A DC lightning arrester and a lightning arrester voltage equalization method

Abstract

A DC lightning arrester includes an arrester body, wherein the arrester body includes a fixed element and a controlled element, and is characterized in that the arrester further includes: a thyristor-controlled switch branch connected in parallel with the controlled element; a voltage-equalizing branch connected in parallel with the fixed element; and voltage equalization of the fixed element and the controlled element in the arrester body is achieved by adjusting the number of series and / or parallel connections of voltage-equalizing resistors in the voltage-equalizing branch. This prevents the fixed element of the arrester from having a high partial pressure under steady-state conditions, thereby increasing leakage current.

Description

Technical Field

[0001] The present invention relates to the field of direct current lightning arresters for hybrid ultra-high voltage direct current power transmission projects, and in particular to a direct current lightning arrester and a lightning arrester voltage balancing method. Background Art

[0002] HVDC transmission technology mainly includes traditional HVDC transmission based on ordinary thyristor converter valves and flexible DC transmission based on new power electronic device converter valves with shutoff capability. Both have their own advantages and disadvantages and applicable occasions. In order to give full play to the advantages of both and provide a more flexible transmission method, a hybrid multi-terminal ultra-high voltage DC transmission system composed of traditional DC and flexible DC came into being. With the continuous development of hybrid multi-terminal ultra-high voltage DC transmission technology and the increasing number of future planned projects, its reliability will become an important factor affecting the safe and reliable operation of the entire power system. Considering the overvoltage of the hybrid DC converter valve under various transient, steady and various abnormal operating conditions, a DC lightning arrester based on thyristor control is connected in parallel to the DC side bus of the flexible DC converter valve.

[0003] From the structural topology and working principle of the lightning arrester, it can be seen that the lightning arrester bears a DC working voltage for a long time in a steady state. Due to the influence of devices such as the thyristor off-state resistance and the voltage-equalizing resistor in the thyristor trigger switch in parallel with the controlled element, the voltage division of the fixed element is higher under steady-state conditions, resulting in an increase in leakage current, which in turn affects the stable performance of the lightning arrester resistor under long-term working conditions. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a DC arrester, comprising an arrester body, wherein the arrester body comprises a fixed element and a controlled element, and is characterized in that the arrester further comprises:

[0005] a thyristor controlled switch branch connected in parallel with the controlled element;

[0006] A voltage balancing branch connected in parallel with the fixed element;

[0007] By adjusting the number of series and / or parallel connections of the voltage-equalizing resistors in the voltage-equalizing branch, voltage equalization of the fixed components and the controlled components in the arrester body can be achieved.

[0008] Preferably, the voltage balancing branch includes:

[0009] Multi-stage series resistance structure;

[0010] Each level of the resistance structure includes a plurality of voltage-equalizing resistors connected in parallel;

[0011] The number of series-connected stages of the resistor structure and / or the number of parallel-connected voltage-equalizing resistors in each stage of the resistor structure are configured according to the expected resistance value of the voltage-equalizing branch.

[0012] Preferably, the expected resistance value of the voltage-sharing branch is determined according to the off-state resistance value R of the thyristor in the thyristor-controlled switch branch. T , the voltage-equalizing resistor value R in the thyristor-controlled switch branch p , and the damping ratio of the fixed element to the controlled element is determined.

[0013] Preferably, the thyristor controlled switch branch comprises:

[0014] Thyristor;

[0015] A saturable reactor connected in series with the thyristor;

[0016] As well as a resistor-capacitor structure and a voltage-equalizing resistor connected in parallel with the thyristor.

[0017] Preferably, the lightning arrester further comprises:

[0018] A bypass switch connected in parallel with the controlled element.

[0019] Preferably, the fixed element and the controlled element respectively include a plurality of resistors connected in series.

[0020] Based on the same idea, the present invention provides a voltage equalization method for a DC lightning arrester, comprising:

[0021] When the arrester is in a steady-state condition, the thyristor is controlled to be in an off state by using the thyristor-controlled switch branch, and the damping ratio of the fixed element and the controlled element in the arrester body, the off-state resistance value of the thyristor in the thyristor-controlled switch branch, and the voltage-sharing resistance value of the thyristor-controlled switch branch are obtained;

[0022] Determining an expected resistance value of a voltage balancing branch connected in parallel with the fixed element based on the damping ratio, the off-state resistance value, and the resistance value of the thyristor-controlled switch branch;

[0023] By adjusting the number of series and / or parallel connections of the voltage-equalizing resistors in the voltage-equalizing branch, the resistance value of the voltage-equalizing branch reaches the expected resistance value, so as to realize voltage equalization of the fixed elements and the controlled elements in the arrester body.

[0024] Preferably, the calculation formula of the expected resistance value is as follows:

[0025]

[0026] In the formula, R q : is the expected resistance value; R T is the off-state resistance of the thyristor in the thyristor-controlled switch branch, R p is the voltage-equalizing resistor value in the thyristor-controlled switch branch, and m and n are the number of resistors connected in series in the fixed element and the controlled element, respectively.

[0027] Preferably, the step of adjusting the number of series and / or parallel connections of the voltage balancing resistors in the voltage balancing branch includes:

[0028] When the off-state resistance of the thyristor decreases, the number of series-connected resistance structures is reduced and / or the number of parallel-connected voltage-equalizing resistances in each resistance structure is increased;

[0029] On the contrary, the number of series-connected resistance structures is increased and / or the number of parallel-connected voltage-equalizing resistors in each resistance structure is reduced.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] A DC lightning arrester includes an arrester body, wherein the arrester body includes a fixed element and a controlled element, and is characterized in that the arrester further includes: a thyristor-controlled switch branch connected in parallel with the controlled element; a voltage-equalizing branch connected in parallel with the fixed element; and voltage equalization of the fixed element and the controlled element in the arrester body is achieved by adjusting the number of series and / or parallel connections of voltage-equalizing resistors in the voltage-equalizing branch. This prevents the fixed element of the arrester from having a high partial pressure under steady-state conditions, thereby increasing leakage current. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the topological structure diagram of the DC lightning arrester;

[0033] Figure 2 Resistor Rq structure topology diagram. DETAILED DESCRIPTION

[0034] In order to better understand the present invention, the content of the present invention is further described below in conjunction with the accompanying drawings and examples.

[0035] Embodiment 1:

[0036] The present invention provides a DC lightning arrester, such as Figure 1 As shown, it includes a lightning arrester body connected in parallel to the DC side busbar of the flexible DC converter valve, wherein the flexible DC converter valve is connected between the DC system and the AC system, and the lightning arrester body includes a fixed element and a controlled element, and is characterized in that the lightning arrester also includes:

[0037] a thyristor controlled switch branch connected in parallel with the controlled element;

[0038] A voltage balancing branch connected in parallel with the fixed element;

[0039] By adjusting the number of series and / or parallel connections of the voltage-equalizing resistors in the voltage-equalizing branch, voltage equalization of the fixed components and the controlled components in the arrester body can be achieved.

[0040] Among them, when the lightning arrester is in a steady-state condition, the thyristor is controlled to be in a disconnected state (referred to as the off state) through the thyristor-controlled switch branch. When a fault occurs in the flexible DC converter valve, the DC system and / or the AC system, the thyristor is controlled to close through the thyristor-controlled switch branch to achieve diversion of the fault current.

[0041] Preferably, the voltage balancing branch includes:

[0042] Multi-stage series resistance structure;

[0043] Each level of the resistance structure includes a plurality of voltage-equalizing resistors connected in parallel;

[0044] As stated Figure 2 The number of series-connected resistor structures and / or the number of parallel-connected voltage-equalizing resistors in each resistor structure are configured according to the expected resistance value of the voltage-equalizing branch.

[0045] Preferably, the expected resistance value of the voltage balancing branch is determined according to the off-state resistance value of the thyristor in the thyristor-controlled switch branch, the voltage balancing resistance value in the thyristor-controlled switch branch, and the damping ratio of the fixed element to the controlled element.

[0046] Preferably, the thyristor controlled switch branch comprises:

[0047] Thyristor and a resistor-capacitor structure and a voltage-equalizing resistor connected in parallel with the thyristor.

[0048] Preferably, the thyristor controlled switch branch further includes:

[0049] A bypass switch connected in parallel with the thyristor;

[0050] When the arrester is in a steady-state condition, the bypass switch is controlled to be in an open state (referred to as the off state). When a fault occurs in the flexible DC converter valve, the DC system and / or the AC system, the bypass switch is controlled to be closed to further divert the fault current.

[0051] Preferably, the fixed element and the controlled element respectively include a plurality of resistors connected in series.

[0052] Embodiment 2:

[0053] Based on the same inventive concept, the present invention also provides a lightning arrester voltage equalization method, comprising:

[0054] Obtaining the damping ratio of the fixed element and the controlled element in the arrester body, the off-state resistance value of the thyristor in the thyristor-controlled switch branch, and the resistance value of the thyristor-controlled switch branch;

[0055] Determining an expected resistance value of a voltage balancing branch connected in parallel with the fixed element based on the damping ratio, the off-state resistance value, and the resistance value of the thyristor-controlled switch branch;

[0056] By adjusting the number of series and / or parallel connections of the voltage-equalizing resistors in the voltage-equalizing branch, the resistance value of the voltage-equalizing branch reaches the expected resistance value, so as to realize voltage equalization of the fixed elements and the controlled elements in the arrester body.

[0057] Preferably, the calculation formula of the expected resistance value is as follows:

[0058]

[0059] In the formula, R q : is the expected resistance value; R T is the off-state resistance of the thyristor in the thyristor-controlled switch branch, R p is the voltage-equalizing resistor value in the thyristor-controlled switch branch, and m and n are the number of resistors connected in series in the fixed element and the controlled element, respectively.

[0060] Preferably, the step of adjusting the number of series and / or parallel connections of the voltage balancing resistors in the voltage balancing branch includes:

[0061] When the off-state resistance of the thyristor decreases, the number of series-connected resistance structures is reduced and / or the number of parallel-connected voltage-equalizing resistances in each resistance structure is increased;

[0062] On the contrary, the number of series-connected resistance structures is increased and / or the number of parallel-connected voltage-equalizing resistors in each resistance structure is reduced.

[0063] Embodiment 3:

[0064] This arrester is a typical large-capacity multi-column parallel arrester. It changes the residual voltage by controlling the number of resistors in series, thereby limiting the bus overvoltage under different system faults. The primary side of the arrester is mainly composed of fixed components, controlled components, and control switches (composed of thyristor trigger switches and bypass switches), among which fixed components and controlled components are also called arrester bodies. Its working principle is that when the system is in a steady-state condition, the arrester is subjected to the bus DC voltage for a long time, and only leakage current flows through the arrester components; when an AC or DC fault occurs in the system, the arrester residual voltage is reduced by closing the fast switch in parallel with the controlled component, consuming surplus power and suppressing the parallel bus overvoltage. After the fault is crossed, the control switch is opened and the arrester returns to its initial state.

[0065] Metal oxide resistors will gradually age and even eventually cause thermal collapse when charged for a long time during normal operation, which is the main factor determining the life of the arrester. The speed of aging depends on the long-term system operating voltage and the long-term charge of the resistor. In order to ensure the life of the resistor, its long-term operating voltage must be limited. The charge rate refers to the ratio of the long-term operating voltage peak to the operating voltage λ.

[0066] The arrester topology is as follows Figure 1 As shown, MOA1: fixed element, MOA2: controlled element, K1: thyristor trigger switch, K2: bypass switch; T: thyristor, Lv: saturated reactor, R D : Damping resistance, C D : Damping capacitor, R p : Voltage equalizing resistor.

[0067] 1. Design principles

[0068] It is known that this type of arrester is connected in parallel to the busbar side of the DC system converter valve. The fixed component working voltage U1, the controlled component voltage U2, and the busbar working voltage Ub have the following voltage relationship:

[0069] U1+U2=U b (1)

[0070] The voltage division of the fixed element and the controlled element is determined by the number of resistors connected in series to each other. Suppose the number of resistors connected in series to the fixed element is m, and the number of resistors connected in series to the controlled element is n.

[0071]

[0072]

[0073]

[0074] Where:

[0075] R MOV1 : Fixed component resistance;

[0076] R MOV2 : Resistance of the controlled element.

[0077] The design principles are as follows:

[0078] λ1=U1 / U a1 =U2 / U a2 =λ2≤λ o (5)

[0079] Where:

[0080] λ1: fixed component charge rate;

[0081] λ2: charging rate of the controlled element;

[0082] U a1 : Fixed element action voltage;

[0083] U a2 : Action voltage of controlled element;

[0084] λ o : Maximum value of the arrester charging rate.

[0085] The long-term charge rate of the arrester must be lower than λ o In order to ensure the stability of metal oxides.

[0086] 2. Voltage division optimization method

[0087] Depend on Figure 1 It can be seen that the controlled element needs to be connected in parallel with the control switch. K2 is a bypass switch, which is open circuit under steady-state conditions and has no effect on the voltage division of the arrester body components. K1 is a thyristor trigger switch. Under steady-state DC voltage, the thyristor T is not conducting and works in the off state for a long time, showing a high impedance state to the outside. The damping capacitor C D With damping resistor R D The external characteristic of the branch is open circuit, and the voltage balancing resistor R p is the DC resistance. From the above, we can know that the off-state resistance R of thyristor T T With the voltage balancing resistor R p It will affect the steady-state DC voltage division of the arrester.

[0088] When K1 exists, assuming the working voltage of the fixed element of the arrester is U1′ and the working voltage of the controlled element is U2′, the following derivation can be obtained.

[0089]

[0090]

[0091] Known

[0092]

[0093] therefore

[0094] U1′>U1 (9)

[0095]

[0096] When K1 exists, the partial pressure of the fixed element increases and λ1 increases.

[0097] In order to reduce the steady-state charge rate of the fixed part, a resistor R is connected in parallel to the fixed element. q ,like Figure 1 To minimize the voltage divider effect caused by K1, the resistor R q The resistance value should be based on the thyristor off-state resistance R T With the voltage balancing resistor R p For matching, the following relationship exists.

[0098]

[0099] Thus, the following deduction is made:

[0100]

[0101] Substituting equations (2) and (11) into equation (12), we can obtain

[0102]

[0103] Resistor R q The steady-state voltage division effect of this type of arrester due to the introduction of the control switch is reduced, and the steady-state charge rate of the fixed components is reduced.

[0104] 3. Resistance Rq resistance adjustment design

[0105] Thyristor is a nonlinear element. When the ambient temperature is lower than a certain value, the off-state resistance basically does not change. When the ambient temperature is higher than a certain value, the resistance value decreases or even decreases from megohm to kilohm level. In order to ensure the charge rate of the arrester element under any ambient temperature, this patent proposes a method to adjust R q The resistance value is used to reduce the impact of the nonlinear characteristics of the thyristor's off-state resistance.

[0106] Resistor R q Like Figure 2 The device series-parallel design is composed of class a parallel class b series resistors. When the arrester is in steady-state operation, if the ambient temperature is higher than a certain value due to special circumstances, the off-state resistance of the thyristor decreases. The resistance R can be reduced by increasing the parallel number a of the resistor device or reducing the series number b. q Otherwise, the resistance value will be increased, so as to minimize the influence of K1 on the charging rate of the arrester.

[0107] Obviously, the described embodiments are only some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0108] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0109] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0110] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0111] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0112] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. A DC lightning arrester, comprising an arrester body, wherein the arrester body comprises a fixed element and a controlled element, wherein: The lightning arrester also includes: a thyristor controlled switch branch connected in parallel with the controlled element; A voltage balancing branch connected in parallel with the fixed element; By adjusting the number of series and / or parallel connections of the voltage-equalizing resistors in the voltage-equalizing branch, voltage equalization of the fixed components and the controlled components in the arrester body can be achieved; The voltage balancing branch comprises: Multi-stage series resistance structure; Each level of the resistance structure includes a plurality of voltage-equalizing resistors connected in parallel; The number of series-connected stages of the resistance structure and / or the number of parallel-connected voltage-equalizing resistors in each stage of the resistance structure are configured according to the expected resistance value of the voltage-equalizing branch; The expected resistance value of the voltage-equalizing branch is determined according to the off-state resistance value of the thyristor in the thyristor-controlled switch branch, the voltage-equalizing resistance value in the thyristor-controlled switch branch, and the damping ratio of the fixed element to the controlled element; The thyristor controlled switch branch comprises: Thyristor; A saturable reactor connected in series with the thyristor; and a resistor-capacitor structure and a voltage-equalizing resistor connected in parallel with the thyristor; The lightning arrester further comprises: A bypass switch connected in parallel with the controlled element; The fixed element and the controlled element respectively include a plurality of resistor sheets connected in series.

2. A voltage equalization method for a DC lightning arrester, applied to the lightning arrester as claimed in claim 1, characterized in that: include: When the arrester is in a steady-state condition, the thyristor is controlled to be in an off state by using the thyristor-controlled switch branch, and the damping ratio of the fixed element and the controlled element in the arrester body, the off-state resistance value of the thyristor in the thyristor-controlled switch branch, and the voltage-sharing resistance value of the thyristor-controlled switch branch are obtained; Determining an expected resistance value of a voltage balancing branch connected in parallel with the fixed element based on the damping ratio, the off-state resistance value, and the resistance value of the thyristor-controlled switch branch; By adjusting the number of series and / or parallel connections of the voltage-equalizing resistors in the voltage-equalizing branch, the resistance value of the voltage-equalizing branch reaches the expected resistance value, so as to realize voltage equalization of the fixed element and the controlled element in the arrester body; The expected resistance value is calculated as follows: In the formula, R q : is the expected resistance value; R T is the off-state resistance of the thyristor in the thyristor-controlled switch branch, R P is the voltage-equalizing resistor value in the thyristor-controlled switch branch, m and n are the number of resistors connected in series in the fixed element and the controlled element respectively; The step of adjusting the number of series and / or parallel connections of the voltage balancing resistors in the voltage balancing branch includes: When the off-state resistance of the thyristor decreases, the number of series-connected resistance structures is reduced and / or the number of parallel-connected voltage-equalizing resistances in each resistance structure is increased; On the contrary, the number of series-connected resistance structures is increased and / or the number of parallel-connected voltage-equalizing resistors in each resistance structure is reduced.

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