.Modelica.Electrical.QuasiStationary.UsersGuide.Overview.Power

Information

For periodic waveforms, the average value of the instantaneous power is real power P. Reactive power Q is a term associated with inductors and capacitors. For pure inductors and capacitors, real power is equal to zero. Yet, there is instantaneous power exchanged with connecting network.

The series resonance circuit which was also addressed in the AC circuit will be investigated.
Power of a resistor

The instantaneous voltage and current are in phase:

v_r.png
i_r.png

Therefore, the instantaneous power is

power_r.png

A graphical representation of these equations is depicted in Fig. 1

power_resistor.png
Fig. 1: Instantaneous voltage, current of power of a resistor

Real power of the resistor is the average of instantaneous power:

p_r.png

Power of an inductor

The instantaneous voltage leads the current by a quarter of the period:

v_l.png
i_l.png

Therefore, the instantaneous power is

power_l.png

A graphical representation of these equations is depicted in Fig. 2

power_inductor.png
Fig. 2: Instantaneous voltage, current of power of an inductor

Reactive power of the inductor is:

q_l.png

Power of a capacitor

The instantaneous voltage lags the current by a quarter of the period:

v_c.png
i_c.png

Therefore, the instantaneous power is

power_c.png

A graphical representation of these equations is depicted in Fig. 3

power_capacitor.png
Fig. 3: Instantaneous voltage, current of power of a capacitor

Reactive power of the capacitor is:

q_c.png

Complex apparent power

For an arbitrary component with two pins, real and reactive power can be determined by the complex phasors:

s.png

In this equation * represents the conjugate complex operator

See also

Introduction, AC circuit, Reference system
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