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Measurement of low frequency electric fields using electrodeless breakdown of gases

University of British Columbia

There is a need for an electric field meter to measure environmental fields under high voltage transmission lines and their associated switchyards. This thesis describes a new electric field meter based on the electrodeless breakdown of gases in insulating vessels. When a glass bulb filled with a gas (e.g. neon) is placed in an alternating electric field it emits light in the form of pulses. The number of pulses per cycle of the electric field is proportional to the field magnitude. An electric field meter is constructed by conveying the light from the gas filled glass bulb (the sensor) to an electronic counter (the detector) with an optical fiber. The resulting meter has a low weight, non metallic sensor that can be separated from the detector electronics by any desired distance. The sensor shape dictates its directional sensitivity. A spherical bulb has an isotropic response to the field while a cylindrical bulb gives a maximum response when its axis is aligned with the field direction. The size of the bulb is inversely proportional to the threshold below which the field can not be measured. A 25mm bulb has a 10kv m-1 threshold. The transmission of the light signal from the sensor to the detector is immune to electrical noise. The detector electronics is simple because the field magnitude information is contained in the number of pulses not in the magnitude of the pulses. This thesis presents the theoretical, experimental and field test results which explain the operation of the meter and substantiates its advantages. The basic physical model for the sensor is established by describing the relation between optical pulses and field magnitude, the effect of sensor shape on this relation, the operation of the sensor in elliptically polarized (including harmonic) fields and the effect of bulb size and gas composition on the phenomena. The basic practical considerations are investigated by studying the environmental effects on the performance of the meter, the lifetime and stability of the meter, the effect of the sensor on the field being measured and the general engineering of meter. This work has resulted in a fully tested prototype meter whose basic operation is well understood.

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2010-04-22

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http://hdl.handle.net/2429/24076

Engineering Physics

University of British Columbia

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