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The overhead line and ground return circuit of electric street railways
July, I898.]
Electric Railways.
ELECTRICAL
55
SECTION.
Slated glIeelinK, January iI, 1898.
THE O V E R H E A D L I N E AND G R O U N D R E T U R N C I R C U I T ov E L E C T R I C S T R E E T R A I L W A Y S . BY DAVID P~PPER, JR. M e m b e r of the Institute.
On the p r o p e r design and careful construction of the line and g r o u n d return circuit depends, to a g r e a t extent, the satisfactory and economical operation of an electric railway. The practice of the p r e s e n t time is the result of costly experience. W i t h i n the last few years there h a v e been great a d v a n c e s m a d e in the c h a r a c t e r of the o u t s i d e work, and the m a t e r i a l s e n t e r i n g into the c o n s t r u c t i o n have been greatly improved. In the early days of electric street railways, the i m p o r t a n c e of the line, and especially the r e t u r n circuit, was v e r y little t h o u g h t of. T h e c h e a p e s t form of construction that w o u l d cause the cars to move at all was usually installed. M a n a g e r s now find t h a t it is v e r y b a d economy to a t t e m p t to save m o n e y on their o u t s i d e work. The direct loss in receipts and prestige, o w i n g to failure of the outside construction, is v e r y g r e a t ; and the loss in power, owing to poorly p r o p o r t i o n e d or poorly c o n s t r u c t e d work, is a constant loss. T h e o v e r h e a d trolley line should h a v e sufficient s t r e n g t h in all its parts not only to hold up the dead weight of the trolley wire, b u t to resist all s u d d e n and heavy strains caused b y blows from trolley poles, the falling; of outside wires upon the trolley wire, and the b r e a k i n g of the trolley wire. The trolley wire in city work is usually s u p p o r t e d on iron poles placed, a b o u t I25 feet apart, in pairs on opposite sides Of the street. T h e s e poles are u s u a l l y m a d e of from two to three sections of h e a v y iron pipe, telescoped into each o t h e r about 18 inches, and the joints s w e d g e d while hot. On straight line const ruction, unless the street is v e r y wide, poles 28 feet long and w e i g h i n g from 700 to 750 p o u n d s are used.
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On wide streets and l i g h t curves, a n d w i t h extra h e a v y troll e y w i r e , poles from 9o0 to i , t o o p o u n d s are used. On h e a v y curves the poles w e i g h 1,3oo p o u n d s a n d over. In s e t t i n g these poles, g r e a t care m u s t be t a k e n t h a t t h e y are set in such a way t h a t t h e r e is no give at the base of the poles. If the poles give a f t e r the s t r a i n is p u t on t h e m , it will loosen up the entire line, especially at curves and special work, and cause a g r e a t deal of trouble in repairing. T h e l i g h t e r w e i g h t poles, w h e n set in fairly good g r o u n d a n d w i t h a c u r b s t o n e in front, s h o u l d be placed in holes from 18 to ao i n c h e s in diameter, and from 6 to 6} feet deep, and set w i t h a rake to allow for s t r a i g h t e n i n g w h e n strain is placed on them. T h e concrete used should be m a d e of I½ bags of i m p r o v e d n a t u r a l cement, one barrel of sand and sufficient stone to fill the hole. T h e s a n d and c e m e n t should be m a d e into a t h i n mortar, m i x e d with the w e t t e d stone, t u r n e d at least three times, and t h e m i x t u r e t h e n r a m m e d in the hole in six-inch layers. T h e concrete will be worthless if it is not properly r a m m e d , or if t h e r e is too m u c h or too little w a t e r in it. For pull-off poles, and w h e r e there are h e a v y strains, two b a g s of c e m e n t s h o u l d be used and the poles set in larger and deeper holes. In cross suspension work, the span wires are u s u a l l y secured to poles w i t h w r o u g h t iron bands, and one or two m e c h a n i c a l insulators are placed in each end of span, near pole. In the early construction, silicon bronze and solid steel a n d iron wires were used for the spans. It was f o u n d t h a t the tensile s t r e n g t h of these wires, if t h e y were scratched or kinked in any way, was g r e a t l y reduced, and t h a t t h e i r composition was s o m e w h a t uncertain. Sevens t r a n d g a l v a n i z e d steel cable is now used, ~ of an inch in d i a m e t e r for o r d i n a r y single-track suspension and pull-offs, a n d ~ of an inch on l o n g spans and ~- trolley construction. Care should be t a k e n in p l a c i n g spans to allow for the proper sag w h e n t h e suspension device is s p r u n g on the span wire. If the span is tight, say h a v i n g a sag of only 8 inches in 35 or 40 feet, there is g r e a t s t r a i n p u t on t h e pole. If the sag is too great, the line will look b a d and v i o l e n t v i b r a t i o n s will be set np in it e v e r y t i m e a ear passes. T h e
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Electric Railways.
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exact tension of the spans is a m a t t e r of skill on the part of the m a n p u t t i n g t h e m up. T h e i n s u l a t o r s used in the span wire are of m a n y types and makes. T h e i n s u l a t i o n is u s u a l l y h a r d - r u b b e r compound or one of the m a n y special c o m p o u n d s m a d e for this purpose. T h e r e is a h e a v y s t r a i n s o m e t i m e s placed on these span wires, and the c o n s t a n t v i b r a t i o n will quickly find a n y i m p e r f e c t i o n s in the i n s u l a t i n g m a t e r i a l and cause either a break in the wire or a leak to the pole. Those forms of i n s u l a t o r s i n v o l v i n g screw connections are not usually as s t r o n g as those of rigid type ; and, as the take.up is seldom if ever used in practice, it is b e t t e r e c o n o m y to use two solid strain insulators i n s t e a d of a turnbuckle. In m a n y eases where the track is on the side of the street, a single line of poles is used and t h e trolley wire s u s p e n d e d from a pipe bracket, which is u s u a l l y trussed in some manner. A plain b r a c k e t gives a rigid line, which causes a great deal of wear a n d tear. T o overcome this rigidity, brackets are often m a d e so as to rise a little u n d e r the pressure of the trolley, o r the h a n g e r is secured to a span wire u n d e r the bracket. Bracket construction, unless securely g u y e d , is m u c h more liable to serious d a m a g e t h a n span construction, o w i n g to the lack of s t r e n g t h latteraly, if the wire breaks or if the trolley pole comes off and strikes the bracket. W e now come to the m e t h o d of a c t u a l l y s u s p e n d i n g t h e trolley wire. T h e r e is s p r u n g on the span wire a c a s t i n g of malleable iron or bronze, c o n t a i n i n g an i n s u l a t e d bolt of from ~ to ~t of an inch in diameter. T h i s i n s u l a t e d bolt is sometimes placed in the c a s t i n g and the top screwed down. In others it is c o n t a i n e d in the b o d y of the i n s u l a t i n g material w i t h i n the bell. T h e l a t t e r form is p r o b a b l y t h e best, owing to the m u c h b e t t e r p r o t e c t i o n given the insulating m a t e r i a l from blows from the trolley wheel and from the weather. T h e principal a d v a n t a g e claimed for the other form of i n s u l a t e d bolt is t h a t only one portion has to be thrown a w a y in case of failure to work properly. At curves, the trolley wire is s u s p e n d e d by special pulloff hangers placed sufficiently close to p r e v e n t sharp bends
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in the trolley wire. T h e usual d i s t a n c e is from 6 to xo feet, depending, of course, upon the degree of c u r v a t u r e . W h e r e pull-off wires cross the s t r a i g h t line trolley wire, t h e y s h o u l d be secured to it the same as at the spans. T h e pull-off wires s h o u l d all come t o g e t h e r in an extra h e a v y strain i n s u l a t o r at the pull-off pole. I t is well at this point to h a v e a turnbuckle capable of t i g h t e n i n g the entire series of pull-otis. Care should be taken in all pull-offs and special work to h a v e each and every pull-off wire i n s u l a t e d from its neighbor, in such a w a y t h a t in case of a failure of the pull-off i n s u l a t i o n from the trolley to the pull-off wire, only one wire will be alive. W h e n this p r e c a u t i o n is n o t taken, it causes a g r e a t deal of t r o u b l e in l o c a t i n g the leak in a complicated curve. In iron pole construction, the i n s u l a t i o n is an i m p o r t a n t item, first, to p r e v e n t leakage to the trolley pole, which not only causes a s t e a d y loss but, perhaps, the s h u t t i n g down of the lines, and also as a m a t t e r of s a f e t y to the m e n w o r k i n g on the live trolley wire. It is very d i s c o n c e r t i n g to a linem a n w o r k i n g on a l a d d e r or tower w a g o n to u n e x p e c t e d l y discover t h a t the span wire, which he t h o u g h t was insulated, is connected directly to the g r o u n d t h r o u g h the pole. P r o b a b l y one of the m o s t i m p o r t a n t m a t t e r s in trolley c o n s t r u c t i o n is the m e t h o d of s u s p e n d i n g the trolley wire from the hangers, and this is especially true on roads w h e r e the cars r u n at a speed exceeding ten miles an hour. T h e s l i g h t e s t o b s t r u c t i o n on the u n d e r s i d e of the trolley wire will cause the trolley wheel to leave the wire a short distance to come back again with a sharp blow. Each time the wheel leaves the wire t h e r e is an arc formed t h a t takes off a small portion of the wheel or wire. If the o b s t r u c t i o n is sufficient, the wheel will be t h r o w n so far down from the wire t h a t on its r e t u r n it will miss t h e wire and go down the line s t r i k i n g span wires and special work, and s t r a i n i n g every part of the o v e r h e a d construction. T h i s is one of the principal causes of t r o u b l e on the line. P r o b a b l y one of the m o s t s a t i s f a c t o r y m e t h o d s of s u s p e n d i n g the wire is by u s i n g a bronze or composition ear, 15 inches long, with a groove of the d i a m e t e r of the wire, milled in the solid of the
July, t8q8 I
Electric Railways.
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lower portion of the ear, the depth of this groove to be about t h e d i a m e t e r of t h e wire. T h e e x t r a portion of the m e t a l is so" p r o p o r t i o n e d t h a t it can be securely h a m m e r e d d o w n on t h e trolley wire. T h e ear should then be carefully soldered, u s i n g soldering s a l t s and solder; this, w h e n properly done, makes a first-class job, but there is d a n g e r t h a t the wire m a y be d a m a g e d by careless or unskilled workmen. Should the iron be so hot as to partially a n n e a l the trolley wire, there is a very g r e a t reduction in tensile s t r e n g t h at the ear, and the wire m a y be so d a m a g e d t h a t on the first strain it will draw out a n d , break. Only the m o s t skilful m e n should be e n t r u s t e d w i t h this work, as it requires care a n d skill t h a t can only be obtained by practice. To give a s m o o t h u n d e r - r u n n i n g surface to the trolley wire, m a n y devices have been tried. T h e trolley wire h a s been rolled in the form of the figure 8, and a m e c h a n i c a l clamp devised to hold the wire in place, giving, theoretically, a smooth u n d e r - r u n n i n g surface. U n f o r t u n a t e l y the wire, in practice, is likely to be t w i s t e d s l i g h t l y in the erection and at curves, with the r e s u l t t h a t the trolley wheel r u n s on the two loops of t h e wire, g i v i n g e x t r e m e l y u n s a t i s f a c t o r y results. To overcome this trouble, the section of wire was modified to three points, i n s t e a d of two, and this has been found to work m u c h better. A n o t h e r plan, of good p r o m i s e for high speed work, was to take a four n a u g h t r o u n d trolley wire and w i t h a special m a c h i n e to press or mill a groove on each side of the wire, j u s t above the diameter, to fit a d a m p . This device a n s w e r s v e r y well, b u t it is s o m e w h a t difficult to repair work p u t up in this m a n n e r . A n o t h e r class of suspension involves the use of m e t a l below the trolley wire. Others involve the k i n k i n g of the trolley wire. Both of these last-named m e t h o d s are open to serious objections for high-speed roads. A n o t h e r i m p o r t a n t p a r t in the work is the j o i n i n g of the trolley wire. T h i s can p r o b a b l y be best accomplished by a long, hard-rolled copper sleeve, a b o u t i8 inches long, t u r n e d to a cone at each end a n d so a r r a n g e d b y b o r i n g and milling groves t h a t the wires come out t o g e t h e r in the m i d d l e
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of the sleeve. T h e hole is t h e n soldered a n d the surplus wire cut off. A n o t h e r style, w i t h o u t solder, involves some form of d a m p i n g device w i t h i n the tube, the i n n e r chamber b e i n g l a r g e r t h a n the bore for t h e trolley wire to enter. In all special work, such as frogs, cross-overs a n d section breaks, care s h o u l d be t a k e n to choose t h a t w h i c h gives a clear u n d e r - r u n n i n g surface. In high-speed work the tend e n c y is to e n t i r e l y avoid switches and to s u b s t i t u t e for s a m e two trolley wires, or cause t h e trolley to be lowered a n d placed on a n o t h e r wire on ears l e a v i n g the m a i n line. A t a n y speed above ten miles an hour, the chances are g r e a t l y in favo.r of the trolley wheel l e a v i n g the wire. In the early d a y s No. 6 to No. 4 B. & S. g a u g e wire was considered quite h e a v y e n o u g h for the trolley wire. It was soon discovered, however, t h a t this was e n t i r e l y too light, a n d for m a n y years single n a u g h t hard-drawn copper wire was used. T h e t e n d e n e y is s t r o n g l y in favor, for s t a n d a r d city work, of the use of double n a u g h t wire. It has been proved by experience t h a t the troubles from the b r e a k i n g of the trolley wires are r e d u c e d to a b o u t one-third the n u m ber w h e n double n a u g h t wire is used. If single n a u g h t trolley wire is d r a w n so t i g h t l y t h a t the up a n d down vibrations only show for three or four poles, the wire is s t r a i n e d well up towards its s a f e t y limit, and will not s t a n d a s u d d e n a n d violent blow. T h e wire s h o u l d be s t r e t c h e d so t h a t in w i n t e r there will be a sag of a b o u t Io inches in every I25 feet. T h i s will make a c o n s i d e r a b l y looser line in s u m m e r time. In d e c i d i n g u p o n the size of trolley wire, there are several o t h e r problems to be considered besides the tensile s t r e n g t h a n d f r e e d o m f r o m accidents. In a n e t work of wires such as here in P h i l a d e l p h i a , the trolley wire is not u s u a l l y d e p e n d e d upon as part of t h e feeder system, other t h a n for six or e i g h t cars on a single section. In s u b u r b a n lines, w i t h c o m p a r a t i v e l y few cars, t h e q u e s t i o n of u s i n g the trolley wire as p a r t of the feeder s y s t e m becomes an i m p o r t a n t one; a n d the difference b e t w e e n one n a u g h t and two n a u g h t trolley, a n d still more so b e t w e e n two n a u g h t a n d four n a u g h t trolley, will d e t e r m i n e w h e t h e r or n o t a h e a v y feeder will h a v e to be r u n alongside of the trolley
luly, I898. ]
Electric Railways.
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wire. T h e cost of bare copper in the form of two n a u g h t or four n a u g h t trolley is considerably less per circular rail than the cost of a single n a u g h t trolley wire plus the necessary i n s u l a t e d feeder wire. In d e s i g n i n g a n y feeder system, the proposed conditions upon which the line is to be r u n should be v e r y well known, and the line d e s i g n e d for e c o n o m y of c u r r e n t and original i n v e s t m e n t for a v e r a g e load, w i t h the provision m a d e t h a t on very h e a v y loads the voltage will not fall below 375 volts for a few m o m e n t s . One of the causes of the failure of insulation on iron-pole c o n s t r u c t i o n is the effect of l i g h t n i n g d!scharges on the line, w h i c h g r e a t l y weaken and strain the insulators, even if t h e y do not break down on the first discharge. To overcome this, it is usual to place one of t h e well-known and tried makes of l i g h t n i n g a t t e s t e r at each feeder tap, p r o v i d i n g it w i t h a kicking coil, and b e i n g careful t h a t there be as few bends as possible in the wire to the ground. T h e l i g h t n i n g a r r e s t e r s h o u l d preferably have a single n a u g h t t i n n e d wire r u n down inside of the pole and connected securely to the r e t u r n circuit and track. T h e mere g r o u n d i n g of a l i g h t n i n g arrester to a trolley pole set in concrete is not sufficient, as, even on a wet day, there h a v e been cases k n o w n w h e r e the concrete acted as such a good insulator t h a t there was a difference of p o t e n t ~ l of 475 volts from pole to track. On wooden-pole construction, the problem of i n s u l a t i n g is v e r y m u c h simplified, as e i g h t e e n or twenty feet of wooden pole, properly painted, is p r o b a b l y as good an i n s u l a t o r as can be made. W o o d e n poles of sufficient w e i g h t a n d of first-class yellow pine, c h e s t n u t , oak or cedar, p a i n t e d w i t h a p r e s e r v a t i v e c o m p o u n d at the b u t t and p a i n t e d two coats of good paint, are as s a t i s f a c t o r y as iron poles; and, in the long run, as well as in first cost, are a little cheaper. T h e y will last a b o u t one-third as long as the e s t i m a t e d life of an a v e r a g e iron pole properly painted. T h e l i m i t a t i o n s to the overhead trolley are now quite generally recognized. It has been f o u n d t h a t it is difficult to efficiently t r a n s m i t , by m e a n s of the o r d i n a r y form of trolley wheel, more t h a n 15o a m p e r e s from the wire to the wheel w i t h o u t excessive s p a r k i n g and loss. T h e speed at
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which a trolley wheel will s t a y on the wire, t h r o u g h section insulators, special work a n d switches, is l i m i t e d in good practice to n o t m u c h over ten miles an hour. W h e n the trolley s t a n d and wheel are b o t h d e s i g n e d for h i g h 'speed and the line carefully constructed, it is possible to run on straight-line work at a speed of a b o u t t h i r t y miles an hour. Beyond this speed the t e n d e n c y to t h r o w the wheel from the wire, o w i n g to s l i g h t o b s t r u c t i o n s on t h e trolley wire, is very great. If the wheel leaves the wire at this speed, it is almost certain to e i t h e r b r e a k the trolley pole or b r i n g down a large portion of the o v e r h e a d construction. It is ~or this reason t h a t e x p e r i m e n t s h a v e been and are b e i n g tried to s u b s t i t u t e a fixed c o n d u c t o r near the g r o u n d w i t h a large surface c o n t a c t for the o v e r h e a d trolley wire, for h i g h speed and h e a v y currents. A g r e a t deal of a t t e n t i o n has r e c e n t l y been g i v e n to the matter of g r o u n d return. It has been f o u n d t h a t the c u r r e n t on an i m p e r f e c t l y b o n d e d track is v e r y likely to come back to the s t a t i o n t h r o u g h w a t e r and gas pipes and on t h e lead covering of u n d e r g r o u n d cables, s e t t i n g up electrolitie action, which, in some instances, speedily d e s t r o y e d the pipes. In b o n d i n g a track, the first t h i n g to be considered is to g e t as low a resistance as possible at each joint. It is also necessary to h a v e an a s s u r a n c e t h a t the bond will r e m a i n in perfect condition for a l o n g period of t i m e and will s t a n d the m a x i m u m c u r r e n t t h a t will be called upon to go t h r o u g h a special piece of track. T h e a c t u a l cost of t h e m a t e r i a l for b o n d i n g a track, w i t h m o s t m o d e r n s y s t e m s of b o n d i n g , is a small i t e m c o m p a r e d to the original labor of p u t t i n g it in place and the cost of re-bonding the track w i t h i n a few years, w i t h o u t t a k i n g into c o n s i d e r a t i o n the w a t t s daily lost in the b o n d circuit. Few persons realize how low a resistance a pair of nine-inch girder rails have, and t h a t every effort should be m a d e to get the full benefit of this r e t u r n circuit. T h e resistance of the rail is f r o m six to seven times the resistance of the same section of c o m m e r c i a l copper. V e r y few tracks are bonded more t h a n one-fourth or one-third the c a r r y i n g c a p a c i t y of the rail. It has been proved in praetice t h a t the e a r t h and fish plates are not to be d e p e n d e d on as part of the r e t u r n cirCuit for h e a v y currents.
Electric Railways.
ELECTRICAL
55
SECTION.
Slated glIeelinK, January iI, 1898.
THE O V E R H E A D L I N E AND G R O U N D R E T U R N C I R C U I T ov E L E C T R I C S T R E E T R A I L W A Y S . BY DAVID P~PPER, JR. M e m b e r of the Institute.
On the p r o p e r design and careful construction of the line and g r o u n d return circuit depends, to a g r e a t extent, the satisfactory and economical operation of an electric railway. The practice of the p r e s e n t time is the result of costly experience. W i t h i n the last few years there h a v e been great a d v a n c e s m a d e in the c h a r a c t e r of the o u t s i d e work, and the m a t e r i a l s e n t e r i n g into the c o n s t r u c t i o n have been greatly improved. In the early days of electric street railways, the i m p o r t a n c e of the line, and especially the r e t u r n circuit, was v e r y little t h o u g h t of. T h e c h e a p e s t form of construction that w o u l d cause the cars to move at all was usually installed. M a n a g e r s now find t h a t it is v e r y b a d economy to a t t e m p t to save m o n e y on their o u t s i d e work. The direct loss in receipts and prestige, o w i n g to failure of the outside construction, is v e r y g r e a t ; and the loss in power, owing to poorly p r o p o r t i o n e d or poorly c o n s t r u c t e d work, is a constant loss. T h e o v e r h e a d trolley line should h a v e sufficient s t r e n g t h in all its parts not only to hold up the dead weight of the trolley wire, b u t to resist all s u d d e n and heavy strains caused b y blows from trolley poles, the falling; of outside wires upon the trolley wire, and the b r e a k i n g of the trolley wire. The trolley wire in city work is usually s u p p o r t e d on iron poles placed, a b o u t I25 feet apart, in pairs on opposite sides Of the street. T h e s e poles are u s u a l l y m a d e of from two to three sections of h e a v y iron pipe, telescoped into each o t h e r about 18 inches, and the joints s w e d g e d while hot. On straight line const ruction, unless the street is v e r y wide, poles 28 feet long and w e i g h i n g from 700 to 750 p o u n d s are used.
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Pepper ."
[J. F. I,
On wide streets and l i g h t curves, a n d w i t h extra h e a v y troll e y w i r e , poles from 9o0 to i , t o o p o u n d s are used. On h e a v y curves the poles w e i g h 1,3oo p o u n d s a n d over. In s e t t i n g these poles, g r e a t care m u s t be t a k e n t h a t t h e y are set in such a way t h a t t h e r e is no give at the base of the poles. If the poles give a f t e r the s t r a i n is p u t on t h e m , it will loosen up the entire line, especially at curves and special work, and cause a g r e a t deal of trouble in repairing. T h e l i g h t e r w e i g h t poles, w h e n set in fairly good g r o u n d a n d w i t h a c u r b s t o n e in front, s h o u l d be placed in holes from 18 to ao i n c h e s in diameter, and from 6 to 6} feet deep, and set w i t h a rake to allow for s t r a i g h t e n i n g w h e n strain is placed on them. T h e concrete used should be m a d e of I½ bags of i m p r o v e d n a t u r a l cement, one barrel of sand and sufficient stone to fill the hole. T h e s a n d and c e m e n t should be m a d e into a t h i n mortar, m i x e d with the w e t t e d stone, t u r n e d at least three times, and t h e m i x t u r e t h e n r a m m e d in the hole in six-inch layers. T h e concrete will be worthless if it is not properly r a m m e d , or if t h e r e is too m u c h or too little w a t e r in it. For pull-off poles, and w h e r e there are h e a v y strains, two b a g s of c e m e n t s h o u l d be used and the poles set in larger and deeper holes. In cross suspension work, the span wires are u s u a l l y secured to poles w i t h w r o u g h t iron bands, and one or two m e c h a n i c a l insulators are placed in each end of span, near pole. In the early construction, silicon bronze and solid steel a n d iron wires were used for the spans. It was f o u n d t h a t the tensile s t r e n g t h of these wires, if t h e y were scratched or kinked in any way, was g r e a t l y reduced, and t h a t t h e i r composition was s o m e w h a t uncertain. Sevens t r a n d g a l v a n i z e d steel cable is now used, ~ of an inch in d i a m e t e r for o r d i n a r y single-track suspension and pull-offs, a n d ~ of an inch on l o n g spans and ~- trolley construction. Care should be t a k e n in p l a c i n g spans to allow for the proper sag w h e n t h e suspension device is s p r u n g on the span wire. If the span is tight, say h a v i n g a sag of only 8 inches in 35 or 40 feet, there is g r e a t s t r a i n p u t on t h e pole. If the sag is too great, the line will look b a d and v i o l e n t v i b r a t i o n s will be set np in it e v e r y t i m e a ear passes. T h e
July, i898. ]
Electric Railways.
57
exact tension of the spans is a m a t t e r of skill on the part of the m a n p u t t i n g t h e m up. T h e i n s u l a t o r s used in the span wire are of m a n y types and makes. T h e i n s u l a t i o n is u s u a l l y h a r d - r u b b e r compound or one of the m a n y special c o m p o u n d s m a d e for this purpose. T h e r e is a h e a v y s t r a i n s o m e t i m e s placed on these span wires, and the c o n s t a n t v i b r a t i o n will quickly find a n y i m p e r f e c t i o n s in the i n s u l a t i n g m a t e r i a l and cause either a break in the wire or a leak to the pole. Those forms of i n s u l a t o r s i n v o l v i n g screw connections are not usually as s t r o n g as those of rigid type ; and, as the take.up is seldom if ever used in practice, it is b e t t e r e c o n o m y to use two solid strain insulators i n s t e a d of a turnbuckle. In m a n y eases where the track is on the side of the street, a single line of poles is used and t h e trolley wire s u s p e n d e d from a pipe bracket, which is u s u a l l y trussed in some manner. A plain b r a c k e t gives a rigid line, which causes a great deal of wear a n d tear. T o overcome this rigidity, brackets are often m a d e so as to rise a little u n d e r the pressure of the trolley, o r the h a n g e r is secured to a span wire u n d e r the bracket. Bracket construction, unless securely g u y e d , is m u c h more liable to serious d a m a g e t h a n span construction, o w i n g to the lack of s t r e n g t h latteraly, if the wire breaks or if the trolley pole comes off and strikes the bracket. W e now come to the m e t h o d of a c t u a l l y s u s p e n d i n g t h e trolley wire. T h e r e is s p r u n g on the span wire a c a s t i n g of malleable iron or bronze, c o n t a i n i n g an i n s u l a t e d bolt of from ~ to ~t of an inch in diameter. T h i s i n s u l a t e d bolt is sometimes placed in the c a s t i n g and the top screwed down. In others it is c o n t a i n e d in the b o d y of the i n s u l a t i n g material w i t h i n the bell. T h e l a t t e r form is p r o b a b l y t h e best, owing to the m u c h b e t t e r p r o t e c t i o n given the insulating m a t e r i a l from blows from the trolley wheel and from the weather. T h e principal a d v a n t a g e claimed for the other form of i n s u l a t e d bolt is t h a t only one portion has to be thrown a w a y in case of failure to work properly. At curves, the trolley wire is s u s p e n d e d by special pulloff hangers placed sufficiently close to p r e v e n t sharp bends
58
P e p p e r ."
[J. F. I.,
in the trolley wire. T h e usual d i s t a n c e is from 6 to xo feet, depending, of course, upon the degree of c u r v a t u r e . W h e r e pull-off wires cross the s t r a i g h t line trolley wire, t h e y s h o u l d be secured to it the same as at the spans. T h e pull-off wires s h o u l d all come t o g e t h e r in an extra h e a v y strain i n s u l a t o r at the pull-off pole. I t is well at this point to h a v e a turnbuckle capable of t i g h t e n i n g the entire series of pull-otis. Care should be taken in all pull-offs and special work to h a v e each and every pull-off wire i n s u l a t e d from its neighbor, in such a w a y t h a t in case of a failure of the pull-off i n s u l a t i o n from the trolley to the pull-off wire, only one wire will be alive. W h e n this p r e c a u t i o n is n o t taken, it causes a g r e a t deal of t r o u b l e in l o c a t i n g the leak in a complicated curve. In iron pole construction, the i n s u l a t i o n is an i m p o r t a n t item, first, to p r e v e n t leakage to the trolley pole, which not only causes a s t e a d y loss but, perhaps, the s h u t t i n g down of the lines, and also as a m a t t e r of s a f e t y to the m e n w o r k i n g on the live trolley wire. It is very d i s c o n c e r t i n g to a linem a n w o r k i n g on a l a d d e r or tower w a g o n to u n e x p e c t e d l y discover t h a t the span wire, which he t h o u g h t was insulated, is connected directly to the g r o u n d t h r o u g h the pole. P r o b a b l y one of the m o s t i m p o r t a n t m a t t e r s in trolley c o n s t r u c t i o n is the m e t h o d of s u s p e n d i n g the trolley wire from the hangers, and this is especially true on roads w h e r e the cars r u n at a speed exceeding ten miles an hour. T h e s l i g h t e s t o b s t r u c t i o n on the u n d e r s i d e of the trolley wire will cause the trolley wheel to leave the wire a short distance to come back again with a sharp blow. Each time the wheel leaves the wire t h e r e is an arc formed t h a t takes off a small portion of the wheel or wire. If the o b s t r u c t i o n is sufficient, the wheel will be t h r o w n so far down from the wire t h a t on its r e t u r n it will miss t h e wire and go down the line s t r i k i n g span wires and special work, and s t r a i n i n g every part of the o v e r h e a d construction. T h i s is one of the principal causes of t r o u b l e on the line. P r o b a b l y one of the m o s t s a t i s f a c t o r y m e t h o d s of s u s p e n d i n g the wire is by u s i n g a bronze or composition ear, 15 inches long, with a groove of the d i a m e t e r of the wire, milled in the solid of the
July, t8q8 I
Electric Railways.
59
lower portion of the ear, the depth of this groove to be about t h e d i a m e t e r of t h e wire. T h e e x t r a portion of the m e t a l is so" p r o p o r t i o n e d t h a t it can be securely h a m m e r e d d o w n on t h e trolley wire. T h e ear should then be carefully soldered, u s i n g soldering s a l t s and solder; this, w h e n properly done, makes a first-class job, but there is d a n g e r t h a t the wire m a y be d a m a g e d by careless or unskilled workmen. Should the iron be so hot as to partially a n n e a l the trolley wire, there is a very g r e a t reduction in tensile s t r e n g t h at the ear, and the wire m a y be so d a m a g e d t h a t on the first strain it will draw out a n d , break. Only the m o s t skilful m e n should be e n t r u s t e d w i t h this work, as it requires care a n d skill t h a t can only be obtained by practice. To give a s m o o t h u n d e r - r u n n i n g surface to the trolley wire, m a n y devices have been tried. T h e trolley wire h a s been rolled in the form of the figure 8, and a m e c h a n i c a l clamp devised to hold the wire in place, giving, theoretically, a smooth u n d e r - r u n n i n g surface. U n f o r t u n a t e l y the wire, in practice, is likely to be t w i s t e d s l i g h t l y in the erection and at curves, with the r e s u l t t h a t the trolley wheel r u n s on the two loops of t h e wire, g i v i n g e x t r e m e l y u n s a t i s f a c t o r y results. To overcome this trouble, the section of wire was modified to three points, i n s t e a d of two, and this has been found to work m u c h better. A n o t h e r plan, of good p r o m i s e for high speed work, was to take a four n a u g h t r o u n d trolley wire and w i t h a special m a c h i n e to press or mill a groove on each side of the wire, j u s t above the diameter, to fit a d a m p . This device a n s w e r s v e r y well, b u t it is s o m e w h a t difficult to repair work p u t up in this m a n n e r . A n o t h e r class of suspension involves the use of m e t a l below the trolley wire. Others involve the k i n k i n g of the trolley wire. Both of these last-named m e t h o d s are open to serious objections for high-speed roads. A n o t h e r i m p o r t a n t p a r t in the work is the j o i n i n g of the trolley wire. T h i s can p r o b a b l y be best accomplished by a long, hard-rolled copper sleeve, a b o u t i8 inches long, t u r n e d to a cone at each end a n d so a r r a n g e d b y b o r i n g and milling groves t h a t the wires come out t o g e t h e r in the m i d d l e
60
_Pepper ."
[j. F. 1,
of the sleeve. T h e hole is t h e n soldered a n d the surplus wire cut off. A n o t h e r style, w i t h o u t solder, involves some form of d a m p i n g device w i t h i n the tube, the i n n e r chamber b e i n g l a r g e r t h a n the bore for t h e trolley wire to enter. In all special work, such as frogs, cross-overs a n d section breaks, care s h o u l d be t a k e n to choose t h a t w h i c h gives a clear u n d e r - r u n n i n g surface. In high-speed work the tend e n c y is to e n t i r e l y avoid switches and to s u b s t i t u t e for s a m e two trolley wires, or cause t h e trolley to be lowered a n d placed on a n o t h e r wire on ears l e a v i n g the m a i n line. A t a n y speed above ten miles an hour, the chances are g r e a t l y in favo.r of the trolley wheel l e a v i n g the wire. In the early d a y s No. 6 to No. 4 B. & S. g a u g e wire was considered quite h e a v y e n o u g h for the trolley wire. It was soon discovered, however, t h a t this was e n t i r e l y too light, a n d for m a n y years single n a u g h t hard-drawn copper wire was used. T h e t e n d e n e y is s t r o n g l y in favor, for s t a n d a r d city work, of the use of double n a u g h t wire. It has been proved by experience t h a t the troubles from the b r e a k i n g of the trolley wires are r e d u c e d to a b o u t one-third the n u m ber w h e n double n a u g h t wire is used. If single n a u g h t trolley wire is d r a w n so t i g h t l y t h a t the up a n d down vibrations only show for three or four poles, the wire is s t r a i n e d well up towards its s a f e t y limit, and will not s t a n d a s u d d e n a n d violent blow. T h e wire s h o u l d be s t r e t c h e d so t h a t in w i n t e r there will be a sag of a b o u t Io inches in every I25 feet. T h i s will make a c o n s i d e r a b l y looser line in s u m m e r time. In d e c i d i n g u p o n the size of trolley wire, there are several o t h e r problems to be considered besides the tensile s t r e n g t h a n d f r e e d o m f r o m accidents. In a n e t work of wires such as here in P h i l a d e l p h i a , the trolley wire is not u s u a l l y d e p e n d e d upon as part of t h e feeder system, other t h a n for six or e i g h t cars on a single section. In s u b u r b a n lines, w i t h c o m p a r a t i v e l y few cars, t h e q u e s t i o n of u s i n g the trolley wire as p a r t of the feeder s y s t e m becomes an i m p o r t a n t one; a n d the difference b e t w e e n one n a u g h t and two n a u g h t trolley, a n d still more so b e t w e e n two n a u g h t a n d four n a u g h t trolley, will d e t e r m i n e w h e t h e r or n o t a h e a v y feeder will h a v e to be r u n alongside of the trolley
luly, I898. ]
Electric Railways.
6t
wire. T h e cost of bare copper in the form of two n a u g h t or four n a u g h t trolley is considerably less per circular rail than the cost of a single n a u g h t trolley wire plus the necessary i n s u l a t e d feeder wire. In d e s i g n i n g a n y feeder system, the proposed conditions upon which the line is to be r u n should be v e r y well known, and the line d e s i g n e d for e c o n o m y of c u r r e n t and original i n v e s t m e n t for a v e r a g e load, w i t h the provision m a d e t h a t on very h e a v y loads the voltage will not fall below 375 volts for a few m o m e n t s . One of the causes of the failure of insulation on iron-pole c o n s t r u c t i o n is the effect of l i g h t n i n g d!scharges on the line, w h i c h g r e a t l y weaken and strain the insulators, even if t h e y do not break down on the first discharge. To overcome this, it is usual to place one of t h e well-known and tried makes of l i g h t n i n g a t t e s t e r at each feeder tap, p r o v i d i n g it w i t h a kicking coil, and b e i n g careful t h a t there be as few bends as possible in the wire to the ground. T h e l i g h t n i n g a r r e s t e r s h o u l d preferably have a single n a u g h t t i n n e d wire r u n down inside of the pole and connected securely to the r e t u r n circuit and track. T h e mere g r o u n d i n g of a l i g h t n i n g arrester to a trolley pole set in concrete is not sufficient, as, even on a wet day, there h a v e been cases k n o w n w h e r e the concrete acted as such a good insulator t h a t there was a difference of p o t e n t ~ l of 475 volts from pole to track. On wooden-pole construction, the problem of i n s u l a t i n g is v e r y m u c h simplified, as e i g h t e e n or twenty feet of wooden pole, properly painted, is p r o b a b l y as good an i n s u l a t o r as can be made. W o o d e n poles of sufficient w e i g h t a n d of first-class yellow pine, c h e s t n u t , oak or cedar, p a i n t e d w i t h a p r e s e r v a t i v e c o m p o u n d at the b u t t and p a i n t e d two coats of good paint, are as s a t i s f a c t o r y as iron poles; and, in the long run, as well as in first cost, are a little cheaper. T h e y will last a b o u t one-third as long as the e s t i m a t e d life of an a v e r a g e iron pole properly painted. T h e l i m i t a t i o n s to the overhead trolley are now quite generally recognized. It has been f o u n d t h a t it is difficult to efficiently t r a n s m i t , by m e a n s of the o r d i n a r y form of trolley wheel, more t h a n 15o a m p e r e s from the wire to the wheel w i t h o u t excessive s p a r k i n g and loss. T h e speed at
62
Pepper.
LJ. F. I,
which a trolley wheel will s t a y on the wire, t h r o u g h section insulators, special work a n d switches, is l i m i t e d in good practice to n o t m u c h over ten miles an hour. W h e n the trolley s t a n d and wheel are b o t h d e s i g n e d for h i g h 'speed and the line carefully constructed, it is possible to run on straight-line work at a speed of a b o u t t h i r t y miles an hour. Beyond this speed the t e n d e n c y to t h r o w the wheel from the wire, o w i n g to s l i g h t o b s t r u c t i o n s on t h e trolley wire, is very great. If the wheel leaves the wire at this speed, it is almost certain to e i t h e r b r e a k the trolley pole or b r i n g down a large portion of the o v e r h e a d construction. It is ~or this reason t h a t e x p e r i m e n t s h a v e been and are b e i n g tried to s u b s t i t u t e a fixed c o n d u c t o r near the g r o u n d w i t h a large surface c o n t a c t for the o v e r h e a d trolley wire, for h i g h speed and h e a v y currents. A g r e a t deal of a t t e n t i o n has r e c e n t l y been g i v e n to the matter of g r o u n d return. It has been f o u n d t h a t the c u r r e n t on an i m p e r f e c t l y b o n d e d track is v e r y likely to come back to the s t a t i o n t h r o u g h w a t e r and gas pipes and on t h e lead covering of u n d e r g r o u n d cables, s e t t i n g up electrolitie action, which, in some instances, speedily d e s t r o y e d the pipes. In b o n d i n g a track, the first t h i n g to be considered is to g e t as low a resistance as possible at each joint. It is also necessary to h a v e an a s s u r a n c e t h a t the bond will r e m a i n in perfect condition for a l o n g period of t i m e and will s t a n d the m a x i m u m c u r r e n t t h a t will be called upon to go t h r o u g h a special piece of track. T h e a c t u a l cost of t h e m a t e r i a l for b o n d i n g a track, w i t h m o s t m o d e r n s y s t e m s of b o n d i n g , is a small i t e m c o m p a r e d to the original labor of p u t t i n g it in place and the cost of re-bonding the track w i t h i n a few years, w i t h o u t t a k i n g into c o n s i d e r a t i o n the w a t t s daily lost in the b o n d circuit. Few persons realize how low a resistance a pair of nine-inch girder rails have, and t h a t every effort should be m a d e to get the full benefit of this r e t u r n circuit. T h e resistance of the rail is f r o m six to seven times the resistance of the same section of c o m m e r c i a l copper. V e r y few tracks are bonded more t h a n one-fourth or one-third the c a r r y i n g c a p a c i t y of the rail. It has been proved in praetice t h a t the e a r t h and fish plates are not to be d e p e n d e d on as part of the r e t u r n cirCuit for h e a v y currents.