Electric trains that use a single wire for power, without a separate positive and negative connection, typically employ a system known as the third rail or overhead line electrification. Let's focus on the third rail system for simplicity.
In a third rail system, the train receives its power from an electrified rail, which typically runs parallel to the tracks. The rail is charged with a high-voltage direct current (DC) power supply. The train itself acts as a conductor, completing the electrical circuit between the rail and the ground. Here's a simplified explanation of how it works:
Power Generation: The electricity required to power the train is generated at a power station. The power station usually converts other forms of energy, such as fossil fuels, nuclear energy, or renewable sources, into electrical energy.
High-Voltage Transmission: The generated electrical energy is then transmitted over long distances at high voltage using overhead power lines or underground cables.
Substation: As the power approaches the area where the train will operate, it passes through a substation. The substation's main purpose is to lower the voltage to a level suitable for use by the train.
Third Rail: The third rail, typically located alongside the tracks, carries the reduced voltage DC power. It is electrically isolated from the ground and poses a safety risk if touched.
Power Collection: The train has a device called a "collector shoe" or "pickup shoe" that makes contact with the third rail. The collector shoe is typically mounted underneath the train and is connected to its electrical systems.
Electrical Circuit: When the collector shoe makes contact with the electrified third rail, it completes an electrical circuit. Electrical current flows from the rail, through the collector shoe, and into the train's electrical systems.
Power Distribution: The electricity collected from the third rail is then distributed to various components on the train, such as traction motors, lights, air conditioning, and other systems that require electrical power.
It's important to note that the electrical system of an electric train can be more complex, involving additional components like transformers, converters, and control systems. However, the basic concept remains the same: the train completes an electrical circuit by making contact with an electrified rail, allowing power to be transferred from the rail to the train's electrical systems.