Wednesday, May 1, 2013

Jointing 66kV cables for the reinforcing of the Christchurch distribution network

Recently I had the opportunity to observe Shaun Baker and Barry Kelly jointing the 1000mm XLPE cable that is being laid to link the McFaddens Rd and Dallington Zone substations.

Shaun and Barry (as seen from my previous post's analysis ) have spent a lot of time in Christchurch jointing and terminating 66kV cables since the devastating February 2011 Christchurch Earthquake.

The joint I observed being done was in joint hole #1, on Ranger St near the intersection of Nancy Avenue in Mairehau (in my previous post, this is where the cable drum was located).

As is typical with all cable jointing, cleanliness is paramount, and the hole is contained inside a 22 foot container supplied by HV contractor Connetics. The container keeps dust and the weather out, and allows the jointers to work in relative privacy (except when being observed by certain Electrical tutors!).

The 'jointing container'

The interior of the container is powered and has block and tackle equipment mounted in it for ease of lifting the heavy cables into position.

The interior

The joint kit being utilised was a Pfisterer MSA 72-XKC. This is a kit utilising a silicon rubber slip-on joint rated at 72kV. The joint is fully contained in a protective housing filled with an insulating compound. 

The procedure is exacting and tolerances down to 1mm are required for the joint to be assembled to Pfisterer's specifications. 

 The joint is started with cutting the cable to the correct length (I asked Shaun how they figure out exactly where to cut it, as this is crucial, and he responded that 'a lot of factors need to be taken into consideration". This is just one of many skills only mastered after years of experience in the trade. 

Shaun cuts the cable while ensuring the strands are secured together
Barry strips the semiconductor and XLPE layers using a precision rotary stripping tool

The XLPE is then polished using progressively finer grit sandpaper

From this finish... this finish....

...and rigorously inspected.
The cable is then protected for installation of the silicon rubber insulator. The insulator is a very tight squeeze, so lubricant and ratchet winches are employed (video later).

The insulator temporarily in place

The final 'lining-up'

And engagement onto the 'Mechanical torque control connector'.
Once in place, the connector's shear bolts are tightened using a battery driver, and than sheared off by hand.

The edges of the remaining shear bolts are deburred and plugs inserted. The silicon sleeve is then winched over the top of the connector.

The sleeve in place.

The earths of the cable are then connected. They are secured in place using heavy clamps and each end of the cable is earthed in a special box on the street. 

Heavy earth clamps

Finishing up the earths

The two ends of the housing are brought together, then the filling compound is mixed and poured into the access holes.

Caps are put on and the joint is complete. The joints are encased in soft concrete with a red-coloured top layer. 

The completed 3x joints

The earth bonding box

The red 'soft' concrete.

I would like to thank Shaun and Barry again for their cooperation in letting me observe their work. They really are a joy to watch, make an extremely technical, challenging job look easy, and are really nice guys.

Shaun's website:

My awesome class looking at completed cable joints..!


Saturday, January 12, 2013

December 2012 - The first pull of new 66kV subterranean cables for Christchurch

On December 4 I observed the laying of the first part of the strengthening of the Christchurch distribution network by the 'pull' and lay of the first 900 metre section of 66kV by the Connetics underground department.

Contractors dug the trench and laid the concrete bedding for the power cables over the last couple of months. My previous post illustrates the map and location of the first joint hole, 900m from the McFadden Zone substation.

Having not witnessed the laying of a really heavy power cable before, this was a particularly exciting time for me. Rollers were laid in the trenches and on the corners with cable layers at intervals to assist the passage of the cable. Conduit was installed in sections and guides inserted into the entries of the conduit.

Rollers with the nylon pulling cable in place for the first cable.

Corner rollers with conduit protective entry

A nylon cable was used to pull the cable and was attached using a cable puller and drawn by a torque-controlled winch set to 7 Newton-metres strain.

The winch

The giant cable drum was mounted on a roller machine with nylon bearings and a makeshift braking system using an 8x4 block of wood.

Me in front of the giant cable drum (with full PPE, of course!)

The drum on it's own
The cable specs on the drum
The drum 'jack' specifications.
I'm 90% sure (!) this is a nylon bearing.

The 7-ton breakaway swivel (the black bit).
The cable puller was attached to a 7-ton breakaway swivel for safety in case of jamming. The cable itself is rated at 7.9 Newton-metres breaking strain.

It seems that, as with a lot of trades, a successful objective can only be achieved with excellent preparation. Everything from placement of rollers to conduit placement and cable lubrication, if done properly, should (being the key word!) lead to a successful outcome. Teamwork and good radio communication is paramount.

So the pull begins. A team of around 6 'follow' the cable down the run, after a an initial 'take up the slack' and check all is running correctly.

The start of the cable run
The nylon drawcable wearing on the conduit insert

Video: the winch

Video: the cable running

Video: Lubricating the cable

Lubrication is essential for the cable as it goes around corners in conduit to ensure the cable is not damaged and also the conduit is not compromised by the friction of the cable.

The lubricating medium.. goop!

Nearly finished.. comms cables to go in..
After nearly a week, delayed by a couple of days of bad weather causing trench issues, the laying of the power cables was complete as well as two (I think!) communications cables (only one shown in the picture, I was too busy to get a photo at the right time!).

The cables are being laid on top of reinforced concrete (in places) and encased in a flowable thermal backfill (a weak concrete) with a red coloured top layer.

The next step is jointing. I'm not sure if I will be able to cover that process, but I did see some terminating at the McFaddens zone substation.. see below:

Analysis: 66kV oil-filled transition jointing

  During my 22-week stint with Connetics from January to July 2011, I kept bumping into a couple of guys doing work on mainly paper-insulated cables.
Sean Baker and Barry Kelly are Cable-Jointing gurus, both ex-UK and supreme at the trade. Their workmanship is second-to-none, and they are effectively the engineering equivalent of surgeons, precision work being their game.

The first time I saw them was doing the final terminations for the 66kV temporary overhead line circuit at the Dallington zone substation in April 2011.

Sean doing 66kV terminations

The beginnings of a SERIOUS lead wipe..
The finished product

The second time I saw them was jointing a damaged 66kV oil-filled cable on Armagh St in the Christchurch city 'Red Zone' in May 2011.

Oil-filled Cable Jointing
Third; a 66kV pole installation near Islington substation.

Barry polishing the XLPE insulation
The pole under construction
And more recently, doing the terminations at McFaddens Zone substation for the new 66kV circuit at the start of this post.

The kit comes together. Shaun and Barry have workhands to assist.
The cables to be joined
Perfectionists; Barry keeps his tools in perfect order and condition while working.
Now THAT is a lead wipe..!
The finished product
The final product is achieved with an Ericsson 52-84kV Transition joint kit.

I'd like to thank Shaun and Barry. They're so passionate about their trade, and have been more than happy to share their trade with me. Nice guys, and great role models.