A dc machine (10 kW, 250 V, 1000 rpm) has Ra = 0.2 2 and Rf = 133 Q2. The machine is self-excited and is driven at 1000 rpm. The data for the OCC curve are: (A) 0 0.1 0.2 0.3 0.4 0.5 0.75 1.0 1.5 2.0 Ea (V) 10 40 80 120 150 170 200 220 245 263 (a) Determine the generated voltage with zero field current (b) Determine the critical field resistance (c) Determine the value of the field control resistance Re if no-load terminal voltage is 250 V (d) Determine the value of no-load generated voltage if the generator is driven at 800 rpm (e) Determine the speed at which the generator is to be driven such that no-load voltage is 200 with R = 0 The self-excited de generator in problem 3 delivers rated load when driven at 1000 rpm. The rotational loss is 500 W. (a) Determine the generated voltage (b) Determine the developed power and torque (c) Determine field current neglecting armature reaction (d) Determine the efficiency