Measurement grounding resistance

Fig. 9-9 Measured grounding resistances of anode installations [the straight line corresponds to Eq. (9-5) with from Fig. (9-3)].

The measured grounding resistances of the anodes were 6.5 Q for the 24-m-long ring anode and 8 Q for the three 7-m-long vertical anodes and were within the range of the calculated design values. By gradual adjustment of values, the protection potential of the initial protection current density amounted to about 450 /tA m. ... 

Figure 22.7 Measuring the ground resistance with the help ot a ground tester...

A simple way to measure the resistivity of soil is a four-pin method in which four probes are drilled into the ground along a straight line at equal distances a and depth b. Then a voltage V is applied to the two inner probes and a current, T, is measured in the two outer probes (Figure 22.16). This test can also be conducted with the help of a ground icster as discussed in Section 22.3, which normally also has a provision for ihis test. 

Guide for measuring earth resistivity, ground impedance and earth stirface potentials of a ground system. Part I Normal measurements... 

Fig. 3-19 Measurement of the grounding resistance of a soil electrode (explanation in text).

The grounding resistance of the three anodes with the stated dimensions of the coke backfill, a soil resistivity of 75 D m and an interference factor, F = 1.2, was calculated from Eq. (24-35) as about 14 Q. After the anode installation was in operation, measurements of the grounding resistance gave a value of about 12 Q. 

Only local cathodic protection can be used for large installations and old installations with electrical contact to components with low grounding resistances that cannot be isolated (see Section 12.6). The measures necessary for tank installations are described in Ref. 10. 

The current requirement depends on the leakage load [Eq. (24-71)] and the dimensions of the protected surface [12]. Measures to reduce the leakage load are described in Section 10.2.2. The level of current output from galvanic anodes or the grounding resistance of impressed current anodes—and with it the necessary rectifier output voltage for supplying the protection current—depend mainly on the soil resistivity. 

For these formulas the grounding resistance on the water surface (p = 54 D cm) of an iron plate was measured with a thin plate with dimensions a x 1 in the electrolytic... 

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