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Head to head – overhead vs underground

Why don’t you just underground the whole network?

We hear this question a lot, particularly after a storm or severe weather which causes damage to the network and widespread customer outages.

The answer isn’t black and white and there are many variables that come into play when deciding what type of electricity network to build or replace in a given area.

We’ve prepared the following broad comparison to help you understand some of our considerations when planning the network.

A balancing act

Like all of our decisions, we are constantly weighing up the community’s desires against our need to invest wisely when it comes to deciding on overhead and underground power.

Generally speaking, the overhead network has a longer lifespan and is more cost-effective.

Yes it is subject to more environmental factors such as trees falling onto powerlines, storm/lightning activity, wildlife interference and erosion which can result in more faults. However because you can see the faults in plain light, they are generally easier to find and quicker to fix than underground power.

In areas with an existing overhead network, it is not cost-effective to replace the network ahead of its normal lifespan – when it’s in, it’s better to maintain than completely replace.

There is a strong argument for installing underground cables in highly congested areas such as the CBD and in new residential areas – in fact all new subdivisions must be built with underground power.

When overhead powerlines reach the end of their lifespan and need to be upgraded, the area is assessed individually and the safest, most reliable and cost-effective solution will be determined – whether that be underground or overhead.

Of course where there is a strong collective customer desire for underground power in residential areas, the 20-year-old State Underground Power Program (SUPP) is a unique program which converts overhead powerlines to underground power. This is done outside the overhead lines’ normal lifespan.

This program is co-funded by the State Government, Western Power, local councils and property owners, as a means of sharing the conversion costs with those who benefit most from the upgrade - namely the local council and property owners.

Property owners who wish to have their electricity supply undergrounded as part of this program should contact their local council and request they apply for the next round of funding, as SUPP only accepts submissions from local governments.

Overhead

Underground

Construction cost

Lower cost upfront


Distribution (low voltage): 33% cheaper
Distribution (high voltage): 61% cheaper
Transmission: 33% cheaper

Higher cost upfront

Faults - Main causes

Vehicles making contact with poles/wires


Vegetation and debris falling/blowing into lines


Fauna (particularly birds) touching wires


Weather impacts

Drilling/digging into cable


Water ingress

Faults - Detection

Easy to find origins of fault

Can be difficult to locate fault

Faults - Repair

Easy to fix due to ease of access

Can be difficult to fix. Time consuming due to the need to locate/dig/repair/refill/switch

Safety

Greater risk of exposure to the general public (though we follow strict safety processes to mitigate risk)

Less hazardous due to the removal of assets from potential public interference

Maintenance (lifespan)

Longer life expectancy

Relatively shorter life

Aesthetics

Aesthetically displeasing (unless you’re a fan of electricity infrastructure!)

Aesthetically pleasing 

While we have simplified the issue for the purposes of this article, the decision of whether to put an underground or overhead electricity supply in any given area is a complex beast that provides ongoing challenges for our network planners and engineers (they love a challenge BTW) to ensure we’re getting the best mix of safety, cost-effectiveness and reliability for each area we work in. 

More of your questions answered

What are some of the non-cost barriers that might prevent an area from having underground power?

  • Physical: Space is required to install infrastructure for underground networks. It can be unfeasible/impossible to trench into rock, or through rivers, lakes and waterbeds.
  • Geographical: In hilly/mountainous areas it is better to string cable than run through the ground.
  • Congestion: Other utilities and telecommunications companies can also occupy real estate under the footpaths. If there is no more room under footpaths, the other option is to drill into roads which can be highly inconvenient for the community.

How much of the network is overhead compared to underground?

As at the 2015/16 reporting period:

  • Overhead lines: 68,000km total – 58,000 high voltage, 9,000 low voltage.
  • Underground lines: 25,000km total – 7,600 high voltage, 17,000 low voltage.

 

 

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