Classification of Lines (Types of Lines)

Classification of Lines

Lines may be classified either electrically or physically

Electrical Classification 

1. Direct Current (DC) Systems

1. DC 2-wire, 1-wire earthed
2. DC 1-wire, earth return 
3. DC 2-wire, mid-point earthed
4. DC 3-wire

2. Alternating Current (AC) System

1. Single-phase, 2-wire, 1-wire earthed,
2. Single-phase, 1-wire, earth return.
3. Single-phase,2-wire, mid-point earthed.
4. Single-phase, 3-wire.
5. Two-phase, 3-wire.
6. Two-phase, 4-wire.
7. Three-phase, 4-wire
8. Three-phase. 4-wire

All these systems are used in practicle. Every system has got its own fields of application. The lines economics varies with the individual system. Direct current 2-wire,mid-point earthed system is uesd for transmission large amounts of power over long distances.

Single-phase A.C. system is rarely used of transmssion purposes Three-phase 3-wire a.c. system finds its greatest use of transmission and primary distribution. For secondary distribution work three-phase , 4-wire system is common. the industrial and other big loads are supplied by three-phase , 4-wire system,The domestic and other small load consumer are supplied with single-phase power obtained from the individual phases of a three-phase supply.