Dry-type transformer definition and selection
We are a manufacturer of transformers, and almost all transformers were done before, but now it is mainly the production of dry-type transformers. Dry-type transformer is a more environmentally-friendly transformer that accords with the developmen……
We are a manufacturer of transformers, and almost all transformers were done before, but now it is mainly the production of dry-type transformers. Dry-type transformer is a more environmentally-friendly transformer that accords with the development of modern society, as opposed to oil-immersed transformers.
So what is a dry-type transformer?
Dry type transformers: rely on air convection cooling, generally used for local lighting, electronic circuits and other small-capacity transformers, power systems, general turbine change, boiler change, ash removal, dust change, desulfurization, etc. are dry change The ratio of change is 6000V/400V for a load with a rated voltage of 380V. Dry-type transformer Cross-flow cooling fan is a kind of air inlet and outlet with no guide vanes, and is specially designed for dry-type variable-temperature cooling cross-flow fans. Its main components are: dedicated single-phase or three-phase induction motors with small power induction, cross-flow impellers, housings, and air guides.
In engineering design, the following points should be noted when selecting the dry-type transformer for electrical engineers:
Ⅰ.A dry-type transformer temperature control system
The safe operation and service life of dry-type transformers depends to a large extent on the safe and reliable insulation of transformer windings. The fact that the winding temperature exceeds the insulation resistance temperature to cause insulation breakdown is one of the main causes of transformer failure. It is very important to monitor the transformer operating temperature and its alarm control.
(1) Automatic fan control: The hottest point of the pre-embedded low-voltage windings Pt100 thermal resistance temperature measurement temperature signal. The transformer load increases and the operating temperature rises. When the winding temperature reaches 110°C, the system automatically starts fan cooling. When the winding temperature is as low as 90°C, the system automatically stops the fan.
(2) Over temperature alarm and tripping: PTC non-linear thermal resistance temperature detection resistor in pre-embedded low-voltage winding collects the winding or core temperature signal. When the transformer winding temperature continues to rise, if the temperature reaches 155°C, the system will output an over-temperature alarm signal; if the temperature continues to rise up to 170°C, the transformer cannot continue to operate, and the overtemperature trip signal must be sent to the secondary protection circuit. Trips quickly.
(3) Temperature display system: Pt100 thermistor in embedded low voltage winding measures temperature change value, directly displays the temperature of each phase winding (three-phase inspection and maximum value display, and can record the highest historical temperature), can be the highest temperature With 4~20mA analog output, if it needs to be transmitted to a remote (distance up to 1200m) computer, it can be equipped with a computer interface, 1 transmitter, and up to 31 transformers can be monitored at the same time. The system over-temperature alarm and trip can also be acted by the Pt100 thermal sense resistor signal to further improve the reliability of the temperature control protection system.
Ⅱ. dry-type transformer protection
Use environmental characteristics and protection requirements, dry-type transformers can choose different shells.
The IP20 protective case is usually used to prevent solid foreign matter with a diameter greater than 12mm and small animals such as rats, snakes, cats, puffins, etc. from entering into, causing short-circuit power failures and other serious faults, providing a safety barrier for live parts. If it is necessary to install the transformer outdoors, IP23 protective enclosures can be used. In addition to the above-mentioned IP20 protection functions, it is possible to prevent water droplets from entering the vertical line within 60°. However, the IP23 enclosure will reduce the cooling capacity of the transformer. When selecting the IP23, the operating capacity of the transformer should be reduced.
Ⅲ. dry-type transformer cooling
Dry-type transformer cooling methods are divided into natural air cooling (AN) and forced air cooling (AF). When air-cooled naturally, the transformer can run continuously for a long period of time under rated capacity. When forced air cooling, the transformer output capacity can be increased by 50%. It is suitable for intermittent overload operation or overload operation of emergency accidents. The overload loss and impedance voltage increase during overloading are in non-economical operating conditions, so they should not be operated continuously for a long time.
Ⅳ. dry-type transformer overload capacity
Dry-type transformer overload capacity is related to ambient temperature, load conditions before the overload (starting load), insulation heat dissipation of the transformer, and heat-generating time constants. If necessary, a dry-change overload curve can be obtained from the manufacturer.
How to use its overload capacity? The author proposes two points for reference:
(1) The choice of calculating the transformer capacity can be appropriately reduced: fully consider the possibility of short-time impact overload of some steel rolling, welding and other equipment – try to use the strong overload capacity of the dry transformer to reduce the transformer capacity; Uniform load locations, such as nighttime lighting and other major residential areas, cultural and recreational facilities, and air-conditioning and daytime lighting as the main shopping centers, can make full use of its overload capacity, appropriately reduce the transformer capacity, make its main run time at full load or short time overload.
(2) It can reduce the spare capacity or the number of units: In some places, there is a high requirement for the standby coefficient of the transformer, so that the transformer capacity of the project is large and the number of transformers is large. The use of dry-change overload capability can be suppressed when considering the reserve capacity; the number of standby units can also be reduced. When the transformer is in overload operation, be sure to monitor its operating temperature: If the temperature rises up to 155°C (with an alarm issued), load shedding measures (minus some minor loads) shall be taken to ensure safe power supply to the main load.
Ⅴ. dry-type transformer low voltage outlet and its interface cooperation
Since dry-type transformers have no oil, there are no problems such as fire, explosion, or contamination. Therefore, electrical specifications and procedures do not require dry-type transformers to be placed in separate rooms. Loss and noise have fallen to new levels, and conditions have been created for transformers and low-voltage screens to be located in the same distribution room.
At present, the annual output of resin-insulated dry-type transformers in China has reached 10,000 MVA, making it one of the world’s largest producers of dry-type transformers. Low-noise (noise control of power distribution transformers up to 2500 kVA has been controlled within 50dB), energy saving (loss of no-load losses up to 25%) SC(B)9 series of popularization and application, China’s dry-type transformer performance indicators and manufacturing technology has reached the world advanced level .
National Building Standard Design Atlas “Dry Transformer Installation” – “99D268”.
The Atlas offers dry-type transformer arrangements and installation methods for a variety of locations. For transformers and low-voltage PC screen interfaces, a variety of options are listed for design and construction options.
The popularization and application of dry-type transformers and their manufacturing and manufacturing technologies have also achieved considerable development. Dry-type transformers will be further developed in the following areas.
(1) Energy-saving and low-noise: New low-consumption silicon steel sheet, foil winding structure, stepped core joints, environmental protection requirements, in-depth noise research, and introduction of new materials, new processes, and new technologies such as computer optimization design will enable future dry-type Transformers are more energy-efficient and quieter.
(2) High reliability: The improvement of product quality and reliability will be the unrelenting pursuit of people. The electromagnetic field calculation, wave process, pouring process, hot spot temperature rise, partial discharge mechanism, quality assurance system and reliability engineering, etc. carried out a large number of basic researches, actively carried out reliability certification, and further improved the reliability and service life of dry-type transformers.
(3) Environmental protection certification: Based on the European standard HD464, research and certification of dry-type transformers for weather resistance (C0, C1, C2), environment resistance (E0, E1, E2) and fire resistance (F0, F1, F2) .
(4) Large capacity: from 50~2500kVA distribution transformers to dry-type transformers, to 10000~20000kVA/35kV power transformers, increasing urban electricity load, substations in urban areas are getting deeper into urban centers and residents. The 35kV large-capacity community center-powered power transformers will be widely used in residential areas, large-scale factories and mines and other load centers.
(5) Multi-functional combination: From single transformer to multi-functional combined transformer with air-cooled, protective enclosure, temperature computer interface, zero-sequence transformer, power metering, enclosed busbar and side outlet.
(6) Development in multiple fields: from distribution transformers to special transformers such as power station plant transformers, excitation transformers, iron traction rectifier transformers, high-current electric furnace transformers, nuclear power plants, marine and oil platforms, and multi-purpose fields.
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