Problems

Find the condition of operation that minimizes the losses in a separately excited DC machine. (Start by writing an equation for Ploss in terms of the field currents and armature currents. Assuming linearity for all the nonlinear functions, establish the relation between armature current and field current, and then find the condition for minimum Ploss.)

Present an argument why it is impossible to achieve maximum efficiency at every operating point ('/'*, *) for a permanent magnet DC machine. (Start by writing an equation for Pioss in terms of T, , and machine flux

Proceeding as in Problem 5.2, explain why it is impossible to minimize losses at any operating point (T*, *) for a series DC motor.

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