Esther C. Cassidy

Optical methods of electrical measurement at high voltage levels

Optical methods to measure electric parameters and transmit the information from high voltage circuits to ground potential are described and evaluated in the light of the specific requirements of high-voltage measurement applications. The history and physics of a variety of optoelectrical methods found suitable for electrical measurement applications are introduced. Existing optical devices for measuring alternating, direct, and impulse currents and voltages in high-voltage circuits are reviewed with emphasis on the operation and features of several selected methods. The use of these techniques in industrial systems, in research laboratory apparatus, and in reference standards laboratories is discussed.

Kerr-effect Studies of an Insulating Liquid under Varied High-Voltage Conditions

Refined Kerr electrooptical fringe-pattern methods are used to study time and space variations in the electric field between the electrodes of parallel-plate capacitors filled with liquid nitrobenzene. Photographs of fringe-pattern data recorded during application of high direct (both positive and negative) and sinusoidal voltages, ranging in frequency from 40 to 200 Hz, are compiled to enable computation of space-charge distortions of the field in bulk of the liquid during the stress of high-field (up to 85-kV/ cm) operation. The measurements reveal significant differences between the field and charge behavior under short pulse (microsecond) voltage conditions, during prolonged dc operation, after sudden changes in the dc voltage level and polarity, and, for the first time, at various intervals over the course of entire cycles of sinusoidal voltage. The results show that space-charge distortion in the interelectrode field is influenced by the level, frequency, and duration of applied voltage. Discussions of effects believed due to particulate charge carriers, to electrohydrodynamic motion of the liquid, and to the electrode materials are also included.

Calibration of a Kerr Cell System for High-Voltage Pulse Measurements

Several techniques for calibration of an electrooptical (Kerr cell) high-voltage pulse measuring system are described. Independent calibrations, without reference to pulse divider measurements, are achieved by application of a direct bias voltage to the Kerr cell. After calibration, experiments with voltages as high as 100 kV demonstrate reasonable agreement (to within 1 percent) between simultaneous Kerr cell and calibrated pulse divider measurements.

Improved Techniques for the Measurement of High-Voltage Impulses Using the Electrooptic Kerr Effect

The purpose of this paper is to present two methods of accumulating, analyzing, and presenting in real time the data generated by a Kerr system in response to a high-voltage impulse. These methods provide immediate information concerning selected electrical parameters in a form which is easily interpretable by most personnel. The first method uses an electronic counter to determine the number of optical transmittance maxima, i.e., light pulses, duritg the high-voltage impulse. From this count, the peak value of impulse can be calculated. The second method, which can be more accurate and does provide information concerning waveshape, uses a digital recorder to store the output waveform from the Kerr system. A computer is then used to reconstruct the voltage impulse and to determine such parameters as the peak value and risetime of the impulse.

Pulsed Laser Kerr System Polarimeter for Electro‐Optical Fringe Pattern Measurement of Transient Electrical Parameters

Novel electro‐optical fringe pattern methods are developed for measurement of transient high voltages and electric fields. Several techniques employing the Kerr effect, a pulsed laser source, and high speed photographic recording equipment are described. Typical fringe pattern results are compared with conventional resistive divider measurements.

Measurement of 60 Hz Voltages Using the Kerr Effect

The Kerr effect has been used to measure 60 Hz alternating voltage up to 30 kV peak. The system behaves much as it does under the influence of a short high‐voltage pulse except that in this case the frequency of the applied voltage is sufficiently low that the space charge effects in the liquid are not negligible.

Recent Refinements and Developments in Kerr System Electrical Measurement Techniques

Kerr system electrical measurement techniques are improved by progress in two important areas: 1) in the development of methods for visualizing and measuring pulsed (microsecond) electric fields and high voltages from time-varying electrooptical fringe patterns recorded using high-speed photographic techniques, and 2) in the development of convenient experimental methods for evaluating and correcting path-dependent errors in Kerr system response. Results demonstrate use of fringe-pattern measurements in achieving accurate pulse voltage measurements and in correction of errors resulting from sizeable end-field variations in existing 300-kV Kerr cells.

Time Resolved Electrical Measurements in High Current Discharges

A method for measurement of the resistive component of the instantaneous voltage across a sample installed in a high voltage, high current circuit is described. Simultaneous measurement of the current permitted time resolved determination of electrical energy dissipation, power, and resistance of the sample. The system was calibrated calorimetrically, and measurements were made with exploding wire samples.

Electric field distributions and space charge behavior in nitrobenzene under low frequency alternating voltage

It has been shown that the electric field distribution and, consequently, the space charge distribution, in a liqUid insulant are different under direct and low frequency alternating voltage and that both differ from ideal distribution predictable from geometry. It has been recently shown that in commercial insulating liquids the breakdown is controlled by space charge.2 For lack of more substantial information, however, authors7 have obtained the breakdown field strength at 60 Hz in an insulating liqUid by measuring the breakdown voltage and calculating field from the electrode geometry. It is shown here that even with plane parallel electrodes the field can differ markedly from the ideal case because the electric field in a liqUid insulator is defined by both the electrode geometry and by the space charge dynamics within the fluid.

Time-Resolved Spectroscopic Studies of Exploding Wires in Controlled Atmospheres

A spectroscopic technique for continuous and time-resolved study of the atomic and molecular species produced by electrically exploded wires is described. A high-speed drum camera is utilized to record the time history of the explosion spectrum. More detailed studies (from photographic plates) of the spectrum at selected times are then conducted by use of a rotating shutter. Results are presented from experiments with aluminum wires exploded in various controlled atmospheres.