About American box open phase protection

Abstract: the author analyzes the causes and harm of American box phase lack operation, puts forward the solution to this problem.

 1, an overview of the
With the deepening of China s urban and rural power grid construction, especially the urban power grid "above cable on the project" step by step, variable because of its American box: small size, full insulation, overload capacity is strong, installation is convenient wait for a series of the use of the advantages and get more and more. From American box in our country gradually extended to the current widely used, less than 10 years experience about the time, it shows that: the development of a good product is overwhelming. Meanwhile from the design departments of electric power to factory for this product in China the applicability of the proposed many views, these views to the American box of localization, "localization" has played a positive role. However, current American box change in terms of the actual use most did not open phase protection measures, this shows the open phase protection problem of the product still did not cause the enough attention of the design departments of electric power, the American box a phase of the dangers of running without widespread and profound understanding.

      And American box in the process of use, if there is a low voltage of fault or a single phase to ground short circuit overload for a long time, especially in the summer heat overload, is likely to lead to the high pressure phase plug-in blown fuse. It should be said that this is American box changes the risk is higher. Therefore, this article want to through the analysis of the problem, can cause the attention of people.

       High-voltage fuse is placed within the Angle of three phase four or five column column products in (hereinafter referred to as product) in the application of the current market account for only a little part, the product is based on the "three-phase noninterference" technical point of view, its characteristics is introduced as follows:

       At present the mainstream of American box change products is still three phase three column Angle of high voltage fuse is placed outside the structure mode (referred to as the Angle of product), the connection mode is shown in figure 2.

       This kind of product when the high pressure phase A blown fuse, it can be seen: high voltage winding form two parallel branch, A, C phase winding in series as A branch, B phase winding is A branch, UBC line voltage is applied on the parallel branch of power supply. So A and C on the phase winding for half of the nominal voltage applied voltage, and B phase winding voltage and rated voltage, so the low voltage: Ubo = U2N, Uao = = 0.5 U2N Uco, namely the low-voltage three-phase voltage for A full voltage, two and A half voltage (actual test neutral point should be reliable grounding, in order to prevent voltage drift). When lack of phase state for A long time (generally for A few minutes to 10 minutes), then A and C on load by two phase electrical equipment such as: motor, refrigerator, air conditioner, washing machine will be in A serious under-voltage and burned, thus caused property damage to the user, and have A negative impact to the power supply quality.

       hrough the above analysis, the visible now use American box variable exists the phenomenon of lack of phase operation is a common problem, in order to avoid possible damage, we should take effective measures to prevent the occurrence of lack of phase operation.

3, open phase protection measures

       European box change application has than change long history in our country, it also adopts high voltage fuse to protect the transformer and the bottom equipment, the difference is Europe type box change the fuse and the load switch have interlocking institutions, as long as there is a high pressure blown fuse, load switch will three-phase disconnected at the same time, so it is not lack of phase operation problems. And American box variable load switch is usually artificial mechanical operation, high voltage fuse for three phase three column Angle placed outside the American box products, to solve the lack of phase operation is the most economic and reliable method in low pressure chamber equipped with American box dedicated intelligent electronic phase protector, once the running state of lack of phase or change a box it will low voltage main feed switch control through the coil to the main switch, pressure loss would be cut, the secondary load effectively avoids the American box phase lack operation of electrical equipment damage.

   About the lack of protection of control wiring principle as shown in figure 3:

4, the conclusion

   American box phase lack operation possibility as gradually increased with the extension of life after it was put into operation, the reason is that American box in the increased load rate, load branch and the complexity of the electricity gradually increased, electrical insulation will gradually aging and so on. And through an electronic phase protection device, can avoid the lack of phase may run to the load equipment damage, in essence is to improve the reliability of power supply, thus it can be seen, the move both for power supply departments and is beneficial to the user.