Exam Question

[IMS Electrics]

Hi Guys im in my first year of a degree course in Electrical Engineering and Renewable Energy and in the middle of an assignment to which one of the questions is :-
If it is not possible to perform an actual Ipf measurement, what other method could be used to obtain the value of prospective fault current?
if anyone could assist in answering this there might be a beer in it ;-)
cheers Danny

 

[mark1979]

calculation? voltage divided by earth loop impedance?

 

[trev]

If you can't measure things you can always calculate them.
You owe Mark a beer or 3

 

[mark1979]

i'll have a guinness thanks.

 

[telectrix]

but only for L-E fault. for L-N it's 2 beers and for 3 phase its 3 x root3 beers.

 

[IMS Electrics]

Guinness it is! i shall be drinking a few of those on my birthday in March

 

[brman]

err... if you can't measure Ipf then I doubt you can measure Ze

surely this is one of the stock questions on a 2391 exam?
Q: How do you obtain the Ze and Ipf?
A: By enquiry or by measurement!
it is even stated on a standard EICR.........

So you get on the phone to the nice people at the DNO and they tell you from their brilliant records. Or something like that!

Mines a Timmy Taylors please although perhaps I need to sober up before starting again :lol:

 

[TaffyDuck]

err... if you can't measure Ipf then I doubt you can measure Ze

surely this is one of the stock questions on a 2391 exam?
Q: How do you obtain the Ze and Ipf?
A: By enquiry or by measurement!
it is even stated on a standard EICR.........

So you get on the phone to the nice people at the DNO and they tell you from their brilliant records. Or something like that!

Mines a Timmy Taylors please although perhaps I need to sober up before starting again :lol:

Spot on, ask the DNO who might be able to tell you what the Ze was 15 years ago if your lucky. I guess however that the question is direct Zs in which case Ze + (R1+R2)

 

[ackbarthestar]

That doesn't strike me as a level 4/5 degree answer and an answer like 'ask somebody else' is likely to get a laugh from the examiner.

This one appears to be a calculation along the lines of

1/ Assess the pfc,psc,Ze, ZLine by referring to DNO / original design cable layouts
2/ Measure from the scaled drawing the length, if not given
3/ Assess the transformer impedance
4/ The cable type and csa
5/ refer to tables of of resistance / meter

Remember, pfc is often stated as the highest value of fault current whether it be an earth fault or a line fault.

Edited for grammer.... should have gone to ... you know where