Selection principle of power transformer capacity

The transformer capacity should be selected according to the calculated load. When determining the transformer capacity, the load rate of the transformer should be determined first. When the transformer no-load loss is equal to the load factor multiplied by the square of the load loss, the efficiency is relatively high. At the point of higher efficiency, the load factor of the transformer is 63%-67%. For a transformer with stable power supply for a single load, the load rate is generally around 85 percent. But this is only a conclusion drawn from the perspective of power saving, not detailed enough. Important factors to be considered are the various economic costs of transformer operation, including fixed asset investment, annual operating costs, depreciation costs, taxes, insurance costs and other nominal costs. When selecting the transformer capacity, increasing the load factor of the transformer to reduce the number or capacity of the transformer, that is, sacrificing operating efficiency and reducing one-time investment, is the only choice.

When installing two or more main transformers, the capacity of each power transformer should be selected according to the power outage of any one of them. The remaining capacity should be at least 60% to 75% of the primary load or the total load of the substation. Generally, 75% of primary substations and 60% of secondary substations are used. The transformer primary power factor is related to the load rate. When operating at full load, the power factor of the primary side is 3%-5% lower than that of the secondary side, and when the load factor is less than 60%, it is 11%-% lower than the power factor of the secondary side. Eighteen. The high load rate is beneficial to improve the power factor of the high-voltage side. As the load rate increases and the capacity of the circuit breaker increases, the investment will increase.

The capacity of a single transformer in a low-voltage 0.4kV substation shall not exceed 1600KVA. When the capacity of the electrical equipment is large, the load is concentrated, and the operation is reasonable, a transformer with a capacity of 2000kVA and above can be selected. In recent years, some manufacturers have been able to produce large-capacity me, ah-type low-voltage circuit breakers and current-limiting low-voltage circuit breakers. There are many 1250kva and 1600KVA transformers used in civil buildings, especially above 1250kva. Therefore, it is recommended that the capacity of a single transformer should not be greater than 1250kva.