What Causes Outages?

 

Everything from car accidents to squirrels can cause power outages. The leading cause, however, is trees—especially when storms blow trees or limbs into electric lines. That’s why KUB prunes trees to minimize outages and help provide safe, reliable service.

 

We also track outages in five major categories to help direct efforts to prevent outages. And, like other electric utilities, we look at how long customers are without power (Customer Minutes of Interruption, or CMI) to get a clearer picture of the overall impact of outages on customers.

 

Acts of Nature:

This category accounts for more than 60 percent of the time when KUB customers were without power in fiscal year 2009–2010. Trees or other vegetation were the leading cause, followed by lightning, then animals.

 

When storms or high winds blow limbs into power lines, a breaker shuts off power to that circuit. The system tries to reset itself (see Momentary Power Outages), but if it can’t, a crew must remove the limb or tree and repair any damage to restore power. If trees are down, crews may have trouble even getting to the damage due to blocked roads.

 

Tall objects, like electric poles, attract lightning. Lightning strikes can damage equipment and cause outages. Small animals like squirrels and birds may also cause a short circuit that knocks out power

 

Equipment Failure: This category includes outages caused by transformer failure, broken insulators, bad underground cable, etc. Ongoing maintenance helps prevent equipment failure, but failure still causes a small number of outages.

 

Acts of Man: In this category, vehicle accidents that damage poles or other equipment cause the most outages. Contractors or homeowners—especially those who forget to call 811 before digging—also contribute to outages when they damage lines during construction or excavation. And vandalism causes some outages.

 

Operational: KUB sometimes shuts off power for employee safety during work on lines or equipment, planned switching, etc.

 

Unknown: For a small percentage of outages, KUB cannot determine the cause.

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