What is Apparent Power?

Apparent power is an amount that represents the capacity of an AC electrical device. Equal to the product of voltage rms and current rms. It is multiplied by the power factor equal to the active power. The unit is volt-ampere and kilovolt-ampere. For example, when designing a single-phase transformer with a rated voltage of 220 volts and a current of 10 amps, the value is 2200 volt-amps. It is equivalent to the maximum active power that can be obtained at a given voltage and current ^[1] .

Apparent power refers to the product of the voltage and current RMS value of a single-port network terminal button in electrical technology. Only when the single-port network is completely composed of resistors, the apparent power is equal to

in

kVA is the output capacity of the device, and the unit is VA or kVA.

It is the apparent power S of the device, and the three-phase apparent power calculation formula is S = 3Up × Ip. The unit is VA or kVA. Here Up and Ip are single-phase phase voltage and phase current. In general calculations, the calculation of apparent power uses line voltage and line current. The formula is

Where U and I are the line voltage and the line current, respectively ^[3]

Since the apparent power is equal to the product of the current and voltage effective values at the end of the network, and the effective value can objectively reflect the size of the sine and its ability to do work, the product of these two quantities reflects that to ensure that the network can work properly ,

We take the common motor in daily life as an example. The motor is widely used in various civilian applications such as elevators, fans, shavers, etc. The motor is a device that uses electric energy to convert work into kinetic energy. Its rated power is marked on the nameplate. ,As shown in Figure 1.

Figure 1 Motor nameplate

This motor has a rated power of 4000W, a rated current of 20.8A, and a rated voltage of 220V. So: rated voltage × rated current = 220 V * 20.8 A = 4576 VA.

Here 4576 is greater than 4000, and the rated power is only equivalent to 87.4% of the product of the rated voltage and the rated current. Therefore, we will have questions. Why are these two different powers? What is the relationship between them?

In fact, 4576VA here is the rated power of the motor, that is, the rated apparent power is greater than the rated power of the motor. The 4KW rated power in the logo is the rated active power and is used to identify the actual motor Convertible electric power.

Why is the apparent power greater than the actual rated active power? The reason is that not only energy-consuming elements such as resistors but also energy-storage elements such as inductors and capacitors are present in the motor (such as a capacitor motor in this example). Therefore, in addition to the power required for normal operation of the external circuit, that is, average power or active power, at the same time, a part of the energy should be stored in the inductor, capacitor and other components. This is why the apparent power is greater than the active power. Only then can the motor equipment work properly.

It can be seen that in a sinusoidal AC circuit, the active power P is generally smaller than the apparent power S, which means that a discount on the apparent power can equal the active power. This discount is Cos, which is called the Power Factor. Cos indicates. which is:

P = S * Cos

Apparent power S, it is a measure of the power supply power demand of an electrical device to a higher-level power supply device, that is, the energy that an external circuit needs to pass to the device to ensure that the network can work normally. It does not indicate the actual power consumed by the AC circuit, but only the maximum power that the circuit may provide or the maximum active power that the circuit may consume ^[4] .