1896.] on the Utilisation of Niagara. 275 



of bronze, with zigzag grooves in which oil under pressure is in 

 constant circulation. Grooves are also cut in the hub of each spider, 

 to permit the circulation of water to cool the bearings, this water 

 coming direct from the city mains at a pressure of 60 lbs. to the 

 square inch. The oil returns to a reservoir and is used over and 

 over again. Provision has been made against undue heating, and 

 plenty of cbance is given for air to circulate. This is necessary, 

 as about 100 horse-power of current is going into heat, due to the 

 lost magnetisation of the iron and the resistance in the conductors 

 themselves. Ventilators or gills in the driver are so arranged as 

 to draw up air from the base of the machine and eject it at consider- 

 able velocity, so that whatever heat is unavoidably engendered is 

 rapidly dissipated. 



In almost all electrical plants the switchboard is a tall wall or slab 

 of marble or mahogany, not unlike a big front door with lots of knobs, 

 knockers and keyholes on it ; but at the Niagara power house it takes 

 the form of an imposing platform, or having in mind its controlling 

 functions, we may compare it to the bridge of an ocean steamer, 

 while the man in charge or handling the wheels answers to the 

 navigating officer. The ingenious feature is employed of using 

 compressed air to aid in opening and closing the switches. The air 

 comes from a compressor located at the wheel pit and driven by a 

 small water motor. It supplies air to a large cylindrical reservoir, 

 from which pipes lead to the various switches, the pressure being 

 125 lbs. to the square inch. Another interesting point is that the 

 measuring instruments on the switchboard do not measure the whole 

 current, but simply a derived portion of determined relation to that of 

 the generators. All told, less than a thirtieth of a horse-power gives 

 all the indications required. To the switchboard, current is taken 

 from the dynamos by heavy insulated cable, and it is then taken off by 

 huge copper bus bars which are carefully protected by layers of pure 

 Para gum and vulcanised rubber, two layers of each being used; 

 while outside of all is a special braided covering, treated chemically to 

 render it non-combustible. The calculated losses from heating in a 

 set of four bus bars carrying 25,000 horse-power, or the total output 

 of the first five Niagara generators, is only 10 horse-power. About 

 1200 feet of insulated cable have been supplied to carry the current 

 from the dynamos to the switchboard in the power house. It has 

 not broken down until between 45,000 and 48,000 volts of alternating 

 current were applied to it. There are 427 copper wires in that cable, 

 consisting of 61 strands laid up in reverse layers, each strand con- 

 sisting of seven wires. Next to the strand of copper is a wall of 

 rubber one-quarter inch thick, double coated. Over this is wrapped 

 absolutely pure rubber, imported from England and known as cut 

 sheet. Then come two wrappings of vulcanisable Para rubber, ne>*t 

 there is a wrapping of cut sheet, and on top of that are two more 

 rubber coats. This is then taped, covered with a substantial braid, 

 and vulcanised. The object in using the cut sheet is to vulcanise it 



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