Transfomer 3PH primary OCP with inside delta SCR control

Status
Not open for further replies.

spectrum

Member
I'm trying to determine what the correct OCP would be for a 1500KVA 480V 3PH 3W delta-delta transformer with inside delta SCR control. No secondary protection. This is a multi-tap transformer that gets tapped occasionally to match the load to the power supply. The resistance of the load changes depending the manufacturing process being used that week. The inside delta SCRs have 1200A fuses (fast acting SCR protection). There is a current limit adjustment on the SCRs that we use to keep amps below the existing 1600A OCP (924A at the SCR = 1600A at the branch circuit feed). Article 450.3(B) gives you the maximum OCP. (1500KVA X 1.25) / (480V X 1.732) = 2255A. Article 220.18 says the calculated load shall not exceed the rating of the branch circuit. 1600A is the largest OCP I can go to. So I guess the question is whether my load is the size of the transformer, 1500KVA, or determined by the current limit setting on the SCRs.
 
Status
Not open for further replies.
Top