(b) A 50 Hz, 415 V, 3-phase, 8-pole, squirrel-cage induction motor, with an internal cooling fan, drives a load whose torque variation is given in the following table. Time period (s) O to 35 35 to 50 50 to 70 Torque (Nm) 100 Linear increase, 100 to 200 200 Linear decrease, 200 to 100 100 70 to 80 80 to 100 100 to 120 If this torque-time cycle is repeated indefinitely, find which of the following continuously rated motors might be suitable for the duty: (3.7 kW, 5.6 kW, 7.5 kW, 9.5 kW, 11.2 kW, 15 kW, 18.7 kW, 22.5 kW, 30 kw, 37.5 kW). Assume that: • the motor remains spinning under zero torque conditions; • the value m = 2 is appropriate in the constant equivalent torque esti- mation. [Note that if part of a duty cycle characteristic can be represented by a straight line joining points (x1, a) and (x1 + X, b), then if all the ordinate values are squared, the area under the resulting curve will be X(a² + b² +ab) / 3.]

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1b

(b) A 50 Hz, 415 V, 3-phase, 8-pole, squirrel-cage induction motor, with an internal
cooling fan, drives a load whose torque variation is given in the following table.
Time period (s)
O to 35
35 to 50
50 to 70
Torque (Nm)
100
Linear increase, 100 to 200
200
Linear decrease, 200 to 100
100
70 to 80
80 to 100
100 to 120
If this torque-time cycle is repeated indefinitely, find which of the following
continuously rated motors might be suitable for the duty: (3.7 kW, 5.6 kW, 7.5
kW, 9.5 kW, 11.2 kW, 15 kW, 18.7 kW, 22.5 kW, 30 kw, 37.5 kW). Assume
that:
• the motor remains spinning under zero torque conditions;
the value m = 2 is appropriate in the constant equivalent torque esti-
mation.
[Note that if part of a duty cycle characteristic can be represented by a straight
line joining points (x1, a) and (x1 + X, b), then if all the ordinate values are
squared, the area under the resulting curve will be X(a² + b² +ab) I 3.]
Transcribed Image Text:(b) A 50 Hz, 415 V, 3-phase, 8-pole, squirrel-cage induction motor, with an internal cooling fan, drives a load whose torque variation is given in the following table. Time period (s) O to 35 35 to 50 50 to 70 Torque (Nm) 100 Linear increase, 100 to 200 200 Linear decrease, 200 to 100 100 70 to 80 80 to 100 100 to 120 If this torque-time cycle is repeated indefinitely, find which of the following continuously rated motors might be suitable for the duty: (3.7 kW, 5.6 kW, 7.5 kW, 9.5 kW, 11.2 kW, 15 kW, 18.7 kW, 22.5 kW, 30 kw, 37.5 kW). Assume that: • the motor remains spinning under zero torque conditions; the value m = 2 is appropriate in the constant equivalent torque esti- mation. [Note that if part of a duty cycle characteristic can be represented by a straight line joining points (x1, a) and (x1 + X, b), then if all the ordinate values are squared, the area under the resulting curve will be X(a² + b² +ab) I 3.]
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