Advantages of 3wire over 2 wire distribution system?

Advantages: (i) Two different voltages are available-high voltage for power load and low voltage for domestic and light load.

(ii) With the same volume of copper, 3 wire dc distribution system is able to deliver more power i.e. twice of that with two wire distribution system without affecting the efficiency.

(iii) If a 3 wire and a 2 wire feeders both transmit the same amount of power over the same distance with the same efficiency, the three wire feeder, if load is balanced and the cross section of middle wire is half of the x-section of either outers, requires only 0.3125 times copper as required by two wire feeder.

Disadvantages: Requirement of additional (third wire), partially reduces safety and necessity of a balancer set causing an increase in cost.

Three wire systems can be obtained by using two generator method or balancer set method. The main drawback of the former method is that two separate generators are required.