A new method of determining rotor leakage reactance and resistance of a three-phase induction motor

The paper develops a new method of determining the rotor leakage reactance and resistance of a 3-phase induction motor. Stationary flux distribution of constant magnitude is produced in the air-gap of the machine by supplying direct current to the stator windings. The rotor is driven at various slip speeds simulating the conditions of a 3-phase induction motor. The power input to the rotor is measured. The flux distribution in the stator teeth per pole pitch is measured by use of search coils and a ballistic galvanometer when d.c. excitation to all three phases of the stator is suddenly removed. The voltage induced per phase in the stator due to this change of flux linkage is calculated. An expression is developed for rotor leakage reactance and resistance. The theory is proved by experimental work. The performance is calculated using the rotor constants measured by this method and is compared with that obtained by no-load and locked-rotor tests and by an actual load test. A comparison of results justifies the determination of rotor constants by this new method.