Common Faults of UPS in Rail Transit Communication Signal Power Supply System and Improvement Scheme of Selection(2)

The ability of UPS system to complete the specified functions under the specified conditions and within the specified time is called reliability. For a long time, people only use the technical performance index of products as a sign to measure the quality of UPS, which only reflects a secondary aspect of the quality of UPS products, but not the main aspect of the quality of UPS products. Because, if UPS products are unreliable, even if its technical performance is no longer excellent, it will not be able to play. In a sense, reliability can comprehensively reflect the quality of UPS products.


First of all, the products follow the principle of standard, and the order is: special product standard → product standard → general standard. That is to say: the standard of special products is high level, which has the highest adaptability and reliability. In terms of power electronic products such as UPS, we usually classify them by application fields. As shown below:

Industrial UPS has three elements in terms of dominance: 

I. high level immunity, which is applied to severe electrical environment (immunity includes:

1. Radiation sensitivity test, 

2. Power frequency magnetic field radiation sensitivity test, 

3. Conduction sensitivity induced by RF field, 

4. Electrical fast transient pulse group immunity, 

5. Surge immunity, 

6. Voltage drop and interruption immunity, 

7 Power line induction / contact,

8. Electrostatic discharge immunity). 

II. The optional high-level IP protection grade is applied to the harsh space environment.

III. the electrical isolation of power frequency transformer can regenerate a TN-S system or it system, i.e. the zero line can serve users flexibly and better, and also reduce system risk. Among these three elements, only the first one has standards to find. In IEC62040-2-2005, EMC standard, UPS is divided into C1, C2, C3 and C4 categories, namely residential area, commercial area and light industrial area, industrial area and special customized area.


In terms of environment, commercial grade UPS is usually used in IDC room, which has strict requirements on temperature, humidity, dust and corrosive gas, and cannot be used in severe occasions, while industrial grade UPS is usually used in high temperature, high humidity, multi dust or salt fog occasions; in terms of reliability, the design life of commercial grade UPS is usually about 5 years, while industrial grade UPS is selected by industrial grade or even military grade Devices, increasing redundancy, strengthening process design and improving safety configuration make the product life reach or even exceed 20 years. In addition, in terms of electrical environment, load characteristics, mechanical strength, electrical isolation, input and output protection, communication interface, bypass requirements, accessory selection, IP protection level and sheet metal requirements, the market requirements for industrial grade ups are far higher than those for commercial grade ups. As mentioned above, the biggest characteristic of industrial UPS is safety and reliability, which is the precondition for industrial ups to achieve everything.


To build a high reliability UPS, the following two points are particularly important:


1. Mature product design and development. The essence of reliability lies in reliability design, which can improve the quality of products. The improvement of reliability mainly focuses on the stage of R&D and before finalization. For industrial grade UPS, a large number of industrial electrical environment data and load conditions are required to verify the adaptability of various main circuits, the layout rationality of PCB and EMC of samples and finished products. Any EMC problem contains three elements, namely interference source, sensitive source and coupling path. Without one of these three elements, EMC problem will not exist. Therefore, when solving the EMC problem, we should start with the analysis of these three elements, find out what these three elements are, and then take appropriate measures to eliminate one of them according to the specific situation. In this way, EMI and EMS of the product can meet the requirements of the standard and operate reliably in the corresponding electrical environment. Secondly, the use environment of UPS products is increasingly harsh. From the tropics to the cold zone, from the land to the blue sea, from the high altitude to the space, it is experiencing different environmental conditions. In addition to temperature and humidity, salt fog, shock, vibration and other effects on UPS will increase the possibility of product failure. Therefore, not only EMC immunity, but also the structural robustness of industrial UPS can be seen from the appearance alone. From this perspective, each industry should have its own dedicated ups.


2. Mature production process. We know that the same product drawings, the product quality of different manufacturers, even in the highly standardized production today, will obviously vary. This is the problem of mature manufacturing technology foundation, which requires long-term experience accumulation, that is to say, it requires a long-term factory to have such characteristics.


Failure of any component or solder joint will lead to failure of UPS system. UPS system is a typical power electronic product. Generally speaking, the birth of power electronic technology is marked by the first thyristor in 1957. The concept and foundation of power electronic technology is established by the development of thyristor and thyristor converter technology. There have been electronic technologies for power transformation before, so the period before the emergence of thyristors can be called the prehistoric or dawn period of power electronic technology. In the late 1970s, GTO, BJT and power MOSFET are the representatives of all control devices, which are developing at full speed. The power electronic technology has entered a new stage of development. In the late 1980s, IGBT, which is represented by the combination of MOSFET and BJT, has the advantages of small driving power, fast switching speed, small on-state voltage drop, high current carrying capacity and superior performance, making it the main guiding device of modern power electronic technology.


The primary problem of power electronic technology in power supply application is heat dissipation. This is quite different from what most people think is to drill holes and add fans. Because the quality of the heat dissipation effect is directly related to the system stability of the product. Some foreign power experts even say that their products have high stability, that is, the area of the heat sink is large, and there is no advanced technology. At home and abroad, the power supply manufacturers' human and material investment in heat dissipation is also valuable. The patented technology of AVIC-Tech (Xiamen) Electric Technology Co.,Ltd., the closed and efficient cooling air duct and fan redundancy design, the whole machine has four independent air ducts, each air duct has more than two fans, and the speed intelligent control design. It is a major patent technology that has been quietly cultivated in the field of industrial power supply for more than ten years, which has improved the heat dissipation effect by more than 25%.

Author of this paper is He Chun, Chief Engineer of AVIC-TECH.

About AVIC-Tech

AVIC-Tech (Xiamen)Electric Power Technology Co.,Ltd is a high-tech enterprise specializing in R&D, manufacture, sales and service of high-end power supply. Our flagship products are industrial UPS (1kVA-800kVA), dynamic voltage restorer (10kVA-2000kVA), and lithium battery system, which are widely used in nuclear power, electric power, petroleum and petrochemical, rail transportation, industrial manufacturing and other fields.

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