" Do they use DC supply for broadcasting? I'm confused, if they do so then how would 50HZ ripple occur." If the three phase is balanced the ripple is 300 HZ, the unbalance (extra voltage on one phase!!) results in a 50 HZ component.
"Practically, i've seen that it is not possible to distribute the load equally", its easy as a consumer, the problem is that the mains distribution agencies, would feed a street with three phase with blocks of houses on each phase, in general the currents balance but not exactly, i.e. a supply current of 500 A and a neutral current of 50 A. Whilst our load on the three phase would be balanced to 5 A in a current of 500 A.
Frank