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When doing the final assessment test I am baffled by question 10 relating to Critical Risk Level, I don't understand how the answer is worked out from the figures they have given and why the answer is (B).
Has anyone done it or can they explain please?
Thanks for reply but I can't see that to be correct as it says at the top they are all Rural so use the fenv of 85 ?
Terrible wording for a question.
Using the values in the question and applying it to the equation CRL=fenv/NgxLp I made every answer to be less than 1000, so they would all require an SPD
Lp being greater than or less than a figure is rather odd - as we need an actual value to plug into the calculation. Since we only take account of the first 1km Lp > 1.0 can be taken as the same as Lp=1.0 so we can put that into the calculation. Likewise if Lp is less than 0.425 we could take it as being equal to 0.425 as worst case and put that into the calculation. Lp >0.6 is tricky though - it's only telling us it's longer than 0.6km but not how much longer - and as longer is worse we can't really use the 0.6 figure directly but would probably have to use the full 1km instead.
So if they're asking us to spot the Lp value we can't use in the calculation, then I'd say it was the > 0.6km one - hence answer B.
"Carry out the following calculation:" does seem a little misleading though.
I'm sure they could have found a less misleading and less tortuous way of asking the question if they put their mind to it (presuming that is what they were trying to ask...)
Are you sure this doesn’t relate to the value of Lp being unlikely to exceed 0.6 in outer London? Perhaps something in the course notes? So in the Borders and Cornwall Lp could be greater than 1 in Manchester Lp is likely to be greater than o.425 and in London Lp will be less than 0.6
Interesting theory - that would mean for instance, that no LV customer in Outer London is more than 500m from their substation and all cables (HV and LV) underground? I don't know the SE well enough to guess whether that's plausible.
I might try and contact them for some clarification.
Kind regards Mike