Answer:
Step-by-step explanation:
To determine the 3Ø rating of the transformer bank required to supply a 3Ø, 45 KVA load, we can use the following formula:
KVA = √3 x VL x IL
Where:
√3 = 1.732 (the square root of 3)
VL = line voltage
IL = line current
For the load:
KVA = 45 KVA (given)
For the transformer bank:
VL1 = 480 V (primary line voltage)
VL2 = 120/208 V (secondary line voltage)
IL2 = KVA / (√3 x VL2) = 45 KVA / (1.732 x 208 V) = 122.5 A (secondary line current)
Since the transformer bank is a 3Ø transformer, the KVA rating of the transformer bank can be calculated using the following formula:
KVA = √3 x VL1 x IL1
Where:
VL1 = primary line voltage
IL1 = primary line current
To solve for IL1:
IL2 = IL1 / √3 (assuming balanced loads and ideal transformer)
IL1 = IL2 x √3 = 122.5 A x √3 = 212.1 A (primary line current)
Therefore, the required 3Ø rating of the transformer bank is:
KVA = √3 x VL1 x IL1 = 1.732 x 480 V x 212.1 A ≈ 174 KVA
So, the transformer bank must have a 3Ø rating of at least 174 KVA to supply a 3Ø, 45 KVA load with a 3Ø, 480 Δ to 120/208-volt "Y" transformer bank.