A Cooperative Electrolysis Survey in Louisville,KentuckyBY W. C. WHITE'

Non-member

Synopsis.-A cooperative electrolysis survey in the city of and indicated mitigation measures are given as typical examples.Louisville, Kentucky, under the direction of an electrolysis com- The advantages of cooperative action in a general electrolysis surveymittee is described. An analysis of a portion of the survey data are shown.

INTRODUCTORY utility of its prorata share of engineering, labor, tools,THE electrolysis problem has existed in the city of meters, circuits, and materials as agreed upon by the

Louisville probably as long as in any other city of general committee. This obviated the necessity forthe United States since Louisville was the third city special accounting and inter-billing among the various

in which street railways were electrically operated. Up utilities.to 1926, the method of attack had been largely upon the The technical committee prepared an outline of abasis of individual action, by each utility owning under- proposed test procedure which was endorsed by theground metallic structures, in an attempt to mitigate general committee and steps were taken to put it intospecific cases of electrolysis hazard. While these had operation. The first item in the outline of test pro-resulted in generally satisfactory conditions of the cedure called for a general check up of the various under-underground cable plants, they had not been as success- ground structures by the individual utilities in order toful with respect to water and gas pipes. The absence correct so far as possible all obviously undesirable orof complete electrolysis data covering the city of Louis- abnormal electrolysis conditions. This check up in-ville augmented the difficulty of reducing the hazard cluded on the part of the railway company a compre-to the latter structures. hensive track bond test of their entire system and the

It was realized that the best engineering solution repair of all bonds found defective; on the part of theof the electrolysis problem as affecting all utilities could cable owning companies investigations to make certainbe obtained onlv upon the basis of very complete data that all cables were properly cross bonded, that electri-covering the electrolysis condition of the affected struc- cal drainage connections were in satisfactory operatingtures and detailed information concerning the railway condition and that there were no undesirable metallicsystem, including those characteristics of the system contacts to other underground structures; on the partaffecting the magnitude and direction of stray return of the pipe owning utilities investigation of all knowncurrent. It was for these reasons that the Gas and or suspected electrical drainage connections to deter-Electric Company suggested a conference of all inter- mine which of these connections were in effectiveested utilities to consider the desirability and practica- operating condition.bility of cooperative action in the making of a compre- When the above work was completed, the technicalhensive study of the Louisville electrolysis situation committee started the field work of the general survey,and determining suitable measures for improving con- which in general comprised a potential survey, a cur-ditions generally. Such a meeting was held early in rent survey, over-all track drops and gradients, and soil1926 and attended by representatives of all interested resistivity tests.utilities including the City Water Department, the POTENTIAL SURVEYRailway Company and the Louisville Public Utilities A potential survey was made of the entire city, testsBureau. being made at more than 600 locations.The outcome of this conference was the formation of It is desired to emphasize the importance of a poten-

the Louisville Electrolysis Committee consisting of tial survey in the investigation of an electrolysis prob-executives representing each interested utility with lem. The potential survey is the qualitative indicationthe chief engineer of the Louisville Public Utilities of the condition of the various sub-surface structuresBureau as chairman. This committee appointed a at the point and at the time tests are made. Therefore,working or technical committee of engineers represent- for all data to be comparable, tests, in general, should being each utility and included a consulting electrolysis made under normal street railway load conditions, andengineer retained by the Gas and Electric Company. the potential relations of the various structures at eachThe expense of the investigation was prorated among test location measured simultaneously. The potentialthe interested utilities through the furnishing by each readings may be taken either with indicating or record-

1. Southern Bell Tel. &; Tel. Company, Atlanta, Georgia. in intuet.I h oivleivsiain uPresented at the Southern District Meeting No. 4, of the A. I. E. E., to both the number of structures involved at each test

Louisville, Kentucky, Novemrber 19-22, 1930. location and to the large area to be surveyed, it was269

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found advantageous to use recording instruments. the points where drainage may be most advantageouslyTwelve recording meters of the smoked chart type were applied; for instance a cable may be positive to earthmounted on a truck and suitable switching arrange- yet negative to rails, which would indicate some otherments provided for connecting these by flexible in- structure as the disturbing element. The use of watersulated conductors between various structures and pipes as a reference system provided for tie readingsbetween structures and earth (See Fig. 1). To assure which served as a check on the reliability of all readingsthat connections to the various structures were of low taken.resistance, provision was made for testing such connec- CURRET Stions with indicating meters and batteries. Six-hour CurRENTsURVEYclock movements were used. As the period of test at A current survey of sub-surface structures supple-each location was approximately 20 minutes, this per- ments the potential survey in determining probablemitted a full day's test of each particular structure at hazardous conditions; and furnishes valuable data forapproximately 10 locations to be recorded on a single consideration in the application of remedial measures.chart. A current survey of cable systems is a relatively

Test locations were selected approximately 1,000 ft. simple procedure and in a great many cases will indicateapart in the outlying areas and approximately 500 hazardous conditions where they would not otherwiseft. apart in the more congested areas, or in areas of be located. For example, the potential survey maypositive-to-rail potentials in the case of piping systems indicate safe conditions at the points of measurement,

while the current survey may show an abrupt changein the magnitude, or even a reversal, of the current inadjacent manholes such as to indicate hazardous con-ditions between the two manholes.

Current surveys of pipe systems are generally difficultand expensive to conduct unless suitable test stationshave been provided for this purpose, since the readingsrequire the exposure of a suitable length of pipe usuallyby excavation. For this reason current test stationsshould be installed on pipe systems, either when main-tenance work is being done on existing lines or duringthe installation of new lines, their proper locationhaving been previously determined by a study of thepil)e systems in conjunction with the railway system.Approximately 72 such test stations were installed

on the water and gas systems at Louisville and 24-hr.smoked chart records obtained of the current. Also

Fic. 1-TYPICAL TItUCK EQUIPPED FOR USE IN COOPF:RATIV' in the study of the problem numerous potential dropsEL1.:CTROLYSIS SIJRVEY

were taken between services for determining the direc-and positive-to-earth potentials in case of cable tion of the current.systems. OVER-ALL TRACK POTENTIAL DROPS AND TRACKThe criterion of electrolysis hazard to metallic sub- POTENTIAL GRADIENTS

surface structures is the potential thereof to immediately The magnitude of stray currents, in general, dependsadjacent earth. The best practical approximation of upon the magnitude of over-all track potential dropsthis in the case of lead sheathed cables is the measure- and track potential gradients. High over-all trackment of potentials to earth via the bottom of a manhole potential drops and track potential gradients resultor an adjacent spare duct. In the case of pipe systems, from long feeding distances with inadequate return cir-due to the fact that they are in such intimate contact cuit conductivity and heavy concentration of returnwith the earth that these values are relatively small current in the rails.and due to the usual inaccessibility of adjacent earth, A large number of over-all track potential drops andthe best practical index is the potential to trolley rail track potential gradients was made on the Louisvilleand other nearby structures. Railway system. The over-all drops were 24-hr.At each location, records were made of potential records and were made from various points of the track

differences between all structures and rail, between all system to the negative bus, or to the point of low poten-structures and water pipes, (the water system having tial in the case of insulated return feeder systems.been selected as a reference due to its being the most The potential gradient measurements were also madeextensive system), and between all cable systems and with recording instruments and covered periods from 30earth. It is the purpose of cable-to-rail readings to min. to one hr. under peak load conditions. Thesedetermine which structure is probably the disturbing data are not only necessary in the study of a generalelement in a particular location as well as to determine electrolysis problem but are of value to the railway

March 1931 WHITE: COOPERATIVE ELECTROLYSIS SURVEY 271

engineers in the design and maintenance of their nega- ANALYSIS OF DATA AND MITIGATIVE MEASUREStive feedersystem from the standpoint of railway econo- The technical committee arranged to meet once eachmies. In the design of a feeder system, the peak load week during the field survey, for the purpose of con-conditions are in general the determining factors. sidering the data as they were obtained and to inter-The obtaining of over-all track potential drop data change information as to the operation or rearrange-

would generally be difficult other than in a cooperative ments of any plants which might affect the electrolysisinvestigation where the telephone company can furnish situation.spare cable pairs to various locations to serve as volt- When sufficient data were obtained in any sectionmeter leads. These leads, of course, should be tested from which definite conclusions could be reached,each time use is made of them to insure reliable results. mitigative measures were recommended in order that

these might be applied as the survey progressed.SOIL RESISTIVITY TESTS While it will not be possible to go into the details

Soil resistivity tests were made of some 180 samples of this phase of the work some of the more importantand while there was a wide range in the resistance of points considered in the analysis of data and in thesome samples, it was found that for the most part the application of remedial measures may be mentioned.soil averaged about 5,000 ohm cm. In general this From various data obtained such as track drops andwould not be considered a high resistance soil and from gradients, drainage currents, and potential readings itthe fairly consistent results obtained it would appear was found that a very considerable improvement in thethat the potential measurements gave directly a fair electrolysis conditions could be made by beginning theindication of relative stray current interchange between operation of the Number 3 substation of the railwayaffected structures and that the resistance of the soildid not by itself account for the areas of high-or-lowpotential differences between structures.

ASSEMBLY OF TEST DATA

At the time potential or current tests were made atselected locations, a card was prepared giving the°number and location of the test point and cross refer-enced with the corresponding smoked chart records. /On the reverse side of this card was shown a diagramof the test point and the location of structures to whichconnections were made. This was done in order thatany test could be repeated with identical connections'at any time. At the conclusion of each day's test thesmoked chart records and cards were sent to the office |where the data on the smoked chart records wereaveraged and recorded on the cards. FIG. 2-ILLUSTRATION OF GRAPHICAL PRESENTATION OF DATAThose portions of the data capable of graphical

presentation were plotted on suitable maps. These company, one hour earlier in the morning and con-maps were skeleton maps of the street railway system. tinuing its operation until one hour later in the evening,The water and gas pipe potentials were plotted to scale and by operating the Number 2 substation for a 24using the railway track system as a base line. The hr. period instead of part time. This recommenda-ordinates of positive potentials were shown to the north tion was carried into effect.and east of tracks and negative potentials to the south From a study of the track drops and gradients it wasand west These ordinates were then connected with felt that some of these were excessive. Additionalstraight lines and the positive areas colored red and the substations, with the resultant shortening of feedingnegative areas blue. The cable data were plotted areas, were recommended as a means for reducingin a like manner using, however, duct runs as base lines the high over-all track drops and these are now beingand plotting the potentials of cables to rails and earth. considered.Over-all track potential drops and gradients were also Even where over-all track potentials are not of them-shown on the maps but the actual numerical values were selves excessive, unequal drops on long paralleling or

used. approximately paralleling lines may produce hazardousThis manner of presenting data is of advantage, electrolysis conditions. This is illustrated by the

especially in a cooperative study, as it furnishes a following case which also shows the necessity for com-composite picture of conditions and assists in determin- plete reliable data in the solution of the problem.ing the disturbing element in any particular location. In the Number 3 substation area there are three long

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paralleling lines, viz.: the Broadway, Madison and While reduction of stray current is of primary im-Market Street lines, with no cross lines for intercon- portance in mitigating electrolysis hazard to under-nection. The potential survey showed that positive ground structures, cable systems usually require, as apipe-to-rail potentials existed throughout the length supplementary measure, the application of a certainof the Madison Street line, which was the center line. amount of drainage for the reason that the corrosiveThe over-all track drops to the Number 3 substation action on lead is rapid and the sheath relatively thin.negative bus were approximately 9, 3, and 8 volts re- Fortunately a cable system lends itself very readily tospectively from Broadw'ay, Madison and Market drainage due to the continuity and good conductivityStreets (see Fig. 2). The Broadway and Market of the sheath. In general, cable drainage should be soStreet Lines were of older construction and heavily designed as to keep the cable system slightly negativeloaded while the Madison line was of new welded rails to earth.and lightly loaded. It was therefore evident that the It has generally been found that electrical drainagepositive potentials were due to shunting currents from is only a partially effective measure in the protection ofthe Broadway and Market lines to the lower potential pipe systems. With pipe systems a more satisfactoryline on Madison Street. The method which was recom- supplementary measure, to the limitation of stray cur-mended and carried out for correcting this condition rent in the earth, is the reduction of pipe system con-provided for additional negative feeders to the Broad- ductivity by the installation of insulating or highway and Market lines, insulating the negative bus in the resistance joints. While there may be some isolatedNumber 3 substation and installing resistance grids in cases where drainage would be beneficial, pipe drainagethe short feeder attached to rails near the junction of should be resorted to only after careful study and thethe Madison Street line. installation should be so made as to be readily accessible

These positive conditions upon the pipes had been for test purposes.known for a number of years but the absence of suf-ficient data made the engineering solution difficult. CONCLUSION

Considerable positive cable-to-earth potentials in In conclusion, it is worthy of note that in the conductthe downtown section were eliminated by equalizing of the general survey, of subsequent special tests, andpotentials through fused interconnections of the cable of all the work undertaken by the Technical Committee,systems. The railway cables were found to be heavily the active interest and cooperation of the representeddrained and it was recommended that these be brought utilities were continuously in evidence. In a largenearer earth potential by limiting the drainage currents. measure the results attained and the work accom-At one point it was found that more than 100 amperes plished were due to this interest and cooperation.was being drained from the power cables and that the Realizing that it would be a serious loss to the cooperat-telephone cables also required drainage at that point. ing utilities individually, and collectively if the benefitsUpon recommendation of the technical committee gained through this cooperation were allowed to lapse,these two cable systems were interconnected and it was the Technical Committee has continued in active exis-then found that a drainage current of approximately 35 tence and functions as a central clearing house for theamperes was sufficient to maintain both systems at a investigation of all matters relating to electrolysis in thesatisfactory negative potential to earth. city of Louisville.