1 Introduction
Step-up transformer and on-load voltage regulation are transformer tap switch voltage regulation mode, the difference is that the non-exciting voltage regulation switch does not have the ability to shift gears with load, because this tap switch in the process of shift gears, there is a short-time disconnect process, disconnect the load current will cause the arc between contacts burn the tap switch or short circuit, so the transformer must be cut off when shifting. Therefore, it is generally used for transformers that are not very strict in voltage requirements and do not need to shift frequently. And the on-load tap switch can be load switching gear, because the on-load tap switch in the shift process, there is no short-time disconnection process, through a transition resistance transition, from one gear to another gear, so there is no load current disconnection arc pulling process. It is generally used for transformers with strict voltage requirements and frequent shifting.
2 Definition
Definition: A transformer is a common electrical device used to convert a value of alternating voltage into another value of alternating voltage at the same frequency. A booster transformer is a transformer used to convert a low value alternating voltage into another high value alternating voltage of the same frequency. It is widely used in the field of high frequency, such as inverter power supply.
3 Classification of high frequency expressions
The high frequency booster transformer adopts the high frequency doubling voltage rectifier circuit, the application of the latest PWM pulse width modulation technology and power IGBT devices, and according to the electromagnetic compatibility theory, the use of special technology, so that the DC generator to achieve high quality, portable. It is composed of two parts: control box and voltage doubling device. It is equipped with protection resistance, which has the functions of voltage zero gate protection, overcurrent protection and overvoltage protection. Small size, light weight, easy to carry, convenient, safe and reliable, suitable for power department field DC high voltage test, arrester DC characteristics test and other occasions requiring DC high voltage.
Straight flow
Dc booster transformer has the characteristics of small volume, light weight, compact structure, complete functions, strong versatility and easy to use. Especially suitable for power system, industrial and mining enterprises, scientific research departments and other high voltage electrical equipment, electrical components, insulation materials under the manifold frequency or DC high voltage insulation strength test. It is an essential and important equipment in high pressure test.
Energy saving and low noise: using high quality cold rolled silicon steel sheet stacked; Full oblique joint; Special processing technology is adopted to effectively reduce the vibration and noise during operation. As well as computer optimization design and other new materials, new process, new technology introduction, make the transformer more energy saving, more quiet.
High reliability: To improve product quality and reliability, will be our unremitting pursuit. In the quality assurance system and reliability engineering of a large number of basic research, active reliability certification, further improve the reliability and service life of the transformer.
Environmental protection properties: heat resistance, moisture resistance, stability, chemical compatibility, low temperature, radiation resistance and non-toxicity.
Alternating flow
Ac booster transformer is a device that transforms AC voltage, current and impedance. When there is AC current in the primary coil, AC flux is generated in the iron core (or magnetic core), so that the voltage (or current) is induced in the secondary coil. A transformer consists of an iron core (or magnetic core) and a coil. The coil has two or more windings. The winding connected to the power supply is called the primary coil, and the rest is called the secondary coil. Ac booster transformer has the characteristics of small volume, light weight, compact structure, complete functions, strong versatility and easy to use. Especially suitable for power system, industrial and mining enterprises, scientific research departments and other high voltage electrical equipment, electrical components, insulation materials to carry out manifold frequency or AC high voltage insulation strength test. It is an essential and important equipment in high pressure test.
Dry type is relative to oil type transformer, dry type booster transformer because there is no oil, there is no fire, explosion, pollution and other problems, so electrical codes and regulations do not require dry type transformer placed in a separate room. Especially with the new series, loss and noise are reduced to new levels, and the transformer and low voltage panel are placed in the same distribution room to create conditions. The safe operation and service life of dry booster transformer largely depend on the safety and reliability of transformer winding insulation. The insulation damage caused by the winding temperature exceeding the insulation resistance temperature is one of the main reasons for the transformer not working normally. Therefore, it is very important to monitor the running temperature of the transformer and its alarm control. According to the environmental characteristics and protection requirements, the dry booster transformer can choose different shells. IP23 protective shell is usually used to prevent the entry of solid foreign bodies with diameter larger than 12mm and small animals such as rats, snakes, cats and finches, which may cause malignant faults such as short circuit and power failure, and provide a safety barrier for live parts. If the transformer must be installed outdoors, you can choose IP23 protection shell, in addition to the above IP20 protection function, but also can prevent water drop and vertical line Angle within 60°. But the IP23 shell will reduce the cooling capacity of the transformer, and attention should be paid to the reduction of its operating capacity when selecting.
Low frequency type
The low frequency transformer core flux is related to the applied voltage. The excitation current in the current does not increase with the load. Although the load increase core will not be saturated, will make the coil resistance loss increase, more than the rated capacity due to the heat generated by the coil can not be timely out, coil will be damaged, if you use the coil is composed of superconducting materials, current increases will not cause heat, but the transformer and the impedance caused by magnetic leakage, but the current increases, the output voltage will drop, the greater the current, The lower the output voltage, so the transformer output power cannot be unlimited. If you say that the transformer has no impedance, then when the transformer flows through the current will produce a particularly large electric power, it is easy to damage the transformer coil, although you have a power unlimited transformer but can not use. It can only be said that with the development of superconducting materials and iron core materials, the output power of transformers of the same volume or weight will increase, but not infinitely large! [1]
4 Physical Properties Physical properties
Transformer ---- A stationary electromagnetic device that converts alternating current energy of one voltage into alternating current energy of another voltage of the same frequency. The main components of a transformer are an iron core and two windings over the core. The principle of transformer is that the coil connected to the power supply receives AC electric energy, which is called the primary winding, and the coil connected to the load sends AC electric energy, which is called the secondary winding, the primary winding, the secondary winding, voltage phasor U1 voltage phasor U2, current phasor I1 current phasor I2, electromotive force phasor E1 electromotive force phasor E2, the number of turns N1 turns N2, and the alternating chain once, The phasor of the magnetic flux of the secondary winding is φm, which is called the primary magnetic flux.
Physical formula
U1/U2=N1/N2 =I2/I1 (U1 and U2 are voltage, N1 and N2 are coil turns, I1I2 is current).
There are many and complex reasons for transformer internal faults and accidents caused by transformer outlet short circuit. It is related to structural design, quality of raw materials, technological level, operating conditions and other factors, but the selection of electromagnetic line is the key. In recent years, the electromagnetic wires selected by transformer based on the static theory design are different from the stress acting on the electromagnetic wires in actual operation.
1. The winding is loose, the transposition is not handled properly, and the electromagnetic wire is too thin, resulting in hanging. From the point of view of accident damage, the deformation is more common in the transposition, especially the transposition of the transposition wire.
2. At present, the calculation program of various manufacturers is based on the idealized model of uniform distribution of leakage magnetic field, the same turns diameter, equal phase force, etc., but in fact, the leakage magnetic field of transformer is not uniform distribution, relatively concentrated in the yoke part, the electromagnetic line in this area is subjected to a large mechanical force; The climbing of the transposition wire will change the direction of force transmission at the transposition point and generate torque. Due to the factor of the elastic modulus of the pad, the unequal distribution of the axial pad will cause delayed resonance of the alternating force generated by the alternating leakage magnetic field. This is also the fundamental reason why the wire cake at the yoke part of the core, the transposition part and the corresponding part with the pressure regulation tap deform first.
3. Improper control of the winding preload causes the wires of the ordinary transposition wires to be misaligned with each other.
4. The influence of temperature on the bending and tensile strength of electromagnetic wire is not considered in the calculation of short-circuit resistance. The anti-short-circuit capability designed at normal temperature can not reflect the actual operation condition. According to the test results, the temperature of the electromagnetic wire has no effect on its yield limit. 0.2 has a great influence. With the increase of the temperature of the electromagnetic wire, its bending strength, tensile strength and elongation all decrease. The bending tensile strength at 250℃ is lower than that at 50℃, and the elongation is reduced by more than 40%. In the actual operation of the transformer, under the rated load, the average winding temperature can reach 105℃, and the most hot spot temperature can reach 118℃. General transformers have reclosing process during operation, so if the short circuit point cannot disappear for a while, it will bear the second short circuit impact in a very short time (0.8s), but because of the impact of the first short circuit current, the winding temperature increases sharply, according to the provisions of GBl094, the maximum allowed 250℃, At this time, the anti-short-circuit ability of the winding has been greatly reduced, which is why the short-circuit accidents of Satons transformer occur most after reclosing.
5, the use of flexible wire, is also one of the main reasons for the transformer short-circuit resistance is poor. Due to the lack of early understanding of this, or winding equipment and process difficulties, manufacturers are reluctant to use semi-hard wire or design without this requirement, from the fault transformer point of view are soft wires.
6. External short-circuit accidents are frequent. The accumulated effect of electric power after multiple short-circuit current impacts causes electromagnetic line softening or internal relative displacement, and eventually leads to insulation breakdown.
7. The winding turns or wires are not cured, and the resistance to short circuit is poor. There is no damage to the windings treated with lacquer in the early stage. [2]
6 Daily Maintenance
1. In order to protect the insulation performance of the insulating oil installed in the high voltage generator and the head, it is generally not appropriate to open the observation window and loosen the fixing screws around, so as to prevent the oil from absorbing moisture or falling dust and reducing the insulation performance.
2. Check whether the lighting, heat dissipation and dust removal equipment around the transformer are in good condition, and wipe the dust on the transformer body and porcelain bottle with a clean cloth.
3, check the transformer high voltage side load switch, to ensure flexible operation, good contact, transmission part for lubrication.
4. Open the high-voltage grounding knife, check that the grounding is in the off position, close the high-voltage load switch, let the transformer test run, and take down the high-voltage side sign plate, pay attention to disconnect or close the transformer high-voltage load switch, there must be more than two people on site.
5, when the need to replace the new oil, should obtain the assistance of the local power department, check the performance of the new oil, the insulation strength is required to be not less than 25,000 volts /2.5 mm; The oil insulation strength in the combined head should be above 30,000 volts /2.5 mm.
6, use 2500V dial to measure the transformer high and low voltage coil insulation resistance value (to the ground and phase), confirm that meet the requirements (at room temperature 30℃, 1OKV transformer high voltage side is greater than 20MΩ, low voltage side is greater than 13MΩ. Before the test, the ground wire should be connected, and after the test, the discharge should be carried out.
7, the high voltage generator or combination head must have a good grounding wire, should often use the ohmmeter to measure the shell, console shell, external ground three are on, and tighten the grounding bolt.