Detailed Description of a DC Generator

A generator is the opposite of a motor; while a motor turns electrical energy into mechanical energy, a generator does exactly the reverse. Unlike alternating current generators, which produce current that periodically changes direction, a DC generator produces unidirectional current.

Features

• All direct current generators include at the minimum a rotating coil of wire; a split ring (with two breaks in it) that rotates together with the coil; two stationary metal brushes that transfer current from the rotating split ring to the external circuit and magnets that generate a magnetic field. The magnets may be permanent magnets or electromagnets. The combination of split ring and brushes is called a commutator.

Function

• As the coil of wire turns in the magnetic field, the magnetic flux (the total number of magnetic lines of force) passing through the loop of wire changes, because the angle between the coil and the magnetic field is always changing. In keeping with Faraday's Law, this change in magnetic field creates a voltage in the coil of wire and thereby generates electric current.

Considerations

• In an AC generator the EMF (electromotive force) if plotted as a function of time is a smooth wave-shaped graph (a sine wave), where the EMF is sometimes positive and sometimes negative. In a DC generator, the EMF rises from zero to max and falls back to zero, but never becomes negative. Some DC generators use more than one coil to smooth out this bumpy wave pattern and produce a more constant current.

Parts of a Dynamo Motor.

A dynamo motor, also known as an generator, is a device that can convert mechanical energy into an electric current. The concept of the dynamo is often attributed to Michael Faraday, who discovered that moving a magnet around a closed electric circuit can induce an electric current to flow in it. Modern dynamos or electric generators are made of several components that are essential for their function.

Magnetic Circuit

• On a modern dynamo motor, the magnetic circuit is made of several parts that include an armature core, a yoke, an air gap, and poles. An armature core is composed of sheet steel with a blanking die and thin magnetic steel laminates. These laminated sheets are either welded or bonded together to keep them from splitting apart.

  The poles are either steel laminates or solid steel, and they have field coils that set up the magnetic fields in the machine. The top and bottom poles are also called a pole head and a pole shoe, respectively. These poles usually fan out and are designed to smooth the flow of air on the air gap. The yoke is the casing where the completed poles are mounted, and it provides the magnetic path between the poles.

Electric Circuit

• The electric circuit is made of an armature winding, a commutator, a field winding and brushes. The armature winding is made up of copper wires that are insulated from the armature core. In a dynamo motor, the armature winding receives the voltage generated by the motor. Armature windings are connected to the commutator. The commutator acts as the mechanical rectifier that converts AC voltage to DC voltage, and it's usually made of silver-bearing copper. The commutator conducts the current to an external circuit through the brushes.

Mechanical Support

• The mechanical support of a dynamo motor is composed of a shaft, a frame, end bells, and bearings. In most cases, the yoke and the frame are the same, and they are usually made of steel or aluminum that encases the whole dynamo motor. The armature is placed inside the frame by using a steel shaft supported by two lubricated bearings that can either be a ball, a roller, or a sleeve type. Once the armature is placed inside the frame, both ends of the frame are enclosed using the end bells. The end bells are usually made of the same material used on frames and yokes.

How to Assemble a Dynamo With a DC Motor?

Electric motors and power generators are often identical in design. An AC motor, for example, may also be used as an alternator. The major difference in function depends upon whether the device is used to generate electricity such as an alternator or generator, or whether electricity is applied to the device to do work.

A DC motor contains a device called a commutator. This device allows a DC motor to produce DC power without adding any other electronics to the motor leads. When force is applied to a DC motor's rotor, the DC motor will work as a DC generator, also known as a dynamo.

* Use the electrical pliers to cut two lengths of electrical wire, with each length being six inches long. Strip 1/2 inch of insulation from the ends of each wire segment.

* Place one end of the first wire on the motor's positive electrical terminal. Melt a small drop of solder to both the electrical terminal and to the end of the first wire. Smooth out the soldered joint with the tip of the soldering iron, making sure that the electrical joint is shiny and free of lumps. Use this procedure to solder one end of the second wire to the negative electrical terminal.

* Attach the crank to the rotor shaft on the motor.

* Turn on the multimeter and set the measurement scale to "Volts DC." Connect the red probe to the loose end of the first wire, which should be attached to the positive electrical terminal. Connect the black probe to the loose end of the second wire attached to the negative terminal.

* Turn the crank and observe the multimeter display. If the crank is turned slowly, the voltage will fluctuate greatly. However, if the crank is turned quickly, the voltage will stabilize.

What Is the Difference Bewteen an Alternator & DC Motor Generator?

Generators were used to power vehicles before the invention of the alternator. DC generators produce direct current while alternators produce AC, or alternating current. The process of changing AC to DC is called rectification.

Function

• In a DC generator the coil of wire called an armature spins in a magnetic field. In an alternator, the magnetic field is spun inside a coil of wire called a stator.

DC Generator Vehicle

• A generator spins its armature to create a current. However, at lower speeds the generator cannot make a current, so vehicles run by generators cannot charge or maintain battery power at idle.

  Commutator

  • The current in a generator’s armature is alternating current, or AC, so to change it or rectify it a device called a commuter must be used. Overall, the output becomes DC.

  Alternator Vehicle

  • All modern-day vehicles have an alternator. The alternator is similar to a generator but can charge the battery and support higher amperages for electronics.

  Diodes

  • In an alternator, diodes change AC current into DC current. The diode can also do this without any moving parts.

Differences Between AC and DC Electric Motors.

An electrical motor converts electrical energy into mechanical energy in the form of torque (rotational energy). There are two types of motors, direct current (DC) and alternating current (AC), which differ both in the type of electrical energy they use and how they generate torque. DC motors were invented earlier, but are less commonly used today. AC motors have a simpler design and are used in most appliances and industrial equipment.

Structure

• Both AC and DC motors contain two essential components: a stator and a rotor. An electrical current creates torque when it moves within a magnetic field, according to Faraday's Law. In a DC motor, the rotor receives a direct current and a commutator reverses the current as the rotor rotates in a stationary magnetic field created by a permanent magnet in the stator. In an AC motor, the rotor receives an induced alternating current, and the stator is an induced magnetic field.

Mechanics

• The advantage of DC motors is that you can easily adjust their speed simply by increasing the voltage. However, DC motors have a more complex design, requiring brushes to transfer energy to the moving parts and a commutator to periodically reverse the voltage. These parts will wear out over time due to friction and eventually need to be replaced. AC motors have a simpler design, but they work at fixed speeds and cannot operate at low speeds.

Usage

• Due to their variable speed, DC motors can be used for both low-power and high-power applications. However, due to their higher cost and need for replacement parts, they are typically only used to power devices that require a variable power input, such as hybrid cars and certain toys. AC motors are cheaper to make and are compatible with the majority of modern appliances which have an AC energy source.

How to Find Torque From HP ?

Horsepower and torque are measures of an engine's output. In automotive engines, torque closely corresponds to how much force an engine generates when you first step on the gas, while horsepower gives an idea about how fast the car will go when you approach the rev limit, which occurs just before you must up-shift into the next gear. Automotive enthusiasts express this concept by saying that "torque gets you going and horsepower keeps you going".

* Get the horsepower for the engine and make sure it's expressed according to SAE standards, which stands for the Standard of American Engineers. If the horsepower is expressed in DIN units, which is more common on Europe, you'll need to convert by dividing the DIN horsepower by 1.0139.

* Multiply the horsepower by 5,252. When converting horsepower to torque, both figures depend on the speed at which the engine operates, which is expressed in revolutions per minute, or rpm. If you know the horsepower of an engine only at a particular rpm, you can calculate the torque figure for that specific engine speed only. If for instance, you are told that an engine makes 300 horsepower at 6,000 rpm and have no further information, you can use this data only to arrive at the engine's torque at 6,000 rpm.

* Divide the product from Step 2 by the rpm. The answer is your torque expressed in pound-feet. Returning to our original example, the torque figure would be 300 times 5,252 divided by 6,000, because the engine output was 300 horsepower at 6,000 rpm. The result will be 262.6 pound-feet. This is how much torque the engine generates at 6,000 rpm.

How to Convert HP to Torque ?

Torque represents a twisting force that causes an object to rotate, such as the force required to tighten a screw or to spin a wheel. In the imperial system of measures, which is used in the United States, torque is measured in foot-pounds. Usually torque refers to circular rotation, such as a spinning gear, but the rotation does not always have to be circular. To convert HP to torque, you also need to know the engine's number of rotations per minute.

* Look up the horsepower of your device in the owner's manual. This can be a car motor, water pump or any other mechanical device.

* Multiply the horsepower by the RPM at which your engine is turning, as in the following formula: HP*RPM. RPM stands for rotations per minute, and is shown on a tachometer, such as the one in a car. For example, if you have a 200 HP engine running at 2,500 RPM, you would multiply 200 by 2,500 to get 500,000.

* Divide the result from step 2 by 5,252 to calculate torque in foot-pounds.

The conversion factor of 5,252 is derived from one horsepower being equal to 550 foot-pounds per second; you have to multiply that number by 60 to convert from seconds to minutes (RPM means rotations per minute) and divide the result by 6.28, because there are 2π radians in a circle.

Finishing our example from the previous step, you would divide 500,000 by 5,252 to find the torque produced by a 200 HP engine running at 2,500 RPM, which equals about 95.2 foot-pounds of torque.

How to Measure Electric Motor Torque ?

Torque refers to the rotational effect produced when force is applied to an object and is measured in Newton-meter (N.m) in metric system, or pound-feet in U.S. system. Electrical energy, measured in watts, can be used to produce torque, and an electric motor is a good example of electrical energy that can produce torque. Measuring electric motor torque requires using a formula.

* Look at the owner's manual of the electric motor, or electrical appliance that has an electric motor (such as a power screwdriver). Find the rating of the motor in terms of volts, amperes, and rpm. Look at the manufacturer's nameplate or tag attached to the motor, or appliance in case there is no owner's manual.

* Multiply the number of volts by the amperes to calculate the number of watts of the motor. For example, the number of watts of a power screwdriver with a rated voltage of 120 volts and 4 amperes is 480 watts (120 volts x 4.0 amps = 480 watts).

* Divide the number of watts by 746 to get the horse power rating of the electrical motor. Using the example numbers, divide 480 watts by 746 to get the equivalent horsepower (480 watts divided by 746 = 0.6434316 horsepower).

* Multiply the horsepower by 5,252 using a calculator. Using the example figure, multiply 0.6434316 by 5,252 to get 3,379.3027.

* Divide the answer by the motor's rated number of rpm to get the measurement of the torque in pound-feet. Using the example figure, divide 3,379.3027 by 2,500 rpm to arrive at 1.351721 pound-feet of torque.

How to Understand Torque in Electric Motors?

Like most motors, electric motors provide torque. This is the twisting motion that a motor uses to move something else, such as a car's wheel, a gear or a variety of other pieces of equipment. The higher a motor's torque capacity, the more it can move with each twist. However, this often comes at the price of lower maximum power. Electric motors produce torque in a specific way, and it is important to understand how they do so in order to understand electrical motors.

* Understand how magnets work. North poles are attracted to south poles and vice versa. So, if a magnet is on a pivot with a south pole on its north side and a north pole on its other side, it will naturally align as the poles attract.

* Build on your understanding of magnets to understand electromagnets. Electromagnets are created when you wrap a wire around a piece of metal and put a charge through it. This turns the piece of metal into a magnet.

* Examine the amount of control that electromagnets allow. By reversing the charge going through them, you can reverse the north and south poles.

* Look at the effect of reversing the charge at just the right moment. As the south poles go toward the north poles, the electromagnet's poles suddenly change, which forces it to start another revolution. Then, as it approaches again, the poles change again. This creates rotational force, or torque.

How to Make Electric Generators at Home?

  So you want to make yourself an electric generator? Well that's great. In a few easy steps, you can make an electric generator to charge a battery and power anything you need. They are great for power on the go, such as camping, hiking, or picnics!
                                                           

1 The first thing to do is find a DC Motor. Any size will work, but you'll need to match your battery to the voltage of your motor. A 12 volt DC Motor is a common size, and will be good for home applications of an electric generator.

2 Make a crank for the shaft of the motor. This can be done a few different ways. One of the easiest is to use a piece of metal or plastic bar stock, and drill a hole that fits snugly over the shaft of your motor. Consider putting a spinning handle on the crank to make it more comfortable to turn. You can model yours after the cranks seen on wind up flashlights and radios.

3 Find a rechargeable battery of comparable voltage to your motor. For a 12 volt DC Motor, use a 12 volt battery. I like to use Sealed Lead Acid (SLA) batteries, since they can be recharged many times, are relatively inexpensive, and can be turned upside without spilling the battery acid (unlike car batteries).

4 Connect the DC Motor's anode and cathode (the prongs at the rear of the motor) to the battery, being sure to match the proper positive and negative. If you aren't sure which is positive and negative, use a volt meter to test. Use wiring that is suitable for the amount of voltage and current the motor is rated for. If you aren't sure, stop by an electronics store such as radio shack, they can help you choose the appropriate sized wiring.

5 Turn your crank on the motor and you will begin generating electricity. Connect a device capable of running on 12 volts (or an inverter for 115 volts) to your battery and you will now be powering your device!

How Does an Electric Generator Work?

Faraday's Law

• Electric generators work because of the effects described by Faraday's Law. This Law is used in the design of numerous electric devices, but for generators it is important because it describes the effects of moving a magnet inside a coil of conductive wire.

Generating Electricty

• The typical generator design uses either one or a set of electromagnets on a shaft. Therefore it requires an outside source of electricity to get started. These are placed inside a coil of conductive wires that are arranged to form a cylinder. The shaft rotates, turning the magnets and their electromagnetic fields. In accordance with Faraday's Law, the changing movement of the electromagnetic field through the conductive materials causes each part of the wire to build a charge. Combined, these can become quite a substantial charge. This electric charge is then transmitted out of the generator.

  Converting Mechanical Power to Electricity

  • Generators use the process described above to convert mechanical energy into electricity. The mechanical energy is what turns the shaft upon which the electromagnets are mounted, and there are a variety of sources used to provide this mechanical, turning motion. Most power plants are thermal power plants. These use a source of heat, such as burning fossil fuels or a nuclear reaction, to boil water into steam. The hot jet of steam passes through a turbine, turning its blades and providing a source of mechanical power, which is then transferred to the generator to turn the shaft. Wind turbines capture the kinetic energy of the wind to turn the shaft, whereas hydroelectric plants do the same thing with the energy of moving water. A portable generator does not burn gasoline to boil water in the same way that a thermal power plant does, but instead uses the mechanical power of an internal combustion engine to turn the shaft.

  Efficiency

  • The typical power plant has an efficiency of 35 percent. That means the conversion of heat or kinetic energy into first mechanical and then electrical energy produces 35 units of usable power for every 100 units put into the process. That might not sound like a lot, but it is actually very good compared to a variety of other machines. A car engine, for example, only has an efficiency rating of about 20 percent.

ANCIENT ELECTRICTY - TOP SEVEN CONTENDERS.

The proposal is simple.  Some historians and independent researchers believe that ancient civilisations were much more technologically advanced than is commonly accepted.  Specifically, they believe that some sectors of society had access to electricity and used it for both practical and religious purposes

Here are the top seven contenders for the existence of ancient electricity.  The electric catfish and the cat fur and amber effect are well recorded and not in dispute.  The Coso Artefact is almost certainly the misinterpretation of evidence.  As for the rest ... well they're open to debate.

1. CAT FUR AND AMBER GENERATOR

There can be no doubt that ancient civilizations were aware of static electricity even if they may not have fully understood it. They also appreciated the godlike power of lightning and must have been curious to observe this effect replicated in miniature when the fur of a cat was rubbed against certain materials in a darkened room.  The effects of static electricity were first recorded by a Greek philosopher, Thales of Miletus, who lived between  624 BC and 546 BC.  He is said to have experimented with amber, which the Greeks referred to as Elektron, and cat fur to create an electrical discharge as well as magnetism. From this observation a simple machine consisting of two spinning disks, one covered with leopard fur and one coated with glass or amber could be connected to gold axles and foil strips which would produce an electrical charge capable of generating sparks several inches in length.

2. ELECTRIC EELS - SHOCK THERAPY

Although it looks like an eel, Electrophorus Electricus is actually a Knife Fish that is able to generate and deliver significant electric shocks of up to 600 volts. The ancient Egyptians referred to an electric catfish, Malapterurus Electricus, as the "Thunderer of the Nile" which indicates that they had already made the connection to storm-related atmospheric discharges - lightning. According to various sources the Greeks and Romans were familiar with these creatures and may well have bred them in captivity. Historic records show that they were certainly farming many other types of exotic fish both for food and for amusement. Scribonus Largus, a physician at the court of the Roman Emperor Claudius (c.47AD), is reported to have written that these 'torpedo fish' could be used to treat a wide variety of ailments. They were used to numb the feet of gout sufferers as well as those suffering from persistent headaches. If this is true then this is the first recorded use of shock therapy. As recently as 2009 doctors in Boston have been successfully experimenting with electric currents to block migraines.

3. THE BAGHDAD BATTERY

In 1938 the Director of the National Museum of Iraq, Wilhelm König, discovered a number of curious terracotta pots in the archives.  Each one was approximately 13 cm in height with a capped 3.3 cm opening at the top.  Each pot contained an open-ended copper cylinder and inside this was a small iron rod. These artefacts strongly resembled simple galvanic batteries and in 1940 König published a scientific paper proposing that these objects may well have been used to generate electrical current which could have been used for electroplating objects with either gold or silver. Mainstream archaeologists continue to doubt this theory even though reproductions using lemon juice as an electrolyte have been proven to work and no other sensible explanation exists for the iron and copper contents.  The pots are likely to have been created during the Sassanid Period (224 AD - 640 AD). The debate continues.

4. THE LIGHTHOUSE OF PHAROS

Considered to be one of the seven wonders of the ancient world, construction of the 130m tall Pharos Lighthouse probably began around 280 BC on a small island just off the coast of Alexandria, Egypt. Originally commissioned by the Macedonian general, Ptolemy Soter who became ruler of Egypt after the death of Alexander the Great, it was completed during the reign of his son Ptolemy Philadelphos. Today the island of Pharos has become part of the mainland and shields a natural harbour. The building was erected to house a brilliant light to assist ships to find the port at night. Historic reports claim that the light could be seen nearly thirty miles out to sea and that it housed a beam so bright that could blind sailors and burn enemy ships. This has given rise to the theory that only an electrical arc lamp and a huge concave mirror could have created this effect. Proponents of this theory admit that the source of the power is a mystery but that an electric light is the only possible explanation for the extraordinary intensity of the lamp.

5. THE DENDERA LIGHTS

Within the Temple of Hathor, which is part of the Dendera (Tentyra) Temple Complex in Egypt, are a series of carvings that many people believe depict the sophisticated use of electricity to generate light. Items identified are as follows: an arc light lamp (horizontal) several upright lamps, lamp socket, arc light flicker (snake) electric cables, an isolator and even a large upright battery.  If historians and archaeologists believed that the Egyptians from this period used electricity then this would probably be considered a classic example.  A further point that is often overlooked is that Hathor was a goddess who is usually shown with a sun disk suspended between two horns exactly like the reflecting mirror of an arc lamp - even the dimensions are optimal. Although the equipment in the images may seem obvious it should also be noted that many historians, archaeologists and Egyptologists strongly deny that the images are anything more than the representation of a fertility rite based on Egyptian mythology. Proponents of the 'lights' theory are often dismissed as fringe scientists while mainstream Egyptologists are often accused of hiding behind conveniently concocted myths and retentive thinking. Both groups seem certain in their beliefs.

6. THE ABYDOS MACHINES

Roughly 450 kilometres south of Cairo is the ancient city-complex of Abydos.  It is widely considered to be one of the most important archaeological sites in Egypt although for some quite differing reasons. Mainstream Egyptologists recognise it as the site of the Osiris and Isis cult while proponents of ancient electricity believe it holds definite proof that ancient civilisations were significantly more advanced than historians will acknowledge.  The reason for this is that within the Hypostyle Hall of the Temple of Seti I there are a series of carvings that clearly depict modern aircraft, particularly a helicopter and dirigible. Mainstream archaeologists claim that they are merely a coincidence caused by over-carving while proponents of ancient technology state that this is actually misleading and that attempts to recreate the over-carving effect have been less than conclusive.  In addition, they point out that the coincidence required to produce these images is staggeringly unlikely.

7. THE COSO ARTEFACT

The area around the town of Olancha in California, America, is popular destination for 'rock hunters'  and attracts both professional and amateur geologists.  On Monday the 13th February 1961 three geode collectors, Wallace Lane, Mike Mikesell and Virginia Maxey discovered an interesting specimen which Mike Mikesell took home and cut in half with a diamond edged saw.  Inside the specimen he discovered what appeared to be an off-white ceramic cylinder with a small metal core running through the centre - in short, a sparkplug. According to Ms. Maxey the specimen was examined by a professional geologist who estimated that the casing was at least 500,000 years old.  The identity of the geologist has never been revealed. The discovery caused significant controversy with some experts claiming that the rock was nothing more than a 'concretion' of rust and localised fossils.   Perhaps because of the controversy the finders refused to further display or discuss the artefact after 1969.  The location of the artefact is currently unknown as are the people who found it although it is believed that Lane passed away in 2008.

small science electical projects

Science Fair Projects with Electromagnets

• 

  Build an electromagnet with common materials: copper wire, a large nail and a lantern battery. Alternatively, purchase a kit with the needed materials from a hobby shop or online store. Choose from among a variety of experimental projects that use electromagnets. For example, you can study the effect of temperature on an electromagnet's strength by testing how many paperclips or small nails the electromagnet can pick up after being exposed to a variety of temperatures. Experiment with other variables, such as the effects of using different gauges (thicknesses) of wire, or of constructing the electromagnet with more or fewer coils of wire.

Science Fair Projects Using an Electric Generator

• 

  For science fairs that only require a display project with no experimentation, build a hand-powered electrical generator and demonstrate its use. For fairs that require an experimental process, use the generator in a variety of projects. Experiment with construction variables of the generator, such as wire gauge or the number of coils used, or use parts made of different materials such as steel or copper. Measure the effect of the variables on the electrical output with a voltmeter or multimeter.

Science Experiments Studying the Effects of Resistance and Conductivity

• 

  The electrical properties of resistance and conductivity also offer possibilities for projects, most of which require that a simple electrical circuit be built. Introduce variables into the circuit, and then measure the effects of those variables. For example, study the conductivity of water as a current passes through it by comparing the conductivity of salt, tap and distilled waters. Or, compare the conductivity of different materials--copper wire to aluminum wire, for example--used in the circuit's construction. A different project involves comparing two different types of circuits. Build a circuit with components running in series (one after the other) or in parallel (the current splits and feeds each component equally). Measure the effects on the current with a multimeter to determine differences in voltage and conductivity.

  Solar-Electric Device

  • Building a solar-powered device for a science fair is an educational and interesting project. A simple device can be a solar-powered car or a solar-powered boat. Purchase or locate a small solar cell, with 1 to 2 volts of power-generation capability. Link this up to a small, simple motor. Assemble the basic car or boat construction, then hook the rear axle of the car up to the solar-powered motor, or hook the propeller of the boat up to the solar-powered motor. Record your steps and findings within a logbook. This is a fun and relatively inexpensive project.

  Potato-Powered Lightbulb

  • An interesting science fair project is the classic potato-powered lightbulb. As potatoes contain water soluble chemicals, it is possible to draw an electric current from them. Installing a simple positive-lead (copper-wire) and a negative lead (a nail) inside a large potato draws an electric current, although you may need to hook together multiple potatoes to power a lightbulb. Record your procedure in a logbook and present the findings along with your working potato-powered lightbulb.

  
  

Electric locomotive

An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or an on-board energy storage device (such as a chemical battery or fuel cell). Electrically propelled locomotives with on-board fuelled prime movers, such as diesel engines or gas turbines, are classed as diesel-electric or gas turbine-electric locomotives because the electric generator/motor combination only serves as a power transmission system. Electricity is used to eliminate smoke and take advantage of the high efficiency of electric motors; however, the cost of railway electrification means that usually only heavily used lines can be electrified.

Characteristics

One advantage of electrification is the lack of pollution from the locomotives themselves. Electrification also results in higher performance, lower maintenance costs and lower energy costs for electric locomotives.

Power plants, even if they burn fossil fuels, are far cleaner than mobile sources such as locomotive engines. Also the power for electric locomotives can come from clean and/or renewable sources, including geothermal power, hydroelectric power, nuclear power, solar power and wind turbines.^[1] Electric locomotives are also quiet compared to diesel locomotives since there is no engine and exhaust noise and less mechanical noise. The lack of reciprocating parts means electric locomotives are easier on the track, reducing track maintenance.

Power plant capacity is far greater than what any individual locomotive uses, so electric locomotives can have a higher power output than diesel locomotives and they can produce even higher short-term surge power for fast acceleration. Electric locomotives are ideal for commuter rail service with frequent stops. They are used on high-speed lines, such as ICE in Germany, Acela in the US, Shinkansen in Japan, China Railway High-speed in China and TGV in France. Electric locomotives are also used on freight routes with consistently high traffic volumes, or in areas with advanced rail networks.

Electric locomotives benefit from the high efficiency of electric motors, often above 90% (not including the inefficiency of generating the electricity). Additional efficiency can be gained fromregenerative braking, which allows kinetic energy to be recovered during braking to put some power back on the line. Newer electric locomotives use AC motor-inverter drive systems that provide for regenerative braking.

The chief disadvantage of electrification is the cost for infrastructure (overhead power lines or electrified third rail, substations, and control systems). Public policy in the US currently interferes with electrification—higher property taxes are imposed on privately owned rail facilities if they have electrification facilities. Also, US regulations on diesel locomotives are very weak compared to regulations on automobile emissions or power plant emissions.^{[citation needed]}

In Europe and elsewhere, railway networks are considered part of the national transport infrastructure, just like roads, highways and waterways, so are often financed by the state. Operators of the rolling stock pay fees according to rail use. This makes possible the large investments required for the technically, and in the long-term also, economically advantageous electrification. Because railroad infrastructure is privately owned in the US, railroads are unwilling to make the necessary investments for electrification.

Electric locomotive types

An electric locomotive can be supplied with power from

• Rechargeable energy storage systems, as battery or ultracapacitor-powered mining locomotives.
• A stationary source, such as a third rail or overhead wire.

This is in marked contrast to a diesel-electric locomotive, which combines an onboard diesel engine with an electrical power transmission or store (battery, ultracapacitor) system.

The distinguishing design features of electric locomotives are:

• The type of electrical power used, either alternating current or direct current.
• The method for store (batteries, ultracapacitors) or collecting (transmission) electrical power.
• The means used to mechanically couple the traction motors to the driving wheels (drivers).

Direct and alternating current

The most fundamental difference lies in the choice of direct (DC) or alternating current (AC). The earliest systems used direct current as, initially, alternating current was not well understood and insulation material for high voltage lines was not available. Direct current locomotives typically run at relatively low voltage (600 to 3,000 volts); the equipment is therefore relatively massive because the currents involved are large in order to transmit sufficient power. Power must be supplied at frequent intervals as the high currents result in large transmission system losses.

As alternating current motors were developed, they became the predominant type, particularly on longer routes. High voltages (tens of thousands of volts) are used because this allows the use of low currents; transmission losses are proportional to the square of the current (e.g. twice the current means four times the loss). Thus, high power can be conducted over long distances on lighter and cheaper wires. Transformers in the locomotives transform this power to a low voltage and high current for the motors.^[24] A similar high voltage, low current system could not be employed with direct current locomotives because there is no easy way to do the voltage/current transformation for DC so efficiently as achieved by AC transformers.

AC traction still occasionally uses dual overhead wires instead of single phase lines. The resulting three-phase current drives induction motors, which do not have sensitive commutators and permit easy realisation of a regenerative brake. Speed is controlled by changing the number of pole pairs in the stator circuit, with acceleration controlled by switching additional resistors in, or out, of the rotor circuit. The two-phase lines are heavy and complicated near switches, where the phases have to cross each other. The system was widely used in the northern part of Italy until 1976 and is still in use on some Swiss rack railways. The simple feasibility of a fail safe electric brake is an advantage of the system, while the speed control and the two-phase lines are problematic.Rectifier locomotives, which used AC power transmission and DC motors, were common, though DC commutators had problems both in starting and at low velocities. Today's advanced electric locomotives use brushless three-phase AC induction motors. These polyphase machines are powered fromGTO-, IGCT- or IGBT-based inverters. The cost of electronic devices in a modern locomotive can be up to 50% of the total cost of the vehicle.

Electric traction allows the use of regenerative braking, in which the motors are used as brakes and become generators that transform the motion of the train into electrical power that is then fed back into the lines. This system is particularly advantageous in mountainous operations, as descending locomotives can produce a large portion of the power required for ascending trains.

Most systems have a characteristic voltage and, in the case of AC power, a system frequency. Many locomotives over the years were equipped to handle multiple voltages and frequencies as systems came to overlap or were upgraded. American FL9 locomotives were equipped to handle power from two different electrical systems and could also operate as conventional diesel-electrics.

While recently designed systems invariably operate on alternating current, many existing direct current systems are still in use – e.g. in South Africaand the United Kingdom (750 V and 1,500 V); Netherlands, Japan, Mumbai, Ireland (1,500 V); Slovenia, Belgium, Italy, Poland, Russia, Spain (3,000 V) and the cities of Washington DC (750 V).

Power transmission

Electrical circuits require two connections (or for three phase AC, three connections). From the very beginning, the trackwork itself was used for one side of the circuit. Unlike model railroads, however, the trackwork normally supplies only one side, the other side(s) of the circuit being provided separately.

The original Baltimore and Ohio Railroad electrification used a sliding shoe in an overhead channel, a system quickly found to be unsatisfactory. It was replaced with a third rail system, in which a pickup (the "shoe") rode underneath or on top of a smaller rail parallel to the main track, somewhat above ground level. There were multiple pickups on both sides of the locomotive in order to accommodate the breaks in the third rail required by trackwork. This system is preferred in subways because of the close clearances it affords.

However, railways generally tend to prefer overhead lines, often called "catenaries" after the support system used to hold the wire parallel to the ground. Three collection methods are possible:

• Trolley pole: a long flexible pole, which engages the line with a wheel or shoe.
• Bow collector: a frame that holds a long collecting rod against the wire.
• Pantograph: a hinged frame that holds the collecting shoes against the wire in a fixed geometry.

Of the three, the pantograph method is best suited for high-speed operation. Some locomotives are equipped to use both overhead and third rail collection (e.g. British Rail Class 92).

Driving the wheels

During the initial development of railroad electrical propulsion, a number of drive systems were devised to couple the output of the traction motors to the wheels. Early locomotives used often jackshaft drives. In this arrangement, the traction motor is mounted within the body of the locomotive and drives the jackshaft through a set of gears. This system was employed because the first traction motors were too large and heavy to mount directly on the axles. Due to the number of mechanical parts involved, frequent maintenance was necessary. The jackshaft drive was abandoned for all but the smallest units when smaller and lighter motors were developed,

Several other systems were devised as the electric locomotive matured. The Buchli drive was a fully spring-loaded system, in which the weight of the driving motors was completely disconnected from the driving wheels. First used in electric locomotives from the 1920s, the Buchli drive was mainly used by the French SNCF and Swiss Federal Railways. The quill drive was also developed about this time and mounted the traction motor above or to the side of the axle and coupled to the axle through a reduction gear and a semi-flexible hollow shaft - the quill. The Pennsylvania Railroad GG1 locomotive used a quill drive. Again, as traction motors continued to shrink in size and weight, quill drives gradually fell out of favour.Another drive example was the "bi-polar" system, in which the motor armature was the axle itself, the frame and field assembly of the motor being attached to the truck (bogie) in a fixed position. The motor had two field poles, which allowed a limited amount of vertical movement of the armature. This system was of limited value since the power output of each motor was limited. The EP-2bi-polar electrics used by the Milwaukee Road compensated for this problem by using a large number of powered axles.

Modern electric locomotives, like their Diesel-electric counterparts, almost universally use axle-hung traction motors, with one motor for each powered axle. In this arrangement, one side of the motor housing is supported by plain bearings riding on a ground and polished journal that is integral to the axle. The other side of the housing has a tongue-shaped protuberance that engages a matching slot in the truck (bogie) bolster, its purpose being to act as a torque reaction device, as well as a support. Power transfer from motor to axle is effected by spur gearing, in which a pinionon the motor shaft engages a bull gear on the axle. Both gears are enclosed in a liquid-tight housing containing lubricating oil. The type of service in which the locomotive is used dictates the gear ratio employed. Numerically high ratios are commonly found on freight units, whereas numerically low ratios are typical of passenger engines.

[edit]Wheel arrangements

The Whyte notation system for classifying steam locomotives is not adequate for describing the varieties of electric locomotive arrangements, though the Pennsylvania Railroad applied classes to its electric locomotives as if they were steam or concatenations of such. For example, the PRR GG1class indicates that it is arranged like two 4-6-0 class G locomotives that are coupled back-to-back.

In any case, the UIC classification system was typically used for electric locomotives, as it could handle the complex arrangements of powered and unpowered axles and could distinguish between coupled and uncoupled drive systems.

Battery locomotives

A battery locomotive (or battery-electric locomotive) is a type of electric locomotive powered by on-board batteries; a kind of battery electric vehicle. Such locomotives are used where a conventional diesel or electric locomotive would be unsuitable. An example of use is the hauling of maintenance trains on electrified lines when the electricity supply is turned off, such as by the London Underground battery-electric locomotives.

Another use for battery locomotives is in industrial facilities – as an alternative to the fireless locomotive – where a combustion-powered locomotive (i.e.,steam- or diesel-powered) could cause a safety issue, due to the risks of fire, explosion or fumes in a confined space. Battery locomotives are preferred for mines where gas could be ignited by trolley-powered units arcing at the collection shoes, or where electrical resistance could develop in the supply or return circuits, especially at rail joints, and allow dangerous current leakage into the ground.^[36] An early example was at the Kennecott Copper Mine,Latouche, Alaska, where in 1917 the underground haulage ways were widened to enable working by two battery locomotives of 4½ tons.^[37]

In 1928, Kennecott Copper ordered four 700-series electric locomotives with on-board batteries. These locomotives weighed 85 tons and operated on 750-volt overhead trolley wire with considerable further range whilst running on batteries.^[38] The locomotives provided several decades of service usingNickel-iron battery (Edison) technology. The batteries were replaced with lead-acid batteries, and the locomotives were retired shortly afterward. All four locomotives were donated to museums, but one was scrapped. The others can be seen at the Boone and Scenic Valley Railroad, Iowa, and at theWestern Railway Museum in Rio Vista, California.