American-style box transformer
The Hua style box transformer consists of three parts: a high-voltage room, a transformer, and a low-voltage room. Each room is separated into independent intervals by partitions, and there are inlet and outlet holes in the right box body for easy installation and maintenance. The internal layout structure is set according to the requirements of the standard design drawings. The transformer adopts natural cooling method, and the temperature of the low-voltage chamber is controlled below 60 ° C through the cooling device inside the cabinet, ensuring a good operating environment for the secondary equipment. Communication cabinets (including switches, fiber optic boxes, etc.) and UPS battery cabinets should be installed on the transformer cabinet. The temperature rise during 1.1 times continuous long-term overload operation (with oil temperature not exceeding 85 ° C in the project environment), 12 times continuous 3-hour overload operation (with oil temperature not exceeding 85 ° C in the project environment), and 1.5 times short-term overload operation should comply with the "General Equipment for Transmission and Transformation Projects of State Grid Corporation of China" (typical specifications for 66kV and below substations).
Dehumidification, explosion prevention, and anti condensation measures should be taken inside the transformer box. The cable holes in the high and low pressure chambers should be sealed with polymer flexible sealing material TS-68 on the basis of fireproof mud sealing. Install sealing strips on the cabinet door of the transformer. The sealing strip is made of EPDM rubber, which has excellent heat resistance, weather resistance, ozone resistance, corrosion resistance, and aging resistance.
High voltage cable heads, busbars, wiring terminals and other live parts should be fully insulated with flame-retardant and thermally conductive silicone rubber insulation material TS-10. Low voltage busbars should be able to withstand a voltage of 2.5kV for 1 minute after insulation treatment. High voltage bushing porcelain bottles, insulation rods, insulators and other insulation components are coated with high self-cleaning anti fouling flash coating SRTV, with a coating thickness of 0.4+0.1mm. Adding a cooling fan can achieve external circulation ventilation and cooling. The design service life of the transformer should not be less than 30 years. Each compartment of the transformer should be equipped with a combination of low-power constant heating and dehumidifier, and ventilation holes should be reasonably set according to the cabinet volume. The temperature and humidity signals of the transformer should have remote transmission function and be uploaded to the transformer measurement and control device through a communication interface.
The European style box transformer installs high and Low Voltage Switchgear and transformers inside an outdoor box, with a grid or cross shaped mechanism layout. It is equipped with conventional medium voltage switchgear/ring main unit, low voltage box and transformer, and has a large product volume. The high voltage side of the European box transformer is protected by a load switch and a current limiting fuse. When a phase fuse is blown, use the firing pin of the fuse to simultaneously disconnect the three phases of the load switch to avoid phase loss operation. The load switch is required to have the ability to cut off the transfer current. The low-voltage side is protected by a load switch and a current limiting fuse.
The American box type transformer simplifies the structure of load switches, ring network switches, and fuses by immersing them in oil in the transformer oil tank. The lightning arrester also uses oil immersed zinc oxide lightning arrester. The transformer eliminates the oil pillow, and the oil tank and radiator are exposed to the air, resulting in a smaller integrated installation volume. The high-voltage side of the American box transformer is protected by fuses, while the load switch only functions to switch and cut off the high-voltage load current, with a smaller capacity.
When a phase fuse is blown on the high voltage side, the voltage on the low voltage side decreases, and the undervoltage protection or overvoltage protection of the plastic shell automatic air switch will be activated, and low voltage operation will not occur.
The Chinese style transformer integrates the advantages of American and European styles, especially 40.5kV, achieving miniaturization and low cost. The independent structures of each unit are equipped with transformer rooms, high-voltage switch rooms, and low-voltage switch rooms, which are connected by wires to form a complete power supply system. Adopting a containerized integrated machine, the product volume is larger than that of American style boxes.
The Hua style box transformer uses one fuse per phase instead of the two fuses in the American style box transformer for protection. Its biggest feature is that when any phase fuse is blown, it will ensure that the load switch trips and cut off the power supply. Moreover, the main switch can only be closed after replacing the fuse, which is not available in American style box transformers.
Compared with American style box transformers, Chinese style box transformers have added grounding switches and lightning arresters. There is a mechanical interlock between the grounding switch and the main switch, which ensures absolute personal safety during maintenance of the box transformer.