How to determine the reasonable capacity of the transformer

1. Basic Investigation and Analysis

First, a comprehensive investigation should be conducted, including the power supply voltage, the user's real-time load characteristics, equipment type, and local environmental conditions. The rated technical parameters marked on the transformer nameplate should be carefully reviewed.

2. Core Selection Basis: Load Capacity and Nature

The selection of transformer capacity is crucial for its rational application and must be determined based on the total capacity of all user equipment, load characteristics (e.g., constant load, intermittent load, impulsive load), and expected load operating time. Under normal operating conditions, the transformer's load rate should ideally be maintained between 75% and 90% of its rated capacity. This range is generally considered the optimal operating range for energy efficiency and economy.

3. Load Rate Monitoring and Capacity Adjustment

During long-term operation, the actual load of the transformer needs to be monitored:

If the actual average load consistently falls below 50% of the rated capacity, it means the transformer is operating at a "large capacity for a small load," which is uneconomical. Replacing it with a smaller capacity transformer should be considered.

If the load exceeds the rated capacity, it is considered overload operation, which will seriously affect the transformer's lifespan and power supply safety. Immediate replacement with a larger capacity transformer is necessary. 4. Voltage and Wiring Selection

Voltage Matching: The rated voltage of the primary coil must match the power grid voltage. The output voltage of the secondary coil should be determined based on the voltage requirements of the electrical equipment.

Preferred Solution: On the low-voltage distribution side, a three-phase four-wire power supply is recommended. This wiring method can supply not only three-phase power loads but also single-phase lighting power, offering high flexibility.

5. Special Load Considerations: Motor Starting Current

When selecting capacity, special attention must be paid to equipment with high starting currents, such as motors. Since the starting current of a motor can reach 4 to 7 times its rated operating current, an improperly selected transformer capacity may prevent normal starting due to a sudden voltage drop. Therefore, the selected transformer capacity must be able to meet the instantaneous current requirements of the largest motor starting in the system.