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..!