2l6 



CHAPTER XI 



In these installations the prime mover has been a non-condensing steam 

 turbine, making about i,8oo r.p.m., direct coupled to a dynamo the 

 current from which drives a motor making 450 r.p.m. The motor in turn 

 drives through herring-bone spur and pinion gearing, with a gear ratio of 

 1 : 10, what corresponds to the first motion pinion of the ordinary- 

 steam-driven train. 



It is easy to see that the combination of djaiamo and motor forms nothing 

 else than a reducing gear, to which has to be added the first motion spur 

 and pinion gear before the system is reduced to the first motion pinion 

 of the steam drive. 



Considered in this hght the arrangement appears to be a rather expensive 

 train of gearing. As regards the steam consumption, the latest tests give 



Fig. 122 



a distinctly higher rate to the non-condensing turbine than to the non-con- 

 densing Corliss engine in units of the size installed. The determinations 

 approximate to 33 and 30 lbs. of steam per indicated horse-power-hour. 

 To the difference between these figures is to be added the power lost in the 

 electric reduction gear. This is taken as 8 per cent, in both dynamo and 

 motor, and 2 per cent, in the wiring, so that only 83 per cent, of the power 

 represented by the steam turbine reaches the second motion pinion of the 

 train of gearing corresponding to the first motion pinion of the steam drive. 

 Allowing for the increased consumption in the turbine, it would then follow 

 that about 30 per cent, more steam must be delivered to the turbine than 

 to the Corliss engine. Another factor tends to increase the steam qoj^- 

 sumption. The prime motor driving a milUng plant must be capable for 

 a limited period of developing power much above the normal load. TJ^^, 

 regulation of the electric machinery is by means of an external resistaHjC^^,, 



