The selection of the capacity of prefabricated substations mainly follows these steps:
1. Load Forecasting
The total load of all potential users within the power supply area must be accurately calculated. This involves statistically analyzing all existing and potentially future electrical equipment, taking into account their actual usage frequency.
Common load calculation methods include the demand factor method, power per unit area method, unit index method, and utilization factor method.
For residential buildings, the power per unit area method or unit index method is typically used to estimate the average power consumption per square meter of building area.
For example, in residential community scenarios:
In more developed areas, the load per household can be considered as 12 kW; in general areas, 9 kW; and in areas with lower electricity consumption, 6 kW.
If considering the building area, houses with a building area exceeding 120 m² are calculated at 12 kW, those between 90 and 120 m² at 10 kW, and those less than 90 m² at 8 kW. If there are storefronts, an additional 100W/m² is applied. In addition to the residential portion mentioned above, the load generated by public facilities such as landscape lighting and streetlights also needs to be considered.
2. Capacity-to-Load Ratio Considerations
When selecting the main transformer capacity, besides directly based on the current load, the capacity-to-load ratio (i.e., the ratio of the transformer's rated capacity to the maximum load) must also be considered. This ratio is determined according to local power grid planning guidelines. A reasonable capacity-to-load ratio ensures sufficient reserve capacity to maintain system stability even with load growth.
3. Reserving Future Development Space
Considering that electricity demand changes over time, an appropriate margin should be reserved when selecting the capacity of the prefabricated substation to cope with future load growth. This means that even if there is no obvious trend of load increase in the short term, a slightly larger transformer capacity should be selected to avoid cost waste and technical difficulties caused by frequent equipment replacement.
4. Economic Benefit Analysis
A comprehensive evaluation of the return on investment of different capacity options should be conducted to select the optimal solution that meets both current load demand and long-term development.