Closed rotor slot effect on negative sequence impedance [in induction motors]

This paper presents experimental results concerning the negative sequence impedance Z/sub n/ of induction motors with different rotor slot constructions. Z/sub n/ is used as a fault index for shorted turns in stator windings, or can be used to distinguish negative sequence current due to unbalanced supply voltage from negative sequence current due to stator shorts. Although Z/sub n/ is largely independent of speed changes, experiments show that it can vary strongly with motor loading. Results presented show that, depending on rotor slot type, negative sequence reactance can change by as much as 10% to 50%, especially in motors with closed rotor slots.