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Dry-type air-core reactor used in railway power supply system


2021-02-08

I. Overview

1.1. In order to ensure the normal operation of the train, the voltage of the traction network should not be lower than 21kV at any point, and in the most serious case, it should not be lower than 19kV. Therefore, we must increase the voltage of the traction network. Generally, the method of parallel capacitance compensation is used to increase the voltage of the traction network.

1.2. The connection method of the capacitor compensation device in the substation is shown in Figure 1. Capacitors C1 and C2 are compensation capacitors, L1 and L2 are discharge coils, and DK is a filter reactor.

 

2. Wiring method

2.1. The function of the reactor is to filter out the high-order harmonics generated by electric locomotives and reduce the impact of high-order harmonics on the power system. In recent years, a new type of outdoor dry-type air-core reactor has emerged. This type of reactor overcomes the shortcomings of oil-filled reactors and has the advantages of low noise and convenient maintenance. However, this type of reactor also has its shortcomings: it is difficult to test the inductance of the reactor on site, and it has been found in practice that this type of dry-type air-core reactor is not suitable for the use of iron grids.

2.2. When the reactor is put into operation, a current i that changes sinusoidally with time is added to the reactor, which is expressed as: where ω=2πf and i is the initial phase angle.

2.3. The reactor adds current i, which enters from the head end (end A or B), and flows out from the tail end (DA or DB). Then, the magnetic flux Φ is generated in the reactor coil. According to the law of electromagnetic induction, an electric potential is induced at both ends of the coil ADA (or BDB) along the direction of the voltage drop of the reactor coil, and the magnetic flux is: Φ=Φmsinωt.

 

3. The detailed description

3.1. We know that when building a magnetic field, only reactive power needs to be sent from the power supply. Therefore, the current that generates the magnetic flux Φm is in phase with the magnetic flux Φm, and the phase behind the voltage source voltage UA is 90º, which is called the magnetizing current, denoted by Iro, and also called the reactive component of the excitation current. The permeability μ of ferromagnetic materials is much larger than that of non-ferromagnetic materials, about several hundred times. Under alternating magnetization conditions, there is hysteresis in the iron grid, and there is hysteresis loss. In addition to the reactive power sent from the power supply to the establishment of the magnetic flux Φm, active power must also be sent to provide the active power required for the hysteresis loss in the grid. Obviously, the active power can only be sent in through a current that has the same phase as the power source UA. In addition, due to the alternating magnetic flux Φm, there is still a large eddy current in the grid, and a large heat loss is also generated under the action of the eddy current, that is, the eddy current loss.

3.2. The current of hysteresis loss and eddy current loss in the grid is called the active component Ioa of the excitation current. The result of hysteresis and eddy current loss consumes active power, which is converted into heat in the grid. The grid is made of iron material, and the permeability μ is very large. During the magnetization process, the magnetic domains in the ferromagnetic material are arranged according to the applied magnetic field. Due to the reciprocating swing of the magnetic domains, a certain amount of energy is consumed when they encounter resistance between each other. This part of the energy lost in the form of heat generated by the hysteresis phenomenon is the hysteresis loss. The higher the frequency of reciprocating alternating magnetization, the greater the hysteresis loss. It can be proved that the hysteresis loss is proportional to the frequency of the current used during magnetization, so the hysteresis loss in the grid is lost in the form of heat. In addition, when the Φm of the alternating magnetic flux passes through the cross section of the grid, induced current is generated on the cross section. Under the action of the eddy current, heat loss, that is, eddy current loss, occurs. The eddy current loss is proportional to the square of the current frequency in the reactor coil, and the grid is a closed loop composed of ferrous materials with strong magnetic permeability, so that the eddy current generated by Φm is also relatively large, that is, Ioa is relatively large. It can be seen from IA=Ior+Ioa that when Ioa increases, if IA does not change, Ior will decrease accordingly. In other words, the active component of the excitation current IA=Ior+Ioa of the reactor increases, and the reactive component decreases. This is very unfavorable for the substation. The active component in the grid will be transformed into a large Heat.

3.3. We have no specific measurement of this active power component, but judging from the on-site operation, when the reactor is put into operation, the grid vibrates, and the insulating porcelain bottle at the bottom of the reactor vibrates relatively loudly (a louder vibration sound is emitted). ), meanwhile the grid heats up. The longer the reactor is put in, the hotter the grid will be, the lock of the grid door will become red hot, and the grid will be hot. In response to the above situation, we replaced all the grids and replaced them with brick walls. In this way, it is not only economical, economical, and beautiful, but also all the disadvantages we analyzed above are eliminated, and it is safer and more reliable for people and equipment. Practical applications have proved that this is an effective and good method to ensure the safe and reliable operation of dry-type air-core reactors.

 

I. Overview

1.1. In order to ensure the normal operation of the train, the voltage of the traction network should not be lower than 21kV at any point, and in the most serious case, it should not be lower than 19kV. Therefore, we must increase the voltage of the traction network. Generally, the method of parallel capacitance compensation is used to increase the voltage of the traction network.

1.2. The connection method of the capacitor compensation device in the substation is shown in Figure 1. Capacitors C1 and C2 are compensation capacitors, L1 and L2 are discharge coils, and DK is a filter reactor.

 

2. Wiring method

2.1. The function of the reactor is to filter out the high-order harmonics generated by electric locomotives and reduce the impact of high-order harmonics on the power system. In recent years, a new type of outdoor dry-type air-core reactor has emerged. This type of reactor overcomes the shortcomings of oil-filled reactors and has the advantages of low noise and convenient maintenance. However, this type of reactor also has its shortcomings: it is difficult to test the inductance of the reactor on site, and it has been found in practice that this type of dry-type air-core reactor is not suitable for the use of iron grids.

2.2. When the reactor is put into operation, a current i that changes sinusoidally with time is added to the reactor, which is expressed as: where ω=2πf and i is the initial phase angle.

2.3. The reactor adds current i, which enters from the head end (end A or B), and flows out from the tail end (DA or DB). Then, the magnetic flux Φ is generated in the reactor coil. According to the law of electromagnetic induction, an electric potential is induced at both ends of the coil ADA (or BDB) along the direction of the voltage drop of the reactor coil, and the magnetic flux is: Φ=Φmsinωt.

 

3. The detailed description

3.1. We know that when building a magnetic field, only reactive power needs to be sent from the power supply. Therefore, the current that generates the magnetic flux Φm is in phase with the magnetic flux Φm, and the phase behind the voltage source voltage UA is 90º, which is called the magnetizing current, denoted by Iro, and also called the reactive component of the excitation current. The permeability μ of ferromagnetic materials is much larger than that of non-ferromagnetic materials, about several hundred times. Under alternating magnetization conditions, there is hysteresis in the iron grid, and there is hysteresis loss. In addition to the reactive power sent from the power supply to the establishment of the magnetic flux Φm, active power must also be sent to provide the active power required for the hysteresis loss in the grid. Obviously, the active power can only be sent in through a current that has the same phase as the power source UA. In addition, due to the alternating magnetic flux Φm, there is still a large eddy current in the grid, and a large heat loss is also generated under the action of the eddy current, that is, the eddy current loss.

3.2. The current of hysteresis loss and eddy current loss in the grid is called the active component Ioa of the excitation current. The result of hysteresis and eddy current loss consumes active power, which is converted into heat in the grid. The grid is made of iron material, and the permeability μ is very large. During the magnetization process, the magnetic domains in the ferromagnetic material are arranged according to the applied magnetic field. Due to the reciprocating swing of the magnetic domains, a certain amount of energy is consumed when they encounter resistance between each other. This part of the energy lost in the form of heat generated by the hysteresis phenomenon is the hysteresis loss. The higher the frequency of reciprocating alternating magnetization, the greater the hysteresis loss. It can be proved that the hysteresis loss is proportional to the frequency of the current used during magnetization, so the hysteresis loss in the grid is lost in the form of heat. In addition, when the Φm of the alternating magnetic flux passes through the cross section of the grid, induced current is generated on the cross section. Under the action of the eddy current, heat loss, that is, eddy current loss, occurs. The eddy current loss is proportional to the square of the current frequency in the reactor coil, and the grid is a closed loop composed of ferrous materials with strong magnetic permeability, so that the eddy current generated by Φm is also relatively large, that is, Ioa is relatively large. It can be seen from IA=Ior+Ioa that when Ioa increases, if IA does not change, Ior will decrease accordingly. In other words, the active component of the excitation current IA=Ior+Ioa of the reactor increases, and the reactive component decreases. This is very unfavorable for the substation. The active component in the grid will be transformed into a large Heat.

3.3. We have no specific measurement of this active power component, but judging from the on-site operation, when the reactor is put into operation, the grid vibrates, and the insulating porcelain bottle at the bottom of the reactor vibrates relatively loudly (a louder vibration sound is emitted). ), meanwhile the grid heats up. The longer the reactor is put in, the hotter the grid will be, the lock of the grid door will become red hot, and the grid will be hot. In response to the above situation, we replaced all the grids and replaced them with brick walls. In this way, it is not only economical, economical, and beautiful, but also all the disadvantages we analyzed above are eliminated, and it is safer and more reliable for people and equipment. Practical applications have proved that this is an effective and good method to ensure the safe and reliable operation of dry-type air-core reactors.