For Immediate Release: December 28, 2017

SMUD using X-ray technology to see inside high-voltage lines

Workers suspended from helicopters carry out preventive strategy to keep the SMUD system reliable

An outage on a transmission line can significantly impact any utility’s electrical system and potentially leave thousands of customers in the dark, which is why SMUD always looks for ways to prevent them. 

A new tool SMUD has in its box is state-of-the-art portable X-ray photography to inspect major transmission lines that feed the SMUD grid. Transmission lines are typically strung atop high lattice-style towers. Maintenance and repairs on them can involve a lot of work, sometimes more than a hundred feet above the ground. 

SMUD conducted a pilot project using the X-ray technology to inspect its transmission lines in El Dorado County that enable SMUD to deliver power from its Upper American River Project (UARP), SMUD’s huge system of hydroelectric power plants in the Sierra. The UARP’s nearly 700 megawatts of clean power can provide about 20 percent of SMUD’s power in a normal water year, which can be crucial especially in summer months when market power is more expensive.

To do the work and make the repairs while keeping the lights on, SMUD brought in lineworkers from Western Area Power Administration (WAPA), who are certified to do what’s called “barehand” work on energized transmission lines high above the ground. While suspended from a helicopter, barehanding is a technique that safely allows transmission lineworkers to "bond on" and have direct contact with energized, high-voltage lines to perform work. Special protective clothing, including gloves, socks and boots, place the lineworker within the field of electricity that surrounds the energized conductor, allowing the electricity to flow around their body.

As transmission lines are strung or repaired over time, a splice that looks like a tubular sleeve is sometimes used to join the two ends of the cable together to create a continuous line. Splices can degrade over time and become compromised. The lineworkers use the new portable X-ray photography technology to see inside the critical splices on the transmission lines.

The X-ray technology eliminates any guess work, allowing engineers to see which splices are strong and which need repairs. Since the data collected is live, any potential issues are found immediately and repairs are promptly made.

The work is part of many ongoing projects to improve and enhance reliable power delivery. Reliability is a core value of SMUD, a policy set by the SMUD Board of Directors who is elected by SMUD customers. To fulfill that policy, SMUD continues to bolster the infrastructure that comprises SMUD’s grid. For more information about SMUD, visit