Groundbed 3

We have not had access to this TR and have no information about it's performance or settings. It will be necessary to carry out a groundbed profile and a ground potential survey with this TR switching over the zinc strip anode section.

This is because if there are sufficient charges in the ground to overcome the EMF of the zinc, then that is where the current will flow, protecting the zinc interfering with the 'AC mitigation'

In the case of this particular groundbed it is likely that the majority of the current will flow through the zinc ribbon anodes and that increasing the output (in either voltage or current) will have little influence over the spread of protection towards ICCPS 4.

We visited this groundbed with Roger Barker and carried out a partial groundbed potential profile with the TR set at about 5.9 volts.



It can be seen that the 2 volts between the two half-cells can be plotted as the actual ground potentials and these can be related to the potentials that were taken using the pipeline as zero.

The pipe to soil voltages at the TR were 1.89v and 2.19v with the half-cell moved from far side to closer to the groundbed showing that the immediate area of influence extends over the pipeline at this location.



It is likely that the charges are flowing through the zinc to the pipe in a short circuit that restricts the spread of CP current.

There is also the possibility that increasing the output of this TR could cause the ground below the pylons to be at a higher potential than the ground below other pylons that are using a connected earth wire. This might offer another path in the distribution of charges fron this TR.

All this can be tested by switching this TR alone and recording the effects at remote test posts on this pipeline.

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