Pole/Crossarm Fires 3

[MikeDB]

Is anyone aware of papers or articles addressing the problem of fires originating at the thru-bolt connection of wood crossarms to wood poles? I would also be interested in hearing from others who have experienced this type of problem. Specifics regarding voltage, type of construction, grounded or ungrounded hardware and ambient weather conditions would be of interest.

Thanks in advance for your information.

Mike

 

[ItAintMe]

Sorry I don't know of any papers on the subject but do have some experience with it. With the long dry period here, recent slight rains brought on quite a spate of pole top fires. They almost always occur at the bolt securing the insulator to the crossarm or the king bolt securing the crossarm to the pole. I'm aware of problems at voltages between 11kV and 132kV.

The fires occur because the insulators become polluted or start to fail internally (less common) causing increasing leakage currents. Because the timber is a poor conductor, the currents tend to concentrate around these wood/metal interfaces, increasing current density and producing localised heating which ultimately results in fires. Reduction of leakage currents is one reason for live line insulator washing programmes in vulnerable areas.

Various solutions have been tried, including use of metal paints or gang nails at these interfaces, to reduce the current density and so the localised heating. We have not had any problems I'm aware of on poles where we've replaced crossarms with post type insulators, especially composite types. So remedial options include washing, insulator replacement, care in selection of insulator types, replacing crossarms with post insulator construction, or reducing current densities.

One other cause I just recalled is cinders and burning debris from bushfires coming to rest on the crossarm or even in knot holes of the pole (another good rason for sealing up knot holes).

Some companies can supply you with insulation testers and devices that measure leakage currents to help identify susecptible locations.
Hope that is of some assistance and not too long.

 

[stevenal]

We found that plastic pole gains burn pretty good. I think we use galvanized now. We don't bond the insulator bases for fear of nuisance trips. Climate here is coastal, with lots of salt fog in the summer.

 

[sparky1976]

I've experince the same problems with concrete poles, metal crossarms, the bolts that secure the crossarm is burn/melted, grounding to every crossarms fix the problems. In 3 years untill now we donot experince the problem again, climate is coastal also.

 

[jbartos]

Suggestion: Visit

http://www.usace.army.mil/publications/armytm/tm5-684/app-c.pdf

for WQC Program