Transformer (Transformer) is undoubtedly one of the common devices in life, and many devices have transformers. Without a transformer, many devices in life cannot function normally. It mainly uses the principle of electromagnetic induction to change the AC voltage device. The main components are primary coil, secondary coil and iron core (magnetic core). The main functions are: voltage conversion, current conversion, impedance conversion, isolation, voltage stabilization (magnetic saturation transformer), etc. In order to enhance everyone's understanding of transformers, this article mainly introduces the main technical parameters and types of transformers.
1. Main technical parameters of transformer:
Under the specified use environment and operating conditions of the transformer, the main technical data are generally marked on the nameplate of the transformer. It mainly includes: rated capacity, rated voltage and its tap, rated frequency, winding connection group, rated performance data (impedance voltage, no-load current, no-load loss and load loss) and total weight.
A. Rated capacity (kVA): The capacity that can be delivered when it operates continuously at rated voltage and rated current.
B. Rated voltage (kV): The working voltage that the transformer can withstand during long-term operation. In order to meet the needs of grid voltage changes, there are taps on the high-voltage side of the transformer. Adjust the output voltage of the low-voltage side by adjusting the number of turns of the high-voltage winding.
C. Rated current (A): Under the rated capacity of the transformer, the current allowed to pass through for a long time.
D. No-load loss (kW): When the rated voltage at rated frequency is applied to the terminal of one winding and the other windings are open-circuited, the active power drawn. It is related to the performance of the core silicon steel sheet, the manufacturing process, and the applied voltage.
E. No-load current (%): When the secondary side of the transformer is no-loaded at the rated voltage, the current passing through the primary winding is generally expressed as a percentage of the rated current.
F. Load loss (kW): short-circuit the secondary winding of the transformer, and pass the rated current at the rated tap position of the primary winding. At this time, the power consumed by the transformer.
G. Impedance voltage (%): Short-circuit the secondary winding of the transformer, and slowly increase the voltage in the primary winding. When the short-circuit current of the secondary winding is equal to the rated value, Once at this time
H, number of phases and frequency: three-phase starts with S, and single-phase starts with D. The Chinese national standard frequency f is 50Hz. There are 60Hz countries abroad (such as the United States).
I. Temperature rise and cooling: The temperature difference between the transformer winding or upper oil temperature and the surrounding environment of the transformer is called the temperature rise of the winding or upper oil surface. Oil-immersed transformer The winding temperature rise limit is 65K, and the oil surface temperature rise is 55K. There are also many cooling methods: oil-immersed natural cooling, forced air cooling, water cooling, tube type, sheet type, etc.
J. Insulation level: There are insulation level standards. The expression method of insulation level is as follows: the insulation level of a transformer with a high-voltage rated voltage of 35kV and a low-voltage rated voltage of 10kV is expressed as LI200AC85/LI75AC35, where LI200 means that the high-voltage lightning impulse withstand voltage of the transformer is 200kV, and the power frequency withstand voltage It is 85kV, the low-voltage lightning impulse withstand voltage is 75kV, and the power frequency withstand voltage is 35kV. The insulation level of the current oil-immersed transformer products of Oakes Technology Co., Ltd. is LI75AC35, which means that the high-voltage lightning impulse withstand voltage of the transformer is 75kV, and the power frequency withstand voltage is 35kV. The withstand voltage is 35kV, because the low voltage is 400V, it can be ignored.
K, connection group label group. In order to distinguish different connection groups, the clock notation is often used, that is, the phasor of the high-voltage side line voltage is used as the long needle of the clock and fixed on 12, and the phasor of the low-voltage side line voltage is used as the short needle of the clock. See where the short needle points A number is used as the label of the connection group. For example, Dyn11 means that the primary winding is (triangular) connection, the secondary winding is (star) connection with a center point, and the group number is (11) points.
2. Five categories of transformers:
(1) Power transformer
Currently, representative products already in operation in the system include: 1150KV, 1200MV·A, 735～765KV, 800MV·A, 400～500KV, 3-phase 750MV·A or single Phase 550MV·A, 220KV, 3-phase 1300MV·A power transformer; DC transmission ±500KV, 400MV·A converter transformer. Power transformers are mainly oil-immersed, and the product structure is divided into two types: core type and shell type. The production volume of core type accounts for 95%, and that of shell type only accounts for 5%. There is no overwhelming advantage between the core type and the shell type, but the core type process is relatively simple, so it is adopted by most enterprises; while the shell type structure and process are more complicated, only traditional factories use it. The shell type is especially suitable for high voltage and large capacity. It has advantages in insulation, machinery and heat dissipation, and is suitable for transportation of hydropower stations in mountainous areas.
Power transformers are one of the main equipment in power plants and substations. The role of the transformer is multifaceted. It can not only increase the voltage to send electric energy to the power consumption area, but also reduce the voltage to the voltage of all levels to meet the needs of power consumption. In short, both step-up and step-down must be done by the transformer. In the process of electric energy transmission in the power system, two parts of voltage and power will inevitably be lost. When the same power is transmitted, the voltage loss is inversely proportional to the voltage, and the power loss is inversely proportional to the square of the voltage. Using the transformer to increase the voltage reduces the power transmission loss.
(2) Distribution transformer
Distribution transformer refers to a static electrical device used in power distribution system to transform AC voltage and current according to the law of electromagnetic induction and transmit AC power. The capacity of foreign distribution transformers can reach 2500KV·A, and there are circular and oval core forms. The circular ones account for the vast majority, and the elliptical ones use less material because of the small M0 (the distance between the core columns), and the corresponding coils are elliptical. Low-voltage coils are wirewound and foil, and oil tanks are available with heat pipes (few) and corrugated (most).
(3) Dry-type transformer
The dry-type transformer is mainly composed of an iron core composed of silicon steel sheets and a coil casted by epoxy resin. An insulating cylinder is placed between the high and low voltage coils to increase electrical insulation, and it is supported by pads And the restraint coil, the fasteners of its components overlap have anti-loosening performance. There are four structures of dry change: epoxy resin casting, filling casting, wrapping and impregnation. Due to the advantages of strong short-circuit resistance, small maintenance workload, high operating efficiency, small size, and low noise, dry-type transformers are often used in places with high performance requirements such as fire protection and explosion protection.
(4) Amorphous alloy transformer
Although amorphous alloy transformers have poor short-circuit resistance and high noise, they are energy-saving, so the future development prospects are promising. Based on energy supply and environmental protection factors, amorphous alloy transformers are widely used in large developing countries such as China and India. Based on the current electricity consumption of China and India, if amorphous alloy transformers are fully used in the distribution network, about 25-30TWh of power generation can be saved each year, and 20 to 30 million tons of carbon dioxide emissions can be reduced.
(5) winding core transformer
Wound core transformer is an energy-saving power transformer, which creatively reforms the laminated magnetic circuit structure and three-phase layout of traditional power transformers, making the product performance more optimized . There are not many three-dimensional wound core transformer manufacturers with a certain production capacity in the country. Due to technical reasons, the production of three-dimensional wound core transformers is mainly concentrated in oil-immersed distribution transformers below 10kV315kVA, which are mainly used in rural power grid reconstruction projects.
