why outages occur
There are many and varied reasons why outages (blackouts) occur on the electricity system.
About 90% of outages on the United Energy network are unplanned and result
from a range of causes including, trees, animals, weather and pole fires. About
10% of United Energy's outages are planned shutdowns and are undertaken for
maintenance or upgrades on the network.
Major causes:
Unplanned Outages
Trees
Overhanging branches and trees get caught in power lines causing loss of
power to customers. Rural areas with large native trees and urban areas with
large street trees are most likely to cause problems.
Animals and Birds
The major cause of sustained interruptions are birds and animals
(predominantly possums). Possums climb along power lines, are electrocuted and
cause loss of power whereas birds will often perch on overhead assets.
There are tens of thousands of possums in suburban Melbourne with Glen
Waverley, Brighton, and Beaumaris areas having the major possum problems within
United Energy's territory.
Third Party
Third party faults are caused by external human interference. This includes
cars colliding with poles, vandalism, underground assets dug up by other
authorities and trees cut down onto power lines by members of the public.
Weather (Lightning & Wind)
Unplanned outages due to the weather, such as lightning damage or high winds,
are a significant cause of interruptions to power supply. Extremes in weather
such as heat waves also occasionally contribute to power interruptions.
Underground Plant Failure
Underground equipment is extremely reliable, being buried away from the
weather and external influences such as trees or birds. However, if it does
fail, it invariably takes longer than average to identify the fault location and
isolate the problem.
Overhead Plant Failure
Overhead plant failure includes faults on switches, transformers, insulators
and conductors. Although most of these items are extremely reliable with a
failure rate much less than 1% per annum, the sheer volume installed across the
network means that despite best efforts there will be some failures each
year.
Planned outages are undertaken to replace assets, perform maintenance or to
upgrade the network. Over the past few years, United Energy linesmen have been
trained in the use of "glove and barrier" work practices to allow them to work
with the lines live. This has enabled a reduction in the effect of planned
interruptions needed to maintain and upgrade the network. Now customers
experience less than half of the planned shutdowns they did in 1995 due to this
work practice.
