Page 107 - Industrial Power Engineering and Applications Handbook

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Torque curve
/- obtained

With rotor's
own R2

-T

\

Speed - L
Ns
S1 52 s3 s4

Figure 5.6(a) Torque curve with a five-step external resistance

From (a) and (b)

where R2,, RZ2, . . . RZs etc. are total rotor resistances per
phase after introducing the external resistances, or
... R22 = p. R2,
(5.2)
RZ3 = p R,, = P' . R,, etc.
At the start, when SI = 1 and R2 = P. RZ5
= P ' P4 . R2,
= ps . R2,
Similarly R
or p5 = s,,,
or R 2- -p5.2
Smax
:. p =

Generalizing this for a number of resistance steps a,
R21
R,,
R22
or - etc. = - P= G
=
~
s2 s3 Smax (5.3)