9.

Oscillator 1 controls a monostable multivibrator 2 which, via a Schmitt-trigger 3, acts upon a flip-flop circuit . The latter delivers control pulses to ignition circuits 7 » 8 and 10 , 11 which are electrically coupled with Inverters 5 and 6 respectively.

Controlled rectifiers 119, 126, 122 , 123 in the inverter 5 are ignit ed in pairs in accordance with the ignition impulses, so that due to the direct-current source 13» there results a rectangular or squarewave-shaped partial voltage E^. This voltage E^ is phase displaced by the aiigle with respect to the control impulse UQZ of the oscillator 1. The magnitude of this phase displacement is determined by the differential signal which differential amplifier 14 delivers to monostable multivibrator 2. The amplifier 1 is coupled with a load 149 and continually compares the reference voltage with the actual voltage at the load. The magnitude of the differential signal, and thus, the phase displacement of the voltage E^ with respect to the voltage ϋ is proportional to the deviation of the re-ference voltage from the actual voltage. The inverter 6 composed of controlled rectifiers 132 , 1 2, 135, 139 » is controlled by the ignit ion impulses from the ignition circuits 10, 11. The partial voltage Eg at the output of inverter 6 and produced from the direct-current voltage source 13 » is likewise of squarewave-shape but is not phase displaced with respect to the control impulses of the oscillator 1. With additive coupling of both of these partial voltages E-^, E2, for instance by means ©f transformers 1 3 , 1 4 at the outputs of the inverters 5» 6» there results a stepped voltage from which it is possible to form a sinusoidal voltage by means of, for instance, a subsequently connected filter arrangement. This alternating-current voltage appears across the conductors 150 and 151 of a two-conductor transmission system. This system is explained in greater detail in the aforementioned Austrian patent 257¾? 6, s© that only the essential details have been considered herein.

Figure la shows the vector Vtot of the sinusoidal alternating voltage for a two-conductor transmission system. The vector is obtained by vectorial addition of the two component voltage vectors E^, Eg, the vector having the phase angle in relation to the vector Eg. The voltage vector U^ot is at an angle in relation to the voltage vector' UQZ of the oscillator 1. In order that the voltage t may be maintained constant in its value with variable voltage conditions at the load 1^9» the angle of the component voltage is changed through the differential amplifier 14, the control unit 9 and the inverter 5· At the same time, however, the angle also changes. With a two-conductor arrangement, however, this is not critical. The disadvantage that the phase pi of the voltage vector U^.ot also changes on voltage regulation because of conditions at the load, takes effect only with a three-conductor transmission system and with asymmetrical loading.

For a better understanding, the three voltage vectors Utotl* Utot2 Utot3 Detween tne neutral conductor and the conductors 1, 2, 3 are shown in Figure lb. These vectors of the total voltage are at 120° to one another. The vector Utotl is composed of the component vectors E^, Eg^ of the two inverters acting on the conductor 1. The vector is obtained by vectorial addition of the two component voltages E^g, Egg. The latter component voltages are generated by the two inverters acting on the conductor 2. The vector υ¾0¾ is formed of the vectos E-j^, E^ of the two inverters acting on the conductor 3· Therefore, six inverters are present for the formation of the circular rotating field, the inverters acting in pairs on one c nductor. In each pair, only one* inverter can carry out the phase shift through the angle ^ , The voltage vectors E^, E12> E^ thus form the phase angles .^, <^2, j with their associated voltage vectors E21> E22, Eg^. With the symmetrical load assumed in Figure lb, These angles are = (?2 = (pj. Consequently, the angles β2, ^ between the vectors Utotl 2 3 of tlle indivi<*ual conductor voltages and the vectors of the oscillator voltages Uol» u02» Uo3* are e¾ual* Eaen pa r of inverters acting on one conductor is therefore constructed as illustrated in Figure 1. Consequently it comprises one oscillator and one control unit with striking circuits. The oscillators apply their control pulses at intervals of 120° to the multivibrator 2, so that a circular rotating field according to Figure lb with an angular velocity i is set up. The voltages between the individual conductors, which are also known as interlinked voltages, are equal in their value and in their angle to one another.

This is apparent from Figure lb if the peaks of the voltage vectors U¾0¾2» utot3 are joined together. This has not been done in the drawing i order not to Impair its clarity. The described conditions also remain constant on regulation in dependance upon symmetrical voltage changes at the load, because the angles 2, are changed in the same way. Consequently, the angles (¾2» ^3 are, always equal to one,another.

If an asymmetrical load, however, Is applied between the individual conductors in the three-conductor system, a vector diagram according to Figure lc is obtained, in which the vectos of the componen voltages Ej^* Bg^ between the ®&sSMo%or- 1 * the neutral eondiaf%&r, l^*. K^g- between, the conductor 2 and the neutral conductor, a¾d between the conductor 3 and the neutral c©k- ductor have been addejd in the same way therein to form the vectors U. .... t » ¾ . ~ ©f the total voltage existing in each conductor, totl* f'otZ In accordance with the asymmetrical loading of each conductor, the angle Figure 2 illustrates a circuit arrangement according t© the instant invention in which an oscillator 1 acts on two control units 9, 12. Each control unit is of like construction. Therefore* the same reference numerals have been chosen. The oscillato eon-tains a monostable multivibrator 2, a Sehmitt-trigger 3» «. flip-flop circuit 4, and two striking circuits 7, 8, 10, 11 in each' instance. The latter apply striking pulses to controllable; rectifiers 119, 126, 122, 123 in the inverter 5 and to controllable rectifiers 132» 142, 135» 139 the inverter 6. The inverters 5» 6 are connected to a direct-current source I3. Connected to the monostable multi,-vibrator 2 in the control unit 9, 12 is the differential amplifier' 14, which is connected to the load or loads 1 9. Depending upon the difference between, the desired and actual voltages at the load, the control pulses are phase-shifted in relation to the pulses of the oscillator 1 i each monostable multivibrator 2. The differential amplifier 14 so controls the two monostabl.e multivibrators 2 that the upper one applies control pulses shifted by the angle 90° + (p/2 and the lower one applies control pulses shifted thr©¾gl the angle 90° - /2 to the sequentially connected Schmltt-trlgger 3, the flip-flop circuit 4 and the striking circuits 4, 10. These striking circuits apply their striking pulses to the rectifiers 119» 126 in the inverter 5 and to the rectifiers 132 , 142 in the inverter 6. The other striking circuits 8, 11 apply striking pulses staggesred through I80 to the rectifiers 122, 123 in the inverter 5 and to the rectifiers 135» ^-39 the inverter 6 , in dependence upon the first-mentioned striking circuits. Therefore* both in the inverter 5 and . in the inverter 6, rectangular component voltages E^, Eg are pro?-duced from the direct-current source 13 » which are phase-shifted in relation to the control pulse in the oscillator 1 by the phase angle 90° + ψ/2 and 90° - (0/2... Each inverter has a transformer 1*1-3, 14-4 as its output. There is set up at the. transformer 143, the component voltage E-j^, and at the transformer 1^4, the component voltage Eg. For a better comparlsion, the voltage of the control pulses of the oscillator 1 has also been shown. Since the two component voltages E^, Eg are added together because of the series connection of the transformers 143, 144, a stepped total voltage is obtained between the conductor 1^1 and the neutral conductor 150. A sinusoidal conductor voltage is produced from the stepped voltage by a n©n- illustrated sequentially connected filter.

I Figure 2a, the voltage vector t for the conductor voltage between the conductor 151 and the neutral conductor 150 is shown. The t¾r© vectors of the component voltages E^, Eg of the inverters 5» 6 are arranged symmetrically in relation to the voltage vector U^o¾. tie vector of the component voltage E^ has a phase shift angle o£* 90° + ψ/2 and the vector of the component voltage E2 has a phase shift angle $ = 90° - ψ/2 in relation to the vector of the oscillator pulse UQ. Depending on the regulation by the differential amplifier 14, the vector of the component voltage is shifted through the angle O between 90° and 170°. The same takes place with the vector of the component voltage Eg. The angle lies between 90° and 10°. The angle between the vector of the conductor voltage U^Q^. and the vector of the oscillator voltage UQ, however, always remains constant at 90°» because the two vectors of the component voltages always change symmetrically in relation to the vector Figure 2b shows the vector diagram in a three-conductor transmission system with symmetrical loading in each conductor. The three-conductor transmission system is produced by triplicating the circuit arrangement of Figure 2. It is unnecessary for the oseilla-tor 1 to also be triplicated. Alternatively, a single oscillator 1 for the control units 9» 12 may be provided in triple construction. It is essential for the oscillator or oscillators to emit three control pulses at intervals of 120° with a fixed frequency of, for example, 0 c/s. In the case of a three-conductor system, three differential amplifiers are employed, so that the difference between the actual and desired voltages in each conductor is separately determined and utilized for the regulation. In the vector diagram of Figure 2b, the same reference numerals are employed for the component voltages E of the total voltages U^ofc and the oscillator pulse voltages UQ for the three conductors 1, 2 and 3 as in Figure lb. In accordance with the regulation by the differential amplifiers 1 , the angles O^, lf1 for the conductor 1 and the angles 02» for the conductor 2, and the angles OCy $j for the conductor 3 are so adjusted that the vector Utotl of the voltage in the conductor 1, the vector Uto¾2 of the voltage in the conductor 2, and the vector Utot3 °^ tle vo^-taSe in ^11® conductor 3 are always perpendicular to the associated vector of the oscillator voltage UQ^, UQ2» uo3* The absolute values of the vectors for the component voltages E and for the total voltages Uto¾ are the same for each conductor, he same applies to the interlinked voltages between two conductors. A circular rotating field is thus produced, which rotates at the angular velocity xl.

However, if an asymmetrical load is present in a three-conductor system constructed in accordance with the instant invention, the conditions In each conductor do not change despite the regulation by the differential amplifiers 1 . This is apparent from Figure 2c, in which a highly asymmetrical loading is shown. The same circuit arrangement is provided as has been briefly explained with reference to Figure 2b. it is thus a question of a triple arrangement of the circuit arrangement of Figure 2. For the vector diagram of Figure 2c, the same reference numerals have been chosen. In the case of the asymmetrical loading, the absolute values of the component voltage vectors E and their angles O and dif er considerably in the Individual conductors because of the automatic regulation by the differential amplifiers 1 . Nevertheless, the interlinked voltages between the individual vectors of the conductor voltages Utot are constai¾ *' iii' fe. the circuit arrangement according to- Figure 2 , therefore,, the great advantage is obtained' 'that the vol-tages remain eo s «n both in their angle and in their absolute. va¾ue •*: .;: regardless of the differing regulation in each conductor. r-" ≠, In the foregoing, reference has been made..to 'th&:? a.-t lation of the asymmetrical load through the di erential amplifiers I . The adjustment of . the frequency of the alternating voltage appearing at the output of the inverters has not been mentioned.' Of course, the oscillator 1 may apply its control pulses to the control unit with any desired repetition frequency, so thaf -loaii¾s such as radar equipment, for example, may be directly connected through a nmlticonduetor system. Since the oscillator 1 ©an continuously change its epartitio frequency, it is also possible to, control the speed of one or more asynchronous or synchronous gen--erators. .

In Figure 3 , there is shown a practical example of a circuit arrangement according t© the invention. There is denoted ~ by 15 a consumer or load which ma be connected to the circuit arrangement hrough a three-conductor transmission .system. ¾¾t.e. load represents, for example, a computer in which a particularly high asymmetrical loading is often present between the three conductors . The computer 15 may be connected both to the conductors R* , S», T' of the inverter pairs 17 » 13» 19 and to the conduc|i r R, S» T of an existing supply system 20 through a three-pole switch 16. This change-over is of advantage when the load 15 is to be · energized. Since the circuit-closing current may reaeji a value which is a number of times (even more than β times) the value of the rated current , the voltage, would drop by more than JQ during the circuit-closing time in the case of current supply from the inverter pairs 17, 18, 19. The computer, however, could comprise a supervisory devic wkich immediately cuts off the current suppl at a voltage ·.^6«¾#i|JL©n of about 30 provided only th¾j§ ^e ejd¾c i©ia lasts one e erie (fo example at 50 c/s or 20 ms.) of* longer. In order to avoid t¾is cut-off, the computer 15 is first connected to the supply s stem ,20. This is effected by closing of the switch 21. The change-0Yer switch 16 lies in the illustrated position at the contacts l6a, 16c, l6d.

In order to ensure a synchronous change-over, oscillator 27 is permanently connected to the conductor Ή of the su p y*'sys e¾ 20 and applies control pulses to the> requency multiplier 28 at a 1 repetition frequency of, for example 50 c/s. There is set up sat the output of this frequency multiplier the third harmonic oscillation at a frequency of 150 c/s which is applied to the three oscillators 1. These three oscillators are constructed in this example as a so-called ring counter. The outputs of the ring counter are connected to the control units 9, 12. The construction of the control units is apparent from Figure 2. There are set up at each of the three outputs, control pulses of 50 c/s with a mutual shift of 120®. The inverter pairs 17» 18, 19 thus receive strikin pulses of 50 c/s staggered at 120° and, as already described «ri%¾ reference to Figure 2, generate from the dlrect^current supply system 13» which may be a direct-current source 22 and/or a rectifier arrangement 23 supplied by an AC voltage source, the desired conductor Voltages and interlinked voltages according to Figure 2b. As already described with reference to Figure 2, there are provided at the outputs of the inverter pairs 17, 18, 19 transformers whose secondary windings are connected, for example, in star. These transformers as well as filters are indicated in Figure 3 only" by the references 17 j 18a, l It will now, be assumed ha the inverter pairs 1?, 18, 19 generate the desired voltage under no load. A phase discriminator situated between a conductor, for example R, of the supply system 20 and the corresponding conductor, for example R' of the circuit arrangement monitors whether the voltage vectors of the supply system and of the circuit arrangement have the same angle. If there is no agreement between the angles, the phase discriminator 24 applies a difference signal to the phase shifter 25, whereby the oscillator 2? is so regulated that the inverter pairs 17, 18, 19. generate at the conductors H* , S* , T* ■ conductor voltages and Interlinked voltages whose values and angles are the same as those of the conductor voltages and interlinked voltages at the conductors R, S, T of the supply system 20. When agreement, is reached, the zero discriminator 26 receives a signal from the phase discriminator 2 . The relay 29 receives current and energizes the relay ©oil of the change-over switch 16 by means of its contact. The change-over switch 16 then changes over from the supply system 20 to the inventive circuit arrangement. This change-over takes place without any Interruption, the conductors R, S, T of the supply system 20 being briefly connected together with the conductors R* , S*, T* of the circuit arrangement through the contacts l6e, 16a; 16b, l6f; l6c, l6d during the change-over action, whic connection may be brought about by means of a special contactor or by two independent contactors. As soon as the change-over switch lies on the contacts l6e, l6b, l6c, the computer 15 receives its current supply through the circuit arrangement and is thus independent ©f the mains supply system. The switch, 21 remains closed. The oscillator 27 continues to be synchronized with the suppl system 20 through the phase discriminator 2k and the phase shifter 25· In this case, one speaks of a mains-cominutated inverter. If the computer 15 must continue to be operated even during a sudden failure of the mains, it is readily possible to sever the oscillator 27 from its mains control and to construct it as a freely oscillating oscillator. In this case, one speaks o a self-commutating inverter, because the oscillator 27 applies its control pulses, to the striking circuits of the inverters 17» 18, 19 Independently of the mains. This possibility of a self-comautating inverter and thus the function thereof as a permanent current supply means is not, however, shown in detail in Figure 3· In any case, the differential amplifiers Ik regulate any asymmetrical load betx^een the conductors R* , S', T* , as already described in Figure 2» It is therefore immaterial whether the system functions as a mai s-commutated inverter or as a self-commutating inverter. The phase shifter 25 has a fixed phase shift of 90° in relation to the voltage vectors in the conductor R of the supply system 20. This is necessary because of the special voltage regulation in the circuit arrangement,.

It should now be apparent that the objects set forth at the outset of this specification have been successfully achieved.

Claims (7)

HAVING STOW particularly described and ascertained the nature of our said invention and in what manner the s^¾e is to be performed, we declare that what we claim is:

1. A method for influencing the vectors of output voltages of a current supply device in the presence of an asymmetrical load effected by at least one consumer connected to said current supply device by means of a multieonductqr transmission system, said current supply device being of the type comprising a direct-current voltage source connected to said conductors through inverters associated therewith and control devices for said inverters adapted to provide ignition iapulses thereto, said method comprising. displacing the ignition impulses delivered by one control device to an associated inverter by & phase angle of to provide one partial voltage vector; and displacing the ignition impulses delivered by another control device to another associated inverter by a phase angle of - /2 to provide a second partial vo'Jtage vector.

2. A method as defined in claim 1, further including the step of: combining said first and second partial voltage vectors to generate an output voltage vector of variable magnitude and constant phase.

3. · A power supplying apparatus for a multiconductor transmission system connected to a Idatd, said power supplying apparatus comprising: a source of direct-current; a plurality of inverter means for connecting said sources of direct-curren to said multiconductor trans-? mission system; control . means for said plurality of Inverters, said control means delivering ignition impulses to said inverters, each control means including a multivibrator; scillator means for providing control impulses to said multivibrators; and differential amplifier means for providing an error signal indicative f the difference between a desired load voltage and the actual load voltage, said differential amplifier being connected between said load and said multivibrators of said control means, said error signal causing a phase-shift of said ignition impulses of each control means relative to the control impulses of said oscillator means.

4. An apparatus as defined in. claim 3, wherein two inverter means are provided for each conductor pair of said multi-conductor transmission system; and wherein a control means is provided for each of said two inverter means associated with a conductor pair, the phase-shift of said ignition; impulses produced by one of said control means provided for one of said two inverter means being equal in angular magnitude and opposite in direction with respect to the phase-shift of said Ignition pulses produced by the other control means provided for the other of said two inverter means.

5. · An apparatus as defined in claim wherei each inverter means includes four controlled rectifiers arranged in two pairs; each jof said control means including two ignition circuits, each ignition circuit feeing connected to a respective one of said pairs of controlled rectifiers, each of said control means further including a monostable multivibrator connected through a Schmitt-trigger to a flip-flop.

6. An apparatus as defined in claim 3» further including a alternating current supply system selectively connectable t© said multiconductor transmission system and synchronizing means for synchronizing said power supplying apparatus with said alternating current supply system, -said synchronizing means including a phase discriminator connected between said alternating current supply system and the inverter means outputs to said multiconductor transmission system, a phase shifter connected to an output of said phase discriminator, a phase-shift controlled oscillator means connected to an output of said phase shifter, said phase-shift controlled oscillator means influencin said oscillator means for providing control impulses, and -a zero-phase discriminator means connected to said output of said phase discriminator for selectively connecting and disconnecting said alternating current suppl system with said multicondustor transmission system.

7.» A power supplying apparatus for a multiconductor transmission systein, said power s pplyi apparatus comprising: a source of direct-current; means for converting said direct-current into two alternating-current partial wave components for each of said conductors; means responsive to said two alternating-current partial wave components for generating a total wave component for each of said conductors; and means for varying the magnitude of said total wave component for each of said conductors, said means comprising phase-shift means for phase-shifting each of said two partial wave components through the same angular magnitude and to opposite angular directions. Dated this 19th day of September,1967