Final answer:
The blocked-rotor test on an induction motor is used to determine the winding resistance and leakage reactance. For the equivalent per-phase circuit under blocked-rotor condition, the motor's electrical characteristics are represented by stator and rotor resistances and reactances in series, and there is no back EMF induced.
Step-by-step explanation:
Blocked-Rotor Test Analysis
When conducting a blocked-rotor test on an induction motor, the purpose is to determine the parameters such as winding resistance and the leakage reactance when the rotor is at standstill. The test simulates the conditions when the motor is starting. The per-phase equivalent circuit of an induction motor under blocked-rotor condition can be represented as a simplified model. This circuit includes the stator resistance (Rs), stator leakage reactance (Xs), rotor resistance referred to stator (R'r), and rotor leakage reactance referred to stator (X'r). All these components are in series and represent the motor's electrical characteristics during a blocked-rotor condition.
Since the rotor is not turning, there is no back EMF induced in the rotor, and the voltage applied is across the combined impedances. The input power (P), line current (I), and line-to-neutral (L-N) voltage (V) measured during the test are used to calculate these impedances. Specifically, with the given test results, one could determine the stator resistance and reactance by dividing the power by the square of the current and subtracting it from the square of the line-to-neutral voltage.