45kva transformer amps

The current calculation and selection suggestions for a 45kVA transformer (480V to 120V) are as follows:

### I. Current Calculation Formulas

1. **Current on the Three-phase Primary Side (480V)**

2. **Current on the Single-phase Secondary Side (120V)**

### II. Precautions for Practical Applications

1. **Influence of Power Factor**

   - If the load is an inductive device (such as a motor), the current needs to be corrected according to the power factor (usually 0.8 - 0.9):

For example, when the power factor is 0.8, the secondary current is approximately

2. **Suggestions for Circuit Breaker Selection**

   - **Primary Side**: Configure a 63A circuit breaker for three-phase (a 20% margin is required).

   - **Secondary Side**: Configure a 400A circuit breaker for single-phase (it is recommended to use branch control to avoid single-circuit overload).

3. **Reference for Cable Specifications**

   - **Primary Side**: 6mm² copper-core cable (current-carrying capacity ≥ 60A).

   - **Secondary Side**: 95mm² copper-core cable (current-carrying capacity ≥ 400A).

 III. Explanation of Special Scenarios

1. **Application of Three-phase to Single-phase Conversion**

   - If it is necessary to convert from three-phase 480V to single-phase 120V, it is recommended to select a three-phase transformer (such as a star connection method), and ensure that the load is evenly distributed to the three phases.

2. **Overload Capacity**

   - The short-term overload capacity of the transformer is usually 120% - 150% of the rated capacity (duration ≤ 2 hours), but frequent overloads should be avoided.

 IV. Safety and Compliance

1. **Grounding Requirements**

   - The grounding resistance of the neutral point ≤ 4Ω, and the enclosure grounding needs to comply with the GB 50169 standard.

2. **Protection Level**

   - For outdoor installation, the protection level should be above IP54, and for indoor installation, IP20 + a cooling fan is recommended.

*Conclusion**: The three-phase current on the primary side of the 45kVA transformer is approximately 54A, and the single-phase current on the secondary side is approximately 375A (which needs to be adjusted according to the load characteristics). When selecting, the circuit breaker, cable specifications, and heat dissipation conditions need to be matched to ensure the safe operation of the system.