Concept of power of electric current
Power of electric current
Before speaking about electric power, it is necessary to decide on the concept of power in a general sense. Usually, when people speak about power, they mean the certain force which is possessed by this or that subject (the powerful electric motor), or action (powerful explosion).
But, as we know from school physics, force and power are different concepts though they have the dependence.
Originally power (N) is the characteristic relating to the specific event (action) and if it is tied to some subject, then also conditionally correlate the concept of power to it. Any physical action means influence of force. Force (F) by means of which the certain way (S) was passed will equal to perfect work (And). And the work done in a definite time (t) will also be equated to power.
Power is the physical quantity which is equal to the relation of perfect work that is carried out for some period, to the same period. As work is the energy change measure, still it is possible to tell so: power is the speed of transformation of energy of system.
Having dealt with the concept of mechanical power, it is possible to pass to consideration of electric power (power of electric current). As you have to know, U is the work performed when moving 1 C, and current of I — quantity of the Coulomb passing for 1 sec. Therefore the work of current on tension shows the full work performed for 1 sec. that is electric power, or power of electric current.
Analyzing the given formula, it is possible to draw very simple conclusion: as the electric power of P to the same extent depends on current of I and on U tension, therefore, the same electric power can be received or at big current and small tension, or, on the contrary, at the big tension and small current (it is used at electric power transmission on remote distances from power plants to places of consumption by transformer transformation on the raising and lowering power substations).
Active electric power (it is the power which will irrevocably be transformed to other types of energy — thermal, light, mechanical, etc.) has the unit of measure — W (Watt). It is equal to the work of 1 V on 1 A. In life and on production power it is more convenient to measure in kW (kilowatts, 1 kW = 1000 W). At power plants larger units — MW are already used (megawatts, 1 MW = 1000 kW = 1 000 000 W).
Reactive electric power is the size which characterizes such type of electric loading which are created in devices (electric equipment) by energy fluctuations (inductive and capacity character) of the electromagnetic field. For normal alternating current it is equal to the work of the working current of I and voltage drop of U on the phase shift sine of the angle between them: Q = U×I×sin (corner). Reactive power has the unit of measure under the name PITCH (reactive volt-ampere). It is designated by the letter Q.
Active and reactive electric power on the example can be expressed so: the electrotechnical device which has heating tena and the electric motor is given. Tena are, as a rule, made of material with the high resistance. When passing electric current on Teng's spiral electrical energy will completely be transformed to heat. Such example is characteristic active electric power.
The electric motor of this device has the copper winding inside. It represents inductance. And as we know, the inductance has effect of the self-induction, and it promotes partial return of the electric power back in network. This energy has some shift in values of current and tension that causes the negative impact on the power supply network (in addition overloading it).
Similar abilities also the capacity (condensers) has. It is capable to accumulate the charge and to give it back. The difference of capacity and inductance consists in the opposite shift of values of current and tension relatively each other. Such energy of capacity and inductance (displaced on the phase concerning value of the feeding power supply network) also, in fact, will be reactive electric power.Top