SDG&E's power shut-down plan

On October 3, Sempra Energy introduced a number of steps to reduce the potential for fires during our high risk season. Most controversial among the measures to be taken is the proactive shutting off of power under certain extreme weather conditions.

Identified as one of five triggering conditions is a localized sustained wind speed greater than 35mph or gusts greater than 55 mph, both common occurrences during Santa Ana season. Of particular concern to Sempra is a condition called “galloping,” a wind-generated, mechanical vibration or whipping of the power lines, which can result in power surges that may damage transformers or a physical detachment of the power line from its pole, either which might result in sparks that can ignite a wildfire.

Although burying lines is considered cost prohibitive, Sempra should be applauded for installing steel poles along with heavier wire in certain sections of their system. Not mentioned, and therefore probably not being implemented, are two measures that are commonly employed to reduce galloping in high wind areas: interphase spacers and detuning pendulums.

Interphase spacers are vertical ties that bind together all of the wires mid-span between the poles, dramatically reducing any wind-generated vibration. Detuning pendulums provide a counter-balancing force proven effective in controlling line galloping.

As many as 10,000 customers can be adversely affected by proactive power shut-downs in any one given area. Many essential appliances may suddenly become deactivated when most in need. It is reasonable for us to expect that our power utility employ all readily available cost-effective measures to limit line galloping, before resorting to the shutting down of our electrical service.

Tom Casey

Rainbow