need help with energy let thru data

[ianphilip007]

can anybody help me with reguards to the i2t (energy let through data) some manufactures provide a graph and others state a figure. im confused as to what value of I2t (energy let thru to use) for a given fault current when trying to calculate minimum cpc for fault currents <0.1s

I2t < s2k2

please can anyone help.

 

[ianphilip007]

im confused as to which fault current to use. do you use the fault current rating of the mcb eg (6000) or the fault current for the circuit eg Uo/zs hmm very confused

 

[Guest55]

Use mcb rating data for let through energy calc.

 

[ianphilip007]

do you mean the PSC rating of the mcb eg 6kA or 3 kA ??

 

[Guest55]

If the 3ka is your PSC at the supply then this will be used to look up the I2t rating of the mcb , but each manufacterer and mcb type is different so you'll need the mcb makers info.

 

[ianphilip007]

right thankyou biff , so if my PSC at supply is 1.8kA (measured) then i would use this as my fault current when looking up the I2t on the manufactures graph.

some manufactures just supply figures for 3ka 6ka 10ka mcb rating ect (max values of i2t ) if your max PSC is only 1.8kA what figure would be used for i2t sorry if im beeing thick just confused as the data is presented in different ways.

trying to work out if a cpc has been incorectly sized. i used the adiabatic and manufactures time/current graph due to low zs and discconection time being 0.01s and it appeared fine. now when using i2t <k2s2 im not sure as to which figure i need to use for i2t if that makes any sense

 

[Guest55]

Sounds challenging stuff , not usually done in such detail for regular work , is this for a college course ?
If your doing this stuff often i'd recommend bying the IEE design guide book , it gives working examples of the I2t calcs.

 

[ianphilip007]

your right im going too deep ill just stick with the adiabatic calclations seem to work out fine

zs 0.35. i = 230/0.35 =657.14 A. k= 115. t = 0.01s (manfactures data)

so S = sqrt(657.14^x0.01) /115

= 0.57mm2 so 1.5mm2 cpc should be perfectly ok.

 

[Guest55]

your right im going too deep ill just stick with the adiabatic calclations seem to work out fine

zs 0.35. i = 230/0.35 =657.14 A. k= 115. t = 0.01s (manfactures data)

so S = sqrt(657.14^x0.01) /115

= 0.57mm2 so 1.5mm2 cpc should be perfectly ok.

^^^ All that for 1.5 lol ?! wouldnt blame you if it was 185mm SWA at £200 a metre lol.
Good effort on the calcs though