Open Cutout Fuse Failure

[jghrist]

One of our clients had a 65KS fuse in a 12.5 kV open type cutout "vaporize" instead of blow and drop out. No evidence of a fault was found. Could this be caused with load current by the link being improperly installed, perhaps not secured under tension? The fuse had been initially installed about two weeks prior to the failure.

 

[waross]

If this is the type of cut-out that I visualize, tension on the fuse link holds the toggle in position.
When the fuse blows, the spring clip is supposed to snap the fuse link down and out and allow the toggle to collapse to let the cut-out swing free.
If the bottom connection of the fuse link was not electrically secure due to looseness or dirt and corrosion then you could get a micro arc generating heat.
The heat produces heat corrosion that binds the toggle and the spring clip. The heat conducts up the fuse link and eventually takes out the fusible link.
When the link fuses, the toggle fails to collapse due to the heat damage.
Have you seen the hardware? Does the toggle look to be compromised by heat?

For toggle and spring clip, read Trunnion and Flipper Spring.
Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Hello again.
I was looking for a better picture of the fuse link fastening on the bottom of the cutout and I came across something interesting.
Apparently some cutouts require Arc Shortening Rods that must be installed in the fuse link. Failure to install the Rod may result in the fuse failing to extinguish the arc.
Link
Were any dead birds found near the base of the pole?

Bill
--------------------
"Why not the best?"
Jimmy Carter