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# Open Delta Calculation

1. ## Open Delta Calculation

Three 1000kVA single phase transformers were connected to form a closed delta connection. If one of these transformers was removed and the remaining configured as an open delta. What is the output capacity of this new configuration?

A) 1260kVA
B) 1740kVA
C) 2020kVA
D) 2360kVA

So, my memory of open delta configurations or faulted 3-phase delta transformers are capable of 58% of total inital power. I assume three 1000KVA transformers would combine to a single 3000KVA Delta transformer thus the 58% of that would equal 1740KVA. The answer was wrong, am I wrong somewhere in my calculations?

Here's an link to a PE Exam review that explains where I get the 58% on question 14:

https://www.electricalpereview.com/o...er-connection/  Reply With Quote

2. Originally Posted by Kalbi_Rob Three 1000kVA single phase transformers were connected to form a closed delta connection. If one of these transformers was removed and the remaining configured as an open delta. What is the output capacity of this new configuration?

A) 1260kVA
B) 1740kVA
C) 2020kVA
D) 2360kVA

So, my memory of open delta configurations or faulted 3-phase delta transformers are capable of 58% of total inital power. I assume three 1000KVA transformers would combine to a single 3000KVA Delta transformer thus the 58% of that would equal 1740KVA. The answer was wrong, am I wrong somewhere in my calculations?

Here's an link to a PE Exam review that explains where I get the 58% on question 14:

https://www.electricalpereview.com/o...er-connection/

You are correct and the answer in the database is 1740kVA, its unclear why this would be marked incorrect. This must have been a software error, thank you for reporting. Please let us know if this happens again.  Reply With Quote 