70mm SWA

[zeroberto]

Just connected a 70mm 3 core SWA sub main. I'm in the sticks, no Industrial work here at all so out of the ordinary for us (few farm buildings etc) & our usual swa size is 16 or 25mm. Sheltered life I know!

Anyway just want to tip my hat to you guys who work with this size of cable on a regular basis - what a beast to work with. Nice bit of job satisfaction when we finally got the glands on though.

Again, industrial guys I salute you!, hopefully never see this again for a few years.

cheers

 

[Engineer54]

i believe the key phrase may be "non-ferrous" metals.
which have no electromagn. properties.
;-)

Most believe that aluminium can't affect circulating currents, but the truth is they can when enough current is flowing.
Aluminium or ("non-ferrous" metals) restricts, rather than cancel out circulating currents, I never use any metallic gland plates, whether supplied by the panel manufacturer or not for on our switchboards. Always use 6/8mm Paxoline boards/plates (or whatever it's called now) for our gland plates, where single core cables are being used.

 

[Deleted member 9648]

I'm informed you can slot ferrous metal plates between the glands to negate eddy currents rather than use insulated plates,never tried it though.

 

[johnboy6083]

Yeah the two posts above are how you combat AWA singles.
its common to use non ferrous gland plates. I've seen Ali and Brass gland plates used. I spent half an hour drilling an M50 hole through a 10mm brass gland plate! It was hard graft!
the slotting works also, but you need to seal the slot, usually with some sort of sealant or resin.

Its common to isolate the glands from earth at one end of AWA singles. On DNO supplies, it's usually the load side that wooden gland plates (if any) are used. I've seen this lots of times, usually in the treatment works/pumping stations I work in. The transformer end is usually glanded properly.
this is called single point bonding, and is used to stop circulating currents.

 

[Brightspark2]

2 x 300mm 4 core SWA in parallel is the biggest SWA IIRC. Took quite a few of us to pull the cables in. The dist board was over 7Ft tall. Sadly not available from screwfix at £55.

Using 400mm singles in parallel at the moment, part of the run is around 20M vertical too, that wasnt easy to get in, took about 3 day's. Cable alone coming to around £25,000.

 

[Knobhead]

Anyone else waiting on Tonys input on this one? I reckon he's done a few 1000mm's!

Certainly have.

Don’t like the bloody things, it’s like bending scaffold poles. As for terminating them, just looking at the crimper was enough to give you a rupture.

 

[Outspoken]

I can confirm some of the comments above about Eddy Currents, on our recent install for the 400mm² and 630mm² singles all had aluminium armouring and the gland plates are made "onsite" out of two sections, one of 6mm paxolin with a inner plate of 6mm stainless steel for strength. In the past we have found that a terminated AWA will snap the paxolin like a twig if flexed too much so we now use the stainless steel plates to solve the problem, this also removes the Eddy Currents problem.

I have helped to install some serious mega sized 1200mm² Aluminium singles that also have Aluminium armouring. Bending them is a reach biatch because of the inherent strength of aluminium and it's resistance to bending..thankfully that was a long time ago when I was younger and fitter than now ..just the thought of them now would have me tired!!

 

[Knobhead]

Gland plates can be made of steel if slotted

 

[Tidy Max]

I am sure someone posted the equation on here on how to calculate what size slot you must cut into a ferrous plate to stop eddys?

Bit ---- like but does anyone know it?

 

[Knobhead]

Don’t know of a formula. I was taught as an apprentice the slot was to be as wide as the plate thickness. All our transformers came with factory fitted gland plates.

The only time I had a failure was when a contractor pocketed the brass locknuts and fitted steel. No one will notice. I didn’t see it but I heard the explosion when it failed.

 

[Spoon]

7 years ago did a design for a press that had the power cabinets supplied from 0° supply, +30°, -15° & +15° transformers. Each cabinet had 2 x 400mm 3 core cable going to them. The installation guys were not happy.

 

[Knobhead]

What transformers were you using?

 

[Guest55]

i'm sick of hearing about this bloke eddy and his current buns , someone should give him the boot.
;-)

 

[Spoon]

What transformers were you using?

865kVA phase shift transformers from Transmag Power

 

[Knobhead]

Can you send details of them please?

Brentford used to make some strange transformer but normally used for variable DC supplies. The secondary was a combined ∆Y with a weird sliding contact set up. It couldn’t run advanced unless it had internal switching on the HV.

Are you talking of a Buck/Boost transformer? Never worked on one but have got the drawings from the 1930’s for one.

 

[Spoon]

Can you send details of them please?

Here is the details of the -15° and +15° transformers.
Don't know if you are after more detail. I have the quotes of the transformers in the contract folder. If you send me your email address I will email them to you. (of course with certain details blanked out not relating to the transformers)