YNd11 Transformer Solid Grounding?

[AHMED ELEC]

Hi

I want to install step up 400V-6.6kV YNd11 transformer.(Star on high side and delta on LT side).
Can I use solid grounding on high(6.6kV) side?
Transformer is to be used for utility application with utility generator.

 

[protoslash]

i think you need to ask the utility on this. Assume the utility is operating at 6.6kV

A wye delta transformer is a ground source. when you solidily ground the wye side, it increase the 6.6kV system grounding effectiveness. This lead to increase overall ground fault current, but reduces the zero sequence current from the utility end which might desensitize their ground fault protection. Depending on the grid design, they may or may not allow this which is why you need to ask them.

 

[waross]

Are you aware that a grounded wye/delta transformer will increase the available current for line to ground faults?
Check with the utility.
They may require a floating wye point or a wye/wye transformer.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[AHMED ELEC]

Thanks

Transformer size is 100kVA,and installation required is with 400V generator for small facility utility power supply.
Utility transmission is at 6.6kV which is stepped down to 400V at user end(substations).
I have option of installing Dyn11 (Delta High side and Y on Low side) for this application.
Which one should I install?

 

[waross]

Is this standby or cogeneration?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[FreddyNurk]

The question is more of both what will the utility require me to use, and in the absence of a utility (you're running your own network, as an example) how do I detect and clear faults on the 6.6kV network?
Solidly grounded YNd arrangements along with earth fault detection are common if you're the only source feeding a network. As you haven't indicated these constraints it is unclear as to whether this is suitable for you.

EDMS Australia

 

[Kiribanda]

When your generator is connected to 6.6kV Utility network, Utility has to make sure that still their network is effectively earthed.
To fulfill that your step-up transformer should have WYE so that it will be a zero seq source. By using a DELTA at the Utility side
it is not possible to full fill eff. earthed condition.Therefore, the main issue is detecting and tripping phase to earth faults
on a DELTA system. All in all, your transformer should be 6.6kV(WYE SOLID EARTHED)/ 400V(delta).
But by using a WYE EARTHED transformer on their side the Utility contribution to an earth fault is lowered and that is another
reason why some utilities donot support or silent about using a WYE EARTHED on their side.
Since your transformer is 100kVA only, it looks like you are a small IPP. Therefore, without asking too many questions from the
Utility, still you can use a 6.6kV DELTA transformer. But in that case provide earth fault protection on the 6.6kV side
using a VECTOR SHIFT & ROCOF relay which is very widely used in mini hydro generation. It will ensure that phase to earth faults
on the 6.6kV DELTA system are detected, tripped & isolated.