Question

A 8-Pole Separately Excited Dc Motor Is Rated At 100hp,320 V. The Field Winding Is Supplied From A 250 V Supply. The Field Winding Resistance Is 25Ω And Is Connected In Series With A 20Ω Rheostat. The Armature Winding Has 24 Slots, Wave-Wound, With 25 Conductors Per Slot And A Flux Per Pole Of 6.39mWb. When The Motor Is Delivering 58hp At 1100rpm Its efficiency is 87% at 58 hp output find.

the armature current

Answer 1

To calculate the armature current of a separately excited DC motor delivering 58hp at 1100 RPM with an efficiency of 87%, we first convert the horsepower to watts and then account for the efficiency to get the input power. the armature current is found by dividing the input power by the motor's voltage. the calculation yields an armature current of approximately 155.416 A.

Step-by-step explanation:

The question involves the calculation of armature current for a separately excited DC motor when it is delivering 58 horsepower (hp) at 1100 RPM with an efficiency of 87%. to find the armature current we need to first determine the output power in watts.

Output power (mechanical) can be calculated using the formula:

Output Power (W) = Horsepower (HP) × 746

For an output of 58hp, the mechanical output power is:

Output Power = 58 HP × 746 W/HP = 43268 W

Now we use the efficiency η to find the input electrical power:

Input Power = Output Power / Efficiency

Input Power = 43268 W / 0.87 ≈ 49733 W

Finally, to find the armature current (Ia), we divide the input electrical power by the motor voltage (320V):

Ia = Input Power / Voltage

Ia = 49733 W / 320 V = 155.416 A

Therefore, the armature current when the motor is delivering 58hp at 1100 RPM with 87% efficiency is approximately 155.416 A.