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The power system is a three-phase system. In the high and medium voltage networks, the majority of the load are three-phase symmetrical loads. In some cases, such as with the supply of the railways, the load is connected between two phases. In low-voltage networks, most of the connections are single phase connections. The aim is to distribute all single-phase loads in such a way that the three phases are loaded as equally as possible. As a result, the voltage in the distribution grid will be mostly three-phase symmetrical. The deviation of the three phase voltages with respect to the three-phase symmetry is indicated by the asymmetry. The asymmetry is visible if in a three-phase system the effective values of the voltages of the three phases are not equal to each other or are not shifted by 120 degrees relative to each other.
Asymmetry is caused by non-symmetrical loads. This is the case, for example, when single-phase loads are not properly distributed over the different phases of a three-phase connection. But also cause by heavy loads between two phases
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