Abstract: This paper first introduces the definition of low-voltage electrical appliance reliability, its importance and research significance, and the development history of reliability. Then, it reviews the current status and achievements of low-voltage electrical appliance reliability work at home and abroad. Finally, it looks forward to future work on low-voltage electrical appliance reliability.
Keywords: Low-voltage electrical appliances; Reliability; Overview
0 Introduction
The reliability of low-voltage electrical appliances refers to the ability of a product to perform its intended function under specified conditions and within a specified time. Product reliability is an important component of product quality. Strictly speaking, product quality should include both performance and reliability. Even if a product has high performance indicators, it cannot be considered a high-quality product if its reliability is low. The reliability of an automatic control system basically depends on the reliability of the components used in the system. At the same time, the reliability of the system generally decreases as the number of components used in the system increases. With the development of systems towards larger scale, the number of components used in an automatic control system is increasing. If one component fails, it can generally lead to the failure of the entire automatic control system, which may cause significant economic losses. Therefore, the reliability of electrical components used in automatic control systems is becoming increasingly important [1,2] . Various low-voltage electrical appliances are used in power systems and low-voltage distribution systems. If these low-voltage electrical appliances fail, it will lead to the failure of the power system and low-voltage distribution system, causing power outages and even endangering the safety of power supply lines and electrical equipment. The resulting economic losses will be even greater. Therefore, it is of great significance to carry out reliability research and application work on various low-voltage electrical appliances.
Reliability technology is a new technology that developed after World War II. Reliability research began in the United States, where in the 1940s, in-depth research on the reliability of electronic components and equipment was conducted, and standards were established for reliability management, reliability design, and reliability testing. By the 1960s, the United States had matured in reliability research for electronic products, which played a significant role in improving the reliability of American electronic products. From the 1970s onwards, reliability work in the United States gradually expanded to industries such as machinery, power, electrical engineering, and chemicals. The United States is the country in the world that conducted the earliest, most extensive, and most effective reliability research. Following the United States, the former Soviet Union, Japan, Germany, the United Kingdom, and France also actively carried out reliability work and made considerable progress.
1 Overview of the reliability of low-voltage electrical appliances abroad [3]
1.1 Development of Reliability Standards
In foreign electrical companies and various international organizations (such as IEC and IEEE), reliability is highly valued. Many well-known electrical companies have established reliability management departments or have dedicated reliability engineers. Some products have specified reliability indicators, while others, though not yet having specified indicators, have already conducted internal reliability research. Product reliability has become a crucial competitive factor among foreign companies. In 1965, IEC established Technical Committee TC56 (Reliability and Maintainability Technical Committee), which has since published numerous fundamental or common standards on reliability and maintainability, such as IEC 300 "Reliability and Maintainability Management," IEC 605 "Equipment Reliability Testing," and IEC 706 "Maintainability Guidelines." The development of reliability standards for electrical products is not yet systematic, clear, or complete. For example, IEC 255-0-20 "Contact performance of electrical relays", IEC 25-0-10 "Application of electronic component quality assessment systems with or without relays", and IEC 255-19 "Quality assessment of electromechanical relays with or without relays" in the IEC 255 electrical relay standard do not include reliability content. In June 1988, IEC SC41A issued document No. 46, which only proposed to supplement the existing IEC standards with "reliability testing of relays with or without relays for low current". The 2002 standard IEC 60050-444 "Electrical terminology: basic relays" only includes 12 terms related to reliability in section 444-07.
1.2 Reliability test study [4]
In the United States and Japan, computer control is widely used in the reliability life testing of relays. Countries such as the United States and Japan are also researching the models, methods, and data analysis methods for accelerated life testing of electrical products. For example, Japan conducted accelerated life testing of switches using load voltage and load current as acceleration variables, and calculated the acceleration coefficient for different load voltage and load current values based on the test results.
1.3 Research on the Physics of Reliability
Research on reliability physics began abroad in the 1960s. The U.S. Air Force's ROME Aeronautical Development Center was the first to conduct failure analysis on field-failed components in the early 1960s. J. Vaccro first proposed using the concept of "failure physics" to study component reliability. From 1962, the U.S. held an annual "Failure Physics" conference, which was renamed the "Reliability Physics" conference in 1967. Research in reliability physics is a fundamental measure to improve product reliability. Countries such as the United States and Japan attach great importance to research in reliability physics.
1.4 Reliability Academic Conference
International academic exchange on reliability is also very active, with international academic conferences related to reliability including: the IEEE Holm Electrical Contact Conference (held annually); the International Electrical Contact Conference (held every two years); the International Conference on Reliability Physics (held annually); and the International Conference on Reliability and Maintainability (held annually).
2. Overview of the Reliability Operation of Low-Voltage Electrical Appliances in China
The former Ministry of Machinery Industry attached great importance to the reliability of electrical products. As early as 1980, the Electrical Engineering Bureau of the former Ministry of Machinery Industry commissioned Hebei University of Technology to hold two training courses on new electrical technologies, with reliability technology being one of the main topics. In October 1983, the China Electrotechnical Society's Electrical Product Reliability Research Association was established. Under the organization of this association, research and academic exchange activities on the reliability of electrical products were carried out, and numerous training courses on electrical product reliability and seminars on reliability for leading cadres in the electrical industry were held, which played a certain role in promoting the reliability work of my country's electrical industry. The former Ministry of Machinery Industry held several reliability work conferences, deploying the "time-limited assessment of reliability indicators for electromechanical products" in the electromechanical industry. From 1986 to 1991, seven batches (a total of 1,189 specifications) of electromechanical products with time-limited reliability indicators were released, including relays, contactors, transformers, measuring relays, motors, and power electronic devices. This played a significant role in promoting the reliability work of electrical products in my country. In 1994, the former Ministry of Machinery Industry convened a conference on reliability in the machinery industry. The conference emphasized that reliability must begin with product design and stipulated that all projects included in the development plans of the ministry or provincial/municipal machinery departments and major technical equipment breakthrough projects should strengthen reliability design and testing research. It required that reliability design objectives and key research areas be proposed at the project initiation stage, and that reliability objectives be reviewed and evaluated during product appraisal or project acceptance. The conference also decided to further develop reliability certification for electromechanical products. From the mid-1980s to the present, my country has made the following progress in electrical reliability research and application.
2.1 Electrical Reliability Research
Since the mid-1980s, institutions such as Hebei University of Technology, Shanghai Electrical Apparatus Research Institute, Chengdu Machine Tool Electrical Apparatus Research Institute, Xuchang Relay Research Institute, and Guangzhou Electrical Apparatus Research Institute, in collaboration with enterprises, have been conducting research on electrical reliability through a combination of industry, academia, and research. Through theoretical analysis and statistical analysis of a large amount of experimental data, they have investigated the failure mechanisms of products and proposed improvement measures for product design and manufacturing processes, resulting in significant improvements in the reliability of these products and achieving certain results.
2.2 The establishment of academic organizations related to reliability and domestic and international academic exchanges
The Electrical Products Reliability Research Association of the China Electrotechnical Society was established in 1984. Since 1994, Hebei University of Technology has served as the chairman unit of the association, with its secretariat also located there. The association has undergone two leadership changes since 1998, with our university serving as the chairman unit for three consecutive terms. In these ten years, in addition to successfully hosting five National Conferences on Electrical Products Reliability, Professor Lu Jianguo, as the conference chairman, successfully organized the 1st and 2nd International Conferences on Electrical Products Reliability and Electrical Contact in 2004 and 2007. All conference papers were indexed by ISTP, and 29 papers from the 2nd conference were simultaneously indexed by SCI and EI. Internationally renowned experts, including the vice-chairman of IEEE TC-1 and the chairman of the International Electrical Contact Advisory Committee, participated in the conferences. IEEE TC-1 published information and detailed reports on the conferences. Both international conferences received high praise from renowned experts both domestically and internationally, further enhancing our university's influence in the domestic higher education and academic community. The 3rd International Conference on Reliability and Electrical Contact of Electrical Products will be held in mid-October 2009.
2.3 Formulation of Electrical Reliability Standards
Hebei University of Technology, as the responsible unit, formulated six industry standards for reliability testing of major electrical products in 2007. Based on these standards, eight national standards for reliability testing of electrical products were formulated in 2008 (see Table 1), which have been approved and published by the state [5-11] . The reliability testing equipment developed to implement these standards has reached the international advanced level and has been widely used in China's electrical industry. In addition, it has established electrical reliability testing laboratories for more than ten units, including the National Electrical Quality Supervision and Inspection Center, promoting the scientific and technological and economic development of the national electrical industry, providing theoretical and technical support for the leapfrog development of China's electrical industry, and contributing to China's economic development.
2.4 Development of Reliability Testing Equipment [12-17]
Hebei University of Technology established the Electrical Appliance Research Institute Testing Center, which was accredited by the China National Accreditation Committee for Laboratories in May 2001. It is the only nationally accredited electrical reliability testing institution in the domestic electrical industry, qualified to conduct relevant electrical reliability certification tests. The center has developed microcomputer-controlled reliability testing devices for relays and contactors (see Figure 1), miniature circuit breakers (see Figure 2), residual current operated protective devices (see Figure 3), molded case circuit breakers (see Figure 4), and overload relays (see Figure 5). The research project "Research on Low-Voltage Electrical Appliance Testing Technology," completed by Hebei University of Technology as the primary research unit, won the second prize of the 2002 National Science and Technology Progress Award.
[img=558,378]http://www.chuandong.com/uploadpic/THESIS/2009/5/2009050714262063708B.jpg[/img]2.5 Research on Electrical Reliability Design
Hebei University of Technology and other institutions have conducted research on the reliability design of electrical electromagnetic systems and contacts, and presented their preliminary research results at the American Relay Conference in 1988 and the 17th International Conference on Electrical Contacts in 1994. The research project "Modern Design Theory and Experimental Research of Electrical Equipment," a collaborative project between Hebei University of Technology and Tsinghua University, further explored the reliability optimization design methods for electrical electromagnetic systems. The research achievement "Research on Reliability Design and Testing Technology of Low-Voltage Electrical Appliances," with Hebei University of Technology as the primary completing institution, won the second prize of the National Science and Technology Progress Award in 2000.
2.6 Research on the Reliability Design of Protective Electrical Appliances [17]
Given the significant challenges in researching the reliability of protective electrical appliances, while the internationally authoritative organization IEEE has conducted a survey report on circuit breaker reliability, it failed to propose reliability indicators and evaluation methods. Hebei University of Technology creatively proposed success rate as a key reliability indicator for protective electrical appliances and a success rate verification test scheme, publishing its first monograph, "Reliability Theory and Application of Low-Voltage Protective Electrical Appliances," thus solving the aforementioned problems. Based on this theoretical achievement, Hebei University of Technology was the first in China and abroad to formulate industry standards for the reliability of major low-voltage protective electrical appliances, which were approved and published by the National Development and Reform Commission. The achievement, "Research and Application of Key Technologies for Low-Voltage Protective Electrical Appliances," with Hebei University of Technology as the primary completing unit, won the second prize of the 2008 National Science and Technology Progress Award.
3. Development Prospects and Outlook for Low-Voltage Electrical Reliability Work
Although my country has made some progress in the reliability research of electrical products in the aforementioned aspects, due to the late start of this research, many electrical products have not yet undergone rigorous reliability design and manufacturing during new product development. In particular, most enterprises in my country's electrical industry do not place sufficient emphasis on reliability work, and its implementation has not been thorough. Consequently, the reliability level of Chinese electrical products is generally lower than that of products from developed countries. In market economic competition, winning through superior quality and reliability will inevitably become a consensus. We must not only develop high-performance electrical products but also highly reliable ones; this will be the development trend of my country's electrical products. Especially now that my country has joined the WTO and faces greater international competition, reliability work is even more crucial. It is believed that with the joint efforts of academic institutions, research institutions, and the electrical industry, the reliability research and application of electrical products in my country will be further improved. It is foreseeable that in the 21st century, the reliability level of my country's low-voltage electrical products will be significantly improved, revitalizing my country's national low-voltage electrical industry.
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Overview of the Reliability of Low-Voltage Electrical Appliances at Home and Abroad and Its Development Prospects
