Diagnosis-oriented sequence circuit-based modeling of eccentric rotor traction induction motors accounting for cage damping and split-phase currents

Abstract

A 1130kW squirrel-cage induction motor used for railway traction is analyzed in this paper in case of eccentric rotor. Since the motor has parallel-connected windings, the air gap unbalance makes rise unbalanced currents in the stator branches, and the split-phase current signature analysis can be attempted for fault detection. The split-phase currents are better analyzed when transposed in the complex domain, by using symmetrical components. Moreover, the rotor cage currents must be carefully taken in account in the model, since they develop a powerful damping effect on the signature of static eccentricity. This paper shows that the faulted machine can be represented by the superimposition of five equivalent circuits corresponding to five centered-rotor virtual machines, useful for fault-related split-phase current calculation. The mathematical modeling shown in this paper is useful to carry out a diagnostic method, as shown in a companion paper. The latter also reports confirmatory simulations of the faulted 1130kW motor, based on winding function approach.

Validation of sequence circuits useful for split-phase current signature analysis (SPCSA) and diagnosis of eccentric-rotor traction cage motors

“…Fig. 1 shows the symmetrical stator winding structure, made up of pole-phase groups (PPGs, or groups of series-connected coils of a phase under a pole, called SI, ... ,Sn in Fig.l of [6]). The rotor cage is decomposed in elementary loops R], ... , Rm fonned by couples of consecutive bars and by the joining ring segments (mesh-model).…”

“…Resume of Theory From [6] The machine model introduced in [6] describes a squirrel cage induction motor with parallel connections in the stator and generic rotor eccentricities. Fig.…”

“…The model proposed in [6] is validated in this paper for a practical 1130kW motor used for high-speed railway traction drives. The fault-related currents calculated by using the sequence circuits theoretically derived in [6] are compared with the values directly obtained by dynamic simulations with a complete mesh-model based on winding function approach (WF A), at no-load and full-load conditions, and with various combinations of SRE and DRE.…”

“…The fault-related currents calculated by using the sequence circuits theoretically derived in [6] are compared with the values directly obtained by dynamic simulations with a complete mesh-model based on winding function approach (WF A), at no-load and full-load conditions, and with various combinations of SRE and DRE. A good match is obtained, which makes the sequence-circuit modeling suitable for further future developments of fault indicators useful for machine condition monitoring.…”

“…[NTRODUCTION Paper [6] proposed a symmetrical component-based modeling of squirrel-cage parallel-connected induction motors with REs, which allows machine decoupling in five equivalent circuits (sequence circuits) of five virtual centered-rotor machines. These circuits are useful for calculation of fault related stator currents, taking in account the very important damping effect developed by the rotor cage.…”