Wednesday, April 13, 2011

Week 10 - Line Mechanic - The start of the Bromley-Dallington line build

Well, a new week, a new trade!

Trucks 'locked and loaded'!

Work log:

Monday 4th April: Start installing 66kV poles on Strathfield Avenue.

Strathfield Avenue approximate pole locations

Pole vertical waiting for digger

Tuesday 5th April: Install poles down Gayhurst Road.

Gayhurst Road approximate pole locations

Tuesday Gayhurst Road in the rain

Wednesday, Thursday, Friday 6th-8th April: Install poles down McBratneys Road almost to the river.

The McBratneys Road approximate pole locations.

Lifting the pole

Reflection on first week in Lines:

On Monday, I went to the yard, where Phil (my primary contact at Connetics) introduced me to Peter (Head of Lines), who in turn introduced me to Carl (Leading Hand). Carl would be my supervisor also for at least the 66kV job we were to do (covered later in 'Analysis').

I had a fantastic time, getting the taste of a whole new ballgame in lines. Compared to jointing, where nearly everything is underground, this week involved digging three-and-a-half metre deep holes for treated Australian hardwood poles that are 15 and a half metres tall, protruding 12 metres above the ground. Insulators and crossarms were installed on the poles previous to erection, and poles were set according to a plan, some slightly angled on purpose.

Me holding the crossarm in place while 'somebody' gets the washers and bolts!

Difficulties included poor weather, traffic, hole dynamics, and the public. Once again, as with all Connetics work activity, safety is paramount, and all the Connetics workers I worked with showed a competence and confidence that put my mind at ease. As with the Cable Jointers, the Line Mechanics are extremely proud of their  work, and set extremely high standards for themselves. I am going to refrain from commenting on the psyche of a Line Mechanic, I'll get to know them better first! Once again, I consider myself extremely lucky to be part of the Christchurch recovery and see history being made by these highly competent workers.

Analysis: Installing 66,000 volt poles in the ground

Installing such massive poles of wood in the ground in an urban area is no easy task. Navigating traffic, dealing with different soil types, poor weather conditions and avoiding other underground services are just some of the challenges facing Line Mechanics.

The reason that the 66kV overhead is being installed from Bromley Substation to Dallington Substation is to consolidate the damaged Christchurch power network due to the 22 February earthquake.

The 66kV overhead circuit plan
 Four large 66kV underground cables were seriously damaged in Christchurch as well as the New Brighton Substation sinking, damaging the building and associated electrical equipment. The New Brighton Substation has been rapidly repaired already and had a 66kV overhead run to it, but it will be also relocated to Rawhiti Domain, where there is a lesser chance of further liquefaction. See HERE.

The first point if call for the Line Mechanic is to consult the 'plan'. A schematic diagram is available that shows the position the poles are to be inserted into the ground. This plan also shows other underground services, which gives the Line Mechanic an idea of where to dig.

The plan.

Network planners also visit the site previously and mark the ground in spraypaint where other services are and where the recommended position is for the pole to be placed.

Poles are then assembled, in our case, a nearby lot was converted to an 'assembly area' of sorts. Insulators, crossarms and rodent guards are attached to the suitable poles and the poles are subsequently transported to where they will be installed.

Assembling the crossarms
Rodent guard in place and attaching crossarm

Holes are initially dug very carefully, some by hand and some by very skilled digger drivers, depending on what the level of risk is of hitting an underground service. The Line Mechanics watch very carefully to see any sign an underground service (power cables, telecommunication cables, water mains, sewer mains and stormwater drains) has been exposed. Once the one-metre depth is hit, the chance of hitting a service reduces significantly, so the mechanical digger is then employed to dig to the 3.5 metre depth. The shape of the hole (in our particular case, as it changes) is a 'slot', the digger using a bucket about 500mm wide. The length of the slot varies depending on the amount of available room.

A 'pole hole', well, slot! Complete with water table water in the bottom.
Looking out for other services

Soil types can impede the correct depth being reached. Sandy and wet soil can 'cave-in' quickly, so the process is done reasonably rapidly, still whilst maintaining safety. An interesting occurrence for me was the range of different soil types that we struck while digging. We struck black coarse sand, jelly-like mud, yellowy  beach-like sand and also clay.

Sandy soil..note how it's given way under the tarmac footpath.

'Jelly-like' mud.. might explain all the 'wobbling'...
To ensure rapid insertion, the pole is stood vertically next to the hole and held in place using the Line Mechanic truck's hydraulic crane and a heavy-duty chain. Once the 3.5 metre depth is reached, the pole is lifted and guided into the hole. This can be another challenge, as trees, overhead low-voltage and telecommunication cables must be avoided also. Skilled hydraulic crane drivers guide the poles in the ground.

Guiding the pole in

Once the pole is in place, the hole naturally starts to 'cave-in', but also the diggers replace some of the soil dug up, and also put gravel in too. Cement powder is added sparingly, to make the soil 'firm', but not so firm as the pole will be removed with difficulty. During refilling, the pole is monitored for vertical angle and that the insulators are aligned correctly. Poles that are set at purpose (less than vertical) angles are braced underground with short hardwood horizontal poles.

Carl measuring verticality using a 'plumb-bob'.

Looks all good to me..

Filling the hole

Awesome Pete getting a difficult pole lined up
Jono the Connetics CEO (right) on a site visit
Poles into the distance.. 

Finally, the soil is compacted, topsoil and grass seed is applied. Reflective markers are attached to the poles, and they are finished! Next; installing the cables (next week!)

My dream job!


selena said...

Hi Andrew,

great to read your blog this morning. The analysis section is a very good description of the process :) How can you use this to not only provide a description of the process, but for your students to also 'critique' and learn from reading the description? Thereby, attaining some of the skills the line machanics take for granted - how deep to dig, what to look for with underground services, how to deal with different soil types etc.

Have a good week, Selena

yanni said...

Hi Andrew

Love this blog.I'm a final year Electrical Engineering student and it's pretty rad to see the vast array of skills needed by contractors to bring the Engineer's/Planner's drawing to life.

Much respect and I look forward to more posts.


Andrew said...

Thanks, Selena, will do next week. Thanks also, Yanosh! Nice to get feedback! If you've got specific questions, feel free to ask.