MA 



466 ELECTRICAL EQUIPMENT 



dent that reactors in the generator leads offer no protection to 

 troubles of this nature. 



In hydro-electric power systems with slow- or medium-speed 

 multi-polar generators, the inherent reactance of these is, as a rule, 

 sufficiently high and the construction such that the machines can 

 safely withstand momentary short-circuits, and generator reactors 

 are very seldom used in hydro-electric plants. If such reactors 

 are used, they should be placed in the line leads as close to the 

 generator as possible and not in the neutral. 



Bus Reactors. These are very extensively used in hydro- 

 electric stations and permit of an unlimited extension of the sys- 

 tem. The bus-bars are divided 

 into sections by reactors (Fig. 

 290), and trouble may thereby 

 be confined to the particular sec- 

 tion on which the short-circuit 

 takes place, while under normal 

 operation a free exchange of cur- 

 rent may take place, thereby 

 retaining the advantage of par- 

 FIG. 290. Bus Reactor. allel operation. A short-circuit 



then can seriously involve one 



bus-bar section only, and the destructive power of a short-circuit 

 is limited to the generating capacity of that one section plus the 

 limited power which can flow from the two adjoining sections. 



The voltage of the section upon which the short-circuit takes 

 place falls to zero and the reactors connecting the two adjacent 

 sections each thus consume the total voltage during the transfer of 

 the short-circuit current. Strictly speaking, the transfer does not, 

 however, take place by a drop of voltage between the sections, 

 but by a phase displacement between the voltages of the bus-bar 

 sections, as explained later. 



Bus reactors afford, of course, no protection to the generators 

 connected to the section on which the trouble occurs, but they 

 give added protection to the generators on the other sections. 



Transformer and Feeder Reactors. With modern high-voltage 

 transmission systems where the transformers are connected on the 

 unit principle so as to form a part of the transmission line, reactors 

 in the low-tension transformer leads (Fig. 291) may be of consid- 

 erable value for protecting against short-circuits in the lines, 



o o o o 



