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Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
I got my hands of a old NEBB (Norsk Elektriske Brown Boveri) medium voltage fuse, rated for 7200 V, 200 A and 350 MVA. My best guess from the company name is that it originates from before 1988 where NEBB was merged with ASEA into ABB.
Medium voltage fuses are used at the secondary side of distribution transformers, which are often the link from the transmission grid to the distribution grid.
Here is the video of the teardown and below are some of the pictures, which also are used in the video.
The fuse implements a Striker system that is a series of trigger mechanisms to let a spring loaded pin fly out of one end, in case of a fuse failure, to activate a mechanical shutdown or electrical feedback when there is a blown fuse due to over-voltage, over-current or too high temperature.
Here the disassembled fuse can be seen, the blown fuse element and the single small parts of the chain that has blown apart nice and evenly.
The still intact fulgurites from the melted fuse element can be seen here in greater detail. It is really interesting to see how the inside is now a insulated glass tunnel and the small silver beads have been pressed out and fused with the sand. The structure of the fuse element creates fulgurites that has alternating white stribes containing silver beads and yellow stribes that is only sand/glass.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
We used such fuses in motor starters in metal clad switch gear. If one blew the pin would trip the breaker controls. Protection against single phasing.
Almost always bad news. Of course, chance it, and maybe it let go due to old age.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
I was also surprised to find out that the silver fuse element has a working temperature between 180 and 230 degrees Celsius.
Did you ever had to pull a freshly blown one out? How warm was the tube, because as I understand the melting temperature trigger in the striker/end cap will fail at 100 degrees Celsius.
Those two temperatures is however not related, I guess the end cap temperature trigger must be there in case of heating for poor contact to the fuse holder.
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Teardown of a medium voltage fuse (7200 V / 200 A)
