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A 100KW, 250 V, 400 A, a long shunt compound generator has an armature resistance of 0.025 ohms. There are 1000 shunt fields turns per pole and 3 series field turns per pole. The series field is connected in a such a fashion that positive armature current produces direct-axis MMF which adds to that of the shunt field. Compute the gross MMF at the rated terminal current when shunt field current is 4.7A and speed is 1150 rpm.
How should the field mmf be with respect to armature mmf to reduce the armature reaction?
Which of the following statements are true? a. As load increases armature current decreases, regardless of excitation. b. For under and over excited motors, power factor tends to approach zero with increase in load c. With normal excitation when load is increased, change in armature current is greater than in power factor which tends to become increasingly leading. d. Both with under and over excitation, change in power factor is greater than in armature current with increase in load.
400-V dc shunt motor takes a current of 5.6 A on no-load and 68.3 A on full-load. Armature reaction weakens the field by 3%. What is the ratio of full-load speed to no-load speed? Given: Ra = 0.18 Ω, brush voltage drop= 2 V, Rf = 200 Ω.
In an alternator, the armature winding is kept stationary while the field winding is kept rotating for the following reasons: 1. Armature handles very large current and high voltage 2. Armature fabrication, involving deep slots to accommodate large coils, is easy if armature is kept stationary 3. It is easier to cool the stator than the rotor Which of the above reasons are correct?
Consider the following statements: The armature reaction mmf in a dc machine is: 1. Stationery with respect to the field 2. Rotating with respect to the field poles 3. Rotating with respect to the armature Which of these statements are correct?
Consider the following statements regarding the starting of a dc shunt motor: a. External field resistance should be minimum b. External field resistance should be maximum c. Reduced voltage should be applied to the armature d. Increased voltage should be applied to the armature Which of the above statements are correct?
A synchronous motor on load draw a current at a leading power factor angle ϕ. If the internal power factor angle which is the phase angle between the excitation emf and the current in the time phasor diagram is ψ. Then the air gap excitation mmf lags the armature mmf by
Consider the following statements: In the above figure, the curves pertain to the DC motor A. Speed vs Armature current characteristic of a DC shunt motor B. Torque vs Armature current characteristic of a DC shunt motor C. Speed vs Armature current characteristic of a DC series motor D. Torque vs Armature current characteristic of a DC series motor
Consider the following statement: 1. Initial load tests and routine load tests are carried out on test piles and working Piles, respectively. 2. In a pile load test, the allowable load can be taken equal to half the ultimate load at which the total settlement amounts to one-tenth of the pile diameter. 3. In a pile load test, the allowable load can be taken equal to two-thirds of the total toad which causes a plastic settlement of 6 mm. Which of the above statements are correct?