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Hi Kiribanda, Is there a standard (preferably IEC or AS) which specifies this? I certainly support this approach(especially since the switchboard does not have a shorter time rating). However I have been getting some pushback saying this is overly conservative, and would like something concrete...

My question is for the generators in my network, which impedance (sub-transient, transient or synchronous) is used when trying to establish if the 25kA/1sec fault rated bus is adequately rated.

Hi, I have a bus which has a 25kA/1sec fault rating. Is this normally compared to IEC 60909-0 sub-transient, transient or steady state fault level? Any help is appreciated.

Jghrist, ignoring appendix E and only looking at Section 5.3: En is in J/cm^2 and E is in J/cm^2

What I am saying is that IEEE 1584 provides the following formula to convert from normalized incident energy to the actual incident energy: E = 4.184*Cf*En(t/0.2)(610^x/D^x) And E and En are both in J/cm^2. Therefore why do we have a 4.184 factor?

If En is in J/cm^2 and E is in J/cm^2 then why are we introducing the 4.184 cal->J conversion factor.

Hi, in IEEE 1584 equation (4) (page 11) it states "En is the incident energy (J/cm^2) normalised..." Then in equation (6) E = 4.184*Cf*En(t/0.2)(610^x/D^x) E is the incident energy (J/cm^2) and in section E.3.1 Equation (E.1) E= Cf*En*(t/0.2)(610^x/D^x) in cal/cm^2 Is En from equation (4) in...

It is an IEC Application.

ABB SACE Protection and Control Devices appears to show that the instantaneous setting can be turned off (I have attached the relevant page). Also Icu and Ics are much higher than the instantaneous override maximum...

Should the impedance correction factor be applied to the minimum fault calculations aswell or only the maximum fault calculations? I have seen a similar question to this where there was debate since the formula only mentions cmax, but not cmin.

Hi, I was wondering what reason is behind IEC 60909's transformer impedance correction factor. Is this replace transformer impedance tolerance, or should they both be applied?

The reason I though it might have one is that in the ABB white paper "Working with the Trip Characteristic Curves of ABB SACE Low Voltage Circuit-Breakers" Figure 13 shows a TCC of the PR222DS/P-LSIG (with Tmax T4H250 CB) with I protection not activated. In the figure, the Instantaneous Override...

Hi, does anyone know what the instantaneous override current of an ABB Tmax T4S circuit breaker with PR222 trip unit is? I cannot seem to find an ABB document which has this.

Hi dpc, is this also the case for electronic trip units? Specifically I am looking at curves from PR222DS/P trip units for ABB T4S and T5S circuit breakers, and PR331/P trip units for ABB T7H circuit breakers.

Hi all, I am currently using ABB circuit breakers, which has an uninterruptible current rating equal to their frame size. However the long time pickup of their associated trip devices has a tolerance of 1.05 to 1.20. Does the continuous current rating of the CB preclude me from using the...

Hi all, In ETAP I have added LV circuit breaker opening times in the "Min. Delay" field under the Ratings Tab. However the opening times do not appear in the sequence of events or arc flash study results, and the arc flash fault clearing times appear to just use the trip device TCC time at the...

However, doesn't the 3*Zn come about, because the zero sequence currents are in phase, and all travelling on the return path (so the algebraic trick is to change 3*In*Zn to In*(3*Zn))?

dpc, when you say ETAP should be able to explain their methodology and what their Z0 represents where do you think I can get this information? I sent an email to ETAP's help desk, but they have not responded. Also redfurry, I believe Zn includes the zero sequence impedance of the return path...

My understanding was that for a single line to ground fault If = 3*V / (Z1 + Z2 + Z0 + 3*Zn) With V the phase line to neutral voltage, Z1, Z2, Z0 the sequence impedances of a phase line, and Zn the zero sequence impedance of the neutral conductor. I guess what I am after is how does the zero...

When attempting to validate IEC 60909 L-G fault calculations from ETAP, I find that the fault levels are higher than I calculated. It appears that ETAP is doing Sqrt(3) c U / |2*Z1 + Z0|, with Z0 taken directly from the R0 and X0 in the cable library entry, rather than using Z0 = Z0 phase...