Schwatzernov
Electrical
- Sep 5, 2006
- 47
Hi,
I wonder why the IEC60076-5 requires that the system source impedance be added up to the transformer short circuit impedance and used in calculating the through fault current for transformer damage curve instead of using only the transformer impedance ? When the %Z of transformer was fixed before purchasing, after that when we calculate relay setting and plot the damage curve, the source impedance of system should not cause the damage curve shifted lower(less strength to short circuit) since the transformer was designed with its impedance alone which is always less than that the system impedance included which means that the transformer was designed to withstand higher fault current than it is put into the system which the actual fault current is lower. So the damage curve of transformer shouldn't be shifted lower(less withstand capability).
The transformer damage curve for mechanical damage from time at 2.0 sec and below down to 0.25 sec plotted by ETAP based on IEC transformer has two options. The " calculated " option will cause the ETAP calculating transformer damage curve by including system source impedance in the damage curve calculation and plotting.
The " user define" option, the user can determine whether to include or not the system source impedance with the transformer impedance for damage curve calculation and plotting.
I wonder that which method is correct in calculating transformer damage curve between using only transformer impedance and combination of system source impedance with transformer impedance for the case that we have already specified the transformer impedance and purchased transformer. Which curve is correct in plotting the protection coordination with relay between only transformer impedance alone and that the system impedance included.
I wonder why the IEC60076-5 requires that the system source impedance be added up to the transformer short circuit impedance and used in calculating the through fault current for transformer damage curve instead of using only the transformer impedance ? When the %Z of transformer was fixed before purchasing, after that when we calculate relay setting and plot the damage curve, the source impedance of system should not cause the damage curve shifted lower(less strength to short circuit) since the transformer was designed with its impedance alone which is always less than that the system impedance included which means that the transformer was designed to withstand higher fault current than it is put into the system which the actual fault current is lower. So the damage curve of transformer shouldn't be shifted lower(less withstand capability).
The transformer damage curve for mechanical damage from time at 2.0 sec and below down to 0.25 sec plotted by ETAP based on IEC transformer has two options. The " calculated " option will cause the ETAP calculating transformer damage curve by including system source impedance in the damage curve calculation and plotting.
The " user define" option, the user can determine whether to include or not the system source impedance with the transformer impedance for damage curve calculation and plotting.
I wonder that which method is correct in calculating transformer damage curve between using only transformer impedance and combination of system source impedance with transformer impedance for the case that we have already specified the transformer impedance and purchased transformer. Which curve is correct in plotting the protection coordination with relay between only transformer impedance alone and that the system impedance included.
![[ponder]](/data/assets/smilies/ponder.gif "[ponder] [ponder]")