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Friday, August 2, 2019

What are the causes of voltage imbalance in power transmission lines?

There are three primary causes for voltage imbalance in transmission lines not caused by elements connected external to the sending and receiving terminals:

. Unequal conductor position spacing,

.Unequal mutually coupling with other transmission lines,

.Unbalanced loading.

Most transmission lines don’t have mutual coupling with other lines and, for the most part, the loading on transmission systems is well balanced. Therefore, the most common reason for voltage imbalance is due to conductor spacing.

           Here are two transmission lines

 The delta configuration has nearly equal phase spacings and will be balanced provided the load is balanced and there is no mutual coupling. The horizontal configuration has unequal phase spacing and some degree of voltage imbalance. For short transmission lines, phase spacing is not really an issue. For long lines, phase transpositions are used to balance the line as shown below:

Each phase occupies a position for one-third of the line length and this will balance the line.

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