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A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remain constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm?
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A 200V DC shunt motor has an armature resistance 0.4 ohm and field res...
Problem Statement
A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remains constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm?
Solution
Step 1: Find the back emf and armature current at 750 rpm
Back emf, Eb = V - IaRa (where V = 200V, Ia = 25A, Ra = 0.4 ohm)
Eb = 200 - (25 x 0.4) = 190V
At 750 rpm, Eb = KΦN (where K = constant, Φ = flux, N = speed)
190 = KΦ x 750
Φ = 0.253 Wb
Armature current, Ia = Is - If (where If = Vf/Rf, Vf = Eb)
If = Vf/Rf = 190/200 = 0.95A
Ia = 25 - 0.95 = 24.05A
Step 2: Find the new field resistance for 500 rpm
At 500 rpm, Eb = KΦN (where K = constant, Φ = flux, N = speed)
190 = KΦ x 500
Φ = 0.38 Wb
New armature current, Ia = Is - If (where If = Vf/Rf, Vf = Eb)
If = Vf/Rf = 190/Rf
Ia = 25 - (190/Rf)
From the speed torque characteristic of the motor, torque is proportional to flux
Thus, the ratio of the torque at 500 rpm to the torque at 750 rpm is equal to the ratio of the flux at 500 rpm to the flux at 750 rpm
Torque at 500 rpm/Torque at 750 rpm = Φ at 500 rpm/Φ at 750 rpm
Torque is proportional to current
Thus, (25 - (190/Rf)) x 500/(25 - 0.95 x 750) = 0.38/0.253
Rf = 154.7 ohm
Step 3: Find the reduction in field resistance
Reduction in field resistance = 200 - 154.7 = 45.3 ohm
Conclusion
The reduction in field resistance necessary to reduce the speed of the motor from 750 rpm to 500 rpm is 45.3 ohm.
Community Answer
A 200V DC shunt motor has an armature resistance 0.4 ohm and field res...
A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remain constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm
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A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remain constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm?
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A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remain constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm? for Class 11 2024 is part of Class 11 preparation. The Question and answers have been prepared according to the Class 11 exam syllabus. Information about A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remain constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm? covers all topics & solutions for Class 11 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remain constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm?.
A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remain constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm? for Class 11 2024 is part of Class 11 preparation. The Question and answers have been prepared according to the Class 11 exam syllabus. Information about A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remain constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm? covers all topics & solutions for Class 11 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remain constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm?.
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A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remain constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm?, a detailed solution for A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remain constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm? has been provided alongside types of A 200V DC shunt motor has an armature resistance 0.4 ohm and field resistance 200 ohm. The motor runs at 750 rpm and takes a current Is to be 25 Amp. Assuming that the load tongue remain constant, find the reduction in the field resistance necessary to reduce the speed to 500 rpm? theory, EduRev gives you an
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