Study of Train Overloading and Its Impact on the Traction Motors: Case of AA-LRT N-S line

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Addis Ababa University


The Addis Ababa Light Rail Transit (AA-LRT) trains are being subjected to a high volume of passenger overcrowding especially during peak hours of the day. Due to this, the traction motors are meeting a mechanical load that exceeds the designed overload capacity of the train. As per the vehicle specification of AA-LRT, a single train carries 254 passengers as a normal rating and 317 passengers with seats and standing in an overloaded condition. But, the operational scenario revealed that one train is carrying up to 60 passengers more than the permitted maximum number of passengers in the worst traffic scenario. The improper passenger load on AA-LRT trains has various impacts on the traction motor while the train moving. Among those problems is that the traction motor is subjected to relatively high RMS current, higher copper loss, lower efficiency, and higher heating. To evaluate the overloading of the drive, the train dynamics including the resistive forces acting on the traction motor has been modeled and analyzed. The dynamic model of the motor is simulated using MATLAB/Simulink. The North to South site of AA-LRT is selected as a case study due to its irregular track geometry, and frequent operational as well as system problem scenario on the line. This study has indicated that passenger overcrowding has a considerable impact on the traction motor especially when the train is in acceleration. To quantify that impact, the value of traction motor parameters in improper train overloading is compared with the permissible train overload recommended by the designers. Based on that the following deviations are found due to improper passenger load. RMS current rise of about 36.5%, active power consumption increased by about 69.1%, reactive power consumption increased by about 15.93%, stator copper loss increased by about 32.25%, rotor copper loss increased by about 37.5%, and the efficiency dropped by about 77.7%, reduction in speed of the motor and the train speed. Particularly while carrying improper passenger load, when the train is about to start accelerating, speed reduction of about 56.65% is observed when compared with the speed of the motor when train has permissible passenger load. The passenger overloading phenomena can also be followed by several operational and system problems like track gauge misalignment, train speed restriction, wear out of wheel flange, wheel-rail slip, passenger discomfort, and train body mechanical overloading.



Traction motor, Track gauge, Wheel flange, Wheel rail slip, Traction motor overloading, Stator, Rotor