ACCC conductor takes a direct hit from an EF5 tornado

Grid resilience— CTC ACCC composite core was undamaged by direct tornado hit 500x277px

Written by admin

May 30, 2013

As many of us recently learned, a devastating tornado in Moore, Oklahoma, caused an estimated $2 billion in damage. Many lives were lost and people injured. While our hearts go out to those impacted, we commend OG&E and their contractors for working around the clock to help restore power. The tornado passed directly across a 138 kV ACCC line.  While the CTC Global ACCC conductor required repair, its composite core was undamaged and the line did not fall to the ground.

Tornado Moore Oklahoma 1080x256px

On Monday afternoon, May 20, 2013, an EF5 tornado, with peak winds estimated at 210 miles per hour (340 km/h), struck Moore, Oklahoma, and adjacent areas, killing 24 people, and injuring 377 others. The tornado was part of a larger storm that produced several other tornadoes over the previous two days. The tornado touched down west of Newcastle at 2:56 p.m. CDT, staying on the ground for 39 minutes over a 17-mile (27 km) path, crossing through a heavily populated section of Moore. The National Weather Service reported that the tornado was 1.3 miles (2.1 km) wide at its peak.

In 2006, OG&E installed approximately 56 km of ACCC Drake size composite core conductor on new steel monopoles to carry current from the McClain power plant north towards Oklahoma City.  The steel monopoles were approximately 122 feet (37 meters) above ground level.  The path of the tornado crossed directly over the southernmost section of the 138 kV ACCC line just across the North Canadian river 0.9 miles north of the power plant.

During the tornado one of the steel monopoles yielded to the high winds and/or was possibly hit by a large object.  The force caused the pole to drop towards the east. Two adjacent poles also deflected to the east due to the extreme tension placed on the conductor.

The tension carried by the conductor was so intense that it actually snapped the aluminum strands in one location. Surprisingly, the ACCC conductor’s composite core was not damaged.  However, due to the extent of the damage to the aluminum strands, a 30 foot long (9 meter) section of new ACCC conductor was spliced in using 2 full-tension splices after the monopole was replaced.

Two other sections of ACCC conductor near this location were also replaced due to extensive strand damage from flying debris. One section required splicing in a new 80 foot (24 meter) piece of ACCC conductor using 2 full-tension splices.  The other section, of approximately 800 feet (244 meters), used one splice and terminated at a dead-end.

Approximately one mile to the northeast a double circuit 345/138 kV lattice steel tower line experienced a structural failure which dropped it’s double-bundled conductors on the underbuilt 138 kV ACCC and adjacent distribution line.  After the 345 kV line was repaired, the areas of the ACCC conductor that were impacted were covered with armor rod to reinforce potentially damaged strands.

Moore Oklahoma tornado line damage

The 138 kV ACCC conductor line was re-energized on Tuesday, May 28th.

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