Ferroresonance in distribution systems
Ferroresonance in distribution systems
(OP)
We have a 1200' run of 13.8 kV underground cable feeding a 3 phase padmounted 500 kVA Yg-Yg transformer from 3 single phase fuses. I have found some new information on ferroresonance that suggests that there still may be ferroresonace occuring in the YY transformer because of the newer low loss 5 legged core designs of recent years.
Is anyone aware of ferroresonance avoidance steps or guidelines that I might use to determine if there is an issue in the above or other cases??
Thank you,
Veman....
Is anyone aware of ferroresonance avoidance steps or guidelines that I might use to determine if there is an issue in the above or other cases??
Thank you,
Veman....






RE: Ferroresonance in distribution systems
Also IEEE C57.105-1978
Title: IEEE Guide for Application of Transformer Connections in Three-Phase Distribution Systems
Abstract: The characteristics of the various transformer connections and possible operating problems under normal or abnormal conditions are treated for three-phase distribution systems. These systems are characterized by primary voltages up to and including 34.5 kV, usually have a preponderance of connected transformers with low-voltage windings below 1000 V, and furnish electric service to consumers. All combinations of Delta and Y, grounded and ungrounded, T connected, zigzag, and certain special connections are considered. Only two-winding transformers are included. Phasing procedures and loading practices are not covered.
RE: Ferroresonance in distribution systems
for a fairly comprehensive paper on ferroresonance.
Regards
Marmite
RE: Ferroresonance in distribution systems
RE: Ferroresonance in distribution systems
We have seen ferroresonace under the conditions you describe. The optimum solution is to do three pole switching at the riser pole or if you are lucky to have a LBOR swith in the transformer primary.
Jim
RE: Ferroresonance in distribution systems
RE: Ferroresonance in distribution systems
RE: Ferroresonance in distribution systems
As another option, you could add some load on the transformer, but you typically need about 2% of the transformer rating to suppress the ferroresonance. That would be 10 kW in your case. Sounds like a lot of heat to deal with, so I don't think it's practical!
RE: Ferroresonance in distribution systems
Yes, seen this in grnd wye/grnd wye. Some literature in the past did say that it was minimized with this type of connection implying that you would not get ferroresonaces. But we did see it.
Jim
RE: Ferroresonance in distribution systems
However, with a three-phase 5-legged core, you get a coupled voltage from the other phase(s) that leads to ferroresonance.
It is more likely with 25 and 35 kV systems, but, with sufficient cable, it does happen on 15 kV systems (12.5, 13.2, 13.8, etc.).