WYe Grounded PTs on Pure delta system

[mooreaaryan]

Good morning all
I have a Primary transformer DELTA/DELTA 70KV TO 12KV. within the last five years the facility has added solar to the site with BESS. The old system has a MV distribution of wye delta transformer in the plant and the new system has wye grounded PTs for measuring and the SEL ground fault protection. When we deenergize the system for maintenance or inspection we cannot get the plnat back on line with out deracking the PTs and force the system on


How does the PTs wye grounded and the DELTA system interact? Why does is not consistently interact? How would someone approach fixing this system to ensure its safety and operations

 

[LarryFine]

Is the 12kv grounded or floating?

 

[mooreaaryan]

The 12kv is floating

 

[jim dungar]

Are you sure the problem is the PTs and not the SEL relay programming?

 

[jim dungar]

How does the PTs wye grounded and the DELTA system interact?

The grounded wye PTs are creating an artificial neutral point. This is a pretty common thing to do. Is the BESS backfeeding the PTs?

 

[mooreaaryan]

Are you sure the problem is the PTs and not the SEL relay programming?

I was not aware that the program could cause a fault like this? would be a setting for the PT value Delta WYE? coudl phase shift casue this?

 

[electrofelon]

The grounded wye PTs are creating an artificial neutral point. This is a pretty common thing to do. Is the BESS backfeeding the PTs?

Is that typical to have grounded wye PT's on an ungrounded system? Doesnt that ground the system or at least effect your fault detection scheme?

 

[jim dungar]

I was not aware that the program could cause a fault like this? would be a setting for the PT value Delta WYE? coudl phase shift casue this?

What is your fault mode? Is a relay operating preventing a breaker from closing?

 

[jim dungar]

...effect your fault detection scheme?

Yes, your PT arrangement needs to be considered as your protection functions are configured.

 

[mooreaaryan]

The breaker is closing in most situations. The fault is CAG T but when we investigate and run throught the entire system we dont find a real fault.

 

[mooreaaryan]

Is that typical to have grounded wye PT's on an ungrounded system? Doesnt that ground the system or at least effect your fault detection scheme?

I have not done enough MV Microgrid to Existing facilities to know if this is typical. I understand that the grounded wye PTs are needed to ensure the Ground Fault Protection scheme has a reference to ground to engage protection.