Electric power – the physical quantity determining the speed of transformation of electric energy. Power is measured in watts (W) and depending on the considered work of an alternating or direct current can be determined by the corresponding rules.
Instruction
1. It is known that current with a force of 1 And at a tension in an electrical network of 1 V gives power in 1 W. But this ratio can be used for finding of power only at constant values of potential difference and current. I.e. when determining power (P) in network of a direct current. For this purpose use one of following formulas, depending on the parameters set in a task: Р = I*U, R = I²*R, where I – value of a direct current, U – tension, R – resistance.
2. However most often it is required to determine power in variation electric field, in chains of sinusoidal current. At the same time take the work of values of current and tension when accounting phase shift between these sizes for the full capacity of a contour, i.e. reactive and active components of power and also power factor.
3. Find the active power of variation field. For this purpose, besides value of current, it is necessary to know resistance (R) to the considered chain. Substitute preset values in a formula Ra = to I²*R and calculate value. If in an electrical circuit there are several its separate parts (resistors), determine active power for each of them. Put the found values of active capacities of all chain.
4. Calculate the reactive power of a chain of alternating current. It approximately describes processes of transformation of energy in fields of induktivnost and tanks. And the reactive power of active and inductive loading of an element is positive size and, on the contrary, negative – at the resistive-capacitive nature of loading. It means that in the presence in an inductance coil chain its reactive power will have the positive sign, and the power of the capacitive condenser – negative. For calculation of reactive power of an element of inductance (Rl) or the condenser (Rs) use the same formula P = I²*R where R is resistance of a concrete element. Consistently calculate capacities for each element. Determine the general reactive power of a chain. Put the found values, at the same time consider the sign of reactive power of the condenser: Rr = Rl1 + Rl2 – Rs.
5. Determine the full capacity of a chain of alternating current. It is connected with active and reactive capacities the following ratio: S = √ (Ra² + Rr²). Substitute the found values of capacities in a formula and calculate final result.