Wednesday, April 20, 2011

Week 11-Finishing the Bromley-Dallington build

Poles in on the 66kV line from Bromley to Dallington, time to run the conductors (lines).

Work log:

Monday 11th April: Install conductors on Gayhurst Road.

Tuesday & Wednesday 12th & 13th April: Install conductors on McBratneys Road.

Thursday 14th April: Install conductors on Strathfield Road.

Friday 15th April: Install 2x poles and associated conductors for termination into Dallington Substation.

Analysis: Installing 66kV conductors on poles

Unprecedented in Christchurch, these lines are a 3-year 'stop gap' to keep electricity running in Eastern Christchurch. Easier to maintain and repair than underground 66kV cables, these are a sensible solution in the meantime until new underground cables can be run. Orion has produced a time line of work they want done on the Christchurch network HERE.

Now that the poles are in place, which are effectively the anchor points for conductors, the conductors can now be run. Preparation for this involves having drums of the conductor loaded onto big cable drum rollers on trailers.

Three cable drum rollers. These have a braking system on them. The concrete block is for restraining poles on the end of the run.

The conductor, referred to also as 'line' or 'cable'. Aluminium outer with steel wire core for hanging strength. 

Cross section of the conductor. The aluminium outer cores can be seen  and the inner smaller steel cores in the centre.

Labelling on the drum.  The 6/4.72 HDAL refers to 6 cores of 4.72mm diameter high density aluminium. The +7/1.57 GSW refers to additional 7 cores of 1.57mm diameter general steel wire. 'Dog ACSR' refers to a name the manufacturer gives to the cable, i.e. Dog, Jaguar, Mink, Raven, etc. and ACSR is an acronym for 'aluminium conductor, steel reinforced'.

When running overhead conductors which are higher than other live conductors, care must be taken to avoid contact with those conductors. Insulators are attached to live conductors that the conductor being run may potentially come into contact with.

Attaching insulators to live conductors so contact cannot be made with the new conductor being run. Note the fibreglass ladder, not metal, so it itself is insulated. 

More insulators attached
The insulators are designed to stay on once attached.
Once the insulator protection is in place, and rollers are installed in place on the poletop insulator arms, the conductors can then be run. Depending on the length of run, they can be pulled by hand. The trick is to thread them up and over all associated overhead services. High Voltage rated gloves are worn by all Line Mechanics in case the conductor does contact live conductors.

Conductors running through rollers for tightening

Pulling the conductor by hand whilst threading it.
On longer runs, the weight of the conductor needs to be pulled by something more substantial than by hand as it becomes too heavy.

Ensuring conductors don't contact other live conductors.

Conductors loosely in place

The conductors are then tightened loosely, and a temperature is taken at the height of the poletop insulators. This temperature is compared to a table and the correct tension 'droop' of the conductors is set. Temperature is taken to allow for expansion and contraction of the conductor. Once the correct tension is set using winches, the rollers in the poletop insulators are replaced with conductor clamps and 'line protectors' are installed.

Peter installing 'line protectors'. These are another layer of high tensile aluminium cores on the outside of the conductor cores.  There's a knack to installing these!
'Line protectors'. These are for 'Dog' conductor.

Conductor clamp (undone)

Clamps tightened and finished pole. The 'line protectors' are clearly visible.
The 'ends' of each run are terminated using 'pistol grips'. These are specially shaped crimps that form conductor terminations at corners and junctions. The 'pistol grips' are tightened using hydraulic crimpers.

'Pistol grips'. These are also filled with paste to reduce aluminium oxidization, which is an insulator. Note the length increases once crimped, which is taken into account.

Crimping on the ground

Crimping in the air!
Task: Count the pistol grips!

I was also lucky enough to observe Independent Lines' Line Mechanics' solution to getting across the Avon River without contacting any of the sewer-ridden water. See below (note, this is not a 'standard procedure'!)...

The video below shows a tour of the circuit from Dallington to Bromley.

Next week: Final terminations and connection into the substation.

Pedagogical analysis: Electrical glossary/jargon

As with all trades, all electrical careers carry technical terminology. Some descriptions have multiple terms, for example, a conductor of electricity (I've used 'conductor' in this weeks' blog), can also be termed line(s), wire, cable, mains, straps, links, amongst many others. What is really interesting is the terminology changes for each different occupation. Clearly the occupation 'Line Mechanic' refers to conductors being 'lines', whereas Cable Jointers do use the term 'conductor'. House wiring electricians also use the term 'cable' and wire(s), but the New Zealand Electrical Wiring Regulations 1997 (2010 Revision) calls them all 'conductors', which is why I use that particular term.

Other terms are linked to the course theory. For example, what is voltage? A simple, accurate description of voltage is not really that easy. Analogies can help here; voltage can be described as electrical 'pressure'. If we consider the 'flow' of electricity, which is linked to electrical current, be compared to the flow of water, instead of valence electrons (the outer orbit electrons in an atom), which is what current actually is.

Voltage can be described as the pressure of the water in a pipe, current the speed of flow of that water, and insulation being the pipe outer, which is holding the pressure in. If the 'insulation' fails, the pipe will leak, however, electricity needs a conductor to 'leak' through. A spade or or digger bucket conducts electricity nicely, being made of metal, and can result in accidents if they contact a conductor. Unfortunately, even though humans conduct poorly, the can, however conduct well enough to be killed by electricity.

Electrical theory, being a subsidary of the physical sciences, uses a substantial amount of mathematics, so theory must encompass an understanding of mathematical terms, particularly SI units (The International System of Units (abbreviated SI from French: Système international d'unités) uses different terms for large and small numbers. For example; "'I travelled 120,000 meters to Tekapo", clearly kilometres is used to describe the distance more easily. 66kV=66,000 volts. 

Trainees need to be encouraged to self-research terminology to understand it better. Electrical theory is difficult, and is widely regarded as one of the most, if not the most technical trade. There are literally thousands, if not millions of resources online, and other resources such as libraries should be encouraged. On-job instruction sometimes may not be good enough to satisfy a trainees' thirst for knowledge on a particular topic. The key is to reference the trainee to trusted sources.

For myself, as a tutor, familiarity with the multiple similar terms cable, conductor, wire, etc. is needed to explain theory to trainees/students. A 'pocketbook' should be encouraged, as most trainees and tradespeople carry one to take notes and appointments. Essentially trainees need to 'learn how to learn'. This I believe is not just part of becoming a tradesperson, it is part of growing up and becoming an adult.

Roger Sutton, CEO of Orion, who came down to see how the guys were going and to thank them for their awesome work.  A true hero of Christchurch and more than happy to have a picture with some insane polytech guy!

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!