274 Mr. Thomas Commerford Martin [June 19, 



Westinghouse Electric Co. "upon whom the responsibility was thrown 

 for its success. 



Each generator, from the bottom of the bed plate to the floor of 

 the bridge above it is 11 feet 6 inches high. Each generator weighs 

 170,000 lbs. and the revolving part alone weighs 79,000 lbs. In 

 most dynamos the armature is the revolving part, but in this case 

 it is the field that revolves while the armature stands still. It is 

 noteworthy that if the armature inside the field were to revolve in 

 the usual manner instead of the field, its magnetic pull would be 

 added to the centrifugal force in acting to disrupt the revolving mass ; 

 but as it is, the magnetic attraction towards the armature now acts 

 against the centrifugal force exerted on the field, and thus reduces 

 the strains in the huge ring of spinning metal. The stationary 

 armature inside the field is built up of thin sheets of mild steel. 

 Along the edges of these sheets are 187 rectangular notches to 

 receive the armature winding in which the current is generated. This 

 winding is in reality not a winding, as it consists of solid copper bars 

 11.^ by -j^ inch, and there are two of these bars in every square hole, 

 packed in with mica as a precaution against heating. These copper 

 conductors are bolted and soldered to V-shaped copper connectors, 

 and are then grouped so as to form two separate independent 

 circuits. A pair of stout insulated cables connect each circuit with 

 the power house switchboard. 



The rotating field magnet outside the armature consists of a huge 

 forged steel ring, made from a solid ingot of fluid compressed steel, 

 54 inches in diameter, which was brought to a forging heat and then 

 expanded upon a mandril, under a 14,000-ton hydraulic press, to the 

 ring, 11 feet 7^ inches in diameter. On the inside of this ring are bolted 

 twelve inwardly-projecting pole pieces of mild open hearth steel, and 

 the winding around each consists of rectangular copper bars encased 

 in two brass boxes. Each pole piece with its bobbin weighs about 

 li tons, and the speed of this mass of steel, copper and brass, is 9300 

 feet, or If miles per minute, when the apparatus is running at its 

 normal 250 revolutions. Not until the ring was sjDceded up to 800 

 revolutions, or six miles per minute, would it fly asunder under the 

 impulse of centrifugal force. As a matter of fact, 400 revolutions 

 is the highest speed that can be attained. This revolving field 

 magnet is connected with the shaft that has to turn it, and is supported 

 from above, by a six-armed cast steel spider keyed to the shaft, this 

 spider or driver forming a roof or penthouse over the whole machine. 

 The shaft itself is held in two bearings inside the castings around 

 which the armature is built up, and at the bearings is nearly 13 

 inches in diameter. At the lower end is a flange fitting with the 

 flange at the top of the turbine shaft, and at the upper end is a taper 

 over which the driver fits. The driver and shaft have a deep keyway, 

 and into this a long and massive key fits, holding them solidly 

 together. The driver is of mild cast steel, having a tensile strength 

 of 74,700 lbs. per square inch. The bushings of the bearings are 



