Main data on the power of electric current

Work of the source of the electric power when moving the charge of q along some site is equal to the proyoizvedeniye of this charge on U tension between the ends the uchayostka:

And = qU.

Схема возникновения электрического тока в металлических проводниках

The scheme of emergence of electric current in metal conductors.

If this transfer of charges is made evenly during t time by current of I, then

q = It,

on the basis of what

And = Ult,

i.e. at the invariable tension and current work is equal to tension proizveyodeniye on current intensity and for a while. Thus, the ediyonitsa of work of J = In x And x sec.

But for assessment of power conditions important as far as бы­стро work is made. The relation of work And to the sootvetstvuyuyoshchy period of tnazyvayetsya with power R. Tayoky in the way, in the electric circuit

P = A/t = UI,

power unit of watts (W), W = (J: sec.) = In x And.

Схема движения потоков электронов

Scheme of the movement of flows of electrons.

The watt is the power at which for 1 sec. SI is made the raboyot in 1 Dzh. V it is used as unit for the most distinguished types of power. For electric circuits of watts there is the power of electric current in 1 A at the tension on the ends of the conductor in 1 Century.

Multiple power units: kilowatt (kW) = 1000 W and megawatt (MW) = 1 000 000 W

The main energy unit and works, joule, is too small for measurements in electrical power devices. As practical unit of electrical energy serves the kilowatt-hour (the kw • ч). Is the work made at the invariable power in 1 kW during 1 p.1 by W x sec. = in 1 J, in 1 W хч = 3600 W x sec. = 3600 J. Sledovatelno, 1 kW хч = 3 600 000 J.

Expression of power of electric current can be preobyorazovat, having replaced in it is mute, on the basis of the Ohm's law U tension = Ir or current of I = Ug. Therefore, it is possible to make three expressions of power of electric current:

P = UI = I²r = U²g

It is necessary to apply this or that expression of power  depending on conditions of the studied chain.

The same power can be received as at low tension and big current intensity, and at high tension and small current intensity.

Let's consider how tension influences distribution of the moshchyonost in the simplest power transmission system consisting of the power source, the transmission line and nekotoyory loading. Tension of the source of Un consists of the napryayozheniye of loading of Un  and loss of tension in Irl line wires.


U = I ² Rl + Un

Схема имерения силы и напряжения тока

Scheme of the imereniye of force and tension of current.

Having increased this equation by the current intensity of I, we will receive the equation of distribution of power in the chain:

UI = Irl + UNI,

where UI — the power given by the electric power source;

I2rl — the power loss in line wires (on heating);

UNI — the power consumed by loading. If, without changing loading power to increase twice tension on its clips by increase in tension of the source that the current intensity of loading has to be reduced twice, i.e. up to the size I '=1/2.

It will cause reduction of losses of the moshchnoyosta in line wires four times:

I 2 rl = I 2/4 x rl

Therefore, for reduction of losses it is desirable to transfer the electric power at perhaps more high tension in the transmission line.

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