V.T secondary fuse housing 1

[EEJaime]

Good day all,

I have an existing substation with a 500kV primary to 4.16kV secondary station transformer. We are extending the secondary overhead 3" aluminum busway to allow for us to connect a 10 mW solar power plant. I am mounting the VT's on the structures supporting the overhead busway. I am housing the fuses for the 4.16 kV and for the 120V side of the Vt's on the support structures. I had called for housing the fuses, clips and wiring terminals in non-metallic Hoffman type fiberglass enclosures. We have a comment from the client LADWP that questions our use of these enclosures because he says they are not designed for medium Voltage applications. I have three 2 Amp fuses and clips along with a couple of terminal strips to house in an enclosure. I want it in an enclosure as this is out in the high desert and don't want them exposed to the constantly blowing wind and sand. What do those of you whom do this on a daily basis use? Does a fiberglass enclosure need to be listed for mV use?

As always, thank you in advance and kind regards,
EEJaime

 

[jghrist]

I am housing the fuses for the 4.16 kV and for the 120V side of the Vt's on the support structures. I had called for housing the fuses, clips and wiring terminals in non-metallic Hoffman type fiberglass enclosures.

Does this mean that the Hoffman enclosures will include both 4.16 kV and 120V fuses? If so, then they would have to be suitable for 4.16 kV, but I can't quite picture how this is going to be installed.

 

[EEJaime]

Jghrist,
I guess my description was a bit vague. I don't have the facilities here to include a sketch so will try to describe the connection in more detail. I will do so for one of the three phases for clarity.

1) From the terminal pad where the ACSR conductor which connects to the circuit breaker, a second terminal pad connects to the overhead aluminum bus with another ACSR lead which terminates to a terminal on the primary side of a 4.16kV fuse clip and fuse.

2) This assembly is housed in a fiberglass enclosure mounted to the structure. The secondary side of the fuse clip then has a terminal where another ACSR conductor connects it to the primary terminal of a 20:1 P.T.

3) This PT is bracket mounted to the structure below the 4.16kV fuse enclosure.

4) The secondary side wiring from the PT ,(now 120V wiring), then connects to another fuse clip/fuse assembly housed in a second enclosure below the PT/shelf assembly.

5) The conductors then proceed the meters, synch check relay etc....

So the structure viewed in elevation would have from top to bottom:
1) @+15'-0"- 3Phase, 4.16kV, 3" dia., IPS aluminum bus assembly.
2) @+12'-0 - 3Phase, 4.16kV, 2Amp fuses in fuse clips mounted in a "Hoffman" fiberglass encl.
3) @+9'-0" - 3-20:1,(2400:120), PT's on a bracket
4) @+6'-0" - 3- 120 V fuses/fuse clips housed in a fiberglass housing.
5) from there routed below grade to the circuit breaker bay and relay house-120V wiring.

Sorry for the tedious description, had I been near the home or office, I'd have sent a sketch.
Good evening, (here in southern California anyway),
EEJaime

 

[jghrist]

It would be better to use open type cutouts for the primary VT fuses. These would be properly insulated and could be opened with hotsticks to isolate the VTs. How do the ACSR leads get into and out of the fiberglass enclosure holding the primary fuses? The fiberglass enclosure is not proper insulation between the primary bare ACSR and the structure.

 

[scottf]

Why put 5 kV class fuse in an enclosure? As said above, the normal practice would be to use outdoor, cut-out type fuses.

 

[EEJaime]

jghrist, scottf,
Thank you, you are right, that makes much more sense. I will proceed with that,that should clean up the installation quite nicely. Appreciate the input.
Regards,
EEJaime