The Diseases Of Electrical Machinery

58 THE DISEASES OF phase machine, a break affects only that phase in which the break occurs. As a result, as can be seen from Fig. 28, under such circumstances a two-phase generator will then only work single-phase. The effect of a break upon the running of a three- phase generator depends upon the method of connec- tion, whether A or star. If the machine is star- connected, then a break in phase 3 (Fig. 27) has the result that the machine will only work single-phase. Namely, the lamps between the terminals 1 and 2 will only burn while the lamps between 2 and 3 and 1 and 3 go out Is the machine, on the other hånd, A-connected, then if a break occur in phase 3 it ap- pears as if the machine would only run two-phase. In reality, however, the machine still runs three-phase. There are really still three voltages generated in the machine. The pressure between 1 and 3 is, however, not produced in the defective phase 3, but is the re- sultant of the phases 1 and 2. As a result of the break, the remaining phases will obviously be much more heavily loaded. Contact of Different Phases.—Short-circuits to copper and iron have naturally the same effects with polyphase machines as were above described in the case of single-phase machines. Short-circuits between two different phases are, however, especially dan- gerous, whether due to a direct contact between the copper, or whether both coils are short-circuited to the iron. This fault will be at once noticed—leaving out