Wind-swept fires that killed more than 40 people in California have jolted the state’s biggest utilities, Pacific Gas & Electric (PG&E) and Southern California Edison (SCE). State regulators and trial lawyers are probing the utilities’ tree trimming and line maintenance — common culprits in prior California fires. But they also examining a utility device that produces sparks by design: automatic circuit reclosers.
Automatic reclosers are pole-mounted circuit breakers that can quickly restore power after outages, but they can also multiply the fire risk from damaged lines. While SCE is adjusting recloser operations to reduce fire risks, PG&E’s practices are less clear. And only their neighbor to the south — San Diego Gas & Electric (SDG&E) — is tapping advanced recloser technology that is safer by design.
Reclosers make quick work of many line faults, the great majority of which result from temporary insults such as a branch striking a line or the electrocution of an unlucky squirrel. As Australian recloser manufacturer NOJA Power puts it: “Like the success of Vanilla Ice, Dexy’s Midnight Runners and Devo, most network faults are transient.” In such cases the recloser detects a power surge, momentarily interrupts electricity flow, and then automatically re-closes its contacts to restart flow down the affected line.
Reclosers usually try restarting a line 2-3 times before giving up and “locking out” a line. Sometimes multiple attempts are needed to do the job, writes NOJA Power, such as when high-temperature electrical arcing at the site of the fault burns away hung trees or tree limbs.
Under the wrong conditions, however, such arcing and ignition can obviously spark a fire. Reclosers contributed to several of Australia’s deadly Black Saturday bushfires of February 7, 2009, according to the official report of the Victorian Bushfires Royal Commission.
The commission concluded that that Kilmore East fire that killed 119 people “probably would not have started” were it not for a recloser’s three attempts to revive a wind-felled line. Experts testified that the recloser’s attempts delivered 3.4 seconds of 5,000 C° electrical arcing that likely started the fire.
The Black Saturday commission called for limiting reclosers to one restart attempt on high risk fire days and suggested that some be totally disabled during high risk periods. Not all California utilities are heeding such advice.
PG&E, in a response to questions from California’s Public Utilities Commission after the fires north of San Francisco in October, wrote that it could set reclosers on its overhead lines to attempt line restarting 1, 2 or 3 times. It indicated that it could disable that function only on reclosers associated with its underground lines. The San Francisco-based utility did not respond to Spectrum’s requests for comment.
A grid operations manager for Rosemead, Calif-based SCE told Spectrum on background that the utility disables automatic restart capability for all reclosers that its operators can remotely control in areas under “Red Flag” fire warnings. He told Spectrum that SCE tightened its recloser policy shortly before this month’s fires to permanently disable restarting by reclosers that require manual adjustment by field technicians.
SDG&E, SCE’s neighbor to the south, has gone one step further to increase recloser safety. Like SCE it restricts recloser operation on fire days, but it has also deployed advanced technology in its territory’s high-risk Fire Threat Zone to reduce the sparking that reclosers generate at faults.
S&C Electric’s pulse technology sends 50-100 times less energy to a fault [left] than conventional reclosers [right]
SDG&E uses 172 of S&C Electric Company’s IntelliRupters — so-called pulse reclosers that probe lines after a fault rather than simply restarting power flows. S&C’s intelligent breaker recloses its contacts for just 1-2 milliseconds and then evaluates the power that flows back. If the flow looks normal it restarts the line. And if the power signal matches the signature of a permanent fault, it locks the line out.
An IntelliRupter probing a permanent fault generates less than 2 percent as much fault energy as a conventional recloser according to independent tests. Christopher McCarthy, a U.K.-based managing director for S&C who helped commercialize the technology a decade ago, says they developed it as a way to reduce the wear that large fault currents inflict on substation transformers and other utility equipment.
But McCarthy says there is also a clear safety benefit — one that is dramatically evident in the smaller shower of sparks released from faults by its pulse reclosers in side-by-side runs against conventional reclosers [image above]. “We can’t say that it’s not going to cause fires,” he says, “but it’s clearly much safer.”
NOJA Power derides some of the growing criticism of reclosers as “unfair.” As the company tells utilities via its website: “There is no need to be ashamed of your arcs and sparks – when it isn’t fire season, use the very power you are charged with delivering to strike the objects that dare get in your way of reliability.”
However, California utilities appear to be reevaluating their technology options. SCE tells Spectrum that it is “actively exploring the use of pulse reclosers.
Utilities may have little choice, because they face a potentially existential threat if they can not convince both state officials and the public that they are doing everything possible to prevent fires.
A suite of lawsuits filed by residents affected by the October wine country fires allege that PG&E’s reclosers are to blame. And one state lawmaker has called for PG&E to be broken up if an ongoing investigation by Sacramento-based state agency CalFire finds it caused the fires.
This post was created for Energywise, IEEE Spectrum’s blog about the future of energy, climate, and the smart grid