IEC shortcircuit two phase faults
IEC shortcircuit two phase faults
(OP)
Hello,
I would like to receive your feedback related to shortcircuit analysis using IEC 60909 methodology to calculate two phase and two phase to earth faults because, there are not all of the currents determined by the software.
We already read the standard and it talks about only initial and peak currents for these sort of faults.
This is very different from the three phase and single phase to ground faults where initial, breaking, peak and thermal currents are calculated.
The question is:
Does anybody know the reasson for IEC 60909 not calculate breaking and thermal currents for two phase and two phase to earth faults?
I thank you in advance your comments!
I would like to receive your feedback related to shortcircuit analysis using IEC 60909 methodology to calculate two phase and two phase to earth faults because, there are not all of the currents determined by the software.
We already read the standard and it talks about only initial and peak currents for these sort of faults.
This is very different from the three phase and single phase to ground faults where initial, breaking, peak and thermal currents are calculated.
The question is:
Does anybody know the reasson for IEC 60909 not calculate breaking and thermal currents for two phase and two phase to earth faults?
I thank you in advance your comments!






RE: IEC shortcircuit two phase faults
RE: IEC shortcircuit two phase faults
I thank your answer, however our concern it is not related to the magnitude of the values.
It is oriented mainly to the customer requirement to "see" all of the values for all of the faults.
RE: IEC shortcircuit two phase faults
RE: IEC shortcircuit two phase faults
"the double earth fault is not included in Fig. 3-7 [Diagram for determining the fault with the highest short-circuit current from IEC 909-the former edition of IEC 60909] ;it result in smaller currents than a two-phase short-circuit"
It seems that is not always true.
From ABB Switchgear Manual Table 3-2 :
Two-phase-to-earth fault:
I"kE2E=1.1*SQRT(3)*ULL/[Z1+ZO+ZO*Z1/Z2]
Phase-to-phase fault -clear of earth=
I"k2=1.1*ULL/[Z1+Z2]
Phase-to-earth fault=
I''k1= 1.1*sqrt(3)*ULL/[Z1+Z2+ZO]
Let say Z=X neglecting R for Z1,Z2 and Zo
Let say: K21=Z2/Z1; KO1=Zo/Z1 then:
K2p=Two-phase-to-earth fault/ Phase-to-earth fault
K2p= I"kE2E/ I'k1=1.1*sqrt(3)*ULL/[Z1+ZO+ZO*Z1/Z2]/ 1.1*sqrt(3)*ULL/[Z1+Z2+ZO] or:
K2p= [1+K21+KO1]/]1 +KO1+KO1/K21]
K2E2P= Two-phase-to-earth fault/ Phase-to-phase fault -clear of earth
K2E2P= I"kE2E/ I'k2=1.1*sqrt(3)*ULL/[Z1+ZO+ZO*Z1/Z2]/ 1.1*ULL/[Z1+Z2] or:
K2E2P=sqrt(3)*(1+K21)/(1+KO1+KO1/K21)
If K21=1 then for KO1=0 to 1
K2p= 0 to 1 K2E2P= 0 to 1.15
If K21=0.5 then for KO1=0 to 1
K2p= 0.5 to 1.25 K2E2P= 0 to 1.73
See Table 3-2 on the attachment.
Regards
RE: IEC shortcircuit two phase faults
I thank your responses, they are very usefull!
However, the main question is:
Why does not IEC Std for shorcircuit calculations determine thermal and breaking currents for two phase faults?
What I have seen is that the three phase fault is the highest current magnitude unless, there could be some syncronous motor connected at the same bus, in this last case, the two phase fault gives a higher current magnitude.
I thank in advance your feedback
RE: IEC shortcircuit two phase faults
Regards