Component structure and voltage level of box type substation
1、 High voltage side power receiving equipment:
When selecting high-voltage side power receiving equipment for box type substations, it is advisable to choose components with small size and low price as much as possible while meeting performance and environmental requirements.
1. High voltage switch (Circuit Breaker):
At present, there are many types of domestically produced 10 kV circuit breakers, such as KLF-10, ELC-24, XYn-10, etc. SF circuit breakers have a trend of replacing low oil switches in box type substations due to their long lifespan, low maintenance workload, and reliable performance.
2. Fuse:
Fuse is a supporting component of high-voltage switch, which is the main protective device for high-voltage side grounding and phase to phase short circuit. It has high reliability requirements and should have clear signs for closing and opening. Such as the current drop out fuse or the recently developed fuse with a red flag protruding after gas production, it can be pulled and closed with an insulating rod for easy maintenance and repair of the circuit breaker. In recent years, a type of double fuse has been introduced abroad, which is sensitive to temperature and current, also known as double sensitive fuse. The application of this fuse has improved the reliability of high-voltage switches.
3. Lightning arrester:
At present, metal oxide lightning arresters are commonly used, which have good performance in preventing atmospheric overvoltage and can also absorb surge currents during switch opening and closing. It is more suitable for distribution Vacuum Circuit Breakers and can absorb their operating overvoltage, such as Y5 W zinc oxide lightning arresters.
2、 Transformer:
The transformer used in outdoor box type substations is a step-down transformer, which generally reduces the 10kV level power supply to 380V/220V for user use.
The capacity of a transformer is generally 160-1600kVA, while the commonly used capacity is 315-630kVA. Transformers can be oil immersed, fire-resistant, resin based, etc. Most of them use Oil Immersed Transformers because they are cheaper in price. In places with strict fire prevention requirements, non oil immersed transformers should be used, such as dry-type transformers in high-rise buildings. The utilization rate of dry-type transformers in developed countries has reached 80% -90%. In recent years,dry-type transformers have developed rapidly in China, such as oxygen grease injection type SCL-2, pressure immersion type VPI, and wrapped type (also known as Thunderbolt type). Various dry-type transformers have been widely used in combination substations
3、 Selection of components for low-voltage distribution equipment:
The low-voltage distribution equipment is equipped with a main switch and a branch switch. The branch switch is generally 4-8 units, and can reach up to 12 units at most. The branch switch occupies a considerable amount of space in the box type substation, and by reducing the size of the branch switch, more branch switches can be installed. When selecting main and branch switches, short arcing or zero arcing products should not be selected except for volume requirements.
There are two forms of low voltage chambers: one with an operating corridor and the other without. The width of the operating corridor generally needs to be 1000 mm. If there is no operating corridor, the low-voltage room door panel can also be made into a wing door flip up type, and the flip up panel can provide shade and rain protection during operation. This structure is common in foreign power distribution facilities.
DW15 and DWX15 low-voltage circuit breakers are commonly used in the main circuit, both of which are automatic low-voltage switches that can be operated manually or electrically. Equipped with overload and short circuit long and short delay protection, as well as multiple automatic release devices for voltage loss and shunt excitation, it constitutes a relatively complete protection measure. In various branch circuits, DZ20 air circuit breakers are often used, which also have thermal trip protection for short circuits.
Voltage level of box type substation:
At present, the voltage levels of domestically produced box type transformers are 3-35kV on the high voltage side and 0.4-10kV on the low voltage side. The capacity of a transformer can range from several hundred kilovolt amperes to tens of thousands of kilovolt amperes when the rated voltage ratio is 35/10, 6, and 0.4 kV, and from several tens of kilovolt amperes to several thousand kilovolt amperes when the rated voltage ratio is 10, 6/0.4 kV.
Also known as box type transformers, prefabricated substations, etc., they are divided into American type box transformers and European type box transformers.
The electrical equipment components in the box type substation are all selected from standardized products, and the technical performance of the components meets the corresponding standard requirements. Box type substations also have functions of energy detection, display, and measurement, and can achieve corresponding protection functions. They are also equipped with dedicated grounding conductors and have obvious grounding signs.
In order to adapt to outdoor working environments, the top of the box transformer usually adopts a partition structure, which is equipped with insulation materials. There are cooling inlet and outlet ports between the bottom of the box and each chamber, using various forms such as natural air cooling and automatic controlled forced air cooling to ensure the normal heat dissipation of electrical equipment. It has measures such as rain and dust prevention, and preventing small animals from entering.
Components of box type substation: components of high-voltage side power receiving equipment, transformers, and low-voltage distribution equipment;
1、 High voltage side power receiving equipment:
When selecting high-voltage side power receiving equipment for box type substations, it is advisable to choose components with small size and low price as much as possible while meeting performance and environmental requirements.
1. High voltage switch (circuit breaker):
At present, there are many types of domestically produced 10 kV circuit breakers, such as KLF-10, ELC-24, XYn-10, etc. SF circuit breakers have a trend of replacing low oil switches in box type substations due to their long lifespan, low maintenance workload, and reliable performance.
2. Fuse:
Fuse is a supporting component of high-voltage switch, which is the main protective device for high-voltage side grounding and phase to phase short circuit. It has high reliability requirements and should have clear signs for closing and opening. Such as the current drop out fuse or the recently developed fuse with a red flag protruding after gas production, it can be pulled and closed with an insulating rod for easy maintenance and repair of the circuit breaker. In recent years, a type of double fuse has been introduced abroad, which is sensitive to temperature and current, also known as double sensitive fuse. The application of this fuse has improved the reliability of high-voltage switches.
3. Lightning arrester:
At present, metal oxide lightning arresters are commonly used, which have good performance in preventing atmospheric overvoltage and can also absorb surge currents during switch opening and closing. It is more suitable for distribution vacuum circuit breakers and can absorb their operating overvoltage, such as Y5 W zinc oxide lightning arresters.
2、 Transformer:
The transformer used in outdoor box type substations is a step-down transformer, which generally reduces the 10kV level power supply to 380V/220V for user use.
The capacity of a transformer is generally 160-1600kVA, while the commonly used capacity is 315-630kVA. Transformers can be oil immersed, fire-resistant, resin based, etc. Most of them use oil immersed transformers because they are cheaper in price. In places with strict fire prevention requirements, non oil immersed transformers should be used, such as dry-type transformers in high-rise buildings. The utilization rate of dry-type transformers in developed countries has reached 80% -90%. In recent years, dry-type transformers have developed rapidly in China, such as oxygen grease injection type SCL-2, pressure immersion type VPI, and wrapped type (also known as Thunderbolt type), which have been widely used in combination substations.
3、 Selection of components for low-voltage distribution equipment:
The low-voltage distribution equipment is equipped with a main switch and a branch switch. The branch switch is generally 4-8 units, and can reach up to 12 units at most. The branch switch occupies a considerable amount of space in the box type substation, and by reducing the size of the branch switch, more branch switches can be installed. When selecting main and branch switches, short arcing or zero arcing products should not be selected except for volume requirements.
There are two forms of low voltage chambers: one with an operating corridor and the other without. The width of the operating corridor generally needs to be 1000 mm. If there is no operating corridor, the low-voltage room door panel can also be made into a wing door flip up type, and the flip up panel can provide shade and rain protection during operation. This structure is common in foreign power distribution facilities.
DW15 and DWX15 low-voltage circuit breakers are commonly used in the main circuit, both of which are automatic low-voltage switches that can be operated manually or electrically. Equipped with overload and short circuit long and short delay protection, as well as multiple automatic release devices for voltage loss and shunt excitation, it constitutes a relatively complete protection measure. In various branch circuits, DZ20 air circuit breakers are often used, which also have thermal trip protection for short circuits.
Voltage level of box type substation:
At present, the voltage levels of domestically produced box type transformers are 3-35kV on the high voltage side and 0.4-10kV on the low voltage side. The capacity of a transformer can range from several hundred kilovolt amperes to tens of thousands of kilovolt amperes when the rated voltage ratio is 35/10, 6, and 0.4 kV, and from several tens of kilovolt amperes to several thousand kilovolt amperes when the rated voltage ratio is 10, 6/0.4 kV.