How Much Does DC Power System Ground Current Corrode Rebar and Ground Rings/Rods?

March 17, 2020
11:30 am  -  12:10 pm

Telecommunications has long used DC powering, with attendant DC currents flowing on the grounding system (sometimes intentionally, and sometimes not; although DC currents flowing on the grounding systems of telecommunications sites have generally been decreasing [the reasons for this will be covered]).  DC power systems also appear sometimes in Data Centers (although this is more common internationally at present than it is in North America).  Telecommunications facilities also serve electric generating sites that are natively DC, such as solar farms (even wind farms usually have a DC portion).  With the growth in non-predictable wind and solar power as a percentage of the electric grid’s supply, Battery Energy Storage Systems (BESS), which are natively DC, are often being collocated with large wind and solar farms to provide smoothing of the supply.  Finally, buried copper telecommunications cables also can have unintentional influence from other industrial DC (or high ripple DC) ground currents, such as Light Rail. 

 

All of the above do, will, or can lead to DC currents on site grounding systems, and these DC currents corrode buried grounding systems and any structural steel (think rebar) that is bonded to the site grounding system.  What is less well known is how much corrosion actually occurs, and how to accurately measure DC currents so that corrosion rates can be calculated. 

 

This presentation aims to educate the audience on how much DC-current-caused corrosion really occurs on ground systems and structural rebar at sites, and how to accurately measure the DC current so that corrosion rates can potentially be calculated.  Measuring DC current accurately is much more difficult than measuring AC current because the DC magnetic field set up by the DC current doesn’t induce a current into a CT (therefore, Hall Effect sensors are used, and these are inherently less accurate than the measurement of induced current).  Guidance will be provided on how to accurately measure grounding system DC currents (especially small currents).