44 - Power in AC Circuits 1 | Power Triangle - Apparent, Real and Reactive Power

Summary

In this video, the focus is on understanding the three types of power in an AC circuit: active power (P), reactive power (Q), and apparent power (S). The presenter explains the power triangle, showing how active and reactive power relate to apparent power. The video also covers the power factor and its behavior in purely resistive, inductive, and capacitive circuits. A detailed example problem is solved to illustrate concepts like calculating frequency, resistance, inductance, and power absorbed in an inductive circuit.

Takeaways

• ⚡ Active power, denoted by P, is measured in watts and represents the real or actual power in an AC circuit.
• 🔄 Reactive power, represented by Q, is measured in volt-amperes reactive (VAR) and depends on the load reactance (X).
• 🔌 Apparent power, denoted by S, is measured in volt-amperes (VA) and is the combination of active and reactive power.
• 📐 The power triangle shows active power on the horizontal axis, reactive power on the vertical axis, and apparent power as the resultant.
• ⚖️ The square of apparent power (S²) is equal to the sum of the squares of active power (P²) and reactive power (Q²).
• 🔋 In a purely resistive circuit, the power factor is unity (cosine of phase angle = 1), meaning current and voltage are in phase.
• 🔄 In a purely inductive or capacitive circuit, the power factor is zero, as current lags or leads voltage by 90 degrees.
• 📉 A circuit containing a resistor, inductor, and capacitor has a power factor between 0 and 1, which could be leading or lagging depending on current and voltage phases.
• 🧮 Resistance (R) and inductance (L) in an inductive circuit can be calculated using impedance (Z) and phase angle (φ).
• 🔋 The real power (P) absorbed in the circuit is calculated as the product of the RMS voltage, RMS current, and cosine of the phase angle.

Q & A

What are the three types of power in an AC circuit?

The three types of power in an AC circuit are active power (P), reactive power (Q), and apparent power (S). Active power is measured in watts, reactive power is measured in volt-amperes reactive (VAR), and apparent power is measured in volt-amperes (VA).

What is the difference between active, reactive, and apparent power?

Active power (P) is the actual power delivered to a load, which depends on the load resistance. Reactive power (Q) is the energy exchange between the source and the reactive parts of the load, depending on the load reactance. Apparent power (S) is the combination of active and reactive power and represents the total power in the circuit.

How is the power triangle used to represent these powers?

In the power triangle, active power is represented along the horizontal axis, reactive power is on the vertical axis, and the resultant of these two is the apparent power. The angle between active and apparent power is the phase angle (φ).

What is the formula for calculating active power from apparent power?

Active power (P) is calculated using the formula: P = S × cos(φ), where S is the apparent power and φ is the phase angle between the voltage and current.

What is the power factor, and how does it vary for different types of circuits?

The power factor is the cosine of the phase angle (φ) between voltage and current. For a purely resistive circuit, the power factor is 1 (unity). For a purely inductive or capacitive circuit, the power factor is 0. For a circuit with a resistor, inductor, and capacitor, the power factor is between 0 and 1.

What happens to the current and voltage in a purely resistive circuit?

In a purely resistive circuit, the current is in phase with the voltage, meaning the phase difference between them is zero. As a result, the power factor is equal to 1.

What is the power factor of a purely inductive circuit?

In a purely inductive circuit, the current lags the voltage by 90 degrees. The power factor in this case is 0.

What does it mean when a circuit has a lagging or leading power factor?

A lagging power factor means the current lags behind the voltage (common in inductive loads), while a leading power factor means the current leads the voltage (common in capacitive loads).

How do resistors, inductors, and capacitors each handle power in a circuit?

A resistor consumes active power, an inductor consumes reactive power, and a capacitor does not consume power but instead supplies reactive power or reduces reactive power consumption.

How can you calculate the impedance (Z) of an inductive circuit using voltage and current?

Impedance (Z) in an inductive circuit can be calculated using the formula Z = V / I, where V is the voltage and I is the current. Once converted to polar form, the impedance can be used to find resistance (R) and inductive reactance (XL).