Find the effect on the speed of the motor when the frequency is changed from 40 Hz to 80 Hz.

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Chapter 54, Problem 2SQ

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Find the effect on the speed of the motor when the frequency is changed from 40 Hz to 80 Hz.

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Excitation circuit internal resistance of a shunt excited DC generator of 150 kW, 250 V, 1350 rpm Rf = 10 Ω, armature circuit internal resistance Ra = 0.05 Ω. Excitation to adjust the end voltage of the machine A rheostat of Rreo = 40 has been installed in its circuit. Friction and ventilation losses are neglected. According to this, a) When the entire rheostat in the excitation circuit is activated and the generator is operating under rated conditions, a1) Calculate the load current, excitation and armature currents. a2) Calculate the emf induced in the armature and the power taken from the shaft. a3) Calculate the efficiency with the moment taken from the shaft. b) Spindle revolutions are reduced to n = 1000 rpm. In this case, Va = 250 V and Ea value in (a) What value should the rheostat be adjusted to keep the value found constant? In this new situation Calculate the power given.