Their prototype, built at the request of a local utility company, consists of a lightweight aluminum frame that uses rope and a lever-and-pulley system to enable the worker to detach a transformer’s power connector (known as a load-break elbow). This operation sometimes triggers an explosive arc that can cause serious skin burns and eye injuries. Such arcs can travel as far as 8 feet from the transformer. The new device, however, would enable workers to disconnect the line from 10 to 12 feet away.
“We’re very pleased with the outcome of this project,” said Bruce R. Hirsch, a Baltimore Gas & Electric Co. (BGE) representative who worked with the students. “What they’ve given us is a good start. It’s a very simple design, and they’ve suggested some further refinements.”
To acquire the new safety tool, the utility last year turned to Johns Hopkins undergraduates enrolled in the two-semester Engineering Design Project course, offered by the Department of Mechanical Engineering. BGE’s project was aimed at protecting technicians who work in the above-ground, pad-mounted transformer boxes commonly found in residential neighborhoods.
The Goal: Simplicity
Currently, because of the risk of an electrical arc, such workers must wear safety goggles, flame-retardant clothing, protective gloves and a hard hat, and must use an 8-foot-long “hot stick” to disconnect lines that typically carry 7,600 volts. BGE asked the students to devise a system that would allow the workers to remove such lines from the reach of an explosive arc.
This challenge was assigned to a team consisting of seniors Kyle Azevedo of Bridgewater, Conn.; Julie Blumreiter of Muskego, Wis.; and Doo Hyun Lee of Seoul, Korea. BGE provided an unpowered, out-of-service residential transformer box for the team members to use in developing their tool.
The students initially considered complex designs that would employ hydraulic or pneumatic power. “We finally decided on an all-mechanical design that would require no batteries or motors,” said Azevedo. “One of our primary goals for this tool was simplicity.”
The finished prototype features three guide rails that surround the transformer’s elbow connection. A sliding component houses a clamp that grabs onto the connector. The utility technician can then use the lever and pulley system to detach the power line from a safe distance.
Compared to the current hot stick procedure, this device requires the worker to exert only a third as much force, the students said. In addition, the tool also should be simple to transport and utilize during repair assignments.
“We wanted to make this device as small and as light as possible so that one worker could easily operate it alone,” said Lee.
The undergraduates spent about $9,600 to make the prototype but estimated that it could be mass-produced for far less. The prototype has been turned over to BGE, which will conduct further tests and consider refinements in the device before deciding whether to deploy it in the field.
