US1947062A - Alternating current long distance line - Google Patents

Description

Feb. 13, 1934. R, RUDENBERG 1,947,062

ALTERNATING CURRENT LONG DISTANCE LINE Filed Feb. 8. 192@ INV E N TO R Re/'n ho/d fudenbefjg BY, M1/JM Patented Feb. 13, 1934 ALTERNATING CUPiRENT LONG DISTANCE INE Reinhold Rudenberg, Berlin-Grunewald, v Germany, assignor to Westinghouse Electric &

Manufacturing Company,

Pennsylvania a corporation of Application February 8, 1929. Serial No. 338,435, and in Germany December 21, 1928 9 Claims. (Cl. 172-246) My invention relates to improvements in alternating-current long-distance lines.

This application is an improvement on, and a a continuation-in-part of, my application Serial b No. 336,405, filed January 31, 1929, wherein the claims are directed to combinations lacking the ohmic line-voltage-drop compensator, to compensate, for the power exchanged at the regulating station, as subsequently described hereinafter.

Alternating-current long-distance lines experience disturbing phenomena primarily by reason of the action of the capacity and the self-induction, which generate charging wattless power and 5 inductive wattless power. Systems have been developed for compensating for these two wattless powers by the supply of external wattless power,

as far as they do not counteract each other inherently. The long distance line is then trav- 0 ersed substantially only by in-phase power current and behaves in a manner similar to a directcurrent line.

In such compensated long distance lines in which the eiiects of the above-mentioned main disturbing phenomena have been eliminated, there still remains a secondary disturbing phenomenon in the shape of the ohmic drop in the resistance of the line. This resistance drop is caused primarily by the substantially exactly inphase currents and, in long lines, brings about a considerable drop in the voltage between the power-generating station and the power-receiving station.

The principal object of my invention is to provide a regulating system comprising an element which is responsive directly to the real power withdrawn from the line at any intermediate point, or to the difference between the real power currents in the two line sections on opposite sides of an intermediate point, for the purpose of compensating for the ohmic voltage drops resulting from the .flow of the inphase power currents in the line sections, as will subsequently be explained in detail.

In the drawing aiiixed hereto and forming part of my specification, some embodiments of my invention are illustrated by way of example.

In the drawing Figs. 1 and 2 illustrate diagrammatically a long-distance line with two end stations and three intermediate stations,

Fig. 3 shows the vector diagram of a section of the line,

Fig. 4 shows the distribution of the wattless currents along all of the sections of the line,

Fig. 5 shows thevalue and the distribution of this wattless current at the various end stations and intermediate stations, and

Fig. 6 shows an embodiment of my improved system. f y

Referring to Figs. 1 and 2 of the drawing, I have shown, by way of example, the distribution of the active or in-phase current JW along the line. The rightand left-hand end stations are assumed to be feeding power into the line, and the three intermediate stations are assumed to be consuming power. A considerable ohmic voltage drop then occurs from the terminal feeding stations to the central consumer stations, and this ohmic drop may reverse its direction, if, for instance, one of the intermediate'stations feeds and one of the end stations consumes power.

According to my invention, this ohmic voltage drop of the active or in-phase power current is to be compensated by the inductive voltage of wattless or reactive currents, which are supplied from external sources and regulated artificially either in the line as a whole or in the individual line sections between the various stations.

Referring to the vector diagram of a line section in Fig. 3, the difference in voltage between two successive stations will be seen, the two voltages E1 and E2 differing from each other only by a relatively small phase angle, as given by wherein R indicates the resistance and wL the inductive reactance, JW the active or in-phase current and Jb the reactive or wattless current in the section of the line. To make the voltage dif,- ference between the stations disappear, it is necessary that a wattless current should flow in the line section of the value Jb= -ERZ J... 2)

In other words, the wattless current drop wLJb must be equal and opposite to the ohmic active current drop RJW.

Fig. 4 of the drawing shows the distribution of the wattless currents which are necessary for the compensation of the ohmic drops in all the sections of the long-distance line. Referring to this figure, it will be seen that the wattless currents along the entire line must have different values according to the distribution of the active currents in the line at any instant.

These wattless currents should be supplied to the line at the individual stations, preferably at the same stations at which the active current is CLI also introduced or discharged. In order that the wattless currents prescribed by Equation (2) may ow in both directions from each of the intermediate stations, it is necessary, according to Fig. 4, to supply, at each station, the difference between the wattless currents required in the adjoining right and left-hand sections, that is, an amount wherein Jwi and Jwz indicate the active currents in the adjoining line sections and Jws the difference between these two active or in-phase power currents, which gives the active power-component current drawn by the station itself.

In Fig. 5, the value and distribution of this wattless current is plotted at the various end and intermediate stations. It will be seen that the intermediate stations withdrawing active current must feed inductive wattless current into the line, while end stations feeding active current into the line must withdraw inductive wattless current, or, what is the same thing, must feed capacitive wattless current into the line. The synchronous machines at the end stations must, therefore, be underexcited.

According to my invention, the wattless-current component of each station, serving for the compensation of the ohmic drop, shall be so regulated, according to Equation (3), that it is at all times proportional to the active current of the station, with a proportionality factor determined by the ratio of the ohmic resistance and the inductance of the adjacent line sections. If such regulation is carried out automatically, the voltage of all the stations on the long distance line remains automatically adjusted accurately to a constant value.

According to my invention, an over-compensation of the ohmic voltage drop may also be easily obtained, if the component of wattless current Jb is chosen slightly larger than according to Equation (3). If, for instance, this component of wattless current of all or some of the stations is so regulated that it has double the value given by Equation (3), we obtain, instead of a voltage drop, a voltage rise, in direction of the flow of the active output. According to Equations (l) and (2), this rise in voltage would amount to My invention thus makes it possible for the longdistance line to be compensated or over-compensated to any desired extent.

If, in contrast with Fig. 3, the phase angle between two adjacent stations is of considerable size, the conditions become somewhat more complicated, but, even then, it is always possible to compensate or over-compensate for the ohmic voltage drop by an adequate regulation of the wattless current of each station.

Preferably, the regulation of the wattless-current component for the compensation or overcornpensation of the ohmic drop is carried out automatically. This may be done most simply by measuring the active in-phase line currents, or by comparison of the power output or input of the station with the voltage E by means of a wattmetric instrument, and exerting an additional iniiuence upon the other existing regulating apparatus which is normally provided for controlling either the wattless current or the voltage of the station, as the case may be. If, for instance, the station is one which has previously been so regulated that the balance of the various wattless powers resulting from the charging current, reactive drop and wattless-current regulating-devices connected to the line is represented by an indicator, for instance, according tc the equation as shown in elements 1, 2, 3 and 4 in Fig. 6, an additional force may be allowed to act upon the indicator, which corresponds to the voltampere product:-

if it is desired to obtain perfect compensation of the ohmic drop. For this purpose, the indicator, as shown in Fig. 6, may be fitted with an additional element 5 which is controlled by the voltage E and the in-phase or active power current Js of the station, according to Equation (5), with a proportionality factor which contains the ratio of resistance to inductance of the adjacent line sections. Since this ratio of resistance to inductance is generally a small figure, the additional element 5 in Fig. 6 generally acts with only a small additional torque and causes the wattless output of the station to rise by the value of the left-hand side of Equation (5).

By adding Equation (5) to the preceding equation We obtain wherein J s indicates the current which would have existed in the station if no provision had been made for ohmic compensation, and AJb is the additional wattless current for the ohmic compensation. The equation expressing the condition for complete compensation of all wattless outputs and voltage drops thus reads From this equation, it will be seen that the third member, for compensating the ohmic line-voltage drop resulting from the energy withdrawn from the line at the station, has the same sign as the two last members of the left-hand side, which express the inductive voltage drop on the line. On withdrawing more and more power from the line at the station, the wattless current in the line must, therefore, be reduced, by proper regulation of the second member of the Equation (7), in order to maintain the equation. When power is fed into the line, the sign of the ohmic member is reversed, while that of the inductive members remains the same.

The compensation of the ohmic voltage drops in the line and the regulation of the line voltage according to my invention is entirely independent of the length of the sections. The regulation of each individual station and of the line section connected to it is independent of the regulations carried out by the other stations. Even if any one station fails completely, the regulation of the others and, thus, the total ohmic compensation, remains completely intact. This originates from the fact that, according to the method described herein, only the wattless current in the stations is strengthened or weakened to such an extent that the compensating wattless currents in the adjacent line sections automatically adjust themselves correcly.

The value of the compensating member, according to my invention, that is, the third member of the Equation (7), usually amounts to a small percentage of the other members in the usual long-distance line having a high inductance. In cables, however, where the inductance is inconsiderable, this third member in Equation (7) may become even greater than the last two members which reiiect the influence of the inductive voltage drop. My invention is, therefore, of special importance for high-tension cable systems.

The essential feature of the mode of operation according to my invention is that the wattless current for the ohmic compensation, as expressed in Equation (3), or the corresponding wattless output, or volt-ampere capacity, as expressed in Equation (5), as shown in Fig. 3 of the drawing, operates on the regulation of synchronous condensers or other wattless-current generatingmeans.

Each of the members of Equation (7) can be represented by an element of the indicator, as shown in Fig. 6, and effects a corresponding adiustment of the station wattless current. If it is desired to eliminate one of the measuring elements in the indicator, the second and third members of the Equation (7) may be combined to It is, therefore, necessary to give such a combined measuring element a proportionality factor and an angular displacement, which are determined by the ratio of R and wL. In other words, the element 2 of the indicating device of Fig. 6 may be adjusted to satisfy Equation (8), and the element 5 may then be omitted.

If the individual sections of the line at both sides of a station have resistances and self-inductions of different values, so that their ratios R/wL vary, the combination of the active currents, if the ohmic Voltage drop is to be compensated, can no longer be carried out according to Equation (3). The compensating wattless current, according to Equation (2), now holds good for each line section separately. It is, therefore, now necessary to supply to the station a Wattless current of the value R R EAL): "(llEi COS 1-E2 COS (1)2) (10) For reproducing these quantities in the indicator.

the active currents flowing in the line sections of each station are preferably allowed to operate on separate wattmetric elements, while the torque is adapted to the ratio of the resistance to the inducance of each of the lines.

Various modifications and changes may be made without departing from the spirit and the scope of the invention, and I desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art.

I claim as my invention:

1. An alternating-current transmission line of the type having a substantial balance of the various wattless powers resulting from 'the chargingcurrent power (wCEZ), the reactive line drops E(-wLJ2) and the wattless-current powers l2(--EJS sin e) supplied thereto from external sources, characterized by regulating means for responding severally to the several quantities just indicated and correcting therefor so as to substantially maintain said balance, and additional control means for so modifying the externally supplied wattless-current powers 2(-EJS sin qb), in response to the in-phase-current powers E EJS cos e) supplied to or withdrawn from the line at various intermediate points so as to compensate for the difference between the corrective wattless currents required in the two line-sections meeting at any such intermediate point where power (EJs cos o) is supplied to or withdrawn from the line, to compensate for the line voltage resistance-drops caused by the vflow of in-phase currents in the several line-sections.

2. A long-distance high-voltage power-transmission system comprising: a line connected to power-supply and load circuits and extended beyond the normally inherent stability limits of distance for such a line so connected; and wattless-current generating-means intermediately connected to said line within said stability limits and having such rating and regulation as to be adequate to segregate and to maintain a substantial balance of the Various wattless powers resulting from the charging-current power (wCE), the reactive line drops 2(-wLJ2) and the Wattless-current powers 2)(--EJS sin qs) supplied thereto from said wattless-current generating means and from the power supply and load circuits, whereby such regulation is effective to maintain the stability of the system for rated through power-transmission along the line from no load to peak load, such line-regulation for through transmission being dominant over whatever local regulation is employed in power-supply or load circuits on the line, characterized by means responsive to the local in-phase power derived from or supplied to the line at one or more of said wattless-current generator stations for introducing an additional regulating effect on said wattless current.

3. An alternating-current transmission line, power-supply and load circuits connected thereto, wattless-current generating means intermediately connected to said line, and means for regulating said wattless-current generating means, characterized by the fact that said regulating means comprises means segregatively responsive to the in-phase power current withdrawn from or supplied to the line at any wattless-current station for causing the supply of a wattless-current component substantially proportional to said in-phase power current.

4. An alternating-current transmission line, power-supply and load circuits connected thereto, characterized by the fact that special regulating means segregatively responsive to the inphase power current are provided at one or more of the stations where material iii-phase power currents are taken from or supplied to the line, said special regulating means being operative to supply additional wattless current of such value that the ratio of additional wattless current to the in-phase power current of the station is subance to the inductance of said line.

5. An alternating-current transmission line. power-supply and load circuits connected thereto, including at least one intermediate station Where iii-phase power current is taken from or supplied to the line, compensating means for supplying regulable wattless currents at said intermediate station and control means segregatively operative to control said compensating means in such manner that the additional wattless current for compensating the ohmic voltage drop of the line is automatically regulated in response to the inphase power current of said intermediate station.

6. An alternating-current transmission line, power-supply and load circuits connected thereto, including at least one intermediate station where in-phase power current is taken from or supplied to the line, compensating means for supplyingregulable wattless currents at said intermediate sta-- tion and control means for regulating the wattless output of said intermediate station, characterized by having a control element segregatively operative to respond to a predetermined fraction of the iii-phase power of said station, said fraction being substantially equal to the ratio of resistance to the inductance of said line.

7. An alternating-current transmission line, power-supply and load circuits connected thereto, including at least one intermediate station where in-phase power current is taken from or supplied to the line, compensating means for supplying regulable wattless currents at said intermediate station and control means therefor including control means segregatlvely responsive, in effect, to the difference between the in-phase power-currents in the line on both sides of said intermediate station, the response to each of said power currents being substantially according to the ratio of the resistance to the inductance o! the corresponding branch of the line.

8. The invention, as defined in claim 1, characterized by a regulating means in which the inphase power regulating-means responding to (-EJ, cos (p) and the wattless power controlmeans responding to (-EJS sin fp) are combined into a common element of appropriately modined amplitude and phase angle.

9. The invention, as dened in claim 7, characterized by the fact that the line sections adjoining an intermediate station have unequal characteristics EJ; cos 45g),

n d wLI cos du, an cos 1,

R R EAL, EJ, cos alwLZ Where E is the voltage of the line and J1 and J2 1 are the respective currents in the line-sections.

REINHOLD RUDENBERG.

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