In a previous article, we briefly discussed the selection of the number of transformers in substations. This article will further explore how to determine the number of transformers required for a substation.
Ⅰ. Determining the Number Based on Load
The transformer load is mainly determined by the requirements for power supply reliability and the potential losses or impacts of power outages.
1、Primary Load:
Primary loads refer to those where power interruptions can cause significant political and economic losses or impacts. For example, the anti-theft power supply for a large museum. If the power supply is interrupted, it may lead to the theft of precious cultural relics and exhibits. Under such conditions, at least 2 transformers are required to ensure that if 1 transformer or power line fails, the other transformers or lines can take over the load, ensuring uninterrupted power supply.
2、Secondary Load:
Secondary loads refer to those where power interruptions can cause considerable political and economic losses or impacts. For instance, power outages in large theaters and shopping malls, which are important public places with large crowds, can lead to disorder. Secondary loads typically require backup power measures but are not as stringent as primary loads. Generally, 2 transformers are used, 1 main transformer and 1 backup transformer.
3、Tertiary Load:
Tertiary loads refer to other power loads that do not fall into the primary and secondary categories. For example, some non-critical commercial facilities that do not have special power supply requirements and can tolerate longer power outages typically need only 1 transformer.
4、Other Loads:
In addition to the above types of loads, there are other types of loads. For example, seasonal loads change due to seasonal variations, usually related to climate and temperature; concentrated loads occur when a large amount of power demand is concentrated on a single transformer or substation, often in industrial areas with high power demands. For these types of loads, at least 2 transformers should be installed.
Ⅱ. Determining the Number Based on Voltage Levels
1、Low Voltage:
Substations with voltages of 1kV or below are considered low-voltage substations, mainly serving local loads such as small factories and residential areas. These small substations typically install 1 transformer. For scenarios with high power supply reliability requirements, 1 backup transformer can be considered.
2、Medium Voltage:
Substations with voltages of 1kVA to 35kVA are considered medium-voltage substations, mainly used in urban grids and industrial and mining enterprises’ distribution systems. In practice, medium-voltage substations typically install 1-2 transformers.
3、High Voltage:
Substations with voltages of 35kV to 220kV are high-voltage substations, serving as the main lines for power transmission, capable of transmitting power from power plants to distant power consumption areas. In practice, high-voltage substations typically install 2-3 transformers. To ensure power supply reliability and flexibility, it is generally recommended to configure at least 2 transformers.
4、Extra High Voltage:
Substations with voltages of 220kVA to 765kVA are considered extra-high voltage (EHV) substations, mainly used for long-distance power transmission and the backb1 of large power systems. In practice, extra-high voltage substations typically install 3-4 transformers, with specific numbers varying according to actual needs. Redundant design (e.g., N+1 or N+2) is an important measure to ensure high reliability in power supply.
5、Ultra High Voltage:
Substations with voltages of 1000kVA or above are considered ultra-high voltage (UHV) substations, mainly used for ultra-long-distance power transmission and international grid interconnections. In practice, ultra-high voltage substations install at least 4 transformers, with specific numbers varying according to actual needs. Additional transformers are installed for redundancy and backup.
6、High Voltage Direct Current:
DC substations are typically used for high-voltage direct current (HVDC) transmission systems, which are employed for long-distance transmission, submarine cable connections, and specific power applications. In practice, high-voltage DC substations typically install 4-6 transformers. Additional transformers are installed for redundancy and backup.
7、Ultra High Voltage Direct Current:
Ultra-high voltage direct current (UHVDC) substations are typically used for long-distance, high-capacity power transmission, such as international power exchanges or long-distance transmission. In practice, UHVDC substations install at least 6 transformers. Additional transformers are installed for redundancy and backup.
Ⅲ. Determining the Number Based on Substation Size
1、Small Substation:
Small substations with capacities ranging from a few MVA to dozens of MVA serve small industrial areas, commercial areas, small residential areas, and rural distribution. They typically install 1-2 transformers, with relatively simple equipment, suitable for areas with low load demand.
2、Medium Substation:
Medium substations with capacities ranging from dozens of MVA to hundreds of MVA serve urban distribution grids, medium industrial areas, large residential areas, and regional distribution centers. They typically install 2-3 transformers, with more complex equipment, suitable for areas with moderate load demand.
3、Large Substation:
Large substations with capacities of several hundred MVA or more serve large urban power grids, important industrial areas, and main power transmission networks. They typically install 3 or more transformers, with complex equipment and high reliability and redundancy designs, suitable for areas with high load demand and critical power nodes.
4、Ultra Large Substation:
Ultra-large substations with capacities ranging from several hundred MVA to thousands of MVA serve long-distance power transmission, large urban and industrial power supplies, and international grid interconnections. These substations typically install 4-8 transformers, with additional transformers for redundancy to ensure high reliability. They are also equipped with auxiliary equipment such as circuit breakers, synchronous compensators, and protection devices to handle emergencies and maintenance needs.
Ⅳ. Determining the Number Based on Economic Conditions
1、Low Economic Conditions:
– Small Substation: Typically configures 1 transformer to save costs, with fewer backup transformers.
– Medium Substation: Typically configures 1-2 transformers, considering costs and basic power supply needs.
– Large Substation: Typically configures 2-3 transformers, considering power supply reliability and redundancy.
– Ultra Large Substation: Typically configures 3-4 transformers based on large capacity power supply needs and a certain degree of power supply reliability.
2、Moderate Economic Conditions:
– Small Substation: Typically configures 1-2 transformers, with at least 1 backup transformer to enhance power supply reliability.
– Medium Substation: Typically configures 2 transformers, with 1 backup transformer.
– Large Substation: Typically configures 2-3 transformers, with 1 backup transformer.
– Ultra Large Substation: Typically configures 4-6 transformers based on large capacity power supply needs and power supply reliability requirements.
3、High Economic Conditions:
– Small Substation: Typically configures 2 transformers, with 1 backup transformer.
– Medium Substation: Typically configures 2-3 transformers, with 1 or more backup transformers.
– Large Substation: Typically configures 3-4 transformers, with 1-2 backup transformers.
– Ultra Large Substation: Typically configures 4-8 transformers, with additional backup transformers as needed.
The number of transformers not only depends on the above factors but also needs to be designed and planned according to the specific requirements of the power system. Different countries and regions have their own classification methods and standards. Additionally, with technological advancements and growing power demands, the scale and voltage levels of substations are constantly changing. Therefore, there is no fixed standard for the number of transformers in a substation.
