zero sequence impedance
zero sequence impedance
(OP)
Attempting to calculate the zero sequence impedance for a delta-wye transformer. Basically, typical transformer has a zero sequence impendance value of 85%-95% of impedance. I need to design for 120%-170% of impendance. What variable will allow for a larger ratio of zero sequence impendance to impedance? Thanks.






RE: zero sequence impedance
RE: zero sequence impedance
In a core-type transformer, the zero-sequence flux path typically must leave the iron. This reduces the inductance slightly.
To make the zero seq impedance higher, you would have to figure out a way to make the leakage reactance seen by zero sequence current greater than the leakage reactance seen by the positive seq current. I don't see how this can be done, but I'm not a transformer designer.
It should be quite simple to add a grounding resistor or reactor to the transformer to restrict ground fault current to whatever you desire. This is quite commonly done on medium voltage systems.
Hope this helps.
dpc
RE: zero sequence impedance
The only way to increase ZSI value up to 120 to 170% is to add a reactance or resistor between neutral and ground. You must take into account that neutral impedances increase ZSI value in an amount equivalent to three times their own value.
Hope to help you
Julian