Power factor explained | Active Reactive Apparent Power correction

Summary

This video explains the fundamental concepts of power in electrical circuits, comparing DC and AC systems. It covers how power is calculated in both, introducing the impact of reactive components like inductors on energy transfer. The video delves into real, reactive, and apparent power, and the importance of power factor in determining efficiency. It also provides practical insights on improving power factor by adding capacitors to AC circuits, thereby reducing energy waste. Aimed at increasing understanding of electrical circuit behavior, the video emphasizes the significance of optimizing power usage in both residential and industrial applications.

Takeaways

• 😀 A light bulb behaves as a purely resistive load when powered by DC, consuming all the power supplied by the source.
• 😀 In AC circuits, power is calculated by multiplying RMS values of voltage and current, or by calculating instantaneous power and averaging it.
• 😀 When an inductive reactance is added to an AC circuit, the current lags the voltage, and the power graph shows both positive and negative regions.
• 😀 Negative power regions in inductive AC circuits don't indicate generation of energy; they reflect energy temporarily returning to the source due to the inductor's magnetic field.
• 😀 The power received by the light bulb in an AC circuit with an inductor is reduced because part of the power is used to energize the inductor's magnetic field.
• 😀 In circuits with inductive reactance, the total apparent power may be higher than the real power due to reactive power caused by phase differences between voltage and current.
• 😀 Reactive power (measured in VARs) oscillates back and forth between the power source and the inductor, without performing any useful work.
• 😀 Active or real power (measured in watts) is the actual power doing the work in the circuit, while reactive power contributes to inefficiency.
• 😀 The power factor represents energy efficiency, and a low power factor indicates wasted energy due to reactive power, which requires oversized infrastructure and increases costs.
• 😀 Inductive loads, such as motors, cause a low power factor. To improve the power factor, capacitors can be added to the circuit to counteract the inductive reactance and reduce wasted energy.

Q & A

What happens when a light bulb is powered by a DC source?

When a light bulb is powered by a direct current (DC) source, it turns on, and the voltage and current across it remain constant. The power consumed by the light bulb can be calculated by multiplying the constant voltage and current.

How is the power calculated in an alternating current (AC) circuit?

In an AC circuit, power is typically calculated using the root mean square (RMS) values of voltage and current. RMS values are derived by dividing the peak values of voltage and current by the square root of two.

What is the difference between instantaneous power and average power in an AC circuit?

Instantaneous power in an AC circuit is calculated by multiplying the instantaneous voltage and current. The average power is the mean value of this instantaneous power over a complete cycle and equals the power calculated using RMS voltage and current.

What effect does adding an inductor have on the current in an AC circuit?

When an inductor is added to an AC circuit, the current lags the voltage. This causes a phase shift, meaning the current does not change instantaneously with the voltage, but rather after it, leading to a time delay in the current response.

What is reactive power in an AC circuit?

Reactive power is the power that alternates between the source and the reactive components, such as inductors and capacitors, without performing any useful work. It is stored and released by reactive components, causing an increase in current but not contributing to work.

What is the difference between real power and apparent power?

Real power (active power) is the power that performs useful work in the circuit, typically measured in watts (W). Apparent power, measured in volt-amperes (VA), is the total power supplied by the source, including both real and reactive power. Apparent power accounts for the phase difference between voltage and current.

Why is the power factor important in AC circuits?

The power factor is important because it measures the efficiency of power usage in a circuit. A power factor of 1 indicates that all power supplied is being used effectively, while a lower power factor means that a significant portion of the power is wasted as reactive power, leading to inefficiency and higher costs.

How does inductive reactance affect the power factor?

Inductive reactance causes the current to lag behind the voltage, which reduces the power factor of a circuit. This results in more reactive power and less real power being used to perform work, thus lowering the overall efficiency of the circuit.

How can the power factor be improved in an inductive load circuit?

To improve the power factor in a circuit with inductive loads, capacitors can be added to counteract the inductive reactance. The capacitors lead the current, helping to offset the lag caused by inductors, thereby improving the overall power factor.

What is the relationship between real, reactive, and apparent power in the power triangle?

In the power triangle, the real power (P) is represented by the horizontal side, the reactive power (Q) by the vertical side, and the apparent power (S) by the hypotenuse. The angle between real and apparent power represents the impedance phase angle. The power triangle helps visualize the interrelationship between these types of power and how they contribute to the total power in a circuit.