Electrical characteristics of horizontal glass melting furnaces and delivery Systems

Abstract

Leakage currents and their low resistance paths through refractories from the interior of glass melting furnaces to the binding steel are discussed. By defmition, a ground current flows from an electrode, through the intervening glass to ground through grounding conductors. All melters have leakage currents and may have ground currents. Current and voltage characteristics and phasor diagrams have been analyzed for some circuits that can be used in horizontal melters. The furnaces may be heated solely with electricity or in conjuncdon with fossil fuels. Phasor diagrams may be helpful in the design stage of a melter, may be useful for trouble-shoodng and to display electrical distributions for all parts in a precise form. Hence, totally unexpected voltage differences become easily understandable. Phasor diagrams can disclose wiring errors and/or undesirable voltage distributions and may suggest ways to improve electrical characteristics. For symmetrically built and cross-fired furnaces they show side-to-side symmetry and indicate that the central plane of these units can be Virtual or phantom grounds. They may also indicate the conditions minimizing voltage differences between adjacent electrodes. Voltage phasor diagrams are even more useful for longitudinally fired furnaces. For these units they also explain why ground currents occur and how to minimize them. Data from a salt water model with two cross-fired circuits connected to the same phase disclosed linear relations between the electric currents and voltages over a large range. In this ränge each line current was a hnear function of the two line voltages and vice versa and these variables could be treated as scalars. In addition, either line current could be forced to zero by appropriate voltage(s) in the other circuit. Somewhat similar results were obtained when two different phases were used but now neither current could be forced to zero by adjusting the voltage in the other circuit. Again in the linear range each hne current was a linear function of the line voltages and vice versa but the variables now had to be treated as phasors and not as scalar quantities. Salt water modelling with a longitudinally fired melt end yielded representative data showing how the applied voltages may be located on a ground current's voltage phasor in both the capped and uncapped condition.