Effect of oil quality on electrostatic charge generation and transport

A physical model is developed for the charge transfer boundary condition in semi-insulating liquids. The boundary condition is based upon interfacial chemical reactions and extends established relations for the interface by including the effects of interfacial surface charge and charge desorption at the interface. A steady state model for flow electrification in a rotating cylindrical electrode apparatus incorporated this boundary condition and described polarity changes in the open-circuit voltage and short-circuit current as a function of the fluid velocity, the volume charge density dependence an the terminal constraints, and the charge density dependence on applied dc voltages. Previously used boundary conditions are shown to be special cases of the chemical reaction rate boundary condition. A general methodology is developed for combining the volume charge density and voltage/current terminal measurements to estimate the parameters describing the interfacial charge transfer kinetics. Volume charge densities /spl rho//sup w/ on the liquid side of the interfaces of 1 to 20 mC/m/sup 3/ were estimated from the open-circuited electrode measurements, with the stainless steel /spl rho//sup w/ typically larger than that of copper but smaller than that of transformer pressboard. Activation energies for an Arrhenius temperature dependence of /spl sim/0.16 eV for pressboard, 0.25 eV for stainless steel and 0.28 eV for copper were obtained. Interfacial adsorption reaction velocities, estimated to be 10/sup -5/ m/s, were not large enough to make the terminal current transport limited which contradicts the often used assumption that the reaction velocities can be considered 'infinite'. Estimated surface reaction rates at a 70/spl deg/C stainless steel/oil interface of /spl sim/20 /spl mu/m/s for adsorption and /spl sim/0.5 s/sup -1/ for desorption were obtained. The additive BTA reduced the /spl rho//sup w/ for pressboard and stainless steel at concentrations >8 ppm in transformer oil.

A chemical reaction-based boundary condition for flow electrification

Space charge density at the wall in the case of heptane flowing through an insulating pipe

Scuffing detection of TU3 cam–follower contacts by electrostatic charge condition monitoring

Space charge density in dielectric and conductive liquids flowing through a glass pipe

In this paper we examine the flow electrification process appearing in power transformer in which oil is circulating. Our interest is focussed on the physicochemical reaction occurring at the contact between the oil and the pressboard. The study is divided in two sections. In the first one, we present two different models for the process of flow electrification when oil is flowing past the pressboard. The first model assumes that the ions provided by the pressboard are always in sufficient quantity to have a physicochemical reaction in equilibrium on the wall. In the second one we suppose that the wall shearing stress contribute to the production of these ions. In both cases we compute the evolution, in terms of the distance to the entry of the pipe, of the space charge density on the wall, of the total current and of the wall current density. The experimental work is divided into three parts. In the first one, we describe the general device on which we worked and the precautions we took to be sure to measure the flow electrification only. In the second part, we describe the experiments we did on duct 1 in order to get information on themore » migration of the charges from the interface oil-pressboard towards an earthed wall. In the third and last part of that experimental section, on duct 2 we study the phenomenon of charge of the pressboard when it is electrically isolated. Then we conclude with a comparison between the experimental and theoretical results.« less

Flow electrification in power transformers

The aim of our work is to understand better the mechanisms of flow electrification due to oil circulating inside a rectangular pressboard channel. This research has been done because of technical incidents in power transformers in which oil is flowing past pressboard with a velocity in the range of several meters per second. A possible explanation of the wall current observed along the channel is proposed. >

O. Moreau

Papers

Flow electrification in power transformers

Flow electrification in power transformers. Explanation of the wall-current measurements