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Dry-type transformers: relying on air convection for cooling, generally used for small-capacity transformers such as local lighting and electronic circuits. In power systems, general steam turbines, boilers, ash, dust, desulfurization, etc. are dry-type transformers. The ratio is 6000V/400V for a load with a rated voltage of 380V. The cross-flow cooling fan for dry-type transformers is a type of inlet and outlet with no guide vanes, and is dedicated to dry-type transformer cooling horizontal flow fans. Its main components are: special single-phase or three-phase low-power induction asynchronous motor, cross-flow impeller, casing and air guiding device.
Dry transformer temperature control system
The safe operation and service life of dry-type transformers depend to a large extent on the safety and reliability of the transformer winding insulation. The winding temperature exceeds the insulation withstand temperature and the insulation is destroyed, which is one of the main reasons that the transformer can not work normally. It is very important to monitor the temperature of the transformer and its alarm control. Now introduce the GTB series temperature control system.
(1) Fan automatic control: The temperature signal is measured by Pt100 thermal temperature measuring resistor embedded in the hottest part of the low voltage winding. The transformer load increases and the operating temperature rises. When the winding temperature reaches 110 °C, the system automatically starts the fan cooling; when the winding temperature is as low as 90 °C, the system automatically stops the fan.
(2) Over-temperature alarm, trip: The winding or core temperature signal is collected by the PTC nonlinear thermal temperature measuring resistor in the embedded low-voltage winding. When the temperature of the transformer winding continues to rise, if the temperature reaches 155 °C, the system outputs an over-temperature alarm signal; if the temperature continues to rise to 170 °C, the transformer can no longer continue to operate, and the over-temperature trip signal must be sent to the secondary protection circuit. Quickly trip.
(3) Temperature display system: The temperature change value is measured by the Pt100 thermistor embedded in the low voltage winding, and the temperature of each phase winding is directly displayed (three-phase inspection and maximum value display, and the history can be recorded). The Zui high temperature can be output in 4~20mA analog output. If it needs to be transmitted to a remote computer (distance up to 1200m), it can be equipped with a computer interface, 1 transmitter, and more than 31 transformers can be monitored at the same time. The system's over-temperature alarm and trip can also be acted upon by the Pt100 thermal sensing resistor signal to further improve the reliability of the temperature control protection system.
Dry type transformer protection
Dry-type transformers can be selected from different enclosures depending on the environmental characteristics and protection requirements. IP20 protective casing is usually used to prevent solid foreign objects larger than 12mm in diameter and small animals such as rats, snakes, cats, and birds, which cause malignant faults such as short-circuit power failure and provide a safety barrier for live parts. If the transformer needs to be installed outdoors, the IP23 protective casing can be used. In addition to the above IP20 protection function, it can prevent water droplets from entering within 60° of the vertical line. However, the IP23 housing will reduce the cooling capacity of the transformer, and pay attention to the reduction of its operating capacity when selecting.
Dry type transformer cooling method
Dry-type transformer cooling methods are divided into natural air cooling (AN) and forced air cooling (AF). When naturally air cooled, the transformer can run continuously for a long 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 emergency accident overload operation; due to overload and load voltage increase during overload, it is in non-economic operation state, so it should not be in continuous continuous overload operation.
Dry transformer overload capability
The overload capacity of the dry-type transformer is related to the ambient temperature, the load condition before the overload (starting load), the insulation heat dissipation of the transformer, and the heating time constant. If necessary, the dry-loading overload curve can be obtained from the manufacturer.
How to use its overload capacity?
(1) Selecting the calculation of transformer capacity can be appropriately reduced: fully consider the possibility of short-term impact overload of some steel rolling, welding and other equipment - try to use the strong overload capacity of dry-type transformer to reduce the transformer capacity; Places with uneven load, such as residential areas for night lighting, cultural and recreational facilities, and air-conditioning and daylight-based shopping malls, can make full use of their overload capacity, appropriately reduce transformer capacity and make it the main running time. At full load or short time overload.
(2) It can reduce the spare capacity or the number of units: In some places, the spare coefficient of the transformer is required to be high, which makes the transformer of the project optional and has a large number of units. The dry-overload capability can be compressed when considering the spare capacity; it can also be reduced when determining the number of spares. When the transformer is in overload operation, be sure to monitor its operating temperature: If the temperature rises to 155 ° C (with alarms issued), load shedding measures (minus some minor loads) should be taken to ensure safe power supply to the main load.
Dry-type transformer low-voltage outlet mode and its interface
Since dry-type transformers have no oil, there is no fire, explosion, pollution, etc., so electrical specifications, procedures, etc. do not require dry-type transformers to be placed in separate rooms. Especially in the new SC(B)9 series, the loss and noise have dropped to a new level, and the transformer and the low-voltage screen have been placed in the same power distribution room.
(1) Low-voltage standard closed busbar: If the closed wiring (also called plug-in busbar or dense busway) is used for the engineering wiring, the corresponding transformer can provide standard closed busbar terminal to facilitate the connection with the external busbar.
With housing (IP20), the enclosed busbar flange is provided on the top cover of the housing; without the outer casing (IP00), only the closed busbar terminal block is provided.
(2) Low-voltage standard horizontal side outlet: When the transformer is placed side by side with the low-voltage power distribution panel, in order to facilitate the connection between the terminals, the transformer can provide a low-voltage horizontal side outlet, which is usually matched with low-voltage screens such as GGD, GCK, and MNS. The transformer factory and the switch factory shall sign the interface with the minutes, confirm the detailed dimensions of the interface, and ensure the smooth installation on site.
(3) Low-voltage standard vertical row side outlet line: similar to the horizontal row side outlet line, when the busbar of the domino screen is used as the vertically arranged low-voltage power distribution panel, the transformer can provide the low-voltage vertical row side outlet.
At present, the annual output of China's resin-insulated dry-type transformers has reached 10,000 MVA, making it one of the countries with the largest production and sales volume of dry-type transformers in the world. With low noise (noise of 2500kVA distribution transformer noise has been controlled within 50dB), energy saving (no-load loss reduced by 25%) SC(B)9 series of popularization and application, the performance index and manufacturing technology of China's dry-type transformer Has reached the world's advanced level.
With the popularization and application of dry-type transformers, its manufacturing technology has also made considerable progress. It can be predicted that the future dry-type transformers will be further developed in the following aspects.
(1) Energy-saving and low-noise: With the introduction of new low-cost silicon steel sheets, foil winding structures, stepped core joints, environmental protection requirements, in-depth study of noise, and computer optimization design, new materials, new processes, and new technologies are introduced. Will make future dry-type transformers more energy-efficient and quieter.
(2) High reliability: Improving product quality and reliability will be the unremitting pursuit of people. A large number of basic researches have been carried out on electromagnetic field calculation, wave process, casting process, hot spot temperature rise, partial discharge mechanism, quality assurance system and reliability engineering, and reliability certification has been actively carried out to further improve the reliability and service life of dry type transformers.
(3) Environmental characteristics certification: Based on the European standard HD464, the weather resistance (C0, C1, C2), environmental resistance (E0, E1, E2) and fire resistance (F0, F1, F2) characteristics of dry-type transformers are studied. With certification.
(4) Large capacity: from 50 to 2500kVA distribution transformer-based dry-type transformers, expanding to 10000～20000kVA/35kV power transformers. With the increasing urban power load, the urban network substation is getting deeper and deeper into the city. Central area, residential areas, large factories and mines and other load centers, 35kV large capacity community center power transformers will be widely used.
(5) Multi-functional combination: from a single transformer to a multi-functional combined transformer with air-cooled, protective casing, temperature computer interface, zero-sequence transformer, power metering, enclosed busbar and side outlet.
(6) Development in many fields: from distribution transformers to transformers, excitation transformers, metro traction rectifier transformers, high-current electric furnace transformers, nuclear power plants, marine and oil production platforms, etc. .
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