Electric generator

U.S. NRC image of a modern steam turbine generator (STG).
Early Ganz Generator in Zwevegem, West Flanders, Belgium
The Faraday disk was the first electric generator. The horseshoe-shaped magnet (A) created a magnetic field through the disk (D). When the disk was turned, this induced an electric current radially outward from the center toward the rim. The current flowed out through the sliding spring contact m, through the external circuit, and back into the center of the disk through the axle.
Hippolyte Pixii's dynamo. The commutator is located on the shaft below the spinning magnet.
This large belt-driven high-current dynamo produced 310 amperes at 7 volts. Dynamos are no longer used due to the size and complexity of the commutator needed for high power applications.
Ferranti alternating current generator, c. 1900.
A small early 1900s 75 kVA direct-driven power station AC alternator, with a separate belt-driven exciter generator.
The Athlone Power Station in Cape Town, South Africa
Hydroelectric power station at Gabčíkovo Dam, Slovakia
Hydroelectric power station at Glen Canyon Dam, Page, Arizona
Mobile electric generator
Protesters at Occupy Wall Street using bicycles connected to a motor and one-way diode to charge batteries for their electronics

Device that converts motive power into electric power for use in an external circuit.

- Electric generator

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Electric motor

Electrical machine that converts electrical energy into mechanical energy.

Animation showing operation of a brushed DC electric motor.
Cutaway view through stator of induction motor.
Faraday's electromagnetic experiment, 1821
Jedlik's "electromagnetic self-rotor", 1827 (Museum of Applied Arts, Budapest). The historic motor still works perfectly today.
An electric motor presented to Kelvin by James Joule in 1842, Hunterian Museum, Glasgow
Electric motor rotor (left) and stator (right)
Salient-pole rotor
Commutator in a universal motor from a vacuum cleaner. Parts: (A) commutator, (B) brush
Workings of a brushed electric motor with a two-pole rotor and PM stator. ("N" and "S" designate polarities on the inside faces of the magnets; the outside faces have opposite polarities.)
A: shunt B: series C: compound f = field coil
6/4 pole switched reluctance motor
Modern low-cost universal motor, from a vacuum cleaner. Field windings are dark copper-colored, toward the back, on both sides. The rotor's laminated core is gray metallic, with dark slots for winding the coils. The commutator (partly hidden) has become dark from use; it is toward the front. The large brown molded-plastic piece in the foreground supports the brush guides and brushes (both sides), as well as the front motor bearing.
Large 4,500 hp AC induction motor.
A miniature coreless motor
A stepper motor with a soft iron rotor, with active windings shown. In 'A' the active windings tend to hold the rotor in position. In 'B' a different set of windings are carrying a current, which generates torque and rotation.

An electric generator is mechanically identical to an electric motor, but operates with a reversed flow of power, converting mechanical energy into electrical energy.

Mechanical energy

Sum of potential energy and kinetic energy.

An example of a mechanical system: A satellite is orbiting the Earth influenced only by the conservative gravitational force; its mechanical energy is therefore conserved. The satellite's acceleration is represented by the green vector and its velocity is represented by the red vector. If the satellite's orbit is an ellipse the potential energy of the satellite, and its kinetic energy, both vary with time but their sum remains constant.
A swinging pendulum with the velocity vector (green) and acceleration vector (blue). The magnitude of the velocity vector, the speed, of the pendulum is greatest in the vertical position and the pendulum is farthest from Earth in its extreme positions.

Many devices are used to convert mechanical energy to or from other forms of energy, e.g. an electric motor converts electrical energy to mechanical energy, an electric generator converts mechanical energy into electrical energy and a heat engine converts heat to mechanical energy.


Rotor (lower left) and stator (upper right) of an electric motor
Stator of a 3-phase AC-motor
Stator of a brushless DC motor from computer cooler fan.
Stator winding of a generator at a hydroelectric power station.
Stator of a 3-phase induction motor

The stator is the stationary part of a rotary system, found in electric generators, electric motors, sirens, mud motors or biological rotors.

Electrical network

Interconnection of electrical components or a model of such an interconnection, consisting of electrical elements (e.g., voltage sources, current sources, resistances, inductances, capacitances).

A simple electric circuit made up of a voltage source and a resistor. Here, v=iR, according to Ohm's law.

Practical examples of such sources include a battery or a generator.

Commutator (electric)

Commutator in a universal motor from a vacuum cleaner. Parts: (A) commutator, (B) brush, (C) rotor (armature) windings, (D) stator (field) windings, (E) brush guides, (F) electrical connections.
Cross-section of a commutator that can be disassembled for repair.
A tiny 5-segment commutator less than 2 mm in diameter, on a direct-current motor in a toy radio control ZipZaps car.
Various types of copper and carbon brushes.
Compound carbon brush holder, with individual clamps and tension adjustments for each block of carbon.
Different types of brushes have different brush contact angles
Commutator and brush assembly of a traction motor; the copper bars can be seen with lighter insulation strips between the bars. Each dark grey carbon brush has a short flexible copper jumper lead attached. Parts of the motor field winding, in red, can be seen to the right of the commutator.
Commutating plane definitions.
Centered position of the commutating plane if there were no field distortion effects.
Actual position of the commutating plane to compensate for field distortion.
Brush advance for Self-Induction.
Low voltage dynamo from late 1800s for electroplating. The resistance of the commutator contacts causes inefficiency in low voltage, high current machines like this, requiring a huge elaborate commutator. This machine generated 7 volts at 310 amps.

A commutator is a rotary electrical switch in certain types of electric motors and electrical generators that periodically reverses the current direction between the rotor and the external circuit.

Rotor (electric)

A selection of various types of rotors
Rotor from Hoover Dam generator
Salient pole rotor
Cylindrical rotor

The rotor is a moving component of an electromagnetic system in the electric motor, electric generator, or alternator.

Alternating current

Electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction.

Alternating current (green curve). The horizontal axis measures time (it also represents zero voltage/current) ; the vertical, current or voltage.
A schematic representation of long distance electric power transmission. From left to right: G=generator, U=step up transformer, V=voltage at beginning of transmission line, Pt=power entering transmission line, I=current in wires, R=total resistance in wires, Pw=power lost in transmission line, Pe=power reaching the end of the transmission line,  D=step down transformer, C=consumers.
Three-phase high-voltage transmission lines use alternating currents to distribute power over long distances between electric generation plants and consumers. The lines in the picture are located in eastern Utah.
A sine wave, over one cycle (360°). The dashed line represents the root mean square (RMS) value at about 0.707.
The Hungarian "ZBD" Team (Károly Zipernowsky, Ottó Bláthy, Miksa Déri), inventors of the first high efficiency, closed-core shunt connection transformer
The prototype of the ZBD transformer on display at the Széchenyi István Memorial Exhibition, Nagycenk in Hungary
Westinghouse Early AC System 1887
(US patent 373035)

In a power plant, energy is generated at a convenient voltage for the design of a generator, and then stepped up to a high voltage for transmission.

Magnetic field

Vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials.

The shape of the magnetic field produced by a horseshoe magnet is revealed by the orientation of iron filings sprinkled on a piece of paper above the magnet.
Right hand grip rule: a current flowing in the direction of the white arrow produces a magnetic field shown by the red arrows.
A Solenoid with electric current running through it behaves like a magnet.
A sketch of Earth's magnetic field representing the source of the field as a magnet. The south pole of the magnetic field is near the geographic north pole of the Earth.
One of the first drawings of a magnetic field, by René Descartes, 1644, showing the Earth attracting lodestones. It illustrated his theory that magnetism was caused by the circulation of tiny helical particles, "threaded parts", through threaded pores in magnets.
Hans Christian Ørsted, Der Geist in der Natur, 1854

Rotating magnetic fields are used in both electric motors and generators.


Difference in electric potential between two points, which is defined as the work needed per unit of charge to move a test charge between the two points.

Batteries are sources of voltage in many electric circuits.
The electric field around the rod exerts a force on the charged pith ball, in an electroscope
In a static field, the work is independent of the path
Working on high voltage power lines
Multimeter set to measure voltage

Electric potential differences between points can be caused by the build-up of electric charge (e.g., a capacitor), and from an electromotive force (e.g., electromagnetic induction in generator, inductors, and transformers).

Homopolar generator

Faraday disk, the first homopolar generator
Faraday disc
The remains of the ANU 500 MJ generator
Basic Faraday disc generator
Working principle of a homopolar generator: due to Lorentz force FL negative charges are driven towards center of the rotating disk, so that a voltage shows up between its center and its rim, with the negative pole at the center.

A homopolar generator is a DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field.