Abstract: with the joining of WTO, in the 21st century, low-voltage electrical appliances in China is facing a bigger challenge, in order to accelerate the development of low voltage electrical appliances in China, so as to adapt to the new situation need, timely development dynamic analysis of low voltage electrical appliances at home and abroad, to understand and grasp the new technology of low voltage apparatus is of great significance. This article from the intelligent electrical appliances, communications electronics and information appliances; The simulation technology and virtual electronics; Environmental protection appliances; High performance, miniaturization and structure of the electrical design of modern aspects are discussed in this paper.
With joining the WTO, in the 21st century, low-voltage electrical appliances in China is facing a bigger challenge, in order to accelerate the development of low voltage electrical appliances in China, so as to adapt to the new situation need, timely development dynamic analysis of low voltage electrical appliances at home and abroad, to understand and grasp the current new technology of low voltage apparatus is of great significance. This article from the intelligent electrical appliances, communications electronics and information appliances; The simulation technology and virtual electronics; Environmental protection appliances; High performance, miniaturization and structure of the electrical design of modern aspects are discussed in this paper.
A, smart appliances, communications electronics and information appliances
Microprocessor and computer technology introduction of low voltage apparatus, on the one hand, make the function of low voltage apparatus with intelligent, on the other hand make low voltage switch electric appliances, including intelligent circuit breaker and intelligent motor controller to realize the two-way communication with the central control computer. Into the 1990 s, with the development of computer information networks, low-voltage distribution system and the motor control center has been unified to form the intelligent monitoring, protection and information network system.
Intelligent low-voltage circuit breaker and the motor controller is intelligent low-voltage switchgear and motor control center, the main electrical components. Microprocessor is introduced into low voltage circuit breaker, first of all make the protection function of the circuit breaker greatly enhanced. Such as: its three broken feature of short time delay can be set to I2t protection feature, in order to better match with the level of protection; The earthing protection can realize selectivity, intermittent arc grounding fault with memory function.
Current industrial electricity used in the electric network of a large number of soft starter and uninterrupted power supply, power electronic control device, etc., these devices will make higher harmonic distribution system, and analog electronic tripping device generally reflect the peak value of fault current, and power supply will cause the higher harmonic circuit breaker misoperation. Intelligent circuit breaker with microprocessor reflect the actual value of the load current (RMS value), its sampling and holding circuit can eliminate higher harmonic of input signal, thus can avoid misoperation caused by higher harmonic, its central processing unit can ensure the correct circuit breaker.
Compared with the traditional bimetal thermal relay, intelligent overload relay has a series of advantages. It can protect the variety of the motor starting conditions, has the very high reliability. It not only can protect motor overload and phase failure, and to protect the earth, three-phase imbalance, reverse phase or low current, etc. By the further development of intelligent motor protection relay smart motor controller, both the function of the monitoring, protection and communication, it also more intelligent motor protection relay protection.
By a new type of low voltage electrical components and the central control computer network system and the traditional low voltage power distribution system composed of compared with motor control center has the following advantages:
(1) to implement the central computer centralized control, improve the degree of low-voltage distribution system automation. Low voltage switch equipment and the central control computer of the data information two-way transmission refers to: on the one hand, the intelligent circuit breaker or other switchgear to the central control computer transmission lines and operation parameters of protection objects, the set values for the protection and fault information; On the other hand, the central control computer to intelligent circuit breaker or other switch equipment operating instructions, change and adjust the protection setting values.
(2) make the low-voltage distribution and control system of scheduling and maintain reached a new level. Through the information transmission, the central control computer can store lines and equipment to be protected the operational parameters of the past and even 10 times before the 50 times failure condition. This information combined with powerful computer integrated computation ability, help the operator prior to predict fault production and make corresponding decision, make the line and equipment downtime maintenance time is greatly reduced; Information transmission and improve the ability of the distribution system of electric power dispatching, can guarantee in the peak phase, for important customers safe and reliable power supply; Information transmission chain can realize regional protection, make intelligent circuit breaker selective protection to obtain reasonable level before and after the match.
(3) as a result of a new type of digital monitoring element, make the switchgear plane information has greatly increased. Through the liquid crystal display panel can be measured and display the phase line current, voltage, power factor, power and other parameters, can also according to protected objects and the operation of parameter and fault lines in the past, it can also be graphically display by setting circuit breaker protection features.
(4) monitoring components compared with traditional directives and instructions of electrical appliances, wiring is simple, easy to install, improve the reliability of the work.
(5) can realize data sharing, reduce duplicate information and information channels
Increasingly require the user to the development of network communication, and equipment between the openness and compatibility, and formulate a unified communications protocol is a key problem presses for solution. Is composed of intelligent appliances and central computer through the interface automation communication network is developing from centralized control to distributed control. The emergence of fieldbus technology, not only provide the conditions for constructing the distributed computer control system, and it plug and play, expansion and maintenance is convenient, and the technology become the focus of attention at home and abroad at present.
Fieldbus is the connection between fully digital intelligent field devices and control room, open two-way local communication network. Fieldbus is a lot of more phyletic, more influential include: CAN, Lonworks and Profibus, etc. They have their own characteristics and advantages in different fields have different application value. But it is also the fieldbus technology is varied and communication standard of fragmented, bring adverse effect to the development of this technology. The international electrotechnical commission and the fieldbus foundation is committed to the unity of the fieldbus standards, some units are doing this work in our country, we put the based on field bus technology, which has the function of communication is called the can communication electrical appliances. The fieldbus technology is extending both ends up and down, its top and enterprise network backbone Ethernet, Intranet and Internet communications, the bottom extending to the scene of the industrial control area. There are Siemens AS interfaces and rockwell company Devicenet two bus system, the two bus is applied to the lower regions, is a kind of low cost communication connection, it control the industrial use of sensors and actuators, including: limit switches, photoelectric sensor, motor starter, button indicator, multi-function relay AS simple control components such AS connected to the network from the device, and AS the main equipment of the control computer or programmable logic controller (PLC) communication, the contact of the relay contact control system in the transformation of traditional information into a binary digital information through the serial interface and addressing the communication, this makes the traditional low voltage control element has a revolutionary change, such AS Siemens Logo multi-function relay AS bus application in the system is actually a small PLC, it can delay, latch, counter and pulse relay, and other functions.
Make smart appliances to further realize the informationization, is to make intelligent electrical appliances in Internet/Intranet function is implemented in the field level, its core technology is the realization of TCP/IP protocol. The embedded TCP/IP protocol in the ROM of smart appliances, make the signal to send and receive all, on the basis of TCP/IP information function of the further development of intelligent electric appliance. Use of Internet/Intranet function, not only make the enterprise's network of authorized users, and in any open area can by browsing the Internet information sharing site, on the basis of intelligent electrical appliances on site and remote online control, programming, and configuration, etc., which makes intelligent electric appliance has entered a new era of information appliances.
Is an important function of low voltage apparatus on-off capability, in recent years the development of the intelligent electrical appliances another way is through the intelligent control of the microprocessor to improve electrical performance on and off. An interesting new trend is admiralty - moeller companies to develop a new generation of DIL - M series contactor, in its 185 a intelligent control technology is adopted in the above current levels. Contactor close contact wear is mainly due to contact bounce, as a result of the intermittent arc contactor under AC - 3 tasks to closing under rated voltage 6 times the rated current, so it is one of the main factors affecting the service life of electrical contact. DIL - M series intelligent control contactor electromagnet coil by a pulse rectifier voltage power supply, can be stored in the microprocessor in the a and counterforce characteristics with the best suction characteristic curve to adjust the coil current, wide in the contactor and phase input pulse voltage, safe and reliable to make the main contact and, in the maintenance phase the input narrow pulse voltage, under the condition of enough to maintain close contact and energy saving. With intelligent control, the contactor under the condition of saving contactor material, can achieve 1.3 X106 electrical life, using the intelligent control, different specifications of the contactor, the cross section of the electromagnetic system geometry size is consistent, brought convenience to the production and saving, thus compensation because of the extra spending caused by electronic control.
The development of the intelligent electric appliance, the electromagnetic compatibility EMC become more and more important problem. EMC requirements include two meanings, on the one hand, requires low voltage electrical appliances in use at work, is not subject to external electromagnetic interference caused by misoperation, and on the other hand require electrical operation of the electromagnetic field near the noninterference electronic equipment. Currently overseas for intelligent electrical and mechanical and electrical products of EMC problems together very seriously, because the electromagnetic interference can cause this kind of system failure and misoperation, cause huge economic losses. Intelligent electric appliance and its protection and monitoring system is sensitive to the digital electric components are in a strong current and high voltage electromagnetic field to make the electromagnetic anti-interference ability of this equipment in the design and operation of the equipment has become an important factor, therefore in abroad in the design of intelligent electric appliance and its system electromagnetic compatibility of the initial phase, the strict control and management plan, the project mainly includes the product or system EMC analysis, EMC design specifications, design plan, standards, implementation plan and the test methods and so on, and put the plan as one of the most important aspects of the product or system design. EMC analysis and design is the key work in order to meet the requirements of EMC technology, including analysis of the radiation degree and the anti-interference ability of electronic circuits and systems integration performance of electromagnetic compatibility, EMC design including electromagnetic shielding, grounding, the determination of lead spacing, and consider the electromagnetic coupling between the printed circuit board wiring, the current with high frequency electromagnetic field numerical analysis and computer hard years of development, using modern simulation technology to replace the traditional test methods and empirical analysis method, has plays a more and more important role in EMC analysis.
Second, the simulation technology and virtual appliances
In recent years, domestic factories and design institutes are introduced such as', Pro/E 3 d computer aided design software, this software can realize parts in 3 d space and entity modeling, assembly and automatically generating engineering drawings, and according to the design of parts for mould design and generate nc code automatically. The software makes the domestic low voltage electrical design work on a new step, but further to make product design meet the requirements of the original technical conditions, reach a predetermined electrical and mechanical performance, you will need to adopt simulation technology.
For the design of a low voltage electrical products, when the technology according to the given conditions, determine the preliminary product design and size, after engineering analysis must be conducted or prototype experiments, to verify whether design conforms to the original order technical requirements. For a long time people use the traditional engineering calculation methods for characteristic analysis, the accuracy is very poor, especially as the main characteristics of low voltage switch electrical appliances, the open circuit characteristic cannot be computed, so people had to rely on the prototype manufacture and experiment to verify the feasibility of the design scheme, this would take a lot of manpower and material resources, and makes the product development cycle, long affect new product market competitiveness.
In order to solve the above problems, in recent years, computer simulation and the simulation technology to get fast development, rely on the new technology, people can accurately before prototype production design of the product performance, reduce the repeated prototype production and experimental cost, speed up the product development cycle, and improve the product performance, this is the current means of low voltage apparatus product development the important content of modernization.
The basic characteristic of the low voltage apparatus including the breaking capacity, temperature rise, the strength of the parts, electric stability and thermal stability, insulation and other electrical properties, etc. This needs to design objects of electromagnetic field, stress field and magnetic field simulation and analysis on the physical field. The progress of computer imitation and simulation technology and finite element analysis software to improve the performance of goods for the application of this new technology in low voltage apparatus. Before and after the 70-80 - s finite element analysis software, work is very intricate, such as a large transformer of electric field analysis, three dimensions of parts of the input raw data, such as general a few days or even weeks of hard labor. Into the 90 s, commercialization of finite element analysis software and visualization technology, input feature modelling way 3 d graphics instead of every lock data input, input work is very simple and intuitive, and post-processing part make the output data or 3 d graphics, convenient for observation and analysis. Meanwhile, as the need to solve the problem of complex engineering, the simulation and analysis software is extended to fluid dynamics, mechanical vibration and institutional dynamics, etc. At present, the market has been able to provide all kinds of precise computer simulation and analysis software, this software is divided into two types, one is a general software, the other is a special software, such as ANSYS (ANSYS) and NISA finite element simulation and analysis software (EMRC company) belongs to the first category, the software includes stress, temperature field, electromagnetic field and flow field analysis module, can a single field analysis, also can make a comprehensive analysis, such as the calculation of the fuse protection features, first of all, to compute the distribution of the melt in the current field, and then the calculation of thermal characteristics, it is current field and the transient thermal field of comprehensive, specialized software is used for special occasions, such as the ADAMS software is used for dynamic analysis, VACTOR FIELDS software dedicated to the analysis of the electromagnetic field problems. Both before and after the software has a visual processing touch block, and there are workstations and two versions of a microcomputer. Famous companies abroad in recent years is the characteristic of the computer simulation and analysis as a means of product development modernization is an important measure, such as Japan's Fuji company in the development of new SC series contactor, think that the computer simulation and adopting new material, is to make the new series contactor reached a high level of key performance, they have developed a set of the contactor movable part of the dynamic simulation software system, the contactor movable parts, including core and contact system dynamic simulation, analyzed the various parameters on the core and the influence of the contact bounce after collision, so as to select the optimum design parameters, Japan's mitsubishi and German admiralty - moeller companies on the basis of commodity computer analysis software, through the secondary development to build their own low voltage circuit breaker design and development of the computer simulation system.
Product design and the feasibility of the scheme is obtained with a computer simulation, the design scheme that meet for the requirements of technical conditions, but it is not economic and technical index of the optimal solution, in order to achieve the best economic and technical indicators, this would require the combination of simulation and optimization method. Some merchandise to the simulation software, ANSYS software is as mentioned above will provide a series of optimization tools, can automatically adjust the design geometry of an object, the target to achieve the optimal. Such as Germany famous low-voltage expert professor Lindmayer using ANSYS software, combining magnetic field simulation and optimization, change the core sizes and coil position, realized the optimal design of the electromagnet.
The development of computer graphics technology, a new kind of 3 d machine interactive graphic technology, namely the emergence of Virtual reality (Virtual reality) technology to the development of computer simulation technology, opened up a new heaven and earth, with the traditional Virtual reality interactive 3 d graphics technology is different, the latter is in the real world outside the computer operators of computer graphics, which can make the operator into the Virtual world on its position in a computer, the technology and computer simulation combining can design the product inside a computer, this product we called Virtual product, designers can in the "Virtual" environment to simulation and optimization of products, this is the development direction of computer simulation technology. Long-term since, our country low voltage electrical products often is related research institute and factory technical personnel to the concentrated in one place, and conduct joint design, make the most of the designers from this way our environment and cause so much inconvenience. Since the 90 s the Computer collaborative Design CSCD (Computer Supported Cooperative Design) technology, can provide remote collaborative Design environment, it is based on Internet and implementation of the new concept of a group, recently foreign Computer aided Design software such as PRO/E, and the Internet have added this aspect of the function. Can rely on the technology, people in different places through the Internet to discuss design, draw and modify the design drawing.
Three, the environmental protection appliances
With the development of agriculture and industry, the increasingly serious environmental problems, the extensive use of low voltage electrical appliances put forward new requirements. Low-voltage electrical appliances in almost 80% of the material is plastic, so for these materials, on the one hand, to ensure reliability of long life and electric equipment itself, and environmental protection requirements, should also be considered as no pollution, and can be recycled. Now do not contain CFC or halogen flame retardant plastics has been promoted and used.
For a long time since AgCdO have better arc erosion resistant ability, thus in low-voltage electrical appliances, especially as the control of electrical contact material widely used. But in recent years due to the toxic AgCdO materials, starting from the requirements of environmental protection, replace AgCdO with AgSnO2 materials has been promoted. AgSnO2 contact temperature rise too high, however, has been a key technical problem. At present some international contact material factory are studying how to stop the contact surface by adding additives SnO2 film production to reduce the temperature rise of the contact. Germany Degussa AG on WO3 and BiO3 two materials compound as additive AgSnO2SPWIII new brand material, not only have with AgCdO phase close to the temperature rise, and on arc erosion resistance and penetration resistance of the older brand AgSnO2 materials have a larger increase.
Using vacuum technology and power electronic technology is a important way of solving the environmental protection appliances. At present, the vacuum technology in the field of medium voltage switch has dominance, in the field of low voltage switch also has a great development in recent years. There is no gas in the vacuum, when open circuit fault circuit can only produce energy less metal vapor arc, the strength, the arc time and the ablation of contact less than in the air, and therefore the vacuum switch is out of the need to maintain. From the point of view of environmental protection, the vacuum switch contact system is closed in the vacuum tube and shell, contact open circuit when the arc does not affect the environment, and it can work in the harsh work environment. In the field of low voltage apparatus, although its price is the price of general air of arcing switch electric appliance to be high, but its role has excellent performance and environmental protection is more and more aroused people's concern. Original vacuum contactor is commonly used in special circumstances, at present, due to the vacuum technology progress, the application of the vacuum technology has been extended to general contactor. Recently, the German admiralty - moeller companies new contactor series, its rated current 580 a - 820 - a specification adopted vacuum contactor. The contactor has very high electrical life, and because no arcing, you need less installation space, the shell of Windows for observation the abrasion of contact. Vacuum technology is also used in low voltage circuit breaker, Siemens in the mid - ninety - s first introduced 3 ws1 vacuum low voltage circuit breaker, the rated current is 630 a and 2500 a, the breaking capacity of 50 ka. The present domestic research institutes and factories also is actively developing the products, the main goal is to improve the ability of its rated current and open circuit.
Due to the development of power electronic technology, new electronic devices such as decision, GTR, IGBT as the three generations of the emergence of high power semiconductor switching devices, solid-state non-contact switch also get great development in recent years. Compared with mechanical switch, it is a kind of no arc switch, so it has a long life, and without the need to maintain, from an environmental point of view, on the one hand, because there is no electric arc, arc not because cause contact materials and plastic gasification and pollute the environment, on the other hand also won't because of pollution of the environment and make the contact oxidation film and impact contact reliability on the head. Since there is no contact, touched the hair because of the action of electric arc thermal mechanical switch phenomenon does not exist, this non-contact switch can achieve very high operating frequency, solid state circuit breaker, because of the large loss in the process of work and the lack of enough rated voltage and current of power electronics, coupled with large volume, high price, thus limits its application. But in nearly a decade of research make its drawbacks gradually to overcome, Takamu [2] this paper presents a hybrid solid-state circuit breaker, it is applied to 400 v low voltage circuit, main circuit by can turn off thyristor's decision and vacuum switch in parallel, in order to ensure the normal work of the by vacuum switch circuit, so as to reduce the power loss of the decision. Solid state circuit breaker with sensitive relay circuit used in a rapid response of the over-current protection, to reduce the short circuit current of thyristor decision overheating, failure occurs when the circuitry, overcurrent relay to send out the signal at the same time open the vacuum switch and turn on the decision device, vacuum switch on the arc voltage transfer fault current to the decision circuit. Then, decision off quickly, make the circuit breaker open circuit fault current, the circuit to reduce the burden of decision depends on the sensitive relay for quick action. Another line routing Brice [3] is put forward, such as the hybrid solid-state circuit breaker with polymer PTC resistor. PTC is a kind of positive temperature characteristics of thermosensitive element, it's fast, when the temperature rises to the Curie temperature, its resistance increases sharply, to limit the short circuit current. Solid state circuit breaker with PTC, PTC current-limiting resistor and decision device series, when open circuit fault current, rely on PTC current-limiting effect, reduce the burden of the decision mechanism. In the above two kinds of solid state circuit breaker, the metal oxide surge arrester and absorbing circuit is used for over-voltage absorption's decision to break.
Four, high performance, miniaturization and structure design of modernization
Due to the development of the city power grid, power distribution transformer capacity increases, high performance, miniaturization are put forward for low voltage switch electrical requirements. In order to improve the breaking capacity of low voltage switch electric appliances, foreign companies and puts forward some new arc extinguishing system and current limiting technology, including Japan's mitsubishi VJC technology developed in the company and on the basis of a ISTAC technology are put forward. The technology on the one hand, by special arrangement to increase the function of conductive loop in the moving contact rod of electric power, on the other hand using VJC materials formed to strengthen the narrow gap arc cooling effect. Tianjin merlin gerin companies have launched a current-limiting revolving double breakpoints structure, and put forward at the level before and after protection feature with a new concept "energy matching". In recent years, as has been mentioned above PTC thermal current limiting resistor is people's great interest, first of all, the current limiting resistor and molded case switches in series, can greatly enhance the current limiting effect, the PTC resistance can also be used as a current limiter, alone and application range have expanded to the field of medium voltage.
Switch electrical miniaturization has two meanings, on the one hand, is the size of the electric equipment itself, on the other hand is to reduce the arc spraying distance or implementation arc "no fly" to install the electrical switch cabinet size shrink. Mitsubishi company put forward a new type of contactor, in adding the arcing chamber air outlet used to suppress the heat flow of porous metal plate, can make the temperature of the jet stream is reduced to 10% of the original, the new design in our country S series and TM30 series molded case circuit breaker and DW40 fly arc frame circuit breaker have been made to zero.
For contactor, because of the electronic device in the control system, thus increasingly important electronic devices such as interface with PLC, Fuji company design the new series of NEO SC series of auxiliary contact designed to 5 v and 3 ma with electronics interface. Contactor coil energy-saving technology also has a great development in recent years, Fuji company NEO SC series contactor adopts improved super magnet, not only keep the original design of the energy saving and power supply voltage drops to limit value can be reliable work characteristic, and can guarantee 50% rated voltage is reliable and conditions, and at the rated voltage is more than in the original design of the suction characteristic, make good reaction performance of absorption, so that the new series contactor in timeliness, its impact is the original ones by 80%. The improved super electromagnet for general electronic control, still further development for the above introduction of intelligent control, using microprocessor to control the dynamic behavior of the electromagnet. Now in addition to the admiralty - moeller companies, ABB company to launch a similar product.
The current low voltage electrical appliances are widely used in the structural design of modular generalization, modularization, modular and parts. Modularity is electrical appliance manufacturing process was simple, through the combination of different modules, modular, make electrical appliances can obtain different additional features. Combination to make different functional appliances together, is advantageous to the electrical structure is compact, reducing the varieties of the required components in line, and make the protection performance of good cooperation. Modular electrical dimension standardization, easy to install and combination. Different rating or different types of electrical parts generalization, for manufacturers, will greatly reduce the cost of product development and production; For users, also facilitate maintenance and reduce spare parts inventory. Current, low voltage electrical design modernization have new development, ABB company launched a new series contactor product proposed the new concept of the low-voltage distribution system integration design, a new type of molded case circuit breaker panel, there is a small door, all kinds of function module through the small door can be installed in the operating mechanism of spare clearance on both sides, to shrink the volume of the switchgear. Japan's mitsubishi and Fuji new series molded case circuit breaker design all kinds of specifications of the current product as the same level for the switchgear arrangement, schneider company Masterpact from 800 a to 800 a product using the same frame size, such not only easy to install, and that the commonality of parts. The introduction of the man-machine engineering makes the appearance of the circuit breaker model changed the monotonous style in the past, become lively and beautiful. Westinghouse, put forward the "transparent" point of view of panel design, the requirements of low voltage electrical panel to do friendly interface, all on the front panel of the operating handles, buttons and a display to be obvious, and the operator safety and reliability.