what's the advantage of power lines (12.47kv) that have phases bundled together?

Question

Often I have seen utility companies prefer this construction: they bundle the three phases close together using plastic star looking separating insulators. Why do some power comapanies prefer this? Does the advantages outwiegh the cost?

Answer 1

The total current flow in a bundle is zero; the current flowing in one direction is equal to that flowing in the opposite direction. Thus bundling results in cancellation of the external magnetic field (see "AC MAGNETIC FIELDS" in the ref.) and presumably less power loss due to electromagnetic radiation.