Edward F. Kelley

The electric field distribution associated with prebreakdown phenomena in nitrobenzene

The electric field distribution between a prebreakdown tree and the electrode toward which it is propagating is determined. The electric field is measured in nitrobenzene, using the electro‐optic Kerr effect. High‐speed photography is used to provide a 10‐ns resolution of the transient, prebreakdown events. The measurements show that to predict the Kerr fringe pattern, and thus the electric field distribution, it is sufficient to model the prebreakdown tree as a spherical conductor about the same size as the tree and at the potential of the electrode from which the tree is propagating.

Observation of Prebreakdown and Breakdown Phenomena in Liquid Hydrocarbons II. Non-Uniform Field Conditions

The prebreakdown and breakdown processes have been recorded in n-hexane toluene and Marcol 70, both in a pure state and with selected impurities. The study was carried out using a point-plane geometry. A low ionization potential additive had only a small effect on the breakdown voltage or the streamer propagation speed but did significantly alter the shape of the prebreakdown streamer when the needle was positive, an anode. For a negative needle, a cathode, chemical impurities affected the breakdown voltage. The significance of these findings is discussed in detail.

Electro-Optic Measurement of the Electric Field Distribution in Transformer Oil

A system has been developed to measure the electric fields in transformer oil using the electro-optic Kerr effect. The system performance was verified by measuring the electric field and space charge in nitrobenzene. The field distributions were measured in clean oil, in oil which had been used as a wash for a radiator used in a power transformer, and in oil which was removed from a transformer that had failed. Measurements were made from room temperature to 100°C. Under the conditions studied, the electric field strengths were generally within 10% of the strengths that would be predicted assuming that space charge was negligible.

Display Daylight Ambient Contrast Measurement Methods and Daylight Readability

We propose two composite metrics to characterize display reflection, contrast, and readability under daylight illumination. A measurement of the reflection under directed illumination simulating the sun is combined with a measurement of the reflection under uniform diffuse illumination to simulate the sky. The measurements are performed separately in a laboratory, and then the measurement results are combined and scaled to daylight levels with attention to the proper spectra involved for the skylight and sunlight.

Observation of prebreakdown and breakdown phenomena in liquid hydrocarbons

The prebreakdown and breakdown processes have been recorded in n-hexane toluene and Marcol 70, both in a pure state and with selected impurities. The study was carried out using a point-plane geometry. A low ionization potential additive had only a small effect on the breakdown voltage or the streamer propagation speed but did significantly alter the shape of the prebreakdown streamer when the needle was positive, an anode. For a negative needle, a cathode, chemical impurities affected the breakdown voltage. The significance of these findings is discussed in detail.

Prebreakdown Cathode Processes in Liquid Hydrocarbons

Measurements are presented of the initiation of prebreakdown streamers at a point cathode in liquid hydrocarbons. Using a computer implementation of the method of images, the electric field is computed for selected geometries to confirm that the field strengths in the vicinity of these streamers are probably high enough so that electron multiplication processes can occur. High magnification photographs of streamer initiation show that the initial streamer velocity is (2.8±0.4) x 104 cm/s in toluene.

Display Reflectance Model Based on the BRDF

Abstract Many flat panel displays (FPDs) have anti-reflection surface treatments that differ in character from those of traditional cathode-ray-tube displays. Specular reflection models (mirror-like, producing a distinct image) combined with diffuse (Lambertian) reflection models can be entirely inadequate to characterize the reflection properties of such displays. A third reflection component, called haze, exists between specular and diffuse. Display metrology should account for the haze component of reflection. That is best done using the bidirectional reflectance distribution function (BRDF). The effects of using oversimplified reflectance models are discussed in contrast with a parameterized BRDF.

11.3: Sensitivity of Display Reflection Measurements to Apparatus Geometry

Reflection measurements made upon electronic displays can suffer from non-reproducibility owing to their possible strong dependence upon apparatus geometry. The geometrical dependence arises from non-Lambertian diffusion properties. We show the inadequacies of several conventional reflection measurement methods and offer some guidance on how these methods might be improved or replaced.

Electrical Breakdown in Composite Insulating Systems: Liquid-Solid Interface Parallel to the Field

A study is presented which identifies some of the characteristics of electrical breakdown at a liquid-solid interface. The primary emphasis is on paper interfaces in transformer oil and studies are performed using impulse and using 60 Hz waveforms. The interfaces are parallel to the electric field. Several cylindrically-symmetric electrode geometries are employed ranging from plane-plane to sphere-sphere. The electrode system is split along the symmetry axis to hold the paper parallel to the field. Among the conclusions drawn from this study are the following: First, the breakdown frequently occurs at positions other than the interface for both impulse and 60 Hz waveforms. Second, no significant difference is identified between the breakdown voltage with or without an interface in the system or between the breakdown voltage when a breakdown occurs at an interface and when it does not.

Prebreakdown phenomena between sphere‐sphere electrodes in transformer oil

Measurements have been made of the propagation velocities of both cathode and anode streamers in transformer oil using sphere‐sphere electrodes. Under the conditions of these experiments, the cathode streamer development was a three‐step process, while the anode streamer development was a two‐step process. The average propagation velocities for the three‐steps of the cathode process were 2.4×104, 1.5×105, and 3.9×106 cm/s. The two steps of the anode process propagated at average velocities of 3.8×105 and 4.4×106 cm/s.