Civil Engineering Reference
In-Depth Information
also increased, as a result of cold-working prior to EAF experiments. Further,
research by Dzialo et al. [
26
] showed that, above the critical threshold current
density, the efficiency of the applied electricity increased with the percentage of
alloyed Zn in copper specimens during micro-forming.
11.5 Overhead Transmission Line Design Using EAF
Overhead transmission lines (OHTL's) deliver electricity from the generation point
(i.e., the power plant) to the customer (i.e., homes or businesses). In the EAF tech-
nique, electricity is applied to a metal while it is mechanically deformed. Overhead
electric transmission lines are simply coated metal cables in static tension loading
with high-power electricity flowing through them. From the statements above, there
are some similarities between the EAF technique on a forging process and what goes
on within a high-power electric transmission line. This section will include an expla-
nation of the electrical system grid, different transmission line structures and set-ups,
commercially available conductors and sizing procedures, conductor sag and what it
means, the effect of high temperatures on transmission line longevity, and finally how
the EAF technique explained in this thesis could be applied to the analysis of OHTL's.
11.5.1 The Electricity Transmission Grid
Electrical transmission lines are placed throughout the USA, thus forming a trans-
mission “grid” that can transport the electricity to where it is needed. There are
two types of transmission lines (high-voltage and low-voltage). The high-voltage
lines are used to transport the electricity over very large distances quickly with
little loss. The low-voltage lines are used to deliver the electricity closer to the cus-
tomers. High-voltage lines can be rated from 100 up to 1,000 kV, whereas low-
voltage lines can be rated from 4 to 46 kV [
27
]. Note that the voltage coming
directly into a residence is typically 240 V; the above values are for distribution.
In general, the size of the conductors is determined from estimating the poten-
tial power use of the customers at the end of the lines. Outages can occur if the
voltage in the lines is more than that for which the line is rated. If one link in the
grid is down, the electricity can reroute itself; thus, adding more voltage to the
amount which the other line was already carrying. Ultimately, the overloading of
several lines within a grid could lead to a blackout.
11.5.2 Transmission Line Structures and Setups
There are several different types of transmission line structures. For each of these
structures, there are clearance limitations and structural compliances. Most recently,
