As I heard, neutral of grid (zigzag transformer) and the neutral of generator are connected till they are synchronized. It is disconnected when the synchronization is done.

Can someone let me know why it has to be so? If it is not, how the neutral is used?

Thank you in advance...

 

Lakmalp...

the most likely reason is the system designer wanted to minimize ground/earth-fault current.

Regards,
Phil Corso

 

your system is an unearthed system. And normally the zigzag transformers are used to feed the restricted earth fault current. the full load rating of zigzag transformers must be equal to the system designed earth fault rating.

if both the zigzag transformers are ON, then because of parallel path the earth fault current will be double of its designed value. that is why you must keep only one zigzag transformer ON.

If you put the generator neutral side transformer then any earth fault in the system will be fed through the generator which is better to avoid, i.e., keep the grid side zigzag transformer ON.

 

Thank you a lot for your response. I am not familiar with zigzag transformer. Better read about it first and then read your reply. Will post if anything is unclear... (Y)