A volt-ampere in electrical terms, means the amount of apparent power in an alternating current circuit equal to a current of one ampere at an emf of one volt. This article deals with power in AC systems See Mains electricity for information on utility supplied AC power An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second Electromotive force ( emf, \mathcal{E} is a term used to characterize electrical devices such as Voltaic cells thermoelectric devices electrical The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. It is equivalent to watts for non-reactive circuits. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second.
Hence;
- 10 kV·A = 10,000 watts capability (where the SI prefix k equals kilo)
- 10 MV·A = 10,000,000 watts capability (where M equals mega)
While the volt-ampere (abbreviated VA) and the watt are dimensionally equivalent one may find products rated in both VAs and watts with different numbers. An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol to form a Decimal multiple or This is common practice on UPSs (Uninterruptible Power Supplies). The VA rating is the apparent power that a UPS is capable of producing, while the watt rating is the real power (or true power) it is capable of producing, as opposed to reactive power. An uninterruptible power supply ( UPS) also known as a continuous power supply ( CPS) or a battery backup is a device which maintains a continuous This article deals with power in AC systems See Mains electricity for information on utility supplied AC power This article deals with power in AC systems See Mains electricity for information on utility supplied AC power This article deals with power in AC systems See Mains electricity for information on utility supplied AC power Reactive power arises due to the effects of capacitance and inductance of components in the load to be powered by the AC circuit. Capacitance is a measure of the amount of Electric charge stored (or separated for a given Electric potential. In Electrical circuits, any Electric current i produces a Magnetic field and hence generates a total Magnetic flux \Phi acting In a purely resistive load (incandescent lights for example), the apparent power is equal to the true power and the amount of VAs and watts used would be equivalent. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general However, in more complex loads, such as computers (which UPSs are intended to power) the apparent power used (VAs) will be larger than the true power used (watts). The ratio of these two quantities is called the power factor. The power factor of an AC electric power system is defined as the Ratio of the real power to the apparent power, and is a number between 0 and
In the strictest sense, a volt-amp and a Watt are the same. However based on the fact that your device has a Watt equal to 70% of a volt-amp, they are not used to mean the same thing. The volt-amp refers to the maximum power flow, while the Watt refers to a time-averaged power flow. The Power flow varies as a sine function. The "root-mean-square" rate of flow is approximately 70% of the maximum flow.
Watts can be calculated with the equation: W = VA * 0. 7
VA can be calculated with the equation: VA = W / 0. 7
See also
References
- Calculating VA & Watts: http://www.powervar.com/Eng/ABCs/CalcVAWATTS.asp
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