Electrical earthing testing. We are asked frequently - How do you test an Earth in London?
Here’s the scenario. You’re faced with Electrical earthing testing a substation that is located right in the middle of a heavily built-up area. With hard surfaces everywhere together with congested buried infrastructure in every direction.
Any lead deployment is invariably obstructed by something, e.g. roads, cars, walls, buildings, etc. And, assuming the leads can be accommodated. A test is likely to suffer in-ground noise and/or interference from the city’s / town’s infrastructure. Not to mention the curious passers-by: who would like nothing more than to see you struggle for a laugh by stealing your test leads when you’re back is turned.
EN 50522:2010, pg 30, states:
Measurements shall be carried out after construction, where necessary, to verify the adequacy of the design.
Design and installation of the earthing system shall allow measurements to be carried out periodically or following major changes affecting fundamental requirements, or even for continuity tests.
We’ve posted a number of blogs on the importance of following best practice when doing Fall-of-Potential testing, and some of the pitfalls with the technique. But sometimes it’s simply not possible to deploy leads to the distance required to escape the area of influence of the Earth system while avoiding physical obstructions. This is quite common in built up areas like London.
In situations like this, it’s really important to have an accurate soil model, using the Wenner method, and to use a bit of ingenuity. Perhaps you can’t deploy leads to fully escape the area of influence of the Earth system, but you can escape the area of influence of 1 rod, or maybe you can use a clamp meter. The key aim of these tests is to validate the soil model against what you actually encounter on site.
If you can get good agreement between the resistances. You CAN measure on site and in the model. Then use the modelled Earth resistance as your “real world” earth resistance - you have effectively calibrated your model against the real world.
This is another of these situations where the CDEGS version becomes really important. Only HIFREQ can accurately model the interactions between the test leads and the earth system, to give you full confidence that the model truly agrees with the measured results.
These techniques, in combination with CDEGS, trained and accredited engineers allow us to deliver right-sized designs in the most complicated of environments.
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Hugh is a Research Engineer at GreyMatters, joining in 2014. He graduated from the University of Bath, sponsored by the IET's Power Academy scheme. Hugh has a strong technical background with National Grid working on T&D schemes at voltages from 132 kV to 400 kV. Outside of work, you can find him cycling and fly fishing, or backstage at various local amateur dramatic companies.