Do you know the power calculation method of three-phase electricity?

What is three-phase electricity? How should it be calculated? When it comes to the power calculation of three-phase electricity, everyone knows that a three-phase AC circuit is composed of three voltage sources (or electromotive force) with the same frequency, equal amplitude, and a phase difference of 120°. system. They form a symmetrical three-phase power supply, each of which is called a phase. The instantaneous values ​​of each phase voltage are that they have the same amplitude Um and frequency, but the phases of the three differ from each other by 120° electrical angle (i.e. 1/3 cycle). How should we start with such power and current, and how should we calculate it?

1. Calculation of 380V power and current

For example, an electric motor:

1. Formula:

Current=power/voltage*1.732*power factor

2. Calculation:

1000/380*1.732*0.8=1.9-2A

The power factor is selected as 0.8.

That is, the operating current of each 1KW motor is calculated as 2A.

3. Note:

The direct starting current of a three-phase motor is 4-7 times the rated current.

Therefore, when calculating the current, leave a margin when wiring and selecting switches.

2. Relationship between line voltage and phase voltage

Phase voltage: The voltage between the live wire (phase wire L) and the neutral wire N, usually 220V from the mains.

Line voltage: The voltage between any two live wires (phase wire L), usually 380V.

Line voltage: 380V, phase voltage: 220V.

1. The relationship formula between line voltage and phase voltage:

Line voltage =√3 phase voltage

2. Calculation:

220V*√3≈380V

Three-phase electricity is three phase wires, and there is 380V between the phase wires.

There is 220V between any phase line and neutral line.

The method that requires 220V voltage is to take a phase wire and a neutral wire to form a connection on 380V.

Schematic diagram of three-phase load power measurement

3. Calculation of power and current of 220V resistive electrical appliances

Resistive electrical appliances:

Incandescent lamps, electric heaters, electric cups, rice cookers, electric irons, etc.

When resistive electrical appliances work, the current waveform is a sine wave, and the power factor is very high, close to 1.0.

That is, Cosφ=1. This situation will only occur when there is a purely resistive load in the circuit, or when the inductive reactance and capacitive reactance in the circuit are equal.

1. Formula:

Current=power/voltage*power factor

2. Calculated current of 1000W:

I=1000/220=4.5A

That is, the working current of resistive electrical appliances with 1KW power is 4.5A.

Power = voltage * current * power factor 0.6

4. Calculation of power and current of 220V inductive electrical appliances

Sensitive electrical appliances:

Electric motors, electric hand drills, electric fans, ceiling fans, washing machines, etc.

During operation, the current waveform will be distorted and no longer a sine wave, and the power factor is generally around 0.6-0.8.

1. Formula:

Current=power/voltage*power factor

2. Calculated current of 1000W:

1000/220*0.6=7.5A

Through the above calculations, draw inferences from one instance, draw analogies and apply them flexibly. The above is the calculation method of three-phase electricity. I hope it can help you.