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Direct Current

Direct current

Direct current (DC or "continuous current") is the constant flow of electric charge from high to low potential. This is typically in a conductor such as a wire, but can also be through semiconductors, insulators, or even through a vacuum as in electron or ion beams. In direct current, the electric charges flow always in the same direction, which distinguishes it from alternating current (AC). A term formerly used for direct current was Galvanic current. term formerly used Historically, the first commercial electric power transmission (developed by Thomas Edison in the late nineteenth century) used direct current. Because alternating current is more convenient than direct current for electric power distribution and transmission, today nearly all electric power transmission uses alternating current. See War of Currents

Various Definitions

Within Electrical Engineering, the term DC is also a synonym for constant. For example, the voltage across a DC voltage source is constant as is the current through a DC current source. The DC solution of an electric circuit is that solution where all voltages and currents are constant. In this context, a voltage (current) that is changing with time cannot be a DC voltage (current) even if the polarity (direction) does not change. However, it can be shown that such a changing voltage or current can be decomposed into the sum of a DC component and an AC component. The DC component is defined to be the average value of the voltage or current over all time. The average value of the AC component is exactly zero as with, for example, a sine wave. Although DC stands for "Direct Current", DC is generically used to refer to constant polarity voltages. Some forms of DC vary wildly in voltage, such as the raw output of a rectifier. Running them through an RC low-pass filter will produce more stable voltage. Other forms of DC (such as that produced by a voltage regulator) have almost no variations in voltage (but may still have wild variations in output electric power and current).

Applications

Direct current installations usually have different types of sockets, switches, and fixtures, mostly due to the very low voltages used, from those suitable for alternating current. It is usually extremely important with a direct current appliance to not reverse polarity unless the device has a diode bridge to correct for this. (Most battery-powered devices don't.) High voltage direct current is used for long-distance point-to-point power transmission and for submarine cables, with voltages from a few kilovolts to approximately one megavolt. DC is commonly found in many low-voltage applications, especially where these are powered by batteries, which can produce only DC, or solar power systems, since solar cells can produce only DC. Most automotive applications use DC, although the generator is an AC device which uses a rectifier to produce DC. Most electronic circuits require a DC power supply. Most telephones connect to a twisted pair of wires, and internally separate the AC component of the voltage between the two wires (the audio signal) from the DC component of the voltage between the two wires (used to power the phone).

External links

- "[http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html AC/DC: What's the Difference]?". Edison's Miracle of Light, [http://www.pbs.org/wgbh/amex/index.html American Experience]. (PBS) Category:Electricity Category:Electrical engineering ko:직류 ja:直流

Current (electricity)

In electricity, current refers to electric current, which is the flow of electric charge. Lightning is an example of an electric current, as is the solar wind, the source of the polar aurora. Probably the most familiar form of electric current is the flow of conduction electrons in a metallic wire. This is how utility companies deliver electricity. In electronics, electric current is most often the flow of electrons through conductors and devices such as resistors, but it is also the flow of ions inside a battery or the flow of holes within a semiconductor.

Relation between current and charge

The symbol typically used for the amount of current (the amount of charge Q flowing per unit of time t) is I, from the German word Intensität, which means 'intensity'. :

I =

Formally this is written as :

i(t) =

or inversely as

q(t) = \int_^ i(x)\, dx

Conventional current

Conventional current was defined early in the history of electrical science as a flow of positive charge. In solid metals, like wires, the positive charges are immobile, and only the negatively charged electrons flow in the direction opposite conventional current, but this is not the case in most non-metallic conductors. In other materials, charged particles flow in both directions at the same time. Electric currents in electrolytes are flows of electrically charged atoms (ions), which exist in both positive and negative varieties. For example, an electrochemical cell may be constructed with salt water (a solution of sodium chloride) on one side of a membrane and pure water on the other. The membrane lets the positive sodium ions pass, but not the negative chlorine ions, so a net current results. Electric currents in plasma are flows of electrons as well as positive and negative ions. In ice and in certain solid electrolytes, flowing protons constitute the electric current. To simplify this situation, the original definition of conventional current still stands. There are also instances where the electrons are the charge that is physically moving, but where it makes more sense to think of the current as the movement of positive "holes" (the spots that should have an electron to make the conductor neutral). This is the case in a p-type semiconductor. The SI unit of electrical current is the ampere. Electric current is therefore sometimes informally referred to as amperage or ampage, by analogy with the term voltage. Though this is a valid term, some engineers frown on it.

The speed of an electric current

The charged particles whose movement causes an electric current do not always move in straight lines. In metals, for example, they follow an erratic path, bouncing from atom to atom, but generally drifting in the direction of the electric field. The speed at which they drift can be calculated from the equation: :

I=nAvQ \!\

where :I is the current :n is number of charged particles per unit volume :A is the cross-sectional area of the conductor :v is the drift velocity, and :Q is the charge on each particle. For example, in a copper wire of cross-section 0.5 mm², carrying a current of 5 A, the drift velocity of the electrons is of the order of a millimetre per second. To take a different example, in the near-vacuum inside a cathode ray tube, the electrons travel in near-straight lines ("ballistically") at about a tenth of the speed of light. However, we know that an electric signal travels much faster than this; usually close to the speed of light. These results show that the speed of the charged particles is not necessarily related to the speed of the electric signal. To understand how signals travel faster than the particles that carry them, it is necessary to understand the properties of electromagnetic waves (see article).

Current density

Current density is the current per unit (cross-sectional) area. Mathematically, current is defined as the net flux through an area. Thus: :

I = j \cdot A

where, in the MKS or SI system of measurement, :I is the current, measured in amperes :j is the "current density" measured in amperes per square metre :A is the area through which the current is flowing, measured in square metres The current density is defined as: :

j=\int_i n_i \cdot x_i \cdot \mathbf

where :n is the particle density (number of particles per unit volume) :x is the mass, charge, or any other characteristic whose flow one would like to measure. :u is the average velocity of the particles in each volume Current density is an important consideration in the design of electrical and electronic systems. Most electrical conductors have a finite, positive resistance, making them dissipate power in the form of heat. The current density must be kept sufficiently low to prevent the conductor from melting or burning up, or the insulating material failing. In superconductors, excessive current density may generate a strong enough magnetic field to cause spontaneous loss of the superconductive property.

Electromagnetism

Every electric current produces a magnetic field. The magnetic field can be visualized as a pattern of circular field lines surrounding the wire. Electric current can be directly measured with a galvanometer, but this method involves breaking the circuit, which is sometimes inconvenient. Current can also be measured without breaking the circuit by detecting the magnetic field it creates. Devices used for this include Hall effect sensors, current clamps and Rogowski coils.

Ohm's law

Ohm's law predicts the current in an (ideal) resistor (or other ohmic device) to be the quotient of applied voltage over electrical resistance: :

I = \frac

where :I is the current, measured in amperes :V is the potential difference measured in volts :R is the resistance measured in ohms

Electrical safety

The danger of an electric shock depends on the current (in milliamperes), duration and the current's path in the body:
- 1 mA causes a tingle
- 5 mA causes a slight shock
- 50 to 150 mA may result in death, e.g. through rhabdomyolysis (muscle breakdown) and resultant acute renal failure
- 1-4 A causes ventricular fibrillation
- 10 A causes cardiac arrest (only at this current will a typical home fuse break the circuit) Currents through the heart and the nervous system are the most dangerous. As most dangerous sources are voltage sources, the current present depends on the resistance of the body between the points of contact and any current limiting built into the source. The comparison between the dangers of alternating current and direct current has been a subject of debate ever since the War of Currents in the 1880s. DC tends to cause continuous muscular contractions that make the victim hold on to a live conductor, thereby increasing the risk of deep tissue burns. On the other hand, mains-frequency AC tends to interfere more with the heart's electrical pacemaker, leading to an increased risk of fibrillation. AC at higher frequencies holds a different mixture of hazards, such as RF burns and the possibility of tissue damage with no immediate sensation of pain.

External links

- [http://www.unitconversion.org/unit_converter/current.html Online Current Converter] - convert between various units of current, such as ampere, biot, abampere, statampere, and so on
- [http://www.unitconversion.org/unit_converter/current-v.html Interactive Current Conversion Table] - convert selected unit to all other units of current
- [http://amasci.com/amateur/elecdir.html Which direction does electricity really flow?] Category:Electromagnetism Category:Magnetism ko:전류 ja:電流 th:กระแสไฟฟ้า

Electric potential

Electric potential is the potential energy per unit charge associated with a static (time-invariant) electric field, also called the electrostatic potential, typically measured in volts. Metaphorically, electric potential may be conceived of as "electric pressure" that can push electric charges to different locations. Technically, it is the potential φ (a scalar field) associated with the conservative electric field E (E = −∇φ) that occurs when the magnetic field is time invariant (so that ∇ × E = 0 from Faraday's law of induction). Like any potential function, only the potential difference (voltage) between two points is physically meaningful (neglecting quantum Aharonov-Bohm effects), since any constant can be added to φ without affecting E. The electric potential is therefore measured in units of energy per unit of electric charge. In SI units, this is: :joules/coulombs = volts. The electric potential can also be generalized to handle situations with time-varying magnetic fields, in which case the electric field is not conservative and a potential function cannot be defined everywhere in space. There, an effective potential drop is included, associated with the inductance of the circuit. This generalized potential difference is also called the electromotive force (emf).

Introduction

Objects may possess a property known as electric charge. In the presence of an electric field, a force is exerted on such objects, accelerating them in the direction of the force. This force has the same direction as the electric field vector, and its magnitude is given by the size of the charge multiplied with the magnitude of the electric field. Classical mechanics explores the concepts such as force, energy, potential etc. in more detail. There is a direct relationship between force and potential energy. As an object moves in the direction that the force accelerates it, its potential energy decreases. For example, the gravitational potential energy of a cannonball at the top of a tower is greater than at the base of the tower. As the object falls, that potential energy decreases and is translated to motion, or inertial energy. For certain forces, it is possible to define the "potential" of a field such that the potential energy of an object due to a field is dependent only on the position of the object with respect to the field. Those forces must affect objects depending only on the intrinsic properties of the object and the position of the object, and obey certain other mathematical rules. Two such forces are the gravitational force (gravity) and the electric force in the absence of time-varying magnetic fields. The potential of an electric field is called the electric potential. The electric potential and the magnetic vector potential together form a vector of dimension 4, so that the two kinds of potential are mixed under Lorentz transformations.

Mathematical introduction

The concept of electric potential (denoted by: φ,

\phi_\mathrm

or V) is closely linked with potential energy, thus: :

U_\mathrm = q\phi

where

U_\mathrm

is the electric potential energy of a test charge q due to the electric field. Note that the potential energy and hence also the electric potential is only defined up to an additive constant: one must arbitrarily choose a position where the potential energy and the electric potential is zero. The proper definition of the electric potential uses the electric field E: :

\phi_\mathrm = - \int_C \mathbf \cdot \mathrm\mathbf

where s is an arbitrary path connecting the point with zero potential to the point under consideration. When

\nabla\times\mathbf E = 0

, the line integral above does not depend on the specific path C chosen but only on its endpoints. Note: this equation cannot be used and the electric potential is not defined if

\nabla\times\mathbf E \ne 0

, i.e., in the case of a nonconservative electric field (caused by a changing magnetic field; see Maxwell's equations).

Special cases and computational devices

The electric potential at a point

\mathbf

due to a constant electric field

\mathbf

can be shown to be: :

\phi_\mathrm = - \mathbf \cdot \mathbf

The electric potential created by a point charge q, at a distance r from the charge, can be shown to be, in SI units: :

\phi_\mathbf = \frac

The electric potential due to a system of point charges is equal to the sum of the point charges' individual potentials. This fact simplifies calculations significantly, since addition of potential (scalar) fields is much easier than addition of the electric (vector) fields. The electric potential created by a tridimensional spherically symmetric gaussian charge density

\rho(r)

given by: :

\rho(r) = \frac\,e^,

where q is the total charge, is obtained by solving the Poisson's equation (in cgs units): :

\nabla^2 \phi_\mathbf = - 4 \pi \rho.

The solution is given by: :

\phi_\mathbf(r) = \frac\,\mbox\left(\frac\right)

where erf(x) is the error function. This solution can be checked explicitly by a careful manual evaluation of

\nabla^2 \phi_\mathbf

. Note that, for r much greater than σ, erf(x) approaches unity and the potential

\phi_\mathbf

approaches the point charge potential

\frac

seen above, as expected.

Applications in electronics

This electric potential, typically measured in volts, provides a simple way to analyze electric circuits without requiring detailed knowledge of the circuit shape or the fields within it. The electric potential provides a simple way to analyze electrical networks with the help of Kirchhoff's voltage law, without solving the detailed Maxwell's equations for the fields of the circuit.

References

- [http://www.rwc.uc.edu/koehler/biophys/4b.html Electric Potential]

External links

- [http://www.phy.duke.edu/~rgb/Class/phy42/node12.html Potential vs. Potential difference] Category:Electrostatics Category:Introductory physics ja:電位 ko:전위

Conductor (material)

:See conductor for other meanings of the word. In science and engineering, conductors are materials that contain movable charges of electricity. When an electric potential difference is impressed across separate points on a conductor, the mobile charges within the conductor are forced to move, and an electric current between those points appears in accordance with Ohm's law. While many conductors are metallic, there are many non-metallic conductors as well, including all plasmas. See electrical conduction for more information on the physical mechanism for charge flow in materials. Under normal conditions, all materials offer some resistance to flowing charges, which generates heat. Thus, proper design of an electrical conductor includes an estimate of the temperature that the conductor is expected to endure without damage, as well as the quantity of electrical current. The motion of charges also creates an electromagnetic field around the conductor that exerts a mechanical radial squeezing force on the conductor. A conductor of a given material and volume (length x cross-sectional area) has no real limit to the current it can carry without being destroyed as long as the heat generated by the resistive loss is removed and the conductor can withstand the radial forces. This effect is especially critical in printed circuits, where conductors are relatively small and the heat produced, if not properly removed, can cause fusing of the tracks. Non-conducting materials lack mobile charges and are called insulators. A material can be an electrical conductor without being a thermal conductor, although a metal can be both an electrical conductor and a thermal conductor. Electrically conductive materials are usually classified according to their electrical resistance; ranging from high to null resistance, there are semiconductors, ordinary metallic conductors (also called normal metals), and superconductors.
Power engineering
In power engineering, a conductor is a piece of metal used to conduct electricity, known colloquially as a wire.
Conductor size
In United States, conductors are measured by American wire gauge for smaller ones, and circular mils for larger ones. For example, a '4/0' conductor is about a half inch in diameter, while a '795 000' conductor is about an inch in diameter. In other places, conductors are often measured by their cross section in square millimeters.
Conductor materials
Of the metals commonly used for conductors, copper has the highest conductivity. Silver is more conductive, but due to cost it is not practical except as a thin plating to mitigate skin effect losses at high frequencies. Because of its ease of connection by soldering or clamping, copper is still the most common choice for most light-gauge wires. Compared to copper, aluminium has worse conductivity per unit volume, but better conductivity per unit weight. In many cases, weight is more important than volume making aluminium the 'best' conductor material for certain applications. For example, it is commonly used for large-scale power distribution conductors such as overhead power lines. In many such cases, aluminium is used over a steel core that provides much greater tensile strength than would the aluminium alone [http://slate.msn.com/id/2123556/][http://www.eurekalert.org/features/doe/2005-03/drnl-mpt030905.php]. Gold is occasionally used for very fine wires such as those used to wire bond integrated circuits to their lead frames. Because of its corrosion resistance, electrical connectors often gold-plated as well.
Conductor voltage
The voltage on a conductor is determined by the connected circuitry and has nothing to do with the conductor itself. Conductors are usually surrounded by and/or supported by insulators and the insulation determines the maximum voltage that can be applied to any given conductor.
Conductor ampacity
The ampacity of a conductor, that is, the amount of current it can carry, is related to its electrical resistance: a lower-resistance conductor can carry more current. The resistance, in turn, is determined by the material the conductor is made from (as described above) and the conductor's size. For a given material, conductors with a larger cross-sectional area have less resistance than conductors with a smaller cross-sectional area. For bare conductors, the ultimate limit is the point at which power lost to resistance causes the conductor to melt. Aside from fuses, most conductors in the real world are operated far below this limit, however. For example, household wiring is usually insulated with PVC insulation that is only rated to operate to about 60 C, therefore, the current flowing in such wires must be limited so that it never heats the copper conductor above 60 C. Other, more expensive insulations such as Teflon or fiberglass may allow operation at much higher temperatures. The American wire gauge article contains a table showing allowable ampacities for a variety of copper wire sizes.
See also

- Resistivity
- Charge transfer complex
- Bundle conductor Category:Electricity Category:Hardware (mechanical) Category:Power engineering ja:導体

Insulator

:This page refers to electrical insulation. For thermal insulation see insulation, and for sound insulation see sound proofing. Insulator is also a DNA-sequence that prevents eucariotic gene regulatory proteins from influencing distant genes, see Insulator (DNA)

Definition

An Insulator is a material or object which resists the flow of electric charge.

Electrical insulator

electric charge wire]] The term electrical insulator has the same meaning as the term dielectric, but the two terms are used in different contexts.The opposite of electrical insulators are conductors and semiconductors, which permit the flow of charge. Semiconductors are strictly speaking also insulators, since they prevent the flow of electric charge at low temperatures, unless doped with atoms that release extra charges to carry the current. However, some materials (such as silicon dioxide) are very nearly perfect electrical insulators, which allows flash memory technology. A much larger class of materials, (for example rubber and many plastics) are "good enough" insulators to be used for home and office wiring (into the hundreds of volts) without noticeable loss of safety or efficiency.

High voltage insulators

High voltage insulators used for high voltage power transmission are either porcelain insulators or composite insulators. Porcelain insulators are made from clay, quartz or alumina and feldspar. Alumina insulators are used where high mechanical strength is a criterion. In recent times there is a shift towards composite insulators which have a central rod made of fibre reinforced plastic and outer weathersheds made of silicone rubber or EPDM. Glass insulators were, and in some places are still used to mount electrical power lines. Most insulator manufacturers stopped making glass insulators in the late 1960's, switching to ceramic materials. Composite insulators are less costly, light weight and have excellent hydrophobic capability and hence can be used in polluted areas.

Low voltage insulators

Insulating materials such as PVC (polyvinyl chloride) are used to minimise the possibility of a person coming into contact with a 'live' wire. Some appliances such as electric shavers and hair dryers are doubly insulated to protect the user. They can be recognised because their leads have two pins, or on 3 pin plugs the third (earth) pin is made of plastic rather than metal. In the EU, double insulated appliances all are marked with a symbol of 2 squares, one inside the other. Double insulation requires that cables have basic and supplementary insulation, each of which is sufficient to prevent electric shock. Usually, the internal electrical components are totally enclosed in an insulated packaging which prevents any contact with live parts.

External links

- http://www.myinsulators.com/downtownseattle/ — one person's obsession with telephone pole insulators
- [http://CPRR.org/Museum/Ephemera/Brooks_Insulator.html Transcontinental Telegraph Insulators, 1867]
- [http://www.insulators.com www.insulators.com]
- [http://www.insulatorscanada.com www.insulatorscanada.com]
- http://www.nia.org — National Insulator Association Category:Insulators ja:絶縁体

Electron beam

A charged particle beam is a spatially localized group of electrically charged particles that have approximately the same velocity (speed and direction). The kinetic energies of the particles are typically measured in keV or MeV, much larger than the energies of particles at ambient temperature. The high energy and directionality of charged particle beams make them useful for applications. For practical purposes, a charged particle beam is characterized by:
- the species of particle, e.g. electrons, alpha particles, or hydrogen ions
- the energy of the particles, typically expressed in kiloelectronvolts or megaelectronvolts,
- the particle current, expressed in amperes,
- the beam diameter, and
- the emittance, a measure of the degree to which the particle trajectories are non-laminar. These parameters can be expressed in various ways. For example, the current and beam size can be combined into the current density, and the current and velocity can be combined into the perveance K = I V^-3/2. The (technologically) most important types of charged particle beams are:
- electron beams, consisting of electrons.
- ion beams, consisting of ions.

Alternating current

An alternating current (AC) is an electrical current where the magnitude and direction of the current varies cyclically, as opposed to direct current, where the direction of the current stays constant. The usual waveform of an AC power circuit is a sine wave, as this results in the most efficient transmission of energy. However in certain applications different waveforms are used, such as triangular or square waves. Used generically, AC refers to the form in which electricity is delivered to businesses and residences. However, audio and radio signals carried on electrical wire are also examples of alternating current. In these applications, an important goal is often the recovery of information encoded (or modulated) onto the AC signal.

History

William Stanley Jr designed one of the first practical coils to produce alternating currents. His design was an early precursor of the modern transformer, called an induction coil. From 1881 to 1889, the system used today was devised by Nikola Tesla, George Westinghouse, Lucien Gaulard, John Gibbs, and Oliver Shallenger. These systems overcame the limitations imposed by using direct current, as found in the system that Thomas Edison first used to distribute electricity commercially. The first long-distance transmission of alternating current took place in 1891 near Telluride, Colorado, followed a few months later in Germany. Thomas Edison strongly advocated the use of direct current (DC), having many patents in that technology, but eventually alternating current came into general use (see War of Currents). Charles Proteus Steinmetz of General Electric solved many of the problems associated with electricity generation and transmission using alternating current.

Distribution and domestic power supply

AC voltage can be stepped up or down by a transformer to a different voltage. High-voltage, direct current electric power transmission systems contrast with the more common alternating-current systems as a means for the bulk transmission of electrical power. However, these tend to be more expensive and less efficient than transformers, or did not exist when Edison, Westinghouse and Tesla were designing their power systems. Use of a higher voltage leads to more efficient transmission of power. The power losses in a conductor are a product of the square of the current and the resistance of the conductor, described by the formula

P= I^2R

. This means that when transmitting a fixed power on a given wire, if the current is doubled, the power loss will be four times greater. Since the power transmitted is equal to the product of the current, the voltage and the cosine of the phase difference φ (

P = IV \cos \phi

), the same amount of power can be transmitted with a lower current by increasing the voltage. Therefore it is advantageous when transmitting large amounts of power to distribute the power with extremely high voltages (sometimes as high as hundreds of kilovolts). However, high voltages also have disadvantages, the main ones being the increased danger to anyone who comes into contact with them, the extra insulation required, and generally increased difficulty in their safe handling. In the power plant the voltage is generated on three phase low voltage, with a frequency of either 50 or 60 hertz, and stepped up to a high voltage for distribution and stepped down, with a neutral, to a relatively low level for the consumer, generally around 200 V to 500 V between phases and 100 V to 250 V between each phase and the neutral. Three-phase electrical generation is very common and is a more efficient use of commercial generators. Electrical energy is generated by rotating a coil inside a magnetic field, in large generators with a high capital cost. However, it is relatively simple and cost effective to include three separate coils in the generator stator (instead of one). These sets of coils are physically separated and at an angle of 120° to each other. Three current waveforms are produced that are 120° out of phase with each other, but of equal magnitude. Three-phase systems are designed so that they are balanced at the load; if a load is correctly balanced no current will flow in the neutral point. Also, even in the worst-case unbalanced (linear) load, the neutral current will not exceed the highest of the phase currents. For three-phase at low (normal mains) voltages a four-wire system like this is normally used, reducing the cable requirements by one third over using a separate neutral per phase. When stepping down three-phase, a transformer with a Delta primary and a Star secondary is often used so there is no need for a neutral on the supply side. For smaller customers (just how small varies by country and age of install) only a single phase and the neutral or two phases and the neutral are taken to the property. For larger installs all three phases and the neutral are taken to the main board. From a three-phase main board both single and three-phase circuits may lead off (and in some cases also circuits with two phases (not to be confused with two-phase) and a neutral are led off). Three-wire single phase systems, with a single centre-tapped transformer giving two live conductors, is a common distribution scheme for residential and small commercial buildings in North America. A similar method is used for a different reason on construction sites in the UK. Small power tools and lighting are supposed to be supplied by a local center-tapped transformer with a voltage of 55V between each power conductor and the earth. This significantly reduces the risk of electric shock in the event that one of the live conductors becomes exposed through an equipment fault whilst still allowing a reasonable voltage for running the tools. A third wire is usually (should be always but there are many older, non-compliant, or third-world installs where it is not) connected between the individual electrical appliances in the house and the main consumer unit or distribution board. The third wire is known in Britain and most other English-speaking countries as the earth wire, but in (English-speaking) North America it is the ground wire. Exactly what happens to the ground wire before the main board varies, but there are three main possibilities, which are listed here by their European names:
- TT (customer's earth not connected to neutral at all)
- TN-S (neutral and earth run back separately to the transformer star point)
- TN-C-S (neutral and earth are joined at the intake position). There is also TN-C where neutral and earth are joined right through the install, but this is much less common than the others and requires special procedures to make it safe. A system should be designed so that, in the event of a short to earth on any part of the system, some form of fuse or breaker will make the system safe. In a TT system the high earth loop impedance means that a Residual-Current Device (RCD) must be used. In other earthing systems this can be covered by the normal overcurrent protection devices. RCDs may still be used on such systems though as they can protect against small earth faults such as through a person.

AC power supply frequencies by country

Electrical equipment is made by the manufacturer to be used on a specific frequency, in general 50 or 60 hertz or for both frequencies. If specified for one frequency this equipment cannot and should not be used on the other frequency, because of burn out and therefore fire reasons. The frequency of the electrical system varies by country; most electric power is generated at either 50 or 60 Hz. The 60 hertz countries are: American Samoa, Antigua and Barbuda, Aruba, Bahamas, Belize, Bermuda, Canada, Cayman Islands, Colombia, Costa Rica, Cuba, Dominican Republic, El Salvador, French Polynesia, Guam, Guatemala, Guyana, Haiti, Honduras, South Korea, Marshall Islands, Mexico, Micronesia, Montserrat, Nicaragua, Northern Mariana Islands, Palau, Panama, Peru, Philippines, Puerto Rico, Saint Kitts and Nevis, Suriname, Taiwan, Trinidad and Tobago, Turks and Caicos Islands, United States, Venezuela, Virgin Islands (U.S.), Wake Island._{[http://www.philip.allen.org/voltages.htm]} The following countries have a mixture of 50 Hz and 60 Hz supplies: Bahrain, Brazil (mostly 60 Hz), Japan (60 Hz used in western prefectures), Liberia (now officially 50 Hz, formerly 60 Hz and many independent 60 Hz generating plants still exist). _{[http://www.50hz.com/pwchrt2.htm]} Also see List of countries with mains power plugs, voltages and frequencies. Very early AC generating schemes used arbitrary frequencies based on convenience for steam engine, water turbine and generator design, since frequency was not critical for incandescent lighting loads. Frequencies between 16 2/3 Hz and 133 Hz were used on different systems, with lower frequencies favoured where loads were primarily composed of motors, and higher frequencies preferred to reduce lighting flicker. For example, the city of Coventry, England, in 1895 had a unique 87 Hz single-phase distribution system that was in use until 1906. Once induction motors became common, it was important to standardize frequency for compatibility with the customer's equipment. Standardizing on one frequency also, later, allowed interconnection of generating plants on a grid for economy and security of operation. It is generally accepted that Nikola Tesla chose 60 hertz as the lowest frequency that would not cause street lighting to flicker visibly. The origin of the 50 hertz frequency used in other parts of the world is open to debate but seems likely to be a rounding off of 60 Hz to the 1-2-5-10 structure, called a set of preferred numbers, popular with metric standards. Other frequencies were somewhat common in the first half of the 20th century, and remain in use in isolated cases today, often tied to the 60 Hz system via a rotary converter or static inverter frequency changer. 25 Hz power was used in Ontario, Quebec, the northern USA, and for electrified railroads. In the 1950s, much of this electrical system, from the generators right through to household appliances, was converted and standardised to 60 Hz. Some 25 Hz generators still exist at the Beck 1 and Rankine generating stations near Niagara Falls to provide power for large industrial customers who did not want to replace existing equipment; and some 25 Hz motors in New Orleans' floodwater pumps [http://www.dotd.louisiana.gov/press/pressrelease.asp?nRelease=513]. A low frequency eases the design of low speed electric motors, particularly for hoisting, crushing and rolling applications, and commutator-type traction motors for applications such as railways, but also causes a noticeable flicker in incandescent lighting and objectionable flicker of fluorescent lamps. 16.67 Hz power (1/3 of the mains frequency) is still used in some European rail systems, such as in Sweden and Switzerland. Off-shore, textile industry, marine, computer mainframe, aircraft, and spacecraft applications sometimes use 400 Hz, for benefits of reduced weight of apparatus or higher motor speeds. AC-powered appliances can give off a characteristic hum at the multiples of the frequencies of AC power that they use. Most countries have chosen their television standard to match (or at least approximate) their mains supply frequency. This helps prevent unfiltered powerline hum and magnetic interference from causing visible beat frequencies in the displayed picture.

Mathematics of AC voltages

television Alternating currents are usually associated with alternating voltages. An AC voltage v can be described mathematically as a function of time by the following equation: :

v(t)=A \times\sin(\omega t),

where :A is the amplitude in volts (also called the peak voltage), :ω is the angular frequency in radians per second, and :t is the time in seconds. Since angular frequency is of more interest to mathematicians than to engineers, this is commonly rewritten as: :

v(t)=A \times\sin(2 \pi f t),

where :f is the frequency in hertz. The peak-to-peak value of an AC voltage is defined as the difference between its positive peak and its negative peak. Since the maximum value of sin(x) is +1 and the minimum value is −1, an AC voltage swings between +A and −A. The peak-to-peak voltage, written as V_P-P, is therefore (+A) − (−A) = 2 × A. In power distribution, the AC voltage is nearly always given as a root mean square (rms) value, written V_rms. For a sinusoidal voltage: :

V_\mbox=

V_rms is useful in calculating the power consumed by a load. If a DC voltage of V_DC delivers a certain power P into a given load, then an AC voltage of V_rms will deliver the same average power P into the same load if V_rms = V_DC. Because of this fact rms is the normal means of measuring voltage in mains (power) systems. To illustrate these concepts, consider the 240 V AC mains used in the UK (it should be noted that the UK is now officially 230 V +10% −6% but in reality voltages are still closer to 240 V than 230 V in most cases). It is so called because its rms value is (at least nominally) 240 V. This means that it has the same heating effect as 240 V DC. To work out its peak voltage (amplitude), we can modify the above equation to: :

A=V_\mbox \times \sqrt 2

For our 240 V AC, the peak voltage V_P or A is therefore 240 V × √2 = 339 V (approx.). The peak-to-peak value V_P-P of the 240 V AC mains is even higher: 2 × 240 V × √2 = 679 V (approx.) Note that non-sinusoidal waveforms have a different relationship between their peak magnitude and effective (RMS) value. This is of practical significance when working with non-linear circuit elements that produce harmonic currents, such as rectifiers. Also notice the balanced 3 phase system: the neutral is supposed to have zero current. This follows from: :

\cos + \cos + \cos = 0

(

2\pi/3

is an angle of 120°). The European Union (including the UK) have now officially harmonized on a supply of 230 V 50 Hz. However they made the tolerance bands very wide at ±10%. Some countries actually specify stricter standards than this for example the UK specifies 230 V +10% −6%. Most supplies to the old standards therefore conform to the new one and do not need to be changed.

External links

- "AC/DC: [http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html What's the Difference]?". Edison's Miracle of Light, [http://www.pbs.org/wgbh/amex/index.html American Experience]. (PBS)
- "AC-DC: [http://www.pbs.org/wgbh/amex/edison/sfeature/acdc_insideacgenerator.html Inside the AC Generator]". Edison's Miracle of Light, American Experience. (PBS)
- Kuphaldt, Tony R., "Lessons In Electric Circuits : [http://www.faqs.org/docs/electric/AC/index.html Volume II - AC]". March 8, 2003. (Design Science License)
- Nave, C. R., "[http://hyperphysics.phy-astr.gsu.edu/hbase/electric/accircon.html Alternating Current Circuits Concepts]". HyperPhysics.
- "[http://www.ndt.net/article/az/mpi/alternating_current.htm Alternating Current] (AC)". Magnetic Particle Inspection, Nondestructive Testing Encyclopedia.
- "[http://www.apcs.net.au/nav/article/fg40400.html Alternating current]". Analog Process Control Services.
- Hiob, Eric, "[http://www.math.bcit.ca/examples/elex/trig_vectors/ An Application of Trigonometry and Vectors to Alternating Current]". British Columbia Institute of Technology, 2004.
- "[http://www.tpub.com/neets/book2/index.htm Introduction to alternating current and transformers]". Integrated Publishing.
- "Wind Energy Reference Manual Part 4: [http://www.windpower.org/en/stat/unitsac.htm Electricity]". Danish Wind Industry Association, 2003.
- Chan. Keelin, "[http://www.jcphysics.com/toolbox_indiv.php?sub_id=17 Alternating current Tools]". [http://www.jcphysics.com/ JC Physics], 2002.
- "[http://www.apcs.net.au/nav/kn/ff4050901.html Measurement -> ac]". Analog Process Control Services.
- Williams, Trip "Kingpin", "[http://www.alpharubicon.com/altenergy/understandingAC.htm Understanding Alternating Current], Some more power concepts".
- "[http://www.salestores1.com/woreltab.html Table of Voltage, Frequency, TV Broadcasting system, Radio Broadcasting, by Country]".
- [http://www.technology.niagarac.on.ca/people/mcsele/Rankine.html Professor Mark Csele's tour of the 25 Hz Rankine generating station]
- [http://www.henkpasman.com 50/60 hertz information] Category:Electric power Category:Nikola Tesla ja:交流

Archaism

In language, an archaism is the deliberate use of an older form that has fallen out of current use.

Usage

Archaisms are most frequently encountered in poetry, law, and ritual writing and speech. Their deliberate use can be subdivided into literary archaisms, which seeks to evoke the style of older speech and writing; and lexical archaisms, the use of words no longer in common use. Archaisms are kept alive by these ritual and literary uses and by the study of older literature. Should they remain recognised, they can be revived, as the word anent was in this past century.

English

In English, one sure indicator of a deliberately archaic style is the contemporary use of the second person singular pronoun thou and its related case and verb forms. Ironically, the word thou fell out of English speech because it was thought abruptly colloquial, like French tu (see T-V distinction). Thou is now seen in current English usage only in literature that deliberately seeks to evoke an older style, though there are also some still-read older works that use thou, especially religious texts like the King James Bible. The word ye and its related forms also are indicative of archaism, however in spoken English it might be hard to tell the difference, especially if the speaker has an accent that seems strange to the listener.

Syntax here

The compound adverbs and prepositions found in the writing of lawyers (e.g. heretofore, hereunto, thereof) are usually thought of as archaisms. Archaic syntax is also typically found in these ritual and legal contexts. (e.g. "With this ring I thee wed.") Archaisms are also used in the dialogue of historical novels in order to evoke the flavour of the period. Some may count as inherently funny words and are used for humorous effect.

Alternative meanings

In anthropological studies of culture, archaism is defined as the abscence of writing and subsistence economy. In history, archaism is used to connote a superior,albeit mythical, "golden age."

Electric power transmission

:Power line redirects here. For the blog, see Power Line. :Power grid redirects here. For the board game, see Power Grid (board game). Power Grid (board game)]] Electric power transmission is one process in the delivery of electricity to consumers. It refers to the 'bulk' transfer of electrical power from place to place. Typically power transmission is between the power plant and a substation in the vicinity of a populated area. This is distinct from electricity distribution which is concerned with the delivery from the substation to the consumers. Due to the large amount of power involved, transmission normally takes place at high voltage (110 kV or above). Electricity is usually sent over long distance through overhead power transmission lines (such as those in the photo on the right). Rarely is power transmitted underground, due to the high capacitive and resistive losses incurred. A power transmission system is sometimes referred to colloquially as a "grid". However, for reasons of economy, the network is rarely a grid (a fully connected network) in the mathematical sense. Redundant paths and lines are provided so that power can be routed from any power plant to any load center, through a variety of routes, based on the economics of the transmission path and the cost of power. Much analysis is done by transmission companies to determine the maximum reliable capacity of each line, which, due to system stability considerations, may be less than the physical limit of the line. Deregulation of electricity companies in many countries has lead to renewed interest in reliable economic design of transmission networks. The separation of transmission and generation functions is one of the factors that contributed to the 2003 North America blackout.

AC power transmission

2003 North America blackout AC power transmission is the transmission of electric power by alternating current. Usually transmission lines use three phase AC current. In electric railways, sometimes single phase AC current is used as traction current for railway traction. Today, transmission-level voltages are usually considered to be 110 kV and above. Lower voltages such as 66 kV and 33 kV are usually considered sub-transmission voltages but are occasionally used on long lines with light loads. Voltages less than 33 kV are usually used for distribution. Voltages above 230 kV are considered extra high voltage and require different designs compared to equipment used at lower voltages.

History

In an AIEE Address, May 16, 1888, Nikola Tesla delivered a lecture entitled A New System of Alternating Current Motors and Transformers, describing the equipment which allowed efficient generation and use of alternating currents. Tesla's disclosures, in the form of patents, lectures and technical articles, are useful for understanding the history of the modern system of power transmission. The first transmission of three-phase alternating current using high voltage took place in the year 1891 on the occasion of the international electricity exhibition in Frankfurt. In that year, a 25 kV transmission line, approximately 175 kilometres long, was built between Lauffen at the Neckar and Frankfurt. The rapid industrialization in the 20th century made electrical transmission lines and grids a critical part of the economic infrastructure in most industrialized nations. Initially transmission lines were supported by porcelain pin-and-sleeve insulators similar to those used for telegraph and telephone lines. However, these reached a practical limit of 40 kV. In 1907 the invention of the disc insulator by Harold W. Buck of the Niagara Falls Power Corporation and Edward M. Hewlett of General Electric allowed practical insulators of any length to be constructed, which allowed the use of higher voltages. The first large scale hydroelectric generators in the USA (engineered and installed under the technical oversight of Nikola Tesla) were installed at Niagara Falls and provided electricity to Buffalo, New York via power transmission lines. The first three-phase alternating current power transmission at 110 kV took place n 1912 between Lauchhammer and Riesa,Germany. On April 17, 1929 the first 220 kV line in Germany was completed, running from Brauweiler near Cologne, over Kelsterbach near Frankfurt, Rheinau near Mannheim, Ludwigsburg-Hoheneck near Austria. The masts of this line were designed for eventual upgrade to 380 kV. However the first transmission at 380 kV was erected in Germany on October 5, 1957 between the substations in Rommerskirchen and Ludwigsburg-Hoheneck. In 1967 the first extra-high-voltage transmission at 735 kV took place on a Hydro-Québec transmission line. In 1982 the first transmission at 1200kV took place in the Soviet Union.

Bulk power transmission

A transmission grid is a network of power stations, transmission circuits, and substations. Energy is usually transmitted within the grid with 3-phase alternating current (AC). The capital cost of electric power stations is so high, and electric demand is so variable, that it is often cheaper to import some portion of the variable load than to generate it locally. Because nearby loads are often correlated (hot weather in the Southwest portion of the United States might cause many people there to turn on their air conditioners), imported electricity must often come from far away. Because of the irresistible economics of load balancing, transmission grids now span across countries and even large portions of continents. The web of interconnections between power producers and consumers ensures that power can flow even if one link is disabled. alternating current Long-distance transmission of electricity is almost always more expensive than the transportation of the fuels used to make that electricity. As a result, there is economic pressure to locate fuel-burning power plants near the population centers that they serve. The obvious exceptions are hydroelectric turbines -- high-pressure water-filled pipes being more expensive than electric wires. The unvarying portion of the electric demand is known as the "base load", and is generally served best by facilities with low variable costs but high fixed costs, like nuclear or large coal-fired powerplants.

Grid input

At the generating plants the energy is produced at a relatively low voltage of up to 25 kV (Grigsby, 2001, p. 4-4), then stepped up by the power station transformer to a higher voltage for transmission over long distances to grid exit points (substations).

Losses

It is necessary to transmit the electricity at high voltage to reduce the percentage of energy lost. For a given amount of power transmitted, a higher voltage reduces the current and thus the resistive losses in the conductor. Long distance transmission is typically done with overhead lines at voltages of 110 to 765 kV. However, at extremely high voltages, more than 2 million volts between conductor and ground, corona discharge losses are so large as to offset the advantage of lower heating loss in the line conductors. Transmission and distribution losses in the USA were estimated at 7.2% in 1995 [http://climatetechnology.gov/library/2003/tech-options/tech-options-1-3-2.pdf], and in the UK at 7.4% in 1998. [http://www.powerwatch.org.uk/energy/graham.asp] In an alternating current transmission line, the inductance and capacitance of the line conductors can be significant. The currents that flow in these components of transmission line impedance constitute reactive power, which transmits no energy to the load. Reactive current flow causes extra losses in the transmission circuit. The fraction of total energy flow (power) which is resistive (as opposed to reactive) power is the power factor. Utilities add capacitor banks and other components throughout the system—such as phase-shifting transformers, static VAr compensators, and flexible AC transmission systems (FACTS)—to control reactive power flow for reduction of losses and stabilization of system voltage.

HVDC

High voltage DC (HVDC) is used to transmit large amounts of power over long distances or for interconnections between asynchronous grids. When electrical energy is required to be transmitted over very long distances, it can be more economical to transmit using direct current instead of alternating current. For a long transmission line, the value of the smaller losses, and reduced construction cost of a DC line, can offset the additional cost of converter stations at each end of the line. Also, at high AC voltages significant amounts of energy are lost due to corona discharge, the capacitance between phases or, in the case of buried cables, between phases and the soil or water in which the cable is buried. Since the power flow through an HVDC link is directly controllable, HVDC links are sometimes used within a grid to stabilize the grid against control problems with the AC energy flow. One prominent example of such a transmission line is the Pacific Intertie located in the Western United States.

Grid exit

At the substations, transformers are again used to step the voltage down to a lower voltage for distribution to commercial and residential users. This distribution is accomplished with a combination of sub-transmission (33 kV to 115 kV, varying by country and customer requirements) and distribution (3.3 to 25 kV). Finally, at the point of use, the energy is transformed to low voltage (100 to 600 V, varying by country and customer requirements).

Communications

Operators of long transmission lines require reliable communications for control of the power grid and, often, associated generation and distribution facilities. Fault-sensing protection relays at each end of the line must communicate to monitor the flow of power into and out of the protected line section. Protection of the transmission line from short circuits and other faults is usually so critical that common carrier telecommunications is insufficiently reliable. In remote areas a common carrier may not be available at all. Communication systems associated with a transmission project may use:
- Microwaves
- power line carrier
- Optical fibres Rarely, and for short distances, a utility will use pilot-wires strung along the transmission line path. Leased circuits from common carriers are not preferred since availability is not under control of the electric power transmission organization. Transmission lines can also be used to carry data: this is called power-line carrier, or PLC. PLC signals can be easily received with a radio for the longwave range. Sometimes there are also communications cables using the transmission line structures. These are generally fibre optic cables. They are often integrated in the ground (or earth) conductor. Sometimes a standalone cable is used, which is commonly fixed to the upper crossbar. On the EnBW system in Germany, the communication cable can be suspended from the ground (earth) conductor or strung as a standalone cable. Some jurisdictions, such as Minnesota, prohibit energy transmission companies from selling surplus communication bandwidth or acting as a telecommunications common carrier. Where the regulatory structure permits, the utility can sell capacity in extra "dark fibres" to a common carrier, providing another revenue stream for the line.

Electricity market reform

Transmission is a natural monopoly and there are moves in many countries to separately regulate transmission (see New Zealand Electricity Market). In the USA the Federal Energy Regulatory Commission had issued a notice of proposed rulemaking setting out a proposed Standard Market Design (SMD) that would see the establishment of Regional Transmission Organizations (RTOs). The first RTO in North America is the Midwest Independent Transmission System Operator (MISO) [http://www.midwestmarket.org]. MISO's authority covers parts of the transmission grid in the United States midwest and one province of Canada (through a coordination agreement with Manitoba Hydro). MISO also operates the wholesale power market in the United States portion of this area. In July 2005, the new FERC chairman, Joseph Kelliher announced the end of SMD efforts because "the rulemaking had been overtaken by the voluntary formation of RTOs and ISOs" according to FERC. Spain was the first country to establish a Regional Transmission Organization. In that country transmission operations and market operations are controlled by separate companies. The transmission system operator is Red Eléctrica de España (REE) [http://www.ree.es/ingles/i-index_quien.html] and the wholesale electricity market operator is Operador del Mercado Ibérico de Energía - Polo Español, S.A. (OMEL) [http://www.omel.es]. Spain's transmission system is interconnected with those of France, Portugal, and Morocco.

Health concerns

It is argued by some that living near high voltage power lines presents a danger to animals and humans. Some have claimed that electromagnetic radiation from power lines elevates the risk of certain types of cancer. Some studies support this theory, and others do not. Most studies of large populations fail to show a clear correlation between cancer and the proximity of power lines, but a 2005 Oxford University study did find a statistically significant elevation of childhood leukaemia rates [http://www.hpa.org.uk/hpa/news/articles/press_releases/2005/050603_childhood_cancer_voltage.htm]. Recent studies (2003) connect DNA-breakage with low level AC magnetic fields. The current mainstream scientific view is that power lines are unlikely to pose an increased risk of cancer or other somatic diseases. For a detailed discussion of this topic, including references to a variety of scientific studies, see the [http://www.mcw.edu/gcrc/cop/powerlines-cancer-FAQ/toc.html Power Lines and Cancer FAQ]. The issue is also discussed at some length in Robert L. Park's book Voodoo Science.

Alternate transmission methods

Hidetsugu Yagi attempted to devise a system for wireless power transmission. Whilst he managed to demonstrate a proof of concept, the engineering problems proved to be more onerous than conventional systems. His work however, led to the invention of the yagi antenna. Another form of wireless power transmission has been studied for transmission of power from solar power satellites to the earth. A high power array of microwave transmitters would beam power to a rectenna in an unpopulated desert area. Formidable engineering, environmental, and economic problems face any solar power satellite project. There is a potential for the use of superconducting cable transmission in order to supply electricity to consumers, given that the waste is halved using this method. Such cables are particularly suited to high load density areas such as the business district of large cities, where purchase of a right of way for cables would be very costly. [http://www.futureenergies.com/print.php?sid=237]

Special transmission grids for railways

In some countries where electric trains run on low frequency AC (e.g. 16.7 Hz and 25 Hz) power there are separate single phase traction power networks operated by the railways. These grids are fed by separate generators in some power stations or by traction current converter plants from the public three phase AC network. Sample transmission voltages include:
- 25 kV (United Kingdom)
- 25 and 50 kV (South Africa)
- 66 and 132 kV (Switzerland)
- 110 kV (Germany, Austria)

Records

- Highest transmission voltage (AC): 1150 kV on Powerline Ekibastuz-Kokshetau
- Highest transmission voltage (DC): +/-600 kV on HVDC Itaipu
- Highest pylons: Pylons of Pearl River Crossing (height: 253 metres and 240 metres)
- Longest powerline: Inga-Shaba (length: 1700 kilometres)
- Longest span of powerline: 5376 metres at Ameralik Span
- longest submarine cables: Basslink (under construction, length of submarine/underground cable: 290 kilometres, total length: 357.4 kilometres), Baltic-Cable (length of submarine/underground cable: 249 kilometres, total length: 261 kilometres)

External links

- [http://www.ucte.org/ Union for the Co-ordination of Transmission of Electricity (UCTE)], the association of transmission system operators in continental Europe, running one of the two largest power transmission systems in the world
- [http://monographs.iarc.fr/htdocs/monographs/vol80/80.html Non-Ionizing Radiation, Part 1: Static and Extremely Low-Frequency (ELF) Electric and Magnetic Fields (2002)] by the IARC.
- [http://www.greenfacts.org/power-lines/index.htm A summary of the IARC report] by GreenFacts.

References

- Grigsby, L. L., et al. The Electric Power Engineering Handbook. USA: CRC Press. (2001). ISBN 0-8493-8578-4

19th century

:Alternative meaning: Nineteenth Century (periodical) The 19th century lasted from 1801 to 1900 in the Gregorian calendar (using the Common Era system of year numbering). Historians sometimes define a "Nineteenth Century" historical era stretching from 1815 (The Congress of Vienna) to 1914 (The outbreak of the First World War).

Europe

For Europe, the period is marked with revolution, social upheaval, and the emergence of a united conservatism from the monarchs of Europe in response to the emerging republican firestorm spreading from revolutionary France. There were many revolutions in Europe in 1848. Furthermore, the later end of the century was dominated by what many call the New Imperialism, which was the rapid aquisition of colonies worldwide by European powers, most noteworthy is the Scramble for Africa. Many countries in Europe underwent an Industrial Revolution, especially Britain and Germany, that spread elsewhere by the end of the century, with factories and railway lines built all over the continent. The start of the 19th century there was a struggle between France and Britain and their allies for control of Europe and the world during the Napoleonic Wars, with Napoleon being finally defeated at Waterloo in 1815. During the rest of the century, the British empire became the largest and most powerful empire in history, during the period known as the Pax Britannica.

Americas

In the Americas, the United States slowly grew economically, militarily, and politically, but nevertheless faced dramatic changes domestically, best seen in the Civil War, the end of slavery, and the expansion across the American continent known as Manifest Destiny. Industrially, America will explode following the Civil War, and would eventually begin expansion outward across the Pacific Ocean and in Latin America.

Other countries

For the rest of the world, there were few places not influenced by the West in some fashion, whether through colonialism, imperialism, or war. European powers gained increasing influence in China, where Qing control had weakened, and wars were fought by the western powers against China, such as the first and the second Opium wars and Sino-French War. Japan, which was forcibly opened to Western trade, began a rapid industrialisation. Africa which was largely free from European control at the start of the century, was almost completely dominated by Europe at the end of it, with the Scramble for Africa in the 1880s and 1890s. Large European settlement, especially British, of colonies such as Australia, New Zealand and the Cape Colony continued during the nineteenth century.

Events

- 1801: The Kingdom of Great Britain and the Kingdom of Ireland merge to form the United Kingdom of Great Britain and Ireland.
- 1803: The United States buys out France's territorial claims in North America via the Louisiana Purchase.
- 1804-06: Americans Meriwether Lewis and William Clark lead an expedition to the Pacific Coast and back.
- 1805-48: Muhammad Ali modernizes Egypt.
- 1806: Holy Roman Empire dissolved as a consequence of the Treaty of Lunéville.
- 1809: Napoleon strips the Teutonic Knights of their last holdings in Bad Mergentheim.
- 1813-1917: The contest between the British Empire and Imperial Russia for control of Central Asia is referred to as the Great Game.
- 1815: Congress of Vienna redraws the European map.
- 1815: Napoleon's defeat at Waterloo brings a conclusion to the Napoleonic Wars and marks the beginning of a Pax Britannica which lasts until 1870.
- 1816: Year Without a Summer
- 1816-28: Shaka's Zulu kingdom becomes the largest in Southern Africa.
- 1819: The modern city of Singapore is established by the British East India Company.
- 1820: Liberia founded by the American Colonization Society for freed American slaves.
- 1830: France invades and occupies Algeria.
- 1830: The Belgian Revolution in the United Kingdom of the Netherlands led to the creation of Belgium.
- 1833: Slavery Abolition Act bans slavery throughout the British Empire.
- 1834: Spanish Inquisition officially ends.
- 1835-36: The Texas Revolution in Mexico resulted in the short-lived Republic of Texas.
- 1837-1901: Queen Victoria's reign is considered the apex of the British Empire and is referred to as the Victorian era.
- 1845-49: Irish Potato Famine
- 1848: The Communist Manifesto published.
- 1848: Revolutions of 1848 in Europe
- 1848-58: California Gold Rush
- 1850: The Little Ice Age ends around this time.
- 1851-60s: Victorian gold rush in Australia
- 1851-64: The Taiping Rebellion in China
- 1854: The Convention of Kanagawa formally ends Japan's policy of Sakoku.
- 1855: Bessemer process enables steel to be mass produced.
- 1856: World's first oil refinery in Romania
- 1857-58: Indian rebellion of 1857
- 1859: The Origin of Species published.
- 1864-67: French intervention in Mexico
- 1865-77: Reconstruction in the United States
- 1866: Successful transatlantic telegraph cable follows an earlier attempt in 1858.
- 1866: Creation of the North German Confederation and the Austrian-Hungarian Dual Monarchy.
- 1866-69: Meiji Restoration in Japan
- 1867: The United States purchased Alaska from Russia.
- 1867: Canadian Confederation formed.
- 1869: First Transcontinental Railroad completed in United States.
- 1869: The Suez Canal opens linking the Mediterranean Sea to the Red Sea.
- 1870-71: Unifications of Germany and Italy.
- 1871-1914: Second Industrial Revolution
- 1870s-90s: Long Depression in Western Europe and North America
- 1872: Yellowstone National Park created.
- 1874: The British East India Company is dissolved.
- 1877: Great Railroad Strike in the United States may have been the world's first nationwide labor strike.
- 1877-78: The Balkans are freed from the Ottoman Empire after another Russo-Turkish War.
- 1878: First commercial telephone exchange in New Haven, Connecticut.
- 1880-1902: Great Britain conquers Dutch settlers in South Africa in two Boer Wars.
- 1882: First electrical power plant and grid in Manhattan.
- 1884-85: The Berlin Conference signals the start of the European Scramble for Africa. Attending nations also agree to ban trade in slaves.
- 1885: Unification of Bulgaria
- 1890: The Wounded Knee Massacre is the last battle in the American Indian Wars.
- 1894-95: After the First Sino-Japanese War, China cedes Taiwan to Japan and grants Japan a free hand in Korea.
- 1895-1896: Ethiopia defeated Italy in the First Italo-Abyssinian War.
- 1896: Olympic games revived in Athens.
- 1896: Klondike Gold Rush in Canada
- 1898: The United States gains control of Cuba, Puerto Rico, and the Philippines after the Spanish-American War.
- 1898-1900: The Boxer Rebellion in China is suppressed by an Eight-Nation Alliance.

Wars

List of wars 1800–1899
- 1799-1815: Napoleonic Wars.
- 1801-15: Barbary Wars between the United States and the Barbary States of North Africa.
- 1806-12: Russo-Turkish War
- 1810-21: Mexican War of Independence.
- 1810s-20s: South American Wars of Independence.
- 1812-15: War of 1812 between the United States and Great Britain.
- 1821-32: Greek War of Independence.
- 1828-29: Russo-Turkish War, 1828-1829
- 1833-76: Carlist Wars in Spain.
- 1839-60: After two Opium Wars, Great Britain, France, the United States and Russia gain many concessions from China.
- 1854-56: Crimean War between Great Britain, France, the Ottoman Empire and Russia.
- 1861-65: American Civil War between the Union and seceding Confederacy.
- 1866: Austro-Prussian War.
- 1877-78: Russo-Turkish War.
- 1879: Anglo-Zulu War in South Africa.
- 1879-84: War of the Pacific between Peru, Bolivia and Chile.
- 1880-81: First Boer War.
- 1894-95: First Sino-Japanese War.
- 1895-96: First Italo-Abyssinian War.
- 1899-13: The Philippine-American War.

Significant people

- Gilbert and Sullivan, playwright, composer
- William Gilbert Grace, English cricketer
- Baron Haussmann, civic planner
- Sándor Körösi Csoma, explorer of the Tibetan culture
- Fitz Hugh Ludlow, writer and explorer
- Florence Nightingale, nursing pioneer
- Ignaz Semmelweis, founder of hygiene
- Dr. John Snow, the founder of epidemiology
- F R Spofforth, Australian cricketer

Direct current

Various Definitions

Applications

External links

Current (electricity)

Relation between current and charge

Conventional current

The speed of an electric current

Current density

Electromagnetism

Ohm's law

Electrical safety

See also

External links

Electric potential

Introduction

Mathematical introduction

Special cases and computational devices

Applications in electronics

See also

References

External links

Conductor (material)

Power engineering

Conductor size

Conductor materials

Conductor voltage

Conductor ampacity

See also

Insulator

Definition

Electrical insulator

High voltage insulators

Low voltage insulators

See also

External links

Electron beam

See also

Alternating current

History

Distribution and domestic power supply

AC power supply frequencies by country

Mathematics of AC voltages

External links

Archaism

Usage

English

Syntax here

See also

Alternative meanings

Electric power transmission

AC power transmission

History

Bulk power transmission

Grid input

Losses

HVDC

Grid exit

Communications

Electricity market reform

Health concerns

Alternate transmission methods

Special transmission grids for railways

Records

See also

External links

References

Further reading

19th century

Europe

Americas

Other countries

Events

Wars

Significant people

Anthropology

Painters

Music

Literature