Selection of Power Transformer for Wind Power Plant

[ShaikhSahab]

We are installing 49.5 MW wind power project. Wind Turbine Generators are Double Fed asynchronuos Generator, wound rotor. WTG will import power from Grid for excitation. We will produce power at 690Volts and evacute to power purchaser at 132kV level.

What will be Vector Group of GSU Transformer to step up from 690v/22kV and then power Transformer from 22kV / 132kV. Here is a confusion
If we select power transformer YnD11 (Yn at 132kV side and D at 22kV side) then how earth fault at 22kV Delta side will be sense during import of power from Grid?

If we select power transformer DYn11 (D at 132kV side and Yn at 22kV side) then how earth fault at 132kV Delta side will be sense during export of power to Grid?

I propose two solutions

1- Yn Yn 11 to protect both sides in any senario importing / exporting power from / to Grid.

2- YnD11 with earthing trasnformer (But it is very costly solution and extra switchgear/protection of earthing trasnformer will be required.

Please see this link on which i have uploaded diagram of different scenarios for your better understanding

http://files.engineering.com/getfil...4d3f-9ea8-60726cf0f904&file=Vector_Group.pptx

Expert comments are requested to all for selection of best economical solution. Thanks

 

[Marmite]

In the UK transformers at 132kV and above have a star primary. The transformer is cheaper that way rather than delta because the insulation is graded down to the star point. Also the 132kV system here is solidly earthed. If your wind farm was being built here it would probably have a Yd 132/22kV transformer with an interconnected star/star earthing transformer per main transformer to provide the 22kV earth point and also to derive a low voltage station service. The 22kV/690V transformers would be Dy with the LV star point neutral solidly earthed. Wind farm protection is in my experience always designed to operate the same way as distribution protection with the fault infeed from the system rather than the wind farm, as this is where the bulk of the fault current will come from. The elctronics in the wind turbines will act very quickly to limit the contribution from the turbine.
Regards
Marmite

 

[lz5pl]

Thank you, Marmite, I am on the same stage as ShaikhSahab - determination of vector groups of station trafo and WTG's transformers. Your post confirms our solution. The only difference is that here for 20 kV grid we use YNyn0d transformers 110/20kV, (tertiary winding with reduced power, used only for separating of zero sequence systems), 20 kV neutral grounded through current limiting resistor. For 33 kV grid, as will be our project, transformers are Ynd11, 110/33 kV, with grounding transformer ZN and current limiting resistor.
Station auxiliary services are from separate trafo 20(33)/0,4 kV. Hope this will help also ShaikhSahab.

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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[rockman7892]

Marmite

You mentioned a wye/star primary on the 132kV utility side solidly grounded and a Delta connection on the 22kV side with an interconnected transformer.

Is it not possible or practible to use a wye/wye transformer with the wye solidly grounded on both sides of the transformer or is this connection avoided for the purpose of passing zero sequence from one side to the other. I'm interested in learning why this wye/wye transformer is not practical in this application.

Is it awlays customary for the utility side of the transformer to be a star connection? What about for voltages lower than 132kV?

 

[ShaikhSahab]

Thank you very much Marmite and lz5pl,

Your opinions are very helpful.

I have convinced to use YNyn0d Power transformer 132/22kV, (with tertiary winding used for separating of zero sequence systems)because use of separate earthing transformer will be costly solution (Cost of Switchgear / protection will increase overall project cost moreover it will occupy space and increased M&R), while in YNoynOd with tertiary winding, all protections will be in service during both cases import and export of power from / to Grid due to star point on both MV and HV side.

What is your opinion if we use same configuration YNyn0d with tertiary winding for 22kv/690V transformer?

What will be significance of current limiting resistor in above configurations?

I have attached ppt file of different vector group configurations.

http://files.engineering.com/getfil...52-a03b-4df802713358&file=Configurations.pptx

Please review and suggest suitable configuration.

Regards,