Equipment Earthing, Single point vs. two or more
Equipment Earthing, Single point vs. two or more
(OP)
In a substation or power plant, equipment are earthed from two points or more to provide redundant connection paths in case of losing one (cut, loose connection,...etc).
Some other practices limit the connection to equipment and foundations to one only to avoid circulating fault currents within them. (this case is similar to two point bonded cable sheaths).
any clue?
Some other practices limit the connection to equipment and foundations to one only to avoid circulating fault currents within them. (this case is similar to two point bonded cable sheaths).
any clue?






RE: Equipment Earthing, Single point vs. two or more
It is, to some extent, dependent on what distribution system you have. TN, IT, TT or whatever.
In my opinion, the dreaded "circulating fault current" is coveted and beneficial. The more low impedance paths there are, the lower the potential difference between different parts of a plant. That is why you have ground grids with multiple connections from machinery to grid and also, at least in process plants, an "above-ground" grid of conducting pipes and steel structures.
The "hum pick up" that so often is referred to is usually less when you have multiple connections to a good ground grid. The ultimate version is a continuous ground plane.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Equipment Earthing, Single point vs. two or more
Other area for the foundation earthing/bonding limitation is where the soil is highly corrosive and the foundation is protected.
Another area for such restriction could be the location where the cathodically protected installations are present. The presence of a slab reinforcement grid may cause draining of DC currents from co-located cathodic protection systems. Under such circumstances, due attention shall be paid to corrosion and CP aspects.
Otherwise, all earthing and bonding connections between the slab reinforcement grid, foundations, driven piles, construction elements and earth plates shall be in place.
Hope this helps.
RE: Equipment Earthing, Single point vs. two or more
RE: Equipment Earthing, Single point vs. two or more
RE: Equipment Earthing, Single point vs. two or more
NZ practice puts only one conductor per foundation.
RE: Equipment Earthing, Single point vs. two or more
Krisys. Due to electrolytic action the earth can be eaten away. I have been toying with the idea of putting in sacrificial plates of Zinc which will corrode faster and thus save the copper. I can’t get an answer from the environmental guys.
IEC 62305-3:2011, table 5 gives a table of materials with recommendations and indications of where corrosion will occur.
Karls2. We connect all our transformers with two separate earths to the earth bar. No daisy chain connections. I do not have access to IEEE standards.
mls1. We only have one point grounded at any one time. Besides the circulating currents, it can split your earth fault current and then the protection can’t see the full current and may fail to operate as designed.
Power0020. It looks like you are in New Zealand. I though you used the British regs. I would be interested to learn more about this one conductor per foundation. Please can you elaborate.
RE: Equipment Earthing, Single point vs. two or more
Regards
Marmite
RE: Equipment Earthing, Single point vs. two or more
Some times it's not only "is sized to carry the full prospective earth fault current" but sized for phases short circuit current also. (especially if you have 2 earth fault on two different phases)on the same site.
RE: Equipment Earthing, Single point vs. two or more
this is usually used for outdoor foundations.
Buildings are excluded from this required and rebars are eathed every 5 m.( that is usually not an issue with fault current circulation since the number and size of rebars in buildings will represent a huge conductor and hence no major heating)