Insulation matching device and method for extra-high voltage flexible direct current converter station

Abstract

The invention discloses an extra-high voltage flexible DC converter station insulation cooperation device and method. The extra-high voltage flexible direct current converter station insulation matching device comprises a positive electrode extra-high voltage flexible direct current system and a negative electrode extra-high voltage flexible direct current system, and each of the positive electrode extra-high voltage flexible direct current system and the negative electrode extra-high voltage flexible direct current system comprises a lightning arrester, the configuration parameters comprise the highest continuous operation voltage, the reference voltage, the operation impact protection level, the matching current and the energy at different lightning arrester positions and the operation impact insulation level needing to be tolerated by the lightning arrester at each position. Lightning arresters with configuration parameters meeting the performance design indexes of the extra-high voltage flexible direct current system are installed at different positions of the extra-high voltage flexible direct current converter station, and insulation cooperation of the extra-high voltage flexible direct current converter station is achieved through multiple types of lightning arresters which are installed at different positions and have reasonable parameters and mutual cooperation. And the insulation level of the extra-high voltage flexible direct current equipment and the economic cost of the whole-station equipment are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible DC transmission, and particularly to an insulation coordination device and method for a UHV flexible DC converter station. Background Art

[0002] In recent years, large-scale energy development has taken place in the western region of China, but the local power consumption capacity is insufficient, and there is an urgent need for long-distance transmission of a large amount of electric power resources. Flexible DC transmission can be adjusted flexibly and quickly, has strong system adaptability, and does not have commutation failure problems. It is particularly suitable for connecting to AC systems containing large-scale new energy and DC multi-infeed AC systems. With the successful development of 5kA IGBTs, the transmission capacity of flexible DC has been greatly improved, and UHV flexible DC will play an increasingly important role in the new power system in the future.

[0003] The insulation level of the UHV flexible DC system determines the equipment cost of the UHV flexible DC converter station and the air clear distance of the UHV flexible DC converter station, directly affecting the overall cost of the UHV flexible DC converter station. Especially for UHV flexible DC converter stations in high-altitude areas of 4000m, after altitude correction, the insulation level will become a decisive factor restricting the cost and land occupation. Adopting a reasonable insulation coordination scheme and optimization measures to suppress the transient overvoltage of the DC system can significantly improve the project economy. Summary of the Invention

[0004] The present invention provides an insulation coordination device and method for a UHV flexible DC converter station to solve the technical problems of high overvoltage, high equipment manufacturing difficulty and high economic cost existing in the existing UHV flexible DC converter station.

[0005] The present invention provides an insulation coordination device for a converter station, including a positive UHV flexible DC system and a negative UHV flexible DC system. Both the positive UHV flexible DC system and the negative UHV flexible DC system include:

[0006] Arresters with configuration parameters meeting the performance design indexes of the UHV flexible DC system; the arresters are used to achieve insulation coordination of the UHV flexible DC converter station; the arresters include ground arresters and / or inter-terminal arresters; the configuration parameters include one or more of the following: the highest continuous operating voltage at different arrester positions of the UHV flexible DC system, and the reference voltage, operation impulse protection level, coordination current, energy of the arresters of the UHV flexible DC converter station, and the operation impulse insulation level that each position arrester needs to withstand;

[0007] The ground lightning arresters include one or more of the following: the valve side lightning arrester of the high-end converter transformer, the valve side lightning arrester of the low-end converter transformer, the valve side lightning arrester of the high-end upper bridge arm reactor, the valve side lightning arrester of the high-end lower bridge arm reactor, the valve side lightning arrester of the low-end upper bridge arm reactor, the valve side lightning arrester of the low-end lower bridge arm reactor, the valve top lightning arrester, the DC bus lightning arrester at the midpoint of the high and low-end converter valves, the DC line side lightning arrester, the first neutral line lightning arrester and the second neutral line lightning arrester, the ground electrode line lightning arrester and the metal return line lightning arrester; and / or

[0008] The inter-terminal lightning arresters include one or more of the following: the inter-terminal lightning arrester of the high-end upper bridge arm of the converter valve, the inter-terminal lightning arrester of the low-end upper bridge arm of the converter valve, and the overall inter-terminal lightning arrester of the high-end converter valve.

[0009] In a further embodiment, the inter-terminal lightning arresters further include one or more of the following:

[0010] The inter-terminal lightning arrester of the high-end lower bridge arm of the converter valve, the inter-terminal lightning arrester of the low-end lower bridge arm of the converter valve, and the parallel inter-terminal lightning arrester of the DC reactor.

[0011] Furthermore, the present invention also provides a method for insulating coordination of a UHV flexible DC converter station based on the foregoing embodiments of the insulating coordination device of the UHV flexible DC converter station, including:

[0012] Performing a transient overvoltage simulation to determine whether the configuration parameters of the lightning arresters meet the performance design indexes of the UHV flexible DC system to achieve the insulating coordination of the UHV flexible DC converter station;

[0013] In the case where the configuration parameters of the lightning arresters do not meet the performance design indexes of the UHV flexible DC system and the insulating coordination of the UHV flexible DC converter station cannot be achieved, adjusting the lightning arresters;

[0014] Performing a transient overvoltage simulation until the adjusted configuration parameters of the lightning arresters meet the performance design indexes of the UHV flexible DC system and the insulating coordination of the UHV flexible DC converter station is achieved.

[0015] In a further embodiment, determining the highest continuous operating voltage at the position of the ground lightning arrester includes:

[0016] According to the converter transformer turns ratio, the number of converter valves, the maximum operating voltage of the DC pole line, and the maximum steady-state operating modulation ratio, respectively determining the highest continuous operating voltage at the position of the valve side lightning arrester of the high-end converter transformer and the highest continuous operating voltage at the position of the valve side lightning arrester of the low-end converter transformer;

[0017] According to the maximum operating voltage of the DC pole line, the maximum operating voltage of the midpoint bus of the high- and low-end converter valves, the maximum operating voltage of the neutral line, and the maximum fundamental frequency voltage and second harmonic voltage borne by the arm reactor, determine the maximum continuous operating voltage at the position of the valve-side arrester of the high-end upper arm reactor, the maximum continuous operating voltage at the position of the valve-side arrester of the high-end lower arm reactor, the maximum continuous operating voltage at the position of the valve-side arrester of the low-end upper arm reactor, and the maximum continuous operating voltage at the position of the valve-side arrester of the low-end lower arm reactor respectively;

[0018] According to the maximum operating voltage of the DC pole line, determine the maximum continuous operating voltage at the position of the valve-top arrester and the maximum continuous operating voltage at the position of the DC line-side arrester respectively;

[0019] According to the maximum operating voltage of the neutral line, determine the maximum continuous operating voltage at the position of the first neutral line arrester, the maximum continuous operating voltage at the position of the second neutral line arrester, the maximum continuous operating voltage at the position of the ground electrode line arrester, and the maximum continuous operating voltage at the position of the metallic return line arrester respectively;

[0020] Determine the maximum continuous operating voltage at the position of the inter-terminal arrester, including:

[0021] According to the maximum operating voltage of the DC pole line and the maximum overvoltage operating multiple, determine the maximum continuous operating voltage at the positions of the high-end converter valve upper arm inter-terminal arrester, the low-end converter valve upper arm inter-terminal arrester, the high-end converter valve overall inter-terminal arrester, the high-end converter valve lower arm inter-terminal arrester, and the low-end converter valve lower arm inter-terminal arrester respectively;

[0022] The maximum continuous operating voltage at the position of the shunt arrester between the terminals of the DC reactor does not exceed the first preset voltage value.

[0023] In a further embodiment, determine the reference voltage of the arrester, including:

[0024] According to the maximum continuous operating voltage at the position of the arrester and the charging rate, determine the reference voltages of the valve-side arresters of the high-end converter transformer, the valve-side arresters of the low-end converter transformer, the valve-side arresters of the high-end upper arm reactor, the valve-side arresters of the high-end lower arm reactor, the valve-side arresters of the low-end upper arm reactor, the valve-side arresters of the low-end lower arm reactor, and the valve-top arrester;

[0025] The reference voltage of the ground electrode line arrester is less than the reference voltage of the metallic return line arrester, and the reference voltage of the metallic return line arrester is less than the reference voltage of the second neutral line arrester;

[0026] According to the overvoltage withstand capacity of the insulated gate bipolar transistor, determine the reference voltages of the arresters between the upper arm terminals of the high-end converter valve, between the upper arm terminals of the low-end converter valve, between the lower arm terminals of the high-end converter valve, and between the lower arm terminals of the low-end converter valve respectively.

[0027] In a further embodiment, determining the switching impulse protection level of the arrester includes:

[0028] According to the voltage ratio and reference voltage of the arrester, determine the switching impulse protection levels of the valve-side arresters of the high-end converter transformer, the valve-side arresters of the low-end converter transformer, the valve-side arresters of the high-end upper arm reactor, the valve-side arresters of the high-end lower arm reactor, the valve-side arresters of the low-end upper arm reactor, the valve-side arresters of the low-end lower arm reactor, and the valve-top arresters respectively;

[0029] According to the number of sub-modules in a single arm, the overvoltage withstand capacity of the insulated gate bipolar transistor of the arrester, and the protection margin, determine the switching impulse protection levels of the arresters between the upper arm terminals of the high-end converter valve, between the upper arm terminals of the low-end converter valve, and between the overall terminals of the high-end converter valve, the DC busbar arrester at the midpoint of the high and low-end converter valves, between the lower arm terminals of the high-end converter valve, and between the lower arm terminals of the low-end converter valve respectively;

[0030] According to the overvoltage suppression coefficient and the maximum operating voltage of the DC pole line, determine the switching impulse protection level of the first neutral line arrester.

[0031] In a further embodiment, determining the coordination current of the arrester includes:

[0032] The coordination current of the arrester satisfies the first current range.

[0033] In a further embodiment, determining the energy of the arrester includes:

[0034] According to the energy unevenness coefficient, the number of series-connected resistor chips, the number of parallel columns of the arrester, the energy of a single resistor chip, and the withstand voltage of a single resistor chip, determine the energy of the arrester.

[0035] In a further embodiment, determining the switching impulse insulation level that the arrester needs to withstand includes:

[0036] According to the switching impulse protection level and insulation margin of the arrester, determine the switching impulse insulation level that the arrester needs to withstand.

[0037] Compared with the prior art, the insulation coordination device and insulation coordination method for a UHV flexible DC converter station in the embodiments of the present invention have at least the following beneficial effects:

[0038] In the present invention, lightning arresters are installed at different positions of a UHV flexible DC converter station, and the configuration parameters of the lightning arresters installed at different positions meet the performance design indexes of the UHV flexible DC system. Thus, the insulation coordination of the UHV flexible DC converter station can be realized through the lightning arresters installed at different positions, the economic cost of the insulation coordination of the UHV flexible DC converter station can be reduced, and the overvoltage of the UHV flexible DC converter station and the manufacturing difficulty of equipment can be reduced. Description of the Drawings

[0039] Figure 1 is a schematic structural diagram of an insulation coordination device for a UHV flexible DC converter station provided by an embodiment of the present invention;

[0040] Figure 2 is a schematic flow diagram of an insulation coordination method for a UHV flexible DC converter station provided by an embodiment of the present invention;

[0041] Fig. 3(a) is a schematic diagram of the overvoltage suppression effect of an embodiment before optimization of the insulation coordination method for a UHV flexible DC converter station provided by an embodiment of the present invention;

[0042] Fig. 3(b) is a schematic diagram of the overvoltage suppression effect of an embodiment before optimization of the insulation coordination method for a UHV flexible DC converter station provided by an embodiment of the present invention;

[0043] Fig. 3(c) is a schematic diagram of the overvoltage suppression effect of an embodiment after optimization of the insulation coordination method for a UHV flexible DC converter station provided by an embodiment of the present invention;

[0044] Fig. 3(d) is a schematic diagram of the overvoltage suppression effect of an embodiment after optimization of the insulation coordination method for a UHV flexible DC converter station provided by an embodiment of the present invention. Detailed Embodiments

[0045] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0046] Transient overvoltage is a short-term high-voltage phenomenon in the power system, which may cause insulation breakdown or damage to equipment. Especially for UHV flexible DC systems, where the DC voltage is higher than ±800 kV and various overvoltages rise sharply. To withstand these overvoltages, equipment needs to have a higher insulation level, which usually means higher material costs and manufacturing difficulties. The applicant found through research on the prior art that by optimizing the insulation coordination scheme of the UHV flexible DC system, transient overvoltage can be effectively suppressed, the insulation requirements of the equipment can be reduced, and thus the equipment cost can be reduced. For example, the insulation material costs of equipment such as converter valves and converter transformers will be significantly reduced.

[0047] A high insulation level usually requires a larger air clearance and equipment size. Especially in high-altitude areas, the thin air leads to a decrease in insulation performance, further increasing the equipment size and floor area. The applicant found through research on the prior art that after suppressing the transient overvoltage, the equipment size and air clearance can be reduced, thereby reducing the floor area and civil engineering costs of the UHV flexible DC converter station.

[0048] Transient overvoltage will cause mechanical and electrical stresses on the equipment. Long-term accumulation may lead to equipment aging or damage, increasing maintenance and replacement costs. The applicant found through research on the prior art that by suppressing the transient overvoltage, the stress damage of the equipment can be reduced, the service life of the equipment can be extended, and the maintenance and replacement costs can be reduced.

[0049] Transient overvoltage may cause equipment failures or system power outages, resulting in economic losses. The applicant found through research on the prior art that suppressing the transient overvoltage can improve system reliability, reduce power outage losses, and enhance the overall economic benefits.

[0050] The present invention optimizes the coordination position and coordination parameters of lightning arresters according to the main wiring characteristics and equipment configuration of the UHV flexible DC transmission system to ensure that the overvoltage is suppressed to an acceptable level under various fault conditions. By reasonably configuring lightning arresters, overdesign is avoided, the cost of lightning arresters is reduced, and at the same time the insulation requirements of the equipment are reduced. According to the system characteristics, a reasonable insulation coordination scheme is designed to effectively control the maximum transient overvoltage, current, and energy levels under AC and DC side faults. By optimizing the insulation coordination, the insulation materials and size of the equipment are reduced, and the equipment cost and floor area are reduced.

[0051] The present invention is also applicable to special environments in high-altitude areas (such as above 4000 meters) for the modified design of the insulation level to ensure the reliable operation of the equipment under high-altitude conditions. Through precise insulation modification, overdesign is avoided, and the cost and floor area of the UHV flexible DC converter station in high-altitude areas are reduced.

[0052] In addition to economic cost control, the present invention also aims to solve the following key problems:

[0053] 1. Insulation coordination design issues of UHV flexible DC

[0054] The insulation level of the UHV flexible DC transmission system directly affects the cost of UHV DC equipment and the engineering feasibility. Especially in high-altitude areas, after altitude correction, the insulation level may become a decisive factor restricting the cost and land occupation. By optimizing the insulation coordination design method of the UHV flexible DC system, ensure that the maximum transient overvoltage, current and energy levels under various fault conditions are effectively controlled, and achieve the optimal balance between economy and technical performance.

[0055] 2. Transient overvoltage suppression issues

[0056] Due to the existence of a large number of energy storage capacitors, under the conditions of long-distance and large-capacity power transmission, the transient overvoltage characteristics of the UHV flexible DC system are quite different from those of the short-distance and small-capacity non-UHV flexible DC system and the UHV DC system based on thyristor converter valves. The overvoltage develops rapidly, with a high amplitude, a long duration, and is difficult to suppress, which may cause a huge impact on the safe operation of equipment and the stability of the system. Adopt advanced transient overvoltage suppression technologies, optimize the parameter coordination of surge arresters, reduce the amplitude and duration of transient overvoltage, and improve the system reliability.

[0057] 3. Insulation correction issues in high-altitude areas

[0058] In high-altitude areas (such as above 4000 meters), the thin air leads to a decline in insulation performance. Traditional insulation designs may not meet the requirements and are costly. Conduct insulation level correction design for high-altitude areas, deeply explore the optimization ability of insulation coordination, ensure the reliable operation of equipment under high-altitude conditions, and at the same time avoid over-design and reduce costs.

[0059] 4. Particularities of long-distance and large-capacity power transmission systems

[0060] Currently, there is no long-distance and large-capacity UHV flexible DC transmission system with a current level of 5 kA in operation. For the UHV flexible DC system with long distance, large capacity, high voltage and large current, compared with the previous high-voltage flexible DC transmission system and the UHV DC system based on thyristor converter valves, there are essential differences in the generation mechanism of overvoltage, and existing experience and technologies are difficult to directly draw on. By studying the characteristics of the long-distance and large-capacity UHV flexible DC system, propose targeted insulation coordination optimization methods to ensure the safe and stable operation of the system.

[0061] In the long-distance and large-capacity UHV flexible DC system of the present invention, compared with the short-distance and small-capacity UHV flexible DC system, the following main differences exist:

[0062] 1. Transient overvoltage characteristics

[0063] The transient over-voltage amplitude of a long-distance large-capacity system is higher, the duration is longer, and the propagation characteristics are more complex. This is caused by the increase in line length, the enhancement of capacitance effect, and the change of system impedance. The higher transient over-voltage poses higher requirements for the insulation level of equipment, increasing the equipment cost and engineering difficulty. The present invention effectively controls the transient over-voltage and reduces the insulation requirements of equipment by optimizing the parameter matching of lightning arresters, designing a reasonable insulation coordination scheme, and adopting advanced transient over-voltage suppression technologies.

[0064] 2. System stability

[0065] The stability problem of a long-distance large-capacity system is more prominent. Especially under fault conditions, the voltage and current fluctuations are greater, which may lead to system instability. System instability may cause large-scale power outages or equipment damage, resulting in serious economic losses. The present invention enhances the system stability by optimizing the main wiring design, improving the response speed of protection devices, and suppressing transient over-voltage.

[0066] 3. Influence of high-altitude areas

[0067] Long-distance transmission lines may pass through high-altitude areas. The thin air leads to a decrease in insulation performance, and traditional insulation designs may not meet the requirements. The insulation correction in high-altitude areas increases the design complexity and engineering cost. The present invention conducts insulation level correction design for high-altitude areas to ensure the reliable operation of equipment under high-altitude conditions, while avoiding over-design and reducing costs.

[0068] 4. Equipment cost and engineering cost

[0069] The equipment cost and engineering cost of a long-distance large-capacity system are significantly higher than those of a short-distance small-capacity system, especially under high insulation requirements and complex working conditions. The high cost may affect the feasibility and economy of the project. The present invention reduces the equipment cost and engineering cost by optimizing the insulation coordination design, suppressing transient over-voltage, and reasonably configuring lightning arresters.

[0070] 5. System complexity and design difficulty

[0071] The design of a long-distance large-capacity system is more complex and requires considering more variables and working conditions, such as line impedance, capacitance effect, fault type, etc. The increase in design difficulty may lead to an extension of the project cycle and an increase in cost. The present invention simplifies the design process and reduces the design difficulty by optimizing the main wiring of the system, transient over-voltage suppression technology, and insulation correction in high-altitude areas.

[0072] See Figure 1 , Figure 1 is a schematic structural diagram of an insulation coordination device for a UHV flexible DC converter station provided by an embodiment of the present invention. As Figure 1As shown, the device includes a positive ultra-high voltage flexible DC system and a negative ultra-high voltage flexible DC system. Both the positive ultra-high voltage flexible DC system and the negative ultra-high voltage flexible DC system include:

[0073] Lightning arresters with configuration parameters meeting the performance design indicators of the ultra-high voltage flexible DC system; the lightning arresters are used to achieve insulation coordination of the ultra-high voltage flexible DC converter station; the lightning arresters include ground lightning arresters and / or inter-terminal lightning arresters; the configuration parameters include one or more of the following: the highest continuous operating voltage at different positions of the lightning arresters in the ultra-high voltage flexible DC system, as well as the reference voltage, operation impulse protection level, coordination current, energy of the lightning arresters in the ultra-high voltage flexible DC converter station, and the operation impulse insulation level that the lightning arresters at each position need to withstand;

[0074] The ground lightning arresters include one or more of the following: the valve side lightning arrester AVH of the high-end converter transformer, the valve side lightning arrester AVL of the low-end converter transformer, the valve side lightning arrester LVHp of the high-end upper bridge arm reactor, the valve side lightning arrester LVHn of the high-end lower bridge arm reactor, the valve side lightning arrester LVLp of the low-end upper bridge arm reactor, the valve side lightning arrester LVLn of the low-end lower bridge arm reactor, the valve top lightning arrester CBH, the DC bus lightning arrester CBL at the midpoint of the high and low-end converter valves, the DC line side lightning arrester DL, the first neutral line lightning arrester CBN, the second neutral line lightning arrester E, the ground electrode line lightning arrester EL, and the metal return line lightning arrester EM; and / or

[0075] The inter-terminal lightning arresters include one or more of the following: the inter-terminal lightning arrester V1 of the high-end converter valve upper bridge arm, the inter-terminal lightning arrester V3 of the low-end converter valve upper bridge arm, and the overall inter-terminal lightning arrester C of the high-end converter valve.

[0076] An ultra-high voltage flexible DC converter station refers to a station established in a high-voltage (or ultra-high voltage) DC power transmission system to complete the conversion of alternating current to direct current or direct current to alternating current and meet the requirements of the power system for safety, stability, and power quality. The main equipment or facilities that should be included in an ultra-high voltage flexible DC converter station are: converter valves, converter transformers, smoothing reactors, AC switchgear, AC filters and AC reactive power compensation devices, DC switchgear, DC filters, control and protection devices, off-station ground electrodes, and remote communication systems, etc.

[0077] Among them, each ultra-high voltage flexible DC converter station includes a positive ultra-high voltage flexible DC system and a negative ultra-high voltage flexible DC system, and in the present invention, the configuration of the lightning arresters in the positive ultra-high voltage flexible DC system is the same as that of the lightning arresters in the negative ultra-high voltage flexible DC system. Specifically, both the positive ultra-high voltage flexible DC system and the negative ultra-high voltage flexible DC system include lightning arresters, and the lightning arresters include ground lightning arresters and / or inter-terminal lightning arresters.

[0078] In the present invention, the configuration parameters of the lightning arresters in the insulation coordination device of the UHV flexible DC converter station meet the performance design indexes of the UHV flexible DC system, and the lightning arresters are used to achieve the insulation coordination of the UHV flexible DC converter station. Among them, the configuration parameters of the lightning arresters include one or more of the following: the maximum continuous operating voltage at different positions of the lightning arresters in the UHV flexible DC system, as well as the reference voltage, the operating impulse protection level, the coordination current, the energy of the lightning arresters in the UHV flexible DC converter station, and the operating impulse insulation level that the lightning arresters at each position need to withstand.

[0079] In a further embodiment, both the positive UHV flexible DC system and the negative UHV flexible DC system further include: a high-end commutation area, a low-end commutation area, a pole line area, and a neutral line area;

[0080] The commutation area includes: an upper arm reactor, an upper arm of the commutation valve, a commutation transformer, a lower arm of the commutation valve, and a lower arm reactor;

[0081] The pole line area includes a pole line DC reactor;

[0082] The neutral line area includes a neutral line DC reactor, a grounding electrode line, and a metallic return line jumper.

[0083] The installation positions and functions of the lightning arresters in each area are described as follows:

[0084] 1. The high-end commutation area of the positive or negative UHV flexible DC system

[0085] Installation position: on the AC side and the DC side of the high-end commutation valve.

[0086] Specific positions: between the high-end commutation transformer and the upper arm of the high-end commutation valve, with one side connected between the upper arm of the high-end commutation valve and the upper arm reactor; the arrester V2 across the ends of the lower arm of the high-end commutation valve is connected across the two ends of the lower arm of the high-end commutation valve, with one side connected between the high-end commutation transformer and the lower arm of the high-end commutation valve, and the other side connected between the lower arm of the high-end commutation valve and the lower arm reactor; the arrester C across the entire valve ends of the high-end commutation valve is directly connected across the entire valve ends of the high-end commutation valve, with one side connected between the upper arm of the high-end commutation valve and the upper arm reactor, and the other side connected between the lower arm of the high-end commutation valve and the lower arm reactor.

[0087] The AC side arrester: installed between the high-end commutation valve and the high-end commutation transformer, used to suppress the transient overvoltage in the connection area between the high-end commutation transformer and the high-end commutation valve. The voltage at this position shows the characteristics of DC voltage superimposed on AC voltage. The arrester at this position is the high-end converter valve side arrester AVH.

[0088] DC-side lightning arrester: Installed between the high-end converter valve and the arm reactor, it is used to suppress the transient overvoltage on the DC side of the high-end converter valve, including the valve-side lightning arrester LVHp of the high-end upper arm reactor and the valve-side lightning arrester LVHn of the high-end lower arm reactor.

[0089] Function: Protect the high-end converter valve from overvoltages on the AC side and DC side.

[0090] 2. Converter area at the low end of the positive or negative UHVDC flexible DC system

[0091] Installation location: On the AC side and DC side of the low-end converter valve.

[0092] Specific location:

[0093] Crossing the high-end converter valve or arm: The inter-terminal lightning arrester V3 at the upper arm end of the low-end converter valve is connected across both ends of the upper arm of the low-end converter valve. One side is connected between the low-end converter transformer and the upper arm of the high-end converter valve, and the other side is connected between the upper arm of the low-end converter valve and the upper arm reactor; the inter-terminal lightning arrester V4 at the lower arm end of the low-end converter valve is connected across both ends of the lower arm of the low-end converter valve. One side is connected between the low-end converter transformer and the lower arm of the high-end converter valve, and the other side is connected between the lower arm of the low-end converter valve and the lower arm reactor. AC-side lightning arrester: Installed between the low-end converter valve and the low-end converter transformer, it is used to suppress the transient overvoltage in the connection area between the low-end converter transformer and the low-end converter valve. The voltage at this position shows the characteristics of a DC voltage superimposed on an AC voltage. The lightning arrester at this position includes the valve-side lightning arrester AVL of the low-end converter transformer.

[0094] DC-side lightning arrester: Installed between the low-end converter valve and the arm reactor, it is used to suppress the transient overvoltage on the DC side of the low-end converter valve, including the valve-side lightning arrester LVLp of the low-end upper arm reactor and the valve-side lightning arrester LVLn of the low-end lower arm reactor.

[0095] Function: Protect the low-end converter valve from overvoltages on the AC side and DC side.

[0096] 3. Pole line area of the positive or negative UHVDC flexible DC system

[0097] Installation location: Near the pole line and its connected equipment of the positive UHVDC flexible DC system or the negative UHVDC flexible DC system.

[0098] Specific location: The valve-top lightning arrester CBH and the DC line lightning arrester DL are installed at the pole line outlet of the positive UHVDC flexible DC system or the negative UHVDC flexible DC system, and are used to suppress the transient overvoltage of the bus.

[0099] Function: Protect the pole bus and its connected equipment from damage caused by DC overvoltage.

[0100] 4. Neutral Line Region of Positive or Negative Ultra-High Voltage Flexible DC System

[0101] Installation Location: Near the neutral line and its connecting equipment of the positive ultra-high voltage flexible DC system or the negative ultra-high voltage flexible DC system.

[0102] Specific Location: The first neutral line arrester CBN and the second neutral line arrester E are installed at the outlet of the neutral line of the positive ultra-high voltage flexible DC system to suppress the transient overvoltage on the neutral line side.

[0103] Function: Protect the neutral line and its connecting equipment from damage caused by overvoltage.

[0104] In a further embodiment, continue to refer to Figure 1 , the inter-terminal arrester further includes one or more of the following:

[0105] The inter-terminal arrester of the lower arm of the high-end converter valve V2, the inter-terminal arrester of the lower arm of the low-end converter valve V4, and the parallel arrester DR at the inter-terminal of the DC reactor.

[0106] In the present invention, the high-end converter transformer valve side arrester AVH and the low-end converter transformer valve side arrester AVL are respectively configured on the valve sides of the high-end and low-end converter transformers of the positive ultra-high voltage flexible DC system and the negative ultra-high voltage flexible DC system. The valve side of the converter transformer in the ultra-high voltage flexible DC converter station is vulnerable to high-amplitude transient overvoltage. Configuring the arrester can effectively suppress the overvoltage and protect the transformer. It can significantly reduce the insulation requirements of the converter transformer, extend the equipment life, and improve the system reliability.

[0107] In the present invention, the high-end upper arm reactor valve side arrester LVHp and the high-end lower arm reactor valve side arrester LVHn are respectively configured on the valve sides of the high-end upper arm and lower arm reactors of the positive ultra-high voltage flexible DC system and the negative ultra-high voltage flexible DC system, and the low-end upper arm reactor valve side arrester LVLp and the low-end lower arm reactor valve side arrester LVLn are respectively configured on the valve sides of the low-end upper arm and lower arm reactors. The arm reactor bears high voltage stress in the ultra-high voltage system. Configuring the arrester can suppress the overvoltage and protect the converter valve and the reactor. It can reduce the risk of insulation damage of the reactor, reduce the maintenance cost, reduce the air clearance in the valve hall, and reduce the space and investment.

[0108] In the present invention, the valve top arrester CBH is configured at the valve top of the positive ultra-high voltage flexible DC system and the negative ultra-high voltage flexible DC system, and the line arrester DL is configured at the line outlet. The valve top is a key part of the converter valve and is vulnerable to the impact of high-amplitude overvoltage. It can protect the converter valve from overvoltage damage and improve the system stability. The DC limit is the key sending position of the DC system. Reducing the insulation level can significantly reduce the equipment manufacturing difficulty and improve the economy.

[0109] The present invention configures surge arresters CBL at the midpoint DC busbars of the high and low - end converters in both the positive - pole UHV flexible DC system and the negative - pole UHV flexible DC system. The DC busbar is a key connection part of the system and is vulnerable to transient over - voltages. It can suppress the over - voltage of the DC busbar and protect the busbar and its connected equipment.

[0110] The present invention configures DC line surge arresters DL on the DC line sides of both the positive - pole UHV flexible DC system and the negative - pole UHV flexible DC system. DC lines are vulnerable to lightning and switching over - voltages during long - distance power transmission. It can protect the DC lines and their connected equipment and improve the power transmission reliability.

[0111] The present invention configures a first neutral - line surge arrester CBN and a second neutral - line surge arrester E on the neutral lines of both the positive - pole UHV flexible DC system and the negative - pole UHV flexible DC system. The neutral line plays a role in balancing voltage in the system and is vulnerable to over - voltages. It can protect the neutral line and its connected equipment and improve the system stability.

[0112] The present invention configures earthing - pole line surge arresters EL and metal - return line surge arresters EM on the earthing - pole lines and metal return lines of both the positive - pole UHV flexible DC system and the negative - pole UHV flexible DC system. The earthing - pole lines and metal return lines play key roles in the system and are vulnerable to over - voltages. It can protect the earthing - pole lines and metal return lines and improve the system reliability.

[0113] Special features of the UHV system: The UHV flexible DC converter station has a high voltage level and a complex system, and the problem of transient over - voltage is more prominent, requiring a more comprehensive surge - arrester configuration. Influence of high - altitude areas: The insulation performance in high - altitude areas decreases, and targeted surge - arrester configurations are needed to suppress over - voltages. Long - distance and large - capacity power transmission: The transient over - voltage characteristics of long - distance and large - capacity power transmission systems are different from those of short - distance and small - capacity systems, requiring more refined insulation coordination design. Reducing equipment costs: By suppressing transient over - voltages, the insulation requirements of equipment are reduced, and equipment costs are decreased. Improving system reliability: A comprehensive surge - arrester configuration effectively protects key equipment, improving system stability and reliability. Extending equipment life: Reducing the damage of over - voltages to equipment, extending the service life of equipment, and reducing maintenance costs.

[0114] See Figure 2 , Figure 2 which is a schematic flow chart of an insulation coordination method for a UHV flexible DC converter station provided by an embodiment of the present invention. As Figure 2 shown, the method includes:

[0115] S201, conduct transient over - voltage simulation to determine whether the configuration parameters of the surge arresters meet the performance design indicators of the UHV flexible DC system to achieve the insulation coordination of the UHV flexible DC converter station;

[0116] S202. When the configuration parameters of the lightning arrester do not meet the performance design indicators of the UHV flexible DC system and the insulation coordination of the UHV flexible DC converter station cannot be achieved, adjust the lightning arrester.

[0117] S203. Conduct a transient overvoltage simulation until the configuration parameters after the lightning arrester adjustment meet the performance design indicators of the UHV flexible DC system and the insulation coordination of the UHV flexible DC converter station is achieved.

[0118] In a further embodiment, the configuration parameters include one or more of the following: the highest continuous operating voltage at different lightning arrester positions of the UHV flexible DC system, and the reference voltage, operation impulse protection level, cooperation current, energy of the lightning arrester of the UHV flexible DC converter station, and the operation impulse insulation level that each position lightning arrester needs to withstand.

[0119] In a further embodiment, determining the highest continuous operating voltage at the position of the lightning arrester to the ground includes:

[0120] According to the converter transformer turns ratio, the number of converter valves, the maximum operating voltage of the DC pole line, and the maximum steady-state operating modulation ratio, respectively determine the highest continuous operating voltage at the position of the high-end converter transformer valve side lightning arrester AVH and the highest continuous operating voltage at the position of the low-end converter transformer valve side lightning arrester AVL.

[0121] 1) The determination of the highest continuous operating voltages U4 and U8 at the positions of the high-end converter transformer valve side lightning arrester AVH and the low-end converter transformer valve side lightning arrester AVL considering the number of series converter valve groups in the converter transformer valve side configuration. For a ±800 kV flexible DC system, there are 2 converter valves per pole, i.e., N = 2. U4 and U8 can be calculated according to Equations (1) to (4), and take the maximum value of each position:

[0122] U8 = Udcmax*(N + 1) / (2*N) + Udcmax / (Mmax*N*2) (1)

[0123] U4 = Udcmax / (2*N) + Udcmax / (Mmax*N*2) (2)

[0124] U4 = Udcmax*(N + 1) / (2*N) + U13*N2 / [N1*(1 - n*T)] (3)

[0125] U8 = Udcmax / (2*N) + U13*N2 / [N1*(1 - n*T)] (4)

[0126] Among them, Udcmax is the maximum operating voltage of the DC pole line with measurement deviation, Mmax is the maximum steady-state operating modulation ratio, n is the maximum negative gear of the converter transformer, and T is the gear pitch of the converter transformer.

[0127] According to the maximum operating voltage of the DC pole line, the maximum operating voltage of the midpoint bus of the high and low-end converter valves, the maximum operating voltage of the neutral line, and the maximum fundamental frequency voltage and double-frequency voltage borne by the arm reactor, respectively determine the highest continuous operating voltage at the positions of the valve-side arresters LvHp of the high-end upper arm reactor and LvLp of the low-end upper arm reactor, and the highest continuous operating voltage at the positions of the valve-side arresters LvHn of the high-end lower arm reactor and LvLn of the low-end lower arm reactor.

[0128] The highest continuous operating voltages U3, U5, U7, and U9 at the positions of the valve-side arresters LvHp of the high-end upper arm reactor, LvLp of the low-end upper arm reactor, LvHn of the high-end lower arm reactor, and LvLn of the low-end lower arm reactor configured on the valve side of the arm reactor need to consider the maximum DC operating voltage at their respective positions, and superimpose the maximum fundamental frequency U L50 and double-frequency voltage U L100 And, U3, U5, U7, and U9 can be calculated according to equations (5) to (7):

[0129] U3 = Udcmax + U L50 + U L100 (5)

[0130] U5 = U7 = Udcmax / N + U L50 + U L100 (6)

[0131] U9 = Udcnmax / N + U L50 + U L100 (7)

[0132] Among them, Udcnmax is the maximum operating voltage of the neutral line with measurement deviation.

[0133] According to the maximum operating voltage of the DC pole line, respectively determine the highest continuous operating voltage at the position of the arrester CBH on the valve top and the highest continuous operating voltage at the position of the DC line-side arrester DL.

[0134] The highest continuous operating voltages U2 and U1 at the positions of the arrester CBH on the valve side and the DC line-side arrester DL configured on the valve side and the line side of the DC reactor of the DC pole line can both be considered according to Udcmax.

[0135] Based on the maximum operating voltage of the neutral line, determine the maximum continuous operating voltage at the first neutral line arrester CBN, the maximum continuous operating voltage at the second neutral line arrester E position, the maximum continuous operating voltage at the ground electrode line arrester EL position, and the maximum continuous operating voltage at the metal return line arrester EM position, respectively.

[0136] A CBN arrester is configured on the valve side of the DC reactor of the DC neutral line. E arresters and EL arresters are configured at the grounding electrode line end of the DC reactor. The maximum continuous operating voltages U10, U11, and U12 at the position of the EM arrester configured on the metal return line can all be considered according to Udcnmax.

[0137] Determine the maximum continuous operating voltage at the position of the inter-terminal arrester, including:

[0138] Based on the maximum operating voltage of the DC pole line and the maximum overvoltage operating multiple, determine the maximum continuous operating voltage at the position of the inter-terminal arrester V1 on the upper arm of the high-end converter valve, the inter-terminal arrester V3 on the upper arm of the low-end converter valve, the overall inter-terminal arrester C of the high-end converter valve, the inter-terminal arrester V2 on the lower arm of the high-end converter valve, and the inter-terminal arrester V4 on the lower arm of the low-end converter valve, respectively.

[0139] An inter-terminal arrester V1 is configured on the upper arm of the high-end converter valve, an inter-terminal arrester V3 is configured at the upper arm end of the low-end converter valve, and an arrester C is configured between the high-end converter valves. The inter-terminal arresters V2 on the lower arm of each pole's high-end converter valve and V4 on the lower arm of the low-end converter valve can be selected as needed. The maximum continuous operating voltages UV1, UV3, UC, UV2, and UV4 at the position of each arm's inter-terminal arrester are the same, all being k3*Udcmax / N. Among them, k3 is the maximum overvoltage operating multiple of each valve group, considered as not exceeding 1.05 at most.

[0140] The maximum continuous operating voltage at the position of the parallel arrester DR connected in parallel between the terminals of the DC reactor does not exceed the first preset voltage value. A parallel arrester DR is configured between the terminals of the DC reactor of the DC pole line. During normal operation, the maximum continuous operating voltage at the position between the terminals of this arrester is relatively small, generally not exceeding 50 kV. That is, the first preset voltage value is 50 kV.

[0141] In a further embodiment, determining the reference voltage of the arrester includes:

[0142] Based on the maximum continuous operating voltage and the charging rate at the position of the arrester, determine the reference voltages of the high-end converter transformer valve side arrester AVH, the low-end converter transformer valve side arrester AVL, the high-end upper arm reactor valve side arrester LVHp, the high-end lower arm reactor valve side arrester LVLn, and the valve top arrester CBH.

[0143] The Uref of high - voltage DC arresters to ground such as the valve - side arrester AVH of the high - end converter transformer, the valve - side arrester AVL of the low - end converter transformer, the valve - side arrester LVHp of the high - end upper - bridge - arm reactor, the valve - side arrester LVLp of the low - end upper - bridge - arm reactor, the valve - side arrester LVHn of the high - end lower - bridge - arm reactor, the valve - side arrester LVLn of the low - end lower - bridge - arm reactor, and the valve - top arrester CBH can be calculated by Equation (8).

[0144] Uref = CCOV / c1 (8)

[0145] Where c1 is the ratio of the continuous operating voltage CCOV of the arrester to the reference voltage Uref, called the charge - rate, which represents the aging characteristic of the arrester. Generally, c1 is less than 1. The larger C is, the easier it is to age. For UHV flexible DC systems, Uref of high - voltage DC arresters can take values from 0.75 to 0.85.

[0146] The reference voltage of the ground - electrode line arrester EL is less than the reference voltage of the metal - return - line arrester EM, and the reference voltage of the metal - return - line arrester EM is less than the reference voltage of the second neutral - line arrester E.

[0147] The Uref of low - voltage arresters to ground in the neutral - line area such as the second neutral - line arrester E, the ground - electrode line arrester EL, and the metal - return - line arrester EM is not determined by the aging characteristic. Generally, it is not determined according to Equation (8), but is determined by the protection level required by the equipment after a fault. And according to the positions and functions of each arrester, the reference voltage satisfies Uref_EL < Uref_EM < Uref_E.

[0148] According to the over - voltage withstand of insulated gate bipolar transistors, determine the reference voltages of the inter - arm arresters V1 of the high - end converter valve upper arm, V3 of the low - end converter valve upper arm, V2 of the high - end converter valve lower arm, and V4 of the low - end converter valve lower arm respectively.

[0149] The inter - arm arresters V1, V2, V3, and V4 are mainly used to protect the converter valve and its core component IGBT. After a fault, the stress they bear is relatively large. Uref is not determined by the aging characteristic. Generally, it is not determined according to Equation (8), but is determined by the protection level required by the converter valve after a fault, that is, determined by the over - voltage withstand level of IGBT.

[0150] Specifically, in an UHV flexible DC converter station, the reference voltage of the DC arrester (equivalent to the rated voltage of the AC arrester) is a key parameter to ensure that it can effectively suppress over - voltage and protect equipment. The reference voltage of the arrester is mainly determined by the following two factors: the protection level required by the converter valve after a fault: that is, the maximum over - voltage that the converter valve can withstand under fault conditions. The production and manufacturing capacity of valve - parallel equipment: that is, the technical level and manufacturing capacity of the arrester and its parallel equipment.

[0151] 1. Protection level required for converter valve after fault

[0152] 1.1 Determine the maximum withstand voltage of the converter valve

[0153] 1. Analyze the transient overvoltage characteristics of the converter valve under fault conditions through simulation or experiment to determine its maximum withstand voltage (Vmax).

[0154] 2. Consider the operating voltage (Voper) of the system and the fault type (such as single - pole ground fault, bipolar short - circuit fault, etc.), and calculate the overvoltage multiple (k) of the converter valve under fault conditions

[0155] 3. The maximum withstand voltage Vmax = k×Voper. If the system operating voltage is 800 kV and the overvoltage multiple under fault conditions is 1.5, then the maximum withstand voltage of the converter valve is 1200 kV.

[0156] 1.2 Determine the reference voltage of the arrester

[0157] 1. Determine the reference voltage Vref of the arrester according to the maximum withstand voltage Vmax of the converter valve.

[0158] 2. The reference voltage of the arrester should be slightly higher than the maximum operating voltage of the system but lower than the maximum withstand voltage of the converter valve to ensure effective operation under fault conditions.

[0159] 3. Usually, the reference voltage Vref of the arrester can be calculated by the following formula: Vref = Voper(1 + α)

[0160] where α is the safety factor, usually taken as 0.1 - 0.2. If the system operating voltage is 800 kV and the safety factor is taken as 0.15, then the reference voltage of the arrester is 920 kV.

[0161] The inter - terminal arrester C and the middle - part ground - to - earth arrester CBL are used to protect the converter valve and IGBT, and to limit the converter valve parallel equipment. They bear relatively large stresses, which are determined by the protection level required for the converter valve after fault and the manufacturing capacity of the valve parallel equipment.

[0162] The low - end lower - bridge anti - valve - side ground - to - earth arrester CBN will bear a large reverse overvoltage after fault. Uref is not determined by the aging characteristics, but by the manufacturing capacity of the nearby low - voltage equipment after fault.

[0163] In a further embodiment, determining the switching impulse protection level of the arrester includes:

[0164] Based on the voltage ratio and reference voltage of the lightning arrester, respectively determine the switching impulse protection levels of the lightning arrester AVH on the valve side of the high-end converter transformer, the lightning arrester AVL on the valve side of the low-end converter transformer, the lightning arrester LVHp on the valve side of the high-end upper arm reactor, the lightning arrester LVHn on the valve side of the high-end lower arm reactor, the lightning arrester LVLp on the valve side of the low-end upper arm reactor, the lightning arrester LVLn on the valve side of the low-end lower arm reactor, and the lightning arrester CBH on the valve top.

[0165] The switching impulse protection levels SIPL of the DC lightning arresters such as the lightning arrester AVH on the valve side of the high-end converter transformer, the lightning arrester AVL on the valve side of the low-end converter transformer, the lightning arrester LVHp on the valve side of the high-end upper arm reactor, the lightning arrester LVHn on the valve side of the high-end upper arm reactor, the lightning arrester LVLp on the valve side of the high-end lower arm reactor, the lightning arrester LVLn on the valve side of the high-end lower arm reactor, the lightning arrester CBH on the valve top, the second neutral line lightning arrester E, the ground electrode line lightning arrester EL, and the metal return line lightning arrester EM can be calculated by Equation (9).

[0166] SIPL = k * Uref (9)

[0167] Among them, k is the voltage ratio of the lightning arrester, insulated by the physical characteristics of the lightning arrester resistor chips, generally 1.2 - 1.4, and the resistor characteristics of each manufacturer are different.

[0168] Based on the number of sub-modules in a single bridge arm, the overvoltage withstand of the insulated gate bipolar transistor of the lightning arrester, and the protection margin, respectively determine the switching impulse protection levels of the lightning arrester V1 between the upper arm ends of the high-end converter valve, the lightning arrester V3 between the upper arm ends of the low-end converter valve, the lightning arrester C between the overall ends of the high-end converter valve, the lightning arrester CBL on the midpoint DC bus of the high and low-end converter valves, the lightning arrester V2 between the lower arm ends of the high-end converter valve, and the lightning arrester V4 between the lower arm ends of the low-end converter valve.

[0169] The switching impulse protection levels SIPL of the lightning arresters such as the lightning arrester V1 between the upper arm ends of the high-end converter valve, the lightning arrester V3 between the upper arm ends of the low-end converter valve, the lightning arrester V2 between the lower arm ends of the high-end converter valve, and the lightning arrester V4 between the lower arm ends of the low-end converter valve can be estimated by Equation (10):

[0170] SIPL ≤ Nb * Upr * kp (10)

[0171] Among them, Nb is the number of sub-modules in a single bridge arm, Upr is the overvoltage withstand ability of the IGBT, and kp is the protection margin, generally 0.9 - 0.95.

[0172] The switching impulse protection levels SIPL of the lightning arresters such as the lightning arrester C between the overall ends of the high-end converter valve and the lightning arrester CBL on the midpoint DC bus of the high and low-end converter valves can be estimated by Equation (11) and need to be less than the maximum switching withstand level between the ends of the parallel equipment of the converter valve.

[0173] SIPL ≤ 2 * Nb * Upr * kp (11)

[0174] Determine the switching impulse protection level of the first neutral line arrester CBN according to the overvoltage suppression coefficient and the maximum operating voltage of the DC pole line.

[0175] The switching impulse protection level SIPL of the first neutral line arrester CBN can be estimated by Equation (12) and needs to be less than the maximum switching withstand level between the terminals of the parallel equipment of the converter valve.

[0176] SIPL ≤ Udcmax * kp (12)

[0177] Wherein, kp is the overvoltage suppression coefficient, generally 0.6 - 0.7.

[0178] If it is difficult to manufacture UHV DC equipment, the switching protection level SIPL of the arrester can be optimized reversely according to the equipment manufacturing capacity.

[0179] In a further embodiment, determining the coordination current of the arrester includes:

[0180] The coordination current of the arrester satisfies the first current range.

[0181] The coordination current I of each arrester is first configured according to experience, generally 0.5 - 5 kA, and then corrected according to the simulation results.

[0182] In a further embodiment, determining the energy of the arrester includes:

[0183] Determine the energy of the arrester according to the energy non-uniformity coefficient, the number of series-connected varistors, the number of parallel columns of the arrester, the energy of a single varistor, and the withstand voltage of a single varistor.

[0184] The energy E of each arrester can be calculated according to Equations (13) and (14).

[0185] E = k1 * n1 * n2 * E1 (13)

[0186] n1 = CCOV / U0 (14)

[0187] Wherein, k1 is the energy non-uniformity coefficient of the arrester, generally 0.85 - 0.95, n1 is the number of series-connected varistors per column, n2 is the number of parallel columns of the arrester, E1 is the energy of each varistor, U0 is the withstand voltage of a single varistor, and CCOV is the highest continuous operating voltage at the position of the arrester.

[0188] In a further embodiment, determining the switching impulse insulation level that the arrester needs to withstand includes:

[0189] According to the switching impulse protection level and insulation margin that the lightning arrester needs to withstand, determine the switching impulse insulation level that the lightning arrester needs to withstand. The switching impulse insulation level refers to the peak voltage that the lightning arrester can withstand under switching impulse. Specifically, according to the switching impulse protection level of the lightning arrester, the production and manufacturing capabilities of UHV flexible DC equipment, and the necessary insulation margin, determine the switching impulse insulation level that the lightning arrester needs to withstand.

[0190] The switching insulation level SIWL of each lightning arrester can be calculated by Equation (15).

[0191] SIWL = k2 * SIPL (15)

[0192] Among them, k2 is the insulation margin, generally not less than 10% - 15%.

[0193] Among them, adjusting the lightning arrester includes:

[0194] Increasing the switching impulse protection level of the lightning arrester, increasing the commutation current of the lightning arrester, increasing the lightning arrester, and equalizing the parameters between lightning arresters at different positions so that they can cooperate with each other and the overvoltage is reasonable.

[0195] In addition, the configured parameters meet the performance design indicators of the UHV flexible DC system, mainly including:

[0196] The maximum continuous operating voltage at different positions of the lightning arrester in the UHV flexible DC system does not exceed the preset maximum continuous operating voltage at the lightning arrester position. Among them, those skilled in the art can flexibly adjust the preset maximum continuous operating voltage of different lightning arresters according to actual needs. The preset maximum continuous operating voltage at different lightning arrester positions can be the same or different.

[0197] The reference voltage of the lightning arrester does not exceed the preset reference voltage of the lightning arrester. Among them, those skilled in the art can flexibly adjust the preset reference voltage of different lightning arresters according to actual needs. The preset reference voltage of different lightning arresters can be the same or different.

[0198] The switching impulse protection level of the lightning arrester does not exceed the preset switching impulse protection level of the lightning arrester. Among them, those skilled in the art can flexibly adjust the switching impulse protection level of different lightning arresters according to actual needs. The preset switching impulse protection level of different lightning arresters can be the same or different.

[0199] The commutation current of the lightning arrester does not exceed the preset commutation current of the lightning arrester. Among them, those skilled in the art can flexibly adjust the commutation current of different lightning arresters according to actual needs. The preset commutation current of different lightning arresters can be the same or different.

[0200] The energy of the lightning arrester does not exceed the preset energy of the lightning arrester. Among them, those skilled in the art can flexibly adjust the energy of different lightning arresters according to actual needs. The preset energies of different lightning arresters can be the same or different.

[0201] The switching impulse insulation level that the lightning arrester needs to withstand does not exceed the preset switching impulse insulation level of the lightning arrester. Among them, those skilled in the art can flexibly adjust the switching impulse insulation levels that different lightning arresters need to withstand according to actual needs. The preset switching impulse insulation levels of different lightning arresters can be the same or different.

[0202] Figures 3(a) to 3(d) They are respectively schematic diagrams of the overvoltage suppression effects of the embodiments of the insulation coordination method for the UHV flexible DC converter station provided by the embodiments of the present invention. Fig. 3(a) is the voltage U between the upper arm ends of the high-end converter valve before optimization V1 ; Fig. 3(b) is the voltage U between the ends of the high-end converter valve before optimization C ; Fig. 3(c) from top to bottom are: the voltage U between the upper arm ends of the high-end converter valve after optimization V1 , the energy E of the lightning arrester V1 between the upper arm ends of the high-end converter valve V1 , the stress of the lightning arrester V1 between the upper arm ends of the high-end converter valve after optimization; Fig. 3(d) from top to bottom are the voltage U between the ends of the high-end converter valve after optimization C ; the energy E of the overall lightning arrester C between the ends of the high-end converter valve C , the stress of the overall lightning arrester C between the ends of the high-end converter valve after optimization.

[0203] As Figures 3(a) to 3(d) shown, after adding the lightning arrester V1 between the upper arm ends of the high-end converter valve and configuring appropriate parameters, the overvoltage between the upper arm ends of the high-end converter valve is reduced by 38%. After adding the overall lightning arrester C between the ends of the high-end converter valve and configuring appropriate parameters, the overvoltage between the ends of the high-end converter valve is reduced by 29%. The overvoltage suppression effect is very significant, ensuring the safe operation of the equipment. By optimizing the midpoint DC bus lightning arrester CBL of the high- and low-end converter valves, the overvoltage between the ends of the low-end converter valve can be reduced, and the trend is basically the same as that of the overall lightning arrester C between the ends of the high-end converter valve. Due to the reduction of the overvoltage between the ends, the number and cost of the sub-modules of the high- and low-end converter valves can be correspondingly reduced by about 10%. For the UHV flexible DC system, it can save about 500 million yuan in construction costs, and the economic benefits are very significant.

[0204] The present invention has the following beneficial technical effects:

[0205] 1. A insulation coordination design method for the UHV flexible DC converter station proposed by the present invention can adapt to application scenarios such as large capacity, long distance, extra high voltage, and high altitude.

[0206] 2. The insulation coordination design method for UHV flexible DC converter stations proposed by the present invention can be extended and applied to multi-terminal UHV flexible DC systems and hybrid UHV DC systems, and can adapt to various operating modes such as single-pole, double-pole, forward transmission, reverse transmission, high power, and low power.

[0207] 3. The insulation coordination design method and device proposed by the present invention provide very valuable references for the insulation coordination design of subsequent UHV flexible DC transmission systems, and can be widely applied to various UHV flexible DC transmission systems for large-scale centralized collection and external transmission of clean energy in western and northern China, playing an important role in the construction of new power systems.

[0208] In summary, the insulation coordination device and method for UHV flexible DC converter stations provided by the present invention install lightning arresters at different positions of the UHV flexible DC converter station, and the configuration parameters of the lightning arresters installed at different positions meet the performance design indicators of the UHV flexible DC system. Therefore, the insulation coordination of the UHV flexible DC converter station can be achieved through the lightning arresters installed at different positions, reducing the economic cost of the insulation coordination of the UHV flexible DC converter station.

[0209] It can be understood that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0210] The above embodiments only represent several implementation manners of the present invention, and the description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. An insulation coordination device for a UHV flexible DC converter station, characterized in that: It includes a positive ultra-high voltage flexible DC system and a negative ultra-high voltage flexible DC system, and the positive ultra-high voltage flexible DC system and the negative ultra-high voltage flexible DC system both include: Arrester whose configuration parameters meet the performance design index of the UHV flexible DC system; the arrester is used to achieve the insulation coordination of the UHV flexible DC converter station; the arrester includes a ground arrester and / or an end-to-end arrester; the configuration parameters include one or more of the following: the maximum continuous operating voltage at different arrester positions of the UHV flexible DC system, and the reference voltage, operating impulse protection level, coordination current, energy and operating impulse insulation level that the arrester at each position needs to withstand of the arrester of the UHV flexible DC converter station; The ground arrester includes one or more of the following: a high-end converter transformer valve side arrester, a low-end converter transformer valve side arrester, a high-end upper bridge arm reactor valve side arrester, a high-end lower bridge arm reactor valve side arrester, a low-end upper bridge arm reactor valve side arrester, a low-end lower bridge arm reactor valve side arrester, a valve top arrester, a high- and low-end converter valve midpoint DC bus arrester, a DC line side arrester, a first neutral line arrester and a second neutral line arrester, a grounding electrode line arrester and a metal return line arrester; and / or The terminal arrester includes one or more of the following: a high-end converter valve upper bridge arm terminal arrester, a low-end converter valve upper bridge arm terminal arrester and a high-end converter valve overall terminal arrester.

2. The insulation coordination device for a UHV flexible DC converter station according to claim 1, characterized in that: The terminal arrester also includes one or more of the following: Lightning arresters between the lower bridge arm ends of the high-end converter valve, lightning arresters between the lower bridge arm ends of the low-end converter valve, and parallel lightning arresters between the DC reactor ends.

3. An insulation coordination method for a UHV flexible DC converter station based on the insulation coordination device for a UHV flexible DC converter station according to claim 1 or 2, characterized in that: include: Perform transient overvoltage simulation to determine whether the configuration parameters of the arrester meet the performance design indicators of the UHV flexible DC system to achieve insulation coordination of the UHV flexible DC converter station; When the configuration parameters of the lightning arrester do not meet the performance design index of the UHV flexible DC system and the insulation coordination of the UHV flexible DC converter station cannot be achieved, adjusting the lightning arrester; Transient overvoltage simulation is performed until the configuration parameters of the lightning arrester after adjustment meet the performance design indicators of the UHV flexible DC system to achieve insulation coordination of the UHV flexible DC converter station.

4. The insulation coordination method for a UHV flexible DC converter station according to claim 3, characterized in that: Determining the maximum continuous operating voltage at the location of the ground arrester, including: According to the transformation ratio of the converter transformer, the number of converter valves, the maximum operating voltage of the DC pole line and the maximum steady-state operation modulation ratio, the maximum continuous operating voltage at the position of the lightning arrester on the high-end converter transformer valve side and the maximum continuous operating voltage at the position of the lightning arrester on the low-end converter transformer valve side are determined respectively; According to the maximum operating voltage of the DC pole line, the maximum operating voltage of the midpoint busbar of the high-end and low-end converter valves, the maximum operating voltage of the neutral line, and the maximum fundamental frequency voltage and double frequency voltage borne by the bridge arm reactor, respectively determine the maximum continuous operating voltage at the valve side lightning arrester position of the high-end upper bridge arm reactor and the maximum continuous operating voltage at the valve side lightning arrester position of the high-end lower bridge arm reactor, the maximum continuous operating voltage at the valve side lightning arrester position of the low-end upper bridge arm reactor, and the maximum continuous operating voltage at the valve side lightning arrester position of the low-end lower bridge arm reactor; According to the maximum operating voltage of the DC pole line, respectively determine the maximum continuous operating voltage at the position of the valve top lightning arrester and the maximum continuous operating voltage at the position of the DC line side lightning arrester; According to the maximum operating voltage of the neutral line, respectively determine the maximum continuous operating voltage at the first neutral line arrester, the maximum continuous operating voltage at the second neutral line arrester, the maximum continuous operating voltage at the grounding line arrester, and the maximum continuous operating voltage at the metal return line arrester; Determine the maximum continuous operating voltage at the location of the terminal arrester, including: According to the maximum operating voltage and the maximum overvoltage operating multiple of the DC pole line, the highest continuous operating voltage at the locations of the lightning arrester between the upper bridge arm ends of the high-end converter valve, the lightning arrester between the upper bridge arm ends of the low-end converter valve, the lightning arrester between the entire ends of the high-end converter valve, the lightning arrester between the lower bridge arm ends of the high-end converter valve, and the lightning arrester between the lower bridge arm ends of the low-end converter valve are determined respectively; The highest continuous operating voltage at the position of the parallel lightning arrester between the DC reactor terminals does not exceed the first preset voltage value.

5. The insulation coordination method for a UHV flexible DC converter station according to claim 4, characterized in that: Determine the reference voltage of the lightning arrester, including: According to the highest continuous operating voltage and charge rate at the arrester position, determine the reference voltage of the high-end converter transformer valve-side arrester, the low-end converter transformer valve-side arrester, the high-end upper bridge arm reactor valve-side arrester, the high-end lower bridge arm reactor valve-side arrester, the low-end upper bridge arm reactor valve-side arrester, the low-end lower bridge arm reactor valve-side arrester and the valve top arrester; The reference voltage of the grounding line arrester is smaller than the reference voltage of the metal return line arrester, and the reference voltage of the metal return line arrester is smaller than the reference voltage of the second neutral line arrester; According to the insulated gate bipolar transistor withstanding overvoltage, the reference voltages of the lightning arresters between the upper bridge arm ends of the high-end converter valve, the lightning arresters between the upper bridge arm ends of the low-end converter valve, the lightning arresters between the lower bridge arm ends of the high-end converter valve, and the lightning arresters between the lower bridge arm ends of the low-end converter valve are determined respectively.

6. The insulation coordination method for a UHV flexible DC converter station according to claim 5, characterized in that: Determine the arrester's switching surge protection level, including: According to the voltage ratio and reference voltage of the arrester, the switching impulse protection levels of the high-end converter transformer valve-side arrester, the low-end converter transformer valve-side arrester, the high-end upper arm reactor valve-side arrester, the high-end lower arm reactor valve-side arrester, the low-end upper arm reactor valve-side arrester, the low-end lower arm reactor valve-side arrester, and the valve top arrester are determined respectively; According to the number of submodules in a single bridge arm, the withstand overvoltage and protection margin of the insulated gate bipolar transistor of the arrester, the switching impulse protection levels of the arrester between the upper bridge arm ends of the high-end converter valve, the arrester between the upper bridge arm ends of the low-end converter valve and the overall end-to-end arrester of the high-end converter valve, the DC bus arrester at the midpoint of the high-end and low-end converter valves, the arrester between the lower bridge arm ends of the high-end converter valve, and the arrester between the lower bridge arm ends of the low-end converter valve are determined respectively; The switching impulse protection level of the first neutral line lightning arrester is determined based on the overvoltage suppression coefficient and the maximum operating voltage of the DC pole line.

7. The insulation coordination method for a UHV flexible DC converter station according to claim 3, characterized in that: Determine the coordination current of the arrester, including: The coordination current of the lightning arrester satisfies the first current range.

8. The insulation coordination method for a UHV flexible DC converter station according to claim 3, characterized in that: Determine the energy of the lightning arrester, including: The energy of the arrester is determined based on the energy unevenness coefficient, the number of series-connected resistors, the number of parallel-connected columns of the arrester, the energy of the single-chip resistor and the withstand voltage of the single-chip resistor.

9. The insulation coordination method for a UHV flexible DC converter station according to claim 6, characterized in that: Determine the level of switching impulse insulation that the arrester needs to withstand, including: Based on the switching impulse protection level and insulation margin of the lightning arrester, determine the switching impulse insulation level that the lightning arrester needs to withstand.

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