5. • Introduction:
Electric power transmission is the bulk
movement of electrical energy from a generating
site, such as a power plant, to an electrical
substation. The interconnected lines which
facilitate this movement are known as a
transmission network.
The combined transmission and distribution
network is known as the National Grid .
8. Primary Transmission Line:
The primary line
constants are parameters
that describe the
characteristics of conductive
transmission lines, such as
pairs of copper wires, in
terms of the physical
electrical properties of the
line.
9. Secondary Transmission Line:
• The primary transmission line terminates at the receiving
station (RS) which usually lies at the outskirts of the city.
At the receiving station, the voltage is reduced to 33kV
by step-down transformers. From this station, electric
power is transmitted at 33kV by 3-phase, 3-wire
overhead system to various sub-stations (SS) located at
the strategic points in the city. This forms the secondary
transmission.
10. Various Systems of Power Transmission:
The different possible systems of transmission are :
1. D.C. system
(i) D.C. two-wire.
(ii) D.C. two-wire with mid-point earthed.
(iii) D.C. three-wire.
2. Single-phase A.C. system
(i) Single-phase two-wire.
(ii) Single-phase two-wire with mid-point earthed.
(iii) Single-phase three-wire.
3. Two-phase A.C. system
(i) Two-phase four-wire.
(ii) Two-phase three wire.
4. Three-phase A.C. system
(i) Three-phase three-wire.
(ii) Three-phase four-wire.
11. Primary distribution: The secondary transmission line
terminates at the sub-station (SS) where voltage is reduced
from 33 kV to 11kV, 3-phase, 3-wire. The 11 kV lines run
along the important road sides of the city. This forms the
primary distribution.
Secondary distribution: secondary distribution system
consists of feeders, distributors and service mains.
12. Important Terms of Distribution System:
1.Feeder
2.Distributor
3.Service Mains
• Feeder: A feeder is a conductor which connects the sub-
station (or localised generating station) to the area where
power is to be distributed. The main consideration in the
design of a feeder is the current carrying capacity.
13. • Distributor: A distributor is a conductor from which
tappings are taken for supply to the consumers.
• Service mains: A service mains is generally a small
cable which connects the distributor to the consumers’
terminals.
