Active power that does real work, is represented on the real axis. Note that the reactive power is represented on the imaginary axis of the diagram. In the power triangle, P is the active power, Q is the reactive power, φ is the phase angle of voltage relative to current, and | S| is the apparent power. However, the wires that provide energy, will become hot (because they are resistive!) and will heat the environment.Īll three power values are pictured in the diagram called the power triangle. So, a purely reactive load will produce no heat itself. Though this power is called imaginary and wattless, it really heats the grid wires when it goes back and forth over them. It is measured in volt-amperes reactive or vars. Vars: Reactive power, Q is the “imaginary” power in a reactive (capacitive or inductive) load, which represents the exchange of energy between the power source and the reactive load where no power is lost. It is possible, however, just to add the individual VA ratings and the total value will be just an estimate of the total power or current consumed by several devices. Because the majority of loads are non-linear nowadays, there is no straightforward way to obtain an exact total power of several loads by simply adding their currents because they are not in phase with each other (we will talk about it later). Volt-amperes are useful because if the voltage of a device is known, you can calculate the expected maximum current to ensure that the wires and cables supplying this device can withstand it. We will show below that the current in the majority of loads used at home is not sinusoidal - that is why you will need a true RMS digital multimeter. To calculate the apparent power in volt-amperes, you can measure the RMS current and the RMS voltage using a multimeter that can measure the true RMS value of any signal. The apparent power is always higher than the real power because it covers the real and reactive power consumption in the loads. The grid must be built to transport the apparent energy. The RMS calculation includes the effects of all harmonics that are usually present in the current and voltage. It is the product of RMS voltage and current and as such, it is valid regardless of the waveform shape of the voltage and current. Volt-amperes (VA): Apparent power, | S| is the power the electrical grid must be able to withstand.
In single-phase AC circuits with pure sinusoidal current, the real power is equal to the product of the RMS current I and voltage U and the cosine of the phase shift between them φ, that isįor non-sinusoidal AC current, the real power is equal to the sum of the corresponding average powers of the individual harmonic components. These measurements are also useful to determine the energy consumed by your devices at home since you pay your utility company for real power. You need to measure the real power, for example, to get rid of the heat generated by the servers in a data center. Real power is usually used for the power rating of resistive loads like ovens and heaters. Ultimately, all real power is converted into heat. It is the rate at which energy is generated or consumed. Watts (W): Real power, P (also called actual power and active power) is the power that actually powers lamps, TVs, computers, and equipment and performs useful work and generates heat. We will also discuss the current waveform distortion in non-linear loads. These values and their calculation are discussed below. Electrical and electronic products always show one or another power value and sometimes they also show the power factor as well to provide information about the energy they consumed. A 5 amp fuse would be ok.Both watts and volt-amperes are units of measurement for electric power. Q A food mixer with a 400 watt motor runs in the US on 120 volt supply. Q A 60 watt car spotlight is showing a drain of 5.5 amps on the ammeter. Q What is the biggest electric fire that can be run on a 13 amp fused plug in the UK?Ī Mains voltage in the UK is 240v so Watts = 13 x 240 = 3120 watts or just over 3kW the volts / volts on the right hand side canceling each other out to leave amps. the amps / amps on the right hand side canceling each other out to leave volts.Īnd by dividing both sides by volts you get - Watts / Volts = Amps
We remember the formula as WAV - Watts = Amps x Voltsīy dividing both sides of the formula by amps you get - Watts / Amps = Volts Lots of people every day visit our website enquiring about voltage converters, we have added this table and several examples to hopefully help you understand what converter you need.
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