Difference between ac and dc traction pdf

This extra power is wasted off as heat and the destruction of the traction motors. As we all know electricity or current is nothing however the movement of electrons through a conductor. The main work of a dc motor is done by the windings on the armature rotor and that poses a minor problem with cooling. The armature winding of the synchronous motor is energized from an ac source and its field winding from a dc source. Use of a device called a rectifier that converts ac to dc. Thats why this system is preferred only for suburban and road transport services wherein stops are frequent and also distance between stops is small. Difference between ac and dc alternating current ac alternating current is defined as the flow of charge that changes direction periodically. Difference between dc and ac motors difference between. Whats the difference between ac, dc, and ec motors. Ac vs dc alternating current vs direct current difference. Despite its disadvantages, the age of semiconductors forced the return of dc.

Every battery is designed to produce only one voltage level, and that voltage of direct current cannot travel very far until it begins to lose energy. Lets discuss the technical advantages and disadvantages of both ac and dc power transmission lines systems. Energy efficiency and infrastructure costs determine which of these is used on a network, although this is often fixed due to preexisting electrification systems. Direct current is a bit easier to understand than alternating current. Pdf distribution of the traction return current in ac and dc. As already mentioned, dc is prone to lose power as heat a characteristic that edison exploited to light the first bulb.

Ac motors are powered by an alternating current while dc motors use a direct current as a power source. Basically electricity flows in 2 ways in which one is ac or second is dc. Difference between ac and dc in tabular form physics. An ac electric motor consists of several parts but the main parts are the stator and rotor. Phet interactive simulations, university of colorado, their link is posted below. Design of power supply system in dc electrified transit. The ac drive works by converting the traction alternator output to dc direct current and reconverting it to a variable frequency ac which powers ac traction motors. Why, alternating current and direct current, of course. Review of characteristics of different types of dc and ac motors used traction and their suitability moduleiv 10 hours rating and heating of electric drives, power loss, heating and cooling of motors, classes and duty and selection of motors, drives for specific application like steel, paper, textile mills. Difference between three phase induction motor and synchronous motor. Dc is constant with time while ac changes at every instant of time. Alternating current replaced dc in the 1880s as the current used in power lines because of difficulty in transmitting dc over long distances.

A traction motor is an electric motor used for propulsion of a vehicle, such as locomotives. Where did the australian rock band ac dc get their name from. Introduction, advantages, classification post before proceeding further. Typically, engineers can choose between directcurrent dc or alternatingcurrent ac motors. The primary advantages of ac traction are adhesion levels up to 100% greater than dc and much higher reliability and reduced maintenance requirements of ac traction motors. Difference between ac alternating current motor and dc direct current motor. A three phase synchronous motor is a doubly excited machine, whereas an induction motor is a single excited machine. Rather than oscillating back and forth, dc provides a constant voltage or current. This is the main disadvantage of dc traction system. As redneckrailfan and others pointed out all of the newer locomotives have alternators and produce an alternating current and then convert it to dc. Example of short fully enclosed busbars duct between transformer and rectifier general description and design the pd rectifiers family is designed for the supply of dc traction loads like urban transport systems or mainline railways in ranges of following standard output voltages. A dc motor converts an electric power into mechanical power. Mit school of engineering whats the difference between. Difference between ac and dc motor compare the difference.

Distribution of the traction return current in ac and dc electric railway systems. Ac or alternating current is literally a current that alternates in the direction that it flows. An ac motor consists of two main parts a rotor, a component that rotates, and a stator, which is stationary. Difference between ac and dc with comparison chart. Difference between ac and dc motors precision electric. There are some advantages and disadvantages of both systems.

In direct current dc, the electric charge current only flows in one direction. Nov 30, 2015 despite all these advantages, dc electrical system necessitates ac to dc conversion substations relatively at very short distances. The result obtained will be, the voltage level also reverses along with the current. A drive is a combination of various systems combined together for the purpose of motion control. Optimising power management strategies for railway traction. An ac generator equipped with a device called a commutator can produce direct current. Each battery is designed to produce only one voltage, and that voltage of dc cannot travel very far until it begins to lose energy. Jan 07, 2018 unlike ac, a direct current undergoes no switching. A simple way to visualize the difference is that, when graphed, a dc current looks like a flat line, whereas the flow of ac on a graph makes a sinusoid or.

The system which use electrical power for traction system i. In addition, only a fraction of the windings are active at any given instant this creates a more severe heating problem less copper to carry the current and also imposes a minimum speed requirement motor needs to turn fast enough that the active winding doesnt overheat. The basic difference between ac and dc locomotives is that the commutation on the traction motors. Ohio electric motors indicates that the main difference between ac and dc motors is the power source. In comparison, a converter changes the voltage level but does not change its type. There are several practical differences between traction motors and other industrial machines.

The major drawback of using dc is, it starts deteriorating with distance. The major difference between ac and dc is that dc is unidirectional current while ac is bidirectional current. The impact on the infrastructure will be different for the unidirectional flow of iron ions from a structural steel element due to dc stray. Electric drives brushless dc ac and reluctance motors. Ac and dc motors also differ in their construction. A c motor works on the concept of alternating current, whereas dc motor works of the direct current. The difference between ac and dc electrification systems lies in where the ac is converted to dc. I prefer continuous voltage and alternate voltage but these names are not used because current is the result of a load put on the terminals of a power source.

Jan 29, 2019 some disadvantage due to remove dc traction 1. It is highly recommended to read the electrical drives. Explaining the difference between direct current and alternating current. Dc or direct current motors work in particular situations whereby the speed of the motor needs to be externally controlled. Electric motors were fed directly from the traction supply and were controlled using a combination of resistors and relays that.

But ac s voltage from a generator, in a power plant, can be bumped up or down in strength by another mechanism called a transformer. This post explains the difference between ac and dc drives. This report presents a comprehensive comparison of ac traction vs. Both ac and dc describe types of current flow in a circuit. There are no periods and the current flows in a single direction with a steady voltage. A traction motor is an electric motor used for propulsion of a vehicle, such as locomotives, electric or hydrogen vehicles, elevators or electric multiple unit traction motors are used in electrically powered rail vehicles electric multiple units and other electric vehicles including electric milk floats, elevators, roller coasters, conveyors, and trolleybuses, as well as vehicles with. A variant of the dc system is the acoperated series motor, which is essentially the same device. Ac traction for locomotives is a major improvement over the old dc systems.

Difference between alternating current ac and direct. Ac is an acronym of alternating current while dc is an acronym of direct current. Difference between induction motor and synchronous motor. Ac motors the ac electric motors stator has coils that are supplied with the alternating current and produces a rotating magnetic field. Difference between ac and dc motors commonly ran by an ac variable frequency drive, an ac electric motor operates by applying alternating current ac power to the electric motor. The main difference between ac and dc lies in the direction in which the. On the other hand ac or alternating current electric motors are used in a completely different process drawing upon the kind of ac motor being used. Berggren, professor of electrical engineering at mit, the fundamental difference between ac and dc is the direction of flow. What is the difference between ac and dc latest open tech.

Often, people ask about the differences between ac and dc motors as used in. An inverter changes a dc voltage into an ac voltage or ac to dc and either increases or decreases it into the appropriate level. Converter vs inverter difference and comparison diffen. Created for the general public and other railroading admirers taken into consideration. Traction power supply abb traction rectifiers diode. Dec 16, 2007 the main work of a dc motor is done by the windings on the armature rotor and that poses a minor problem with cooling. Sep 21, 2005 on a dc locomotive, a run 8 throttle setting could be supply 200% or more of the power thats needed to just go faster. Electric traction b disadvantages because of difficulty of installing a condenser on a locomotive, the steam engines employed are of noncondensing type, therefore, efficiency is very poor 6 to 8%. While in the direct current it flows in a single direction steadily. The tractive effort of a locomotive whether ac or dc is defined by the equations. Ac traction vs dc traction greenville, south carolina republic.

The wires outside of our house are connected at two ends to ac generators. Ac traction and dc traction free download as word doc. Electric charge in alternating current ac, on the other hand, changes direction. Jun 26, 2008 the difference between ac and dc is that ac is an alternating current the amount of electrons that flows in both directions and dc is direct current that flows in only one direction. Machine design has covered the difference between basic types of motors in the past. Electric drives brushless dc ac and reluctance motors description and applications brushless motors. Dc vs ac traction system why use ac traction remove dc. Ac traction and dc traction electric motor rectifier scribd. Dc is direct current and as is implied by the name the current flows only in one direction. The track electrification refers to the type of source supply system that is used while powering the electric locomotive systems. A comparison of ac traction and dc traction in locomotives. Because ac motors operate at approximately the frequency of the current, the drives must adjust the frequency so that the motors can have a speed range of zero to maximum rpm.

May 29, 2012 an electromechanical device converts electrical energy to mechanical energy. An electromechanical device converts electrical energy to mechanical energy. In alternating current, current keeps switching directions periodically forward and backward. Brushless motors such as permanent magnet and switched reluctance motors depend on electronic drive systems which produce rotating magnetic fields to pull the rotors around. Ac motor is an electromechanical device that works on ac electricity while the dc motor works on dc electricity. The height difference between the two rails is called the cant. Basically, ac is used to deliver power to industries, houses, office buildings, etc. The main source of the ac motor is current coming from the three phase or the single phase supply mains. There are three types of drives namely 1 group drive. The ac alternating current drive, also known as variable frequency drive, used in locomotives is currently also being adopted in most of the new dieselelectric locomotives. Another difference between ac and dc involves the amount of energy it can carry. Alternating current ac is an electric current which periodically reverses direction, in contrast to direct current dc which flows only in one direction. Ac traction vs dc traction greenville, south carolina. Ac traction motors only ever get about 5% more than what they are already handling, never mind what the engineer is asking for.

So we will tell you the difference between difference between ac and dc flow. Alternating current is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions, fans and electric lamps. The ac electric motors rotor rotates inside the electric motors coils and is attached to an output shaft th. Ac voltage from a generator in a power plant can be bumped up or down in strength by another mechanism.