Reliability

Grounded! The facts on undergrounding

The debate over underground versus overhead power lines typically resurfaces every time a major storm downs lines and triggers outages.

If power lines were underground, the logic goes, they would not be as susceptible to damage by falling trees or poles, nor would they pose a danger to public safety. Plus, utilities wouldn't have to deal with the negative public opinion on the unappealing aesthetics of overhead lines.

Indeed, there has been a distinct trend toward the installation of more underground distribution lines.

"The problem you run into in the overhead-to-underground argument is the cost," said Mike Hyland, senior vice president for engineering services at the American Public Power Association. "The rule of thumb has been that it's going to cost you 10 times the amount to put those lines underground."

The added cost comes from the need for more expensive materials, excavation, longer installation, and property restoration. And even after that, underground lines are susceptible to water damage. Conventional wisdom in the industry says underground outages take longer to repair because it takes longer to locate the faults.

Well, not quite. "Some of our data suggest that there is no difference between overhead or underground when it comes to length of outages," said Hyland, whose engineering team at the Association has been working with data analytics to gather reliability data for members. "With new smarter technologies like switches, we're starting to pinpoint exactly where the faults are underground, and that allows us to get in there and fix the problem quicker."

Hyland has found that many engineers in the industry agree with him. "If your underground equipment is new, if it's properly installed and maintained, and if you do a real nice job with your protection schemes, you'll have less frequent outages and even the same outage duration as with overhead lines. This is going to improve your reliability statistics overall," he adds.

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