With the accelerated construction of smart cities, the urban distribution network is constantly being upgraded and renovated, and the construction of overhead line undergrounding projects is also progressing steadily. A large number of 10 kV overhead lines are being replaced by underground cables. Considering the current situation such as limited space on some urban roads and a shortage of equipment installation locations, higher requirements are placed on the volume, structure, and performance of traditional prefabricated substations.
Based on the application of traditional prefabricated substations, this article conducts research and analysis and designs a miniaturized, intelligent, and landscaped prefabricated substation. This prefabricated substation features a compact structure, stable performance, strong practicality, and high power supply reliability. It can make intensive use of the core urban space, achieve harmony and unity with the surrounding environment, and can be widely applied to the upgrading and renovation projects of urban distribution networks.
Taking into account requirements such as geographical location, space utilization rate, and environmental limitations, the miniaturized intelligent prefabricated substation adopts a long and narrow layout. Its volume is only two-thirds of that of the original prefabricated substation. The casing (including the top, doors, bottom, and internal metal components) and its attachments are all made of 304 stainless steel, while the interior uses SGCC hot-dip galvanized thin steel plates, and heat-insulating and flame-retardant materials are added to the surrounding walls. The outer surface is painted dark green, which is both aesthetically pleasing and environmentally friendly.
The casing has sufficient mechanical strength and seismic performance to ensure that it is not easily damaged or deformed during transportation, installation, and hoisting. The top of the casing adopts a "herringbone" structure with a slope of 5°. It is a double-layer structure that has the effect of isolating sunlight radiation. It is equipped with an anti-backflow eaves and a ventilation duct, and the top of the casing is detachable. The doors of the casing are of a double-layer anti-theft bolt structure and open outward. The bottom of the casing is hot-dip galvanized and seamlessly connected to the casing body. There is a manhole at the bottom, and sealing strips are installed around the manhole. Flammability-resistant cable sealing devices are provided on both sides, with good sealing and complete moisture-proof measures.
All welding parts and the joints of external components of the miniaturized intelligent prefabricated substation are well sealed, and it has characteristics such as water resistance, dust resistance, corrosion resistance, and protection against ultraviolet radiation. It is both beautiful and environmentally friendly. Without the need for maintenance, its normal service life can reach up to 40 years.
The structure of the miniaturized intelligent prefabricated substation is simple. The interior of the casing is divided into six main functional rooms: the transformer room, high-voltage room, low-voltage room, automation room, communication room, and power consumption collection room. These functional rooms are completely separated from each other and arranged in an "eye" shape.
This substation can have doors on all four sides, meeting the maintenance requirements of opening doors on three sides. The protective doors of the high-voltage room and the low-voltage room are equipped with mechanical interlocks to ensure that the high-voltage room door can only be opened when the low-voltage room door is open. Each functional room adopts an independent natural ventilation method to meet the requirements of all electrical equipment for temperature and humidity. When necessary, heaters, dehumidifiers, and other equipment can be added to ensure its safe and reliable operation outdoors.
The main components of this substation include: oil-immersed transformers, 10 kV ring main unit low-voltage plastic shell air switches (on the low-voltage side) sealed with SF6 gas, standardized emergency power supply quick interfaces (on the low-voltage busbar side), as well as station terminal units, 台区 general meters, concentrators, intelligent configuration terminals, optical fiber communication terminals, etc.
(1) Transformer Room. The transformer room includes transformers, radiators, busbar wiring, and safety protection nets, etc. The transformer uses a first-level energy efficiency fully sealed silicon steel sheet or amorphous alloy oil-immersed distribution transformer. The high-voltage side is equipped with prefabricated pluggable cable heads, and the low-voltage bushings are equipped with insulation protection sleeves. The capacity can be selected as 500 kV·A or 630 kV·A.
(2) High-Voltage Room. The high-voltage room is composed of 10 kV ring main units, which are divided into incoming line and outgoing line unit cabinets, and the two are independently enclosed. The ring main unit is of a fully insulated and common box structure, using SF6 gas for arc extinguishing and insulation. The gas box is equipped with a gas pressure display device with a normally open alarm auxiliary node. The gas box and the cabinet body are made of 304 stainless steel and high-quality aluminum-clad zinc plate materials respectively, and the surface of the cabinet body adopts an electrostatic epoxy spraying process.
The unit cabinet is divided into a secondary room, a load switch room, and a cable room from top to bottom. The secondary compartment is located at the upper part of the unit cabinet. The panel of the compartment is equipped with on-off switches, on-off indicator lights, remote/local transfer switches, as well as fault and live indicators, etc. The load switch unit of the unit cabinet generally selects a combined electrical appliance of a load switch and a current-limiting fuse. Among them, the load switch can break the specified load current and the transfer current when a fault occurs on the low-voltage side of the transformer; the current-limiting fuse can cut off various phase-to-phase, grounding short-circuit currents, and overload currents.
The load switch can achieve opening, closing, and grounding through electric and manual operations, and the operation is simple and convenient. The load switch unit and the grounding switch unit have a reliable "five-prevention" interlocking function. The cable room of the unit cabinet mainly uses the high-voltage cable trench for incoming and outgoing lines from underground. The positions of the incoming and outgoing cable terminals are convenient for installation, and an open-type high-voltage current transformer is installed.
(3) Low-Voltage Room. The low-voltage room is mainly composed of low-voltage switchgear, emergency power supply compartments, and manholes, etc. The color of the low-voltage cabinet body is the same as that of the high-voltage cabinet, using RAL7035. A pluggable digital multi-functional meter is installed on the panel of the low-voltage cabinet, which can display voltage and current and supports RS-485 communication. The low-voltage outgoing lines use 4-circuit zero-flying-arc plastic shell air switches. The low-voltage side is provided with a neutral line and a ground line, both of which are arranged at the bottom of the low-voltage cabinet.
The low-voltage busbar of the transformer is introduced into the low-voltage switchgear from the emergency power supply compartment, designed to be detachable. After wiring conversion, it becomes a low-voltage feeder to the outgoing cable at the bottom of the low-voltage cabinet. The number of output circuits can be flexibly designed according to requirements. The emergency power supply compartment should be accompanied by operation instructions, and the manhole is convenient for manual maintenance.
(4) Automation Room. The prefabricated substation is equipped with an independent automation room, in which the distribution automation terminal (DTU) monitors and controls the operating conditions of the 10 kV incoming and outgoing line circuits, achieving functions such as remote measurement, remote signaling, remote control, and remote adjustment. The DTU preferentially uses mains power for power supply. When there are no conditions for mains power supply, it uses a potential transformer for power supply and uses a supporting storage battery as a backup power source.
It has a built-in power management module, which can meet the output of AC220V and DC24V and provides an AC220V alternating current power source for the electric operation mechanism of the ring main unit.The DTU supports multiple communication methods and communication protocols, and has 2 RS-485 serial interfaces and 2 network interfaces (RJ45), which are compatible with protocols such as IEC101, IEC104, and CDT; the DTU is installed as a whole in a wall-mounted cabinet, using an aviation plug, which is convenient for on-site disassembly, installation, and maintenance, and can meet the space layout requirements of a set of terminals and backup power sources.
(5) Communication Room. The prefabricated substation is equipped with an independent communication room, which is internally configured with an optical distribution frame, an industrial Ethernet switch, and an optical network unit, and reserves the wiring slots and incoming and outgoing holes for communication optical cables, pigtails, and power cables. This room can transmit the monitoring data inside the prefabricated substation to the intelligent monitoring platform, so as to monitor its operating status and data in real time.
(6) Power Consumption Collection Room. The power consumption collection room is located above the communication room. It is equipped with installation positions for intelligent distribution transformer terminals, concentrators, and general meters of the transformer area, as well as installation spaces for terminal blocks and combined wiring test boxes, and reserves the wiring slots and incoming and outgoing holes for sampling signals and communication cables.
This room is responsible for measuring various operating parameters of the prefabricated substation and is the communication hub of electric energy data. On the one hand, it collects and stores the electric energy data output in the form of serial communication by digital electric energy meters. On the other hand, it transmits the collected electric energy data to the upper computer of the main station of the electric energy billing automation system through the upstream channel.
The grounding electrode of the miniaturized intelligent prefabricated substation uses a galvanized iron pipe. The grounding busbar of the channel steel base is provided with 2 copper grounding terminals connected to the grounding electrode, with an electrical contact cross-sectional area of 160 mm² and obvious signs. The low-voltage neutral line of the transformer is directly connected to the grounding body. Among them, the transformer room, high-voltage room, and low-voltage room are connected to each other using grounding terminals.
The secondary safety grounding wires of electrical equipment are added with transparent protective sleeves, and the copper wires have a cross-sectional area of 4 mm²; all cabinet doors, metal parts, and metal frames are continuously and reliably connected to the ground. The external grounding grid of the foundation is introduced into the bottom of the prefabricated substation from the inner side of the foundation and connected to the grounding terminals in the station, using a direct burial method. The grounding resistance of the prefabricated substation is not greater than 1 Ω.
The miniaturized intelligent prefabricated substation is suitable for the distribution network of a 10/0.4 kV three-phase AC system. It integrates high-voltage switchgear, distribution transformers, and low-voltage distribution devices according to a specific wiring scheme. The high-voltage side adopts a single busbar wiring, with two incoming lines and one outgoing line. A fuse protection is set on the transformer side. After being transformed by the distribution transformer, the low-voltage busbar can be designed with 4 low-voltage feeder lines according to needs, and no low-voltage main switch is set.
This miniaturized intelligent prefabricated substation is widely applicable to outdoor places such as urban distribution network renovation, residential communities, factories and enterprises, commercial office buildings, business districts, public green areas, cultural protection areas, and parks.
- Altitude: not exceeding 1,000 m.
- Ambient temperature: the lowest is -25 °C, the highest is 45 °C; the highest annual average temperature does not exceed 20 °C, and the highest monthly average temperature does not exceed 35 °C.
- Relative humidity: at 20 °C, the highest monthly average does not exceed 90%, and the highest daily average does not exceed 95%.
- Seismic resistance: the ground horizontal acceleration does not exceed 0.2 g (g represents the acceleration due to gravity), and the ground vertical acceleration is 0.1 g.
- Sunshine intensity: when the wind speed is 0.5 m·s⁻¹, the solar radiation intensity does not exceed 0.1 W·cm⁻².
- Maximum ice coating thickness: 10 mm.
- Pollution level: not exceeding level III
- Ground inclination: not greater than 3°.
- Installation location: outdoor, without explosion hazards, fires, chemical corrosion, or severe vibrations.
If it does not conform to the above normal environmental conditions for use, it needs to be negotiated and resolved between the user and the manufacturer.
The miniaturized intelligent prefabricated substation was prototyped by Jiangsu Qihou Intelligent Electrical Equipment Co., Ltd. The Quality Inspection Center for High-Voltage Transmission and Distribution Equipment of the Machinery Industry conducted tests on the main components according to relevant national standards and industry standards, and the test results were qualified. The State Grid Shanghai Electric Power Company conducted a comprehensive acceptance of the size, appearance, and performance of this prototype, and the acceptance results were qualified.
The miniaturized intelligent prefabricated substation developed in this article integrates the advantages of existing prefabricated substations at home and abroad. It has the advantages of a simple structure, a small footprint, safety and reliability, beauty and environmental protection, exemption from inspection and maintenance, and low maintenance requirements. It has important promotional and application value in the construction and renovation of urban distribution networks.
