Zigzag transformer - Zero sequence impedance
Zigzag transformer - Zero sequence impedance
(OP)
Zigzag transformer is supposed to offer low impedance for zero sequence currents. Any typical value??
IEEE 62.92.4 has a typical calculation for sizing the zigzag transformer and arrives at the required transformer per phase zero sequence impedance value as 5ohms.
Thanks in anticipation.
IEEE 62.92.4 has a typical calculation for sizing the zigzag transformer and arrives at the required transformer per phase zero sequence impedance value as 5ohms.
Thanks in anticipation.






RE: Zigzag transformer - Zero sequence impedance
Bahram7
www.Simtech-Intl.com
RE: Zigzag transformer - Zero sequence impedance
The 33kV system I am working is supposed to be solidly grounded. This means that the earth fault current magnitudes shall be 95% of the phase fault currents (very effectively earthed - IEEE 62.92.1) and it means the zero sequence impedance (phase-earth) needs to be lower than 5 ohms when the 132/33kV transformer is 50MVA with 12.5% impedance.
Do you think the same is achievable!
Thanks once again for sharing.
RE: Zigzag transformer - Zero sequence impedance
RE: Zigzag transformer - Zero sequence impedance
It sounds like you are working with IEC voltages. You can get typical zero zequence values for various transformer connections in Table 1 of IEC 60076-8 "Application Guide for Transformers".
Hope this helps.
Kiri
RE: Zigzag transformer - Zero sequence impedance
You can also use a standard delta-wye transformer as a grounding transformer.
RE: Zigzag transformer - Zero sequence impedance
I would check in the IEC for typical values as suggested by Kiribanda. Thanks.
dpc, the standard of my client specifies 132/33kV, YNd1 grid transformer with Zig zag earthing transformer. I do not have much experience with sizing / specifying these transformers. Thanks.
RE: Zigzag transformer - Zero sequence impedance
I reviewed the Table 1 in IEC 60076-8. The table doesn't include zero sequence impedance values for Zigzag transformers.
RE: Zigzag transformer - Zero sequence impedance
RE: Zigzag transformer - Zero sequence impedance