Transpositions and unbalance of high-voltage lines

UNTIL ABOUT 20 years ago, transmission engineers felt that transpositions at fairly close intervals were a necessity on high-voltage lines in order to co-ordinate communication and power systems. However, in many large high-voltage systems, the number of transposition structures has been reduced greatly and the matter of co-ordination has not produced any difficulties. Many new lines have been built with no transpositions, and remedial measures necessary for inductive co-ordination have been few since these lines were placed in service. The change in practice is the result of several factors. Separate rights of way for communication and power lines, use of underground cables or otherwise shielded circuits for communication purposes, reduced susceptibility of the communication equipment to noise, and improved designs of transformers and rotating machines leading to better wave shapes are some of the reasons.