34.5kV service disconnect

[don_resqcapt19]

I was looking at the drawings for a 34.5 kV service disconnect and see that the 15 kVA control power transformer has a 19,220 volt primary and is connected phase to ground. Only the 3 phase conductors are run from the utility pole to the service disconnect switch. Is that the way this is normally done, or should the CPT have had a 34.5 kV primary and been connected line to line?

 

[Smart $]

I was looking at the drawings for a 34.5 kV service disconnect and see that the 15 kVA control power transformer has a 19,220 volt primary and is connected phase to ground. Only the 3 phase conductors are run from the utility pole to the service disconnect switch. Is that the way this is normally done, or should the CPT have had a 34.5 kV primary and been connected line to line?

With no grounded/grounding conductor run from the pole, I'd say the latter.

At 15kVA I'm guessing this CPT for a power-operated disconnect...???

 

[don_resqcapt19]

With no grounded/grounding conductor run from the pole, I'd say the latter.

At 15kVA I'm guessing this CPT for a power-operated disconnect...???

Actually it is the power for the lights, heat, and battery charger in the outdoor enclosure. The breaker is 48 volt DC.

It just didn't look right to me...seems like a SWER installation.

 

[Smart $]

Actually it is the power for the lights, heat, and battery charger in the outdoor enclosure. The breaker is 48 volt DC.

It just didn't look right to me...seems like a SWER installation.

With no grounded/grounding conductor, it'd have to be.

Are you sure the phase conductors don't have a grounded shield that's used for the 'return'? Aren't cables at that voltage required to have a grounded shield?

 

[don_resqcapt19]

With no grounded/grounding conductor, it'd have to be.

Are you sure the phase conductors don't have a grounded shield that's used for the 'return'? Aren't cables at that voltage required to have a grounded shield?

I don't see a connection to a utility conductor at the pole for the shields. It appears that the shields are only connected to the earth.

 

[Sahib]

Combined neutral and ground conductor not permitted by NEC. Perhaps equipment drawing of foreign origin?

 

[fmtjfw]

Combined neutral and ground conductor not permitted by NEC. Perhaps equipment drawing of foreign origin?

Combined neutral and ground conductor is permitted by NESC. A single ground/neutral conductor is frequently used by POCOs. POCOs more frequently use equipment rated 34.5kV than users who operate under NEC.

 

[Smart $]

I don't see a connection to a utility conductor at the pole for the shields. It appears that the shields are only connected to the earth.

I guess that would still amount to SWER... and I have to refute my statement regarding no grounded/grounding conductor run with phase conductors. The shields would have to be connected to a utility grounded conductor, not earth, to be non-SWER.

 

[texie]

I was looking at the drawings for a 34.5 kV service disconnect and see that the 15 kVA control power transformer has a 19,220 volt primary and is connected phase to ground. Only the 3 phase conductors are run from the utility pole to the service disconnect switch. Is that the way this is normally done, or should the CPT have had a 34.5 kV primary and been connected line to line?

It would seem to me that 250.186 would apply here.

 

[don_resqcapt19]

It would seem to me that 250.186 would apply here.

That section is new to the 2014 code. The installation is about 40 years old, but there is no real "service disconnect" now. When the plant was built the 34.5 kV distribution and the 34.5 to 480 transformers in the plant were all utility owned. A number of years ago the ownership of all of the equipment on the load side of the utility CTs and PTs was transferred to the plant, but no service disconnect was installed. The utility does have fused cutouts on the line side of their metering equipment.

 

[texie]

That section is new to the 2014 code. The installation is about 40 years old, but there is no real "service disconnect" now. When the plant was built the 34.5 kV distribution and the 34.5 to 480 transformers in the plant were all utility owned. A number of years ago the ownership of all of the equipment on the load side of the utility CTs and PTs was transferred to the plant, but no service disconnect was installed. The utility does have fused cutouts on the line side of their metering equipment.

Yes, I meant to mention that it was new. At various code meetings, the discussions indicated that reason for this was to correct what was always intended. Of course it would only apply if the system is grounded at ANY point.
But in your case, based on the voltages you have mentioned indicate that this is a Y system, I can't imagine a Y system like this being ungrounded.

Of course I'm just speculating here based on limited knowledge of high voltage distribution as this is not an area I can claim much experience in.

 

[don_resqcapt19]

Yes, I meant to mention that it was new. At various code meetings, the discussions indicated that reason for this was to correct what was always intended. Of course it would only apply if the system is grounded at ANY point.
But in your case, based on the voltages you have mentioned indicate that this is a Y system, I can't imagine a Y system like this being ungrounded.

Of course I'm just speculating here based on limited knowledge of high voltage distribution as this is not an area I can claim much experience in.

I don't have much experience in this area either. I am guessing that the 34.5 from the utility is a grounded Y, but am not sure.

The phase to ground connection on the CPT just jumped out at me when I was looking at the drawings.