Electrical-leak testing could reduce Metro meltdowns, but it’s not a fast fix
As smoke and “arcing” issues continue to plague Metro, agency officials say relief may be in sight: a preventive maintenance program starting in July that will allow workers to begin testing for electrical leaks along the system’s power cables and tracks.
But there’s one problem: The testing process is slow, cumbersome and time intensive — and it will probably be a while before riders start noticing results.
“What we’re striving for is a sustainable solution,” said SafeTrack director Laura Mason. “There’s no quick fix to problems that can take years to evolve.”
Electrical events are a recurring problem on the transit system, evidenced by the most recent series of problems with smoldering stud bolts near the heart of the Red Line. One of those events resulted in an hourslong shutdown near Metro Center last month that some riders called the worst Metro commute of their lives.
The electrical problems come in two main forms. The first is cable insulation: The copper cables that run electricity from power substations to the third rail are supposed to be covered in a thick layer of insulation. Some of those cables are 40 years old, and insulation is beginning to wear thin in spots. Many of those cables need to be replaced — but with hundreds of miles of cable, it’s hard to know which to prioritize.
The other problem occurs on the opposite side of the tracks from the third rail — where electricity that powers the train’s propulsion system leaves the train through its metal wheels and travels back toward the power substation. The electricity is supposed to travel straight from the running rail that supports the wheels, into another set of cables and back into the power system.
But there are plenty of other metal components that stabilize the rails and affix the tracks to the ground. Those components are supposed to be insulated with rubber gaskets so they can’t be electrified. But the insulation on those components has aged and worn, too. The buildup of water, dirt, dust or mud can serve as a conductor. It becomes easy for those components to become electrified, overheat and emit sparks or plumes of smoke as the electricity travels from those components into the ground.
In both cases, it’s an issue of bad insulation and electricity traveling to places where it shouldn’t. And in both cases, those problems are difficult to see with the naked eye.
That’s why Metro plans to kickstart two strategies to help cut down on those incidents by detecting electrical leaks before they become full-blown arcing incidents or cable fires. The timeintensive process is one of the reasons Metro rallied so hard to roll back late-night service and launch the preventive maintenance program that is supposed to start July 1.
In both processes — called “cable meggering” and “stray current testing” — technicians must first isolate individual sections of the track or the power cables. They have to turn off power to the tracks, and it’s not as simple as flipping a switch. Workers don protective outfits that look like spacesuits and pull out giant breakers from the power substations that surround the targeted section of the tracks. It’s a process that can take more than an hour.
Workers then inject the cables or the third rail with electricity, measure the voltage and check for abnormalities that could indicate electricity is leaking.
But that’s the easy part. If the tests indicate that electrical current might be straying from its intended circuit, workers have to track down the source of the leak. And that can take a while.
Mason outlined the mathematical challenge of the endeavor: There are about 80 metal fasteners per 100 feet of track. The stretch of tracks that might be tested at one time is a couple thousand feet. That’s 1,600 fasteners to check — and it takes just one poorly insulated fastener to result in a smoke emission that could ruin a commute for tens of thousands of riders.
“You quickly increase the number of components that you’re checking and measuring,” Mason said. Ultimately, she said, Metro’s goal is to get to a place where every stretch of the tracks gets tested for stray current once every four years, though more problematic sections of the system probably would receive more frequent treatment.
That’s also why stray current testing and cable meggering were not performed frequently during SafeTrack. You can’t do the tests while you’re performing other repair work on the tracks. Metro officials thought that other work should take priority, rather than using up golden periods of round-the-clock uninterrupted track time to perform electricity tests.
It can take as long as three nights of testing to determine the source of stray current in one relatively short segment of the tracks. And even then, it’s not clear whether the defect that caused the electricity to bleed to the track components is actually a problem that would ever have caused a full-blown arcing incident.
Metro used to have a meggering program, though it was suspended years ago. Before the agency decided to revive the protocol, staff sent a survey to seven other transit agencies to learn about whether, and how often, they test for leaking cables, said Mike Hass, Metro’s general superintendent of traction power maintenance. The results varied: Some tested constantly, others only used the process in response to a specific problem. Several major transit agencies had beefed up their electrical-leak testing programs only in the past couple of years.
It turns out that meggering and stray current testing is often scrimped on at other transit agencies for the same reason the results aren’t immediate: It’s a long process, and you spend a bunch of time hunting down a defect that might never result in a problem for passengers.
“It’s like playing whack-a-mole a little bit,” said Randy Clarke, vice president of operations and member services at the American Public Transportation Association. “You’ve got to keep doing all this work to find something that may or may not be a big problem for you.”
And because the testing can only happen at night — power must be shut off to both sides of the tracks, so no single-tracking — workers only have one or two hours each night to test those individual components before they must get off the tracks, reconnect the power and allow morning service to resume.
“WMATA is not alone in this,” Clarke said. “You can be chasing something that only happens randomly. Even though you might think it’s fixed, the problem reappears. It’s time consuming and can be frustrating.”