Method and system for suppressing zero loss based on phase selection closing device
By selecting the phase closing device, the closing phase angle and closing time change threshold are calculated, and the zero point loss phenomenon in the transmission system is suppressed, and the problem of additional circuit breakers and high overvoltage surge current in the prior art is solved, thereby realizing the protection of system stability and insulation performance.
Patent Information
- Application Number
- CN202510463230.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-14
- Publication Date
- 2025-06-20
AI Technical Summary
In the prior art, when suppressing the loss of current zero point in the power transmission system, additional circuit breakers are required, which can easily cause high closing overvoltage and closing inrush current, affecting the insulation performance of the line and the stable operation of the system.
By using a method based on the phase selection and closing device, the closing phase angle and closing time change threshold are calculated using mathematical model and Kirchoff's voltage law, and the closing phase angle is selected to be between the critical closing phase angle and 90° to suppress the loss of zero point and control overvoltage and inrush current.
It realizes that without additional circuit breakers or damping, effectively suppress zero point loss, reduce the level of closing overvoltage and inrush current, and protects insulation performance and system stability.
Smart Images
Figure CN120184887A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of transmission line control, and particularly relates to a method and system for suppressing zero - point loss based on a phase - selection closing device. Background Art
[0002] In recent years, cables are gradually replacing overhead lines due to their advantages such as small floor area, high reliability, and little environmental impact. As the use of cable lines in the power transmission system increases, the phenomenon of zero - point loss of current in the power transmission system occurs more frequently. Among them, when closing a cable line with a shunt reactor, the zero - point loss phenomenon is likely to occur. This may cause the circuit breaker to be unable to disconnect within a certain period of time, and then the system loses protection and is prone to failures.
[0003] Methods for preventing the zero - point loss phenomenon are still being analyzed and compared to find the most suitable suppression measures. Previous studies have shown that the zero - point loss time of the closing current of a compensated cable line is related to the closing phase angle, compensation degree, size of the closing resistor, and input time, etc. Using a circuit breaker with a closing resistor will shorten the zero - loss time of the current flowing through the circuit breaker, but the failure rate of the closing resistor is relatively high, and a suitable resistance value needs to be configured. The scheme of de - energizing the reactor will reduce the line compensation degree and prevent the zero - point loss phenomenon from occurring, but it will cause insufficient inductive reactive power compensation in a certain area. With the application of phase - selection closing technology in engineering, by using a phase - selection closing device to close the cable line at an appropriate phase angle, the zero - point loss phenomenon can be prevented.
[0004] Since closing at the peak of the bus voltage will not result in zero - point loss, currently, closing at the peak of the bus voltage is often used to prevent the zero - point loss phenomenon. However, at the same time, using this method will generate a relatively high closing over - voltage and closing inrush current, which will damage the insulation performance of the power transmission system. There are many current suppression measures for zero - point loss, but they all have obvious defects: Closing the shunt reactor and the cable simultaneously at the peak of the bus voltage will result in a relatively high closing over - voltage and closing inrush current, endangering the insulation performance of the line and the stable operation of the system. Using a circuit breaker with DC - bias damping is relatively expensive, requires considering the thermal effect of the resistor, and requires selecting a suitable resistance value for the damping. De - energizing the reactor requires installing a separate circuit breaker for the reactor and may cause insufficient reactive power compensation in a certain area. Sequential closing (including cable first closing and shunt reactor first closing) requires installing a separate circuit breaker for the shunt reactor. In summary, among the current suppression measures for zero - point loss, additional circuit breakers need to be configured, and it is easy to cause relatively high closing over - voltage and closing inrush current, affecting the insulation performance of the line and the stable operation of the system. Summary of the Invention
[0005] The present invention provides a method and system for suppressing zero - point loss based on a phase - selective switching - on device, aiming to solve the problems in current zero - point loss suppression measures, such as the need to configure additional circuit breakers, which easily causes relatively high switching - on over - voltage and switching - on inrush current, affecting the insulation of the line and the stability of the power system.
[0006] To achieve the above object, the present invention adopts the following technical solutions: The present invention provides a method for suppressing zero - point loss based on a phase - selective switching - on device, including the following steps: S1. Based on the mathematical model of the closing cable line, write a differential equation set according to Kirchhoff's voltage law, and solve the expression of the current flowing through the circuit breaker when closing the cable line, where: The expression of the current flowing through the circuit breaker when closing the cable line consists of a DC component and an AC component; S2. According to the expression of the current flowing through the circuit breaker, analyze the condition for the current flowing through the circuit breaker not to have zero - point loss; where: The condition is that the maximum value of the DC component of the current is less than or equal to the amplitude of the AC component; S3. By making the maximum value of the DC component equal to the amplitude of the AC component, calculate the critical closing phase angle, and select the closing phase angle between the critical closing phase angle and 90° to suppress the zero - point loss phenomenon; S4. According to the mechanical dispersion of the circuit breaker closing time, calculate the closing - time change threshold by presetting the tolerable decay time, and ensure that the actual closing phase angle does not exceed the difference range between the critical closing phase angle and the closing - time change threshold, so as to suppress zero - point loss and control over - voltage and inrush current.
[0007] In some embodiments, in S1, the mathematical model of the closing cable line is established through a lumped - parameter circuit.
[0008] Further, in S1, the expression of the current flowing through the circuit breaker when closing a compensated cable line is the following formula (1): (1); Where, is the current flowing through the circuit breaker, is the AC component of the current, is the DC component of the current, is the amplitude of the power - supply voltage, is the angular frequency of the power - frequency voltage, is the equivalent capacitance of the cable line, is the inductance of the shunt reactor, is the equivalent resistance of the line, is the closing phase angle.
[0009] Further, in S1, the current flowing through the shunt reactor and the current flowing through the cable line satisfy the following formula (2): (2); Wherein, is the current flowing through the reactor, is the current flowing through the cable line, is the shunt compensation degree.
[0010] In some embodiments, in S1, the current expression is obtained by solving a differential equation system written based on Kirchhoff's voltage law for a lumped parameter circuit including a power source, a shunt reactor, and a cable line. Further, in S2, by making the maximum value of the DC component in the current expression flowing through the circuit breaker equal to the amplitude of the AC component, the following formula (3) can be obtained: (3); Wherein, is the critical closing phase angle, When, the DC component is less than the amplitude of the AC component.
[0011] In some embodiments, in S3, the expression of the critical closing phase angle is as follows formula (4); (4).
[0012] In some embodiments, in S4, the expression of the closing time change threshold is as follows formula (7); (7); Wherein, is the phase angle difference corresponding to the closing time change threshold, is the closing phase angle corresponding to the closing time change threshold; is calculated by the following formula (6): (6); Wherein, is the preset tolerable decay time.
[0013] In some embodiments, in S4, based on the actually tolerable decay time and on the premise of the mechanical dispersion of the circuit breaker closing time, a phase angle greater than the critical closing phase angle is selected for closing.
[0014] The present invention also provides a system for suppressing zero - point loss based on a phase - selection closing device. The system includes an expression calculation module, a condition analysis module, a calculation and selection module, and a calculation and verification module, wherein: Expression calculation module: used to write a differential equation system based on the mathematical model of the closing cable line by Kirchhoff's voltage law, and solve the expression of the current flowing through the circuit breaker when closing the cable line, where: The expression of the current flowing through the circuit breaker when closing the cable line consists of a DC component and an AC component; Condition analysis module: used to analyze the condition that the current flowing through the circuit breaker does not lose its zero point according to the expression of the current flowing through the circuit breaker; where: The condition is that the maximum value of the DC component of the current is less than or equal to the amplitude of the AC component; Calculation and selection module: used to calculate the critical closing phase angle by making the maximum value of the DC component equal to the amplitude of the AC component, and select the closing phase angle between the critical closing phase angle and 90° to suppress the zero point loss phenomenon; Calculation and verification module: used to calculate the threshold value of the closing time change according to the mechanical dispersion of the circuit breaker closing time by presetting the tolerable decay time, and ensure that the actual closing phase angle does not exceed the difference range between the critical closing phase angle and the closing time change threshold value, so as to suppress the zero point loss and control the overvoltage and inrush current.
[0015] Compared with the prior art, a method for suppressing zero point loss based on a phase selection closing device of the present invention has the following beneficial effects: A method for suppressing zero point loss based on a phase selection closing device of the present invention only uses a phase selection closing device and does not require additional circuit breakers or dampers. It is simple and cheap compared with other methods. At the same time, the closing phase angle selection strategy determined by the present invention can not only suppress the zero point loss phenomenon, but also avoid the overvoltage and inrush current during closing to the greatest extent, which is beneficial to protecting the insulation performance and the stable operation of the system. Finally, the present invention also considers the inherent mechanical dispersion of the phase selection closing device and modifies the closing phase angle selection strategy accordingly, and can select a more appropriate closing phase angle according to the actual engineering situation, with better applicability. Description of the Drawings
[0016] The accompanying drawings in the specification are used to provide a further understanding of the present invention, and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.
[0017] Figure 1 It is a schematic circuit diagram of a method for suppressing zero point loss based on a phase selection closing device of the present invention. Detailed Embodiments
[0018] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. Components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a variety of different configurations.
[0019] Therefore, the detailed description of the embodiments of the present invention provided in the drawings below is not intended to limit the scope of the claimed invention, but is merely representative of selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.
[0020] It should be noted that like reference numerals and letters denote like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
[0021] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper", "lower", "horizontal", "inner", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, or the orientations or positional relationships in which the inventive product is customarily placed during use, it is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention. In addition, terms such as "first", "second", etc. are only used for descriptive distinction and should not be construed as indicating or implying relative importance.
[0022] In addition, if the term "horizontal" appears, it does not mean that the component is required to be absolutely horizontal, but it can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but it can be slightly inclined.
[0023] In the description of the embodiments of the present invention, it should also be noted that unless otherwise clearly specified and limited, if terms such as "set", "installed", "connected", "coupled" are understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.
[0024] A method for effectively suppressing zero - point loss only by using a phase - selection closing device, and the obtained closing phase - angle selection strategy can minimize the levels of closing over - voltage and closing inrush current, avoid excessive closing over - voltage and closing inrush current, and is beneficial to protecting the insulation performance and the stable operation of the system.
[0025] Based on this, as Figure 1 shown, a method for suppressing zero - point loss based on a phase - selection closing device according to the present invention is characterized by including the following steps: S1. Based on the mathematical model of the closing cable line, write a differential equation set by Kirchhoff's voltage law, and solve the expression of the current flowing through the circuit breaker when closing the cable line, where: The expression of the current flowing through the circuit breaker when closing the cable line consists of a DC component and an AC component; S2. According to the expression of the current flowing through the circuit breaker, analyze the conditions under which the current flowing through the circuit breaker does not have the zero - point loss phenomenon; where: The condition is that the maximum value of the DC component of the current is less than or equal to the amplitude of the AC component; S3. By making the maximum value of the DC component equal to the amplitude of the AC component, calculate the critical closing phase - angle, and select the closing phase - angle between the critical closing phase - angle and 90° to suppress the zero - point loss phenomenon; S4. According to the mechanical dispersion of the closing time of the circuit breaker, calculate the closing - time change threshold by presetting the tolerable decay time, and ensure that the actual closing phase - angle does not exceed the difference range between the critical closing phase - angle and the closing - time change threshold, so as to suppress the zero - point loss and control the over - voltage and inrush current.
[0026] A method for suppressing zero - point loss based on a phase - selection closing device according to the present invention solves the expression of the current flowing through the circuit breaker when closing the cable line by using a lumped - parameter circuit; analyzes the conditions under which the current flowing through the circuit breaker does not have the zero - point loss phenomenon according to the obtained expression; and obtains the selection strategy of the closing phase - angle according to the summarized conditions.
[0027] As Figure 1 shown, let the current flowing through the circuit breaker be i ( t ), the currents flowing through the reactor and the cable line are respectively I L ( t ) and i C ( t ), and the power - supply voltage is u ( t ) = U m sin( ωt + α ), where ω is the power - frequency voltage angular frequency, αis the initial voltage phase angle, i.e., the closing phase angle. According to Kirchhoff's voltage law, a differential equation system can be written to solve the current expressions flowing through the shunt reactor and the cable line. Adding the two expressions gives the current expression flowing through the circuit breaker as follows: (1); (2); where is the current flowing through the circuit breaker, is the AC component of the current, is the DC component of the current, is the amplitude of the power supply voltage, is the angular frequency of the power frequency voltage, is the equivalent capacitance of the cable line, is the inductance of the shunt reactor, is the equivalent resistance of the line, is the closing phase angle; is the current flowing through the reactor, is the current flowing through the cable line, is the shunt compensation degree.
[0028] It can be seen from the above formula that the current flowing through the circuit breaker consists of the DC component of the current i dc ( t ) and the AC component of the current i ac ( t ). The AC component of the current can be regarded as consisting of the AC component flowing through the cable line and the AC component flowing through the shunt reactor line. The absolute value of the ratio of the AC component flowing through the shunt reactor line to the AC component flowing through the cable line is equal to the shunt compensation degree K sh .
[0029] At the same time, it can also be seen from the above formula that from the DC component expression part, when the line is closed at the voltage peak ( α = 90°), the DC component is the largest. When the line is closed at the voltage zero crossing ( α = 0°), there is no DC component. In addition, when the DC component of the current flowing through the circuit breaker is greater than the AC component, the current flowing through the circuit breaker cannot cross the zero point even at the reverse peak of the AC component, resulting in the phenomenon of zero point loss. Therefore, it can be found that when the magnitude of the DC component is equal to the amplitude of the AC component, the current flowing through the circuit breaker just does not show the phenomenon of zero point loss. Through this criterion, the present invention determines the selection strategy of the closing phase angle.
[0030] The second part (step 3): Let the maximum value of the DC component in the current expression flowing through the circuit breaker be equal to the amplitude of the AC component, and the following formula can be obtained: (3); Wherein, is the critical closing phase angle, when, the DC component is less than the amplitude of the AC component.
[0031] The obtained closing phase angle α 0 is the critical closing phase angle at which the zero - point loss phenomenon just does not occur. When the closing phase angle is between the critical closing phase angle and 90°, the zero - point loss phenomenon will not occur. When the closing phase angle is between 0° and the critical closing phase angle, the zero - point loss phenomenon will occur.
[0032] Simplifying the above formula, the expression of the critical closing phase angle can be obtained as follows: (4).
[0033] The implementation of this method requires accurately controlling the closing of each phase of the circuit breaker at the preset closing phase angle. In practice, it is very difficult for the circuit breaker to achieve accurate closing, that is, there are generally differences between the actual closing time and the preset closing time. The changes in the closing time can be divided into two types, one is predictable and the other is random. Predictable changes (e.g., long - term aging) do not affect the effectiveness of the phase - selective closing and can be compensated by adaptive control. However, the random changes in the closing time (e.g., inherent mechanical dispersion) may cause the cable and reactor to be energized at a closing phase angle different from the preset one. When the random change in the closing time exceeds a certain threshold, the cable and reactor are closed at a certain point on the voltage waveform, and at this time, the DC component of the line breaker current is greater than the AC component. This means that although the preset closing phase angle can avoid the zero - point loss phenomenon, the zero - point loss phenomenon actually still occurs. Therefore, this method is effective only when the random change in the circuit breaker closing time does not exceed a certain threshold. This invention names this threshold as the circuit breaker closing change threshold. The circuit breaker closing change threshold represents the maximum change in the circuit breaker closing time before and after the critical closing phase angle, so that the current flowing through the circuit breaker crosses the zero - point before the preset time limit. If the change in the closing time causes the actual closing time to exceed the circuit breaker closing change threshold, then the DC component will be greater than the absolute value of the AC component amplitude, and the zero - point loss phenomenon will occur. For the calculation of the circuit breaker closing change threshold, it is necessary to make the DC component after decaying for a certain time equal to the absolute value of the AC component amplitude. The preset tolerable decay time t delay can be changed according to the actual engineering situation. Then we can obtain the following calculation formula: (5); Wherein, is the time, with the unit of second (s).
[0034] Simplifying the above formula, we can get: (6); (7); where is the phase angle difference corresponding to the closing time change threshold, is the closing phase angle corresponding to the closing time change threshold.
[0035] By inputting the preset tolerable decay time into the above formula, the present invention can obtain the closing phase angle corresponding to the corresponding closing time change threshold α 1, and then subtracting it from the critical closing phase angle to obtain the breaker closing change threshold. Finally, based on the actually tolerable decay time, under the premise of considering mechanical dispersion, a phase angle greater than the critical closing phase angle can be selected for closing, so as to minimize the impact of zero-crossing loss while ensuring that the closing overvoltage and closing inrush current are maintained at a relatively low level.
[0036] The present invention also provides a system for suppressing zero-crossing loss based on a phase-selection closing device. The system includes an expression calculation module, a condition analysis module, a calculation and selection module, and a calculation and verification module, where: Expression calculation module: used to write a differential equation set based on the mathematical model of the closing cable line through Kirchhoff's voltage law, and solve the expression of the current flowing through the breaker when closing the cable line, where: The expression of the current flowing through the breaker when closing the cable line consists of a DC component and an AC component; Condition analysis module: used to analyze the condition that the current flowing through the breaker does not have a zero-crossing loss phenomenon according to the expression of the current flowing through the breaker; where: The condition is that the maximum value of the DC component of the current is less than or equal to the amplitude of the AC component; Calculation and selection module: used to calculate the critical closing phase angle by making the maximum value of the DC component equal to the amplitude of the AC component, and select a closing phase angle between the critical closing phase angle and 90° to suppress the zero-crossing loss phenomenon; Calculation and verification module: used to calculate the closing time change threshold by presetting the tolerable decay time according to the mechanical dispersion of the breaker closing time, and ensure that the actual closing phase angle does not exceed the difference range between the critical closing phase angle and the closing time change threshold, so as to suppress the zero-crossing loss and control the overvoltage and inrush current.
[0037] A method and system for suppressing zero - point loss based on a synchronous closing device in the present invention. Only the synchronous closing device is used, without the need to configure additional circuit breakers or dampers. Compared with other methods, the device is simple and inexpensive. At the same time, the closing phase - angle selection strategy determined in the present invention can not only suppress the zero - point loss phenomenon, but also avoid excessive closing over - voltage and closing inrush current to the greatest extent, which is beneficial to protecting the insulation performance and the stable operation of the system. Finally, the present invention also considers the inherent mechanical dispersion of the synchronous closing device and modifies the closing phase - angle selection strategy accordingly, so that a more appropriate closing phase - angle can be selected according to the actual engineering situation.
[0038] The present invention can effectively suppress zero - point loss only by using the synchronous closing device. The obtained closing phase - angle selection strategy can minimize the levels of closing over - voltage and closing inrush current, and at the same time takes into account the inherent mechanical dispersion of the synchronous closing device. The method of the present invention is not targeted and can be applied to the working conditions of most cable lines with shunt reactors during closing, having better applicability.
[0039] Finally, it should be noted that: the above - mentioned is only the preferred embodiment of the present invention, and does not impose any form of limitation on the present invention; any ordinary technical personnel in the industry can smoothly implement the present invention according to what is shown in the specification and the above - mentioned. Any equivalent changes such as slight modifications, decorations and evolutions made by using the technical content disclosed above are equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above - mentioned embodiments based on the essential technology of the present invention still fall within the protection scope of the technical solution of the present invention.
Claims
1. A method for suppressing zero point loss based on a phase selection closing device, characterized in that: The steps include: S1. Based on the mathematical model of the closed cable line, write a group of differential equations through Kirchhoff's voltage law to solve the expression of the current flowing through the circuit breaker when the cable line is closed, where: The expression for the current flowing through the circuit breaker when the cable line is closed consists of a DC component and an AC component; S2. Based on the expression of the current flowing through the circuit breaker, analyze the conditions for the current flowing through the circuit breaker to avoid zero point loss; where: The condition is that the maximum value of the DC component of the current is less than or equal to the amplitude of the AC component; S3, by making the maximum value of the DC component equal to the amplitude of the AC component, calculating the critical closing phase angle, and selecting the closing phase angle to be between the critical closing phase angle and 90° to suppress the zero point loss phenomenon; S4. According to the mechanical dispersion of the circuit breaker closing time, the closing time change threshold is calculated by presetting the tolerable attenuation time to ensure that the actual closing phase angle does not exceed the difference range between the critical closing phase angle and the closing time change threshold, thereby suppressing zero point loss and controlling overvoltage and inrush current.
2. The method for suppressing zero point loss based on a phase selection closing device according to claim 1 is characterized in that: In the S1, the mathematical model of the closing cable line is established by a lumped parameter circuit.
3. The method for suppressing zero point loss based on a phase selection closing device according to claim 2 is characterized in that: In S1, the expression of the current flowing through the circuit breaker when closing the compensation cable line is as follows: （1）； in, is the current flowing through the circuit breaker, is the AC component of the current, is the DC component of the current, is the power supply voltage amplitude, Power frequency voltage angular frequency, is the equivalent capacitance of the cable line, is the inductance of the shunt reactor, is the equivalent resistance of the line, is the closing phase angle.
4. The method for suppressing zero point loss based on a phase selection closing device according to claim 3 is characterized in that: In S1, the current flowing through the shunt reactor and the current flowing through the cable line satisfy the following formula (2): （2）； in, is the current flowing through the reactor, is the current flowing through the cable line, is the parallel compensation degree.
5. The method for suppressing zero point loss based on a phase selection closing device according to claim 1, characterized in that: In S1, the current expression is obtained by solving a group of differential equations for a concentrated parameter circuit including a power supply, a shunt reactor and a cable line using Kirchhoff's voltage law.
6. The method for suppressing zero point loss based on a phase selection closing device according to claim 5, characterized in that: In S2, the maximum value of the DC component in the expression of the current flowing through the circuit breaker is set equal to the amplitude of the AC component, and the following formula (3) can be obtained: （3）； in, is the critical closing phase angle, When , the DC component is smaller than the AC component.
7. The method for suppressing zero point loss based on a phase selection closing device according to claim 6, characterized in that: In S3, the critical closing phase angle is calculated by the following formula (4): （4）。 8. The method for suppressing zero point loss based on a phase selection closing device according to claim 1, characterized in that: In S4, the expression of the closing time change threshold is as follows: （7）； in, is the phase angle difference corresponding to the closing time change threshold, is the closing phase angle corresponding to the closing time change threshold; It is calculated by the following formula (6): （6）； in, is the preset tolerable decay time.
9. The method for suppressing zero point loss based on a phase selection closing device according to claim 1, characterized in that: In S4, based on the actually tolerable decay time and the mechanical dispersion of the circuit breaker closing time, a phase angle greater than the critical closing phase angle is selected for closing.
10. A system based on the method for suppressing zero point loss based on a phase selection closing device as described in any one of claims 1 to 9, characterized in that: The system includes an expression calculation module, a condition analysis module, a calculation and selection module, and a calculation and verification module, wherein: Expression calculation module: It is used to write a differential equation group based on the mathematical model of the closed cable line through Kirchhoff's voltage law to solve the expression of the current flowing through the circuit breaker when the cable line is closed, where: The expression for the current flowing through the circuit breaker when the cable line is closed consists of a DC component and an AC component; Conditional analysis module: used to analyze the conditions for the current flowing through the circuit breaker to avoid zero point loss according to the expression of the current flowing through the circuit breaker; where: The condition is that the maximum value of the DC component of the current is less than or equal to the amplitude of the AC component; Calculation and selection module: used to calculate the critical closing phase angle by making the maximum value of the DC component equal to the amplitude of the AC component, and select the closing phase angle to be between the critical closing phase angle and 90° to suppress the zero point loss phenomenon; Calculation and verification module: used to calculate the closing time change threshold according to the mechanical dispersion of the circuit breaker closing time by presetting the tolerable attenuation time, to ensure that the actual closing phase angle does not exceed the difference range between the critical closing phase angle and the closing time change threshold, thereby suppressing zero point loss and controlling overvoltage and inrush current.