How Three phase motor runs on Single phase supply in Train?
In this post, we discuss how one wire is used to run the three-phase motor in Train.
In the railway system from the AC supply, only one wire is coming through the overhead line (Phase). And Neutral is connected to the track and also connected to earth in many places. The phase and neutral connection are shown in the above picture. There is a step-down transformer inside the train. The phase wire is connected to the transformer through the pantograph. And for neutral no wire comes, the track is used as return wire.
Now the single-phase step down transformer which located inside the engine steps down the voltage. Then the step-down AC voltage is converted to DC by the Rectifier. This rectifier is made using IGBT. This rectifier is controlled is such that we get unity power factor at the input of the rectifier. As a result of there, no power factor improvement is required. After rectifier, an electrolytic capacitor is used for filtration. Now an inverter is used to convert DC to three-phase AC supply. Nowadays this inverter is made of IGBT. The three-phase AC supply is given to the three-phase AC motor. The output voltage and frequency both of the inverter are controlled for controlled the motor speed. So the single-phase becomes three phase using one rectifier and the inverter. There are two systems on the train. If one system is failing still train can run without any problem using another system.
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Mr. Muhammad Saqib, M.Sc. (PAK), Research Fellow (PAK), a member of IEEE, is a Fulbright Alumnus and earned his Master’s Degree in Electrical and Power Engineering from University Of Engineering And Technology Taxila, PAKISTAN.
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