Terminology » RF Basics » Real Power vs. Reactive Power vs. Apparent Power: Key Differences Explained

Real Power vs. Reactive Power vs. Apparent Power: Key Differences Explained

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This article clarifies the differences between real power, reactive power, and apparent power. Real power is also referred to as true power, active power, or actual power. We’ll explore each type, along with their formulas and units of measurement.

A key concept related to these power types is the power factor (PF), which is the cosine of the angle between voltage and current.

real power vs reactive power vs apparent power

Figure 1: Relationship between Real, Reactive, and Apparent Power

Let’s dive into each power type in more detail:

Real Power | True Power | Active Power | Actual Power

Real power represents the power actually consumed by a circuit to perform useful work. It’s associated with dissipative circuit elements, primarily resistors. In essence, it’s the power that’s converted into another form of energy, like heat or light.

The real power can be expressed as:

P=I2∗R=V2RP = I^2 * R = \frac{V^2}{R}

Where:

  • P = Real Power (Watts)
  • I = Current (Amperes)
  • R = Resistance (Ohms)
  • V = Voltage (Volts)

The unit of measurement for real, true, active, or actual power is Watts (W).

Reactive Power

Reactive power is the power that oscillates between the source and the reactive components (inductors and capacitors) in a circuit. It doesn’t perform any real work but is necessary to establish and maintain electric and magnetic fields in these components.

The reactive power can be expressed as:

Q=I2∗X=V2XQ = I^2 * X = \frac{V^2}{X}

Where:

  • Q = Reactive Power (VAR)
  • I = Current (Amperes)
  • X = Reactance (Ohms)
  • V = Voltage (Volts)

The unit of measurement for reactive power is VAR (Volt-Amps-Reactive).

Apparent Power

Apparent power is the total power supplied by the source, regardless of whether it’s doing useful work. It’s the vector sum of real power (P) and reactive power (Q). It’s represented by ‘S’ in Figure 1.

The apparent power can be expressed as:

S=I2∗Z=V2ZS = I^2 * Z = \frac{V^2}{Z}

Where:

  • S = Apparent Power (VA)
  • I = Current (Amperes)
  • Z = Impedance (Ohms)
  • V = Voltage (Volts)

The unit of measurement for apparent power is VA (Volt-Amps).

Also, consider the relationship between Power and Energy to better understand their differences.

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