- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
3300V is not really very high when it comes to insulation. Think of systems of more than 25kV line to line (about 14.4kv line to ground).
Y-Y WHY?
- Thread starter brian john
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Got that backwards.
Easy way to think about this.
The transformer is rated in kVA.
In wye, the voltage across the winding is lower so the current must be higher to get the same kVA.
And maybe a drawing:
Oh well, I'd submitted my post above before I saw that.
That's why it's called medium voltage..
The transformers are 11kV primary which is not greatly different to that in post #1.
It's delta connected on the primary and has two secondaries, one, delta the other, star. That's what the Dd0yn11 designates
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
That's why it's called medium voltage..
The transformers are 11kV primary which is not greatly different to that in post #1.
It's delta connected on the primary and has two secondaries, one, delta the other, star. That's what the Dd0yn11 designates
Medium voltage goes all the way up to 69kV, depending on who you talk to.
Insulation/clearance to ground is fairly easy to maintane to about 15kV, so the wye connection becomes more of an issue for systems with line-line voltages of 25kV, which is more than double the TX you are discussing.
As I said at the begining of this thread, advantages/disadvantages of wye primaries on utility grids are a different discussion than wye primaries on customer owned systems.
And more than double the voltage in post #1 as it happens. So, to that extent, you're confirming my point that the voltage levels, whether star or delta, are not likely to have a huge impact on price for this particular case.
Point accepted.
I don't very often get involved in anything where the supply voltage is above 11kV. It's a fairly common supply voltage for industrial consumers and the primary for local 11kV to 400V transformers for commercial and residential. I have yet to come across one that had a star connected primary and I can't see what advantages that could/would be confer.
Leaving aside the insulation issues that you suggest are not much of and issue up to 25kV, what do you see as the advantages of a star connected primary?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Effectively, there are none, unless you are a utility and are concerned with protective relaying schemes for distribution and transmission.
Same question. How does it help them?
I don't see how but I accept that there might be points that I'm missing.
Distribution and transmission is not my field.
I just know that, at local level here, three wire and delta is how it is done.
see post number 11
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Other topics (some good, some bad)
Arcing faults
Zero sequence currents
Ground faults
Distributed capacitance.
Overvoltages during transient conditions (including switching)
Ferroreonance
I feel industrial power system engineers, power electronics engineers, utility distribution power engineers live in different worlds. Although that may be just a phase I am going through.
T
T.M.Haja Sahib
Guest
The wye-wye transformer is most economical to use till the break-even point of lower purchase cost of the wye-wye transformer compared to the higher running cost of copper losses due to increased phase current.In the present case,the POCO might have calculated this break-even point and taken the economical decision to replace with wye-wye transformer.
Interesting.
All other things being equal, you would need to know the relative cross sectional area of the winding conductors to determine which configuration had the higher copper losses.
They are unlikely to be the same conductors so you cannot reasonably conclude which will have the higher copper losses solely on the basis of configuration.
T
T.M.Haja Sahib
Guest
Say the Y-Y transformer is 100 KVA and delta-Y transformer is also 100 KVA.The purchase cost of this Y-Y transformer is less and its copper loss is more but the total cost is less than that of 100KVA delta-Y transformer.This relation holds up to a certain KVA level of the Y-Y transformer.Suppose it is 500KVA i.e the break even point.Beyond this value,using a Y-Y transformer in place of delta-y transformer will not be economical.This line of reasoning was perhaps the basis of POCO's decision in the present case.
Did you read my previous post?
I don't think you can conclude either way which of the two configurations will have the greater copper loss as a generality.
The windings of the Delta connection will take lower current than those of the WYE connection.
And will have a design rating for that lower current.
Designers of transformers or any wound components don't generally want to include more copper than required if they are to be competitive.
It is thus quite unlikely that same cross-sectional area of conductor would be used on the Delta winding as that required for the higher current in WYE.
In short, the Delta will have thinner conductors than the WYE.
If standard conductors are used, it might happen that there is a nearly exact rating for one and a sub-optimal for the other. But which?
Cost isn't the issue.
Regarding a previous post of my was the fact that the requirement for a 5 or 4 legged core adds significantly to the cost of a Y-Y transformer overlooked? I don'y think the cost of copper is an issue and neither is efficiency. It's the core of the transformer because of having to dealing with ferroresnonance unbalance. If a 5th leg is not added in the transformer core design the path of the magnetic field will flow through the transformer tank or enclosure which will result in heat. A similar issue occurs when an air core reactor that is installed in a steel enclosure.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
In Wisconsin, WE Energies (the largest POCO) uses all y-y connections on their 34.5kV and above systems. These transformers are built using either three individual single-phase transformers, or they use a single three-phase unit (i.e. padmount) built using a 'tri-plex' core, which effectively is three single phase units in a one enclosure. 4 and 5 legged cores construction is cheap compared to tri-plex core. Customer owned transformers are not required to be tri-plex constuction, but it is highly recommended.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
I think the main advantage was given by Hv&Lv in post 11. Utilities tend to switch single phase & this connection allows that with the least amount of disturbances to the system.
Thanks Jim,
Should (3) 1ph transformers be purchased to be configured in a Y-Y in the field I would have had no idea. I have provided many pad mounts but never to utilities where a Y-Y is most likely used as my customer base was commercial/industrial and never had the opportunity to provide a tri-plex core configuration.
What you pointed out make perfect sense.
Should (3) 1ph transformers be purchased to be configured in a Y-Y in the field I would have had no idea. I have provided many pad mounts but never to utilities where a Y-Y is most likely used as my customer base was commercial/industrial and never had the opportunity to provide a tri-plex core configuration.
What you pointed out make perfect sense.
T
T.M.Haja Sahib
Guest
A tertiary winding is necessary only when the HV neutral line is not connected to the transformer HV neutral terminal.When it is connected,there is a path for zero sequence current to flow and then there would be no need for a tertiary winding.And such lower cost, high voltage,small wye-wye transformers are popular with the POCO for their distribution purposes in U.S.
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