Any appliance is characterized by several key parameters including nominal voltage, current and power.Sometimes the data sheet specifies only the power and voltage, current, in this case it is easy to find using the famous formula Ohm (of course, with some reservations - for example, must be known cos).The reverse is also true: knowing the current and voltage, the power calculation can be performed.The global network has a lot of material on the subject, but most of them are intended for specialists.
Let's look at what is meant by the term "electric power", what are its types and how to make a power calculation.The physical sense of power indicates how fast to install (the device) is converted into electricity or that kind of useful work.That's so simple!For non-electrical devices is perfectly acceptable to use the term "productivity".
in electrical engineering division is accepted, according to which there is an active and reactive power.The first is directly converted into useful work, it is therefore considered basic.The unit of measurement is the Watt and derivatives - Kilowatt, Megawatt and so on. In the household appliances specified exactly it.While this does not mean that no reactive component.In turn, the second - an undesirable, since in performing the work is not involved, and is wasted in the various types of losses.Measured in "Var" (volt-ampere reactive) and derivatives - kilovolt-amperes reactive, etc.The amount of active and reactive components form a complete power (volt-amperes VA).
striking example of the consumer with a clear resistive load - an electric heater.When passing through it an electric current is generated by heat, and in direct proportion.Similarly, the consumer acts reactive energy - a classic transformer.In his work in the windings creates a magnetic field which itself is not necessary (using electromagnetic induction property).The magnetic core is magnetized, there are losses.In other words:
Q = U * I * sin Fi,
where sin Fi - sine of the angle between current and voltage.Its sign depends on the nature of the load (capacitive or inductive).
power calculation begins with determining the current type: constant or variable, because the formulas are not universal.
In the first case, a consequence of the classical Ohm's law.Power P is the product of the current I on the voltage U:
P = I * U (W = A * B).
When the chain is taken into account with the power supply direction of the EMF: it is necessary to calculate the resistance of the source.Thus, the generator or the battery, in which current flows from the "-" to "+", giving energy to the load circuit sends a power.If the current flow is opposite to the applied potential (Charging), then the absorption capacity of the source of EMF.
formula for calculating power to alternating current (single-phase circuit) takes into account the factor - "cos phi".It is the ratio of active component to the total capacity.Obviously, in the case of TAN cosine is equal to 1 (perfect) since no reactive component.Otherwise, to reduce the loss of the generator using various joints or other technical solutions.
thus:
P = U * I * cos Fi.
power calculation in three-phase circuits is carried out for each phase, and the resulting values are then added together.For full AC power is calculated as the square root of the sum of squares of real and reactive components.For generating devices (stations) it is more important to know the total power, since on the basis of all the other elements are selected subsequent circuits.It is obvious that in most cases it is impossible to know in advance the nature of the load.
