US1191627A - System for the prevention of electrolysis. - Google Patents

Description

J. B. TAYLOR.

SYSTEM FOR THE PREVENTION OF ELECTROLYSIS.

APPLICATION FILED JAN. 4' I915- Patented July 18, 1916.

UDUUUU I .M 9 ma m e B nn h o J witnessesi- Hi: Atto meg UNITED STATES PATENT OFFICE.

JOHN B. TAYLOR, OF SGHENECTADY, NEW YORK, ASSIGNOR TO GENERAL. ELECTRIC COMPANY, A. CORPORATION. OF NEW YORK.

SYSTEM. FOR THE PREVENTION OF ELECTROLYSIS.

I To all whom it mag] concern trolytic corrosion of earthed metallic structures adjacent the tracks.

Electric railway systems commonly utilize their rails as return conductors, but if the current is large the voltage 'drop therein becomes excessive, operating conditions are unsatisfactory, and part of the current is diverted as stray current through the ground, where it seeks neighboring earthed conductors of low resistance, such as water and gas pipes The flow of current in these plpes results in electrolytic corrosion at the joints ofthe pipes and at those points where,

- because of the1r relative potential, current leaves the pipes to return through the surrounding earth to the adjacent rails and the.

I generator. As is well understood, a considerable potential difi'erence may exist between remote points of the earths surface, and any such difference will be accentuated by the presence of such earthed conductors as the rails of an electric railway. Because of these potential difierences, it is imposslble to say that a conductor carefully earthed at any single point is at true earth potential more truly than a similar conductor at some other point. It should be theoretically possible, however, to determine.

the potential difference between any particular point and true earth by taking true earth asthe average of the potentials of a large number of remote points. For the purpose of the problem, it willundoubtedly be satisfactory to consider true earth as the potential of a point sufliciently remote from local distribution systems and similar disturbing influences so that it is practically Specification of Letters Patent.

Patented July 18, 1916.

Application filed January 4, 1915.. Serial No. 521.

unaffected thereby. With reference to this datum point or potential level, it will be found that both the rails and pipes will be at a lower potential at points near the power-house, and at a higher potential at pointsnear the end of the line. With reference to each other, the pipes will be 'at a higher potential than the adjacent earth and rails at points near the power-house, while at distant points the pipes will be negative to the adjacent earth and rails. It is, therefore, desirable to correct these conditions in such a way that the pipes shall be kept at the same potential as that of the adjacent earth, and also be kept at"true earth potential difference between different points in the pipes. If these results can be obtained, flow of current from pipes to rails and across pipe joints can be prevented.

Various methods have heretofore been proposed by means of which a partial correction is possible. If, for instance, the

pipes are kept at the same potential as the adjacent rails by bonding at frequent intervals, trouble will result from current leaving the pipes for earth return and from flow across the joints of the pipes. If both pos1- tive or outward and negative or return feeders are provided, leading from, the powerhouse to a remote point, then a booster may.

be inserted in the return feeder and excited from the positive feeders so that current will be diverted from the rails in an amount proportional to the load at that point.. At any event, this scheme presupposes that the return current, at any one point is proportional to the power supplied to that point, whereas in a complex system it isunlikely that such a relation will exist. It has also been proposed to insert a resistance in one or more of the return feeders of a system in order to equalize the drop therein. The

potential of the various points of connection of the return feeders to the rails is thereby equalized, and the potential difference between any two points is minimized. The successful operation of this arrange- .ment, however, depends on a distribution of the load substantially the same as that for which the feeder resistances are designed and on holding the negative bus bars below earth potential. Obviously, also, there must be an energy loss in these resistances.

The object of my invention is, then, to devise an arrangement applicable to electric railway systems, whereby these difliculties may be avoided and electrolysis practically eliminated.

Another object is to devise an arrangement whereby the conductivityof the rails may be fully utilized and return feeders avoided.

Still another object is to devise a system so controlled that the desired conditions are maintained regardless of load conditions.

I attain these results by dividing the track into a plurality of sections insulated from one another, interpolating a source of E. M.

between said insulated sections and controlling this E. M. F., by means of a regulator responsive to the potential difference between points in adjacent sections of the track so that the interpolated E. M. F. is essentially equal to the potential drop of the adjacent section, and that there is no difference of potential between the points where the regulator is attached.

One embodiment of my invention is illus trated in the accompanying drawing in Which- Figure l is a diagrammatic view representing a portion of an electric railway having my system applied thereto. Figs; 2 and 3 are diagrams showing the potential gradients of the various conductors before and after the application of my system to an electric railway.

In Fig. 1, a generator 10 is illustrated as having its positive terminal connected to a trolley 11, by means of which power is ap.

plied to cars, such as indicated at 12, and

the rail 13 is used as the return conductor and connected to the negative terminal of the generator. The rail is divided into sections 15, 16 and 17, of any desired length, by means of insulated joints. Buried in the ground near the rails is aline of pipes 18. A source of electromotive force is then interpolated in the rail to by-pass the insulated joints and assist the flow of current toward the generator. This source may take various forms, but, will conveniently be in the form of a dynamo-electric machine 20,

ordinarily termed a booster. This booster may be driven by means of a motor 21 supplied with power from the railway circuit, and may have its field separately excited from an exciter 22 mounted on the same shaft with the booster. As previously described, it is desired that the electromotive force interpolated by means of this booster I should be essentially equal to the drop in the adjacent rail sections, and that this relation shall hold, regardless of load conditions. I

lator comprising a magnet coil 31 responslve to the potential difference between remote points in two sections, such as the points a and b of the sections 15 and 16. This regulator is arranged to short-circuit a resistance 32 in circuit with the exciter field, by attracting a pivoted armature 33 against a, fixed contact when there is a potential difference between the points a and 6 large enough to energize the coil 31. The armature 33 is normally held away from the fixed contact by means of a spring until the coil 31 is energized to a predetermined strength. This arrangement 1s duplicated at each of the insulated joints between adjacent sections, and, obviously, the types of apparatus here shown are only one of several well-known arrangements which would be equally applicable.

In Fig. 2 I have illustrated by means of a diagram the conditions foundin a simple system with an evenly distributed load before the application of my system. In this diagram aswell as in Fig. 3, the ordinates represent voltages, and the zero point is ta (en as the potential of the negative terminal of the generator. The abscissae represent distances from the generator. gradient T may be taken to represent the The of the line, while the horizontal line T E is the datum level which I have termed true earth. The potential gradient R of the rails carrying the return current starts at the negative terminal of the generator,and theoretically maintains a constant slope to the extreme end of the line. At points remote from the generator any metallic earthed conductors, of which the commonest form is a pipe system, will be negative to the rails, while at points near the generator these pipes will be positive to the rails and to the surrounding earth. At the same tune rails and pipes is above the potential of true 'earth at points remote .from the generator,

and below the potential of true earth at points adjacent to the generator. The potential gradient P of the pipes in this simple case will also have a constant slope, since stray currents leaving the rails at remote points will be taken up by the pipes, and, passing through their length, will be delivered up to the rails at points near the power-house. Electrolytic corrosionwill, accordingl be caused at those points where the potential of the pipes is sufficiently above that of the rails to cause a flow of current between the two. i

If my system of prevention is now applied in this simple case, the resulting conditions will be illustrated by Fig. 3. The gradients T and T E will retain the same slopes .will be represented in the diagram as at zero volts. The gradient R representing condition in rail section 15, will have the same slope as the gradient R in Fig. 2. At the insulated joint between sections 15 and 16 I have interpolated an electromotive force ytions so that they will b'e correctly repre 'points in the pipe.

seen that there will be no stray currents of 13,, which: is generated by the corresponding booster 20, thus causing an abrupt change in the rail gradient, and which is here shown as bringing the potential of the near end of the next section down to a value approximately the same as that of the negative generator terminal. Proceeding with the analysis it will be seen that the rail gradient R will then be extended in a parallel direction to the gradient R for a distance corresponding to the section 16, Where another abrupt change will be caused by the interpolated electromotive force B as in the previous case. The diagram will be duplidated as many times as there are insulated joints and interpolated voltages thus giving the gradient R and the interpolated E. M. F. B Under these-conditions it will be found that the potential of the negative terminalof the generator will be nearer true earth potential, and that true earth potential will be approximately at the potential of the mid-point of any rail section. The result'is that the potential difi'erence between true earth and any point in the return rail is greatly minimized and that there is practically no potential difference between the pipe and true earth, and, consequently, no potential difi'erence between various It will, therefore, be

any magnitude flowing from the rails to the pipes, nor from the pipes to therails, and that there will be no flow of current across the pipe joints.

The regulator coil 31 is shown as connected to approximately the mid-points of the rail section, and from a comparison of Fig. 1 and Fig. 3 it will be seen that under ideal conditions there will be no potential difference across this coil, and hence no cur-' rent flow therein. If, however, the actual conditions of practice cause apotential difference to -exist,.then the resistance 32 will be short circuited, and-the-field current of the exciter and, of the booster will be increased. This will correspondingly increasethe interpolated voltage and restore. condisented by the dia ram in Fig. 3. This regulator will prefera lybe of the vibrating type and so designed that it will maintain a constant potential difier'ence between the points to which the coil 31 is connected. Obviously, some potential difference must existbefore the armature 33 can be attracted, but the magnitude of this potential will be deter-' mined by the design of the apparatus, and will approach closely the theoretical conditions which it is desired tomaintain. By means of interpolating voltages between the rail sections I am also enabled .to fully utilize the conductivity of the rail for the return current and to thereby avoid the use of expensive return feeders.

As will be readily understood, the conditions obtained in practice are socomplex that the diagrams here shown will never exactly represent the true state of afi'airs.

For all practical purposes, however, my

analysis is sulficient, and by the use of a regulator operated in the manner described any variation may be compensated. Although I have herein illustrated what I conceive to be apractical and desirable form of my invention, I realize that the same.

result can be obtained by other well known apparatus, and I, therefore, do not desire to be limited to the exact arrangement shown conductor divided into sections, a source of E. M. F. interpolated between two sections of said conductor, and means responsive to the difference in potential between fixed points in said conductor for regulating the E. M. F. of said source. v

2. In combination, a current carrying conductor divided into sections, a source of E.

M. F. interpolated between two sections of said conductor, and means for regulating the E. M. F. of said source so that the poten-- tial diflerence between fixed sections is minimized.

3. In combination, a current carrying conductor divided into sections, a source of points in two E. M. F. interpolated between two sections 3 of said conductor, and means for regulating stant potential difference between fixed points in two sections of the conductor. j

4. In combination, a current carrying conductor divided into sections, a source of" E. M. F. interpolated between-adjacent sec- .tions, and means for controlling said source in, response to the potential difference between substantially the\mid-points of said different potential than the adjacent earth,

means for minimlzingthe escape of current 11-5 the E. M. F. of said source to maintain a confrom said conductor to earth comprising a In witness whereof, I have hereunto set plurality of sources of E. M. F. interpolated my hand this 2nd day of J anuary; 1915.

in said conductor at intervals, and means JOHN B. TAYLOR. for regulating the E. M. F. of each source to Witnesses: 5 minimize the potential difference between all HELEN ORFORD,

points of said conductor. Y BENJAMIN B. HULL.

"It is hereby gertified that in. Lettera Pat'ehtj 1576f i,191.',627 granted Jul 18, 1916, upon the applieatidn ef John B. Taylor, of Schenectady Nevr- Y0rk,.-or an improvement in Systems for the'Prevention of Electrolysis, an error appears in theprintedspeeification requiring correetioliias 'fbllqvzez- Page 1 line 65, before the and; that the said Letters Pat ent should {be read, with thiefcerrect ion han am the eamemay ee hfo y n to the reeerd ofthe case in thePate ntsighed and get-a zed da efA ugust, 1 ,1 1, 1 16. c

i j w- LA I 4am W amend in Letters Patent No. 1,191,627;

I u 3, comma thf? Words 80 thmlhqll 110M501},

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