Computation of grounding conductors

Grounding conductors- these are metallic bodies (electrodes) supplied with a current I and buried underground. The ground has conductivity ?; current spreads in ground towards the second electrode named the collecting one. If through the grounding conductor a current flows for a long time then conductor is called a working one. Because of the stray currents destroying on one's way the metal products owing to electrochemical action, the working grounding conductors are applied as rarely as it is possible. If through the grounding conductor a current flows for a short time because of violation of me normal operation of a plant then conductor is called a protective one. In fig. 1 shown is a protective ground connection having resistance Rgc (a connection of neutral of the three-phase transformer with grounding conductor) for the protection of three-phase network from the earth connections. Special group of the protective ground connections consists of the protective connections, which protect a man from the affection by electric current at man's contact with frame of plant having defective isolation. The alternating current distribution in conducting medium differs from the direct current distribution because in case of alternating current in conducting medium the electromotive forces arise. But owing to big ground's resistivity at power frequency the electromotive forces are negligible in comparison with active voltage drop. That is why analyzing the grounding conductor the d-c field is examined. The resistance of the grounding conductor depends on many factors: a ground state (dry or wet), form and sizes of me conductor etc. That's why the grounding conductors' are computed approximately. It is counted by the involving of me assurance factor kaf—1,5?3. As long as a computation is approximate then the calculated form of the grounding conductor is chosen as simple for the computation as it is possible. The most simply calculated is the grounding conductor having form of a ball or a cylinder (pipe). A computation of the current field of the grounding conductor is fulfilled by method of mirror copies. At the same time necessarily calculated are the resistance of the grounding conductor (resistance between the grounding conductor and collecting electrode by the Ohm's law) and maximal step voltage (voltage on the ground surface in the region of the grounding conductor between two points on distance of pace of average man - 1P=0,8 m).