Answer Happy

(ii) A 3-phase Delta-connected, 800V, 50Hz, 4 pole induction motor has the following constants in ohms per phase referred to stator: r₁=0.30, x₁ = 0.550, r₂ = 0.230, x₂ = 0.610, Xm = 280. Fixed losses (core, friction and windage losses) = 700 watts. For 75% of full mechanical-load operation, compute: (a) The output torque (or shaft torque) and the efficiency at a slip of 0.04. [8Marks] (b) (1) The slip at which the maximum torque occurs, (2) the maximum internal torque, and (3) the corresponding maximum power output. [6 Marks] The starting rotor current and starting torque. [6 Marks] (c) (d) Draw the per-phase equivalent circuit of the motor. Define all parameters in the equivalent circuit [3 Marks] (e) The external resistance to be inserted in the rotor circuit to produce maximum torque at starting. Stator to rotor effective turns ratio is 1.2. [4Marks]