AS3851 Unable to calculate X/R ratio
AS3851 Unable to calculate X/R ratio
(OP)
Hi
I have trying to calculate the fault level (ground fault) by using AS3851 method.
In section 8.5.2.1, the factor k for the R/X and X/R ratios can be obtained using
k = 1.02 + 0.98 * e ^(-3R/X).
I have been given the following:
the source 3 phase max. fault level 3800A
the source 3 phase max. fault level 3600A
the source 1 phase max. fault level 930A.
the source 1 phase max. fault level 910A
So for 3 phase fault, k = 0.746.
The problem is I cannot obtain R/X ratio using k = 1.02 + 0.98 * e ^(-3R/X) due to obvious reasons.
Is there anyway to get around this problem. Please note I need to follow AS3851 standard. Many thanks
I have trying to calculate the fault level (ground fault) by using AS3851 method.
In section 8.5.2.1, the factor k for the R/X and X/R ratios can be obtained using
k = 1.02 + 0.98 * e ^(-3R/X).
I have been given the following:
the source 3 phase max. fault level 3800A
the source 3 phase max. fault level 3600A
the source 1 phase max. fault level 930A.
the source 1 phase max. fault level 910A
So for 3 phase fault, k = 0.746.
The problem is I cannot obtain R/X ratio using k = 1.02 + 0.98 * e ^(-3R/X) due to obvious reasons.
Is there anyway to get around this problem. Please note I need to follow AS3851 standard. Many thanks






RE: AS3851 Unable to calculate X/R ratio
RE: AS3851 Unable to calculate X/R ratio
This is close to what would be expected as an X/R ratio at a final distribution transformer (0.4kV), although those currents look a bit low for that.
RE: AS3851 Unable to calculate X/R ratio
The fault level is given by the supply authority. And this is a 22kV distribution network.
RE: AS3851 Unable to calculate X/R ratio
Is the first one the peak?
I really don't understand what you're asking. Section 8.5 of AS3851 is written so you can work out the peak current (ip).
RE: AS3851 Unable to calculate X/R ratio
If the Utility only provides short-circuit current contribution, then the following is required:
- Max and Min PPP and PE short-circuit contributions from the Utility ( preferably in amps ),
- X/R for PPP = X1/R1,
- X/R for PE = X1+X2+Xo / R1+R2+Ro.
- Was the Utility contribution calculated using the voltage 'c' Factor ?