i need a little help with my homework. if you bank three single phase dual voltage transformers in a delta connection for the primary and do the same for the secondary, do the kva of primary add together or do the kva stay the same because it is connected in delta.it's a 2:1 480v - 240v each transformer is 5 kvais the total kva when connected in delta 15 kva or 5 kva and do you use the formula Pa line current times line voltage times 1.73 to find the rated load current.thanks in advance
Certainly. Normally this would be more expensive. However if you look at local utility poles, they do this all the time to preserve supplies if there is a fault (they have many single phase users so they don't want a fault on one phase to lose power from the others) but they still have 3 phase users OK on this configuration. Placing the transformers on the floor would not affect the operation
With 3-5KVA transformers connected inbank, your total capacity is 15Kva.To find the line current: Kva 1.732[V](I)/1000. Line current, I KVA{1000]/1.732{V) I 15[1000]/480*1.732 I 18.042, volts at primary.
Delta connection it's mean you give 480 V 3 phase, and output 240 V 3 phase. So the total KVA in delta is 5 KVA and the formula like you said. Pa I (current) x Volt x 1.73 (three phase) x cos Q (Cos Phi).
