Stories & features

Bend-and-break: innovative wood pole program pays off

At $7,000 a shot, we don't want to replace poles too early (or too late)

The BC Hydro electricity system features about a million wood poles across B.C., poles that can last between 30 and 70 years depending on factors ranging from the density and type of wood, to the amount of rain in the area, to the presence of termites, ants... and the most persistent culprits of all, woodpeckers.

Each year, we replace about 10,000 wooden distribution poles, those ubiquitous 50-foot poles that hold up lower-voltage power lines in your neighbourhood, and about 700 transmission poles, much thicker poles that hold up high-voltage power lines and which stand up to 100 feet tall. At a replacement cost of about $7,000 for distribution poles (and up to $75,000 for a transmission pole) the replacement costs add up fast.

BC Hydro's combination of in-field inspection/treatment of poles, and bend-until-they-break wood pole testing at Powertech Labs in Surrey, saves millions each year and helps keep BC Hydro rates affordable. Those savings drive BC Hydro's manager of power lines strategy and standards, Jim Papadoulis, to keep improving the wood pole program.  

We now have more information, science, that says this pole we thought wouldn't last any longer, will last longer.

It's all about striking a balance. Replace a pole too early and a good pole, and money, is wasted. Wait too long and you require a costly emergency replacement – or it could weaken and break before you get to it, causing a power outage and potential safety issues.

"We're truth-testing our inspection in the field by testing the pole strength in the lab," says Papadoulis, referring to the pole-bend testing at BC Hydro's subsidiary Powertech Labs. "The thing with wood is that no two trees are the same. They decay in different ways, depending on geography, climate and other factors. Powertech is helping us garner additional knowledge we can take into our asset management program and say, 'we now have more information, science, that says this pole we thought wouldn't last any longer, will last longer."

Pole-bending tests determine how much strength is left

Using data collected in the field during the wood pole inspection program along with testing of poles at Powertech can help Papadoulis' team get a better idea of when to replace a batch of poles of the same age, location and origin. The made-in-BC contracting community inspects poles and provides the data, and BC Hydro pole maintenance coordinators use the information to design and improve our wood pole programs.

"What we're trying to do is determine the remaining strength of poles that have been in service for many years," says Hong Li, who heads asset management at Powertech. "Some poles may have reached their end of life, and some poles may not."

BC Hydro's innovative approach to wood pole maintenance and replacement has utilities across North America watching our every move, and to a large extent, trying to replicate our program and standards. The legacy of wood pole maintenance standards goes back to the 1980's. It starts with the treatment of poles, before they go into service, with CCA (chromated copper arsenate), similar to the preservative evident in the green-hued wood at your local lumber yard. And it continues with inspections and booster shots (after mid-life), this time with boron.

"We used to go back to inspect poles every eight years, but now we go back every 10," says Papadoulis, with considerable pride. "Now we have the confidence, from our experience, from pole testing at Powertech, from wood and preservative materials analysis to inspect them less often."

And the benefits don't end there. Innovation has led to a switch from what Papadoulis calls "controversial" fumigant chemical treatments for poles to the use of boron rods inserted into drilled holes in poles. As moisture seeps into poles, the boron (which has a low toxicity) is activated and moves throughout the pole to kill fungus and deter termites and ants.

"By extending the in-service length of a wood pole, we don't have to use as much fossil fuel to go into the forest, cut trees down, and strip the bark off, which also uses energy and electricity," he says. "The intangible value-add and positive impact on sustainability is huge."

Most poles that are tested break near the base, while others – particularly those damaged by pests or woodpeckers – can break at the mid-point. Show caption
In general, the tighter the growth rings are – an indication of slower growth in a tree – the stronger and longer lasting a pole will likely be.  Show caption
Concrete anchors are used to secure the pole during testing at Powertech Labs in Surrey, where technician Robert DeVita records results of the pole bending test. Show caption

Concrete and pine poles are out, B.C.-grown cedar is in

BC Hydro is sometimes asked what happened to those concrete poles that were used in our distribution system. And to a lesser extent, why less expensive and abundant pine isn't used more often.

The reality was that reports from the field indicated flaws in the concrete poles sometimes led to corrosion and failure of bolts in the poles, causing reliability and safety issues, reports that were substantiated by BC Hydro engineers. And like-wise the pine pole experiment has ended – "We got just awful performance from them," says Papadoulis – with pine being gradually replaced by another grown-in-B.C. product: western red cedar which has excellent strength and resistance to rot and pests.

This is already the practice in some parts of the BC Hydro system and we're seeing clear benefits with this strategy.

BC Hydro is also studying, with Powertech, the relative strength and longevity of the latest generation of cedar poles, which are grown more quickly in managed forests and aren't as strong as the first or old-growth poles from the wild forests that they're replacing. Old growth poles are assessed as stronger as they benefit from a slower growth, tighter or denser grain and fewer knots.

Of course, even a well-treated cedar stands little chance against the mighty woodpecker, which Papadoulis says continues to plague electrical utilities because the birds find the poles ideal.

"What they want is a perch, they look for grubs and mites and they want to make noise, because they want to attract a mate," he says. "And typically our transmission lines are in a clearing, and similarly distribution lines are in a tall open space, where they can have maximum sound penetration for attracting a mate. If they decide to nest in a pole, they'll tap an entry hole and keep digging down. We've found some poles that are like a two-level townhouse."

Over the years utilities have tried to ward off the birds, with little success, with pole wraps, meshes, and even acoustic devices designed to keep them away. BC Hydro's solution? In areas plagued by woodpeckers, take the wood out of the equation and replace the pole with composite materials or steel.