Yes a shield has two primary jobs but ground impedance is far from zero at high frequency. The shield will not stay at fixed potential at high frequency for a noise source.
If there are three-phase input and a ground Cable summed current thru all four may be zero but there may be a current flow from the three-phase Cable to to ground cable. At high frequency impedance in ground cable is far from zero and there will noise on the ground cable. Nicklas Karlsson > On Mon, Mar 16, 2015 at 4:40 PM, Karlsson & Wang < > nicklas.karls...@karlssonwang.se> wrote: > >> I think you are right and will just try to dig a little bit deeper. >> >> A shield is primarily intended to prevent electrostatic coupling from >> the >> outside world. So by grounding in the consuming end the shield will get >> the >> ground potential of the consumer and the signal cables will be shielded >> from different external electric fields. This should motivate why as you >> say the shield should be connected in this end only. If there are >> current >> there is also a potential difference. >> >> I consider the VFD to be a noise source since it have common mode >> voltage >> which will emit an electrical field. There is also a capacitance between >> the VFD cables and shield. Since Shield impedance on high frequency is >> far >> from zero the shield around the VFD cables will not be at GND potential. >> The most common method is to increase common mode inductance by a filter >> but I have also seen active filters which reduce the common mode voltage >> and multiple step voltage inverters. >> >> >> Nicklas Karlsson >> > > > A shield has two primary jobs - keep interference from the outside getting > in, and keeping the signal inside the shield from getting out. > > Mark > ------------------------------------------------------------------------------ > Dive into the World of Parallel Programming The Go Parallel Website, > sponsored > by Intel and developed in partnership with Slashdot Media, is your hub for > all > things parallel software development, from weekly thought leadership blogs > to > news, videos, case studies, tutorials and more. Take a look and join the > conversation now. http://goparallel.sourceforge.net/ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------------ Dive into the World of Parallel Programming The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
