2006-09-06 06:49:41 · 4 answers · asked by Michael A 1 in Science & Mathematics ➔ Engineering
its the same thing
2006-09-06 06:52:08 · answer #1 · answered by iberius 4 · 0⤊ 2⤋
KW and KVA are both measures of power. There is a third, KVAR.
They are all interrelated by something known as the 'Power Factor'.
In an 'AC' electrical circuit, there is an interesting phenomena know as 'Reactive Power'. This power comes from Inductors and Capacitors. These are known as 'Reactive components'.
Both inductors and capacitors store electrical energy. Inductors do so in the form of an electromagnetic field around the coil of wire, whereas Capacitors store their energy as a voltage potential present on two separated plates. The energy stored in either of these forms will have a polarity. The inductor's magnetic field will have magnetic poles, and the capacitors voltage potential will have a '+' and '-' charged plated.
When an 'AC' signal is applied to a standard resistive component, the electrical energy is converted directly into heat. This is a one-way conversion.
When an 'AC' signal is applied to an reactive component, after the current has 'charged' the Inductor/Capacitor and the current begins to flow the opposite direction, these components will 'Discharge' and provide energy BACK to the circuit. When charging, reactive components appear to be loads yet, when discharging, they will appear to be sources of energy.
A KW (KiloWatt) is a measure of REAL power, that is, the rate of energy CONSUMED by the circuit. In a simple circuit, this is usually heat generated by resistors or resistive components.
A KVAR (KiloVolt-Ampere Reactive) is a measure of REACTIVE power, that is, the rate of energy being charged/discharged by the reactive components in a circuit. In a simple circuit, this is the Electromagnetic field of the Inductor, and the Voltage potential of the Capacitor.
A KVA (KiloVolt-Ampere) is a measure of APPARENT power, that is, the rate of energy that is observed, or apparent, at a given point.
The 'Power Factor' is the ratio between real power and apparent power.
Simple Trigonometry of a right triangle can be used to calculate these values.
(A) Real power represents one side.
(B) Reactive power represents the other side.
(C) Apparent power represents the hypotenuse.
(A / C) The 'Power Factor'. Also, Sin (Angle Opposite A)
For example, if you measured 5KVA on a load, and you knew that the power factor was 0.6, you could calculate:
Real Power = Apparent Power X Power Factor = 5KVA X 0.6 = 3 KW
2006-09-06 07:56:25 · answer #2 · answered by Matt 2 · 2⤊ 0⤋
Because "apparent" power (kVA) is a measure of the capability of the plant itself.
The number for "real" power (kW) depends on the impedance of the load. The same power plant can provide widely different kW numbers depending on the power factor of the load.
2006-09-06 13:10:29 · answer #3 · answered by Fred S 2 · 1⤊ 0⤋
Watts are usually measured with RMS voltage, which is correct only for a purely resistive load
VA uses the mean voltage which will take into account any phase shift caused by an inductive load
2006-09-06 07:00:40 · answer #4 · answered by Vinni and beer 7 · 0⤊ 1⤋