Ferroresonant resistant transformer
Ferroresonant resistant transformer
(OP)
Does such a creature exist? Can manufactures (like Howard industries for example) have the ability to build pole and padmounted transformers with a modified saturation curve?
I am entertaining the idea of a 33kv distribution system, however my only hold back is that engineering literature brings up ferresonance being very likely under single phase conditions.
I am entertaining the idea of a 33kv distribution system, however my only hold back is that engineering literature brings up ferresonance being very likely under single phase conditions.






RE: Ferroresonant resistant transformer
But three single-phase transformers can easily be connected in delta. They will not work well if connected in star.
The cores are fairly simple to modify so you get a leakage path for the loose coupling needed between primary and secondary. And saturation is just a question of flux, which is where the resonant part comes in. So, technically, it should be possible to build such a creature. Or rather three of them.
But they have a lot of losses, due to iron saturation, and may not be worth it. Also, it is not very often that 100+ MVA needs to be stabilized. What application is this?
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Ferroresonant resistant transformer
11kv is not known for ferroresonance, single phase switching and blown fuses present no over voltage hazard.
Can you explain what you mean by this? "First, it is resonant only, not resistant." By resistant I mean not likely to go into ferroresoance.
RE: Ferroresonant resistant transformer
You asked for e ferroresonant transformer and those are also known as magnetic stabilizers. You are obviously not at all asking for that. Sorry.
Is ferroresonance (in the bad meaning) a problem in your grid?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Ferroresonant resistant transformer
The thing is I am evaluating going from 11kv to 22 and 33kv, and I am not sure what to expect since single phase switching and cutout protection of equipment is common.
RE: Ferroresonant resistant transformer
They probably do but, when you deal with the volume of distribution transformers in North America, manufacturers tend to standardize on the amount of core steel for a given kVA rating. For three phase transformers, the grounded-wye grounded-wye is preferred over delta grounded-wye for minimizing the likelihood of ferroresonance at the higher voltage systems like 25 kV and 34.5 kV. This grd-y grd-y design was initially thought to be immune from ferroresonance, but the voltage coupling from the adjacent leg caused the overvoltage problem because you then had an open circuit voltage in series with an L-C circuit.
The idea of using three single phase cores in a three phase padmount tank was suggested some thirty years ago to solve the problem with a grounded-wye grounded-wye padmount transformer because, under open phase conditions, the other two phases were not affected as they would be with a five-legged core construction. It didn't prove to be a commercial success even though the cost might have been 10 or 15% more than the standard offering.
If you're looking at 34.5 kV distribution rather than 33 kV, the previous comments apply. My understanding is that the 33 kV (European) distribution systems tend to be three wire circuits so it is a different situation than what I was referring to.
RE: Ferroresonant resistant transformer
Worthwhile comments none the less, the same issue comes up with 34.5kv quite a bit.
There is a trend both overseas and in the US to use 35kv class equipment in new builds.
RE: Ferroresonant resistant transformer
RE: Ferroresonant resistant transformer
Your comment re: cost is still valid, but the extra costs for a special design and build may be avoided.
Bill
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"Why not the best?"
Jimmy Carter
RE: Ferroresonant resistant transformer
What about a higher X/R ratio, or lossier transformer?
Basically would you feel comfortable with this: A 33kv system with fused cutout protected transformers consisting of 50kva single phase, 3 50kva banks and mostly 150-250kva 3 phase 3 limb units. What would the odds be of ferro? I am hoping the load will dampen it out- at least it should on the 3 phase units from the amount of load being served.
RE: Ferroresonant resistant transformer
Mbrooke,As others said, Yn/Yn transformers are not resonance proof. You will find that mistake in literature before 1990.There are several ferro-resonance mitigating measures mentioned in above standard, Main is measures to avoid single phasing during switching.
RE: Ferroresonant resistant transformer
Can you post the main points of Clause 7.3, if permitted? I am not getting it here:
http://odysseus.ieee.org/search?search-input=C57.1...
RE: Ferroresonant resistant transformer
RE: Ferroresonant resistant transformer
I still don't get how Europe does it. I've heard of 22 and 33kv being routine with delta units and fused cutouts. I am starting to think thats why 11kv exists in the first place...
RE: Ferroresonant resistant transformer
Remember that part of the ferroresonance risk includes the cable capacitance. In Europe with denser cities, cable lengths tend to be shorter with a lower capacitance.
RE: Ferroresonant resistant transformer
Given the efficiency gained by bypassing an entire voltage class and eliminating a half dozen substations for every subtranmission substation, its worth weighing the risk.
RE: Ferroresonant resistant transformer
https://www.sandc.com/globalassets/sac-electric/do...