The train operates using a single sliding contact that draws energy from the overhead power lines to supply the induction motor. The motor’s rotor is connected to the wheels, while the other end of the motor is grounded through a wire linked to the wheels via a carbon brush, creating a closed circuit. The wheels always maintain contact with the tracks, which are also grounded.
The voltage transmitted along the overhead lines is very high, reaching up to 25kV, but the motor operates at a much lower voltage. Therefore, a step-down transformer is needed to convert the voltage to the desired level.
The electrical power from the overhead lines initially passes through the primary coil of the transformer, where the circuit is closed by grounding.
Three-phase induction motors are the ideal choice for achieving high uniform torque requirements. However, the three-phase power system from the grid is expensive, so a rectifier and inverter are used to convert single-phase power into three-phase power. The rectifier converts single-phase alternating current to direct current, and then the inverter converts direct current back to three-phase alternating current. Additional pairs of wheels and motors can be attached to enable the train to pull more carriages.
A motor set is constructed with three three-phase induction motors. The pantograph, which is the power collection device, is responsible for drawing electrical energy for the train. Based on the pressure of the pneumatic system, the pantograph can adjust its height.
If, for any reason, the pantograph loses connection with the overhead wire, the train will continue to run freely for several kilometers due to its significant inertia. We can control the speed by changing the frequency of the power supplied to the induction motor. This is achieved by the rectifier and inverter. When the driver shifts the lever to another groove to change the frequency, the speed of the motor will also change accordingly.
This system can apply electric braking to cut the power supplied to the motor. Then, the pneumatic brake is engaged to bring the train to a complete stop. The pneumatic braking system is installed in each carriage beneath each pair of wheels. A secondary coil is placed in the transformer to supply power to all the carriages.
