Whether AC or DC is used on the railway line

Electric locomotives

Railway locomotive knowledge.

The electric locomotive itself does not have a prime mover, and the wheels of the locomotive are driven by a traction motor by receiving the current sent by the catenary as an energy source. The electric locomotive has the main advantages of high power, high thermal efficiency, fast speed, strong overload capacity and reliable operation, and does not pollute the environment, especially suitable for mountain railways with many busy railway trunk lines and tunnels and large slopes.

The electric locomotive obtains electrical energy from the catenary, and the current supplied to the electric locomotive by the catenary has two types: DC and AC. Due to the different current systems, the electric locomotives used are also different, which can basically be divided into three categories: direct-dc electric locomotives, ac-dc electric locomotives, and ac-dc-ac electric locomotives.

The direct DC electric locomotive adopts direct current power supply, and the traction substation is equipped with a rectifier device, which converts the three-phase alternating current into direct current, and then sends it to the catenary. Therefore, the electric locomotive can obtain direct current directly from the catenary to supply the DC series traction motor, which simplifies the equipment on the locomotive. The disadvantage of the DC system is that the voltage of the catenary is low, generally L500V or 3000 V, and the contact wire is required to be very thick, which consumes a lot of non-ferrous metals and increases the construction investment.

AC and DC electric locomotives are powered by AC system, and most countries in the world currently use power frequency (50Hz) AC system, or 25 Hz low-frequency AC system. Under this power supply system, the traction substation converts the three-phase alternating current into single-phase alternating current at an industrial frequency of 25 kV and sends it to the catenary. However, the DC series motor is still used in the electric locomotive (the biggest advantage of this motor is that the speed regulation is simple, as long as the terminal voltage of the motor is changed, it is very convenient to realize the speed regulation of the locomotive in a large range.

However, due to the commutators of this motor, the manufacture and maintenance are complicated and the volume is large), and the task of converting alternating current into direct current is completed on the locomotive. Because the catenary voltage is much higher than that of the DC system, the diameter of the contact wire can be relatively reduced, which reduces the consumption of non-ferrous metals and the construction investment. Therefore, the power frequency AC system has been widely adopted, and the vast majority of electric locomotives in the world are also AC-DC electric locomotives.

AC AC electric locomotive adopts AC commutator-free traction motor (i.e., three-phase asynchronous motor), which is far superior to commutator motor in terms of manufacturing, performance, function, volume, weight, cost, maintenance and reliability. The main reason why it has not been applied to electric locomotives is that it is difficult to regulate the speed. This locomotive has excellent traction capacity and is very promising.

The German-made E120 electric locomotive is one such locomotive.

The working principle of the electric locomotive, the current on the contact wire, through the pantograph into the locomotive through the main circuit breaker and then into the main transformer, the alternating current from the traction winding of the main transformer through the silicon unit rectification, to the six groups of two groups of parallel traction motors to concentrate direct current, so that the traction motor produces torque, converts the electric energy into mechanical energy, and drives the locomotive wheel to rotate through the transmission of gears.

The domestic ones are 25kV, 50Hz single-phase alternating current.

There are also 25kv, 60hz single-phase alternating current (like Japan, South Korea) 15kv in Europe, 16 2 3hz single-phase alternating current (like Germany, Switzerland) Many in Europe use direct current, including 3000V (like Italy, the Czech Republic), 1500V (like parts of France), and a few use 750V (like the British exit of the British-French Undersea Tunnel).

The DC catenary for rails is AC.

1. Direct current power. This kind of locomotive is the most widely used in China, and is used in urban trams, subways, railway transportation, etc., but the locomotive power is limited to a certain extent due to the influence of catenary voltage.

2. The locomotive with AC non-commutator traction motor has been applied in this system, such as the German ICE-type high-speed electric unit Zhuzhou factory DJ2 type, etc., the electric locomotive shirt is composed of mechanical, electrical, and air pipeline three major systems.

Dear, hello, the high-speed rail uses: alternating current. China's high-speed railways use alternating current.

Specifically, high-speed railways use 25 kV or 50 kV alternating current with a frequency of 50 Hz. The railway electrification system transmits electrical energy to the catenary on the railway, and then supplies power through the contact between the pantograph and the catenary on the high-speed train. There are several reasons why high-speed railways use alternating current:

1.The transmission distance of alternating current is long, the loss is small, and it is suitable for long-distance transmission. Rail lines cover a wide range of areas and require a large amount of electrical energy to be delivered, and alternating current meets this demand.

Stunning 2Alternating current facilitates transformer conversion and is suitable for transmission and power supply of different voltage levels. High-speed railways run fast and require a lot of electrical energy**, and the use of alternating current is convenient for power supply conversion of different voltage levels.

3.The safety of alternating current is higher and it is not easy to cause arc and electric shock accidents. As a high-speed interchange and collapse tool, safety is one of the most important considerations, and the use of alternating current can help improve safety.

Summary. High-speed rail trains are generally driven by electricity, and high-speed rail trains in China are usually driven by alternating current. At present, the high-speed rail of China Railway usually uses a 25 thousand volt or 50 thousand volt catenary for power supply, which transmits the power to the train through the catenary, and then combines it with the traction device on the train through the track to achieve high-speed travel of the train.

In the catenary power supply system, the power is converted into 25 thousand volts or 50 thousand volts of high-voltage alternating current by the high-voltage power station through the substation in the railway electrified power supply system, and then transmitted to each power supply station through the transmission line, and then transmitted to the high-speed rail train through the catenary and the power supply system. <>

High-speed rail trains are generally driven by electricity, and high-speed rail trains in China are usually driven by alternating current. At present, the high-speed rail of China Railway usually uses a 25 thousand volt or 50 thousand volt catenary for power supply, which transmits the electricity to the train through the catenary, and then combines the track with the traction device on the train to achieve high-speed travel. In the catenary power supply system, the power is converted into 25 thousand volts or 50 thousand volts of high-voltage alternating current by the high-voltage power station through the substation, and then transmitted to each power supply station through the transmission line, and then transmitted to the high-speed rail train through the catenary and the power supply system.

Specifically, when traction accelerates, the DC traction transformer of the AC power supply system converts AC power into direct current, which is then transmitted to the motor on the high-speed railway locomotive through the pantograph and traction cable, so as to achieve high-speed driving. The main special point of the system is the use of high-voltage alternating current, which can efficiently transmit electricity, improve the utilization rate of the power supply system, and reduce energy waste and pollution. In general, the AC power supply system is one of the mainstream power supply methods for China's high-speed trains, which provides a reliable guarantee for the safe and efficient operation of high-speed trains.

The electrified train is powered by 25,000V single-phase AC (in fact, the output voltage from the transformer of the electrified substation is rated at 27,500V). He gets his alternating current from the power feeder (catenary) on the locomotive, and the rails are his ground wire.

There are two main types of electricity used on electrified trains:

1. One is for power, and the general voltage is relatively high, which is the bulk of the electricity consumption. Especially on the current EMUs. He has rectified the AC-DC system (DC motor is good for speed regulation). At present, most of them are AC-DC-AC systems (frequency conversion technology for speed regulation).

2. The other is to supply electricity for lighting, air conditioning and ventilation systems. He has a system of his own in the locomotive (not electrified trains, not lighting them). The railroad track is the best grounding, and it will not "electrify" people. Rest assured!

China's electrified railways are all AC-DC traction locomotives, and now EMUs and high-speed railways use AC-DC-AC traction locomotives, and the main AC-DC-AC electric locomotives in China are SS-9 series.

For example, the electric locomotives on the Beijing-Kowloon electrified railway are AC-straight, but the AC-straight locomotive will produce harmonics and negative order problems for the traction station, which will have a great impact on the relay protection of the local power grid, especially the high-frequency impedance protection, and will also increase the loss.

The starting torque of the DC motor is much larger, and the DC motor is needed when starting, and the AC motor cannot solve this problem; If you run normally, you can use an AC motor to run the battery; The overall scheme is still optional.

The voltage of the catenary of the high-speed rail is alternating current, and the voltage is kilovolts.

The high-speed railway catenary is a special form of power transmission line erected over the railway line to supply power to electric locomotives. It is composed of several parts: contact suspension, support device, positioning device, pillar and foundation. Contact suspension includes contact wires, hanging strings, load-bearing cables, and connecting parts.

The contact suspension is erected on the pillar by means of a support device, and its function is to transmit the electrical energy obtained from the traction substation to the electric locomotive. Support devices are used to support contact suspension and transfer its load to pillars or other structures.

The voltage level type of the catenary type number leakage: power frequency single-phase AC system: 25kV, 50Hz or 60Hz alternating current (generally 60Hz in the world, 50Hz in China), due to the resistance factor, the actual voltage is.

The catenary power supply mode is as follows:

The catenary power supply mode includes unilateral and bilateral power supply and cross-area power supply. Unilateral and bilateral power supply are normal power supply methods.

1. Unilateral power supply: the power supply mode in which the power supply arm only obtains the current from the substation at one end.

2. Bilateral power supply: the power supply mode in which the power supply arm obtains the current from the adjacent substations at both ends.

3. Cross-area power supply is an abnormal power supply mode (also known as accident power supply mode).

Cross-area power supply means that when a traction substation cannot supply power normally due to a fault, the power supply arm borne by the faulty substation is connected to the adjacent power supply arm through the switchgear component pavilion, and the adjacent traction substation is temporarily powered by the adjacent traction substation. <>

Electric locomotives can run on both direct and alternating current.

The locomotive equipped with a DC series traction motor has a catenary voltage of 1500 volts or 3000 volts DC. In the past, the starting and speed regulation of DC electric locomotives were accomplished by adjusting the starting resistance and the series-parallel conversion of the traction motor. But this starting and speed regulation mode can not be used to adjust the speed continuously and smoothly, and the power consumption loss is large, and the line conversion is complicated.

The catenary voltage of AC electric locomotive is 20 kV or 25 kV, and the single-phase power frequency is 50 or 60 Hz. In a few European countries such as the Federal Republic of Germany, Sweden, Switzerland and other countries, there are also single-phase low-frequency AC systems, at this time the catenary voltage is 11 16 thousand volts, and the single-phase power frequency is 25 Hz.

In the transmission and distribution voltage level of the power grid, the power supply bureau to the factory is alternating current, and the rectifier is the AC into direct current, kilovolts are medium voltage, kilovolts are high voltage, kilovolts are ultra-high voltage, DC 800, AC 1000 kV and above are UHV.

The power grid is a whole composed of substations and transmission and distribution lines of various voltages in the power backup and distribution system, which includes three units: substation, transmission and distribution. The task of the power grid is to transmit and distribute electrical energy and change the voltage. The power grid is composed of overhead lines, cables, towers, distribution transformers, isolation branches, reactive power compensation capacitors and some ancillary facilities, etc., which play an important role in the distribution of electric energy in the power grid.