.4 paper to be presented at the 25th annual conven­tion of the American Institute of Electrical En­gineers, Atlantic City, N. J., June 29-July 2, 1908.

Copyright 1908. By Α. I. Ε. E.

{Subject to final revision for the Transactions?)

CONDUCTOR R A I L M E A S U R E M E N T S

BY S. B . F O R T E N B A U G H

General. The Underground Electric Railways Company of London, Ltd . , control and operate electrically the Metropolitan District Railway and contingent lines, 56 miles of main-line double track, and three deep level " tube " railways, with con­nections, aggregating approximately 28 miles of double track. A detailed description of the electrification of the system, by the writer, appeared in the Street Railway Journal of March 4, 1905.

This company installed a " third " and " fourth " conductor rail on all of the above lines, both the conductor rails being of low carbon steel and supported on brown stoneware insula­tors. The insulators used in supporting the positive (outside) and negative (center) conductor rails are essentially of the same design on the individual roads, the top of the positive insulator being 1.5 in. higher than the negative. A malleable-iron cap and base is used on the District Railway insulators, the differ­ence in height of the positive and negative insulator being partly in the depth of the insulation and partly in the design of the base.

No base or cap is used with any of the insulators on the Tube railways. The top of the positive conductor rail is 10 in. and 10.5 in. above the top of the sleepers on the District and tube railways respectively. Figs . 1 to 4 inclusive. showr the type of insulators, conductor rails, spacing, etc., as installed on the district and tube railways.

The direct-current track-circuit signal system has been in­stalled on these roads and hence the desirability of not using the running rails as part of the main power circuit.

5 9 9

6 0 0 FORT EN Β A UGH: CONDUCTOR RAILS [ J u n e 2 9

I v E A K A G E AND I N S U L A T I O N M E A S U R E M E N T S

Metropolitan District Railway. An extended series of prelim­inary measurements and tests were made on the Hounslow and Putney section of the District Railway early in 1905 with a view of trying to account for the comparatively low insulation resistance of the negative conductor rail. These tests were made during the constructional period; that is, before the intro­duction of commercial electric trains but with the regular steam trains in daily commercial service, and the insulation of the conductor rails was therefore more or less of a variable quantity and subject to the temporary changes and conditions incidental to such work.

The positive (outside) conductor rail, particularly at the

F I G . 1 F I G . 2 P o s i t i v e a n d n e g a t i v e i n s u l a t o r s — D i s t r i c t R a i l w a y

stations, wTas heavily coated with grease from the steam trains and this, together with loose ballast, dirt, etc., made it very difficult and virtually impossible to maintain good insulation during these tests.

The results of these preliminary measurements were very erratic, for the reasons just given, and are therefore not in­cluded in this paper. They plainly indicated, however, the existence of the peculiar phenomena observed on the tube rail­ways where the conditions were much more favorable for the perfectly definite and consistent observations given herewith.

The observations given in Table 1 were made in January , 1906, and show the variation in potential between conductor rails and earth from day to day. These measurements were made on the main line of the District Railway at Earls Court,

1 9 0 8 ] FORTENBAUGH: CONDUCTOR RAILS 6 0 1

the electric trains having been in commercial service since Ju ly 1, 1905.

All sections of the road are tied together and cross-bonded through the sub-station bus-bars under normal operating con­ditions, and these results are therefore representative of the conditions existing over the entire District Railway system, collectively considered. The continuously bonded running rail was used as the earth connection for these measurements.

T A B L E I . — L I N E V O L T A G E 5 8 0

Vol t s be tween e a r t h a n d

D a t e — 1 9 U 6 T i m e P o s i t i v e N e g a t i v e R e m a r k s

J a n . 8 2 .15 p . m . 530 50 G r o u n d v e r y d a m p . " 8 4 . 3 5 " 5 1 2 6 8 « « u

" 9 4 .50 " 5 0 0 8 0 G r o u n d v e r y wet . " 10 10 .00 a . m . 5 2 9 51 F i n e . " 10 5.30 p . m . 5 1 2 68 F i n e a n d d r y . " 12 1 1 . 0 0 a . m . 510 70 F i n e , g r o u n d d a m p . " 12 5 . 5 0 p . m . 5 1 2 68 « « u

" 13 11.00 a . m . 4 9 0 90 G r o u n d v e r y wet . " 15 12,30 p . m . 540 40 V e r y fine. " 15 6 .00 " 520 60 V e r y fine a n d d r y . " 16 5 . 0 0 " 5 1 2 68 S h o w e r y . " 18 12 .45 " 4 7 8 102 V e r y we t . 11 2 2 5 . 0 0 u 520 60 P^ine. " 23 6 .00 " 5 3 2 4 8 F i n e , f ros ty .

Baker Street and Waterloo Railway. The tests on this railway like those on the District Railway, were made about the end of the constructional period and were therefore subject, but in a much lesser degree, to the possibility of the same general disturbances.

The insulators were of brown stoneware with a good glaze, free from grease, and reasonably clean, with the exception of the usual dust from the small granite ballast and construction work. A rectangular section of conductor rail is used on this line, there being no intervening metal cap or support between the rails and insulators. These measurements were not subject to the usual outdoor variation of London weather and tem­perature, the section of track on which the measurements were made being entirely below the surface and far enough removed

6 0 2 FORTENBAUGH: CONDUCTOR RAILS [June 2 9

from the tunnel entrance so as to be, at the most, only pos­sibly indirectly affected:

Up-road, January 2 to 4, 1906. The following measurements were made on the " up-road," between the cable passageway beneath the London Road sub-station and the far end of Baker street station platform, a distance of 18,317 ft. or 3.47 miles. All measurements were made from the London Road sub­station.

8 S L B : R A I L T U B E R A I L W A Y S

F I G . 3 — B o n d i n g a n d s u p p ô t t s for c o n d u c t o r j a i l s

Polarity of conductor rails, normal.

B e t w e e n p o s i t i v e (ou te r ) a n d n e g a t i v e 570 v o l t s a n d e a r t h 510

" n e g a t i v e a n d e a r t h 60 L e a k a g e , p o s i t i v e t o n e g a t i v e 0 . 5 a m p e r e s L e a k a g e cu r ren t per m i l e of s ing le t r a c k 0 . 1 4 4 L e a k a g e , p o s i t i v e e a r t h e d 5 . 0

" n e g a t i v e e a r t h e d 0 . 5 7

Current was on from 2 to 5.30 p.m. on January 1, and from 7 to 10 a.m. January 2; that is, 2.5 hours on the preceding

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afternoon and for 3 hours continuously and immediately pre­ceding the above measurements. The insulators were supposed to have been cleaned prior to above measurements. Current had also been on these rails on several previous occasions for testing purposes and the running of trains.

Polarity of conductor rails, reversed. The polarity of the con­ductor rails was reversed immediately after the preceding readings and the pressure applied continuously for 48 hours, all other conditions remaining the same. Readings were taken regularly between the outer rail (now negative polarity) and earth, the results being shown on Fig. 5.

At the end of the 48 hours the following readings were taken: B e t w e e n p o s i t i v e (cen t re ) a n d n e g a t i v e . 570 v o l t s

" " a n d e a r t h 4 5 5 " n e g a t i v e a n d e a r t h 115

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n e g a t i v e e a r t h e d . . . 0 . 7 "

These results show that the potential between the outer rail and earth was reduced from 510 (positive to earth) to 104 volts (negative to earth) in 24 hours. Some local disturbance then caused a sudden rise to about 118 volts, after which it again slowly but steadily fell to 115 volts at the end of 48 hours. During the first half-hour immediately following the reversal, the leakage current increased steadily from 0.5 to 1.27 am­peres and then gradually became less. It reached the normal value of 0.5 of an ampere on or before the end of the 48 hours. The low-reading ammeter was damaged by a temporary short-circuit about the end of the first hour and was therefore not immediately available for current measurements.

Polarity of conductor rails, normal. The polarity of the con­ductor rails was again made normal—immediately after the 48 hour run with the polarity reversed—the increase in leakage current and the variation in potential between the outer rail and earth for the first two hours being also shown in Fig. 5.

These latter measurements unfortunately could not be con­tinued any longer as the road was needed for the running of trains.

The leakage current rose rapidly immediately following the change from reversed to normal polarity, the maximum value of 1.92 amperes being reached in about 35 minutes.

6 0 6 FORTENBAUGH: CONDUCTOR RAILS [ J u n e 2 9

" Up " road, January 16, 1906. The conductor rails were alive an average of about nine hours per day, normal polarity, from January 4 to 16 inclusive for running trains a total of 117 hours between the readings on January 4 and the following readings on January 16, 1906.

Polarity of conductor rails, normal. B e t w e e n p o s i t i v e (ou te r ) a n d n e g a t i v e 5 6 5 v o l t s

" " a n d e a r t h 530 n e g a t i v e a n d e a r t h 3 5 "

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" n e g a t i v e e a r t h e d . . . 0 . 3 5

" Up " road, January 19 to 22, 1906. The following measure­ments show the effects of reversing the polarity of the con­ductor rails, the rails having been alive about 24 hours, normal polarity, for running trains between the tests of January 16 and 19. The rails were alive continuously for 43.5 hours be­tween the readings of January 19 and 21 with the polarity re­versed ; that is, outer rail negative—and for 21 hours, normal polarity, between the readings of January 21 and 22. Fig. 6 gives full details of these tests and Fig. 5 the details of similar tests on the same road and under practically the same con­ditions. All the " Up " road measurements were made from the London Road sub-station.

G e n e r a l e x h i b i t D a t e of t e s t s —

J a n . 19 J a n . 21

1906

J a n . 22

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1908] FORTENBAUGH: CONDUCTOR RAILS 6 0 9

ings on January 2 0 for 3 0 hours and again made normal for 1 5 hours, a total of 4 5 hours between the readings of January 2 0 and 2 2 .

A temporary but effective " earth " mysteriously appeared on the outer rail about six hours after the reversal on January 2 0 , this condition of affairs being maintained continuously for about 2 8 hours, four hours after the polarity was again made normal on January 2 1 . The effect of this earth on the leakage current, together with the other details of this test, is shown in Fig. 7 . The rails were alive daily, normal polarity, for the running of trains between the readings of January 2 2 and Feb­ruary 1 2 , a total of about 2 6 0 hours between these readings. The -readings for the " down " road, made at the Baker Street sub-station, are as follows:

G e n e r a l E x h i b i t

B e t w e e n p o s i t i v e a n d n e g a t i v e , v o l t s . . 5 7 5 5 7 5 5 7 5 5 7 5 B e t w e e n ou te r ra i l a n d ea r th , v o l t s . . . 5 2 0 5 2 5 5 1 5 4 9 9 B e t w e e n cen t r e ra i l a n d ea r th , v o l t s . . . 55 50 6 0 76 L e a k a g e , p o s i t i v e t o n e g a t i v e , a m p e r e s 0 68 0 58 0 5 5 0 2 A m p e r e s l e a k a g e per m i l e s ing le t r a c k . 0 196 0 167 0 158 0 0 5 8 L e a k a g e , ou t e r ra i l e a r t h e d , a m p e r e s . . 6 7 5 3 0 L e a k a g e , cen t r e ra i l e a r t hed , a m p e r e s . 0 74 0 6 2 0 25 A p p r o x i m a t e d i s t a n c e , m i l e s 3 47 3 47 3 47 3 47

D a t e of t e s t s — 1 9 0 6

J a n . 19 J a n . 20 J a n . 2 2 F e b . 12

The following observations, Table 2 , show the variations in po­tential between the positive conductor rail and earth—both roads--from day to day as well as the variation between the time of switching " o n " and " o f f " - o n the same day. All measurements made by the sub-station attendants at the Lon­don Road sub-station, normal polarity.

D I S C U S S I O N O F R E S U L T S

The following results are corroborated by many other measure­ments made during the years of 1 9 0 3 - 1 9 0 7 , all of which plainly and unmistakably show the existence of the phenomena sub­stantially as illustrated in Figs. 5 , 6 and 7 . There has been consid­erable- study and investigation as to what actually takes place at the time of reversal, the general concensus of opinion being that it is an ordinary case of electrolytic action combined with ordinary insulation resistance conductivity. These results sêëm to depend upon one form of phenomenon which has long been

610 FORTENBA UGH: CONDUCTOR RAILS [ J u n e 29

known in connection with static charges; namely, that a nega­tively charged conductor leaks away its charge with much greater facility than does a positive; or virtually that under the same conditions a positively electrified conductor is better insulated. A negatively electrified conductor appears to be continuously discharging negative ions, which have the effect of conferring

T A B L E I I . — L I N E V O L T A C X E 575

H o u r s V o l t s be tween

H o u r s ra i l s p o s i t i v e a n d e a r t h

a l i v e U p - D o w n -Date—1906 T i m e t o - d a y t o a d r o a d

J a n . 24 7.00 p . m . 19 525 512 " 25 10.30 a . m . 500 510 " 25 8.00 p . m . 9.5 540 512 " 26 10.00 a . m . 500 495 " 26 7.30 p . m . 9.5 540 506 " 27 10.00 a . m . 510 445 " 27 3.30 p . m . 5.5 535 503 " 29 10.00 a . m . 465 410 " 29 7.00 p . m . 9.0 560 575 " 30 10.00 a . m . 530 452 " 30 8.30 p . m . 10.5 565 510 " 31 8.00 a . m . 522 462 " 31 8.30 p . m . 12.5 530 480

F e b . 1 9.00 a . m . 490 430 ι 7.30 p . m . 10.5 540 495 2 8.30 a . m . 498 452 2 7.30 p . m . 11.0 500 465 3 8.00 a . m . 484 444 3 4.30 p . m . 8.5 4 9.00 a . m . 15 463 440 5 8.00 p . m . 20 493 469 7 . 9.00 a . m . 505 480

" 7 9.00 p . m . 12 505 495 9 9.30 a . m . 14.5 486 444

" 10 5.30 p . m . 17.5 520 492

conductivity on the surrounding gas and of causing deposition of moisture from air more or less saturated. It is perfectly con­ceivable, therefore, that this negative discharge should favor the depositing of moisture between the surfaces of insulators progressively in such a manner that a slight conducthdty might be conferred upon the insulator surfaces and that this effect

1908] FORTENBAUGH: CONDUCTOR RAILS 6 1 1

might be expected to be absent with the positive side of the system. The film of liquid existing between the electrodes on a glass surface will gradually move from the positive to the nega­tive electrode, and the negative insulators may therefore lose their insulating properties by having moisture drawn upon them, an action which does not take place on the positive side.

The reducing or chemical action of the ions liberated at the positive rail insulator may result in the formation of compounds which lower the resistance of the negative insulator, while the oxidation which takes place at the positive insulator may im­prove the insulation.

Conclusions. These results, whatever the immediate cause or the reason, have clearly demonstrated certain facts which are probably applicable to all similar installations and may be briefly summarized as follows:

1. That the difference of potential between the positive conductor and earth is always normally considerably greater than the potential existing between the negative conductor and earth.

2. That this difference between the positive and negative insulation becomes more marked the longer the conductors are subjected continuously to a difference of potential in the same direction.

3. That a reversal of the polarity is always instantly accom­panied by a considerable increase in the normal leakage current between the positive and negative conductor.

4. The above phenomena can be repeated indefinitely and are independent of the length of time"that the pressure has been previously applied to the conductors in either direction.

5. That the insulation of the negative conductor to earth can not be proportionately maintained.

Resistance of conductor rails. The resistance measurements given in Table 3 show about what may be expected commercially with a soft conductor rail containing an unusually small amount of manganese and carbon. The resistance of these rails was about 6.4 times that of an equivalent area of copper and the chemical composition substantially as follows :

C a r b o n . . . . Manganese. Sulphur Phosphorus Silicon

0 .05 0 .19 0 .06 0 .05 0 .03

612 FORTENBAUGH: CONDUCTOR RAILS [ J u n e 2 9

I t is interesting to note that the cost o'f this special con­ductor rail was no more than the standard track rail.

T A B L E I I I . — R E S I S T A N C E M E A S U R E M E N T S

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Sec t i on of r a i l w a y

G e n e r a l exh ib i t H o u n s l o w P u t n e y Wimbledon Β . S t . & w.

General Data : D a t e of m e a s u r e m e n t s 5 / 9 / 0 5 5 / 2 7 / 0 5 5 / 2 7 / 0 5 1 2 / 3 0 / 0 5 N e t l eng th m e a s u r e d , f e e t . . 8 8 , 3 0 0 3 7 , 7 0 0 5 3 , 5 0 0 3 6 , 6 0 0 Weigh t of ra i l per yd . , l b . . . 100 100 100 8 5 A r e a of rai l , s q . in 9 . 8 6 9 . 8 6 9 . 8 6 8 . 3 T e m p , of ra i l s , d e g . c e n t . 2 5 2 5 2 5 1 1 . 5 N o . of s w i t c h b o a r d c o n t a c t s 0 4 4 2 N o . of t e r m i n a l p o s t con­

t a c t s 20 20 3 2 6 N o . of ra i l c o n t a c t s 20 24 44 36 N o . of b o n d s per j o in t 4 4 4 4 T o t a l n o . of b o n d e d j o i n t s . 2 ,107 8 3 4 1,160 1,095 A r e a b o n d s per jo in t , s q . in. 1 .57 1 .57 1 .57 1 .33 C o n t a c t a r e a per jo in t , sq .

in 9 . 4 9 . 4 9 . 4 1 2 . 5 6 M easurements.

A, T o t a l r e s i s t a n c e 0 . 5 5 3 0 9 0 . 2 4 4 0 5 0 . 3 6 4 1 2 0 2 4 0 8 8 B , T o t a l r e s i s t a n c e 0 . 5 4 8 5 6 0 . 2 2 9 9 2 0 . 3 5 0 1 3 0 23353 A , R e s . pe r 1000 r a i l - o h m . . 0 . 0 0 6 2 6 4 0 . 0 0 6 4 7 3 0 . 0 0 6 8 0 6 0 0 0 6 5 8 1 B , R e s . pe r 1000 r a i l - o h m . . 0 . 0 0 6 2 1 3 0 . 0 0 6 0 9 9 0 . 0 0 6 5 4 4 0 0 0 6 3 8 1 A . R e s . pe r m i l e - o h m 0 . 0 3 3 0 7 0 0 . 0 3 4 1 8 0 0 . 0 3 5 9 3 6 0 0 3 4 7 5 B , R e s . pe r m i l e - o h m 0 . 0 3 2 8 0 5 0 . 0 3 2 2 0 3 0 . 0 3 4 5 5 2 0 0 3 3 6 9 A , E q u i v . cu . a r e a , s q . i n . . 1 . 3 2 8 1 . 2 8 5 1 . 2 2 2 1 2 B , E q u i v . cu . a r e a , s q . i n . . 1.339 1 . 3 6 4 1 . 2 7 1 1 236 A, R e l . r e s i s t ance , cu . a t 1. 7 . 4 2 7 . 6 7 8 . 0 7 6 92 B , R e l . r e s i s t ance , cu . a t 1. 7 . 3 6 7 . 2 2 7 . 7 5 6 7 2 B , C o n t a c t res . per j t . , o h m . 0 . 0 0 0 0 3 4 1 0 .0000316 0 . 0 0 0 0 5 2 8 0 0 0 0 0 1 0 4 4 B , C o n t a c t res . per b o n d . . .

t e rmina l , o h m 0 . 0 0 0 0 6 8 1 0 .0000632 0 . 0 0 0 1 0 5 6 0 0 0 0 0 2 0 8 8

A inc ludes the r e s i s t a n c e of a l l feeder, t r a c k a n d j u m p e r c a b l e s a n d t h e t e r m i n a l p o s t , ra i l a n d s w i t c h b o a r d c o n t a c t r e s i s t a n c e ; t h a t i s , t h e r e ­s i s t a n c e of t he b o n d e d c o n d u c t o r ra i l s , c a b l e s a n d c o n t a c t s a s i n s t a l l ed a n d r e a d y for c o m m e r c i a l s e rv i ce .

Β s a m e a s " A " l e s s t he c a l c u l a t e d r e s i s t a n c e of a l l feeder, t r a c k a n d j u m p e r c a b l e s ; t h a t i s , i n c l u d e s t h e r e s i s t a n c e of t h e b o n d e d c o n d u c t o r r a i l s a n d a u x i l i a r y c o n t a c t s .

Remarks. Al l c a l c u l a t e d r e s i s t a n c e s a r e b a s e d on t h e t e m p e r a t u r e a t which t h e m e a s u r e m e n t s were m a d e .