jfox
Member
- Location
- Shelbyville, KY
Hello everyone,
A homework question is asking me if you have a 50 hp 480v motor and a 30A 277v load to calculate the transformer size required.
The FLA of the motor is 65A from table 430.250.
My kVA for the motor would be 65*480*1.732= 54 kVA
My single phase kVA would be 30*277= 8.3 kVA
If i understand this right i now add 54 + (8.3*3) = 78.9 kVA as my highest leg would be 54/3=18kVA per leg and 8.3kVA is added to a leg for a total of 26.3kVA. As my highest leg is 26.3kVA this is multiplied by 3 to give me my total 3 phase load, 78.9kVA.
My question is am i done at this point, meaning my answer is 78.9kVA or do i need to add 125% to this value? Someone also told me transformers could be sized up to 300% however im not seeing anything in the code book that supports either of these percentages for sizing the transformer itself.
A homework question is asking me if you have a 50 hp 480v motor and a 30A 277v load to calculate the transformer size required.
The FLA of the motor is 65A from table 430.250.
My kVA for the motor would be 65*480*1.732= 54 kVA
My single phase kVA would be 30*277= 8.3 kVA
If i understand this right i now add 54 + (8.3*3) = 78.9 kVA as my highest leg would be 54/3=18kVA per leg and 8.3kVA is added to a leg for a total of 26.3kVA. As my highest leg is 26.3kVA this is multiplied by 3 to give me my total 3 phase load, 78.9kVA.
My question is am i done at this point, meaning my answer is 78.9kVA or do i need to add 125% to this value? Someone also told me transformers could be sized up to 300% however im not seeing anything in the code book that supports either of these percentages for sizing the transformer itself.