Page 115 - Industrial Power Engineering and Applications Handbook

5/96 Industrial Power Engineering and Applications Handbook
List of formulae used To determine external resistance and
time of start
Selection of rotor resistance
R2
R2l = Si . - (5.2)
ss e2
R21 = R2 + Re = - (5.la) sm,
43 ' 1,l R21, R22, are total rotor resistances per phase after
(Rotor Y, external resistance Y) introducing the external resistances
SI = slip at the beginning of a step
43 . sse2 S,,, = slip at the end of a step
R21 = R2 + 3Re = ___ (5.lb)
Id
(Rotor A, external resistance Y) P= (5.3)
(5.1~)
(Rotor Y, external resistance A)

(5.ld) - R22 - R23 - ....
R22
R2l
(Rotor A, external resistance A) a= no. of resistance steps
R2 = Rotor resistance Wphase
Re = External resistance Rlphase
RZ1 = Total rotor resistance R/phase Resistance for speed control
R = required rotor circuit resistance
sse2 = rotor standstill voltage R21 = -. ss e2 % Speed reduction (5.4)
Iml = required rotor current $j I, % Current at the reduced speed
.