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!


yanni said...

Hi Andrew

We went on a tour of dallington the other day with our lecturer and we noticed the different looking insulators on the strain section that crosses the avon. These insulators can be seen in your picture titled: "Thursday 14th April: Install conductors on Strathfield Road".

On all the other insulators the plates are spaced evenly apart except in a few places they look almost logarithmically spaced with a higher concentration of plates down the "hot" end.

We all had our theories but we're just wondering what the real reason is for the difference.



Selena said...

Hi Andrew,

trust you are having a well earned break over the Easter. A good description of the line installation process in this blog. It provides good information and a resource you can use with students - perhaps an exercise for them to summarise and order the steps taken to run the conductors?

Also your summary provides a good checklist for future use. You could set up a challenge to your students to produce a comprehensive glossary? and share their entries, or refine the entries in pairs, or critique entries in groups?

Keep up the good work and have a good week, Selena

Andrew said...

@Yanosh, good question! I'll find out this week for you..!

@Selena, great ideas and thanks again for the feedback..! We'll talk soon... ;D

Andrew said...

Yanosh, I asked a lot of people and the best answer is that it was the last few poles done by a contractor and they were short of insulators, so they used some different ones! Sorry, that's the best I got!

yanni said...

Thanks Andrew,

That makes sense, trust Engineers to come up with a complicated explanation for something quite simple.

Keep the posts coming.