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A method and system for detecting the occurrence of an actual locked condition in a locomotive system having a locomotive operating in an isolated mode of operation. The locomotive has a plurality of AC traction motors for propelling the locomotive system during normal operations. The AC motors are

A method and system for detecting the occurrence of an actual locked condition in a locomotive system having a locomotive operating in an isolated mode of operation. The locomotive has a plurality of AC traction motors for propelling the locomotive system during normal operations. The AC motors are reconfigurable to operate as AC generators and are connected to a common DC bus. When a potential locked condition in a first motor is detected, the DC bus is energized with an initial voltage using an alternate source of power. The DC bus voltage is regulated with a second motor by reconfiguring the second motor to operate as a generator. The torque produced by the first motor is then measured at a plurality of levels of electromagnetic flux in the first motor. Based on the measured torque, it is determined whether the potential locked condition is an actual locked condition.

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1. A method for detecting the occurrence of an actual locked condition in one or more of a plurality of AC traction motors which are reconfigurable to operate as AC generators, wherein said AC traction motors connected to a common DC bus, said method comprising:detecting a potential locked condition

1. A method for detecting the occurrence of an actual locked condition in one or more of a plurality of AC traction motors which are reconfigurable to operate as AC generators, wherein said AC traction motors connected to a common DC bus, said method comprising:detecting a potential locked condition in a first motor;energizing the DC bus with an initial voltage using an alternate source of power;regulating the DC bus voltage with a second motor of the plurality of AC traction motors by reconfiguring the second motor to operate as a generator;measuring torque produced by the first motor at a plurality of levels of electromagnetic flux in the first motor; anddetermining based on the measured torque whether the potential locked condition is an actual locked condition. 2. The method of claim 1 wherein energizing the DC bus is performed with a low-voltage battery. 3. The method of claim 2 wherein energizing the DC bus including selectively connecting the DC bus to the low-voltage battery until the second motor is operating as a generator then open-circuiting the battery. 4. The method of claim 1 wherein energizing the DC bus is performed with residual voltage from an alternator coupled to the DC bus. 5. The method of claim 1 wherein energizing the DC bus is performed with a diesel engine operating at less than 5% of it rated power. 6. The method of claim 5 wherein:detecting comprises detecting a potential locked axle condition in an axle coupled to the first motor; andwherein determining comprises determining based on the measured torque whether the potential locked-axle condition is an actual locked axle condition. 7. The method of claim 6 further comprising setting the frequency of an inverter which controls the first traction motor coupled to the potentially locked axle to a predetermined frequency value, whereby the level of electromagnetic flux in the first motor is varied, and wherein measuring the torque comprises measuring a torque produced by the first motor as the flux varies step. 8. The method of claim 6 further comprising setting the frequency of an inverter which controls the first motor coupled to the potentially locked axle to a predetermined first frequency value at a first frequency polarity, varying the level of electromagnetic flux in the first motor, measuring torque produced by the motor while operating at the predetermined frequency value and first polarity, setting the inverter frequency to a second value which is substantially the same as said predetermined first frequency value and at a second frequency polarity opposite to the first polarity, wherein measuring the torque comprises measuring torque produced by the first motor while operating at the second frequency value and polarity, and determining based on the respective values of torque measured during the measuring steps whether the potential locked-axle condition is an actual locked axle condition. 9. The method of claim 1 wherein measuring the torque comprises setting the frequency of an inverter which controls the first traction motor to a predetermined frequency value, varying the level of electromagnetic flux in the first motor, and measuring torque produced by the first motor during the flux varying step. 10. The method of claim 1 wherein measuring the torque comprises setting the frequency of an inverter which controls the first motor to a predetermined first frequency value at a first frequency polarity, varying the level of electromagnetic flux in the first motor, measuring torque produced by the first motor while operating at the predetermined frequency value and first polarity, setting the inverter frequency to a second value which is substantially the same as said predetermined first frequency value and at a second frequency polarity opposite to the first polarity, measuring torque produced by the first motor while operating at the second frequency value and polarity, and determining based on the respective values of torque measured durin g the measuring steps whether the potential locked-axle condition is an actual locked axle condition. 11. A system for detecting the occurrence of an actual locked-axle condition in an isolated vehicle having a plurality of AC traction motors which are reconfigurable to operate as AC generators, said AC traction motors connected to a common DC bus, said system comprising:a speed sensor detecting a potential locked axle condition in an axle coupled to a first motor of the plurality of AC traction motors;a power supply energizing the DC bus with an initial voltage using an alternate source of power;a voltage regulator regulating DC bus voltage with a second motor of the plurality of AC traction motors by reconfiguring the second motor to operate as a generator;a torque sensor measuring a torque produced by the first motor at a plurality of levels of electromagnetic flux in the first motor; anda processor determining based on the measured torque whether the potential locked-axle condition is an actual locked axle condition. 12. The system of claim 11 wherein the power supply comprises a low-voltage battery for energizing the DC bus. 13. The system of claim 12 wherein the power supply intermittently connects the low-voltage battery to the DC bus. 14. The system of claim 11 wherein the power supply comprises a residual voltage from an alternator coupled to the DC bus for energizing the DC bus. 15. The system of claim 11 wherein the power supply comprises a diesel engine operating at less than 5% of it rated power for energizing the DC bus. 16. The system of claim 11 wherein the power supply sets the frequency of an inverter which controls the first traction motor coupled to the potentially locked axle to a predetermined frequency value, wherein the voltage regulator varies the level of electromagnetic flux in the first motor, and wherein the torque sensor measures the torque produced by the first motor during the varying flux. 17. The system of claim 11 wherein the power supply sets the frequency of an inverter which controls an AC motor coupled to the potentially locked axle to a predetermined first frequency value at a first frequency polarity, wherein a voltage regulator varies the level of electromagnetic flux in the motor, and wherein the torque sensor measures the torque produced by the motor while operating at the predetermined frequency value and first polarity, wherein the power supply sets the inverter frequency to a second value which is substantially the same as said predetermined first frequency value and at a second frequency polarity opposite to the first polarity, wherein the torque sensor measures the torque produced by the motor while operating at the second frequency value and polarity, and wherein the processor determines based on the respective values of torque measured during the measuring steps whether the potential locked-axle condition is an actual locked axle condition.