主变容量一般根据变电站建成后5-10年的短期负荷规划来选择，并适当考虑

The main transformer capacity is generally selected according to the short-term load planning of 5-10 years after the completion of the substation, and the long-term load development of 10-15 years is appropriately considered. For suburban substations, the main transformer capacity should be combined with urban planning. For long-term benefit, the power station should select the main transformer capacity according to the total load in the near and long term. For the substation with important load, the main transformer should be determined according to the nature of the load and the grid structure. When one transformer is out of service, the capacity of the other transformer should be considered. It should be within the time allowed by the overload capacity to ensure the user's primary and secondary load. Therefore, the rated capacity of each transformer is Sn = 7.0pm, where PM is the maximum load selection of the substation, that is Sn = 0.7 × 38.77 = 27.14kva. When a transformer stops operating, 70% of the load is also guaranteed. Since the non-important load of the general power grid substation accounts for about 25%, in order to ensure the important load of the substation, it is feasible to calculate the main transformer capacity with Sn = 7.0pm. After calculation, the main transformer with rated capacity of 31.5MVA can be selected. In order to ensure the reliability of the power supply and avoid the failure of one main transformer or the impact of maintenance on the power supply, two main transformers are generally installed in the substation. The installation of three or more substations improves the reliability of the substation, but the wiring network is complicated, which increases investment. At the same time, the complexity of power distribution equipment and power protection has increased, as has the complexity of maintenance and switching operations. Considering that the probability of two main transformers failing at the same time is small and suitable for long-term load growth and expansion, the selection of two main transformers in this substation fully meets the requirements.

The main variable capacity is generally selected according to the short-term load planning of 5-10 years after the completion of the substation, and the long-term load development of 10-15 years is given due consideration. For suburban substations, the main variable capacity should be combined with urban planning. In the long-term interest, the power station should choose the main variable capacity according to the near-term and long-term total load, for substations with important load, should be based on the load nature and power grid structure to determine the main change, should consider the retirement of one transformer, another transformer capacity should be in the overload capacity allowed time, to ensure that the user's first and secondary load. Therefore, the rated capacity of each transformer is Sn . 7.0pm, where pm is the maximum load selection for the substation, i.e. Sn s n.s. 38.77 x 27.14kva. When a transformer stops operating, 70% of the load is guaranteed. Since the non-essential load of the general power grid substation is about 25%, it is feasible to calculate the main variable capacity by Sn s 7.0pm in order to ensure the important load of the substation. The main transformer with an optional capacity of 31.5MVA is calculated to be available. In order to ensure the reliability of power supply, to avoid the failure of a main change or the impact of maintenance on the power supply, generally installed in the substation two main changes. The installation of three or more substations has improved the reliability of the substations, but the complex wiring network has increased investment. At the same time, the complexity of power distribution equipment and power protection increases, as does the complexity of maintenance and switching operations. Considering that the probability of two main transformers failing at the same time is small, suitable for long-term load growth and expansion, the choice of two main transformers in this substation is fully satisfied.

The main transformer capacity is generally selected according to the short-term load planning of 5-10 years after the completion of the substation, and the long-term load development of 10-15 years is properly considered. For suburban substation, the main transformer capacity should be combined with urban planning. For the long-term benefit, the power station shall select the main transformer capacity according to the total load in the near and long term. For the substation with important load, the main transformer shall be determined according to the load nature and grid structure. When one transformer is out of service, the capacity of the other transformer shall be within the time allowed by the overload capacity to ensure the primary and secondary load of the user. Therefore, the rated capacity of each transformer is Sn = 7.0pm, in which PM is the maximum load selection of the substation, that is, Sn = 0.7 × 38.77 = 27.14kva. When a transformer stops running, 70% of the load is also guaranteed. Because the non important load of general Grid Substation accounts for about 25%, in order to ensure the important load of substation, it is feasible to calculate the main transformer capacity with Sn = 7.0pm. The main transformer with rated capacity of 31.5MVA can be selected after calculation. In order to ensure the reliability of power supply and avoid the influence of one main transformer failure or maintenance on power supply, two main transformers are generally installed in the substation. The installation of three or more substations improves the reliability of the substation, but the connection network is complex and increases the investment. At the same time, the complexity of distribution equipment and power protection increases, as well as the complexity of maintenance and switch operation. Considering that the probability of two main transformers failure at the same time is small, it is suitable for long-term load growth and expansion, so the selection of two main transformers in this substation fully meets the requirements.<br>