More on drop-out fuses

[Bung]

What is the experience out there with the failure rate of drop-out fuses? Around half of the drop-out fuse operations in the distribution area I work in are not due to electrical faults - the things just drop open seemingly of their own accord. I have a few ideas, mostly concerned with thermal effects (high percentage tin alloys, tin melts at 220C), poor contacts, contact springs possibly annealing, the cheap (and nasty) construction of the elements, and the efforts of big boofy blokes giving the nut a quick wrench with a 20" shifter to make sure it's tight.

The odd thing about it is that sometimes one particular location will be troublesome for a long while (up to 5 or 6 sets of fuses) before it "settles down".

Any ideas / suggestions, or is that just life with a 10 buck protective scheme? BTW, the fuses are generously rated and are used on 11kV/415V 3-phase distribution transformers at all sizes from 63kVA to 1000kVA.

Bung

 

[jbartos]

Suggestion: Visit

http://www.elektrolites.com/dropoutfuses.html

http://www.elektrolites.com/products.html

http://www.energy.com.au/ea/earetail.nsf/AttachmentsByTitle/CIA1146b/$FILE/cia1146B.pdf

http://www.fusegearelectric.com/profile.htm

http://energexdev.indelta.com.au/glossary_D.htm

http://www.yaohua-china.com/yaohua/i3-p3.htm

etc. for more info

 

[Bung]

jbartos, I don't have a problem with what a drop-out fuse is, or what it looks like, or its general application. I'm more interested in others experiences of their failures and failure modes.

Bung

 

[wbd]

On our distribution system (and others in the USA), cutouts (or drop out) fuses have been very reliable. Yes, occasionally one will open for no apparent fault (possible fuse link aging issue?). Recently, failures have been seen in the porcelin body where it cracks and breaks near the 2nd - 3rd skirt from the top.

The brand we use are S&C, 15kv, 100A.

wbd

 

[sunilji]

In the past 15 years, I have energized more then 300 transformers ranging from 63 KVA to 1750 KVA and on voltage levels of 11 kV, 22 kV and 33 kV. I have rarely faced a spurious blowing of a DO fuse while commissioning and most of the fuse failures reported are mostly during the wet season. The common causes I have seen for DO fuse blowing are : Insulator puncture, Lightnening Arrester failure, bird faults, X'mer winding failure and LT main cable faults in that order. Per se', I agree that a DO is a coarse ( read crude ) protection but it is eminently suitable for overhead distribution lines in rural areas where breakdown maintenance on feeders is carried out ( from patrolling to repair to re-energizing ) without the use a single test instrument !
BTW, DO fuses come at 1 buck a pop in my part of the world !!