Synchronization Between Two Different Voltage Souces Via Transformer

[kitloke77gmail]

We need to synchronize an 11kV voltage source with one 415V source. Attached is a simple sketch of connection diagram.

In order to have the synchronization done at 415V bus, I need to first step down the 11kV source to 415V. Can I use the same transformer to feed the 415V supply back to the 11kV bus after synchronization?

Can I use a YNyn transformer so that I can first step-down the 11kV source to 415V to give supply to the 415V Generator Auxiliary (three phase with neutral, connected to the same 415V bus) to start up the 415V generator and then use the same transformer to export the 415V supply to the 11kV bus?

 

[waross]

Yes.

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

 

[rcw retired EE]

That is a common way of doing it.

Check the grounding (earthing) on the YNyn transformer. A gounded neutral on either the 400V or 11 kV side will affect the ground fault current level and may defeat high impedance grounding.

 

[kitloke77gmail]

We are having NER grounding on the 11kv Generator to limit the fault current to 100A. While the 415V Generators are solidly grounded.

 

[waross]

Should be OK but check the transformer for a strap between primary and secondary wye points. Remove it if one is found.

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

 

[kitloke77gmail]

Do you mean we should connect the HT wye point through the 11kV Generator NER and the LV wye point shall be solidly grounded? What will happen if we have both the primary and secondary wye points solidly grounded?

 

[waross]

The fault current will be dependent on the system impedance (grid impedance plus generator step up transformer contribution) rather than being limited by a NGR.

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