VIBRATION CHARACTERISTICS ANALYSIS OF EMU TRACTION MOTOR ROTOR UNDER ECCENTRIC FAULTS

Air-gap eccentricity and mass eccentricity are two common eccentric faults in the traction motor of electric multiple units (EMU), and the resulting unbalanced magnetic pull (UMP) and mechanical unbalance force often induce more complex rotor dynamic vibrations, which may endanger the safe and reliable operation of train traction drive device. To this end, the Jeffcott model for a traction motor rotor system under a static-dynamic air-gap eccentricity and a rotor mass eccentricity is established. Then the air-gap flux density distribution and the Maxwell stress distribution on the rotor core surface are derived when the traction motor with load is running under the static-dynamic air-gap eccentricity, and the unified analytical expressions of UMP are subsequently presented, which are applicable to motors with a static-dynamic air-gap eccentricity, with no-load or load operations, and with any pole-pair number. The fourth-order fixed-step Runge-Kutta algorithm is used to calculate the dynamic response of a certain traction motor rotor under UMP and the mechanical unbalance force, and the effects of an initial static eccentricity, of a mass eccentricity, of radial stiffness and of rotational speed on the vibration characteristics of the system are discussed in detail. Results show that the rotor orbit of the traction motor is elliptical but nearly circular under the eccentric faults. The mass eccentricity, radial stiffness, and rotor speed affect the magnitude of rotor orbit, while the initial static eccentricity and radial stiffness can move the center of orbit along the direction of the static eccentricity. In addition, the existence of the air-gap eccentricity makes the displacement spectrum of motor rotor with a mass eccentricity more obviously contain the components of zero frequency, of natural frequency, of rotation frequency, of double rotation frequency, of double power frequency and its combinations with rotation frequency, and so on.