Potência Reativa Q
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
Q = VI sen φ
About this calculator
The Reactive Power Q calculator allows you to compute the reactive power in an alternating current electrical circuit. Reactive power, measured in volt-amperes reactive (VAR), represents the energy that oscillates between the source and reactive elements such as inductors and capacitors. It does not perform useful work but is essential for the operation of equipment like motors and transformers.
The calculation is based on the formula Q = V * I * sin φ, where V is the RMS voltage in volts, I is the RMS current in amperes, and φ is the phase angle between voltage and current. The sine of φ (reactive power factor) indicates the proportion of apparent power that is reactive. This formula is fundamental in AC circuit analysis, especially in three-phase systems and power factor correction studies.
You should use this calculator when sizing capacitor banks for power factor correction, analyzing the efficiency of electric motors, or designing power distribution systems. It is useful for electrical engineers, technicians, and students who need to determine reactive power to avoid penalties for low power factor or improve energy efficiency.
Important precautions: ensure that voltage and current values are on the same basis (RMS) and that the angle φ is in radians or degrees according to the calculator's configuration. Remember that reactive power can be positive (inductive) or negative (capacitive), depending on the load type. In balanced three-phase systems, multiply the result by 3 if measurements are per phase.
Frequently asked questions
What does negative reactive power mean?
Negative reactive power indicates a capacitive load, where current leads voltage. This occurs in capacitor banks or long transmission lines.
What is the difference between reactive power and active power?
Active power performs useful work (like heating or motion), measured in watts. Reactive power does no work but is necessary for magnetic fields in motors and transformers.
How do I convert angle from degrees to radians?
Multiply degrees by π/180. For example, 60° equals π/3 radians (approximately 1.047 rad).
Does this calculator work for three-phase circuits?
Yes, if you input phase voltage and phase current. For total reactive power in a balanced three-phase system, multiply the result by 3.
What is power factor and how does it relate to reactive power?
Power factor is the cosine of φ. It indicates energy usage efficiency. The lower the power factor, the higher the reactive power for the same active power.