PRACTICAL OPERATION OF DYNAMOS. 199 



ing. A third advantage of leaving the series field coils perma- 

 nently in circuit is that the series field excitation is not suddenly 

 added to the shunt field excitation on closing the switch. In this 

 case the newly connected machine does not take any appreciable 

 load until its shunt field rheostat is adjusted after the machine is 

 connected. On the other hand, the series field coils being dis- 

 connected and the machine being of course brought up to the 

 full station voltage by the shunt field excitation before it is 

 connected, the sudden increase of its field excitation which is 

 produced by connecting the series field coil, tends to make it take 

 its load suddenly, and perhaps to make its load excessive until 

 the shunt field rheostat is again adjusted. 



When the series field coils of all the generators are left per- 

 manently in circuit, the main switches S f and S", Fig. 113, are of 

 course two-pole switches, and each series field coil is provided 

 with a single-pole switch for opening or closing its circuit at will ; 

 but the procedure in starting is essentially as above described. 



88. The operation test. Most electric stations and equipments 

 are installed under contracts which are completed only when the 

 station or equipment has been put into satisfactory operation by 

 the constructing engineer. This of course implies an operation 

 test of the electrical installation under the supervision of the con- 

 structing engineer. This test is a most important one, inasmuch 

 as it frequently brings to light essential details which have been 

 overlooked, and inasmuch as it gives an opportunity for the 

 person who is to take charge of the apparatus to work for several 

 days under the direction of a more experienced engineer. The 

 operation test is carried out by following the procedure involved 

 in the regular management of the installation as explained in the 

 foregoing articles, the various machines being started with the 

 utmost caution and a sharp watch being kept for symptoms indic- 

 ative of trouble. 



The performance test. Aside from the testing of individual 

 machines to make sure that they meet the guaranteed regulation 

 (see Art. 48), efficiency (see Arts. 64, 65 and 68), and rating 



