Cimarron, one of Oklahoma’s largest electrical cooperatives, is no stranger to ice storms. In 2002, two ice storms brought down approximately 16,000 poles, which cost the utility tens of millions of dollars. And a 2013 storm caused more than 800 poles to fail. Because of the utility’s hundreds of miles of straight distribution lines, a single pole failure can lead to the cascading failure of tens of miles of line at a time.
After 2013, the utility committed to increasing the storm resiliency of its system by changing its standard construction practices. The utility partnered with G.H. Guernsey, a consulting engineer in Oklahoma City, to design a stronger system and rebuild 1,250 miles of its distribution system. Changes included shortening span lengths and installing at least four Class 1 McWane ductile iron poles per mile, with two poles being storm poles. The storm poles are effectively inline dead ends because they are guyed in opposite directions in line with the circuit.
The remaining 18 poles per mile are Class 3 wood poles. Cimarron depends on the ductile iron storm poles to limit the cascading of the other poles.
The new system was first tested in May of 2015 when a tornado touched down in Orienta, Oklahoma. The twister took out four wooden poles and transported the conductor a half mile perpendicular to the line at the next standing pole. However, damage stopped at the first ductile iron storm pole. Few expected the poles to withstand a tornado’s high winds and flying debris, but needless to say, the utility was happy with the results. The utility anxiously awaited the next major ice storm to prove the effectiveness of the new storm design.
On December 27, 2015, winter storm Goliath brought heavy freezing rain, which accumulated as ice on Cimarron’s distribution system. Goliath was the storm that Cimarron had been waiting for to test its new storm-hardening strategy. Heavy ice and high winds caused the utility to lose 1,158 poles and hundreds of crossarms in areas where poles did not fail. In total, the storm damage is expected to cost $8.5 million.
There was good news, however. Not a single ductile iron or wood pole fell in the 750 miles that had been rebuilt as part of the storm resiliency project. Regarding the performance of McWane’s ductile iron poles, Reed Emerson, Cimarron’s Senior Vice President of Engineering and Operations, said, “they just work…they did exactly what they were designed to do—stop the domino effect.” In total, the utility lost 1,400 wood poles in the November and December 2015 ice storms, but this is much less than if the rebuild had not been done. Some say the magnitude of ice and wind in Goliath was worse than the storm of 2002. The utility estimates that the cost for an emergency rebuild is roughly $60,000 per mile, so it is reasonable to estimate that the utility saved millions of dollars.
Cimarron now incorporates ductile iron poles into its routine construction practices and installs two ductile iron poles per mile for single-phase construction and four poles per mile for three-phase construction.
