Can be built ? 3

[sberbece]

Hello!

It is possible to build a power transformer with these parameters:
S=250 MVA
V=500 / 30 kV
Vector group: Preferably YNd
?

What is the maximum transformation ratio a power transformer could have?

Thank you in advance!

Regards,
Stefan

 

[davidbeach]

For enough money anything is possible, but why do something so far out of normal practice? I can't think of any justification for going from the highest transmission voltage to a distribution voltage all in one transformer. You're missing a couple of voltages in between.

 

[ScottyUK]

Plenty generator transformers use ratios such as 22/400kV step up and those were built many years ago. So 'yes', it could be built. Other than a GSU transformer I'm not sure where you'd need a 250MVA 30kV transformer - there's going to be an awful lot of copper on the 30kV side.


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If we learn from our mistakes I'm getting a great education!

 

[m3ntosan]

UK TSO has many 400/33 kV and 400/25 kV for distribution, railway supply or costumers connected directly to the transmission system.


May you grow up to be righteous, may you grow up to be true...

 

[sberbece]

Thank you very much all!

David, the application will be an iron ore processing plant. This will have six SAG Mills 25 MW each, 12 Ball Mills 12 MW each, a number of HV supplied pumps and other auxiliary loads. The total plant demand is around 450 MW. Overall, the plant will not be larger than 2 sq km. Incoming power supply 500 kV. Since SIEMENS have 33 kV, 5000 A incomer & busbar GIS switchgear, I believe will be cheaper to drop the intermediate voltage level and use a direct 500/30 kV power transformer.

M3ntosan thank you for your tip.

Again, thank you all for your thoughts.

Stefan

 

[Skogsgurra]

I think that, when you calculate cost for a pure 500 V distribution, you will find that a more normal 33/10 or 33/6 kV distribution will be more flexible and more economical. An iron ore processing plant is rather widespread and you will need heavy gauge cables (probably bus-bars) to avoid too much voltage drop and power losses in the distribution.

Even if the plant is no more than 2 km2 and circular in shape and your big transformer is put in the middle (which is rather unusual and not very practical), you will still have distances up to between 600 and 800 m to cover and that is too far for a 500 V 10+ MW distribution.

Or do I miss anything?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ScottyUK]

"Or do I miss anything?" A lower-case k, perhaps?

500kV, not 500V.


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If we learn from our mistakes I'm getting a great education!

 

[marks1080]

Hahaha.... 500V. I didn't even get that until I went back to read it.

Yes it is possible to built the unit you spec'd.

 

[Skogsgurra]

Why ask about 500 kV to 33 kV? That isn't so far out, even if an intermediate 110 kV may be good to have.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[sberbece]

m3ntosan

What is the size of the transformer and the winding configuration for the 400/25 kV TX you've mentioned?

THX!
Stefan

 

[ScottyUK]

Stefan,

Almost all large generator transformers are constructed as YNd1, so the configuration you are looking for is entirely possible. At this rating the physical size is highly dependant on configuration and cooling method: the most compact would likely be an ODAF cooled design with tank-mounted radiators, unless you get involved in exotic designs such as water cooled types.


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If we learn from our mistakes I'm getting a great education!

 

[m3ntosan]

Stefan,

150 and 180 MVA, YNd1/11

May you grow up to be righteous, may you grow up to be true...

 

[prc]

Stefan,
You are on right track.We can save money and energy by reducing the number of voltage transformations.Transformer engineers can manage any transformation ratios.They are alreday making 22/800 kV GSUs, 33/0.1KV Furnace transformers.So for them 500/33 kV ratio is not an issue.The real problem is the max rating of 33 kV Breaker available in the world market.A couple of years back when a large oil refinery made such an excercise,the max rating of SF-6 type 33KV breaker avialble in the world could manage about 200 MVA.So self supplied 194 MVA 220/33 KV transformers for distributing power inside refinery.I dont know whether breaker technology attained more than that level. You may contcat MV breaker manufacturers for their limit.
When you dont have suitable breaker, the solution is to go for multi LV transformers ie 250/125-125 MVA 500/33-33 KV transformers.Any connection is feasible Ynd1 or 11 or Yy.In case manufacturer is able to manage 250 MVA only with 5 limbed core instead of normal 3 limbed core,then you have to ask for an additional delta stabilising winding if you opt for Yy connection.

Scotty, copper quantity in a transformer winding is same whether 500 KV or 33 kV as long as current density remains the same.Normally the same current density is maintained in HV and LV windings.Some times due to better cooling( due to lesser paper insulation,higher current density is used in LV winding, resulting in less copper in LV winding

 

[ScottyUK]

Hi prc,

I don't think I (intentionally) suggested otherwise. When I mentioned which configuration would be most compact I was really meaning overall footprint of the transformer - for example a transformer with an off-tank radiator bank normally occupies a significantly larger area of land than a type with tank-mounted radiators. Of course the decision is sometimes made simply by the size of the transformer. I haven't seen many 3-phase types bigger than 400MVA with tank-mounted radiators.


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If we learn from our mistakes I'm getting a great education!