694 ECONOMIACL ASPECTS 



The auxiliary power can either be secured by operating old 

 steam plants of the power customers which have been shut down 

 by purchase of power from a water-power company or by con- 

 structing new steam-turbine plants as part of the water-power 

 system. 



Stand-by Stations. Emergency reserve stations are, as a rule, 

 more necessary in the early days of a hydro-electric develop- 

 ment than after the operating conditions become settled. They 

 are, however, essential in order to provide against possible inter- 

 ruptions to the service and contract provisions are often such 

 as to make their installation almost imperative. 



The size of such stations is naturally governed by the load 

 which must be maintained under all conditions. Their location 

 should be close to important distributing centers so as to be use- 

 ful in case of breakdown of the transmission lines. For large and 

 extended systems it may be advisable to provide two or more 

 distributed stations rather than one of the combined capacity. 



A quick start is an essential requirement of an emergency 

 stand-by station. It is, however, not customary to have all 

 the boilers under fire to take over the load immediately in case 

 of an interruption. Some of the boilers are, as a rule, kept 

 under banked fires part of the time to secure the most important 

 load, and the turbines are operated as synchronous condensers 

 to improve the power-factor of the entire transmission system, 

 which may carry a large inductive load. 



Under these circumstances it is particularly easy to respond 

 to sudden load demands because the unit is already up to speed 

 and in synchronism, the turbine is kept warmed up, and only a 

 change in the field excitation is necessary to place the unit on the 

 line, which takes only a few minutes at the most. When storms 

 are approaching, the entire reserve equipment should be made 

 ready to respond immediately to any emergency that may arise. 



The first cost of the station should be low, while efficiency is 

 not such an important item. Consideration should, however, be 

 given to the possibility that it may later be used under other 

 operating conditions requiring the highest efficiency. It is, 

 therefore, often advisable to make provision in the design from the 

 beginning so that economizers and other labor-saving devices may 

 be installed at a future date, should conditions so demand. With 

 large steam-turbine units it is, however, practical to obtain the 



