Tree Trimming

One of the leading causes of outages on our system is contacts from trees with our lines.  This can create a short which can cause the whole line to go down. 

If it is just a branch touching one line then there is generally no outage.  Electricity follows a path of least resistance.  With just a branch touching one line there is generally no resistance.   If there is resistance it could cause a fire which would lead to an outage but that is not a given. 

The larger problems generally happen when the branch or tree touches two lines.  A path for the electricity has now been created and our system does not react well to the electricity flowing in this manner.  There are a range of different reactions to this occurrence.  If the lights are just flickering this probably means there was some incidental contact but it was momentary enough not to cause a short. 

There can also be temporary contacts that are significant enough to cause an outage but do not last.  You will notice these when the power goes out (sometimes just long enough to reset your clocks) but comes on right away.  In these cases a branch or tree has fallen on the lines creating the short but has then has subsequently fallen off the line.  We have devices on our lines called reclosures that automatically try to restore power when this happens.  If there is no longer a contact and the line has not been damaged then power will be restored.

However, if the tree is still on the lines, the line is broken, the pole is broken, a fuse has blown or a transformer has blown then power cannot be restored.  We will then have an outage and our crews must come out to repair the damage.  By the time we get our crew in from their home (these always seem to happen outside normal business hours), find the issue and fix our customers will have been out of power for a while.

The most economical way to reduce outages of this sort is to cut back the trees around the lines.  We call this tree trimming as we trim back the trees away from the line rather than remove them.  We are required to trim 3 meters back from primary lines and I meter back from secondary lines.  Secondary lines are the lines that come out of the transformers and go into the customers house or business.

Tree trimming is a significant budget item for us as we spend over $50k every year.  Each year we try to cover one third of the Town.  NOTL Hydro outsources its tree trimming to expert arborists.  For the past three years this has been Pineridge Tree Service.  We will shortly be going out to tender for the next three years.

Tree trimming is a requirement in the electricity distribution business.  Even our regulator likes to make sure we are not underspending on the tree trimming because they know that shortchanging this expenditure can lead to more outages. 

Tree trimming is a challenge in a number of ways.  We all know that trees are good for the environment and that the current trend and desire is to have more trees and a bigger tree coverage.  We are therefore acting against what is environmentally good behavior when we cut back the trees.  That is one reason why it is tree trimming and not tree removal.

We also only trim trees on public roads.  Any trees on private property are the responsibility of the home owner.

Finally, we know that what we do to the trees is not popular.  Nobody likes to see trees on their property cut back so that they no longer look like a tree should.  I can sympathize.   This picture is the maple tree on my front lawn in St. Catharines.  A quarter of the tree appears to have been removed.  Fortunately, when I look at it from my house, as opposed to from the side like this, it appears normal.

But, being in the industry, I do understand that this is necessary.  The alternative is more outages.

We cannot cut back on the tree trimming but one thing we can do is let you know when it will be happening.  This year we are tree trimming in all of NOTL west of Concession 5.  The tree trimming is underway now and will be for several more weeks.  Going forward we will tweet each year when and generally where we will be tree trimming.