What are the Advantages of bundle conductors over solid conductor?

By bundle conductors, I am assuming that you mean stranded conductors. If you actually mean bundles of wires, then the bundles could be either stranded or solid and your question does not make sense.

Stranded conductors have two main advantages over solid conductors. The first is flexibility. Stranded conductors are much more flexible than their solid counterparts.

The second main advantage is skin surface area. Alternating current tends to travel towards the outer skin of a conductor. This is known as the skin affect. Stranded wire has a lot more skin surface area than solid wire does.

There may be more advantages, but these are the two I could think of off the top of my head.