Electrical insulation paper is an important material in the production process of transformers. Insulated cable paper is used between the winding layers of the oil-immersed transformer, crepe paper is used for the leads, and spliced insulation paper is used for the winding layer. The role of insulating paper is to prevent short circuits, so how to measure its insulation performance, the most important indicator is the resistance value.
Due to the low price and convenient maintenance of copper three-phase oil-filled distribution transformers with finned radiators, oil-filled transformers account for more than 80% of the electrical market, much higher than dry-type transformers. However, the failure rate is also very high, so it is necessary to arrange regular inspections. There are three
common accidents in distribution transformers:
I insulation accident.
The insulation damage accident of the three-phase distribution transformer accounts for 70%-80% of the total accidents. It is damaged by mechanical force or overheating. It also has the insulation strength not meet the requirements at the factory or the insulation is damaged and the strength is reduced. Ability requirements.
The main causes of the failure: 1 oil-filled transformer water is damp. Mainly, the end of the casing is not tightly sealed, the water cooler leaks, the explosion-proof cylinder is accumulated, and there is water in the oil storage cabinet. The presence of moisture will reduce the breakdown strength of the transformer insulating oil and cause insulation accidents. The most insulation accidents are windings, leads and screens. The development of creepage leads to inter-turn and inter-layer short circuits. 2 Foreign matter remaining in the distribution transformer. Metal conductors foreign matter and impurities remaining in the transformer body cause partial discharge or wear and tear, causing insulation breakdown damage in the event of an overvoltage or at a normal operating voltage. 3 lightning strikes. The lightning resistance level of the lightning protection of the medium and low voltage side of the three-phase transformer is too low and the insulation structure of the transformer is weak, which causes the grounding short circuit of the transformer during lightning strike.
II Overheating fault. There are overheating caused by abnormal currents, such as overheating caused by circulation and eddy currents, overheating due to increased resistance of the conductive loop, and overheating due to heat dissipation.
III short circuit damage accident. Copper winding transformers suffer from various short-circuit accidents during operation, such as single-phase, two-phase or two-phase, three-phase short circuit, in which the short circuit at the exit is the most serious.
There are a total of 12 types of outdoor three-phase power transformers, but in order to avoid confusion in manufacturing and use, China has only 5 types of three-phase dual-winding power transformers: Yyn0, Yd11, YNd11, YNy0 and Yy0.
Standard group application
The outdoor power transformer of the Yyn0 group is used in a three-phase four-wire power distribution system to supply power to the hybrid load of power and lighting;
The three-phase transformer of the Yd11 group is used in the line with a low voltage higher than 0.4kV;
The power transformer of the YNd11 group is used in a high voltage line to be grounded at a neutral point above 110kV;
The three-phase power transformer of the YNy0 group is used in the system where the primary side needs to be grounded;
The outdoor three-phase power transformer of the Yy0 group is used to supply power to the line of the three-phase power load.
In the connection group of the power transformer, “Yn” indicates that the primary side is a star-belt neutral line, Y represents a star, n represents a neutral line, and “d” indicates that the secondary side is a delta connection. “11” indicates that the line voltage Uab on the secondary side of the three-phase transformer lags the primary side line voltage UAB by 330 degrees (or 30 degrees ahead).
Since the temperature has a great influence on the performance of the transformer, the finned radiator becomes a new heat exchange device selected for the large and medium-sized three-phase oil-immersed transformers. But how to choose the right radiator to improve the working efficiency of the three-phase oil-immersed transformer with finned radiator:
(1) In order to improve the cooling effect of the heat dissipation center, the position of the junction of the finned radiator on the fuel tank of the three-phase transformer is as close as possible to the top of the tank. When the chip radiator is installed in a centralized manner, it is installed on the frame, and the flange of the main pipe and the transformer tank connection flange is fixed, and the cross-sectional area of the pipe is required to be large enough.
(2) When the fan is running, its vibration may cause damage to the cooling fin weld. To this end, the damping elastic washer should be installed at the fixed position of the fan and the finned radiator on the bracket. If possible, install the fan and finned radiator separately.
(3) When the finned radiator adopts the strong oil air cooling method, the axial flow oil pump should be selected. If a common oil pump is used, the oil pump must be connected in parallel with the cooling pipe, and attention should be paid to correctly operating the opening and closing sequence of the butterfly valve on the parallel circuit to prevent the natural circulation of the oil flow between the three-phase oil-immersed transformer and the radiator.
(4) In order to reduce the noise of the finned radiator or the cooling cooler, a fan of a multi-pole motor with a low speed and a large air volume should be used. The net cover type fan has lower noise than the air duct type fan, and from the viewpoint of noise reduction, the net cover type should be selected. In addition, the finned radiator cooling duct has a large air passage and a small wind resistance, so the full pressure of the fan does not have to be too high (generally 40 to 70 Pa full pressure), and the full pressure is too high to increase the noise of the fan.
ZTELEC Group is registered in China’s national central city, the international metropolis – Zhengzhou. After years of development, ZTELEC has established a relatively complete product service system, with ideas, technology, capital and a large number of high-quality talents, with strong strength to promote related projects. The three-phase oil-immersed transformer with finned radiator produced by ZTELEC has passed the quality inspection of transformer quality supervision and inspection, and the quality inspection of medium and low voltage transmission and distribution equipment, and won the recognition of the majority of users.
Good surface properties of glass fiber pultruded profiles: When the composite material is in contact with chemical media, the surface is generally less corrosive and less fouling. Therefore, it is commonly used to manufacture fluid pipes with low resistance inside the pipe and low friction coefficient. Save a lot of power. Because composite materials are generally not as susceptible to metal ion-contaminated media as metals, this is why polycarbonate products are widely used in the food and pharmaceutical industries. In addition, the composite material has a very high friction (pv) limit value, and its water friction coefficient is small, about 0.01 to 0.03, so it is also a preferred material for wear-resistant products.
With the rapid development of the Internet age, electronic products have become a necessity for people’s daily lives, and therefore promote the development of the pcb industry. But the basis for the development of pcb is the improvement of copper clad laminates. However, in the production of double-sided FR-4 copper clad laminates, the problem of substrate warpage often occurs. If you don’t solve this problem, it will increase the cost of the product.
How to solve the problem of warping of double-sided FR-4 CCL laminate substrate?
1. Start with the resin formula
The use of a relatively long molecular chain, relatively good flexibility and curing agent, which is an important means to overcome substrate warpage. FR4 CCL has effectively solved the problem of substrate warpage since the use of tung oil modified phenolic resin.
Many people are unfamiliar with high-frequency CEM-3 CCL, because these are not seen in everyday life. But if you mention pcb substrates and CORE, most people will know that pcb boards are often used in mobile computers.
Cem-3 CCL has different names when sorting. Today ZTELEC takes everyone to learn the international classification method and naming rules of high frequency CCL.
Method for making pcb by rigid FR4 copper clad board used by DIY players
The designed copper foil pattern is duplicated on the FR4 copper clad copper foil surface, and the special engraving tool grinded with the steel saw blade is directly drawn on the copper clad plate along the edge of the copper foil pattern, and cut into the depth as much as possible. Then, tear off the copper foil that is not needed outside the pattern, and then punch the hole with your hand drill. The key to this method is: the intensity of the painting should be sufficient; the excess copper foil should be removed from the edge of the board. When the operation is good, it can be gradually removed in pieces. You can use small needle-nosed pliers to complete this step. Some small circuit experimental versions are suitable for this method.
How to prevent aging of high-density insulating paperboard, ZTELEC insulating paper gives you five suggestions:
1. Prevent high-density insulating paperboard from being exposed to high temperature for a long time. Because the ambient temperature rises by 8 °C, the life of high-density insulating paperboard will be reduced by 40%.
2. Avoid direct illumination and radiation, because light and radiation will change the molecular structure of the cardboard and reduce the insulation strength;
Aluminum substrates and fr4 copper clad laminates are two common copper clad laminates, but many people do not know them. Today we mainly introduce the basic structure of these two kinds of plates.
Comparing the main characteristics of the aluminum substrate and the FR-4 board: the heat dissipation of the aluminum substrate and the FR-4 board is compared with the heat resistance of the substrate: the substrate is an aluminum substrate, and the FR-4 board is a transistor PCB, and the heat dissipation of the substrate is different, The test data that causes the operating temperature to rise is different.
Performance: Conductor (copper wire) and fuse current on different substrate materials. From the comparison of the aluminum substrate and the FR-4 board, since the metal substrate has a high heat dissipation amount, the wire is remarkably improved, and the high heat dissipation characteristics of the aluminum substrate are explained from another angle. The heat dissipation of the aluminum substrate is related to the thickness and thermal conductivity of the insulating layer. The thinner the insulating layer, the higher the thermal conductivity of the aluminum substrate (but the lower the pressure resistance).