Recirculating currents?
Recirculating currents?
(OP)
Can anyone explain the concept of recirculating earth currents please? It is our practice to earth at one end -or at a single point only, in a distribution system to 'avoid recirculating currents' We have blindly followed this practice without giving it too much thought but now I'd like to know more..
Thanks
PG
Thanks
PG






RE: Recirculating currents?
To avoid the overvoltage situation we've installed surge arrestors on the ungrounded end of long runs.
Also see the following excerpt from Southwire:
http://www.southwire.com/tech/library/pc/pwrcab04.htm
RE: Recirculating currents?
When a system ground fault occurs, the current flowing in the earth results in different potentials at different locations. If you connect separate ends of a cable shield to ground, this creates a parallel path for ground current to flow, giving rise to the effects noted above.
For single end grounding, the shield transfers the potential of the grounded end to the other end, giving rise to the need for surge arrestors and various other means of personnel/equipment protection. In some cases, the shield is grounded at the middle of the cable run to mitigate this condition.
On re-reading the original post, it seems that Powergen may have meant system grounding, rather than cable grounding. If this was the case, then the answer is that single point grounding makes ground fault detection and protection somewhat easier, as all ground fault current returns through the grounded transformer neutral. Multipoint grounding is also widely used in distribution systems, as in the multi-grounded common neutral configuration. For this case, some of the ground fault current returns to the source transformer neutral via the system neutral conductor, as does unbalanced load current.
RE: Recirculating currents?
RE: Recirculating currents?
RE: Recirculating currents?
RE: Recirculating currents?
From a magnetic shielding standpoint, a double-end grounded cable will have a ground current that tends to flow in opposition to the net conductor current, providing a self-magnetic shielding effect against interfering with nearby sensitive circuits. But this circulating current also causes heating which must be accounted for in establishing the cable current-carrying capability.
Also the double-end grounded cable avoids the concern of a large induced voltage which may exist at the ungrounded end of long single-end grounded cables.
As far as how the doulbe-end grounded cable behaves during a fault which might tend to establish differences in ground potential at both ends... I don't know.