Concept and difference of phase voltage and line voltage

What is the phase voltage? What is the line voltage? What are the relationships and differences between them? This article will explain them one by one.

Delta connection and star connection without leading neutral point have three terminal lines of three-phase three-phase system, three live lines, 380V, line voltage. The star connection leading out of the neutral wire counts three live wires, and there are a total of four power wires, three-phase four-wire system, one fire and one zero, 220V phase voltage. The line voltage is the vector sum of the phase voltages of the two phases. Line voltage = 2 * phase voltage * cos30 degrees = root number 3 * phase voltage is 380 = root number 3 * 220

Many times, for the phase voltage, it is generally understood that the voltage between the phases is 380V, and the line voltage is 220V, which is actually the opposite.

concept:

The phase voltage is the 220V household voltage we often say. The voltage between the neutral line and the live line becomes the phase voltage. In fact, all the voltages in our house are phase voltages.

The line voltage refers to the voltage of any two live wires, which is what we often say 380V, which is actually the phase voltage. The phase voltage is 220V and the line voltage is 380V.

Relationship difference:

In the process of long-distance power transmission, the higher the voltage, the lower the loss, which is why the country has been studying ultra-high voltage power transmission (I = U / R). Generally high-voltage power transmission to the end user, and then through the step-down transformer to 220V / 380V mains supply to different users.

In a three-phase four-wire grid, the voltage between any one of the three phase wires and the neutral wire becomes the phase voltage; the voltage between any two of the three phase wires becomes the line voltage. The phase of the three-phase voltage differs by 120 degrees. The line voltage is the vector sum of the phase voltages of the two phases. The relationship between the line voltage and the phase voltage is: line voltage = three times the phase voltage, that is, 380V = three times the root voltage 220V (sorry, the mathematical root of the formula cannot be uploaded to the headline 3).

The two phases are connected to the running three-phase motor, and the motor can still work. This is what we often say is that the motor runs without a phase, but it is easy to burn the motor in this way. When the delta-connected three-phase motor lacks the phase, the output power of the motor will become two-thirds of the original three-phase power supply, and the other two windings only provide one-third of the power, thus causing three-phase Unbalanced, unbalanced current, unbalanced current, the motor is of course more likely to burn out.

After the star-connected three-phase motor is missing, the output power of the motor is completely provided by the two windings, and the load is increased by 50%. The other winding does not work, so the working current is unbalanced and the motor is easily burned out. Connect two-phase electricity to the stopped three-phase motor, the motor can not be started. For a single-phase motor, after the two phase wires of 380V are connected, the voltage becomes 380V, which is originally 220V. If the voltage rises, the motor will definitely burn out.