Question

For installation with a 25-kVA, 3-phase transformer, a 440-volt primary, and a 120-volt secondary. Calculate the maximum overcurrent protection value (not the fuse or circuit breaker rating) using the protection method for primary-only protection. (Round the FINAL answer to two decimal places.)

Answer 1

Answer:

41.053 A

Explanation:

given,

three phase kVA = 25-kVA

voltage = 440 Volt

current = ?

To determine three phase kVA when volts and amperes are know

   three phase kVA = 1.73 x V x I

    $I = \dfrac{three\ phase\ kVA}{1.73 \times V}$

    $I = \dfrac{25000}{1.73 \times 440}$

           I = 32.84 A

the maximum overcurrent protection value is equal to

            = 125 % of I

            = 1.25 x 32.84

            = 41.053 A