Switching appliances and electrical appliances have two main features: one is to open and close the circuit, especially in the event of a fault; the other is to protect the equipment in the line and the line, the latter is dependent on the low-voltage electrical appliances The medium release is used, and the medium voltage switchgear is realized by various protection relays. Rely on microelectronics and computer technology to improve the protection functions of switchgear and complete electrical equipment. Recently, the intelligent operation of the switchgear has been used to improve the on-off performance of the switchgear. This is another way to intelligentize the appliance.
2 The intelligent connection of the low-voltage contactor can also enhance the switching-on and breaking performance of the switching device by using microelectronics and computer technology. Research at home and abroad has pointed out that with the intelligent operation of the electromagnetic system, the electrical life of the contactor under the AC-3 use category can be improved. Under the AC-3 category, the contact erosion of the contactor is mainly due to the closing operation, which is due to the harsh contact conditions of the AC-3 operating category. That is, it is required to close the rated current equivalent to six times the starting current of the motor at the rated voltage, and during the closing process of the contact, the vibration is caused by the collision between the moving and static contacts, and the intermittent arc caused by the vibration is the contact erosion. main reason. The kinetic energy of the moment of collision of the movable part can be calculated by the following formula: The speed of the moving part of the v-moving and static contact is instantaneous. It can be seen from the formula 1 that the speed of the contact is the kinetic energy of the movable part and the main vibration of the contact. Factors, the movable part of the Ministry of Education's doctoral fund funded project (2000069808) speed can be approximated by the following formula, thus operating the dynamic electromagnetic force of the electromagnet, and the function of the stroke is time 11 reaction force vibration causes the contact to open the arc, when When the breaking current is i, the arc energy is 9~12V. The general contact vibration time is 2~5ms, which reduces the vibration time, can reduce the arc energy, and reduce the erosion of the contact by the arc.
It can be seen from Equation 3 that the good dynamic suction force of the operating electromagnet and the reaction force can reduce the speed of the contact moment of the contact, thereby reducing the vibration time and the contact erosion, and improving the life of the contactor under AC-3 conditions.
Admiralty-Merler's St.oigens proposes an adjustment system that controls the dynamic process of the electromagnetic system. The electromagnet coil of the contactor is controlled by an electronic circuit, and its structural block diagram is as shown. The coil of the electromagnet in the figure is powered by an electric circuit through an electronic circuit. The size of the power supply voltage can be adjusted by the optimal combination of the dynamic characteristics of the electromagnetic system to reduce the contact erosion and improve the electrical life of the AC-3 work task. The dynamic parameters of the electromagnetic system itself are used as a feedback signal to be input into the electronic circuit after being detected by various sensors, thereby forming an automatic adjustment system to achieve optimal control of the dynamic characteristics of the electromagnetic system. Here the electromagnetic system 3 can be used as a feedback signal for the intelligent operation of the contactor. An important function of the bookmark3 low-voltage electrical appliance is the on-off capability. Another way to develop smart appliances in recent years is to improve the on-off performance of electrical appliances through intelligent control of microprocessors. Recently, the German Admiralty-Muller company introduced a new generation of DIL-M series contactors, which use intelligent operation technology in the current class above 185A. When the contactor is closed, the wear of the contact is mainly caused by the intermittent arc caused by the contact bounce. Under the AC-3 work task, the contactor should close the rated current six times at the rated voltage, so it affects the electrical life of the contact. The main factor. The traditional contactor has its electromagnetic system uncontrollable, and people can only pass the suction and load characteristics of the electromagnetic system! = Block diagram of intelligent control of AC/DC line operation of electronic control line power In order to achieve intelligent contact of the contactor, TSDavies and H. Nouri of the University of the West of England proposed a DC square wave power supply scheme for the contactor connection process. The HC221CMOS dual monostable multi-harmonic oscillator is used to form an electronic circuit to supply power to the electromagnet coil. The voltage waveform of the coil during the turn-on process is as shown. In the figure, from the instant of switching to tl, the power supply is supplied to the coil at a constant value, and the coil is de-energized within tl~t2, and the voltage is restored from t2 until the magnetic system and the contacts are closed. By changing ti and t2, the energy of the coil excitation can be changed, thereby changing the closing speed of the electromagnetic system in relation to the contact to obtain the minimum contact vibration.
A reasonable fit to reduce the collision of the movable system. The DIL-M series intelligent control contactor has its electromagnetic system controllable. Its electromagnet coil is powered by a pulse rectified voltage and can be adjusted according to a suction characteristic curve which is optimally matched with the suction characteristic stored in the microprocessor. Coil current. The wide pulse voltage is input during the contact phase of the contactor, so that the main contact can be safely and reliably sucked; the narrow pulse voltage is input during the holding phase, and the energy is saved while keeping the contact closed. Thanks to the intelligent control, this contactor can achieve an electrical life of 1.3X106 times under the condition of saving contact material. The intelligent control is adopted, and the contactors of different specifications have the same geometrical dimensions such as the cross section of the electromagnetic system, which brings convenience and economy to the production, thereby compensating for the extra expenses due to the electronic control. Admiralty-Merler's St.orgens compared the intelligently operated contactor DIL-M250A with a non-intelligently operated conventional contactor of the same rated current, a and b respectively indicate contact collision speed, contact vibration time Relationship with coil voltage.
Electrical life under AC-3 operating conditions. In addition, the application of intelligent operation also makes the new system contactor have the following advantages: the coil power supply can be AC ​​or DC.
The energy saving effect is obvious. The power required during the pull-in and hold phases of the magnetic system is significantly reduced, which has the advantage that the required capacity of the control power supply is reduced and the heat generated by the contactor in the switchgear is reduced.
(4) Improved work reliability. When the coil voltage drops to a critical value, the chattering of the contact does not occur and the fuse does not cause the coil to burn out when the overvoltage is applied. If the control voltage is interrupted or dropped below 10ms, the contactor will not be broken.
4 Intelligent operation and product development trend of medium voltage vacuum circuit breaker In recent years, the forefront of foreign vacuum switch intelligentization is to realize intelligent operation, that is, using electronic operation to synchronize operation, realize zero-voltage closing and zero current of switch main contact Time division to greatly improve the on/off characteristics of the switch. By means of the intelligent electronic device, when the voltage between the contacts of the switch is zero, the closing transient process can be cleared, in particular, the shunt capacitor bank which is used as the reactive power compensation device can be eliminated or weakened. Large inrush current and overvoltage generated during switching. Although the closing overvoltage generated by the shunt capacitor bank generally does not exceed twice the rated voltage, since the power system is an integral part of the interaction, the transient process occurring at any position will propagate in the system and affect other equipment. For example, a variable speed drive system consisting of power electronics in the power grid is extremely sensitive to overvoltages in the grid, which can jeopardize its normal operation. Foreign countries have used synchronous operation technology to study the influence of switching parallel capacitor bank on power electronic speed control system. Research shows that the synchronous operation can reduce the overvoltage from 1.7 times to 1.35. By means of synchronous breaking, the switch is divided at the current zero crossing. Since the energy input to the arc gap is zero at this moment, the zero-crossing synchronous breaking can be realized greatly. Improve the breaking capacity of the switch.
The operating system that implements the synchronous operation includes an intelligent detecting device and a quick mechanical operating mechanism. The former can detect the voltage or current zero-crossing moment of the breaking circuit and issue an operation signal in time, and the latter can quickly and accurately close or break the circuit after receiving the former signal. As the latter, the traditional spring energy storage operation structure is difficult to perform this task, and the appearance of the vacuum switch permanent magnet operating mechanism creates conditions for the vacuum switch to realize intelligent operation.
The vacuum switch has obvious advantages in medium voltage switchgear due to its series of advantages such as reliable operation and no maintenance. However, the spring operating mechanism has a complicated structure and poor working reliability is a weak link in use. The permanent magnet operating mechanism introduced in the late 1980s is well matched to the load characteristics of the vacuum switch due to its suction characteristics (as shown). In addition, the permanent magnet mechanism has self-retaining performance without the need for a locking mechanism, so that it does not have a complicated transmission mechanism of the spring mechanism, and the mechanism is very simple, which greatly improves its working reliability, and its mechanical life can reach 100,000. The time is 5~10 times that of the general spring mechanism. It is characterized by fast action speed and precise time, so it is very suitable for the operation mechanism as intelligent operation.
Suction characteristics of permanent magnet and spring mechanism 1. Vacuum circuit breaker load characteristics 2 Characteristics provided by spring operating mechanism 3. Characteristics provided by permanent magnet operating mechanism Since the introduction of permanent magnet operating mechanism by ABB in 1997, a development is currently underway. Intelligently operated synchronous medium voltage vacuum circuit breaker q. It can realize the on/off operation of the circuit breaker and the power grid synchronously, avoiding or shortening the operation transient process and the disturbance to the power grid.
Since the three phases of the power supply differ in phase by 120°, synchronous operation is required. Unlike the conventional three-phase common operating mechanism, each phase must have a separate permanent magnet operating mechanism, as shown. The whole operating system consists of two parts: an electronic control circuit and a permanent magnet operating mechanism. The block diagram of the electronic control circuit is as shown.
After receiving the operation command, the signal processing and timing unit determines the time for the next unit to send the combined or divided signal by processing the current and voltage signals from the line, and operates the control unit of each pole permanent magnet mechanism to ensure the permanent magnet. The operating mechanism completes the operation within the specified tolerance time range. The task of the electronic control circuit is to keep the action time as constant as possible. This is to have an adaptive mechanism and real-time closed-loop control to ensure the operating deviation of the operating time in different environments. The operating time tolerance achieved by the synchronous circuit breaker is: closing operation ±1ms, opening operation ±2ms. Electronic control circuit block diagram The advantages of the intelligent operation of the synchronous vacuum circuit breaker are: 1 reduce the transients experienced by the power grid equipment Overvoltage. 2 Improve the electrical life and performance of the circuit breaker. 3 Improve the quality of grid power and make the power electronic speed control device used on the grid work safely and reliably. 4 The reduction of transformer inrush current can avoid the malfunction of tripping.
5 Summary Whether it is a low-voltage contactor or a medium-voltage vacuum switch, the electronic control of intelligent operation can greatly improve its on-off performance, which is another way to intelligentize electrical appliances. At present, this technology is still in the initial stage, and its promotion and application, including EMC issues, are still to be further explored.
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