Post Syndicated from Peter Fairley original https://spectrum.ieee.org/energywise/energy/the-smarter-grid/breaking-pges-cycle-of-blackouts-and-wildfires
“It’s not cheap to put one in but once you do it, you’ve got 1,000 kilometers of network that’s suddenly a lot safer,” says Monash University professor Tony Marxsen, who chairs the Australian Energy Market Operator, Australia’s power grid regulator, as well as Melbourne-based grid equipment developer IND Technology.
The power diverters—known as Rapid Earth Fault Current Limiters (REFCLs)—react to the surge of current unleashed when a power line strikes the ground or is struck by a tree. When this happens on one of Victoria’s 22-kilovolt distribution circuits, the REFCL instantly begins collapsing the faulted line’s voltage toward 100 volts, and can get there in as few as 40 milliseconds (ms). “If it can do it within 85 ms, you won’t get fires,” he says.
REFCLs exploit a phenomenon discovered in 1914 by German engineer Waldemar Petersen, who showed that a charged coil could neutralize the current in a network if the former’s magnetic field resonated at the right frequency relative to the latter’s electric field. REFCLs employ a resonating coil to neutralize all but a few amps of the current in a faulty line, then use power electronics to squelch the rest.
The beauty of the REFCL is that squelching a faulty line does not cause a widespread blackout. Victoria’s 22-kV distribution circuits consist of three parallel lines. While voltage is collapsing on a faulted line, the REFCL temporarily diverts its power to the circuit’s other two lines. The customer never knows there has been a fault.
REFCL producer Swedish Neutral originally developed the device to maintain throughput in underground power lines, where faults can be hard to fully quench. Through Victoria’s R&D program, they adapted REFCLs for overhead circuits and faster operation.
Marxsen says 20 to 30 percent of the distribution circuits in PG&E’s territory have the appropriate three-phase design for REFCLs, as do a similar proportion of circuits in the territory of Southern California Edison (which is also grappling with grid-sparked wildfires). “It would certainly offer the option of not shutting down the networks when there’s high fire risk,” he says.
Another technology fostered by Victoria’s program is already being tested by PG&E, according to Marxsen, who is leading its commercialization through IND Technology. The hypersensitive detection system combines electromagnetic frequency sensors, which track 1-megahertz to 130-mhz signals, and algorithms that match signal patterns to the condition of the lines. With sensors placed every 4.8 kilometers on distribution lines, the system is so sensitive that it can detect vegetation within 80 millimeters of a line, and so precise that it can locate trouble spots with 10-meter accuracy.
Marxsen says the idea is to identify problems such as weakened lines and faulty transformers so they can be fixed before they cause sparks. Victoria utilities recently completed pilot tests on 250 kilometers of distribution circuit, and he says the results have convinced several to begin rolling out IND’s early fault detectors on some circuits. He expects even better results from the technology in California, based on early data from the PG&E pilot test that began in June.
Home-grown analogs to Australia’s devices are also coming to the fore. San Diego Gas & Electric is already deploying a rapid fault detection and line shutoff system that can beat gravity, squelching current in broken distribution lines before they hit the ground.
Somerville, MA-based LineVision, meanwhile, says one California utility is considering a test of LineVision’s continuous monitoring system, which tracks the condition of more powerful transmission lines. A broken PG&E transmission line sparked the massive Kincade fire that forced 200,000 Sonoma County residents to evacuate last month.
LineVision’s tech uses a combination of lidar and electromagnetic field detectors to spot transmission conductors that are overheating and sagging toward vegetation, or being swayed violently by winds and clashing. It could spot weather-driven line damage, thus preventing some incidents, and also enable utilities to limit forced shutoffs to network segments posing high risk at a given moment, according to LineVision CEO Hudson Gilmer. “PG&E has a plan that includes better weather forecasting and risk analysis, grid hardening, clearing of vegetation. What we find is a missing link is to actually monitor the asset that is causing the problem,” says Gilmer. “These lines are the backbone of our electric grid. It’s ridiculous, frankly, that they’re not monitored,” he says.
None of these solutions is a silver bullet that will completely eliminate fire risk from power grids. REFCLs, for example, are proving hard to configure and less effective on certain Victoria circuits.
And none of this equipment comes cheap. Victoria’s REFCL rollout could ultimately cost AUS $700 million (US $500 million), according to The Age, a Melbourne-based newspaper.
That’s a hefty cost that ultimately will be borne by ratepayers. But it pales in comparison to the devastation wrought in the weekend of bushfires in Victoria in 2009. What came to be known as the “Black Saturday” fires killed 173 people and caused an estimated AUS $4 billion in damage. More than half of the major Black Saturday fires and 159 of those deaths traced back to power lines.