NASA Jet Propulsion Laboratory, California Institute of Technology

Using turbine from dentist's drill and custom hybrid integrated circuit, three-member Jet Propulsion Laboratory group has developed the first hand-held sensor to measure electric fields around direct current power lines.

Team leader Dr. Harold Kirkham and engineers Dr. Alan Johnston and Shannon Jackson worked on the project for three years.

Most power lines relay alternating current (AC) electricity. But more direct current (DC) lines are being constructed since they can channel more power over longer distances.

Sensors to detect AC electric fields have existed for years, but only non-portable coffee pot-sized instruments which must be electrically grounded, have been available to measure DC fields.

"And if they are not physically at ground level, they would distort the fields they are measuring," said Dr. Harold Kirkham, the scientific and engineering group's leader.

For the past 25 years researchers have been studying the possible effects of voltage from power lines on technicians who must work with them and on livestock grazing under the lines.

In addition to the dentist's drill turbine which operates on compressed air, and "four of the smallest watch batteries we could find," the group took advantage of state- of-the-art fiber optics for another essential component of the sensor.

The fiber optics are used to channel the measurements of the field through long piece of tubing to receiver that displays the data. Since the fiber optics also serve as an insulator, the measurement is not distorted.

JPL's sensor is three inches long and one inch in diameter. It is mounted on fiberglass pole and hand-held. "So the person measuring the field can stand several feet away and even the distortion caused by the person is eliminated," Kirkham said.

A portion of the sensor rotates at 25,000 revolutions per minute, because it is necessary to have some motion to detect DC field. The rotor is powered by the small turbine.

JPL built the sensor for the Office of Energy Storage and Distribution of the Department of Energy. The group planned three phases of development, beginning with the "beer can phase," so called because the first sensor was about the size of beer can.

But after the first phase, the group skipped phase two as unneeded and went to phase three. Testing is expected to be completed by the end of September.

"We will build four or five of these prototype sensors, and although JPL won't be using them, we will lend them to some other research institutions interested in studies on the biological effects of electric fields from power lines," said Kirkham.

The next step, he said, is to adapt the DC sensor design to more efficiently detect electrical fields from AC power lines.

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