Reactors and transformers
The reactor (inductance) is the greatest difference in the transformer, and the transformer does not store energy, only transmit energy, and the reactor, in particular the filter reactor, must store energy. Be
The transformer does not store energy, and the primary current is very small at the time of no load, and the electrical current is zero when the transformer is secondary. The current is currently reflected in the second time. Therefore, the effect of the transformer core is only a complete coupling of a secondary secondary, that is, the magnetic field generated by the primary current passes through the secondary winding, and the magnetic field generated by the secondary current is complete through a winding. For transformers, there is only one limit on the core: the magnetic flux density in the core is not too large to cause the iron heart to reach the depth saturation. Therefore, the transformer core generally does not leave the air gap, and the transformer of pure communication work is even more. Be
Filter reactors, otherwise, it must store energy, whether it is a reactor in a resonant loop, or a reactor in a rectifier, must store energy. In order for the reactor to store sufficient energy, there is a gas gap in most reactors (inductance). Of course, the magnetic flux density in the core is still too large to cause the iron core to reach the depth saturation This restriction condition still exists in the reactor, even more than in the transformer, and the magnetic flux density in the core is reduced even if it is shallow saturation. Small and the resonant frequency changes. Therefore, the iron core magnetic flux density in the reactor of the resonance work is often selected more than the magnetic flux density in the DC filter inductor. Be
This can be seen from the transformer used in the switching power supply. The switching power supply of the body is working, whether it is single-ended, push-pull, semi-bridge, all bridge, and its transformer generally does not leave the air gap. The switching power supply of the flyback work is stored in the transformer during the switching tube conduction, and the transformer outputs energy to the load during shutdown period, so the switching power supply transformer of the flyback work must remain in the air gap. The purpose of the gap is to store the largest energy under volumetric weight limit conditions. Be
The relationship between magnetic field strength, magnetic flux density, and storage energy is as follows
This is a vector expression. Since the magnetic flux density in the actual core is always in the same direction as the magnetic field strength, it can be written to write
The normal power frequency transformer is very small at the time of air load, meaning that its inductance is large. The reactor typically requires a certain amount of inductance, which cannot be large, which requires the magnetic material magnetic thermal magnetic permeability. On the other hand, from half of the unit volume magnetic field energy is half of the accumulation of H, in order to make the unit volume magnetic field energy as much as possible, it does not exceed the saturated magnetic flux density, and it is advantageous to reduce the magnetic permeability. In order to maintain a certain flux density, the magnetic permeability is half, the magnetic field strength needs to be increased to twice, and the unit volume magnetic field energy has also increased to twice, and the magnetic field energy is proportional to the magnetic field strength. Be
Therefore, the reactor is inevitably must have a gas gap, even in a hollow. Reactors without air gap are almost impossible. Be
In electronic circuits, small power reactors (inductors, chokes) are designed, generally known operating frequencies, voltage or current, inductance. Three working frequencies, voltage, current, and inductive amounts can only be given, and the fourth should be obtained according to the three items given. Be
Small power reactor (inductance, choke) is designed to process the core, often only use the ready-made core, and the magnetic road can only leave a gas gap (the air gap of the mechanical air gap is actually Two air gaps). Be
Based on the parameters given, it is possible to preliminaryly, it is possible to estimate how much iron cores need to use and need a lot of air gaps. Then calculate according to the initially selected core. The magnetic flux density in the core does not achieve saturation constraints still works, and the magnetic flux density of high linear requirements should be smaller. During the calculation process, adjust the air gap size, number of turns, etc. Final calculation results If the windings cannot be placed in the core window, you must use the iron core of the big one to re-design. If the winding is placed in a window, there is a considerable amount of margin, you should consider the use of small one core redesign. Be
Due to the number of turns, the core model is discontinuous, so reactor design is often repeatedly adjusted to redesign. More than a number of parameters can be freely selected, there may be several different results, and finally, it is necessary to compare costs in different design results, the degree of processing, versatility, etc., select a final result. Be
The iron core that is still used in a relatively small reactor is to minimize volume and cost. Using iron core with air gap, the magnetic field can be constrained in the core without spreading. Whether you leave a few air gaps, the air gap is placed in the heart of the core and cannot be placed outside of the pillar. The hollow reactor is also an electromagnetic housing externally in the reactor winding, and the purpose is to reduce the volume avoiding magnetic field diffusion to other reactors or structural members.
What role does the reactor start in the transformer?
The conventional reactor taken in the power system has a series reactor and a parallel reactor. The series reactor is mainly used to limit the short circuit current, and there is also a high-hard harmonic in the filter in series or in parallel to the capacitor. 220kV, 110kV, 35kV, 1kv grid in the 10kV grid is used to absorb the charging capacity of the cable line. The operating voltage can be adjusted by adjusting the number of parallel reactors. Ultra-high pressure parallel reactor has a variety of functions to improve power system reactive power, including:
1, light empty or light load lines to reduce power frequency transient overvoltage;
2. Improve the voltage distribution on long-range electric lines;
3. The reactive power in the line is balanced as much as possible in the line, preventing unreasonable flow of reactive power, also reducing power loss on the line;
4. Reduce the high-pressure busbar of the high-pressure busbar during the large unit and the system, which is convenient for the generator in the same period;
5, prevent self-excitation resonance phenomena that can occur in long lines of generators;
6. When using the reactor neutral point by a small electrical anti-grounding device, the line phase and the ground capacitance can be used to accelerate the sub-supply current to automatically extinguish.
The connection line of the reactor is tested in series and in parallel. The series reactor typically starts current limiting, and the parallel reactor is often used for reactive power compensation.
1. Semi-core dry parallel reactor: In the ultra-high pressure remote transmission system, it is connected to the trial coil of the transformer. Capacitive charging current for compensating for lines, restricting system voltage rises and operating overvoltage, ensuring reliable lines.
2, half-core dry series reactor: installed in the capacitor circuit, starting from the capacitor circuit. Read more
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