**Show Us Your Installs!!!**

[Spudnik]

Right chaps,

Due to a few unavoidable issues, we have lost the original thread and pics etc.

Sorry about that!!!

So, if you want to re-upload your pics then great, if not, give us something new!


Cheers!!

 

[Stroppy]

Is this force only generated between conductors carrying different phases, or does it happen in single phase cables too? I'm wondering if this effect happens in, say, your domestic T&E to a lesser extent with the lower fault current.

 

[johnboy6083]

To be honest in final circuits, the fault current is very low so although there will of course be repulsion, it will not be anywhere near the levels of the forces generated at the origins of larger industrial installations. Use Archie's formula to try the numbers for yourself. You could transpose it to see what fault current you would need to cause a certain force.

 

[Knobhead]

OK assume a fault current of 0.5KA on a 2.5 T+E, I get 127 N/m. It's not going to do it a lot of good.

To put this in to context under a load of 20A the 2.5MM T+E has got 0.2M/m of force acting within it.

 

[Silly Sausage]

OK assume a fault current of 0.5KA on a 2.5 T+E, I get 127 N/m. It's not going to do it a lot of good.

To put this in to context under a load of 20A the 2.5MM T+E has got 0.2M/m of force acting within it.

That would explain why cables blow themselves to pieces.
It's all starting to make sense now!

 

[Knobhead]

Have a look at Home - Scatco Europa Ltd. I installed quite a few of these. Look for the fault withstand current. It's not the CCC of the bus-bars, it's the current the bars will carry without distortion.

 

[Engineer54]

Have a look at Home - Scatco Europa Ltd. I installed quite a few of these. Look for the fault withstand current. It's not the CCC of the bus-bars, it's the current the bars will carry without distortion.

Along with the bracing to hold those bars in place during a high magnitude fault!! 50KA for 3 secs, takes a fair bit of bracing to be in place!! lol!!

 

[Knobhead]

The bars I watched bending were within 20m of the 1000KVA transformer. Don't know what current they were carrying at the time but couln't have been much above 1500A It was a 100HP DOL motor starting on an already loaded board. Normal running would be about 1100A The board was a Metro Vick open slate panel.

 

[Engineer54]

Never seen bars actually bending, a sight to see that i bet!! lol!!


I have seen package sub-stations (MV/LV) that have come from the factory with next to no bracing on the 3 phase bars entering the LV panel. That was after a factory visit (GE) too, ...where the units that were up for delivery to site were inspected and witness tested by myself!! Those 3 units were fine, but the next 4 units were crap, (12 X 1MVA units in all on that project) and after opening the first unit, instructed the contractor to send them back for remedial work, which both the contractor and myself will inspect at the factory, before they are shipped back to site!! That was in Saudi, but the factory was run and operated by GE (USA) at the time!!

 

[Knobhead]

The Metro Vic panel was from the late 40's, all open at the back. I was the wet behind the ears idiot that got talked in to watching what was happening.

After talking to Archy we’ve revised the figures for the 20KA calculation (I used A and not KA) the new value of F = 1360N/m. Not as bad as it was, but it’s going to throw things about violently if the cables get loose. The last transformer install I did I used 3.5T of cable on the secondary side. I wouldn’t fancy getting clobbered by that lot.
As Archy said the film of the multi-core cable exploding says it all.

 

[Silly Sausage]

You'll notice I've edited a few of my recent posts!!!

 

[Knobhead]

I'll sort mine out tomorrow. I'm knackered at this time in the morning!

PS it gets interesting if you convert it to Kg force

 

[Engineer54]

That would explain why cables blow themselves to pieces.
It's all starting to make sense now!

Many factors involved, depends on the cable size, (they also have a KA/s withhold rating too) length of cable etc. More chance on a short length of cable, say between TX and Main Switchboard, than on a long run (depending where the fault occurs), as the cable will act as resistance/impedance, limiting the fault current the transformer can deliver into the fault...

As i say too many factors involved that can/will influence each other, to pick-up on just one aspect and predict what will happen under a given fault condition.
Safe to say, any fault that involves the full fault current of a transformer, will always be catastrophic, ...and expensive!! lol!!

 

[onions1066]

Engineer 54 you are obviously very knowledgeable but I've never seen you post any pics of your work up, come on I think it's time to show us lol

 

[johnboy6083]

Engineer 54 you are obviously very knowledgeable but I've never seen you post any pics of your work up, come on I think it's time to show us lol

I can see some material requisitions, snagging sheets and emails coming our way lol

 

[onions1066]

I can see some material requisitions, snagging sheets and emails coming our way lol

Not sure what I will get but I'm pretty sure there won't be a plastic tie wrap in sight and I'm pretty sure he will be hugging and earth rod in one of the pics