Design method of device for absorbing distributed capacitance energy

Abstract

The invention discloses a design method of a device for absorbing distributed capacitance energy. The method is based on ignition fault limiting current, the outer diameter of a high-voltage direct-current transmission line, the size of distributed capacitance of a high-voltage direct-current transmission system, the size of space for installing a buffer, the relative permeability of a buffer magnetic core material, the saturation magnetic flux density of the buffer magnetic core material and the width parameter of a magnetic ring of the buffer magnetic core. And calculating the number of magnetic rings and a secondary side resistance value required by the buffer of the distributed capacitance energy absorption device for the high-voltage direct-current transmission line to finish the design of the buffer.

Description

Technical Field

[0001] The present invention relates to a design method for a distributed capacitance energy absorption device, and designs buffer parameters for absorbing energy and surge current released by distributed capacitance of a high-voltage system in a spark failure of a high-voltage DC transmission line. Background Art

[0002] In high-voltage DC transmission systems, there is usually a certain amount of distributed capacitance. During the operation of the high-voltage DC transmission line, the distributed capacitance will store energy, and sparking faults occasionally occur on the high-voltage DC transmission line. The overcurrent caused by the sparking fault will trigger the overcurrent protection of the high-voltage power supply and shut it down. At this time, the energy stored in the distributed capacitance will still be released through the sparking arc and become the reason for maintaining the sparking arc flow. Strong sparking arc flow will cause further damage to the insulation of the ignition point and may have irreversible consequences. Therefore, measures must be taken to absorb the energy released by the distributed capacitance during the sparking fault of the high-voltage DC transmission line and suppress the sparking current. Generally speaking, the buffer composed of a magnetic core and a secondary circuit is one of the main devices for absorbing the distributed capacitance energy of the high-voltage DC transmission line. The current mainstream design method of this device is to design the buffer by calculating the eddy current, equivalent resistance and choke effect that the magnetic core can provide in detail. There are some correction parameters that have not yet been fully determined. Summary of the invention

[0003] The method provided by the present invention starts from the perspective of circuit peak current, assumes that the instantaneous equivalent inductance of the buffer at the peak current is an open circuit, calculates the magnetic flux required to prevent the buffer core from saturating in combination with the buffer secondary resistance, and further determines the remaining design parameters of the buffer.

[0004] The present invention discloses a design method for a device for absorbing distributed capacitance energy. The specific scheme is as follows: at the moment of the occurrence of the spark fault, due to the violent fluctuation of the spark current, the buffer equivalent inductance can be regarded as an open circuit, and the magnetic flux required to prevent the saturation of the magnetic core is calculated based on the initial voltage of the distributed capacitance, the distributed capacitance, and the secondary resistance value. The size of the magnetic ring constituting the buffer magnetic core is determined according to the space size of the buffer that can be installed on the high-voltage DC transmission line, and the magnetic flux that can be provided by a single magnetic ring is calculated in combination with the saturation magnetic flux density and relative magnetic permeability of the magnetic core material. The required number of magnetic rings can be calculated by combining the magnetic flux that can be provided by a single magnetic ring and the magnetic flux required to prevent the saturation of the magnetic core. Further, the equivalent inductance that can be provided by the buffer magnetic core can be calculated based on the total magnetic flux of the buffer magnetic core, and then the equivalent inductance provided by the buffer magnetic core and the secondary resistance mentioned above are used to simulate the spark fault current of the high-voltage transmission line, and the number of magnetic rings and the secondary resistance are further corrected.

[0005] The present invention has the following benefits:

[0006] According to the method provided by the present invention, the number of magnetic rings and the secondary resistance value of the buffer required to absorb the distributed capacitance energy of a high-voltage DC transmission line with an operating voltage of V and a distributed capacitance of C can be quickly calculated. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0008] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above-mentioned purpose, the present invention adopts the following technical scheme.

[0009] The present invention provides a design method for a distributed capacitance energy absorption device, which is used to design a buffer for absorbing distributed capacitance energy and suppressing surge current in a high-voltage DC transmission line. 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 that the buffer core can provide can be calculated. At the same time, the value of the buffer secondary resistance used to absorb the energy released by the distributed capacitance and further suppress the surge current can be obtained.

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

[0011] The method calculates the magnetic flux required to prevent the buffer core from saturating according to the distributed capacitance value, initial voltage value and secondary resistance value of the high-voltage direct current transmission system connected to the high-voltage direct current transmission line.

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

[0013] The present invention first assumes that at the moment of the occurrence of the ignition fault, due to the violent fluctuation of the ignition current, the buffer equivalent inductance can be regarded as an open circuit, and the magnetic flux required to prevent the saturation of the magnetic core is calculated based on the initial voltage of the distributed capacitor, the distributed capacitance, and the secondary resistance value. On the other hand, the size of the magnetic ring constituting the buffer magnetic core is determined according to the size of the space where the buffer can be installed on the high-voltage DC transmission line, and the magnetic flux that can be provided by a single magnetic ring is calculated in combination with the saturation magnetic flux density and relative magnetic permeability of the magnetic core material. The required number of magnetic rings can be calculated by combining the magnetic flux that can be provided by a single magnetic ring and the magnetic flux required to prevent the saturation of the magnetic core. Further, the equivalent inductance that can be provided by the buffer magnetic core can be calculated based on the total magnetic flux of the buffer magnetic core, and then the equivalent inductance provided by the buffer magnetic core and the secondary resistance mentioned above are used to simulate the ignition fault current of the high-voltage transmission line, and the number of magnetic rings and the secondary resistance are further corrected.

[0014] More specifically, the process of the present invention is as follows Figure 1 As shown in the figure, assuming that the working voltage of the high-voltage DC transmission line before the spark 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 inductance provided by the buffer core and the parallel connection of the secondary resistance, when the spark fault occurs, due to the rapid change of current, the buffer core equivalent inductance can be regarded as an open circuit, so according to the required spark fault limiting current I lim , so the value of the secondary resistance can be approximated as:

[0015] (1)

[0016] According to the secondary resistance R obtained from formula (1), the magnetic flux required to prevent the buffer core from saturation can be further calculated:

[0017] (2)

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

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

[0020] (3)

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

[0022] (4)

[0023] Assuming the saturation magnetic flux density of the magnetic material is B, 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 the magnetic ring can provide is:

[0028] (7)

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

[0030] (8)

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

Claims

1. A design method for absorbing distributed capacitance energy, characterized in that: At the moment when the spark fault occurs, the ignition current fluctuates violently, and the buffer equivalent inductance is regarded as an open circuit. The high-voltage DC transmission line is connected to the high-voltage DC transmission system, and the magnetic flux required to prevent the saturation of the magnetic core is calculated based on the initial voltage of the distributed capacitance, the distributed capacitance, and the secondary resistance value of the high-voltage DC transmission system; according to the space size of the buffer that can be installed on the high-voltage DC transmission line, the size of the magnetic ring constituting the buffer core is determined, and the magnetic flux that can be provided by a single magnetic ring is calculated in combination with the saturation magnetic flux density and relative magnetic permeability of the magnetic core material. The required number of magnetic rings is calculated in combination with the magnetic flux that can be provided by a single magnetic ring and the magnetic flux required to prevent the saturation of the magnetic core, and the equivalent inductance that can be provided by the buffer core is further calculated based on the total magnetic flux of the buffer core. The equivalent inductance provided by the buffer core and the secondary resistance are then used to simulate the spark fault current of the high-voltage DC transmission line, and the number of magnetic rings and the secondary resistance are further corrected.

2. The design method of a distributed capacitance energy absorption device according to claim 1, characterized in that: The working voltage of the high-voltage DC transmission system before the spark fault of the high-voltage DC transmission line occurs is V, that is, the initial voltage of the distributed capacitance. The distributed capacitance value of the high-voltage DC transmission system is C. The buffer is equivalent to the inductance provided by the buffer core and the parallel connection of the secondary resistance. When the spark fault occurs, due to the rapid change of the current, the buffer core equivalent inductance is regarded as an open circuit. Therefore, according to the required spark fault limiting current I lim , so 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 saturation is further obtained: （2） Among them, the unit of magnetic flux is Weber Wb; Assuming that the outer diameter of the high-voltage DC transmission line is r1 and the outer diameter of the installable buffer is r2, 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 that constitutes the buffer core is wound with magnetic conductive material. Due to the influence of the surface coating of the magnetic conductive material and the winding process, the actual magnetic conductive material in the magnetic ring has a duty cycle α. The thickness of the magnetic ring is d, and the effective magnetic conductive area of ​​a single magnetic ring with a width of W is: （4） Assuming the saturation magnetic flux density of the magnetic material is B, 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 the 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 that the relative magnetic permeability of the magnetic material is µ and the magnetic permeability of vacuum is µ0, the equivalent inductance that the magnetic core can provide is: （8） At this point, the number of magnetic rings required for the buffer core and the buffer secondary resistance value have been preliminarily calculated. The buffer secondary resistance is increased to 1.33R to prevent the buffer core saturation flux from increasing to 1.5 , at this time the number of magnetic rings required for the buffer core is 1.5n.

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