Page B. Interpretation of Current Measurements on Underground 1. Relation of Stray Current to Corrosion.... 2. Relation of Current to Fires and Explosions... 109 109 2. Polarity of Pipe Changing with Long Periods of Several 111 3. Polarity of Pipes Reversing with Periods of Only a Few 111 4. Polarity of Pipes Reversing with Periods of from Fifteen 111 Table 8. Use of Negative Boosters (United Kingdom).. 129 Sec. 2. Rail Conductors 4. Economic Aspects of the Electrolysis Problem. F. Summary G. European Regulations Adopted and Proposed. Germany Sec. 1. Application of Rules.. Sec. 3. Rail Potential Sec. 4. Resistance Between Rail and Earth.. Sec. 5. Current Density 136 135 137 138 138 140 142 147 148 Chapter 5-Electrolysis Research Further Work Necessary to Arrive at a Solution of the Engineer Page ing Problem. 5. Determination of Safety Criterion for Pipes Where Positive to Earth 159 6. Self-Corrosion 159 7. Fire and Explosion Hazard on Gas and Oil Pipes.... 160 8. Heating of Power Cables Due to Stray Current on Sheaths.. 160 Summary 160 Track Construction, Track Leakage, and Rail Bonding. 162 Figure 2. Figure 1. Single Trolley Electric Railway Showing Paths of Return Current Page Figure 3. Figure 4. Figure 5. Potential Profile Showing Rails and Pipes without Connections Between Pipes and Railway Return Circuit... 33 Effect of Feeding Distance on Stray Current.. Effect of Feeding Distance on Overall Voltages and Potential Difference Between Earth and Rails.......... Figure 6. Reduction of Track Voltage Drop by Additional Power Supply Stations 35 36 37 Figure 7. Relation of Number of Substations to Annual Charges, for Interurban Line 39 Figure 9. Overall Voltage Curves, No Feeders... Figure 10. Figure 11. Figure 12. Graded Insulated Negative Feeder System.... Figure 8. Potential Profile of Two Independent Railway Systems Showing Effect of Interconnection.... Equi-Potential Insulated Negative Feeder System..... Tracks Figure 13. Insulated Negative Feeders Applied to Interurban Lines.. 51 43 45 45 47 49 Figure 17. quency .... Cross-Section of Insulating Joint for Power Cable Sheaths 64 Showing Necessity of Installing Insulating Joints in Services Connected to Mains Laid with Insulating Joints.. 67 Figure 19. Type B Bell for Cast Iron Pipe, Designed for Cement Joints tion Figures 21 and 22. Methods of Installing Leads for Current Test Sta Figure 20. Service Pipes Being Damaged Under Car Tracks by Elec71 trolysis 69 100 Figure 23. Differential Method of Making Roadbed Resistance Meas urements 103 Figure 25. German Tramway Rails.. Figure 24. Method of Making Roadbed Resistance Measurements on Open Track Construction 105 120 121 122 Figure 28. Figure 29. Typical Rail Bonds-United Kingdom.. 123 Figure 30. Track Construction-United Kingdom Figure 31. Track Construction and Rails-Germany.. Figures 32 and 33. Key to Calculation of Voltage Drop in Rails...... 145 Cross-Bonding Details, etc.-United Kingdom.. 125 126 131 PRINCIPLES AND DEFINITIONS A. ELECTROLYSIS IN GENERAL 1. Electrolysis is the process whereby an electric current passing from an electrode to an electrolyte or vice versa causes chemical changes to take place in the electrolyte. Electrolysis also includes any chemical changes at the surface of an electrode resulting from the chemical changes in the electrolyte. Electrolysis is independent of the heating effect of the electric current. NOTE. These changes usually occur in a water solution of an acid, alkali, or salt. By the passage of an electric current through it, water (containing a trace of acid) is decomposed into hydrogen and oxygen, copper is deposited from a solution of copper sulphate, silver from solutions of silver salts. Electroplating, electrotyping, and refining of metals by electrodeposition are useful applications of electrolysis in the arts. Electrolysis is involved in the charge and discharge of storage batteries, and in the operation of primary batteries. In order that electrolysis may occur, the following conditions must be present: (a) There must be a flow of electric current through a conducting liquid from one terminal to another; (b) The conducting liquid must be a chemical compound or solution which can be altered by the action of the electric current. 2. Electrolyte, Electrode, Anode, Cathode. The electrolyte is the solution (or fused salt) through which the electric current flows; the conducting terminals are the electrodes; the terminal by which the current enters the solution is the anode; the terminal by which it leaves is the cathode. NOTE. The chemical changes caused by the current may affect both the electrolyte and the electrodes. In the case of a solution of copper sulphate with copper plates as electrodes, copper is removed from the anode by the current and carried into solution; an equal amount of copper is deposited upon the cathode. In general the metal travels with the current toward the cathode. 3. Amount of Chemical Action. (Faraday's Law.) The amount of chemical action taking place at the anode and also at the cathode (as expressed by Faraday's Law) is proportional to (1) the strength of current flowing, (2) the duration of the current, and (3) the chemical equivalent weights of the substances. NOTE. Otherwise expressed, the quantity of metal or other substance separated is proportional to the total quantity of electricity passing and the electro-chemical equivalent of the substance or substances concerned. The electro-chemical equivalent of a metal is proportional to its atomic weight divided by its valence. Faraday's Law is so exactly realized in practice under favorable conditions that it is used as the basis for the definition of the international ampere, one of the fundamental electrical units. (See Passivity, Paragraph 15.) |