Alternating Current

Definition: Alternating Current

Alternating Current

Noun

1. An electric current that reverses direction sinusoidally; "In the US most household current is AC at 60 cycles per second".

Domain	Definitions
Electrical Engineering	A periodic current having a zero mean value. Source: European Union. (references)
Energy	(AC) Flow ofelectricity that constantly changes direction between positive and negativesides. Almost all power produced by electric utilities in the United States movesin current that shifts direction at a rate of 60 times per second. (references)
	A type of electrical current, the direction of which is reversed at regular intervals or cycles; in the U.S. the standard is 120 reversals or 60 cycles per second; typically abbreviated as AC. (references)
Source: compiled by the editor from various references; see credits.

Alternating current (AC) is electric current which repeatedly changes polarity from negative to positive and back again. The most commonly used form of alternating current does so in a sine wave pattern.

Alternating-current electric power is a form of electrical energy that uses alternating currents to supply electricity commercially as electric power. 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. The present system used today was originally devised by Nikola Tesla in 1882 and overcomes 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. Charles Proteus Steinmetz of General Electric solved many of the problems associated with electricity generation and transmission using alternating current.

Unlike DC, AC can be stepped up by a transformer to a higher voltage. Because of Ohm's law, electrical energy losses are dependent on current flow, not on energy flow. By using transformers, the voltage of the power can be stepped up to a high voltage so that the power may be distributed over long distances at low currents and hence low losses. The voltage can then be stepped down again so that it is safe for domestic supply.

Three-phase electrical generation is very common and is a more efficient use of conductors. Three-phase electricity distribution is common only in industrial premises and many industrial electric motors are designed for it. Three current waveforms are produced that are 120 degrees out of phase with each other. At the load end of the circuit the return legs of the three phase circuits can be coupled together at the neutral point, where the three currents sum to zero. This means that the currents can be carried using only three cables, rather than the six that would otherwise be needed. Three phase power is a kind of polyphase system.

In many situations only a single phase is needed to supply street lights or residential consumers. When distributing three-phase electric power, a fourth or neutral cable is run in the street distribution to provide a complete circuit to each house. Different houses in the street are placed on different phases of the supply so that the load is balanced, or spread evenly, across the three phases when a lot of consumers are connected.

For safety, a fifth wire is often connected between the individual electrical appliances in the house and the main electric switchboard or fusebox. The fifth wire is known in Britain and most other English-speaking countries as the earth wire, whereas in America it is the ground wire. At the main switchboard the earth wire is connected to the neutral wire and also connected to an earth stake or other convenient earthing point (to Americans, the "grounding point") such as a water pipe. In the event of a fault, the earth wire can carry enough current to blow a fuse and isolate the faulty circuit. The earth connection also means that the surrounding building is at the same voltage as the neutral point and prevents a person from receiving an electric shock from the appliance. As many parts of the neutral system are connected to the earth, balancing currents, known as earth currents, may flow between the generator and the consumer and other parts of the system, which are also earthed, to keep the neutral voltage at a safe level. This system of earthing the neutral point to balance the current flows for safety reasons is known as a multiple earth neutral system.

Mathematics of AC voltages

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

where

A is the amplitude in volts (also called the peak voltage),

ω is the angular frequency in radians/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:

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.

The size of an AC voltage is also sometimes stated as a root mean square (rms) value, written V_rms. For a sinusoidal voltage:

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 power P into the same load if V_rms = V_DC.

To illustrate these concepts, consider the 240 V AC mains used in the UK. 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:

For our 240 V AC, the peak voltage V_P-P or A is therefore 240 V × √2 = 339 V (approx.). The peak-to-peak value of the 240 V AC mains is even higher: 2 × 240 V × √2 = 679 V (approx.)

Synonym: Alternating Current

Synonym: AC (n). (additional references)

Antonym: direct current (n). (additional references)

Domain	Title
Books	Alternating Current (reference) Alternating Current Circuit Analysis Through Experimentation (reference) Direct and Alternating Current Circuits (reference) The general theory of alternating current machines : application to practical problems (reference) (more book examples)
Source: compiled by the editor from various references; see credits.

Subject	Topic	Quote
Business		Taiwan's electricity is alternating current (a.c.) 60 cycles, single and three phase 110-220 volts. (references)
Trade	Ireland	Electrical current is provided at an alternating current of 50 cycles, 1 and 3 phase. (references)
Travel	Ireland	The electric current in Ireland is alternating current, 50 cycle, 220 volts. (references)
	South Africa	Electric current in South Africa is alternating current, 50 cycles, 220 / 230 volts, 1, 3 phases, 2, 4 wires; 240 volts for Pretoria; and 250 volts for Port Elizabeth. (references)
Source: compiled by the editor from ICON Group International, Inc.; see credits.

Expressions using "alternating current": alternating current ac ♦ alternating current bus ♦ alternating current filter ♦ alternating current generator ♦ alternating current network ♦ anode alternating current resistance ♦ electrode alternating current resistance. Additional references.
Source: compiled by the editor from various references; see credits.

The following statistics estimate the number of searches per day across the major English-language search engines as identified by various trade publications. Hyperlinks lead to commercial use of the expression at Amazon.com.

Language		Translations for "alternating current"; alternative meanings/domain in parentheses.
Bulgarian		променлив ток (ac). (various references)

Czech		střídavý proud. (various references)

Danish		anoderesistans for vekselstrøm (anode a.c.resistance, anode AC resistance, anode alternating current resistance), alternator (AC generator, alternating current generator, alternator), AC-generator (AC generator, alternating current generator, alternator), vekselstroems generator (AC generator, alternating current generator, alternator), vekselstrømsfilter (alternating current filter, filter), filter (alternating current filter, canister, dust arrester, dust filter, filter, filter zone, screen, strainer), elektroderesistans for vekselstrøm (electrode a.c.resistance, electrode AC resistance, electrode alternating current resistance), elektrode vekselsspændingsresistans (electrode a.c.resistance, electrode AC resistance, electrode alternating current resistance). (various references)

Dutch		zuivere wisselstroom (pure A.C., pure alternating current), zuivere wisselspanning (pure A.C., pure alternating current), wisselstroomweerstand van een elektrode (electrode a.c.resistance, electrode AC resistance, electrode alternating current resistance), wisselstroomgenerator (AC generator, alternating current generator, alternator), wisselstroomdynamo (AC generator, alternating current generator, alternator), ompoler (AC generator, alternating current generator, alternator), koppeltransformator (alternating current filter, filter), inwendige weerstand (anode a.c.resistance, anode AC resistance, anode alternating current resistance), filter (alternating current filter, dust arrester, dust filter, filter, filter cartridge, filter zone, screen, smoothing device, strainer, well screen), draaistroomgenerator (AC generator, alternating current generator, alternator). (various references)

Finnish		vaihtovirta, vaihtosuhde. (various references)

French		courant alternatif (alternating). (various references)

German		wechselstrom (ac, alternating current (AC)). (various references)

Greek		εναλλασσόμενο ρεύμα. (various references)

Hungarian		váltakozó áram. (various references)

Italian		corrente alternata (AC). (various references)

Japanese Kanji		交流 (exchange, intercourse, intermingling). (various references)

Japanese Katakana		�"うりゅう (confinement, detention, exchange, hidden genius, hold a person in custody, intercourse, intermingling, prosperity, rain dragon, rise, slipstream). (various references)

Manx		streeu chirkinagh. (various references)

Pig Latin		alternatingay urrentcay

Portuguese		alternador (AC generator, alternating current generator, alternator), resistência de eléctrodo em corrente alternada (electrode a.c.resistance, electrode AC resistance, electrode alternating current resistance), resistência de ânodo em corrente alternada (anode a.c.resistance, anode AC resistance, anode alternating current resistance), gerador de corrente alterna (AC generator, alternating current generator, alternator), filtro (a.c.filter, alternating current filter, dust arrester, dust filter, filter, filter cigarette, filter zone, percussion, rejector, screen, smoothing device, strainer), corrente alternada (ac current, alternating current ac), circuito de filtragem (a.c.filter, alternating current filter, filter). (various references)

Romanian		curent alternativ. (various references)

Russian		переменный ток. (various references)

Serbo-Croatian		naizmenična struja. (various references)

Spanish		corriente alterna (a.c., ac, alternate current). (various references)

Swedish		växelström (ac). (various references)

Turkish		alternatif akım. (various references)
Source: compiled by the editor from various translation references.

Scrabble® Enable2K-Verified Anagrams
	Words within the letters "a-a-c-e-e-g-i-l-n-n-n-r-r-r-t-t-t-u"
	-5 letters: intergranular.
Source: compiled by the editor from various references; see credits. SCRABBLE® is a registered trademark. All intellectual property rights in and to the game are owned in the U.S.A and Canada by Hasbro Inc., and throughout the rest of the world by J.W. Spear & Sons Limited of Maidenhead, Berkshire, England, a subsidiary of Mattel Inc. Mattel and Spear are not affiliated with Hasbro.

Hexadecimal (or equivalents, 770AD-1900s) (references)

41 6C 74 65 72 6E 61 74 69 6E 67 43 75 72 72 65 6E 74

Leonardo da Vinci (1452-1519; backwards) (references)

Binary Code (1918-1938, probably earlier) (references)

01000001 01101100 01110100 01100101 01110010 01101110 01100001 01110100 01101001 01101110 01100111 00100000 01000011 01110101 01110010 01110010 01100101 01101110 01110100

HTML Code (1990) (references)

&#65 &#108 &#116 &#101 &#114 &#110 &#97 &#116 &#105 &#110 &#103 &#32 &#67 &#117 &#114 &#114 &#101 &#110 &#116

ISO 10646 (1991-1993) (references)

0041 006C 0074 0065 0072 006E 0061 0074 0069 006E 0067 0043 0075 0072 0072 0065 006E 0074

Encryption (beginner's substitution cypher): (references)

Expression	Frequency per Day
alternating current direct versus	102
alternating current	42
alternating current current direct	4
alternating current experiment	2
alternating current theory	2
alternating current current direct vs	2
alternating current direct	2
alternating current generator	2
Source: compiled by the editor from various references; see credits.

Alternating Current

Definition: Alternating Current