Concept about alternating current


Main data on alternating current

Electric current happens to constants and variables. Variable is current in which mean value during force and tension is equal to zero. Such current continuously changes in size and the direction, and there are these changes at regular intervals.

Периодический переменный ток

Periodic alternating current.

It is known that to cause alternating current in the chain, use alternating current generators. In such generators the electromotive force (EMF) arises in the course of electromagnetic induction. In the cavity of the cylindrical form the magnet called by the rotor rotates, and the motionless core with its winding is called the stator.

Alternating current is applied in communication devices (radio, television, wire telephony and so forth), and all this thanks to the fact that tension and alternating-current force can be transformed almost without energy loss.

For the industry and lighting alternating current is developed by the generators given to rotation by water or steam turbines and internal combustion engines.

Alternating current happens single-phase and multiphase. From multiphase the three-phase current - the alternating current system consisting of three electric circuits having the identical frequency and the electromotive force, dephased on 120 ° was widely adopted. The three-phase alternating current system is applied in the industry to the power supply of electric motors, electric furnaces, lighting.

Схема простейшего генератора переменного тока

Scheme of the simplest alternating current generator.

When passing on the conductor alternating current allocates as much heat how many and constant. Time during which one fluctuation is made is called the period (designate the letter T). The condition of alternating current in separate instants is called phases. And number of the periods in the second – frequency. Unit of frequency is the hertz (Hz). If we say that in one second one fluctuation is made, then frequency will be equal to 1 Hz.

By means of rectifiers alternating current can be transformed in constant (the majority of devices requires the direct current).

Long time in electrical equipment exclusively direct current was applied. But then there was the need for long distance power transmission. In life alternating current therefore we will tell in more detail about it and its physical characteristics is usually used.

At electric power transmission on wires in them there are losses proportional to the current square. For reduction of losses it is necessary to reduce current. But transfer of the same power at smaller current requires more high tension. Therefore long distance power transmission can be executed only at high tension.

Transformation with small losses of big low-voltage currents to small high-voltage currents, or on the contrary, can be made only by means of the electromagnetic device of alternating current — the transformer. Therefore now alternating electric current is mainly applied.

The current changing during certain time in size and the direction is called alternating current. The alternating current changing under the sinusoidal law represents the single-phase sinusoidal current:
i = IM sin (wt + cp),
where IM — amplitude value of current.

The period during which one full wave is carried out is called the T period.

The number of the periods in the second is called the frequency which is expressed by the formula
F = 1/T
Frequency is measured in hertz (Hz).

Size w = 2yasr = 2l/T is called angular frequency and is measured in is glad / sec.; the corner of Zwcp is called initial phase.

In practice the greatest distribution was gained by current which changes with the frequency of 50 periods a second, i.e. 50 Hz.

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