Active Power & Reactive Power

How to illustrate "Re active Power" ?

It can be compared to the foam in a glass of beer : it is not the real stuff, but there is no way to avoid it and the glass must be oversized unless you'll have overflow.

In bottle of beer, the bubble of the beer illustrates as reactive power(kvar). The real beer illustrates as real or true power(kw). Just measure it from the bottom of the real beer all the way up to the bubbles in a bottle is called the total power in kva.

In an electrical circuit, the active power P is the real power transmitted to loads such as motors, lamps, heaters, computers … The electrical active power is transformed into mechanical power, heat or light.

In a circuit where the applied r.m.s. voltage is V_rms and the circulating r.m.s. current is I_rms, the apparent power Sis the product V_rms x I_rms.

The apparent power is then the basis for electrical equipment rating. One piece of equipment (transformer, cable, switch …) must be designed in relation to the r.m.s. values of voltage and current.

But what is re active power ?

Re active power Q is present when voltage and current are not in phase. In this situation, the current can be split up into two components:

· one component which is in phase with the voltage, called active current and which is the sole responsible for transmission of active power,

· one component which is in quadrature, called reactive current and which is commonly considered as the generator of flux in ferromagnetic circuits such as transformers, motors, ballasts.

The problem with the reactive power is that it is impossible to manage without it, and it is resulting in an increase of equipment rating.

Note that this is an engineering convention, not a concept from pure physics. When you multiply voltage by current, the total "power" in volt*amps can be a combination of two types of "power". 1. active power = V*I*cos(theta) and 2. reactive power = V*I*sin(theta) where (theta) is the phase angle between the voltage and current. A physicist would say that V*I*sin(theta) is NOT power since it is performing zero work.

If still you want more dope on the subject, go HERE.