The advantages of mechanical winding transformer are high efficiency and beautiful appearance, but winding ring transformer with high and small holes is more troublesome, and the reliability of insulation treatment process is not as good as that of manual winding in place. Manual winding can make the magnetic leakage of the transformer very small, and it can be adjusted at any time according to the layout of the number of turns in the winding process, so the real Hi-end transformer must be hand-wound. The only disadvantages of pure hand winding are low efficiency and slow speed.
2. Which is the best power transformer, ring, EI, R and C?
They have their own advantages and disadvantages, and no one is the best, so strictly speaking, any transformer can do the best. Structurally, the ring type can minimize the magnetic leakage, but the EI type can make the medium frequency density feel better. As far as magnetic saturation is concerned, EI type is stronger than ring type, but ring type is better than EI type in efficiency. Nevertheless, the key to the problem is whether you can give full play to your respective advantages and avoid weaknesses, which is the most fundamental thing to do a good job in transformers.
The application of toroidal transformer is still the mainstream in imported power amplifiers, which basically illustrates a problem. Enthusiasts should evaluate Transformers objectively and fairly. You can't say it's not good if you don't make a good reference. Some people say that toroidal transformer is easy to be magnetically saturated, so why not try to make it difficult to be magnetically saturated? This could have been done by technical means. If you don't work hard or save costs blindly, of course, it is easy to be magnetically saturated. Similarly, as long as you make it with your heart, the efficiency of EI transformer can be high.
The quality of transformer has a great influence on sound, because the transmission energy of transformer is closely related to iron core and coil, and its transmission rate plays a decisive role in the influence of sound. Like EI transformer, people usually think that its intermediate frequency is coarse and its high frequency is fine. Why? Because its transmission speed is slow. What about the ring type? The low frequency is fierce, and the middle and high frequency are slightly weaker. Why? Because its transmission speed is relatively fast, but if you make effective structural changes, you can make both the ring type and the EI type perfect, so it depends on how you do it.
But at least one thing is certain, R transformer is not easy to do. It is possible to use it as the power supply of low-current front-stage power amplifier and CD player, but it has serious defects as the power supply of rear-stage power amplifier. Because the structural form of R-type transformer itself is not easy to change, it is easier for ring type and EI type to achieve the purpose of beautiful sound by changing the structure. The power amplifier power supply made of R-type transformer usually has a hard sound, lacks aura, and often does not bounce at low frequencies, which makes it look hard.
3. Is the silicon content in the silicon steel sheet of transformer core as large as possible?
It can't be seen that the silicon content of silicon steel sheet has little influence on the quality of transformer, but the orientation and non-orientation are related to the type of iron core. Secondly, even if you don't handle the same type of iron core well, the quality varies greatly, sometimes as high as 40% to 50%.
A good iron core and the heat treatment and winding process of the same material are very important. Good heat treatment can reach 15000 gauss at the minimum excitation current of 100 mA, while bad heat treatment can reach the corresponding 15000 gauss at the excitation current of 50mA, which is quite different. Judging the quality of iron core from a professional point of view is mainly based on several indicators such as excitation current, core loss and saturation parameters.
4. If the silicon steel sheet of ring transformer adopts splicing process, does it mean that the quality is definitely not good?
We can't generalize, but it's not easy to splice broken heads too much, because one more broken position will lead to one more magnetic leakage point, so it's best not to exceed three joint points. In the manufacturing process, all broken joints must be pickled first, but strictly speaking, it is best to use silicon steel sheets without joints to manufacture ring transformers of high-grade audio equipment, and its process quality will be more guaranteed.
5. What about the material of silicon steel sheet in transformer?
Because the loss of silicon steel sheet in alternating magnetic field is very small, silicon steel sheet is mainly used as magnetic material in transformer. Silicon steel sheets can be divided into hot rolling and cold rolling. Cold rolled silicon steel strip has the advantages of small volume, light weight and high efficiency because of its high permeability and low loss. The properties of hot-rolled silicon steel strip are slightly inferior to those of cold-rolled silicon steel strip.
Ordinary EI transformers are made of silicon steel sheets into E-type and I-type sheets with a thickness of 0.35–0.5 mm, and then inserted into the windings after heat treatment. Most of these iron cores are hot-rolled silicon steel sheets (the high-quality silicon steel sheets with high silicon content are D4 1, D42, D43, D30 1). The iron cores of ring-type and C-type transformers are wound with cold-rolled silicon steel sheets, and C-type transformers are cut after heat treatment and dipping in paint.
The leakage inductance of transformer is produced by the magnetic flux that does not pass through the primary and secondary coils, and these magnetic fluxes pass through the air to form a closed magnetic circuit. Strengthening the coupling density between primary and secondary of transformer can reduce leakage inductance. The leakage inductance of a good transformer should not exceed1100 of the inductance of the primary coil and1500 of the output transformer of the Hi-Fi pump.
One of the important parameters to judge the quality of silicon steel sheet of audio transformer is the maximum magnetic flux density of silicon steel sheet. The commonly used models of several high-quality silicon steel sheets are as follows: d 41–d42, and the maximum magnetic flux density (unit–GS gauss) is10000–12000 GS; D43, the maximum magnetic flux density is11000–12000gs; D30 1, maximum magnetic flux density12000–14000gs. A, transformer mid-term detection:
A, set the multimeter at R× 1 gear, and check the on-off situation of each winding one by one according to the pin arrangement law of the mid-cycle transformer to judge whether it is normal.
B, test the insulation performance: put the multimeter in R× 10k, and do the following state tests:
(1) Resistance value between primary winding and secondary winding;
(2) the resistance between the primary winding and the shell;
(3) Resistance value between secondary winding and shell.
The above test results are divided into three situations:
(1) Infinite resistance: normal;
(2) The resistance value is zero: there is a short circuit fault;
(3) The resistance value is less than infinity, but greater than zero: there is a leakage fault.
Second, the power transformer detection:
A, by observing the appearance of the transformer to check whether it has obvious abnormal phenomenon. For example, whether the lead wire of the coil is broken and desoldering, whether the insulation material has burnt marks, whether the fastening screw of the iron core is loose, whether the silicon steel sheet is rusted, whether the winding coil is exposed, etc.
B, insulation test. Use multimeter R× 10k to measure the resistance between iron core and primary, primary and secondary, iron core and secondary, electrostatic shielding layer and secondary and secondary windings. The pointer of multimeter should be fixed at infinite position. Otherwise, the transformer insulation performance is poor.
C, coil on-off detection. Put the multimeter in the R× 1 position. If the resistance value of a winding is infinite during the test, it means that the winding has an open circuit fault.
D, distinguish the primary coil and the secondary coil. The primary pin and secondary pin of power transformer are generally led out from both sides. The primary winding is marked with the word 220V, and the secondary winding is marked with the rated voltage value, such as 15V, 24V and 35V. Then identify according to these marks.
E, no-load current detection.
(1) direct measurement method. Open all the secondary windings, and put the multimeter in the AC current block (500mA, connected in series with the primary winding. When the plug of the primary winding is plugged into a 220v AC source, the multimeter displays the no-load current value. This value should not be greater than 10% ~ 20% of the transformer full-load current. The normal no-load current of common electronic equipment power transformer should be about1000 mA. If it exceeds too much, it means that the transformer has a short circuit fault.
(2) Indirect measurement. Connect a 10 in series in the primary winding of the transformer? /5W resistor, secondary or all empty. Set the multimeter to the AC voltage range. After power-on, measure the voltage drop U across the resistor R with two probes, and then calculate the no-load current I-space by ohm's law, that is, I-space = u/r.
F, no-load voltage detection. Connect the primary of the power transformer to the 220V mains supply, and measure the no-load voltage (U2 1, U22, U23, U24) of each winding in turn with a multimeter. The allowable error range is generally: high voltage winding ≤ 10%, low voltage winding ≤ 5%, and the voltage difference between two groups of symmetrical windings with center tap should be ≤ 2.
G. Generally, the allowable temperature rise of low-power power transformers is 40℃ ~ 50℃. If the insulation materials used are of good quality, the allowable temperature rise can be increased.
H, detecting and judging the homonym end of each winding. When a power transformer is used, sometimes two or more secondary windings can be connected in series to obtain the required secondary voltage. When power transformers are used in series, the homonymous ends of series windings must be connected correctly, and no mistakes can be made. Otherwise, the transformer cannot work normally. First, the comprehensive detection and discrimination of power transformer short circuit fault. The main symptoms of short-circuit fault of power transformer are severe fever and abnormal output voltage of secondary winding. Generally, the more short-circuit points between turns, the greater the short-circuit current and the more serious the transformer heating. A simple way to detect and judge whether there is a short-circuit fault in power transformer is to measure the no-load current (the test method has been introduced earlier). The no-load current of transformer with short circuit fault will be much greater than the full-load current of 10%. When the short circuit is serious, the transformer will heat up rapidly within dozens of seconds after no-load power-on, and it will feel hot when touching the iron core with your hands. At this time, it can be concluded that there is a short circuit point in the transformer without measuring the no-load current.
The four major domestic transformer manufacturers are Shenyang Transformer Factory (merged by TBEA in 2004), Xi 'an Transformer Factory, Baoding Transformer Factory and TBEA Co., Ltd., and famous foreign companies include Siemens and ABB. Satellites are thousands to tens of thousands of kilometers from the ground. In order to send all kinds of data back to the earth correctly, it is necessary to avoid the mutual interference between various instruments on the satellite and the influence of the cosmic magnetic field. In telecommunication technology, the coils of some communication equipment will produce mutual inductance; In order to maintain the accuracy of various precision instruments, it is necessary to avoid the influence of stray magnetic fields and geomagnetic fields, which must use magnetic shielding. How to perform magnetic shielding? You can do a simple experimental study first.
Take 1 copper plate (or 1 cardboard) and place it at a certain distance below 1 permanent magnet. Put an iron needle on the table and let the permanent magnet and copper plate (or cardboard) move down slowly. When the permanent magnet is at a certain height from the table, the iron needle will be attracted to the copper plate (or cardboard) and this height will be recorded.
Replace copper plate with iron plate and repeat the above experiment. At this time, the permanent magnet must be placed closer to the iron needle to attract the iron needle to the iron plate, which shows that the iron plate blocks some magnetic induction lines. If a pure iron plate is used, the permanent magnets must be placed closer to attract iron needles. This shows that the pure iron plate blocks more magnetic induction lines.
If the permanent magnets are completely surrounded by pure iron covers and don't touch each other, then even if the iron needle is close to some pure iron covers, it can't be sucked up. This is because the copper plate or cardboard is a nonmagnetic material, and the magnetic induction line can pass through without any obstacle, so the iron needle is easy to suck. Iron plate is a magnetic material with high permeability and good magnetic conductivity. Most of the magnetic induction lines entering the iron plate are concentrated in the iron plate. Make a pure iron shield and seal it with a permanent magnet. Most of the magnetic induction lines of permanent magnets are concentrated in the shielding of pure iron. The thicker the shielding, the better the shielding effect. If permanent magnets or other objects that can generate magnetic fields are placed outside the pure iron shielding cover, the magnetic induction lines outside the cover can basically not enter the cover, and the objects inside the cover can also be protected from the influence of the magnetic field outside the cover, thus achieving the purpose of shielding.
For high frequency alternating magnetic field, the situation is very different. Metals with good conductivity, such as copper and aluminum, are ideal magnetic shielding materials. The reason why the copper sleeve can shield the high-frequency alternating magnetic field is that the high-frequency alternating magnetic field can produce a great eddy current on the copper sleeve. Due to the demagnetization of eddy current, the magnetic field at the copper cover is greatly weakened, which makes the high-frequency alternating magnetic field in the cover unable to pass through the cover. Similarly, the high-frequency alternating magnetic field outside the cover can not penetrate into the cover, thus achieving the purpose of magnetic shielding. Generally speaking, the smaller the resistivity of a metal, the greater the eddy current caused, and the better the shielding effect of a shield made of this metal. The resistivity of magnetic materials such as iron is generally large, so the eddy current caused is small and the demagnetization effect is small; On the other hand, magnetic materials have high high-frequency power loss and poor shielding effect, so they are not used to shield high-frequency alternating magnetic fields.
The principle of shielding is the same. But at high frequency, there is no material with high magnetic permeability for shielding. Materials with high permeability at low frequencies will have low permeability at high frequencies. Even the special high-frequency ferrite is hard to exceed 100, which is much worse than the tens of thousands of magnetic permeability of silicon steel sheet or pure iron at low frequency, and it cannot effectively concentrate the magnetic field. At the same time, these materials are all formed at one time, and cannot be processed twice after firing to meet different needs. So we have to use eddy current loss and back electromotive force to generate reverse magnetic field to realize shielding. The best materials for eddy current generation are low resistivity materials, such as pure copper and pure aluminum.
Transformer use:
A transformer consists of an iron core and a coil. Transformer coils are divided into primary coils and secondary coils. When the primary coil is energized with alternating current, the transformer core generates an alternating magnetic field. The secondary coil induces alternating current with the same frequency as the primary coil. The turns ratio of transformer coil is equal to the voltage ratio. For example, when the primary winding of a transformer is connected with a voltage of 220V, the secondary winding will output an AC voltage of 22 V. The transformer can not only step down, but also step up. Generally, long-distance transmission is adopted.
The statement of DC transformer is wrong. DC cannot be changed. To convert DC into AC, you must first use electronic components, and then use a transformer to convert voltage. This device is called an inverter.
Although the performance and operation quality of distribution transformers have been improved after the transformation of rural power grid and urban power grid, there are still great hidden dangers, which are as follows:
1. According to the general characteristics of urban and rural power grids, the load rate is 30-40% most of the time, but it is often overloaded during peak hours. On the one hand, there are many uncertain factors such as continuous high temperature in summer, sudden increase of air conditioning load and sudden increase of rural power grid load during busy farming or drought, which may cause short-term overload of distribution transformers100%; On the other hand, with the rapid economic growth, the growth rate of industrial and residential electricity demand exceeds the speed of power grid construction, and the overload phenomenon is hard to avoid for a while.
2. Although the distribution transformer has alarm and protection devices, even after alarm or tripping, it is impossible to replace the transformer in a short time, resulting in continuous overload and burning of the distribution transformer.
3. The biggest hidden danger of overload distribution transformer is the possibility of fire, which will produce harmful gas when burning.
4. With the transformation of two power grids and the continuous development of power grids, the consumption of distribution transformers has increased sharply, and the environmental protection and recycling of distribution transformers after scrapping will become a serious problem.
5. Box transformers are widely used in urban power supply, and the supporting transformers include oil-immersed transformers and dry-type transformers. One of the defects of oil transformer is the aging of oil, the decline of insulation performance and the difficulty of maintenance and oil change. The disadvantage of dry-type substation is that its protection level is low and it is not suitable for outdoor operation. Due to the high ambient temperature in the box transformer, the power supply department is worried about the load capacity of the transformer, and it is difficult to determine its full load and overload capacity. Once the overload fails, it is more difficult to replace the transformer.
Foreign power grids have also experienced this situation. From 1960s to early 1970s, Europe and America built distribution networks during the period of economic expansion, and the load rate of distribution transformers was only 40% to 50%. With the rapid economic growth, these power grid systems become obsolete or overwhelmed, especially the load rate of distribution transformers is increasing, and transformers are often overloaded, which leads to the rise of faults and the increase of capacity costs.
Two methods are commonly used abroad to solve the above problems: one is to transform the traditional transformer by using nomex insulation paper and common oil mixed insulation technology, and the equipment capacity is significantly improved after the transformation. Power companies can operate these devices more flexibly, with lower loss when the load drops and greater capacity during the peak load period. Countries that recognize and implement capacity expansion and transformation are: the United States, Britain, India, Canada, Australia and Germany. Secondly, nomex insulating paper and high ignition point oil are used to produce high ignition point oil transformer.
In 1980s, France developed a pole transformer made of silicone oil and nomex insulating paper, which was widely used in densely populated areas. The airborne transformers on domestic electric locomotives also adopt nomex insulation paper and silicone oil insulation system, and have many years of operating experience. Due to the sustainable development strategy and the requirements of environmental protection, manufacturers and experts at home and abroad are constantly exploring. Using nomex insulating paper and clean and decomposable high ignition point β oil to manufacture safe and environmentally friendly distribution transformers will effectively reduce and eliminate hidden dangers.
Dupont nomex insulating paper has a heat-resistant insulation grade of C (that is, 220℃), a burning point lower than the oxygen index, and can be decomposed and recycled after the service life. Its insulation performance and mechanical strength are far superior to ordinary cable paper. The open dry-type transformer made of nomex insulating paper is widely recognized and accepted by domestic users because of its safety and environmental protection characteristics. β oil is a kind of high-tech environmental protection oil with excellent performance produced by dsi company in the United States. Its biggest feature is high ignition point and good flame resistance (tested by the Fire Protection Research Institute of the Ministry of Public Security, its ignition point is 3 10℃, and ordinary oil is 165℃). It is extracted from petroleum, and its composition is 65,438+000% hydrocarbons, which can be completely biological.
The oil transformer made of β oil and DuPont nomex insulating paper with heat resistance up to 220℃ meets the American standard NEC 450-23. This transformer has been used in American National Laboratory, Pentagon, Air Force Base, National Coast Guard, Navy, Aviation Administration and other places, and works well. Where oil transformers with high ignition point are used, the probability of fire and explosion is greatly reduced. This new type of transformer has developed rapidly in the United States in recent years, accounting for 5% of power transformers and the proportion is still rising. The International Electrotechnical Commission is also considering formulating design guidelines for distribution transformers using high-temperature insulation materials as insulation systems.
The oil change of Nomex insulating paper β has the advantages of safety, fire prevention, low operating cost, good environmental protection performance and strong reliability. Using this nomex insulation paper β oil transformer will greatly change the distribution situation.
1, short-term overload will not cause an accident. After calculation and test, after 12 hour overload operation, the hot spot temperature of its coil and oil is lower than its temperature resistance grade, and its insulation life will not be damaged.
2. Long-term use can avoid oil change and maintenance, overcome the shortcomings of existing common oil transformers, and save operating costs.
3. Compared with ordinary transformer oil, the viscosity of β oil is obviously higher than that of ordinary transformer oil; Moreover, the transformer oil tank is equipped with a unique pressure relief device, which will not be over-pressured during operation and will not leak easily.
4. It has unique safety and fire prevention characteristics, which reduces the operation risk;
5.nomex insulation paper β oil transformer has the advantage of dry transformer, which is suitable for both safe and fire-proof high-rise buildings and outdoor operation.
6. For a large number of distribution transformers, the recycling of materials and the biodegradation of wastes are the requirements of sustainable development and environmental protection. Nomex insulating paper is biodegradable after its service life, and the working temperature of β oil itself is much lower than its temperature resistance grade, so it can be recycled after treatment. The treated waste can be decomposed by microorganisms in the soil and has no toxicity, so it will not accumulate in the environment for a long time and cause pollution.
It is worth discussing how to manufacture new distribution transformers with new materials and technologies to eliminate the potential safety hazards and environmental protection problems of distribution transformers.