Dry type transformers /Cast resin transformer
Dry-type transformers Dry type transformer are widely used in local lighting, high-rise buildings, airports, terminal CNC machinery and equipment, etc. Simply speaking, dry-type transformers refer to transformers whose iron cores and windings are not immersed in insulating oil.
Cooling methods are divided into natural air cooling (AN) and forced air cooling (AF). Under natural air cooling, the transformer can run continuously for a long time under the rated capacity. When forced air cooling, the output capacity of the transformer can be increased by 50%. It is suitable for intermittent overload operation or emergency accident overload operation; due to the large increase of load loss and impedance voltage during overload, it is in a non-economic operation state, so it should not be in continuous overload operation for a long time.
Develop
Since the first 400kVA/ 20kV epoxy cast dry-type transformer Cast Resin Transformer developed by German AEG Company in 1964, dry-type transformers have entered a stage of great development. There are two types of dry-type transformers, one is epoxy type and the other is Nomex paper type.
At present, in developed countries such as the United States, Germany, and Japan, the output of dry-type transformers has accounted for more than 20% of the output of distribution transformers. In complete substations, dry-type transformers have accounted for 80 to 90%.
"2013-2017 China Dry-type Transformer Industry Market Demand Forecast and Investment Strategic Planning Analysis Report" shows that my country has become the country with the largest dry-type transformer production and sales in the world. At present, various foreign high and low voltage electrical products occupy some important domestic markets. Only dry-type transformers have hardly been imported from abroad since the end of the 20th century. In domestic key projects and major projects, it is difficult to find foreign dry-type transformers. traces. Under the current organization and construction mode of my country's transmission network, the proportion of 10kV dry-type transformers is increasing year by year.
At present, the pace of urban and rural power grid construction is accelerating, and my country's power generation and electricity consumption are increasing day by day. Generally speaking, every increase of 1kW of power generation requires an increase of 11kVA of total transformer capacity; and the Satons distribution transformer accounts for about 1/3-1/2 of the total transformer capacity. It is estimated that dry-type distribution transformers account for about 1/5-1/4 of all distribution transformers. Driven by investment in power grid construction, the transformer industry is booming, and the output will maintain a growth rate of about 20% after 2010. According to historical experience and changes in transformer voltage level structure, the proportion of distribution transformers is about 40%. According to the calculation of 40%, the output of new dry-type transformers in my country will reach about 200 million KVA.
In my country, in 1966, Shenyang Transformer Factory successfully developed ZSG-1800/10 oriented air-cooled H-class dry-type transformer, and Shanghai Transformer Factory successfully developed SG3-800/10/1.2/0.4 three-coil self-cooling H-class dry-type transformer, in the 1970s At the end, Shanghai Transformer Factory designed and developed SCL-630 epoxy casting transformer by itself. In the past 20 years, with the development of the world economy, dry change has achieved rapid development all over the world, especially in distribution transformers, the proportion of dry change is increasing. According to statistics, in developed countries such as Europe and the United States, , it has accounted for 40 to 50% of the distribution transformer. In my country, it accounts for about 50%. From the perspective of output, the output of dry-type transformers has increased significantly since the second urban network transformation meeting in 1989. Since the 1990s, it has increased at a rate of about 20% every year. Production has approached 10,000 MVA (a value that has greatly exceeded the forecast of 45,000 MVA 10 years ago), while the total production in 2002 reached 20,000 MVA and in 2004 it reached 32,000 MVA. Such a growth rate is unprecedented in the world. From the above data, it can be seen that my country has become one of the countries with the largest production and sales volume of dry-type transformers in the world, and has been at the leading level in the world in terms of factory scale, product capacity, and voltage.
See details information of Prefabricated substation with dry type transformer / Cast resin transformer inbuilt.
Structure type
It is mainly composed of an iron core composed of silicon steel sheets and a coil cast with epoxy resin. An insulating cylinder is placed between the high and low voltage coils to increase electrical insulation, and the coil is supported and restrained by a spacer. loose performance.
Construction performance:
⑴Solid insulation encapsulated winding
⑵ not encapsulated winding
Winding: Among the two windings, the higher voltage is the high voltage winding, and the lower one is the low voltage winding.
From the perspective of the relative positions of the high and low voltage windings, the high voltage can be divided into concentric and overlapping types.
The concentric winding is simple and easy to manufacture, and this structure is adopted.
Overlapped, mainly used for special transformers.
Structural features
Because dry-type transformers have the advantages of strong short-circuit resistance, small maintenance workload, high operating efficiency, small size, and low noise, they are often used in places with high performance requirements such as fire protection and explosion-proof.
1. Safe, fireproof, pollution-free, and can be directly operated in the load center;
2. Adopt domestic advanced technology, high mechanical strength, strong short-circuit resistance, small partial discharge, good thermal stability, high reliability and long service life;
3. Low loss, low noise, obvious energy saving effect, maintenance free;
4. Good heat dissipation performance, strong overload capacity, can increase capacity operation when forced air cooling;
5. Good moisture resistance, suitable for operation in high humidity and other harsh environments;
6. Dry-type transformers can be equipped with a complete temperature detection and protection system. The intelligent signal temperature control system is adopted, which can automatically detect and display the respective working temperatures of the three-phase windings, automatically start and stop the fan, and have functions such as alarm and trip settings;
7. Small size, light weight, small footprint and low installation cost.
iron core
High-quality cold-rolled grain-oriented silicon steel sheet is used, and the iron core silicon steel sheet adopts a 45-degree full oblique joint, so that the magnetic flux passes along the seam direction of the silicon steel sheet.
Winding form
⑴ winding;
⑵ epoxy resin plus quartz sand filling and pouring;
(3) Glass fiber reinforced epoxy resin casting (ie thin insulating structure);
⑷Multi-strand glass fiber impregnated epoxy resin winding type (generally 3 is used because it can effectively prevent the cast resin from cracking and improve the reliability of the equipment).
High voltage winding
Generally, a multi-layer cylindrical or multi-layer segmented structure is used.
Form
⒈Open type: It is a commonly used form, its body is in direct contact with the atmosphere, and is suitable for relatively dry and clean indoors (when the ambient temperature is 20 degrees, the relative humidity should not exceed 85%), generally there are air self-cooling and Air cooling two cooling methods.
⒉Closed type: The body of the device is in a closed shell and does not directly contact the atmosphere (due to poor sealing and heat dissipation conditions, it is mainly used for mining and belongs to explosion-proof type).
3. Pouring type: It is cast with epoxy resin or other resin as the main insulation. It has simple structure and small volume, and is suitable for transformers with smaller capacity.
Feature structure
Temperature control system
The safe operation of the dry-type transformer and its service life largely depend on the safety and reliability of the transformer winding insulation.
Cooling method
Dry-type transformer cooling methods are divided into natural air cooling (AN) and forced air cooling (AF). Under natural air cooling, the transformer can run continuously for a long time under the rated capacity. When forced air cooling, the output capacity of the transformer can be increased by 50%. It is suitable for intermittent overload operation or emergency accident overload operation; due to the large increase of load loss and impedance voltage during overload, it is in a non-economic operation state, so it should not be in continuous overload operation for a long time.
Technical parameter
1. Frequency of use: 50 / 60HZ;
2. No-load current: < 4 %;
3. Withstand voltage strength: 20000V/min without breakdown; test instrument: YZ1802 voltage withstand tester (20mA);
4. Insulation grade: F grade (special grade can be customized);
5. Insulation resistance: ≥2M ohms
Test instrument: ZC25B-4 type megger <1000 V);
6. Connection mode: Y/Y, △/Y0, Yo/△, self-coupling (optional);
7. Allowable temperature rise of coil: I00K;
8. Heat dissipation method: natural air cooling or temperature control automatic heat dissipation;
9. Noise coefficient: ≤30dB.
Working environment
1.0 - 40 ( ℃ ), relative humidity <70%;
2. Altitude: no more than 2500 meters;
3. Avoid being exposed to rain, humidity, high temperature, high heat or direct sunlight. There should be a distance of not less than 40cm between its cooling vents and surrounding objects;
4. Avoid working in places with more corrosive liquids, or gases, dust, conductive fibers or metal fines;
5. Prevent work in vibration or electromagnetic interference places;
6. Avoid long-term upside-down storage and transportation, and can not be subjected to strong impact.
Wiring
1. Short-circuit the "input" and "output" terminals of the transformer and use a megohmmeter to test the insulation resistance between them and the ground wire. When measured by a 1000V megohmmeter, the resistance value is greater than 2M ohms.
2. The cross-sectional wiring of the input and output power lines of the transformer should meet the requirements of its current value; it is appropriate to configure it according to the current density of 2-2.5A/min2.
3. The input and output three-phase power lines should be connected to the A-phase, B-phase and C-phase respectively according to the color of the transformer wiring board busbar, yellow, green and red. The neutral line should be connected with the neutral neutral line of the transformer. The shell and the center point of the transformer are connected. Usually, the ground wire and the neutral wire we say are drawn from the neutral point of the transformer. (If the transformer has a case, it should be connected to the ground wire mark of the case).
Check the input and output lines to make sure they are correct.
4. Power on without load first, and observe and test that the input and output voltages meet the requirements. Observe the machine at the same time
Check whether there are abnormal noises, ignitions, odors and other abnormal phenomena inside. If there is any abnormality, please disconnect the input power immediately.
5. When the no-load test is completed and normal, the load can be connected.
Product selection
Product Definition
Distribution transformer is one of the important equipment in the power supply and distribution system of industrial and mining enterprises and civil buildings. It reduces the 10⑹kV or 35kV network voltage to the 230/400V busbar voltage used by users. This type of product is suitable for AC 50 (60) Hz, three-phase maximum rated capacity 2500kVA (single-phase maximum rated capacity 833kVA, single-phase transformer is generally not recommended)
1) When there are a large number of primary or secondary loads, two or more transformers should be installed. When any one of the transformers is disconnected, the capacity of the remaining transformers can meet the power consumption of primary and secondary loads. The primary and secondary loads should be concentrated as much as possible and should not be too scattered.
2) When the seasonal load capacity is large, special transformers should be installed. Such as large-scale civil S4270D27-29 27 2005.7.29, 3:24 AM air-conditioning refrigerator load, heating electric heating load, etc. in buildings.
3) When the concentrated load is large, a special transformer should be installed. Such as large heating equipment, large X-ray machines, electric arc furnaces, etc.
4) When the lighting load is large or the shared transformer for power and lighting seriously affects the lighting quality and lamp life, a special transformer for lighting can be installed. In general, power and lighting share a transformer.
Select the transformer according to the usage environment:
1) Under normal medium conditions, oil-immersed transformers or dry-type transformers can be selected, such as industrial and mining enterprises, independent or attached substations in agriculture, and independent substations in residential areas. The available transformers are S8, S9, S10, SC(B)9, SC(B)10 and so on.
2) In multi-storey or high-rise main buildings, non-combustible or flame-retardant transformers should be selected, such as SC(B)9, SC(B)10, SCZ(B)9, SCZ(B)10, etc.
3) In places where dusty or corrosive gas seriously affects the safe operation of the transformer, closed or sealed transformers, such as B S9, S9-, S10-, SH12-M, etc., should be selected.
4) High and low power distribution devices without flammable oil and non-oil-immersed power distribution transformers can be installed in the same room. At this time, the transformers should be equipped with IP2X protective casings for safety.
Select a transformer according to the electrical load:
1) The capacity of the distribution transformer should be integrated with the facility capacity of various electrical equipment to obtain the calculated load (generally excluding fire load), and the apparent capacity after compensation is the basis for selecting the capacity and number of transformers. The load rate of the general transformer is about 85%. This method is relatively simple and can be used for estimating capacity.
2) In GB/T17468-1998 "Guidelines for Selection of Power Transformers", the capacity selection of distribution transformers is recommended, and its capacity should be determined according to GB/T17211-1998 "Guidelines for Loading of Dry-Type Power Transformers" and the calculated load. The second guide above provides a computer program and a normal cycle load diagram to determine distribution transformer capacity.
Installation points
The distribution transformer is an important component of the substation. The dry-type transformer without a casing is directly installed on the ground, and protective barriers are added around it; the dry-type transformer with a casing is directly installed on the ground. For its installation, please refer to the National Building Standard Design Atlas. 03D201-4 10/0.4kV transformer room layout and installation of common equipment components in substations.
Selection
Temperature control system
The safe operation and service life of dry-type transformers largely depend on the safety and reliability of the transformer winding insulation. It is one of the main reasons that the transformer can not work normally when the winding temperature exceeds the insulation withstand temperature, and the insulation damage is caused. Therefore, the monitoring of the operating temperature of the transformer and its alarm control are very important.
(1) Automatic fan control: measure the temperature signal through the Pt100 thermistor 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 to cool; when the winding temperature drops to 90°C, the system automatically stops the fan.
(2) Over-temperature alarm and trip: The winding or core temperature signal is collected through the PTC non-linear thermal temperature measuring resistor embedded in the low-voltage winding. When the temperature of the transformer winding continues to rise, if it 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 an over-temperature trip signal must be sent to the secondary protection circuit, which should make the transformer Trip quickly.
(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 highest historical temperature can be recorded). The temperature is output by 4~20mA analog quantity, if it needs to be transmitted to a remote (distance up to 1200m) computer
Protection method
The IP20 protective casing is usually used, which can prevent solid foreign objects larger than 12mm in diameter and small animals such as mice, snakes, cats, and sparrows from entering, causing vicious failures such as short circuit and power failure, and providing a safety barrier for live parts. If the transformer must be installed outdoors, the IP23 protective enclosure can be selected. In addition to the above IP20 protection function, it can also prevent water droplets within an angle of 60° from the vertical line. However, the IP23 enclosure will reduce the cooling capacity of the transformer, so pay attention to the reduction of its operating capacity when selecting it.
Overload capacity
The overload capacity of the dry-type transformer is related to the ambient temperature, the load before overload (initial load), the insulation and heat dissipation of the transformer and the heating time constant, etc. If necessary, the overload curve of the dry-type transformer can be obtained from the manufacturer.
How to use its overload capacity? The author puts forward two points for reference:
(1) When choosing to calculate the transformer capacity, it 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 transformers to reduce the transformer capacity; Places with uniform load, such as residential areas mainly for night lighting, cultural and entertainment facilities, and shopping malls with air conditioning and daytime lighting, can make full use of their overload capacity, appropriately reduce the transformer capacity, and make the main operating time at full load or short-term overload.
Application status
Because dry-type transformers have no oil, there are no problems such as fire, explosion, and pollution. Therefore, electrical codes and regulations do not require dry-type transformers to be placed in a separate room. Losses and noise have been reduced to a new level, creating conditions for placing transformers and low-voltage panels in the same distribution room.
The dry-type transformer is an important equipment of the power system of the offshore oil platform, and its safe and reliable operation is the key to the operation of the power system. Dry-type transformers are prone to insulation partial discharge and local overheating problems in the humid and salt-fog marine environment. The application of the dry-type transformer online monitoring system can effectively realize the online monitoring of the transformer status and ensure the stable operation of the power system of the offshore oil platform. . [8]
The annual output of resin-insulated dry-type transformers in China has reached 10,000MVA, making it one of the countries with the largest production and sales of dry-type transformers in the world. Dry-type transformers are now widely used in almost all electrical power stations, factories, hospitals, etc. With the promotion and application of SC(B)9 series with low noise (noise of distribution transformers below 2500kVA has been controlled within 50dB) and energy saving (no-load loss reduced by 25%), the performance indicators and manufacturing of dry-type transformers in China have been improved. The technology has reached the world advanced level.
Inspection
⒈ Whether there is abnormal sound and vibration.
⒉ Whether there is local overheating. Harmful gas corrosion and other discoloration caused by creepage traces and carbonization on the insulating surface.
3. Whether the air-cooling device of the transformer is operating normally.
⒋The high and low voltage joints should be free from overheating. The cable head should be free of leakage and creepage.
⒌The temperature rise of the winding should be based on the grade of insulating material used in the transformer, and the monitoring temperature rise should not exceed the specified value.
⒍ The supporting porcelain bottle should be free of cracks and discharge traces.
⒎ Check whether the winding pressure piece is loose.
⒏Indoor ventilation, iron core air duct should be free from dust and debris, and iron core should not be rusted or corroded.
Difference
Inverter: It can be adjusted to achieve the required electricity frequency (50hz, 60hz, etc.) to meet our special needs for electricity. Transformer: It is generally a "step-down device", which is often found near the community or near the factory. Its function is to reduce the ultra-high voltage to the normal voltage of our residents to meet people's daily electricity consumption.
Dry-type transformers and oil-immersed transformers are the two most used transformers. Compared with oil-immersed transformers, dry-type transformers have better fire performance and are mostly used in places with high fire protection requirements, such as hospitals, airports, stations, etc. However, relatively speaking, the price is higher, and there are certain requirements for the environment, such as not being too humid, not having too much dust and dirt, etc. In addition, the operational maturity of dry-type transformers is not as good as that of oil-immersed transformers.
Future
With the popularization and application of dry-type transformers, its manufacturing technology has also made great 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-consumption silicon steel sheets, foil winding structures, stepped iron core joints, environmental protection requirements, in-depth noise research, and the introduction of new materials, new processes, and new technologies such as computer optimization design, It will make the future dry-type transformer more energy-saving and quieter.
Protective device
The dry-type transformer microcomputer protection device is an economical protection for the integration of measurement, control, protection and communication; it is tailored for the high-voltage distribution room of the distribution network terminal, with three-stage non-directional current protection as the core, equipped with power grid The parameter monitoring and collection function can save the traditional ammeter, voltmeter, power meter, frequency meter, watt-hour meter, etc., and can transmit the measurement data and protection information to the upper computer through the communication port, which is convenient to realize the automation of distribution network; According to the characteristics of the power supply of the distribution network, the device integrates the automatic switching function of the standby power supply in the device, which can flexibly realize the standby switching of incoming lines and the standby switching function of the bus and branch.
The dry-type transformer microcomputer protection device adopts the international advanced DSP and surface mount technology and flexible field bus (CAN) technology to meet the requirements of different voltage levels of the substation, and realize the coordination, digital and intellectualization of the substation. This series of products can complete the functions of substation protection, measurement, control, regulation, signal, fault recording, power acquisition, low-current grounding line selection, low-cycle load shedding, etc., so that the technical requirements, functions, and internal wiring of the product are more standardized. . The product adopts distributed protection measurement and control device, which can be centrally grouped or installed in a decentralized manner, and the configuration can also be arbitrarily changed according to user needs to meet the requirements of different schemes.
⑵High reliability: improving product quality and reliability will be the unremitting pursuit of people.
(3) Environmental protection characteristics certification: Based on the European standard HD464, carry out research and certification of the weather resistance (C0, C1, C2), environment resistance (E0, E1, E2) and fire resistance (F0, F1, F2) characteristics of dry-type transformers .
⑷ Large capacity: from dry-type transformers based on 50-2500kVA distribution transformers, to 10000-20000kVA/35kV power transformers, with the continuous increase of urban electricity load, urban network regional substations are getting deeper and deeper into the city center , residential areas, large factories and mines and other load centers, 35kV large-capacity residential center power supply power transformers will be widely used.
⑸Multifunctional combination: From a single transformer to a multifunctional combined transformer with air cooling, protective casing, temperature computer interface, zero-sequence transformer, power metering, closed busbar and side outlet. It can be predicted that the distribution transformer in the 21st century will belong to the resin-insulated dry-type transformer with superior performance, low noise and energy saving.
