Name: power factor and ac load behavior
Uploaded: 2024-07-08T13:19:54.000Z
Duration: 1 min 11 s
Channel: JoVE

Le facteur de puissance est le rapport entre la puissance active et la puissance apparente.
Il est déterminé par la différence de phase entre la tension et le courant, qui résulte de la présence d’éléments réactifs dans le circuit.
Une analogie peut être faite avec un verre de café, où le café symbolise la puissance active utile, et la mousse représente la puissance réactive, qui, bien qu’elle n’effectue pas de travail réel, est utilisée dans certains appareils.
Le coût couvre l’ensemble du verre. Pour une valeur maximale, la puissance réactive doit être réduite pour ramener le facteur de puissance près de l’unité.
Pour une charge purement résistive, la tension et le courant en phase produisent un facteur de puissance unitaire, où la puissance apparente est égale à la puissance active.
Pour une charge purement réactive, le facteur de puissance est de zéro, ce qui signifie que la puissance active est nulle.
Entre ces extrêmes, le facteur de puissance est soit en tête, soit en retard. Un facteur de puissance principal indique que le courant est en tête de la tension, ce qui implique une charge capacitive.
Un facteur de puissance retardé signifie que le courant est en retard par rapport à la tension, indiquant une charge inductive.

facteur de puissance

Le facteur de puissance est défini comme le rapport entre la puissance moyenne (ou active) et la puissance apparente, comme l'illustre la relation

<img alt="Equation 2" src="/files/ftp_upload/15122/15122_Equation_1.svg" style="height: 30px;">

Le terme entre parenthèses (θv - θi) est appelé angle du facteur de puissance, car il représente l’angle dont le cosinus donne le facteur de puissance. Si V représente la tension aux bornes de la charge et Ⅰ signifie le courant qui la traverse, l'angle du facteur de puissance équivaut à l'angle de l'impédance de la charge. Essentiellement, le facteur de puissance est le cosinus de la différence de phase entre la tension et le courant, ainsi que le cosinus de l'angle de l'impédance de charge.

De l’équation ci-dessus, on peut déduire que le facteur de puissance est le multiplicateur de la puissance apparente pour produire la puissance réelle ou moyenne. La valeur du facteur de puissance est comprise entre zéro et un. Lorsqu’il s’agit d’une charge purement résistive, la tension et le courant sont en phase, ce qui donne un angle de facteur de puissance (θv - θi) = 0 et un facteur de puissance = 1. Cela indique que la puissance apparente est égale à la puissance moyenne. Pour une charge purement réactive, (θv - θi) = ±90o et un facteur de puissance = 0, ce qui rend la puissance nulle. Entre ces deux extrêmes, le facteur de puissance est soit en avance, soit en retard. Un facteur de puissance avancé suggère que le courant précède la tension, indiquant une charge capacitive, tandis qu'un facteur de puissance retardé suggère que le courant suit la tension, indiquant une charge inductive. Le facteur de puissance a un impact significatif sur les factures d’électricité que les consommateurs paient à leurs sociétés de services publics.

Facteur de puissance

Le facteur de puissance est le rapport entre la puissance active et la puissance apparente.
Il est déterminé par la différence de phase entre la tension et le courant, qui ...

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Power Factor

power factor and ac load behavior

Power factor describes how voltage and current behave in an AC load. It is the ratio of average, or active, power to apparent power. The power factor angle is the phase difference between voltage and current, and the cosine of that angle gives the power factor. It also matches the angle of the load impedance.

Power factor shows how much apparent power becomes real, or average, power. Its value ranges from zero to one. When a load is purely resistive, voltage and current are in phase. In that case, the power factor angle is 0 and the power factor is 1, so apparent power equals average power.

A purely reactive load gives the opposite extreme. The phase difference is ±90°, and the power factor is 0, so the power is zero. Between these limits, the power factor can be leading or lagging. A leading power factor means current leads voltage, which points to a capacitive load. A lagging power factor means current follows voltage, which points to an inductive load.

Power factor also matters in everyday electricity use. It affects the electricity bills customers pay to utility companies. Understanding it helps explain why the phase relationship between voltage and current is important in AC circuits.

Power Factor and AC Load Behavior

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Instantaneous power in an electrical circuit comes from the voltage across an element and the current through it. It is written as p(t) and follows the passive sign convention. For sinusoidal input, this product helps show how power changes at each moment. When instantaneous power is expanded, it has two parts. One part is constant and depends on the phase difference between voltage and current. The other part is a sinusoidal term that varies at twice the frequency of the voltage or current. <br...

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Power consumption in AC circuits is often described with average power. In practical electrical work, the changing value of instantaneous power is less useful than the average over a time period. Average power is found by integrating instantaneous power over that time and then dividing by the duration. The time-domain expression for average power comes from simplifying the equation for instantaneous power. In that form, one cosine term averages to zero over a complete cycle. The result does...

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The RMS value, or effective value, helps measure how much power a periodic voltage or current can deliver. It is the direct current, or DC, value that gives the same average power to a resistor as the periodic signal does. This idea is especially important in AC circuits. To find the effective value of current, calculate the root mean square, or RMS, current. First square the instantaneous current values over one period. Then find the mean of those squared values and take the square root. The...

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Power triangle and complex power help describe how an AC load uses energy. Engineers use complex power to capture the combined effect of parallel loads. It gives a full picture of the power consumed by a specific load. Complex power is found by multiplying voltage by the complex conjugate of current. Using rms values, it is written with the rms voltage phasor and the complex conjugate of the rms current phasor. It can also be written in terms of load impedance. The magnitude of complex power...

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AC power in series and parallel circuits follows a power preservation rule. In AC circuits, the complex power, real power, and reactive power produced by the source are equal to the total complex, real, and reactive powers absorbed by the loads. When two load impedances are connected in parallel to an AC source V, the source power can be written as the sum of the complex powers delivered to loads Z1 and Z2. If those same loads are connected in series with the voltage source, the complex power...

power factor

Power factor describes how voltage and current behave in an AC load. It is the ratio of average, or active, power to apparent power. The power factor angle is the phase difference between voltage and current, and the cosine of that angle gives the power factor. It also matches the angle of the load impedance. Power factor shows how much apparent power becomes real, or average, power. Its value ranges from zero to one. When a load is purely resistive, voltage and current are in phase. In that...

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Reducing Reactive Power in AC Loads

Power factor correction helps AC systems use electrical power more efficiently. In a factory circuit, transmitted power includes apparent power, which is made of active power and reactive power. Power factor is the ratio of real power, measured in kW, to apparent power, measured in kVA. It shows how much of the supplied power becomes useful work. A low power factor often happens when an inductive load draws too much reactive power. This creates a lagging power factor. It can also cause large...

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Power from Multiple AC Sources

Power from multiple AC sources is found by adding the effects of each source separately. In a circuit with two sinusoidal voltage sources, each source acts independently. The superposition principle says the total current is the sum of the currents produced by each source alone. If those currents are labeled i1 and i2, they combine to give the total current. Instantaneous power is the power at one moment in time. In this circuit, it equals the square of the instantaneous current times the...

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Matching Load Impedance for Maximum Power

Maximum power transfer in an AC circuit depends on matching the load impedance to the Thevenin equivalent of the source network. The load draws current, and the circuit delivers power to that load. To analyze the current, the voltages, currents, network impedance, and load impedance are written in rectangular form. The average power delivered to the load comes from the square of the current multiplied by the load resistance. To find the condition for maximum power, the power is differentiated...

key terms and concepts

Learn how power factor links voltage, current, and AC load behavior. Explore phase difference, leading and lagging loads, and why it affects electricity bills.

Power Factor and AC Load Behavior | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

Power Factor and AC Load Behavior

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