Why is a train electrically driven and not directly mechanically driven

Hello Yan Jiangcheng.

Students, the reason why the train uses electric transmission is due to the following reasons:

1. Convenient start.

The train traction load is very high, especially when the train is starting. If a mechanical transmission is used like a car, the friction gradually increases by using a clutch.

The way to gradually increase the torque, it is obviously inappropriate, so that the clutch plate will burn in a few times. Diesel locomotives, on the other hand, use electric transmission, which uses the engine to emit three-phase alternating current.

in warp rectifiers.

Output direct current.

The drive motor on the running part is supplied to drive the wheel rotation. The drive motor generally adopts DC series motor, the nature of this motor is softer, the greater the external resistance, the slower the rotation, the greater the output torque, so as to adapt to the starting characteristics of the train. When we take the train, we feel that the train starts unconsciously and this is the reason.

2. Suitable for traction.

We know that the same internal combustion engine, diesel engine is "harder" than gasoline engine, so the diesel engine must be equipped with a "governor" that can automatically adjust the amount of fuel supply to ensure that it will not be stalled due to changes in resistance. But even so, when the resistance increases, although the fuel supply is increased, the increase is only the power of the diesel engine, however, the output torque has not increased significantly, in order to ensure that the ignition is not turned off, the driver must "reduce the gear" in time. And the train can't use the clutch, so naturally the transmission can't be used.

Otherwise, the gears can be easily damaged. As mentioned above, the nature of the DC series motor is soft, the greater the external resistance, the slower the rotation, and the greater the output torque, so it is also suitable for the traction of locomotives.

3. Suitable for transmission.

Unlike the car, the wheels of the train are mounted on a bogie that can be rotated, and if the mechanical transmission is adopted, it is bound to cause the bogie to always deflect to one side, affecting the safety of the train.

In the early days, trains did use mechanical transmissions, but now they are no longer used. Electric drives are often used in freight locomotives, and some small passenger locomotives also use hydraulic drives for the same reasons as electric drives.

There are some large diesel cargo trucks.

Or on the construction machinery, the transmission part is equipped with a "hydraulic coupling" or "hydraulic torque converter", and its role is similar to that of the hydraulic transmission of the train. There are also some construction machinery, but also use electric transmission.

Now there are also some ways of AC electric transmission, the purpose of which is the same.

The electricity generated by the generators on the train is used for other systems (such as lighting), and the power of the train comes directly from the steam engine, diesel engine, (except for electric locomotives).

The train uses an electric motor as the prime mover, and his transmission mechanism is mechanical.

You're not talking about a concept.

The electric transmission mode of electric locomotives in China includes two types: AC-DC-AC transmission and AC-straight transmission.

The current Harmony series electric locomotives, as well as the new Fuxing series electric locomotives, all adopt AC-DC-AC transmission mode, which is also the current international mainstream method.

The old Shaoshan series locomotives adopt the AC-DC transmission mode.

There are basically two kinds of modern train power, one is the diesel locomotive, the other is the electric locomotive, and the steam locomotive is basically eliminated.

The diesel locomotive is a high-power diesel engine, which drives the synchronous main generator to generate electricity, and then uses the electricity to drive the traction motor, and the train has a traction motor on each axle, which is to drive the train by the motor, so the diesel locomotive relies on AC-DC transmission, rather than the engine acting directly on the wheels like a car;

The structure of the electric locomotive is relatively simple, inside is a large transformer, relying on the pantograph of the locomotive to lead the electricity of the catenary into the locomotive, through the transformer voltage transformation and then provided to the traction motor, generally AC transmission, the electricity of the electric locomotive comes from the power plant, if you have seen the electrified railway, you will understand, the electric catenary is erected over the railway, which is generally 25kv or high-voltage direct current, these electricity comes from the substation, and the electricity of the substation still comes from the power plant. There is a pantograph on the electric locomotive, which is used to direct high-voltage electricity into the locomotive, so as long as there is electricity in contact with the power grid, the locomotive can run.

The principle of transmission of diesel locomotives.

1. Electric transmission.

Direct current drive, AC and DC electric drive and AC-DC (abbreviated as AC) electric drive. Dongfeng, Dongfeng 2 and Dongfeng 3 locomotives are DC electric drive locomotives; The electric drive diesel locomotives developed after Dongfeng Type 4 are all AC and DC electric drive locomotives. After 1999, some AC transmission locomotives appeared one after another.

The more successful ones are the Dongfeng 4DJ of the Dalian plant and the Dongfeng 8CJ of the Qishuyan plant. Domestic electric drive locomotives are named Dongfeng * type, and imported ones are ND * type. The most well-known electric drive locomotives in China are the Dongfeng 11G and Dongfeng 8B manufactured by Qishuyan Locomotive and Rolling Stock Factory.

2. Hydraulic transmission.

General (mechanical commutation) hydraulic transmission and hydraulic transmission of hydraulic commutation; The other is a hydraulic mechanical transmission. The Beijing type and Dongfanghong series locomotives are both hydraulic transmission locomotives; Most of the GK series industrial and mining locomotives are hydraulic reversing locomotives. The domestic hydraulic transmission is generally Dongfanghong * type and Beijing * type, and the industrial and mining locomotive GK series is imported NY * type.

The most well-known hydraulic locomotive in China is the ND5 type of General Electric Company of the United States.

3. Mechanical transmission.

It is rare in the country; It is rarely used in local railways and industrial and mining locomotives with low power.

The principle of action of AC and DC electric drive locomotives.

The locomotive battery is used for 96V starting, and the 80kW starting generator is available. Start the generator engine car diesel engine, the diesel engine runs to drive the synchronous main generator to run, the 45kw induction sub-exciter outputs direct current to the synchronous main generator rotor excitation through the rectifier, and the main generator generates electricity normally, (when the diesel engine is running, the starter generator is converted into a separately excited generator to run and send out 110V constant direct current, supply the air compressor and some locomotive auxiliary equipment, and charge the locomotive battery), the synchronous main generator sends out three-phase alternating current, through the main rectifier cabinet, Six DC traction motors are supplied, and finally, the locomotive is started.

The train does not need external power supply, but can use all the rented motors to generate mechanical energy to drive the train to run is your dear, high-speed rail is the use of electric traction. The traction motor of an electric locomotive or motor vehicle converts electrical energy into mechanical energy to drive the operation of railway trains, electric units, and urban rail transit electric vehicle units. It is mainly composed of power supply, traction substation, catenary (contact rail), track loop, electric locomotive, EMU and other links to achieve electric traction.

Electric traction does not consume precious liquid fuels such as petroleum, and various forms of energy can be utilized. Today, developed countries are choosing a new generation of hand-to-connect tools with a focus on low environmental impact. High-speed rail meets this requirement and is significantly superior to cars and airplanes.