Network integration of wind power - Wind Power Integration: Connection and System Operational Aspects - page 114

worst case constraint for the wind farm - beyond B the load at B has reduced the
flow in 3 and 4. The load at C further reduces the flow in 5 and 6. Considerable
work and practical tests have now been undertaken which shows that there is
advantage in viewing the rating of 1 and 2 dynamically. It is known that the rating
of lines increases dramatically over the first few km/h of wind speed.
There are three major consequences of thermal overloading:

weak spots, e.g. overhead line jumper or joint connections, may fail ●

sag will increase ●

conductor grease may become fluid and be lost ●

The problem is that there are a large number of variables in dynamic line
rating, viz.

wind direction - axial or tangential to the line ●

wind variability throughout the route ●

line topography throughout the route ●

tree or other shielding of conductors ●

Several power system owners have worked with equipment providers to build
models which produce reliable real-time ratings for critical circuits. There is no
theoretical problem in achieving this given a large number of real-time measure-
ments. The 'cleverness' is to use a limited number of measurements to reliably
infer the rating of the circuit. A systematic approach is required. The following
shows the general approach taken:

A detailed overhead line study is required to determine the exact sags, clear-
ances, pole heights and line orientation parameters.

●

A conductor clearance table is required showing the clearance for various
conductor temperatures.

●

Wind speed and direction are used to determine the location of the critical
spans.

●

A limited amount of line up-rating is often planned using higher poles, diver-
sions or high temperature, low sag conductors, e.g. tightly bundled segmented
all-aluminium alloy conductors, gap conductors or carbon cored conductor;
this is to remove the most limiting spans from the problem. It is likely that
these spans are limiting because they are not subject to wind cooling to the
same degree as the rest of the line; this may be because of line orientation or
features in the built or natural environment.

●

With some of the spans up-rated, the remainder can be managed as follows:
*

●

measurements are taken at a number of positions along the line

a calculation (probably using a self-learning programme) locates the cri-
tical span(s) for this level and direction of wind

*

a rating is attributed to the line based upon the critical spans *

To carry out this work a significant number of weather stations located as close
to conductor height as possible and at well selected critical points on the circuit is
needed. These transmit information at least every few minutes to a central