Lightning: Elevated line of rail transit is often easily attacked by lightning. And the cable transmission , steel structure , weak equipment ,and communication system are harmed by it.
Faulty Arc: in the train , faulty arc caused by bad connection on the place of power supply cable , wring terminal ,and electrical components . faulty arc with high heating energy often leads to fire accident.
Harmonic and three phase unbalance:
1 The rail transit power supply system is affected by the harmonics , which caused by the rectifier in the traction substation . in the rectifying device , there is the current AC formed rectangular wave. Power frequency and a high harmonic current create a synthesized waveform . and is an odd multiple of the fundamental frequency of the power .
2 The nonlinear equipment in the supply power of rail transit, is the mainly resource of harmonic. And the interference of power quality is not ignored for whole transportation system.
3 Most of the electric traction substations use V / V or Y / d wiring system. Each electric train has a two-phase load to the power system. So the three-phase load is unbalanced and the load fluctuation which will lead to rapid fluctuations Sequence current.
Effect:
1 Harmonic and unbalance phase current make the transformer , capacitor , cable overheat,due to aging insulation and decrease lifetime of equipment .
2 Harmonic has interference on the communication system and quality of transferring the signal .
3 Harmonic and negative sequence current interfere motor , decreasing reliability of running motor.