A design method for a distributed capacitance energy absorption device

Abstract

This invention discloses a design method for a device for absorbing distributed capacitance energy. Based on parameters such as arc fault limiting current, outer diameter of high-voltage DC transmission line, size of distributed capacitance of high-voltage DC transmission system, size of space available for installing buffer, relative permeability of buffer core material, saturation magnetic flux density of buffer core material, and width of buffer core ring, the method calculates the number of magnetic rings required for the buffer used in the device for absorbing distributed capacitance energy of high-voltage DC transmission line and the secondary resistance value, thus completing the design of the buffer.

Description

Technical Field

[0001] This invention relates to a design method for a device that absorbs distributed capacitance energy, and designs the parameters of a buffer for absorbing the energy released by the distributed capacitance of a high-voltage system and the surge current in a high-voltage DC transmission line arcing fault. Background Technology

[0002] In high-voltage direct current (HVDC) transmission systems, distributed capacitance typically exists. During HVDC transmission line operation, this distributed capacitance stores energy, and arcing faults occasionally occur. The overcurrent caused by arcing triggers the overcurrent protection of the high-voltage power supply, shutting it off. At this time, the energy stored in the distributed capacitance is still released through the arcing arc, contributing to the arcing current. A strong arcing current can further damage the insulation at the arcing point, potentially leading to irreversible consequences. Therefore, measures must be taken to absorb the energy released by the distributed capacitance during arcing faults in HVDC transmission lines and suppress the arcing current. Generally, a buffer consisting of a magnetic core and secondary circuitry is one of the main devices for absorbing distributed capacitance energy in HVDC transmission lines. The current mainstream design method for this device involves detailed calculations of the eddy currents, equivalent resistance, and choking effect provided by the magnetic core. However, some correction parameters are not yet fully determined. Summary of the Invention

[0003] The method provided by this invention starts from the perspective of the peak current of the circuit, assumes that the equivalent inductance of the buffer is open circuit at the instant of the peak current, calculates the magnetic flux required to prevent the magnetic core of the buffer from saturating by combining the secondary resistance of the buffer, and further determines the other design parameters of the buffer.

[0004] This invention discloses a design method for a device to absorb distributed capacitance energy. The specific scheme is as follows: At the instant of an arcing fault, due to the drastic fluctuation of the arcing current, the equivalent inductance of the buffer can be considered as an open circuit. Based on the initial voltage, distributed capacitance, and secondary resistance of the distributed capacitance, the magnetic flux required to prevent core saturation is calculated. The size of the magnetic rings constituting the buffer core is determined according to the space available for the buffer on the high-voltage DC transmission line. The magnetic flux provided by a single magnetic ring is calculated by combining the saturation magnetic flux density and relative permeability of the core material. The required number of magnetic rings can be calculated by combining the magnetic flux provided by a single magnetic ring with the magnetic flux required to prevent core saturation. Furthermore, the equivalent inductance provided by the buffer core can be calculated based on the total magnetic flux of the buffer core. Then, using the equivalent inductance provided by the buffer core and the aforementioned secondary resistance, the arcing fault current of the high-voltage transmission line is simulated, further correcting the number of magnetic rings and the secondary resistance.

[0005] The present invention has the following advantages:

[0006] According to the method provided by the present invention, the number of magnetic rings of the buffer and the secondary resistance value required to absorb the distributed capacitance energy of a high-voltage DC transmission line with a working voltage of V and a distributed capacitance of C can be calculated quickly. Attached Figure Description

[0007] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0008] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of the invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, the invention adopts the following technical solutions.

[0009] This invention provides a design method for a device that absorbs distributed capacitance energy, used to design a buffer for use in high-voltage DC transmission lines to absorb distributed capacitance energy and suppress surge current. According to this method, the magnetic flux required to prevent the buffer core from saturating and the corresponding number of magnetic rings can be designed, and the equivalent inductance provided by the buffer core can be calculated. Simultaneously, the value of the secondary resistance of the buffer used to absorb the energy released by the distributed capacitance and further suppress surge current can be determined.

[0010] This method is designed to address the situation of arcing and breakdown that occurs during high-voltage transmission. When the high-voltage power supply has completed overcurrent protection and been shut down, it absorbs the energy continuously provided by the distributed capacitance of the high-voltage system for the arcing arc and suppresses the surge current caused by the release of charge from the distributed capacitance.

[0011] This method calculates the magnetic flux required to prevent the buffer core from saturating based on the distributed capacitance, initial voltage, and secondary resistance of the high-voltage DC transmission system connected to the high-voltage DC transmission line.

[0012] This method determines the number of magnetic rings required to prevent buffer core saturation based on the saturation magnetic flux density and relative permeability of the selected core material. The specifications of the magnetic rings are determined according to the space available on the high-voltage DC transmission line.

[0013] This invention begins by assuming that at the instant of an arcing failure, due to the drastic fluctuation of the arcing current, the equivalent inductance of the buffer can be considered as an open circuit. The magnetic flux required to prevent core saturation is calculated based on the initial voltage of the distributed capacitance, the distributed capacitance, and the secondary resistance. On the other hand, the size of the magnetic rings constituting the buffer core is determined according to the available space for the buffer on the high-voltage DC transmission line. The magnetic flux provided by a single magnetic ring is calculated by combining the saturation magnetic flux density and relative permeability of the core material. The required number of magnetic rings can be calculated by combining the magnetic flux provided by a single magnetic ring with the magnetic flux required to prevent core saturation. Furthermore, the equivalent inductance provided by the buffer core can be calculated based on the total magnetic flux of the buffer core. Then, using the equivalent inductance provided by the buffer core and the aforementioned secondary resistance, the arcing failure current of the high-voltage transmission line is simulated, further correcting the number of magnetic rings and the secondary resistance.

[0014] More specifically, the process of this invention is as follows: Figure 1 As shown, assuming the operating voltage of the high-voltage DC transmission line before the arcing fault occurs is V, and the distributed capacitance of the high-voltage DC transmission system is C, since the buffer itself can be equivalent to the parallel connection of the inductance provided by the buffer core and the secondary resistance, due to the rapid change in current during the arcing fault, the equivalent inductance of the buffer core can be regarded as an open circuit. Therefore, according to the required arcing fault limiting current I... lim Therefore, the value of the secondary resistance can be approximated as:

[0015] (1)

[0016] Based on the secondary resistance R obtained from formula (1), the magnetic flux required to prevent the buffer core from saturating can be further derived:

[0017] (2)

[0018] The unit of magnetic flux is Weber (Wb).

[0019] Assuming the outer diameter of the high-voltage DC transmission line is r1 and the outer diameter of the installable buffer is r2, then the thickness d of the magnetic ring is:

[0020] (3)

[0021] The magnetic ring constituting the buffer core is made of a magnetically conductive material. Due to the influence of the surface coating of the magnetically conductive material and the winding process, the actual magnetically conductive material in the magnetic ring has a duty cycle α. The thickness of the magnetic ring is d. Then, the effective magnetic conductive area of ​​a single magnetic ring with a width W is:

[0022] (4)

[0023] Let the saturation magnetic flux density of the magnetically conductive material be B, then the saturation magnetic flux of a single magnetic ring is:

[0024] (5)

[0025] Therefore, the number of magnetic rings required to prevent the buffer core from saturating is:

[0026] (6)

[0027] The magnetic circuit length that a magnetic ring can provide is:

[0028] (7)

[0029] Assuming the relative permeability of the magnetic material is µ and the permeability of free space is µ0, the equivalent inductance that the magnetic core can provide is:

[0030] (8)

[0031] At this point, the required number of magnetic rings for the buffer core and the secondary resistance value of the buffer have been preliminarily calculated. Since the equivalent inductance of the buffer core was considered an open circuit when calculating the secondary resistance earlier, but in reality, this equivalent inductance is not completely open, the secondary resistance of the buffer is increased to 1.33R to prevent the saturation flux of the buffer core from increasing to 1.5. At this point, the required number of magnetic rings for the buffer core is 1.5n. The buffer design is now complete.

Claims

1. A design method for a device for absorbing distributed capacitance energy, characterized in that, At the moment of ignition failure, the drastic fluctuation of the ignition current is considered as an open circuit. The high-voltage DC transmission line is connected to the high-voltage DC transmission system. Based on the initial voltage, distributed capacitance, and secondary resistance of the high-voltage DC transmission system, the magnetic flux required to prevent core saturation is calculated. The size of the magnetic rings constituting the buffer core is determined according to the space available for the buffer on the high-voltage DC transmission line. The magnetic flux provided by a single magnetic ring is calculated based on the saturation magnetic flux density and relative permeability of the core material. The required number of magnetic rings is calculated based on the magnetic flux provided by a single magnetic ring and the magnetic flux required to prevent core saturation. The equivalent inductance provided by the buffer core is then calculated based on the total magnetic flux of the buffer core. Finally, using the equivalent inductance provided by the buffer core and the secondary resistance, the ignition failure current of the high-voltage DC transmission line is simulated, further correcting the number of magnetic rings and the secondary resistance.

2. The design method of a distributed capacitance energy absorption device according to claim 1, characterized in that, Before an arcing fault occurs in a high-voltage direct current (HVDC) transmission line, the operating voltage of the HVDC transmission system is V, which is the initial voltage of the distributed capacitance. The distributed capacitance of the HVDC transmission system is C. The buffer is equivalent to the parallel connection of the inductance provided by the buffer core and the secondary resistance. When an arcing fault occurs, due to the rapid change in current, the equivalent inductance of the buffer core is considered to be an open circuit. Therefore, according to the required arcing fault limiting current I... lim Therefore, the value of the secondary resistance is: （1）。 3. The design method of a distributed capacitance energy absorption device according to claim 2, characterized in that, Based on the secondary resistance R obtained from formula (1), the magnetic flux required to prevent the buffer core from saturating can be further derived: （2） The unit of magnetic flux is Weber (Wb). Assuming the outer diameter of the high-voltage DC transmission line is r1 and the outer diameter of the installable buffer is r2, then the thickness d of the magnetic ring is: （3）。 4. The design method of a distributed capacitance energy absorption device according to claim 3, characterized in that, The magnetic ring constituting the buffer core is made of a magnetically conductive material. Due to the influence of the surface coating of the magnetically conductive material and the winding process, the actual magnetically conductive material in the magnetic ring has a duty cycle α. The thickness of the magnetic ring is d. Then, the effective magnetic conductive area of ​​a single magnetic ring with a width W is: （4） Let the saturation magnetic flux density of the magnetically conductive material be B, then the saturation magnetic flux of a single magnetic ring is: （5） Therefore, the number of magnetic rings required to prevent the buffer core from saturating is: （6） The magnetic circuit length that a magnetic ring can provide is: （7）。 5. The design method of a distributed capacitance energy absorption device according to claim 4, characterized in that, Assuming the relative permeability of the magnetic material is µ and the permeability of free space is µ0, the equivalent inductance that the magnetic core can provide is: （8） At this point, the required number of magnetic rings for the buffer core and the secondary resistance value of the buffer have been preliminarily calculated. The secondary resistance of the buffer is increased to 1.33R to prevent the saturation flux of the buffer core from increasing to 1.

5. At this point, the number of magnetic rings required for the buffer core is 1.5n.

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