DIRECT-CURRENT DYNAMOS AND MOTORS. 115 
82. Formulas for Electrical Efficiency.—Inserting 
into (56) and (57) the expressions for W, w,, and w,, in 
terms of E. M. F., current strength, and resistance, the 
following formulas for the electrical efficiency are ob- 
tained: 
Series-wound generator: 
: ie EC é 
Mh, £F. = HOR C L ry ete (58) 
Shunt-wound generator: 
ry EC : 
El. Eff. = EO + Or. + Ontraritt (59) 
Compound-wound generator: 
eat EC 
El. Eff. = EO + Cir. +1.) + Canta”? (60) 
Series-wound motcr: 
ae J C ee Cc (1, - Os 
EA. EF. = EO sy Fea et sas (61) 
Shunt wound motor: 
Tg P aes coke Bs Sle ee (62) 
Compound-wound motor: 
EC —[C. (ra) + Tee!) + Ca’ra”] 
RG ..- (63) 
The symbols used in the above formulas (58) to (63) 
represent EK. M. F., current strengths, and resistances, as 
El. Eff. = 
follows: 
E = terminal voltage of generator, or supply voltage 
of motor; 
C = current output of generator at brushes, or current 
intake of motor at brushes; 
Ca = current flowing in shunt circuit; 
C, = armature current; for a generator, C, = C+ Ca; 
for a motor, C, = C — Ca; 
