FAQ
What is the difference between input power and oscillating power (sometimes referred to as output power) in induction heater specifications?
Input power (Kva) is the product of the input RMS voltage and RMS current. Output Power or oscillating power is a product of the output voltage and current in addition to the reactive power component present in the resonant tank that does not perform real work (var).
What is reactive power (var)?
Reactive power exists in an AC circuit when the current and voltage are not in phase, var is the unit in which reactive power is expressed in an AC power system
Reactive power is the difference between va (apparent power) and w (true power), it is the imaginary component of apparent power that does not contribute to the work load. var = va - w : (volt amp reactive = volt amp - watts)
Reactive power Q, which is a measure of the rate of energy that is sloshing back and forth between an AC source and a reactive (capacitive or inductive) load. It is measured as the product of the RMS voltage, current and the sine of the angle of difference between voltage and current (+ or - 90 degrees). Q = Vrms * Irms * sin(phase angle between the current and voltage)
In the beer analogy below real power that flows to the load and does work (Kw) is expressed as the beer. The imaginary or reactive power (Kvar) is represented by the foam. The apparent power in the circuit that the system must be able to handle (Kva) is represented by the beer + the foam.
What is Power Factor?
Power Factor is the unit used to describe the ratio of real to apparent power in an AC circuit. It is a dimensionless number between -1 and 1 and is derived from the cosine of the angle of difference between voltage and current (+ or - 90 degrees). Thus 1 and -1 represent voltage and current in phase, 0 represents voltage and current out of phase by 90 degrees.
The power factor (pf) of a load tells us what fraction of the apparent power (va) is in the form of real power (w) and performs actual work. A power factor of 1 tells us that kw = kva and is the ideal scenario.
var = va * pf
va = kw / pf
For example to get 10Kw of working power to a load with a power factor of 1 only 10Kva of apparent power needs to be transferred (10Kw ÷ 1 = 10Kva). However as the power factor decreases, more apparent power needs to be transferred to get the same amount of real power to the load. To get the same 10Kw of power to the load at a power factor of 0.65 we need to transfer 15,385va (10Kw ÷ 0.65 = 15,385va).
So the presence of reactive power in an AC circuit causes the real power to be less than the apparent power thus the circuit has a power factor of less than 1.
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