Electric motors were fed directly from the traction supply and were controlled using a combination of resistors and relays that. Introduction, advantages, classification post before proceeding further. An ac motor consists of two main parts a rotor, a component that rotates, and a stator, which is stationary. The overload capacity of steam locomotive is limited.
There are no periods and the current flows in a single direction with a steady voltage. Difference between ac and dc in tabular form physics. The basic difference between ac and dc locomotives is that the commutation on the traction motors. The height difference between the two rails is called the cant. Ac is an acronym of alternating current while dc is an acronym of direct current. Electric charge in alternating current ac, on the other hand, changes direction. Ac motor is an electromechanical device that works on ac electricity while the dc motor works on dc electricity. 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. 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. Both ac and dc describe types of current flow in a circuit. A variant of the dc system is the acoperated series motor, which is essentially the same device. Ohio electric motors indicates that the main difference between ac and dc motors is the power source. Optimising power management strategies for railway traction. 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.
Traction power supply abb traction rectifiers diode. Energy efficiency and infrastructure costs determine which of these is used on a network, although this is often fixed due to preexisting electrification systems. The result obtained will be, the voltage level also reverses along with the current. A with a digital universal measurement, respectively, with 20v ac voltage and 20v dc voltage file measurement, the results will be different. 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. In alternating current, current keeps switching directions periodically forward and backward. An electromechanical device converts electrical energy to mechanical energy. Ac voltage from a generator in a power plant can be bumped up or down in strength by another mechanism.
Ac and dc motors also differ in their construction. Alternating current replaced dc in the 1880s as the current used in power lines because of difficulty in transmitting dc over long distances. The main work of a dc motor is done by the windings on the armature rotor and that poses a minor problem with cooling. Adequate supplies of feed water at regular intervals are required. Ac traction vs dc traction greenville, south carolina. Difference between dc and ac motors difference between. An inverter changes a dc voltage into an ac voltage or ac to dc and either increases or decreases it into the appropriate level. This extra power is wasted off as heat and the destruction of the traction motors. Ac traction motors only ever get about 5% more than what they are already handling, never mind what the engineer is asking for. Created for the general public and other railroading admirers taken into consideration. Ac motors are powered by an alternating current while dc motors use a direct current as a power source.
Apr 16, 2020 another difference between ac and dc involves the amount of energy that each one can carry. A dc motor converts an electric power into mechanical power. Explaining the difference between direct current and alternating current. Electric drives brushless dc ac and reluctance motors description and applications brushless motors.
Difference between ac and dc motors precision electric. An ac electric motor consists of several parts but the main parts are the stator and rotor. Difference between induction motor and synchronous motor. There are three types of drives namely 1 group drive. A comparison of ac traction and dc traction in locomotives.
Where did the australian rock band ac dc get their name from. The armature winding of the synchronous motor is energized from an ac source and its field winding from a dc source. The impact on the infrastructure will be different for the unidirectional flow of iron ions from a structural steel element due to dc stray. So we will tell you the difference between difference between ac and dc flow. Ac traction vs dc traction greenville, south carolina republic. Why, alternating current and direct current, of course. As we all know electricity or current is nothing however the movement of electrons through a conductor. 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. In comparison, a converter changes the voltage level but does not change its type. Difference between ac and dc alternating current ac alternating current is defined as the flow of charge that changes direction periodically. 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. 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. 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.
Basically electricity flows in 2 ways in which one is ac or second is dc. Direct current is a bit easier to understand than alternating current. This report presents a comprehensive comparison of ac traction vs. 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.
Ac or alternating current is literally a current that alternates in the direction that it flows. 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. Converter vs inverter difference and comparison diffen. Dc is direct current and as is implied by the name the current flows only in one direction. Difference between ac alternating current motor and dc direct current motor. Jan 07, 2018 unlike ac, a direct current undergoes no switching. Nov 30, 2015 despite all these advantages, dc electrical system necessitates ac to dc conversion substations relatively at very short distances. A traction motor is an electric motor used for propulsion of a vehicle, such as locomotives. Lets discuss the technical advantages and disadvantages of both ac and dc power transmission lines systems. A three phase synchronous motor is a doubly excited machine, whereas an induction motor is a single excited machine. Distribution of the traction return current in ac and dc electric railway systems.
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. Difference between ac and dc with comparison chart. Typically, engineers can choose between directcurrent dc or alternatingcurrent ac motors. The main difference between ac and dc lies in the direction in which the. As already mentioned, dc is prone to lose power as heat a characteristic that edison exploited to light the first bulb. Berggren, professor of electrical engineering at mit, the fundamental difference between ac and dc is the direction of flow. The major difference between ac and dc is that dc is unidirectional current while ac is bidirectional current. 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. Pdf distribution of the traction return current in ac and dc. Ac vs dc alternating current vs direct current difference. In direct current dc, the electric charge current only flows in one direction. 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. Use of a device called a rectifier that converts ac to dc.
This post explains the difference between ac and dc drives. A drive is a combination of various systems combined together for the purpose of motion control. The ac electric motors rotor rotates inside the electric motors coils and is attached to an output shaft th. May 29, 2012 an electromechanical device converts electrical energy to mechanical energy. Despite its disadvantages, the age of semiconductors forced the return of dc. Ac traction for locomotives is a major improvement over the old dc systems. Ac traction and dc traction free download as word doc. The system which use electrical power for traction system i. It is highly recommended to read the electrical drives. Difference between three phase induction motor and synchronous motor. This is the main disadvantage of dc traction system. Each battery is designed to produce only one voltage, and that voltage of dc cannot travel very far until it begins to lose energy. Phet interactive simulations, university of colorado, their link is posted below. Difference between alternating current ac and direct.
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. Rather than oscillating back and forth, dc provides a constant voltage or current. Electric drives brushless dc ac and reluctance motors. Basically, ac is used to deliver power to industries, houses, office buildings, etc.
Another difference between ac and dc involves the amount of energy it can carry. Dc or direct current motors work in particular situations whereby the speed of the motor needs to be externally controlled. 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. While in the direct current it flows in a single direction steadily. Dc is constant with time while ac changes at every instant of time. 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%. There are some advantages and disadvantages of both systems. Dc vs ac traction system why use ac traction remove 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. As redneckrailfan and others pointed out all of the newer locomotives have alternators and produce an alternating current and then convert it to dc. 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.
Mit school of engineering whats the difference between. The track electrification refers to the type of source supply system that is used while powering the electric locomotive systems. The wires outside of our house are connected at two ends to ac generators. Design of power supply system in dc electrified transit. Often, people ask about the differences between ac and dc motors as used in.
An ac generator equipped with a device called a commutator can produce direct current. Jan 29, 2019 some disadvantage due to remove dc traction 1. What is the difference between ac and dc latest open tech. Thats why this system is preferred only for suburban and road transport services wherein stops are frequent and also distance between stops is small.
A c motor works on the concept of alternating current, whereas dc motor works of the direct current. Whats the difference between ac, dc, and ec motors. The tractive effort of a locomotive whether ac or dc is defined by the equations. There are several practical differences between traction motors and other industrial machines.
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. The difference between ac and dc electrification systems lies in where the ac is converted to 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. Difference between ac and dc motor compare the difference. Ac motors the ac electric motors stator has coils that are supplied with the alternating current and produces a rotating magnetic field.
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