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WIND ENERGY SYSTEMS - Cd3wd

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Chapter 5—Electrical Network 5–6<br />

z 1 + z 2 = x 1 + jy 1 + x 2 + jy 2 =(x 1 + x 2 )+j(y 1 + y 2 ) (5)<br />

Multiplication and division of complex numbers are performed in the polar form:<br />

z 1 z 2 = |z 1 ||z 2 |/θ 1 + θ 2 (6)<br />

z 1<br />

= |z 1|<br />

z 2 |z 2 | /θ 1 − θ 2 (7)<br />

The impedance of the series RLC circuit shown in Fig. 2 is the complex number<br />

Z = R + jωL −<br />

j<br />

ωC = |Z|̸ θ Ω (8)<br />

where ω =2πf is the angular frequency in rad/s, R is the resistance in ohms, L is the<br />

inductance in henrys, and C is the capacitance in farads.<br />

V<br />

R ✎☞✎☞✎☞ L C<br />

∧∧∧<br />

∨∨∨<br />

✲ I<br />

Figure 2: Series RLC circuit.<br />

We define the reactances of the inductance and capacitance as<br />

X L = ωL Ω (9)<br />

X C = 1 Ω (10)<br />

ωC<br />

Reactances are always real numbers. The impedance of an inductor, Z = jX L , is imaginary,<br />

but X L itself (and X C )isrealandpositive.<br />

When a phasor root-mean-square voltage (rms) V = |V |̸ θ is applied to an impedance,<br />

the resulting phasor rms current is<br />

I = V Z = |V |<br />

|Z| / − θ A (11)<br />

Wind Energy Systems by Dr. Gary L. Johnson November 21, 2001

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