Bonding utility service feeding backup power to a substation control enclosure

[SVanL]

There has been an ongoing debate between design EE's concerning how and where to bond a utility service into a control enclosure in an electrical substation. I currently have a pad mount transformer feeding a combination meter socket/main breaker disconnect 220 A, 120/240vac 1 phase. The pad mount transformer and meter socket are about 30' outside the substation fence with an underground PVC conduit feeding the enclosure. It is utilized when the station service transformer in the substation is turned off and the utility service maintains environmental and battery charger functions via an automatic transfer switch. There is also a fused disconnect switch inside the enclosure prior to the transfer switch. NEC requires the first point of disconnect to be bonded to the neutral, which in this case would be the main breaker adjacent to the meter socket. This, in essence would make the main panel inside the enclosure technically a sub panel, but in the case of a substation, a fault high voltage potential could be introduced back on to the utility if a ground conductor is installed in the conduit feeding the service equipment inside the enclosure. We typically treat the main breaker exterior of the substation as if it were not there and bond our utility and station service transformer systems inside the enclosure. Would you also carry the 4/0 substation ground grid out to the structure rack or isolate it and ground using ground rods? I get differing opinions from different engineers. Any questions let me know, but I'm looking for a consensus. Intelligent responses back only please.

 

[tom baker]

Your disconnect at the meter could be labeled as an emergency disconnect with neutral bonding downstream

 

[jaggedben]

...The pad mount transformer and meter socket are about 30' outside the substation fence with an underground PVC conduit feeding the enclosure. ... NEC requires the first point of disconnect to be bonded to the neutral, which in this case would be the main breaker adjacent to the meter socket. This, in essence would make the main panel inside the enclosure technically a sub panel, but in the case of a substation, a fault high voltage potential could be introduced back on to the utility if a ground conductor is installed in the conduit feeding the service equipment inside the enclosure.

I take it you're not proposing to have neither an EGC in the PVC conduit nor bond the neutral inside the enclosure. That would obviously introduce other dangers. But if you're going to bond the neutral inside the enclosure then I don't see what real difference it makes to the high voltage fault. The electrons don't care if the wire is green or white.

 

[Elect117]

Is the primary side of the utility transformer derived from the substation? As in 69kv:16kv and that circuit is feeding the primary side of the utility transformer?

Is the ATS 2 pole or 3 pole (neutral switched)?