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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.

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. Correct Answer 1

If = 400/200= 2 A No-load: Ia0 = 5.6 – 2 = 3.6 A Ea0 = 400 – 0.18 \ 3.6 – 2 = 397.4 V Full-load: Ib>a (fl) = 68.3 – 2 = 66.3 A Ea (fl) = 400 – 0.18 / 66.3 – 2 = 386.1 V n (fl)/n (nl) = = 1.

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