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Me: And I think you are absolutely right that the PFC measured as per the regs isn't the same as the actual PFC, even at the exact time of measuring. This is because firstly the calculation assumes all other loads will still take the same current even during a fault on your installation that would reduce the voltage at other loads ...
JohnW2: No - both my simulations and attempts at mathematical modelling take that into account (see my posted simulations).
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Sorry - "the calculation" I meant as per the regs, your model is clearly far more comprehensive! (although perhaps difficult for any electrician to work out on site.)
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Me: Since we don't know the voltage at the transformer and we don't know the effective impedance of all the other loads, we just have to assume the voltage is sufficient that given the impedence of the other loads, the voltage at the origin is 0.95 of nominal. And we can know that as we pull more current, less volt drop will be caused by other loads on the system so they will be less important. So call it a fudge factor!
JohnW2: That's not quite how I see it. I think the intended purpose of Cmin (currently 0.95) is simply to ensure that calculations remain valid even if supply voltage (without faults) is 0.95 of nominal (as I've said, that would much more logically be 0.94, since it would then correspond with the lowest permissible supply voltage!)
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Sorry I was purely making a statement of fact that as far as the regs are concerned, we effectively "just have to assume" that in all conditions when non fault origin voltage is 0.95 of nominal, the voltage under fault conditions is sufficient [to trip the protective device]. And then I went on to say that's it's not all as bad as we think due to the effect of other loads.
I wasn't saying it makes sense, or that the people who made the regs had the right thing in mind when they thought about it!
Me: And I think you are absolutely right that the PFC measured as per the regs isn't the same as the actual PFC, even at the exact time of measuring. This is because firstly the calculation assumes all other loads will still take the same current even during a fault on your installation that would reduce the voltage at other loads ...
JohnW2: No - both my simulations and attempts at mathematical modelling take that into account (see my posted simulations).
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Sorry - "the calculation" I meant as per the regs, your model is clearly far more comprehensive! (although perhaps difficult for any electrician to work out on site.)
---
Me: Since we don't know the voltage at the transformer and we don't know the effective impedance of all the other loads, we just have to assume the voltage is sufficient that given the impedence of the other loads, the voltage at the origin is 0.95 of nominal. And we can know that as we pull more current, less volt drop will be caused by other loads on the system so they will be less important. So call it a fudge factor!
JohnW2: That's not quite how I see it. I think the intended purpose of Cmin (currently 0.95) is simply to ensure that calculations remain valid even if supply voltage (without faults) is 0.95 of nominal (as I've said, that would much more logically be 0.94, since it would then correspond with the lowest permissible supply voltage!)
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Sorry I was purely making a statement of fact that as far as the regs are concerned, we effectively "just have to assume" that in all conditions when non fault origin voltage is 0.95 of nominal, the voltage under fault conditions is sufficient [to trip the protective device]. And then I went on to say that's it's not all as bad as we think due to the effect of other loads.
I wasn't saying it makes sense, or that the people who made the regs had the right thing in mind when they thought about it!