No phase shift between systems
No phase shift between systems
(OP)
Basically I have come up with an idea to eliminate 30 and 60 degree phase shifts between transmission and distribution. The plan is to step down 132kv to 33kv via a Wye grounded delta transformer (YNd11) which produces a 30 degree shift and have a 33kv to 12kv delta wye (Dyn01) with an apposing 30 degree phase shift relative to the 132/33 transformer. The end result would be having the 12 kv distribution system in phase with the 132kv system.
Playing with a Fermat point I think this is doable?
Is this approach practical?
Playing with a Fermat point I think this is doable?
Is this approach practical?






RE: No phase shift between systems
RE: No phase shift between systems
RE: No phase shift between systems
Delta systems have a tendency to suffere with many interesting problems.
RE: No phase shift between systems
RE: No phase shift between systems
@cranky108: probably a zig-zag fault duty transformer and a 5 ohm resistor.
RE: No phase shift between systems
Regards
Marmite
RE: No phase shift between systems
Do have more info onto exactly how the UK power companies do this? I apologies for seeming so novel. This concept isn't common around here.
The other option which is has been the normal for now has been 132-33kv Ygr-Ygr with a 33-12kv delta zig zag (Dz0) when trying to maintain phase shift.
How does the UKs approach differ to a Dz0?
RE: No phase shift between systems
I've attached a copy of the Central Networks primary design manual which may be of interest.
Regards
Marmite
RE: No phase shift between systems
Alls good but I cant get the link open. It defaults to a blank page.
RE: No phase shift between systems
RE: No phase shift between systems
RE: No phase shift between systems
RE: No phase shift between systems
Good question. Hopefully a UK EE will relieve the secrets behind its application in the UK. I don't believe the UK has my situation at hand but we will see.
The reasoning is twofold.
The first reason has to do with the distribution system itself. Larger load pockets are served directly from transmission, while lesser pockets are served via sub-transmission sometimes called "bulk distribution".
In a some areas 12kv (along with other distribution voltages like 22kv)used to be fed via Ygr-Ygr with a delta tertiary. I believe the reason for this was the insulation could be reduced on the primary and the delta fed ungrounded obsolete distribution voltages where the 12kv acted as sub-transmission before becoming distribution.
As these units were replaced with larger ones zero sequence currents passing into the 132kv system became a concern, especially with units over 30MVA which placed bothersome levels during faults on the 12kv system. A delta primary was chosen, however because of the phase shift older units could not be paralleled with newer ones. Delta-zig zag (Dyn0) were decided upon which allowed for paralleling during maintenance reasons or redundancy.
The 12kv system fed from sub-transmission on the other hand has always had a phase shift due to most 33kv, 46kv and 66kv lines being 3 wire with no neutral run. This lead to delta wye units.
This has never really be an issue, however with automatic load transfer and recloser loop schemes being implemented phase angle and especially transformer phase shift between systems have become a major headache. To increase reliability recloser loop schemes allow distribution to transfer into other neighboring systems fed by different substations. When putting the loop back to normal after the fault is repaired or the substation is put back on line the segment can not be restored via closed transition, the tie point into the neighboring system has to be opened before closing back into the regular system. As a result customers have to experience a second outage. If the first outage was resulting from a sub station outage as many as 12,000 customers have to experience a second outage as each feeder is transferred to the normal feed substation through open transition. Same goes for off loading a substation, 2 outages have to occur in this scenario when closed transition can eliminate both.
The second reason has to do with cogeneration and generation dispatch operations preferences. By having distribution in phase with transmission it is easier to keep an eye on the whole thing, much the same way its a preference (though many, many) times more to have bulk 400kv transmission in phase with 132kv local transmission. Generation feeding into both is in essence at the same rotor angle so to speak.
RE: No phase shift between systems
Would this create a phase offset of a Dyn01?
RE: No phase shift between systems
Then if you swap two phases on the high-side and two phases on the low-side you can get (when combined with rolls) another set of three vector groups offset 60 degrees from the previous set. With the right selection of rolls and swaps you get any of the six possible vector groups for that transformer winding. A swap on only one side of the transformer causes the two sides to have opposite phase sequence, one will be A-B-C and the other A-C-B.
RE: No phase shift between systems
Do any PDFs/excels exist of the various shifts?
RE: No phase shift between systems
At one point the Basler web site had a collection of technical papers that included one on various transformer connections. I haven't looked for it in several years so I wouldn't know if it's still available.
RE: No phase shift between systems
RE: No phase shift between systems
This is "the standard" for understanding transformer phase shifts & vector groups... it took me a while to find this one...
Hope this helps!
http://GeneralPAC.com - A platform to ASK, LEARN, SHARE, & GROW in power protection, automation, and controls.
The Wye Wye Transformer Connection video: http://gpac.link/1GdGRSQ
RE: No phase shift between systems
RE: No phase shift between systems
Sorry the its an jpg, all I had to get it online, but this is what your after.
RE: No phase shift between systems
Yes that is it, having transmission and distribution be at 0 degrees in regard to one another. I really appreciate the your effort, and trust me, the upload is legible.
I will read through the paper to get an idea of what connections are parellable.
One more question that's slightly off and on topic. In cases like this Ive been told that in theory the best solution is delta detla at the transmission and delta delta at the distribution. Deriving a ground point aside (Ive done it many times) is there anything that would stop me such as tap changers from having a delta delta 132 to 12kv or 132 to 33kv transformer? Id imagine tap changes perform differently on a delta secondary as apposed to a wye?