Tuesday, February 15, 2011

Week 2 - Cable Jointing - Tradefit, Halswell Junction Road - Lead wiping

Well, I'm getting the hang of this! Apologies for lateness; busy weekend!

Me working!
This week I've decided I'm going to be more brief about what I'm doing and focusing on certain areas that I feel I will need to teach. I will give a brief description of what I've done for the week, but the focus will now go onto producing course material. The photos on here are not even a tenth of the pics I have taken, so i'm building up the resources!

Week breakdown:

CPIT Tradefit site sub, 11kV and 400V XLPE joints into the back of circuit breakers with Steve. Also Inspection of terminations in boundary boxes on Russley Road.

CPIT Tradefit site

New type boundary box

New type boundary box with cover off

Remove parts from old breakers at Connetics and install in two breakers at CPIT Tradefit site sub with Steve.

Halswell Junction Road (where new motorway will attach), 11kV XLPE-PILCA including 'spiking', phase testing with Steve.

Halswell Junction Road - underground and overhead

Halswell Junction Road 11kV XLPE-PILCA joint with Steve.

Operational requirement work at Connetics site preparing for Orion EAC course Monday.

The first skill I wanted to cover in detail  is lead wiping. This is soldering on a large scale to maintain older cable waterproof and earthing integrity when joining with another cable using the Tyco kits. This skill is rare and Orion in their foresight have elected to keep using it even though other methods are available.

The lead wiping is to construct a blob of solder connecting the steel armour of the outside layer of the cable onto the stripped internal lead armoured layer. This also stops the pitch (tar) under the steel layer seeping into the joint.

I decided to video this being done (I've taken a lot of photos of it being done already) and this will be another way of keeping the skill alive. The video will be integrated into a 'moodle' website that I will be developing to consolidate the teaching with.

Video (apologies for right-hand decorative bar, still getting used to Windows Movie Maker on Windows 7):

The next item I wanted to cover in detail was the 'spiking' of cables. This is the 'last line of defence' for cables to ensure they will be isolated (disconnected from the supply voltage) before being cut into. All possible testing is done beforehand, but to be fully sure, a metal spike is driven into the cable using a blank cartridge (44.40 calibre) tool. If the cable is still live (very rare!) then the spike will cause protection (fuses or circuit breakers) upstream to open, and ensure the cable is safe to work on. The cartridge is operated using a long cord so distance can be maintained for safety (paramount!).

The cartridge

The 'spike'

Hole in cable left by the 'spike'

And another.. Shear bolts.
Shear bolts are used in the final connectors to create the actual cable termination(s). The beauty of shear bolts is that they are designed to shear off at a certain torque, that being the best possible torque to make the connection safe and conductive. A similar system was used on aircraft carrier catapults historically, to hold the plane back until the steam pressure that drove the catapult reached a high enough level to launch the aircraft.
The bolts also eliminate the effect of aluminium oxide, which is an insulator and forms on aluminium surfaces within minutes of exposure to air by 'grinding' the oxide off the surface of the conductor. The inside of the bolts contain a white conductive paste to further assist conduction.

Here are two videos of shear bolts in operation. The first using a battery driver to shear, and the second (due to a flat battery!) using a socket driver.

 To teach these skills, practical demonstration is a must. Tradespeople being predominantly visual/kinaesthetic learners, then teaching focusing on these learning styles is paramount. Vygotsky's 'cognitive apprenticeship' theory is fully applicable here and is commonly used in the trade (as with most trades) with the 'master and apprentice' formula being well used at Connetics. Due to the high cost of jointing kits, and the 'take your time so you do it right' attitude, practical summative assessment should be restricted to one attempt only (if possible). On job assessment could be used as the resit? Certainly this is something I need to think about.

Tip this week: Using kevlar string to cut through the outer layers of insulation to the neutral screen enables you to not damage the neutral (earth) conductors (Steve).

Looking forward to next week: 33kV jointing in Timaru!

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