High-voltage and extra-high-voltage
(EHV) transmission lines interconnect power plants and loads, and
form an electric network. This system contains 500-kV, 345-kV,
230-kV, and 115-kV lines. T
Presently, synchronous ties (AC lines)
interconnect all networks in the eastern U.S. and Canada. Synchronous
ties also (AC lines) interconnect all networks in the western U.S.
and Canada. Several nonsynchronous ties (DC lines) connect the East
and the West. These interconnections increase the reliability of the
electric supply systems.
In the U.S., the nominal voltage of the
high-voltage lines is between 100 kV and 230 kV. The voltage of the
extra-high-voltage lines is above 230 kV and below 800 kV.
The voltage of an ultra-high-voltage
line is above 800 kV. The maximum length of high-voltage lines is
around 200 miles.
Extra-high-voltage transmission lines
generally supply energy up to 400–500 miles without intermediate
switching and var support. Transmission lines are terminated at the
bus of a substation.
1. Tower: The figure shows a lattice,
steel tower.
2. Insulator: V strings hold four
bundled conductors in each phase.
3. Conductor: Each conductor is
stranded, steel reinforced aluminum cable.
4. Foundation and grounding:
Steel-reinforced concrete foundation and grounding electrodes placed
in the ground.
5. Shield conductors: Two grounded
shield conductors protect the phase conductors from lightning.
At lower voltages the appearance of
lines can be improved by using more aesthetically pleasing steel
tubular towers. Steel tubular towers are made out of a tapered steel
tube equipped with banded arms.
The arms hold the insulators and the
conductors. Figure 4.6 shows typical 230-kV steel tubular and lattice
double-circuit towers.
No comments:
Post a Comment