ELECTRIC TRAMWAY SYSTEMS.

Taranaki Daily News, Volume LII, Issue 308, 7 February 1910, Page 3

ELECTRIC TRAMWAY SYSTEMS.

To the Editor. Sir,—With interest 1 read your leading article in Thursday's issue on the tramway system for New Plymouth. As you appear to be off the track at two or three points, may I have the privilege of helping to put you on the right lines. The firs't point of derailment is that "a series of studs Bft Gin apart are attached to an electric cable." The fceeond point is the "chain," termed a "conductor." These two points I will explain in the method of working the G.-B. system. The third point, that

there is a saving in cost of installation as compared with overhead wires, poles', etc., I will also deal with. Before going further I would like to mention that hot only has Lincoln got the GriffithsBedell (G.-B.) system, but the London County Council has it installed on a section on the Mile End road. The method of working the system is, roughly, as follows: A magnetised flexible "skate"—not chain—is' carried under the car. As this passes over a Stud it is attracted down and makes contact with the stud, and at the same time the magnetic flux causes a plunger ito fly out and make contact with the underground live conductor below the Stud. This conductor takes the form of a cable constructed of a centre piece of jute s'tirrounded by copper wires, then galvanised iron wires, and over all this is fitted galvanised iron tubing in sixinch lengths, which forms the bare cable, and which is carried on reel-shaped inssulators in earthenware pipes. The object of the flexible skate is to allow of live studs being flus'h with the road'surface. The skate is made up of a number of cast-iron links threaded on a flexible cable supported by vertical springs in a blot in one pole of a magnet. It is a kittle over'six feet long. The skate is magnetised normally by current from the underground conductor. A battery is provided of about 25 volts, which is l charged when the current is large, and which excites the magnets when the current is cut off. Switches are provided to open the battery circuit when the tar is standing. The distance between the studs is from six to nine feet. At Lincoln they are nine feet, two skates being used. On the London County Council Mile End road Section they are six feet apart, one skate only being used. At points and crossings and under

other special circumstances extra precautions have to be taken. It is quite evident that, if ordinary iron rails were tosed, when the skate came over the rail it would short-circuit the supply. This' is guarded against in two ways. Manganese steel rails are used, or studs of a special type. In these studs the upper part is insulated from the lower, fend the two parts connected through a resistance. Every car is fitted with apparatus for detecting a live s'tud that may be left behind. A steel brush passes Over the stud after the skate has left it. If the stud is alive current is collected by the brush, and either rings a bell or opens the canopy switch by a toil, thus stopping the car. When the ear is stopped in this way the driver closes the switch and drives slowly backwards until the switch opens again. In this way the live stud is found, and a tripod or lamp placed over it until Hie lineman arrives, the service, however, nob being interrupted. The cos't of installation of a surface contact system is averaged at about 10 per cent, more than the overhead trolley, and double that of the conduit (centre rail system). The maintenance cost is also greater. For instance, of nineteo: muni-cipally-operated overhead systems \>!i"e'i had been running for three years o. less, the average cos't for repairs nd maintenance was .79d per car mile : against a corresponding figure on the (Lincoln system (G.-B.) of 1.25 d, which (showed a saving in favor of the over head system of 37 per cent. As regard; the question of safety, with the single exception of the conduit sys'tem, a sur face contact, such as the G.-8., is the safest form of electric traction now ir operation. Toints in favor of the G.-B are reliability, safety, silent running and sightliness. —II am, etc., ELECTRIC POWER.