Unformatted text preview: ( 3 EE 362 HOMEWORK4 DUE :Agril 3Oz 2010z 17:00 A 3- phase , Y-connected, 230 volts line-to-neutral, 50 Hz, 8pole
induction motor drives a constant-torque load of 1340 Nm at a slip of 5% while
delivering full-load power to the load. Neglect friction and windage losses. Induction m/c parameters:
r1: 0.097 9 ' r; = 0,06 :2 x3= 0.196 n x2’= 0.161 n a. Calculate speed and power output for the basic motor. b. Calculate slip and power output for the above load by neglecting erl and x2! in
comparison with ( r2 / s) in the general torque expression. Compare the results
in (b) with those of (a). ’ c. Find the new shaft speed by assuming that frequency of applied stator voltages
is reduced to 25 Hz and (V1 / f) ratio is kept constant. Calculate also power
output and slip. d. Repeat (c) by using the straight line approximation defined in part (b).
Compare and comment on the results of (c) and (d). e. If now the frequency is suddenly reduced to 45 Hz while the system is
operating as in part (a) in the steady-state (V1 / f) ratio is kept constant, what
will happen to the operation mode of the system and that of the induction m/c.
Compute slip, speed, electromechanical torque and gross mech output power
just after frequency reduction. Draw the new rotor power ﬂow diagram. Use the straight line approximation given in (b).
Comment on the results. f. If now the phase sequence of applied stator voltages is suddenly reversed while
the system is operating as in part (a) in the steady-state, what will happen to the
new operation of induction m/c? Draw new rotor power ﬂow diagram. Use the
general torque expression. Comment on the results. ...
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