Reactive Power Converter
Convert reactive power units quickly and accurately.
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Other tools you may find usefulOnline apparent power calculator - calculate S in VA
Apparent powerSis the power that the network and electrical equipment must transmit, regardless of how much of this power is converted into useful work. Our apparent power calculator allows you to quickly calculate S based on the load voltage and current, making it easier to select transformers, cables, protections and power supplies.
apparent power S VA – volt-ampere power calculation from U and I AC systems transformer and UPS selection
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Table of contents
What is apparent power?
There are three types of power in alternating current circuits:
- active power P[W] - converted into work, heat, motion, light,
- reactive power Q[var] - related to electric and magnetic fields (capacitors, coils),
- apparent power S[VA] – geometric sum of P and Q, describing the "full load" of the network.
Apparent power is denoted by the letterS, and its unit isVA (volt-ampere). It combines both active and reactive power, which is why the size of transformers, UPSs, power supplies and cable cross-sections is selected according to the apparent power.
What is the physical meaning of apparent power?
Apparent power is the power that the network must "withstand".This means that although the current associated with reactive power does not perform useful work in the receiver (e.g. motor),still flows in the wires and loads the power source.
The unit of apparent power isVA (Volt Ampere). In the design and operation of power systems, apparent power is crucial because:
- determines the maximum current load of transformers, UPSs and generators,
- influences voltage drops on transmission lines,
- determines the heating of cables and electrical devices,
- allows you to assess whether the installation is designed with an appropriate margin.
Even if the active power P is relatively small but is accompanied by large reactive power Q, the apparent power S may be high. Then the network is heavily loaded with current, even though we do not consume that much "real" useful energy.
How to calculate apparent power for constant load current?
For simple circuits and assumingconstant load current, the apparent power is calculated as the product:
S = U · I
where: S – apparent power [VA], U – load voltage VL [V], I – load current IL [A].
In this basic formulawe do not take into account the phase anglebetween voltage and current - we are only inter