Why outages occur
There are many reasons why electricity outages (blackouts)
We invest in supply improvement initiatives and new technologies
so we can continually improve service delivery and reduce the
number and length of electricity interruptions. These improvement
initiatives concentrate on the major causes of faults.
Major causes for unplanned outages
Approximately 90 per cent of outages on the UE network are
unplanned. These are the most frequent causes of unplanned
Overhanging branches and trees get caught in powerlines causing
loss of supply to customers. High risk areas include rural regions
with large native trees and urban regions with large street trees.
For further information on vegetation management, please click
We have established a cyclical tree cutting program as part of
the UE Vegetation Management Plan. The program includes
daily monitoring of vegetation faults to identify trends and
specific areas of poor performance.
2. Animals and birds
The major cause of sustained interruptions are birds and animals
(predominantly possums). Possums climb along power lines, and can
be electrocuted and cause loss of power, and birds will often perch
on wires. There are tens of thousands of possums in suburban
Melbourne, with Glen Waverley, Brighton, and Beaumaris having the
biggest possum problems in UE’s network distribution area.
We have installed hundreds of possum guards on transformers,
insulated underground cable terminations in specific locations and
installed ‘bird covers’ (ie. extra-long insulators) on “high risk”
poles. In extreme cases, we have upgraded our switches to fully
enclosed gas insulated switches to reduce the possibility of
animals or birds getting caught in our structures.
3. Third party faults
Human interference due to cars colliding with poles, vandalism
and underground assets being dug up by other authorities, can cause
blackouts and outages.
Unplanned outages due to the weather, such as lightning damage
or high winds, are a significant cause of interruptions to power
supply. Heatwaves can also contribute to power interruptions as the
demand in electricity (ie. air conditioners) can sometimes exceed
5. Underground plant failure
Underground equipment is extremely reliable as it is buried away
from the weather and external influences such as trees, birds and
vehicles. However, if underground equipment does fail, it takes
longer than average to identify the fault location, isolate the
issue and fix the problem.
We have installed additional fault indicators which allow
operators to locate faults more quickly and accurately, reducing
the time customers are affected.
6. Overhead plant failure
Overhead plant failures, such as faults on switches,
transformers, insulators and conductors, can cause issues. Although
these items are extremely reliable, with a failure rate much less
than 1 per cent per annum, the volume installed across the network
means that despite best efforts there will be some failures each
- We have installed remote control and monitoring equipment to
switches, automatic circuit reclosers and fault indicators in the
field so that circuits can be controlled and monitored centrally
from our control centre. The centre can quickly locate a fault and
restore supply to customers, speeding up response and supply
restoration times in emergencies to further reduce the impact of
- We are continuing a program initiated in 1997 to inspect, test
or replace insulators on electricity poles that are subject to
pollution build up, such as in coastal regions.
Approximately 10 per cent of our outages are planned shutdowns
and are undertaken for maintenance or upgrades on the network.
Over the past few years, our team members have been trained in
the use of “glove and barrier” work practices to allow them to work
safely with the lines live. This has enabled a reduction in the
number and length of planned interruptions needed to maintain and
upgrade the network. Our customers now experience less than half of
the planned shutdowns they did in 1995, due to this work