Last week’s outburst of heavy winds triggering a round of service outages for the Omaha Public Power District, Nebraska, once again demonstrated the importance of the district’s tree-trimming program. Downed tree limbs caused a large number of the outages experienced by more than 7500 customers for a short time last week, but without a tree-trimming program the problems could have been much worse, say OPPD officials.

“An effective tree-trimming and removal program is vital to maintaining the reliability and the integrity of our transmission and distribution system,” said Tim Burke, vice president of customer operations. “More than one utility has seen the numbers of downed lines caused by fallen tree limbs increase dramatically during storms because tree trimming was not a high priority.

“That is not the case for OPPD. We know from experience that while tree-trimming does not eliminate all outages or service interruptions, it does help reduce them,” said Burke.

OPPD spends approximately five million dollars a year on tree-trimming programs.

“Tree-trimming is a year-round concern for us,” said Jerry Hakenholz, OPPD supervisor of T&D maintenance. “Downed tree limbs not only cause service interruptions due to downed lines, but those downed lines also pose a safety hazard to the public.”

OPPD personnel are already in the process of carrying out the district’s tree-trimming program for this year and will continue over the coming months. Hakenholz notes that one of the biggest misunderstandings about the program is the method used by the district to trim trees.

OPPD adheres to the standards of national arborist organizations when trimming trees. The utility uses a “natural” trimming method in which branches are pruned back to lateral branches within the tree crown. This procedure is healthier than “topping” in which tree branches are indiscriminately cut back to reduce the size of the tree. The “natural” method allows the pruning cuts to heal more rapidly, reducing the chances of insect and disease damage and promotes a healthier re-growth of branches directed away from power lines.

Hakenholz noted that OPPD employs a highly trained staff of foresters, who have college degrees and experience in forestry or national resources, and are certified arborists. The forestry team is responsible for directing the work of the contractor line-clearance crews. Each contractor is licensed by the City of Omaha and each contractor employee and must receive ongoing training to maintain certification as a qualified line-clearance tree trimmer.

In stormy weather, large tree branches not only can break and fall into overhead lines, branches that rub against or fall into power lines may create sparking, possibly causing a fire.

Hakenholz said the best long-term option rather than trimming is planting the right tree in the right location. That means planting a tree that will not grow too close to or into nearby power lines.

“The bottom line for us is the safe and reliable delivery of power. Tree trimming, proper tree planting and practicing safety around power lines are all a big part of that.”