Parallel Transformers at different tappings? 1

[MarTech1]

Hi looking to tap down two identical 11kV/415V transformers these will be done isolated one at a time, however they will need to be momentarily parallelled while they are at different taps I know the risk of circulating currents and fault rating risk of parallel fed LV switchboards. How can I pre-determine what the circulating currents may be to prevent risk of trip?
Has anyone experience of doing this before?

 

[rbulsara]

Refer to this for a good example and calculation method..

http://www.cdnova.com/Portals/0/Link 1 - App11- Introduction to Parallel Control.pdf

Rafiq Bulsara

http://www.srengineersct.com

 

[stevenal]

http://www.beckwithelectric.com/main/doccenter/appnotes/appn-11.pdf

http://www.beckwithelectric.com/main/doccenter/appnotes/appn-13.pdf

 

[jghrist]

You can model the transformers as parallel impedances, with a voltage source in one parallel path equal to the no-load voltage difference between the two unequal ratio transformers.