Views: 6 Author: Site Editor Publish Time: 2023-05-24 Origin: Site
Development history of low voltage capacitors
(1) In the 1950s and 1960s, it was called the first generation of low-voltage capacitors. Its structure used oil-immersed capacitor paper as the medium, the capacitor element was a flat element, and the liquid medium used mineral oil (containing PCB toxic substances), etc., and the product was large in size and active power loss reaching about 0.2 [%] ~ 0.5 [%], the domestic model in my country is the BW series.
(2) In the 1970s, with the application of metallized film instead of capacitor paper, the capacitor element changed from a flat type to a circular structure. Due to its self-healing performance, the field strength of the product was greatly improved, and the product volume was greatly reduced, which was 40［%］of the BW series, most of the liquid medium is mineral oil or resin, and the active power loss is about 0.12 [%]. The domestic models in my country are mainly BZMJ series.
(3) In the 1980s, European capacitor manufacturers have launched the third-generation MKP low-voltage capacitors with a cylindrical structure, and their components use a metallized film of about 7 μm, it is filled with natural oil or resin and sealed in the aluminum shell, the volume is further reduced, and the active power loss is reduced to 0.3W/kvar.Due to the limitation of time and development, the current low-voltage capacitors produced in China were all imported from abroad in the early 1980s, and belong to the second generation of products.For example, capacitor factories in Wuxi, Jinzhou, Guilin and Nanjing have introduced production technology and key equipment from SHIZUKI in Japan, ASEA in Belgium, ARCOTRONICS in Italy and ICAR in Italy,its product structure is square or oval, generally using 8μm metallized film, and the statistical service life is about 2 to 6 years on average.
(4) With the development trend of electrical products towards miniaturization, oil-free and environmental protection, the fourth generation of very new gas-filled low-voltage capacitors (GMKP) uses 5~6μm metallized film to fill special protective gas, and has built-in unique safety protection. The key feature of the device is to realize the revolution of the medium and realize the gasification of the dielectric.As a result, theoretically real dry capacitors and a new generation of products with various characteristics such as fire and flame retardancy, safety and reliability have been produced.
How to install low-voltage capacitors_Installation precautions for low-voltage capacitors
Precautions for installation of low-voltage capacitors
一、The installation method of the high-voltage circuit (high-voltage busbar) that is centrally installed in the substation. This method has less equipment cost and is easy to install, but the effect is not as effective as the installation on the low-voltage side, but only effective on the side of the installation location.
二、When it is installed on the low-voltage side, the closer it is to the load, the better, and each load is ideally connected in parallel with a power capacitor of appropriate capacity.According to this method, the entire power system such as high and low voltage lines and transformers can reduce the power loss, so that the equipment can generate an appropriate amount of margin, but if this method is used, the installation of equipment is relatively expensive.
三、When installed on loads with poor power factor and high-voltage motors, power capacitors with appropriate capacity are installed individually.For other loads, the power capacitor added to the high-voltage circuit is integrated to improve the power factor, that is, the combination of the above two methods is used.
四、When setting, the fuse link capacity (high voltage) should be 1.65 to 2.5 times the rated current of the capacitor. When two or more units are placed side by side, the distance between them should be kept at least 8 cm to facilitate heat dissipation.
五、Avoid using copper plate wiring (high-voltage capacitors and low-voltage outdoor capacitors) when connecting in parallel.
六、Wiring and switchgear capacity should not be less than 1.35 times the rated current of the capacitor.
七、During maintenance work, it is necessary to cut off the power supply (high voltage) for 5 minutes, (low voltage) for 3 minutes,and it can only be implemented when it is confirmed that there is no residual voltage.
八、For other precautions, please refer to the back of the capacitor inspection card.
Wiring and Installation of Low Voltage Shunt Capacitors
When wiring low-voltage parallel power capacitors, how should the relevant electrical components be installed? Now the editor will take you to understand the wiring and installation of low-voltage parallel capacitors.
1. Directly connected to the discharge device
An automatic contact point can be set between the power capacitor and the discharge device, and no switch or fuse can be installed in the middle.
2. Set up a separate protection device
Power capacitors need to be equipped with independent control and protection devices,if it is necessary to improve the power factor of the electrical equipment alone, control and protection devices can be used together with the electrical equipment.
How to install low-voltage capacitors_Installation precautions for low-voltage capacitors
3. Appropriately install a reactor
When the high-order harmonic content in the power environment may exceed the tolerance range of low-voltage shunt capacitors,reactors with different reactance rates should be connected in series.
4. The capacitor should be grounded
When the rated voltage of the power capacitor is the same as the nominal voltage of the power supply grid, the shell of the power capacitor needs to be grounded.
5. Install insulation bracket
When the rated voltage of the power capacitor is lower than the nominal voltage of the power supply grid, it is necessary to insulate the bracket of each phase capacitor, and its insulation level needs to match the nominal voltage of the power supply grid.
