Stray voltages are electric currents in the earth which appear at its use as the carrying-out environment. Under their action there is a corrosion of metal objects which are in the earth or adjoin to it. As a rule, these objects are covers of electric cables, various building constructions and pipelines.
Stray voltages are characteristic of the electrified railway and tram tracks which are served in an inadequate way or emergency leak from power lines. Sometimes such currents call zero currents which exist in not grounded metal designs.
Sources of a stray voltage
Sources of currents in the earth are the subway, the tram electrified by a direct current suburban rail transport. Wires in such means of transport connect to plus a current source, and minus, to the return wire – railway lines.
Humus products, alkali, lime, sour marshy soil the containing lime, slag, ashes – create all conditions for intensive soil corrosion of covers from metal.
Because of weak isolation of a roadbed from the earth, the big resistance of railway lines and also the rail, partially current undergoes violations of joints to power supply minus by means of the earth. Meeting on the way the metal covers of cables, pipelines and other underground buildings, currents pass on these conductors and again return to the earth to get to minus of traction substation. In all this chain of a way of electric current there is an electrolysis phenomenon. Where metal covers of cables and a railway line are electrodes (anode and the cathode), and the damp earth containing a large amount of salts and acids – the electrolytic environment (electrolyte). And when moving a direct current through electrolyte, an electrode with higher potential it is dissolved.
Electrolysis – process of allocation of components of the substances which are in solution when passing through it electric current.
Scientists expected that at the size of a stray voltage in one ampere, in one year 33 kilograms of lead, 3.95 kilograms of aluminum and 9 kilograms of iron collapse. The lead cover on cable lines is exposed to the strongest destruction.
Prevention of stray voltages
Stray voltages take special measures for protection of underground constructions and metal covers of cables against corrosion: - whenever possible as much as possible reduce resistance of a railway line, by means of welding of joints a rail and isolation a rail from soil. - in rails apply special lines from the cable connecting different points a rail to the minus tire of substation to decrease in voltage drop. By these methods reach considerable unloading of rail network and decrease in quantity of stray voltages.