Digsilent zero sequence impedance YYn0

[vlady34]

I use DIgSILENT PowerFactory to simulate grids. But I have the problem that a YYn0 transformer has a Z0 (zero sequence impedance) of 60.88% and impedance transformer 7.42%. By modeling this phase fault current is less than 100 Amp., To obtain the events of the recloser installed on the network can observe single-phase fault current of 829 Amp., This value you can get from PowerFactory if box write zero sequence impedance 0.6088%. I would like to help me if anyone has had these problems and how resolved, and I read the IEC standards and can not find a solution. Thank you.

[surgeArrester]

Is the value of your zero sequence based on nameplate or data sheets or data specs of the said transformer? I ask this because I was wondering how come your zero sequence is way large compared to the Z1 impedance. Most transformers are Z1=Z2=Z0 (in values).

[vlady34]

It's nameplate transformer, according to IEEE 242-2001 Z0 is 0.85 times the Z1 for a delta-wye connection. But according to IEC 60076 for star-star connection with grounded low voltage side of the Z0 is equal or greater than 60%. My question is how to simulate this type of connection DigSilent if in reality the single-phase fault current is much higher than that obtained from PowerFactory.

[surgeArrester]

It's nameplate transformer, according to IEEE 242-2001 Z0 is 0.85 times the Z1 for a delta-wye connection. But according to IEC 60076 for star-star connection with grounded low voltage side of the Z0 is equal or greater than 60%. My question is how to simulate this type of connection DigSilent if in reality the single-phase fault current is much higher than that obtained from PowerFactory.

Ahh.. so you're saying that an actual fault occurred in your system and you want to simulate that fault? And it so happened that you cannot obtained the actual value of the fault based on DigSilent simulation? This is what I think.

a) First, if you say it is a nameplate value, use that nameplate value. Don't override it with the standard.

b) Second, verify if your Yny0 transformer doesn't have any buried delta within. Sometimes, Yny0 transformers have buried delta to stabilize ampere-turns of the transformer.

c) Check if you have the updated fault-level or short circuit level at the source.

d) If you cannot get the value and you think that the transformer has something wrong, have that transformer checked its impedance, it that way you can know the z1, and z0 actual impedance.

[vlady34]

Thanks for your feedback, and after reviewing some research I found that there is a bank YD (23 / 0.240 kV) transformers in the network to a couple of kilometers from the transformer, just this three-phase bank is doing that the system is in reference to earth. The problem was not the simulation but it had not taken into account other network connections, effectively isolating the substation single-phase input currents are low by high zero sequence impedance. Thank you .....