Danfoss VLT AHF005, Руководство по конструкции

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3 Introduction to Harmonics and Mitigation
3.1 What are Harmonics?
3.1.1 Linear Loads
On a sinusoidal AC supply a purely resistive loads (for
example an incandescent light bulb) will draw a sinusoidal
current, in phase with the supply voltage.
The power dissipated by the load is:
P = U × I
For reactive loads (such as an induction motor) the current
will no longer be in phase with the voltage, but will lag the
voltage creating a lagging true power factor with a value less
than 1. In the case of capacitive loads the current is in
advance of the voltage, creating a leading true power factor
with a value less than 1.
In this case, the AC power has three components: real power
(P), reactive power (Q) and apparent power (S). The apparent
power is:
S = U × I
(where S=[kVA], P=[kW] and Q=[kVAR])
In the case of a perfectly sinusoidal waveform P, Q and S can
be expressed as vectors that form a triangle:
S 2 = P 2 + Q 2
P
S
Q
φ
130BB538.10
The displacement angle between current and voltage is
φ
.
The displacement power factor is the ratio between the
active power (P) and apparent power (S):
DPF = PS = cos(ϕ)
Introduction to Harmonics a... AHF005/010 Design Guide
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