Electrical switches in power supply networks (including circuit breakers, transfer switches, and contactors) are typically used to close or disconnect circuits that supply electrical energy for the purpose of power outages, powering, and switching circuits.
When the grid is not normal, such as overload, overvoltage and undervoltage, short circuit, etc., the load can be automatically disconnected from the grid. Because these abnormal conditions will endanger the safety of the operators and the normal operation of the equipment, and even cause personal death or fire.
Power distribution circuit breakers are mainly used for overload, short circuit, over voltage and under voltage protection in low voltage power distribution systems, and can also be used as infrequent operation of circuits. There are two types of circuit breakers for power distribution: selective and non-selective. Non-selective protection features are simpler and are mostly used for branch protection. The main circuit breaker requires a selective type to meet the selective disconnection of various protective appliances in the circuit, and to limit the accident area to a minimum.
The traditional circuit breaker protection function utilizes some physical effects and is realized by the action of the mechanical system. Therefore, the volume is large and the effect is not ideal. In order to prevent the power supply equipment from affecting the entire power supply line and damage the power equipment when the power supply network is abnormal, a more reliable and more protective circuit breaker is gradually developed on the basis of the conventional circuit breaker.
For example, circuit breakers with short-circuit protection, overcurrent and overheat protection, leakage protection, phase loss protection, etc.
With the development of microelectronics technology, the emergence of integrated circuits has greatly reduced the size of ordinary electronic circuits, so multi-function circuit breakers based on ASICs have emerged. This type of circuit breaker has taken a big step over the original mechanical circuit breaker, but it still cannot be called intelligent.
The development of microcomputer technology has provided conditions for the intelligentization of electrical switches. The intelligent electrical switch can not only provide various protection functions of the ordinary circuit breaker, but also display various parameters (current, voltage, power, power factor, etc.) in the circuit in real time.
The motion parameters of various protection functions can also be displayed, set and modified. The fault parameters when the protection circuit is activated can be stored in the non-volatile memory for inquiry. These features can only be implemented after using a microprocessor.
At present, a series of intelligent circuit breakers have been developed abroad.
The performance of these intelligent circuit breakers is much better than traditional circuit breaker products. China's product development in this area is still in its infancy. In this paper, the related technologies of intelligent electrical switches are discussed, and an example of design and development of intelligent circuit breakers for low-voltage power grids is given.
2 The key technology of intelligent electrical switch 2.1 Single-chip microcomputer and its application technology The single-chip microcomputer has been widely used due to its compact structure and rich functions, and has become the core component of intelligent instrumentation. At present, in the development of high-performance, high-precision, multi-function measurement and control instruments, microprocessors and microcontrollers are considered almost without exception. In the measurement and control instrument, using single-chip technology to make it a smart meter, it can solve many difficult problems that traditional instruments can't or can't solve. It can also simplify the control instrument circuit, improve system reliability, reduce the cost of the whole machine and speed up new products. Development speed. With the continuous improvement of integrated circuit manufacturing technology, the size of single-chip microcomputers is getting smaller and smaller, and the functions are more and more abundant. A new generation of microcontroller products, program ROM, timer/counter, serial communication interface, A/D converter, PWM conversion output, waveform generator, WATCHDOG monitor, I2C bus interface, more I/O ports and The internal RAM registers are integrated to accommodate a wider range of uses. On the other hand, simple-function single-chip microcomputers are moving toward low power consumption and miniaturization. A single-chip microcomputer using a serial bus has only eight external pins. Table 1 lists the performance parameters of some typical microcontroller products.
2.2 ASICs Intelligent electrical switches often involve some special and complex functions. If these functions are completely completed by the computer, it will undoubtedly increase the burden on the CPU, and the effect may not be ideal. In fact, before the advent of intelligent electrical switches, many effective ASICs, such as leakage protection ASICs, have been developed. The use of an ASIC can not only reduce the workload of the CPU, but also ensure reliable operation in the event of a CPU failure, and can also improve the response speed of the system to a certain extent.
Table 1 Typical single-chip performance parameters Model on-chip special functions Serial interface ASICs are divided into two categories: one is to implement a special function of the circuit, such as leakage protection integrated circuit, power supply ASIC, phase loss protection integrated circuit Etc; the other type is the arithmetic circuit, mainly used for current protection operations (logarithm, antilogarithm operations), power factor calculations, etc.
2.3 Intelligent integrated sensors With the continuous improvement of power protection technology, the functions and technical requirements of various protection devices are constantly improving. Under normal circumstances, the low-voltage circuit breaker requires the following protection functions: 1 over-voltage and under-voltage protection functions; 2 three-stage current protection function; 3 leakage protection function; 4 phase loss protection function; 5 other abnormal protection functions (instantaneous spike , instantaneous power off, etc.).
To complete these protection functions, there are a variety of sensors. The performance of these sensors is directly related to the performance of intelligent electrical switches. On the other hand, the sensor should have higher precision, wider dynamic range and detection range, and at the same time have a smaller volume, and the output signal should be easy to interface with the intelligent control circuit. This is still difficult to do at the moment. Affected by microelectronics technology, sensors are moving in the direction of small, solid, versatile and integrated. If you can use the latest technology to develop an integrated sensor, the integration of various power sensors will greatly improve their performance. Furthermore, it is also possible to integrate the microprocessor and the sensor. This can improve the overall performance of the intelligent electrical switch by one level.
2.4 Power Technology The circuit of the intelligent electrical switch can have three power supply modes: dedicated power supply, battery power supply and current transformer power supply, the latter also called self-power supply. These three power supply modes can be used alone or in combination to form a redundant power supply system. The first two power supply methods are technically different from the general microcomputer application system. Current transformer power supply is a special power supply mode for circuit breakers. It can save other power supply circuits when used alone, and can automatically start working with the power grid. It is an ideal power supply mode. However, the current transformer power supply has the following problems that need to be properly handled: 1 Since the power source is derived from the current transformer, the current in the grid circuit is insufficient to supply power. 2 When the current of the grid circuit rises slowly, the voltage of the self-power supply also rises slowly. This is not a problem for analog circuits, but for microprocessors and digital circuits, there should be a reliable reset circuit for it to start up and function properly. 3 Since the current transformer needs to be both a current signal and a power source, there is bound to be a crossover effect between the two. That is, the operating current of the intelligent circuit will affect the detection result of the current of the grid circuit. Therefore, there must be a set of methods for compensation and correction.
The redundant power supply of multiple power supply modes can increase the power reliability of the system. However, the redundant power supply mode requires a switching device. Since the operating current of the intelligent circuit is usually small, the switching circuit is technically difficult to implement. The switching control can be directly performed by the microprocessor in conjunction with a dedicated power detection circuit.
2.5 System integration technology Intelligent electrical switch is a mechatronics product with microprocessor as the core. It includes a power supply section (regular power supply, battery power, self-powered current transformer), a sensor, a control section, an adjustment section, an actuator, and a switch body. The various components are related to each other and affect each other. How to coordinate and handle the relationship between the various components so that they can meet all the functional requirements without exceeding the scope of the existing technical conditions (volume, power consumption, reliability, electromagnetic compatibility, etc.) The main content of integrated technology.
Intelligent electrical switches are a class of products with high technical content. Practice shows that the higher the technical content of the product, the greater the impact and effect of system integration technology. Especially in the production practice, due to the large size involved, often a component problem affects the performance and quality of the whole machine. In modern industry, system integration technology embodies the overall level of basic industry.
It is worth mentioning that the rapidly developing CAD/CAM technology has an important impact on system integration technology. CAD/CAM technology has been widely used in the fields of machinery, electronics, electrician, construction, art, clothing and so on. CAD technology is not only a function as a drawing tool, but also capable of calculation, analysis, verification and simulation. These features not only improve design efficiency, reduce design errors, but also enable designers to see the realistic look of the product during the design phase and simulate the actual operation of the product. This allows the participating designers to have an overall understanding of all aspects of the product.
3Intelligent full-function low-voltage trip unit development CM1-Z-type intelligent trip controller is a full-function low-voltage power distribution protection device developed by the author. It is used in distribution switch cabinets to support various trip units. use.
3.1 Main technical requirements for use conditions. Three-phase four-wire system. Operating voltage protection. Three-stage current protection; over-voltage, under-voltage protection; leakage protection; phase loss protection.
Display function. Voltage, current, power, power factor display; setting parameter display; test current display; 10 fault memory and parameter display; fault pre-alarm display; closing, opening status display.
~1.3 times rated current range accuracy is 3%. Power display is kW. Power factor display resolution is 0.01; fault time display resolution is 0.001s. 3.2 Overall structure CM1-Z type intelligent trip controller is powered by switching power supply, 87C552 single-chip microcomputer and its peripheral circuits, signal sampling and filtering amplifier circuit, automatic range switching circuit, phase-locked loop frequency tracking circuit, leakage protection circuit, display and operation panel, function selection switch, RS-485 serial communication interface and E2PROM memory composition. The composition and structural block diagram of the system are listed.
Thanks to the high-performance 87C552 microcontroller, independent and real-time detection of the three-phase four-wire circuit parameters can be performed, and the relevant circuit parameters (voltage, current, power and power factor, etc.) can be displayed according to the user's needs. The unit features conventional three-stage current thermal analog protection with overvoltage, undervoltage, leakage, and phase loss protection. It can effectively and reliably protect electrical appliances such as distribution lines or motors.
The intelligent circuit breaker block diagram shows the appearance of the operation panel as shown. The panel digital display is divided into 6 groups, which are current display (current), voltage display (voltage), power and power factor display (power), setting parameter display (setting), test parameter display (test) and fault parameters. Display (check). If there is no fault during normal operation, the current is always displayed. Press the "Function" button to switch to another display group.
Display operation panel diagram Each group display is divided into several items. Press the "Select" button to switch between them, as listed below.
Current display: Phase A current, Phase B current, Phase C current, N line current.
Voltage display: AB line voltage, BC line voltage, CA line voltage.
Power display: power, power factor.
Set parameter display: long delay current, long delay time, short delay current, short delay time, instantaneous current.
Test parameters show: phase A current, phase B current, phase C current, and N line current.
Fault parameters display: Phase A current, Phase B current, Phase C current, N line current, and fault time.
The current function status and selection status are indicated by corresponding LED indicators. The selection indicator also has an indication of the status of the storage and communication.
3.3 Function Circuit Design The switching power supply is directly powered by the 380V grid, providing multiple sets of power supplies required for the trip controller. In addition, the system also has a backup power interface.
After the current and voltage signals are processed by the filtering and amplifying circuit, they are sent to the single-chip microcomputer for A/D conversion through the multi-way switching switch and then full-wave rectification. The MCU processes the sampled signal to obtain the effective value of each voltage and current.
The auto range switching circuit automatically switches the A/D input to a different amplified signal output according to the size of the input signal.
When any current exceeds the set value, the comparator outputs an over-range control signal, and the multiplexer automatically turns on the output signal of the lower amplification factor.
The phase-locked loop frequency tracking circuit takes the voltage signal as the reference, and sends it to the single-chip microcomputer as the sampling timing signal after 20 times of frequency. When the AC frequency drifts, the sampling timing signal automatically tracks the change in frequency to ensure that each AC cycle is sampled 20 times.
The power factor measurement circuit shapes the voltage and current signals and sends them to the single-chip microcomputer. The single-chip microcomputer uses the timer T2 to automatically sample the phase difference between the two, and after conversion, the power factor can be obtained.
After the single-chip microcomputer obtains each circuit parameter through the above sampling circuit, these parameters are displayed on the display operation panel. Since there is only a single row of LED digital displays, only one value can be displayed at a time. The user can select the displayed parameter by operating the button. Normally, the maximum current is displayed.
The MCU also performs specified detection on each voltage and current signal. An overvoltage or undervoltage trip signal is issued when the voltage is too high or too low. When the phase loss function is valid, if the three-phase current imbalance exceeds the set value, a phase loss trip signal is issued, and each phase current is detected, and a three-stage type (instantaneous motion, short delay, Long delay) current thermal analog protection.
The leakage protection circuit is an independent hardware detection circuit that sends a leakage protection trip signal when a leakage occurs. The circuit also has a leakage simulation test input to manually detect the effectiveness of the circuit.
The special button combination and function selection switch can be used to provide users with a variety of parameter selections: overvoltage protection point selection, undervoltage protection point selection, phase loss protection function is valid, protection action (down to page 50) level 0.5, 5A range current meter 1; 0. 5, 250V range voltmeter 1; 240mm2 copper wire several meters. Press Connect Test. GKi and GK2 are disconnected, and the Xi and Yi points of the test device are respectively connected to the X and Y points of the A, B and C phases of the primary circuit to be tested, and the current is measured by a large current. Adjust the voltage regulator to make the voltmeter reading gradually rise from 0, and when the ammeter rises from 0 to the required current, stop adjusting the voltage regulator, and the actual current loop current can be obtained by conversion. Select the setting value of the overcurrent relay as needed to check whether the relay circuit operates. With this method, not only the response of the signal loop and the trip loop can be checked, but also the actual energization current and the relay setting value can be matched during the test.
Determination method 2 (starting from the control loop, see).
One 250V voltmeter; a few meters of 2.5mm2 copper wire. Test by wiring.
According to the need to select the overcurrent relay setting value, the X2 and Y2 points of the test device are connected to the overcurrent relay coils (L) of phases A, B and C respectively for measurement. Adjust the voltage regulator to make the voltmeter reading gradually rise from 0, and when the ammeter rises from 0 to the required current, stop adjusting the voltage regulator. By converting the current transformer (CT2) flow ratio, the coil can be obtained. Actual current. With this method, the actual relay setting value can be simply verified, and at the same time, the response of the signal loop and the trip circuit can be checked. It can be seen whether there is an error between the preset setting value at this time and the current actually passing through the overcurrent relay coil.
When the three phases are energized at the same time, the same problem of the current transformer must be considered: the current transformer of the test chamber relay circuit is attached to the three-phase power supply of the main circuit. Therefore, the connection with the Ming end is correct, which has a great impact on the relay circuit. When the same terminal is the same, the main circuit three-phase power is also balanced, the current transformer zero line current + 0. When the current transformer is not the same end, the current transformer zero line current (a ten ping 0) It is equal to 2 times the phase current, so it is important to correct the same terminal of the current transformer. Simple solution: string a current meter for measurement on the zero line, let the main circuit pass current (the current can be smaller, so that the main circuit can withstand, the current meter can accurately read) for a few seconds, observe whether there is current on the zero line, judge Is the same Ming is correct? Tongming must be correct before it can be invested.
(Continued from page 16) Delay factor, N-line current influence coefficient: 0, 100%, e2prom memory provides set parameters and 10 times of fault parameter permanent storage, even after power failure can be stored for a long time.
The RS-485 serial communication interface provides communication means with other computers, which can form a multi-level monitoring network.
4 Conclusion Although the application of microcomputers is quite popular in China, the development and application of intelligent circuit breakers is still in its infancy in China. There are still many technical problems that need to be further explored and solved, and the quality of products needs to be further improved and improved.
The development of microcomputer technology is making more and more traditional products develop in the direction of intelligence. Intelligent electrical switches are just one of them. Due to the obvious advantages of intelligent electrical switches, it will gradually replace the traditional switches in the near future and become more and more widely used.
When the grid is not normal, such as overload, overvoltage and undervoltage, short circuit, etc., the load can be automatically disconnected from the grid. Because these abnormal conditions will endanger the safety of the operators and the normal operation of the equipment, and even cause personal death or fire.
Power distribution circuit breakers are mainly used for overload, short circuit, over voltage and under voltage protection in low voltage power distribution systems, and can also be used as infrequent operation of circuits. There are two types of circuit breakers for power distribution: selective and non-selective. Non-selective protection features are simpler and are mostly used for branch protection. The main circuit breaker requires a selective type to meet the selective disconnection of various protective appliances in the circuit, and to limit the accident area to a minimum.
The traditional circuit breaker protection function utilizes some physical effects and is realized by the action of the mechanical system. Therefore, the volume is large and the effect is not ideal. In order to prevent the power supply equipment from affecting the entire power supply line and damage the power equipment when the power supply network is abnormal, a more reliable and more protective circuit breaker is gradually developed on the basis of the conventional circuit breaker.
For example, circuit breakers with short-circuit protection, overcurrent and overheat protection, leakage protection, phase loss protection, etc.
With the development of microelectronics technology, the emergence of integrated circuits has greatly reduced the size of ordinary electronic circuits, so multi-function circuit breakers based on ASICs have emerged. This type of circuit breaker has taken a big step over the original mechanical circuit breaker, but it still cannot be called intelligent.
The development of microcomputer technology has provided conditions for the intelligentization of electrical switches. The intelligent electrical switch can not only provide various protection functions of the ordinary circuit breaker, but also display various parameters (current, voltage, power, power factor, etc.) in the circuit in real time.
The motion parameters of various protection functions can also be displayed, set and modified. The fault parameters when the protection circuit is activated can be stored in the non-volatile memory for inquiry. These features can only be implemented after using a microprocessor.
At present, a series of intelligent circuit breakers have been developed abroad.
The performance of these intelligent circuit breakers is much better than traditional circuit breaker products. China's product development in this area is still in its infancy. In this paper, the related technologies of intelligent electrical switches are discussed, and an example of design and development of intelligent circuit breakers for low-voltage power grids is given.
2 The key technology of intelligent electrical switch 2.1 Single-chip microcomputer and its application technology The single-chip microcomputer has been widely used due to its compact structure and rich functions, and has become the core component of intelligent instrumentation. At present, in the development of high-performance, high-precision, multi-function measurement and control instruments, microprocessors and microcontrollers are considered almost without exception. In the measurement and control instrument, using single-chip technology to make it a smart meter, it can solve many difficult problems that traditional instruments can't or can't solve. It can also simplify the control instrument circuit, improve system reliability, reduce the cost of the whole machine and speed up new products. Development speed. With the continuous improvement of integrated circuit manufacturing technology, the size of single-chip microcomputers is getting smaller and smaller, and the functions are more and more abundant. A new generation of microcontroller products, program ROM, timer/counter, serial communication interface, A/D converter, PWM conversion output, waveform generator, WATCHDOG monitor, I2C bus interface, more I/O ports and The internal RAM registers are integrated to accommodate a wider range of uses. On the other hand, simple-function single-chip microcomputers are moving toward low power consumption and miniaturization. A single-chip microcomputer using a serial bus has only eight external pins. Table 1 lists the performance parameters of some typical microcontroller products.
2.2 ASICs Intelligent electrical switches often involve some special and complex functions. If these functions are completely completed by the computer, it will undoubtedly increase the burden on the CPU, and the effect may not be ideal. In fact, before the advent of intelligent electrical switches, many effective ASICs, such as leakage protection ASICs, have been developed. The use of an ASIC can not only reduce the workload of the CPU, but also ensure reliable operation in the event of a CPU failure, and can also improve the response speed of the system to a certain extent.
Table 1 Typical single-chip performance parameters Model on-chip special functions Serial interface ASICs are divided into two categories: one is to implement a special function of the circuit, such as leakage protection integrated circuit, power supply ASIC, phase loss protection integrated circuit Etc; the other type is the arithmetic circuit, mainly used for current protection operations (logarithm, antilogarithm operations), power factor calculations, etc.
2.3 Intelligent integrated sensors With the continuous improvement of power protection technology, the functions and technical requirements of various protection devices are constantly improving. Under normal circumstances, the low-voltage circuit breaker requires the following protection functions: 1 over-voltage and under-voltage protection functions; 2 three-stage current protection function; 3 leakage protection function; 4 phase loss protection function; 5 other abnormal protection functions (instantaneous spike , instantaneous power off, etc.).
To complete these protection functions, there are a variety of sensors. The performance of these sensors is directly related to the performance of intelligent electrical switches. On the other hand, the sensor should have higher precision, wider dynamic range and detection range, and at the same time have a smaller volume, and the output signal should be easy to interface with the intelligent control circuit. This is still difficult to do at the moment. Affected by microelectronics technology, sensors are moving in the direction of small, solid, versatile and integrated. If you can use the latest technology to develop an integrated sensor, the integration of various power sensors will greatly improve their performance. Furthermore, it is also possible to integrate the microprocessor and the sensor. This can improve the overall performance of the intelligent electrical switch by one level.
2.4 Power Technology The circuit of the intelligent electrical switch can have three power supply modes: dedicated power supply, battery power supply and current transformer power supply, the latter also called self-power supply. These three power supply modes can be used alone or in combination to form a redundant power supply system. The first two power supply methods are technically different from the general microcomputer application system. Current transformer power supply is a special power supply mode for circuit breakers. It can save other power supply circuits when used alone, and can automatically start working with the power grid. It is an ideal power supply mode. However, the current transformer power supply has the following problems that need to be properly handled: 1 Since the power source is derived from the current transformer, the current in the grid circuit is insufficient to supply power. 2 When the current of the grid circuit rises slowly, the voltage of the self-power supply also rises slowly. This is not a problem for analog circuits, but for microprocessors and digital circuits, there should be a reliable reset circuit for it to start up and function properly. 3 Since the current transformer needs to be both a current signal and a power source, there is bound to be a crossover effect between the two. That is, the operating current of the intelligent circuit will affect the detection result of the current of the grid circuit. Therefore, there must be a set of methods for compensation and correction.
The redundant power supply of multiple power supply modes can increase the power reliability of the system. However, the redundant power supply mode requires a switching device. Since the operating current of the intelligent circuit is usually small, the switching circuit is technically difficult to implement. The switching control can be directly performed by the microprocessor in conjunction with a dedicated power detection circuit.
2.5 System integration technology Intelligent electrical switch is a mechatronics product with microprocessor as the core. It includes a power supply section (regular power supply, battery power, self-powered current transformer), a sensor, a control section, an adjustment section, an actuator, and a switch body. The various components are related to each other and affect each other. How to coordinate and handle the relationship between the various components so that they can meet all the functional requirements without exceeding the scope of the existing technical conditions (volume, power consumption, reliability, electromagnetic compatibility, etc.) The main content of integrated technology.
Intelligent electrical switches are a class of products with high technical content. Practice shows that the higher the technical content of the product, the greater the impact and effect of system integration technology. Especially in the production practice, due to the large size involved, often a component problem affects the performance and quality of the whole machine. In modern industry, system integration technology embodies the overall level of basic industry.
It is worth mentioning that the rapidly developing CAD/CAM technology has an important impact on system integration technology. CAD/CAM technology has been widely used in the fields of machinery, electronics, electrician, construction, art, clothing and so on. CAD technology is not only a function as a drawing tool, but also capable of calculation, analysis, verification and simulation. These features not only improve design efficiency, reduce design errors, but also enable designers to see the realistic look of the product during the design phase and simulate the actual operation of the product. This allows the participating designers to have an overall understanding of all aspects of the product.
3Intelligent full-function low-voltage trip unit development CM1-Z-type intelligent trip controller is a full-function low-voltage power distribution protection device developed by the author. It is used in distribution switch cabinets to support various trip units. use.
3.1 Main technical requirements for use conditions. Three-phase four-wire system. Operating voltage protection. Three-stage current protection; over-voltage, under-voltage protection; leakage protection; phase loss protection.
Display function. Voltage, current, power, power factor display; setting parameter display; test current display; 10 fault memory and parameter display; fault pre-alarm display; closing, opening status display.
~1.3 times rated current range accuracy is 3%. Power display is kW. Power factor display resolution is 0.01; fault time display resolution is 0.001s. 3.2 Overall structure CM1-Z type intelligent trip controller is powered by switching power supply, 87C552 single-chip microcomputer and its peripheral circuits, signal sampling and filtering amplifier circuit, automatic range switching circuit, phase-locked loop frequency tracking circuit, leakage protection circuit, display and operation panel, function selection switch, RS-485 serial communication interface and E2PROM memory composition. The composition and structural block diagram of the system are listed.
Thanks to the high-performance 87C552 microcontroller, independent and real-time detection of the three-phase four-wire circuit parameters can be performed, and the relevant circuit parameters (voltage, current, power and power factor, etc.) can be displayed according to the user's needs. The unit features conventional three-stage current thermal analog protection with overvoltage, undervoltage, leakage, and phase loss protection. It can effectively and reliably protect electrical appliances such as distribution lines or motors.
The intelligent circuit breaker block diagram shows the appearance of the operation panel as shown. The panel digital display is divided into 6 groups, which are current display (current), voltage display (voltage), power and power factor display (power), setting parameter display (setting), test parameter display (test) and fault parameters. Display (check). If there is no fault during normal operation, the current is always displayed. Press the "Function" button to switch to another display group.
Display operation panel diagram Each group display is divided into several items. Press the "Select" button to switch between them, as listed below.
Current display: Phase A current, Phase B current, Phase C current, N line current.
Voltage display: AB line voltage, BC line voltage, CA line voltage.
Power display: power, power factor.
Set parameter display: long delay current, long delay time, short delay current, short delay time, instantaneous current.
Test parameters show: phase A current, phase B current, phase C current, and N line current.
Fault parameters display: Phase A current, Phase B current, Phase C current, N line current, and fault time.
The current function status and selection status are indicated by corresponding LED indicators. The selection indicator also has an indication of the status of the storage and communication.
3.3 Function Circuit Design The switching power supply is directly powered by the 380V grid, providing multiple sets of power supplies required for the trip controller. In addition, the system also has a backup power interface.
After the current and voltage signals are processed by the filtering and amplifying circuit, they are sent to the single-chip microcomputer for A/D conversion through the multi-way switching switch and then full-wave rectification. The MCU processes the sampled signal to obtain the effective value of each voltage and current.
The auto range switching circuit automatically switches the A/D input to a different amplified signal output according to the size of the input signal.
When any current exceeds the set value, the comparator outputs an over-range control signal, and the multiplexer automatically turns on the output signal of the lower amplification factor.
The phase-locked loop frequency tracking circuit takes the voltage signal as the reference, and sends it to the single-chip microcomputer as the sampling timing signal after 20 times of frequency. When the AC frequency drifts, the sampling timing signal automatically tracks the change in frequency to ensure that each AC cycle is sampled 20 times.
The power factor measurement circuit shapes the voltage and current signals and sends them to the single-chip microcomputer. The single-chip microcomputer uses the timer T2 to automatically sample the phase difference between the two, and after conversion, the power factor can be obtained.
After the single-chip microcomputer obtains each circuit parameter through the above sampling circuit, these parameters are displayed on the display operation panel. Since there is only a single row of LED digital displays, only one value can be displayed at a time. The user can select the displayed parameter by operating the button. Normally, the maximum current is displayed.
The MCU also performs specified detection on each voltage and current signal. An overvoltage or undervoltage trip signal is issued when the voltage is too high or too low. When the phase loss function is valid, if the three-phase current imbalance exceeds the set value, a phase loss trip signal is issued, and each phase current is detected, and a three-stage type (instantaneous motion, short delay, Long delay) current thermal analog protection.
The leakage protection circuit is an independent hardware detection circuit that sends a leakage protection trip signal when a leakage occurs. The circuit also has a leakage simulation test input to manually detect the effectiveness of the circuit.
The special button combination and function selection switch can be used to provide users with a variety of parameter selections: overvoltage protection point selection, undervoltage protection point selection, phase loss protection function is valid, protection action (down to page 50) level 0.5, 5A range current meter 1; 0. 5, 250V range voltmeter 1; 240mm2 copper wire several meters. Press Connect Test. GKi and GK2 are disconnected, and the Xi and Yi points of the test device are respectively connected to the X and Y points of the A, B and C phases of the primary circuit to be tested, and the current is measured by a large current. Adjust the voltage regulator to make the voltmeter reading gradually rise from 0, and when the ammeter rises from 0 to the required current, stop adjusting the voltage regulator, and the actual current loop current can be obtained by conversion. Select the setting value of the overcurrent relay as needed to check whether the relay circuit operates. With this method, not only the response of the signal loop and the trip loop can be checked, but also the actual energization current and the relay setting value can be matched during the test.
Determination method 2 (starting from the control loop, see).
One 250V voltmeter; a few meters of 2.5mm2 copper wire. Test by wiring.
According to the need to select the overcurrent relay setting value, the X2 and Y2 points of the test device are connected to the overcurrent relay coils (L) of phases A, B and C respectively for measurement. Adjust the voltage regulator to make the voltmeter reading gradually rise from 0, and when the ammeter rises from 0 to the required current, stop adjusting the voltage regulator. By converting the current transformer (CT2) flow ratio, the coil can be obtained. Actual current. With this method, the actual relay setting value can be simply verified, and at the same time, the response of the signal loop and the trip circuit can be checked. It can be seen whether there is an error between the preset setting value at this time and the current actually passing through the overcurrent relay coil.
When the three phases are energized at the same time, the same problem of the current transformer must be considered: the current transformer of the test chamber relay circuit is attached to the three-phase power supply of the main circuit. Therefore, the connection with the Ming end is correct, which has a great impact on the relay circuit. When the same terminal is the same, the main circuit three-phase power is also balanced, the current transformer zero line current + 0. When the current transformer is not the same end, the current transformer zero line current (a ten ping 0) It is equal to 2 times the phase current, so it is important to correct the same terminal of the current transformer. Simple solution: string a current meter for measurement on the zero line, let the main circuit pass current (the current can be smaller, so that the main circuit can withstand, the current meter can accurately read) for a few seconds, observe whether there is current on the zero line, judge Is the same Ming is correct? Tongming must be correct before it can be invested.
(Continued from page 16) Delay factor, N-line current influence coefficient: 0, 100%, e2prom memory provides set parameters and 10 times of fault parameter permanent storage, even after power failure can be stored for a long time.
The RS-485 serial communication interface provides communication means with other computers, which can form a multi-level monitoring network.
4 Conclusion Although the application of microcomputers is quite popular in China, the development and application of intelligent circuit breakers is still in its infancy in China. There are still many technical problems that need to be further explored and solved, and the quality of products needs to be further improved and improved.
The development of microcomputer technology is making more and more traditional products develop in the direction of intelligence. Intelligent electrical switches are just one of them. Due to the obvious advantages of intelligent electrical switches, it will gradually replace the traditional switches in the near future and become more and more widely used.
Construction,Building, Nail,Strip Nail
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