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# What is the basic difference between AC and DC in electrical engineering and the general role of transformer?

Member since:
11 January 2008
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## Best Answer - Chosen by Voters

Direct current (DC) is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow 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 in a constant direction, distinguishing it from alternating current (AC). A term formerly used for direct current was Galvanic current.

Types of direct current.Direct current may be obtained from an alternating current supply by use of a current-switching arrangement called a rectifier, which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be made into alternating current with an inverter or a motor-generator set.

The first commercial electric power transmission (developed by Thomas Edison in the late nineteenth century) used direct current. Because of the advantage of alternating current over direct current in transforming and transmission, electric power distribution today is nearly all alternating current. For applications requiring direct current, such as third rail power systems, alternating current is distributed to a substation, which utilizes a rectifier to convert the power to direct current. See War of Currents.

Direct current is used to charge batteries, and in nearly all electronic systems as the power supply. Very large quantities of direct-current power are used in production of aluminum and other electrochemical processes. Direct current is used for some railway propulsion, especially in urban areas. High voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids.In alternating current (AC, also ac) the movement (or flow) of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again. In direct current (DC), the movement (or flow) of electric charge is only in one direction.

Used generically, AC refers to the form in which electricity is delivered to businesses and residences. The usual waveform of an AC power circuit is a sine wave, however in certain applications, different waveforms are used, such as triangular or square waves. Audio and radio signals carried on electrical wires 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.
A major application of transformers is to increase voltage before transmitting electrical energy over long distances through wires. Wires have resistance and so dissipate electrical energy at a rate proportional to the square of the current through the wire. By transforming electrical power to a high-voltage (and therefore low-current) form for transmission and back again afterwards, transformers enable economic transmission of power over long distances. Consequently, transformers have shaped the electricity supply industry, permitting generation to be located remotely from points of demand. All but a tiny fraction of the world's electrical power has passed through a series of transformers by the time it reaches the consumer.

Transformers are also used extensively in electronic products to step down the supply voltage to a level suitable for the low voltage circuits they contain. The transformer also electrically isolates the end user from contact with the supply voltage.

Signal and audio transformers are used to couple stages of amplifiers and to match devices such as microphones and record player s to the input of amplifiers. Audio transformers allowed telephone circuits to carry on a two-way conversation over a single pair of wires. Transformers are also used when it is necessary to couple a differential-mode signal to a ground-referenced signal, and for between external cables and internal circuits.
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• Member since:
01 October 2007
Total points:
2,139 (Level 3)
DC provides a one state one polarity current flow, AC provides an alternating current flow that moves from negative to positive. The transformer is a type of inductor; which is an electronic component the uses principles of magnetism to store a voltage. A transformer is mainly used to reduce the voltage coming out of your AC outlet at home. In the US , 120 volts comes out of an AC outlet, whatever you plug into the wall has a transformer inside, that reduces the voltage to a lower voltage such as 5 volts or 12 volts as often used in electronic devices. A diode rectifier converts the AC into DC

### Source(s):

ITT Technical Institute
• Member since:
19 March 2009
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2,452 (Level 3)
The basic difference is that in DC the magnitude of the parameter (Voltage or Current) is not varying with respect to time. It is fairly constant. But, in AC, it is constantly varying with respect to time. The rate of change in AC is referred to as frequency.

The transformer is use only in AC to step up or step down the voltage to enable electric power transmission and distribution.
• by goober
Member since:
22 September 2008
Total points:
69,336 (Level 7)
AC means alternating current. The voltage and current change direction, usually going through a complete forward and back cycle in 1/50 or 1/60 of a second. AC is the power provided to your home.

DC means direct current. The voltage and current are always in the same direction. It is the power from batteries and solar cells.

A transformer only works for AC. It changes the magnitude of voltage and current with very little loss of power, which is essentially the product of voltage times current. It can be used to raise the voltage and decrease the current to transmit power efficiently over long distances and then reduce the voltage and increase the current for use.
• by Ankit S
Member since:
08 April 2009
Total points:
80 (Level 1)
in AC supply current flow is alternet i.e. its value changes from + to - while in DC it is constent.................the best way to practically understsnd difference between AC & DC is search on the net about ractifier.........or working of a diode

### Source(s):

study books............