The main function of the circuit breaker is to use it to switch the operation mode during normal operation, to connect the device or circuit to the circuit or to exit the operation, to play a control role; when the device or the line fails, the fault circuit can be rapidly cut off to ensure no failure. Part of the normal operation can play a protective role. Its greatest feature is that it can break the load current and short circuit current in the circuit. Breaking capacity is the basic indicator of the circuit breaker.
Due to the high price of circuit breakers, fuse-load switches are used instead of circuit breakers in some cases. However, with the wide application of power electronic devices, the harmonic components in the power system are large and the number of harmonics is large. When a vacuum circuit breaker is used in a terminal substation, it is often encountered when the brake is operated that the breaking current is a load current containing harmonics. In the type test and factory test of circuit breakers, there has been no test for breaking the items containing harmonic currents in the circuit breakers or testing the ability to break harmonics in the fuse-load switch. However, in the general survey of substations in Shanghai in 1998, the harmonic components of some substations were found to be excessive, which indicates that the Shanghai Education Commission Youth Fund-financed project.
The first author, Pang Shuheng, was born in 1969 and received her PhD from Xi'an Jiaotong University in 1999.
In practice, the vacuum switch should break the load current containing harmonics that is much larger than the national standard. The vacuum switch research has not involved the test and discussion of the vacuum switch breaking harmonic performance. This article focuses on the study of the parameters in the system when there are harmonics in the system and the effect this change may have on the breaking performance of the vacuum switch.
2 Harmonics Model Vacuum switches may encounter harmonic currents when breaking rated load currents or overload currents, and short-circuit currents when breaking short-circuit currents. Therefore, the divided current does not contain harmonics. The connection model from the vacuum switch in the system can clearly reflect the role of the vacuum switch in the system.
A simplified model in which the vacuum switch breaks the load in the system. When a load is a non-linear load (such as power electronics, switching power supply, rectification equipment, etc.), the vacuum switch that operates the load is disconnected from the load current or the overload current. Breaks the current containing harmonics. The Fourier analysis is used to process the current, and the amplitude of the fundamental current is the standard 1. The formula of the total current in the presence of harmonics (excluding the influence of the direct current) has the formula a) the current in the ten formula (1). The maximum value is important for vacuum switches. It is also possible that the maximum value of the current can only be calculated numerically.
4 Influence of Harmonics on Breaking Capacity of Vacuum Switch The total distortion rate of the current containing harmonics is not necessarily very large, even within the range specified by the national standard, but the maximum current may be many times the maximum value of the fundamental current. . When the vacuum switch breaks this current, regardless of the moment it is opened, the arc current flowing through the vacuum switch is still changing according to the current before breaking, under the assumption that the arc voltage is neglected (because the arc voltage of the vacuum switch is relatively low). The law changes. In this case, the vacuum switch needs to break off the harmonic load current with the maximum value and waveform change. For this purpose it is necessary to discuss the ability of the vacuum switch to break this current.
4. Influence on the breaking capacity The ultimate breaking capacity of the vacuum switch is related to the shape of the arc. It is easy to extinguish when the arc maintains the diffusion state, and it is difficult to extinguish the arc after the arc has transformed to the accumulation state. The state of the arc is related to the strength of the longitudinal magnetic field applied. The critical magnetic flux density Bz required to ensure arc diffusion at any current can be expressed as the increase in the maximum (ie, peak) current when harmonics are present, and the critical magnetic flux density required to maintain the arc in the diffusive state. Increased, but there is no linear relationship between current and magnetic field.
Even though the maximum value of the load current containing harmonics increases, it is still very small compared to the limit breaking current of the vacuum circuit breaker. Therefore, the vacuum circuit breaker can break this current. Since the vacuum load switch only breaks the load current, in the occasion where the vacuum circuit breaker is replaced with a vacuum load switch and a fuse, breaking the maximum harmonic current may cause a continuous accident of the vacuum load switch.
4. Impact on the life of the contacts For vacuum circuit breakers, the electrical wear rate of the contacts is mainly determined by the breaking short-circuit current. When breaking the short-circuit current, the arc current is large and the contact wear rate is high. The limit breaking current of the vacuum switch is smaller than the maximum value of the harmonic current. Therefore, the electric wear rate is small when the breaking short-circuit current is taken and the contact life is not greatly reduced.
However, for the vacuum load switch, since its main task is to divide the load current, its electrical life is mainly determined by the breaking load current method (turning to page 19) 0 method to write this value into the database of the embedded integrated platform, and immediately The data in the database will be displayed in the user interface in the specified format.
4.2 Text files Generally, data in text files can be read into memory, and the data can be analyzed to convert ASC codes into binary codes.
This will convert the ASC code to binary code. Based on this, real-time collection and management of the data in the BMS integrated system can be realized.
4.3 Database 15000) Using the EBI database as an example, introduce how the BMS integrates the database: Names to be read in.
After all this data is read in, use the DBCom control to store them in the configuration-based BMS database: where: 21FFIALM.PV is the name of the point defined in the configuration and real is the name of the variable to be written into the data.
Through the above example, the interface between third-party software and BMS integration platform can be realized.
5 Concluding remarks In this paper, the intelligent office building's construction equipment monitoring and management is targeted at, and the integrated management of the building automation subsystem (HoneywellExel5000 system) and the diesel generator subsystem car park management subsystem is effectively realized, providing comprehensive management of the building's property management. Management and support decision-making technology platform.
Applicable to the construction of real estate, parks, bridges and tunnels, construction of harbors and airports, construction of railways and highways, construction of power and communication engineering, construction of dams and water conservancy projects, energy production, and storage Construction and construction, construction of agricultural production, reserve engineering, construction of municipal infrastructure, greening projects, etc.
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