Page 321 - Industrial Power Engineering and Applications Handbook

121300 Industrial Power Engineering and Applications Handbook
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Speed (rpm) - N, = 980

Figure 12.32 Determining the duration of starting current

accelerating torque curve into three sections, A, B and C as
shown, to ascertain the magnitude of the starting current and :. I,, =
acceleration time for the different sections.
= 682% of I,
Section A
(b) T, = 48%
(a) I, = 750% of I, or 215 mkg
/b = 730% of I,
and starting time t,E = 7.71 seconds.
Consider the safe time as 8.8 seconds.
:. la"=
Section C
= 740% Of 1,
(a) I, = 630% of I,
(b) & = 82% of T, 1, = 100% of lr
or - 450 x 974 o,82 :. I,= v-
980 ~
= 367 rnkg = 450% Of I,
1866 x 333.3 (b) & = 80% or
and starting time t,A =
375 x 367
= 358 mkg.
4.52 seconds
and starting time t,C = 4.36 seconds.
Assume the safe time to be 5.2 seconds (considering a safety Consider the safe time as 5.0 seconds.
factor of nearly 15%) Plot the starting current and thermal curve of the motor as in
Figure 12.33.
Section E Considering TJ = 94% and p.f. = 0.85, then
450
(a) lb = 730% of I, I, = x 2.64 x 0.85 x 0.94 Amp. (Max.) at 80% of 3.3 kV
1, = 630% of I, = 123.2 A