I spent pretty much most of the working day today watching two blokes (yeap, not guys, not men, blokes) start, but not complete, the process for joining two segments of power cable together.
As I previously mentioned, in regards to the possible court case work, we will be doing some testing of some cables produced as they should be, and then produced using something that wasn't part of the original instructions. Today, after a brief meeting in the morning to make sure that we were completely clear on what was happening, the blokes who are professional cable joiners got down to work.
After getting the ten lengths of cable moved to where they would be working, they got down to business and cut each length into two, so they could do the joining, as if each cable segment was a separate full length cable. The important aspect was the join and what was happening there so the rest of the cable length was quite irrelevant to this situation. The process of joining is a very long and complicated one, far more than I had originally thought.
The outer plastic layer is cut away to expose stainless steel wire in a twisted mesh. This is the 'armour' of the cable, designed to protect it from accidental mechanical damage such as excavation from unwitting people. These wires were cut away to expose another plastic sheath, this time in black. This too is cut away to reveal three white plastic wrapped bundles and lots of black fibres of plastic. The black fibres are cut away since they are only filler material to fill the space around the three bundles. The white layer is stripped away easily to expose a copper sheeted bundle. This too is stripped away to reveal a black plastic coated bundle. This is a semi-conductor pvc plastic coating (carbon impregnated) and quite difficult to remove. They heat it up using a gas burner and peel it off to expose underneath a HDPE (high density propyl-ethylene) plastic tube. A stripping tool is used to cut this away to finally reveal the aluminium power cable bundle. Phew. Just to get down to this takes a very long time. Each removal of layers has to be done carefully in a manner so that there is gaps between the exposed layers. What I mean is, they measure 455mm to strip away the outer plastic, then 450mm of armour is taken off, then 440mm of plastic sheath is taken off , and as you progress down, less of the layer is removed, with finally only about 150mm of cable is actually exposed.
A crimping tube is inserted over the exposed cables from the two to be joined, for each of the three bundles. Oh, each bundle has the white plastic, copper, black plastic and HDPE layers. Once the wire is exposed, they do also have to cut a bevel angle so it isn't a ninety degree edge to the metal, since the metal also has another conductor coat that needs to be slightly exposed. The crimping tube is then pressure crimped four times on both sides to ensure maximum compaction and structural strength, and connectivity. The taping then begins. Yes, the taping.
Using a semi-conductor tape, three layers of tape (15mm wide tape) is bound and stretched over the bevel exposed coating, across the wire, crimp, wire and then bevel on the other side. This ensures full connectivity and equalises the voltage potential across the join. Otherwise, voltage differences cause sparking which results in the join failing once full power load is put on. Then comes the fun part, more tape. A self amalgamating tape is then bound to cover all of the exposed HDPE from one end to the other and across the join. The thickness of this tape is about 1mm thick. The required thickness across the join segment in the middle is 16mm on either side of the join, ie 32mm thickness. But, you have to wrap it completely around the entirity of the exposured. The bloke who was doing this (he's 73 years old and have been doing it for a very very long time....) used about fifteen meters of the self amalgamating tape on the join, and he still hadn't reached the required thickness yet. And this is just for one of the three joints....
They stopped there for the day and will be coming back to complete it. The next stage once this is done (the 16mm bit) for all three cables is to stick a metal band mesh around the whole lot as a faraday cage conductor. Then a plastic screen mesh is wrapped around the entire thing some more. A sealing tape then is used to waterproof seal the entire bundle and then a resin is pumped into the bundled up region to fill the space left by the screen mesh for mecahnical and waterproofing strength.
Since these guys started 'late' today, they didn't finish one join fully. Normally on a good day, it will take one person all day to do one join solo, if they know what they are doing. It is a very painstaking job.
I was also told that they get a heck of a lot of money. These cables are only 33kv cables (33 000 volts), and one of the guys who was also there for the project told me that the guys who lay the 130kv cables work in four man teams. To join two 130kv cables, it takes four days. They get paid about $90 000 per joining they do. That means, they get paid about $5626/day each. A lot of money eh. Oh yeah. But, as you can imagine, it is a heck of a lot of work, and if you stuff it up, it's your head on a chopping block because an entire power grid could fail, causing chaos and a lot of disgruntled people..... The salary comes for a reason LOL.
It's a boring process to watch mind you, I'd rather be doing the joining than standing around watching it all day long..... But yet I must, so tomorrow, I will be back there again watching them complete the rest of the joint. ~sigh~
As I previously mentioned, in regards to the possible court case work, we will be doing some testing of some cables produced as they should be, and then produced using something that wasn't part of the original instructions. Today, after a brief meeting in the morning to make sure that we were completely clear on what was happening, the blokes who are professional cable joiners got down to work.
After getting the ten lengths of cable moved to where they would be working, they got down to business and cut each length into two, so they could do the joining, as if each cable segment was a separate full length cable. The important aspect was the join and what was happening there so the rest of the cable length was quite irrelevant to this situation. The process of joining is a very long and complicated one, far more than I had originally thought.
The outer plastic layer is cut away to expose stainless steel wire in a twisted mesh. This is the 'armour' of the cable, designed to protect it from accidental mechanical damage such as excavation from unwitting people. These wires were cut away to expose another plastic sheath, this time in black. This too is cut away to reveal three white plastic wrapped bundles and lots of black fibres of plastic. The black fibres are cut away since they are only filler material to fill the space around the three bundles. The white layer is stripped away easily to expose a copper sheeted bundle. This too is stripped away to reveal a black plastic coated bundle. This is a semi-conductor pvc plastic coating (carbon impregnated) and quite difficult to remove. They heat it up using a gas burner and peel it off to expose underneath a HDPE (high density propyl-ethylene) plastic tube. A stripping tool is used to cut this away to finally reveal the aluminium power cable bundle. Phew. Just to get down to this takes a very long time. Each removal of layers has to be done carefully in a manner so that there is gaps between the exposed layers. What I mean is, they measure 455mm to strip away the outer plastic, then 450mm of armour is taken off, then 440mm of plastic sheath is taken off , and as you progress down, less of the layer is removed, with finally only about 150mm of cable is actually exposed.
A crimping tube is inserted over the exposed cables from the two to be joined, for each of the three bundles. Oh, each bundle has the white plastic, copper, black plastic and HDPE layers. Once the wire is exposed, they do also have to cut a bevel angle so it isn't a ninety degree edge to the metal, since the metal also has another conductor coat that needs to be slightly exposed. The crimping tube is then pressure crimped four times on both sides to ensure maximum compaction and structural strength, and connectivity. The taping then begins. Yes, the taping.
Using a semi-conductor tape, three layers of tape (15mm wide tape) is bound and stretched over the bevel exposed coating, across the wire, crimp, wire and then bevel on the other side. This ensures full connectivity and equalises the voltage potential across the join. Otherwise, voltage differences cause sparking which results in the join failing once full power load is put on. Then comes the fun part, more tape. A self amalgamating tape is then bound to cover all of the exposed HDPE from one end to the other and across the join. The thickness of this tape is about 1mm thick. The required thickness across the join segment in the middle is 16mm on either side of the join, ie 32mm thickness. But, you have to wrap it completely around the entirity of the exposured. The bloke who was doing this (he's 73 years old and have been doing it for a very very long time....) used about fifteen meters of the self amalgamating tape on the join, and he still hadn't reached the required thickness yet. And this is just for one of the three joints....
They stopped there for the day and will be coming back to complete it. The next stage once this is done (the 16mm bit) for all three cables is to stick a metal band mesh around the whole lot as a faraday cage conductor. Then a plastic screen mesh is wrapped around the entire thing some more. A sealing tape then is used to waterproof seal the entire bundle and then a resin is pumped into the bundled up region to fill the space left by the screen mesh for mecahnical and waterproofing strength.
Since these guys started 'late' today, they didn't finish one join fully. Normally on a good day, it will take one person all day to do one join solo, if they know what they are doing. It is a very painstaking job.
I was also told that they get a heck of a lot of money. These cables are only 33kv cables (33 000 volts), and one of the guys who was also there for the project told me that the guys who lay the 130kv cables work in four man teams. To join two 130kv cables, it takes four days. They get paid about $90 000 per joining they do. That means, they get paid about $5626/day each. A lot of money eh. Oh yeah. But, as you can imagine, it is a heck of a lot of work, and if you stuff it up, it's your head on a chopping block because an entire power grid could fail, causing chaos and a lot of disgruntled people..... The salary comes for a reason LOL.
It's a boring process to watch mind you, I'd rather be doing the joining than standing around watching it all day long..... But yet I must, so tomorrow, I will be back there again watching them complete the rest of the joint. ~sigh~
2 comments:
how thick are the cables?
what do they do if the power grid is all ok?
you can see how thick it is in the pictures relative to a person I guess.
If the power grid is ok, then... they do nothing? LOL
If the joins are made properly, they have nothing to fear.
New joins are always needed when buildings get big power connections, or factories/facilities, or the power companies lie out new power grids in developing suburbs etc. So these guys get jobs all the time.
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