Engineering students at Johns Hopkins have invented a
tool that would allow utility workers to
disconnect power lines from residential transformers at a
safe distance, beyond the range of
dangerous electrical arcs.
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 students' device would enable
workers to disconnect the line from 10 to 12
"We're very pleased with the outcome of this project,"
said Bruce R. Hirsch of Baltimore Gas &
Electric Co., 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.
This device was made to enhance the safety
of our people, and that's BGE's top priority."
To develop the new safety tool, the utility last year
turned to students enrolled in Johns
Hopkins' two-semester undergraduate Engineering Design
Project course offered by the Department
of Mechanical Engineering. BGE's project was aimed at
protecting technicians who work in the
aboveground, pad-mounted transformer boxes commonly found
in residential neighborhoods.
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 10 to 12
feet away, beyond the reach of an
The utility's challenge was assigned to a team
consisting of seniors Kyle Azevedo, Julie
Blumreiter and Doo Hyun Lee. BGE provided an unpowered
out-of-service residential transformer box
for the team to use in developing its tool.
The students initially considered complex designs that
would employ hydraulic or pneumatic
power but finally decided on an all-mechanical design that
would require no batteries or motors. "One
of our primary goals for this tool was simplicity," Azevedo
The finished prototype features three guide rails that
surround the transformer's elbow
connection. A sliding component of the device 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. The students said that their device, compared to
the current hot stick procedure, requires
the worker to exert only a third as much force.
It 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," Lee said.
The undergraduates spent about $9,600 to make the
prototype but estimate 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.
The student inventors, who recently received their
diplomas, viewed the engineering design
course as an important part of their education. "It gave us
the chance to apply a lot of the knowledge
we'd been gathering over the previous three years from
lectures and textbooks," Blumreiter said. "In
working through this project, we got real-life experience
in the design, manufacturing and assembly
Blumreiter and Azevedo are planning to enter graduate
engineering programs at Stanford
University and Georgia Tech, respectively. Lee plans to
begin working soon as a structural analysis
engineer in New Jersey.
The utility worker's device was one of nine projects
completed this year by students in the
engineering design course, taught by Mike Johnson and other
faculty members. Each team of three or
four students, usually working within budgets of up to
$12,000, had to design a device, purchase or
fabricate the parts and assemble the final product.
Corporations, government agencies and nonprofit
groups provide the assignments and collaborate with the