172 POWER-HOUSE DESIGN 



is especially important with vertical units where the water-wheel 

 rotor is mounted on the same shaft as the generator field, and in 

 which case it should be possible to lift out the whole revolving 

 element by simply removing the top bracket and bearing of the 

 generator. 



The type of crane depends largely on the size of the units, 

 weight of heaviest pieces and the number of units in the station. 

 In small stations a hand-operated crane may be ample, while very 

 large stations will require two electrically operated cranes. A few 

 stations have been equipped with a gantry type of crane just 

 long enough to straddle the generators and high enough for 

 the highest lift. This type deserves more careful consideration 

 than it has had heretofore. The span is shorter and consequently 

 lighter than an overhead crane. The building framework can be 

 designed simply for the roof load, with a material reduction in the 

 steel required. 



The crane should be of sufficient capacity to lift the total 

 revolving element of vertical wheels and generators unless some 

 special arrangement of jacks under the generator rim, or on the 

 shaft, is provided. This support is necessary to relieve the thrust 

 bearing for inspection or repairs. Jacks or supporting blocks 

 under the generator field rim are also of great assistance during 

 the erection of vertical units. 



The question of armature repairs should be considered when 

 designing the crane equipment. A few coils can be replaced in a ver- 

 tical machine by removing two or more field poles. Extensive re- 

 pairs are best handled by lifting the entire armature above the field 

 rim and supporting it on substantial blocking. A temporary floor 

 is laid on the top of the field spider for a working platform. This 

 arrangement does not disturb the line up of the revolving parts 

 and usually makes a very material saving in time and expense. 



Some special arrangernent is usually necessary to provide 

 power for the electric cranes. The exact details depend largely 

 on local conditions and a careful analysis should be made. In 

 some cases a motor generator set may be purchased in advance 

 and later used as part of the permanent exciter equipment. In 

 others, an engine or turbine-driven generator set may be the best 

 solution. In any case, sufficient capacity for the heaviest lifts 

 must be provided. An under-powered equipment where the 

 heavy lifts have to be jumped a few inches at a time is decidedly 



