thread238-410869
Had an engineering manager tell me they are concerned vertical end break switches (VEB) may fail by closing after being opened to isolate equipment for work. I would agree that double-end break (DEB) are generally more reliable/robust.
I have seen switches that failed due to...
Official response from GE: these PTs can be mounted in a vertical position as long as there is NO vibration. Probably not behind an LBS!
Matt Nissen, P.E.
IEEE Senior Member
All 15kV fixed mounted. Original design had bolted covers for access, with the PTs mounted behind a load-break switch. Ideally they would be in a separate compartment, with a hinged access door. The LBS cubicle is very narrow. Not sure draw-out design is possible with metal-enclosed gear -...
Anyone seen this before? I can't find a code reference but I can't confirm the OEM approves either. They are cast coil GE PTG5 2-fuse type.
Matt
M. Nissen,P.E.
Senior Electrical Engineer
Waldron Engineering & Construction
correction:
*Even with an infinite bus its only 500 /(0.4 x 1.732 x 0.05 )=14.5kA (below standard 22kA ratings).
M. Nissen,P.E.
Senior Electrical Engineer
Waldron Engineering & Construction
The 350MVAsc is the rating of a family of MV circuit breakers; if the system is designed properly the max fault from the utility is 350MVA / (11kV x 1.732) ~18.4kA; on these systems 15kA is a better estimate.
use this 11kV fault current thru the transformer and you will get your solution...
Run a short circuit simulation as I described, you can also get the utility fault current/impedance upon request (it may take some time).
Another equipment limitation that should be checked for would be the lightning arrestors that the utility uses; if they are rated for Y-g system, using...
7anoter4 - thanks for the manual calcs; I have to disagree, the GPR is dictated not by system voltage; it is almost purely fault current x impedance to ground. the R and X values are not zero, we calculated the Rgrid=1-2ohms.
thanks for confirming the use of PVC conduit for bare grounds, we...
I would recommend running a simulation using software. Generators have significant impedance and multiple units in parallel, with possibly different qty running will change the fault current. This is not easy to do by hand.
Some sizing criteria from experience:
-The max NGR current is 1 unit...
We have a 13.8kV switchgear located 11 stories above grade. When we run grounding conductors to down to the cellar ground grid in question, the "company standard" is to use bare CU cable in PVC. I am concerned that the GPR (even in rare instances) could damage the cable, conduit, or any other...
I am familiar with outside plant grounding grid design which IEEE addresses. Inside plants get complex. I am assuming a reasonably low soil resistance (~25ohm-m) and high moisture content.
We use ETAP for grounding grid calculations, we have successfully modeled a particular design based on...
Neutral Grounding configurations could come in many flavors. If the transformer neutrals are connected to a single point/bus, you can install a neutral switching system to select which source neutrals are grounded (transformers or generator, generally 1 at a time); this could be as few as...
Each service is required to have a separately derived ground electrode per NEC250. DO NOT CONNECT THE GROUND SYSTEMS! The utility transformer neutral/star point is the common grounding point, by adding parallel paths to ground you could create circulating currents.
M. Nissen,P.E.
Senior...
