1. Smart appliances
Microprocessors and computer technology are introduced into electrical equipment to make electrical appliances have intelligent functions. In addition, switching appliances, including intelligent circuit breakers and intelligent motor controllers, realize two-way communication with the central control computer. Into the 1990s, computer information network development, distribution systems and motor control center has formed intelligent monitoring, protection and information network system.
Intelligent circuit breakers and motor controllers are intelligent main electrical components for switchgear and motor control centers. The introduction of circuit breakers by microprocessors has enabled the protection of circuit breakers to be greatly enhanced. For example, the short delay can be set to the I2t characteristic in the three-stage protection feature so that the protection can be better matched to the next-stage protection; the protection can be implemented selectively, and the interrupted arc connection can be provided with a memory function.
At present, a large number of soft starters, power electronic speed controllers, and uninterruptible power supplies are used in automation control. These devices will cause high-order harmonics in the power distribution system, while analog electronic trip units generally reflect fault current peaks, and the power supply is high. Harmonics can cause circuit breakers to malfunction. With the microprocessor intelligent circuit breaker central processing unit can accurately reflect the true rms value (RMS value ) of the load current, and its sample and hold circuit can eliminate the higher harmonics of the input signal, and can avoid high-order harmonics causing malfunction.
The intelligent overload relay has a series of advantages compared with the conventional bimetal thermal relay. It can protect a variety of motor starting conditions and has high operational reliability. It can protect the motor from overload and phase failure, and can protect the connection, three-phase imbalance, reversed phase or low current. Intelligent motor protection relays are further developed based on intelligent motor controllers that combine monitoring, protection and communication functions.
The network system composed of smart electrical unit and central control computer has the following advantages compared with traditional power distribution system and motor control center: centralized control of the central computer is realized, the degree of automation of the distribution system is improved, and the distribution and control system scheduling and maintenance are achieved. New level. The use of digital new monitoring components has enabled the distribution system and control center to increase the amount of information provided; the monitoring components have been compared with traditional indications and command appliances. The wiring is simple, easy to install, and the reliability of work has been improved; data sharing has been achieved and data reduction has been achieved. Information duplication and information channels.
2. Communication appliances and information appliances
The development of network communication requires the openness and compatibility between users and devices. The development of a unified access agreement is a key issue to be solved urgently. At present, the automatic communication network formed by intelligent appliances and central computer interfaces is developing from centralized control to distributed control. The emergence of fieldbus technology provides the conditions for constructing a distributed computer control system. It is plug-and-play, has good expandability, and is easy to maintain. At present, this technology has become a focus of attention at home and abroad.
Fieldbus is a fully digital, open two-way local communication network that connects intelligent field devices and control rooms. There are many kinds of fieldbuses, and there are more influences: CAN , Lonworks and Profibus . Each has its own characteristics and advantages, and different fields have different application values. But it is also the variety of fieldbus technologies and communication standards that have adversely affected the development of this technology. At present, the International Electrotechnical Commission and the Fieldbus Foundation are working to unify the fieldbus standard. Some units in our country also do this work. We have based on the fieldbus technology and have communication functions as electrical appliances.
At present, fieldbus technology is extending upwards and downwards, and its upper end communicates with enterprise network backbones such as Ethernet , Intranet and Internet , and its lower end extends to the industrial control field area. There are two kinds of bus systems: Siemens AS interface and Rockwell company Devicenet . These two types of buses are used in low-level areas and are low-cost communication connections. They include industrial control sensors and actuators, including limit switches and optoelectronics. Simple control elements such as sensors, motor starters, button indicators, and multi-function relays are connected as slaves to the network and communicate with the master control computer or programmable logic controller (PLC) .
Traditional relays and contactor control systems convert contact information into binary digital information and communicate with serial interfaces and addressing. This has revolutionized traditional control elements. For example, the Siemens AS bus system application Logo multifunction relay is actually A small PLC that can perform functions such as delays, latches, registers, and pulse relays.
The intelligent electrical appliance further realizes the informationization, which is to make the intelligent appliance field level implement the Internet/Intranet function, and its technical core is to implement the TCP/IP protocol. The TCP/IP protocol is embedded in the smart appliance ROM so that signals are sent and received in a TCP/IP manner, and the intelligent appliance information function is further developed. Using the Internet/In-tranet function, remote control, programming and configuration of on-site smart appliances, which makes intelligent appliances have entered a new era of information appliances.
3. Smart release
The tripper definition is constantly changing with its function. In the early days, the trip unit could be defined as being larger than the rated current value. When the overcurrent ( fault current ) circulates, the operating mechanism trips and trips, and the breaker is automatically opened. The development of over-voltage, under-voltage release, and shunt release, especially the intelligent release of the current release, and the development of communication, the release is more and more powerful, and more and more additional functions. The above simple definition obviously does not meet the actual situation.
Now, we put the various circuit breakers that can protect the electrical equipment against overload, short circuit, undervoltage, and overvoltage hazards. These are collectively referred to as trip units. The detection of circuit parameters and signal processing are called electronic trip units; the configuration of a microprocessor system enables communication to be called an intelligent trip unit.
3.1 The status of release
The release is the development of circuit breakers. China's 90- year-old release products are mainly electromagnetic and thermal, with a small number of electronic and intelligent release products. The foreign release device electronics and intelligent research and manufacturing are taking the lead and are now about 5 to 10 years ahead of China.
Intelligent trip units enable circuit breakers to be more powerful. China's newly-developed DW45 series product release devices have communication functions with industrial control computers, PLCs, etc., and can provide switching status, three-phase current, voltage, power factor, active power and other parameters. In terms of communication, all countries are paying more attention to adopting more mature field bus technologies. China currently uses FCS fieldbus systems.
The intelligent trip unit can realize traditional trip functions such as over-current, voltage and shunt. On the hardware, the microprocessor module, the auxiliary function module and the execution unit can all be the same. Different from current and electric signal processing and display, it can be implemented in software design. In addition, the over-current protection function needs to configure the over-current signal detection unit, while the voltage protection needs to configure the power supply, the whole-wave filtering, the voltage regulator, and the under-voltage delay unit, and the shunt-excitation function only needs to add a switch.
3.2 Smart Release Development Trend
Domestic and foreign appliance manufacturers have pushed the market to new products and research trends, smart release has the following trends:
3.2.1 Intelligent Release Productization: The smart release will be made to be independent of the circuit breaker, and its use will be limited to a type of circuit breaker. The detection and maintenance of the release will also be relatively simple. In the past, the circuit breaker product test must be completed after the entire circuit breaker assembly is completed. After the trip device is manufactured, the test can be performed independently of the circuit breaker, which greatly simplifies the entire circuit breaker test procedure, and the test time is also large. cut back.
3.2.2 Release Electronics: The rapid development of semiconductor integration technology, microelectronics and computer technology, smart release control capabilities are increasingly strong, will be intelligent detection and control from the conventional voltage, current, power and other electrical parameters, development To detect and control non-electrical parameters such as contact material wear, arc extinguishing room temperature, etc.
Intelligent and Communicable: The biggest difference between smart and electronic is that it uses a microprocessor. With application software, this kind of hardware has greater applicability and upgradeability under the same circumstances, and communicablization is to add related detection, judgment and communication chips or circuits to the release product to make the tripper various status and operating parameters. Can better transmit media ( such as field bus, serial line, etc. ) and other electrical equipment on the line for information exchange, to adapt to the current trend of intelligent and networked electrical equipment, and the use of field bus technology has a more uniform standard It also provides more reference data for the release testing, testing and maintenance. Electrical product inspection and integrated circuits for working circuits are also current trends.
In China, the specific requirements for the release of the release can be expressed as “ four remote †—telemetry, remote control, remote sensing, and remote adjustment. This is far from the networked capability, but it is more in line with China’s scientific research level and economic level.
3.2.4 Modularity and Versatility: The modular structure brings many benefits to product design, manufacturing and market adaptability, such as reducing product design, manufacturing and new product development complexity, enhancing functional expansion, facilitating maintenance, product market Strong ability to adapt. Modular design, dimensions, parts, etc. are versatile, and in terms of producer design, manufacturing, and technology inheritance, the role and importance of user use, maintenance, etc., are now known to most people.
In addition, improving the high reliability, high stability of the release, and the ease of operation and safety are the main trends in its development. For China's products, materials and processing technology, product appearance and overall layout is also worthy of attention.
The intelligent trip unit has the above functions and features, and can realize multiple functions on the same circuit breaker, so that a single action characteristic may be able to achieve a variety of action characteristics of a protection function; and the circuit breaker may be implemented in a bidirectional manner with a central control computer. Communication constitutes an intelligent monitoring, protection, and information network system, enabling the development of circuit breakers from basic protection functions to intelligent protection functions.
4. Key technologies of smart appliances
4.1 Detection and Sensing Technology
When measuring parameters of line power, the voltage is usually a voltage sensor ( transformer ) , and the current is usually a current sensor ( current transformer ) . The latter has solid and hollow points, and both have advantages and disadvantages. The current is good when using a solid current transformer with a small current, but the core is easy to saturate when the current is high, the linearity is poor, and the measurement range is small. With a hollow current transformer, the linearity is good and the measurement range is wide, but when the current is low, the signal is better. Small, large measurement error. To improve the accuracy of the small current measurement, the number of transformer turns must be changed to increase the mutual inductance secondary output signal. When the current is small, if the output signal of the secondary side is too large, the signal is difficult to sample when the current is high, and the circuit is broken. To improve the measurement accuracy at low currents, taking into account the current measurement range, to achieve full-scale current accuracy measurement.
In addition, after the signal detection unit adopts appropriate sensors, various signal amplifiers should also be adopted to appropriately amplify the electrical signals, and noise filters should be used for noise filtering and other circuits. In addition, there are many factors that need to be considered, such as input and output characteristics, sensitivity, frequency response, time constant, temperature coefficient, and measurement range, which are one of the key technologies for realizing the intelligentization of electrical products.
4.2 microprocessor and its interface technology
4.2.1 The basic requirements for microprocessors are hardware universalization, application flexibility, memory, calculation, and table lookup capabilities. The instruction system is suitable for real-time control and fast execution. This is the core of intelligent appliances. At present, the microprocessor has formed a series of multi-series, multi-category situation, China currently uses more MCS-51 series, there are more than 10 models.
4.2.2 Interface technology refers to the technology of the connection between the microprocessor and the peripheral devices, which includes hardware and software technology. The interface circuit is various, commonly used microprocessor universal interface, keyboard, display interface, printer interface, A/D , D/A interface and so on.
4.3 Application Software Design Technology
It can be said that software is the soul of smart components. The essential difference between microprocessors and digital circuits is that they have software systems. Many hardware circuits can be implemented, and software can also be implemented. When designing hardware circuits, software can be used to implement some or all of them.
The working characteristics of the tripping device quickly reflect the effect of its performance on the work. It is also necessary to adopt advanced algorithms under the premise of strengthening sensor technology research. The ability to detect early increases in short-circuit currents and detect current values ​​alone is not sufficient, and must be able to predict current changes. Observe the first-order or multi-order derivative of the phase current di(t)/dt , that is, the relationship between the actual current i(t) and its derivative in the predicted situation. This also requires advanced sophisticated algorithms.
4.4 Anti-jamming technology
The development of intelligent appliances has made electromagnetic compatibility EMC an increasingly important issue. EMC requirements include two kinds of meanings: When smart appliances are required to be used in a workplace, they are not subject to erroneous actions caused by external electromagnetic interference; in addition, the requirement that the electrical appliances operate to generate electromagnetic fields does not interfere with nearby electronic devices. At present, foreign countries attach great importance to the EMC problem of intelligent electrical appliances and electromechanical integration products. Electromagnetic interference will cause such systems to malfunction and malfunction and cause huge economic losses. Intelligent appliances and their protection and monitoring systems place sensitive digital electrical components in high-current and high-voltage electromagnetic fields. These devices have become a non-negligible factor in the design and operation of electromagnetic anti-jamming capability. The initial design of foreign intelligent appliances and systems The stage is to develop a strict electromagnetic compatibility control and management plan. The plan mainly includes EMC analysis of products or systems, formulates EMC design specifications, design plans, standards, implementation plans and test methods, and makes this plan an important part of product or system design. EMC analysis and design is to achieve EMC technology. Requires key work, including analysis of the degree of radiation of electronic circuits and anti-jamming capabilities and system integration of electromagnetic compatibility; EMC design includes electromagnetic shielding, connection, wire spacing determination, and consideration of electromagnetic coupling between printed circuit board wiring. The current high-frequency electromagnetic field digital analysis and computer hardware development, the use of modern simulation technology to replace the traditional test methods and empirical analysis methods, has played an increasingly important role in EMC analysis.
Electrical and electronic interference comes from all aspects, including electrical interference, changes in ambient temperature, and various factors such as air pressure, vibration, and time, among which electrical interference is a major factor in all types of interference. Intrusion of various lines into the microprocessor system, but also in the form of field intrusion into the computer system from the space, the power supply circuit is the main route for various surge voltage in the power grid. Anti-jamming hardware anti-jamming, software anti-jamming, but also a combination of software and hardware measures. The hardware anti-jamming has the advantages of high efficiency, but it needs to increase the system investment and equipment volume; the software anti-jamming has the advantage of low investment, but it is necessary to reduce the system efficiency, analyze the interference source and the interference wave propagation path, and reasonably choose the anti-jamming measures to be intelligent electrical products. Design and apply important content.
4.5 Reliability Technology
The reliability of electronic products involves a wide range, such as the reliability of components, technical design, technology level and technical management, which together determine the reliability index of electronic products. To improve product reliability, we must master the law of product failure, make a thorough understanding of the law of product failure, and take effective measures to improve product reliability. Based on the basic functions of intelligent electrical products, it is also necessary to implement very useful auxiliary functions. Specific auxiliary functions are as follows:
1) Current and voltage display function;
2) Set parameters for tripping various parameters;
3) Test function; self-diagnosis function;
4) Communication interface function;
5) Remote monitoring and diagnostic functions;
6) Load monitoring function;
7) Simulation function, etc.
In summary, smart appliances have more powerful functions, and the trend of smart appliances depends on the ability of microprocessors to better realize the functions of smart appliances, parameter detection and signal processing units to set corresponding parameters, and a smart appliance can realize traditional In the sense of several electrical product features.
Multi-functionalization is the characteristic of intelligent products, and communicablization is also an important development direction of intelligent appliances. With a common communication interface, it uses a standardized communication protocol to make its computers networked to form a monitoring, protection and information network, enabling smart appliances to implement In-ternet/Intranet functions at the field level. (Source: Internet of Things Online Editorial: China E-Commerce Research Center