Various Systems of Power Transmission:

It has already been pointed out that for transmission of electric power, 3-phase, 3-wire a.c. system is universally adopted. However, other systems can also be used for transmission under special circumstances. The Various Systems of Power Transmission are

1.D.C. system

  • D.C. two-wire.
  • Two-wire with mid-point earthed.
  • Three-wire.

2.Single-phase A.C. system

  • Single-phase two-wire.
  • Single-phase two-wire with mid-point earthed.
  • Single-phase three-wire.

3.Two-phase A.C. system

  • Two-phase four-wire.
  • Two-phase three wire.

4.Three-phase A.C. system

  • Three-phase three-wire.
  • Three-phase four-wire.

From the above possible systems of power transmission, it is difficult to say which is the best system unless and until some method of comparison is adopted. Now, the cost of conductor material is one of the most important charges in a system. Obviously, the best system for transmission of power is that for which the volume of conductor material required is minimum. Therefore, the volume of conductor material required forms the basis of comparison between different systems.

While comparing the amount of conductor material required in various systems, the proper com­parison shall be on the basis of, equal maximum stress on the dielectric.

There are two cases :

When transmission is by overhead system:

In the overhead system, the maximum disruptive stress exists between the conductor and the earth. Therefore, the comparison of the system in this case has to be made on the basis of maximum voltage between conductor and

When transmission is by underground system:

In the underground system, the chief stress on the insulation is between conductors. Therefore, the comparison of the systems in this case should be made on the basis of maximum potential difference between conductors.