Question

III A 208-V, 60 Hz, six-pole Y-connected 25-hp design class B induction motor is tested in the laboratory, with the following results: No load test: Blocked-rotor test: DC test: 208 V, 22.0 A, 1200 W, 60 Hz 24.6 V, 64.5 A, 2200 W, 15 Hz 13.5 V, 64 A a) Find the equivalent cireuit of this motor. (4 marksy)

Answer 1

i) By star - connection, 2 R_1 = V_oc/I_oc rightarrow 2R_1 = 135/64 = 0.21 R_1 = 0.21/2 = 0.105 Ohm R_1 = 0.105 Ohm ii) R_1 + R_2 = (0.2202) cos (36.82 degree) = 0.176 Ohm rightarrow R_2 = 0.176 - R_1 = 0.176 - R_1 = 0.176 - 0.105 rightarrow R_2 = 0.071 Ohm \r\n iii) By class B: - X_1: X_2 0.4: 0.6 rightarrow X_1 = (0.4) (0.528) X^-_1 = 0.211 Ohm rightarrow X_2 = (0.6) (0.528) X_2 = 0.317 Ohm \r\n iv) By Z_ML = X_1 + X_M rightarrow (208/53)/22 = 0.211 Ohm + X_m rightarrow 5.46 Ohm = 0.211 Ohm + X_M X_M = 5.244 Ohm The equivalent circuit is shown below: -