Fused VT's for Customer meter cluster

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prajwal2341995

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New Jersey
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Electrical Engineer
Hello,

I am working on a project, and we need to add the external fuses to VT's/PT's on the meter cluster shown in the image (link).
As per my calculation the fuse sizes are as per the spec sheet I have attached for VT's:
VA Burden= 75VA, IC Voltage=12.45KV

Pri: 75/(12470*1.732)= 0.0034 A = 1Amp fuse
Sec: 75/120= 0.625= 1Amp or 5Amp fuse
Link for image -- https://ibb.co/y0PY3pR
Link for Cutsheet- https://ibb.co/n6YJPjF


My plan is using the fuse cutouts of (3)1Amp, 12.47 KV rated will be installed on the cross arm on the pole and (3)5Amp, 120V rated in the fuse box.
Can anyone please guide me if I am on correct path for this issue? If not, can anyone guide me how we can make these connections happen?
 
Instrument transformer protection is done slightly different than that for small power transformers. Short circuit protection is more of a concern than is overcurrent, so it is common to size to the maximum allowed.
 
Understood. These PTs/VTs are small transformer so we have to size these external fuses in some other ways? If so, then how can I get this done? and what should be the specs for the fuses on both pri and sec of the PTs/VTs.
 
These very low rating (1 amp) medium-voltage fuses are pretty sensitive and prone to nuisance tripping. Many utilities don't even fuse the primary. I agree with Jim, if you are putting in primary fuses, size them at the maximum value allowed by whatever code you are under.
 
Make sense. It means it's better to have the fuse on the secondary side only which again will be 1 Amp to 5Amp. In this condition can we get it away by (2) 5Amp, 120V rated, in fuse box, which we are planning to install inside the SEL meter enclosure?

Here our utility is JCP&L and we are following NEC 2020. This is the requirement coming from JCP&L here.
 
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I really need help with this since I am unable to find the exact solution for this issue. Want to give you all background of this. We are working with JCP&L on a utility scale project with IC V- 12.47KV. As per there requirement they want the PTs/ VTs to be fused on both sides (Pri & Sec). This PTs is 60:1(3) with 0.2% accuracy.

As per the cutsheet attached above the PT primary volt is 12.47KV and Secondary volt is 120V. Currently the PT we have precured is non fused and because of the lead time we cannot afford to buy new fused PTs. So that reason we have come up with the solution of adding external PTs.

The full ampacity is 95A. For the better understanding I am attaching the one line. This can give you better picture.
https://ibb.co/cbXrQ86

As per my calculation I have come up with the fuse size as mentioned above. What should be the specs for the fuses size for this?
 
Based on a primary of .0034 amps, you are probably okay with a 1 amp fuse. Contact your favorite manufacturer for more application assistance. Do you need to spec the fuse cutout as well as the fuse link?
 
jim dungar said:
Based on a primary of .0034 amps, you are probably okay with a 1 amp fuse. Contact your favorite manufacturer for more application assistance. Do you need to spec the fuse cutout as well as the fuse link?
Click to expand...
Understood, thank you Jim. And yes, we also need to spec the fuse cutouts as well.
 
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