Figure 1 – Above-ground high-power lines in the Netherlands
Below, I’m including two short paragraphs from an earlier blog (December 10, 2019) about the ignition of the wildfires in California:
Both situations started with tinderbox conditions (whether metaphorical or more physical) PG&E is accused of being the random neutron that set off these large fires. This accusation triggered massive lawsuits that led to a temporary bankruptcy. The company’s remedy was to turn off the lights for massive numbers of its customers.
There was another solution that really should have been implemented long ago: utility companies ought to have buried the electrical wires underground, effectively insulating them from the dry countryside. As usual, the obstacle to this massive undertaking was cost…
Almost the same can be written about most wildfires, including the recent one in Maui, Hawaii.
And like in California, the Hawaiian power company (Hawaiian Electric) is trying to fight back—this time by denying responsibility:
Even before the inferno that engulfed the Maui resort of Lahaina is fully contained, local officials and Hawaii’s leading utility are at odds over a fundamental question: Did a single fire break out in the hills overlooking the town on the fateful day, or were there two?
The answer may be crucial to establishing the cause of the disaster and the liability for it.
The utility, Hawaiian Electric, acknowledged for the first time late Sunday that its power lines, buffeted by uncommonly high winds, fell and ignited a fire early on the morning of Aug. 8.
But the company said that by 6:40 a.m. — minutes after the first reports of a fire — the windstorm had caused its lines in the area to shut off automatically. And it noted that the fire was later reported “100 percent contained” by the Maui County Department of Fire and Public Safety, which left the scene and later declared that the fire had been “extinguished.”
On the open forum site Quora, Avadhesh Khanna answered the question of, “Which country doesn’t have overhead transmission line system?” While his English grammar is not great, his comment contains relevant, important, details about powerlines:
First of all, question is very generic one. Let me eleborate! There are basically two part of power transmission. One major transmission from source/grid/large sub station to small sub station & industries (HV/MV) and second is ‘distribution’ to household blocks (LV). In former one, they need to have overhead transmission line because cost of underground cables is very high and getting insulation of that voltage and doing construction is not very economical.
Whereas in later case, low voltage distribution is required for house blocks. As human safety is very important, so rich countries like US, England can afford to put underground cables for later case (underground cabling is always costlier than overhead). But developing countries like India cannot afford to have underground cable, so they prefer overhead transmission, human safety is compromised.
In nutshell, no country is having absolute overhead or underground cable. It’s hybrid!
Now a days, developing countris are moving towards underground for houses/blocks but HV transmission is still overhead.
It’s majorly about money !
The general issue of undergrounding, or burying power lines, is summarized on Wikipedia. I have emphasized the issues of cost, as listed under Disadvantages:
In civil engineering, undergrounding is the replacement of overhead cables providing electrical power or telecommunications, with underground cables. It helps in wildfire prevention and in making the power lines less susceptible to outages during high winds, thunderstorms or heavy snow or ice storms. An added benefit of undergrounding is the aesthetic quality of the landscape without the powerlines. Undergrounding can increase the capital cost of electric power transmission and distribution but may decrease operating costs over the lifetime of the cables.
- Less subject to damage from severe weather conditions (mainly lightning, hurricanes/cyclones/typhoons, tornados, other winds, and freezing)
- Decreased risk of fire. Overhead power lines can draw high fault currents from vegetation-to-conductor, conductor-to-conductor, or conductor-to-ground contact, which result in large, hot arcs.
- Reduced range of electromagnetic fields(EMF) emission, into the surrounding area. However, depending on the depth of the underground cable; greater EMF may be experienced on the surface. The electric current in the cable conductor produces a magnetic field, but the closer grouping of underground power cables reduces the resultant external magnetic field and further magnetic shielding may be provided. See Electromagnetic radiation and health.
- Underground cables need a narrower surrounding strip of about 1–10 meters to install (up to 30 m for 400 kV cables during construction), whereas an overhead line requires a surrounding strip of about 20–200 meters wide to be kept permanently clear for safety, maintenance and repair.
- Underground cables pose no hazard to low-flying aircraft or to wildlife.
Underground cables have a much reduced risk of damage caused by human activity
An underground cable marker. Markers are put at regular intervals to show the route and warn of the hazard of digging into the cable.
- Undergrounding is more expensive, since the cost of burying cables at transmission voltages is several times greater than overhead power lines, and the life-cycle cost of an underground power cable is two to four times the cost of an overhead power line. Above-ground lines cost around $10 per 1-foot (0.30 m) and underground lines cost in the range of $20 to $40 per 1-foot (0.30 m).In highly urbanized areas, the cost of underground transmission can be 10–14 times as expensive as overhead. However, these calculations may neglect the cost of power interruptions. The lifetime cost difference is smaller for lower-voltage distribution networks, on the range of 12-28% higher than overhead lines of equivalent voltage.
- Whereas finding and repairing overhead wire breaks can be accomplished in hours, underground repairs can take days or weeks,and for this reason redundant lines are run.
- Underground cable locations are not always obvious, which can lead to unwary diggers damaging cables or being electrocuted.
- Operations are more difficult since the high reactive power of underground cables produces large charging currents and so makes voltage control more difficult. Large charging currents arise due to the higher capacitance from underground power lines and thus limits how long an AC line can be. In order to avoid the capacitance issues when undergrounding long distance transmission lines, HVDC lines can be used as they do not suffer from the same issue.
- Whereas overhead lines can easily be uprated by modifying line clearances and power poles to carry more power, underground cables cannot be uprated and must be supplemented or replaced to increase capacity. Transmission and distribution companies generally future-proof underground lines by installing the highest-rated cables while being still cost-effective.
- Underground cables are more subject to damage by ground movement. The 2011 Christchurch earthquake in New Zealand caused damage to 360 kilometres (220 mi) of high voltage underground cables and subsequently cut power to large parts of Christchurch city, whereas only a few kilometres of overhead lines were damaged, largely due to pole foundations being compromised by liquefaction.
- As underground repair and check up require street digging, it creates patches and potholes, leading to bumpy and unsafe ride for cars and bicycles. Utility work also increase lane closure which leads to the traffic jam and increasing cost of resurfacing work by the local government.
The advantages can in some cases outweigh the disadvantages of the higher investment cost, and more expensive maintenance and management.
International abundance (Same Wikipedia site)
All low and medium voltage electrical power (<50 kV) in the Netherlands is now supplied underground.
In Germany, 73% of the medium voltage cables are underground and 87% of low voltage cables are underground. The high percentage of underground cables contributes to the very high grid reliability (SAIDI < 20). In comparison, the SAIDI value (minutes without electricity per year) in the Netherlands is about 30, and in the UK it is about 70.
Most electrical power in Japan is still distributed by aerial cables. In Tokyo’s 23 wards, according to Japan’s Construction and Transport Ministry, just 7.3 percent of cables were laid underground as of March 2008.
Wikipedia also includes a detailed list of such underground and submarine cables.
In most cases, the main disadvantage is the price. The price difference between keeping the transmission lines overground and burying them underground is shown in Figure 2.
As shown in the California case (temporary bankruptcy after one charge of igniting a major wildfire) and the expected charges in Hawaii, the inclusion of expected damage from hanging wires will probably change the accounting.
Figure 2 – Transmission cost (cost per kilometer length as a function of maximum current in Ampheres) (Source: Power Grid International)