SF 6 Fatigue life analysis method for oil buffer of circuit breaker operating mechanism

Abstract

The present invention relates to the technical field of life state evaluation of key accessories of the operating mechanism of SF6 circuit breakers, and particularly relates to a fatigue life analysis method for the oil buffer of the operating mechanism of SF6 circuit breakers. The simulation method includes establishing an overall three-dimensional model of the circuit breaker operating mechanism to carry out rigid body dynamics calculations to obtain accurate changes in piston force; selecting typical and key positions during the operation process of the oil buffer as calculation points to obtain comprehensive static calculations and fatigue analysis of the oil buffer; calculating the fatigue life distribution of the oil buffer based on Hooke's law, stress life, and the S-N curve of the material. The fatigue life analysis method adopted by the present invention calculates the fatigue life during the operation process of the oil buffer of the SF6 circuit breaker operating mechanism accurately and comprehensively, uses it to find the real life weak points, provides a guiding direction for the subsequent design optimization of the oil buffer, and also provides a theoretical basis for the condition monitoring of the circuit breaker operating mechanism.

Description

Technical Field

[0001] The present invention relates to the technical field of life state evaluation of key accessories of SF 6 circuit breaker operating mechanisms, and more particularly to a fatigue life analysis method for oil buffers used in SF 6 circuit breaker operating mechanisms. Background Art

[0002] As the most widely used switching equipment in the power system, circuit breakers play important roles such as cutting off faults and switching loads, and their status is very important. During long-term operation, the key components of the circuit breaker operating mechanism will continuously deteriorate in health status due to mechanical stress fatigue and damage accumulation until they fail. If not repaired in time, it will lead to circuit breaker failures and power supply interruptions. Spring operating mechanisms are widely used in SF 6 circuit breakers because of their simple principle and structure, small size, light weight, no risk of gas or liquid leakage, low requirements for assembly and commissioning, and the opening and closing speed can fully meet the opening and closing requirements of general circuit breakers. Among domestic in-service circuit breakers, except for a small number of pneumatic operating mechanisms from manufacturers such as Siemens and ABB, basically all are spring operating mechanisms, and the applicable range basically covers the power systems with voltage levels from 10 kV to 550 kV.

[0003] The opening and closing speeds of high-voltage circuit breakers are very high. For an SF 6 circuit breaker with a voltage level of 126 kV, the maximum speed of the moving contact during the opening process can reach 5 m / s. To prevent rigid impacts between moving parts with high speeds, a buffer must be used to absorb and convert the kinetic energy of the impact load, so as to minimize the adverse effects of mechanical impact on the circuit breaker. In addition, during the commissioning process of the mechanism, in addition to adjusting the pre-compressed length of the opening and closing springs and the gaps between different mechanisms, generally, the design and assembly method of the oil buffer will also be adjusted to adjust the mechanical output characteristics of the operating mechanism. Therefore, the oil buffer is very important in the spring operating mechanism.

[0004] The buffer needs to bear multiple loads during the continuous operation of the circuit breaker. Coupled with possible deficiencies in the production process and assembly process, the buffer may age prematurely and fail to reach the expected design life. Therefore, it is necessary to carry out fatigue life analysis on the oil buffer, which can not only find the weak points of the life and provide a guiding direction for the subsequent design optimization of the oil buffer, but also obtain the action characteristics of the oil buffer and provide a theoretical basis for the condition monitoring of the circuit breaker operating mechanism.

[0005] At present, some researchers have carried out static analysis on the oil buffer of the circuit breaker operating mechanism. However, only the static calculation when the pressure of the inner rod is the largest is often considered. However, the action of the oil buffer is a continuous process. Since there are multiple oil drainage damping holes on the wall surface of the buffer cavity, the piston moving to different positions may have different effects on different damping holes and the wall surface of the cavity. The entire movement process of the piston needs to be considered in the fatigue life calculation. Summary of the Invention

[0006] The purpose of the present invention is to propose a method for analyzing the fatigue life of the oil buffer for the circuit breaker operating mechanism of SF 6 to obtain the static analysis and fatigue life during the action process of the oil buffer for the circuit breaker operating mechanism of SF 6 so as to obtain the most vulnerable position of the oil buffer and its cycle life.

[0007] To achieve the above purpose, the present invention provides a method for analyzing the fatigue life of the oil buffer for the circuit breaker operating mechanism of SF 6 including the following steps:

[0008] S1. Establish a simulation model: Establish a three-dimensional model of the operating mechanism according to the actual structural dimensions of the circuit breaker operating mechanism;

[0009] S2. Calculate the change in the force on the piston during the action process of the oil buffer: Set relevant constraints and load conditions according to the actual assembly, and calculate the change in the force on the piston during opening and closing based on the rigid body dynamics equation and the forces on each fitting;

[0010] S3. Select typical piston displacement positions, and select the pressure mutation points and the position where the piston moves to the edge of the damping hole as typical key calculation positions; Considering that the vicinity of the oil drainage damping hole is often a stress concentration point, so select the position where the piston moves above or below a certain damping hole as a characteristic point; At the same time, supplement the mutation points of the piston force;

[0011] S4. Set the calculation boundary conditions, set the load on the wall surface of the lower inner cavity and damping hole of the piston to P; Set the load on the wall surface of the upper inner cavity, damping hole and outer cavity wall of the piston to one atmospheric pressure; Set the external piston rod and the oil cylinder seat of the cylinder body to fixed constraints;

[0012] S5. Static solid mechanics calculation, based on basic parameters such as material density, Young's modulus and Poisson's ratio, calculate the stress and strain distribution of the oil cylinder during opening and closing based on Hooke's law;

[0013] S6. Fatigue life analysis during the action process of the oil buffer, based on the material S-N curve and stress life, calculate the change in the failure cycle life during the action process of the oil buffer, and find out the weak points of the buffer.

[0014] As a further technical improvement, step S2 specifically includes the following steps:

[0015] S2-1. The motion of all components satisfies the rigid body dynamics equation:

[0016]

[0017] In the formula, M is the generalized mass matrix, J is the generalized moment of inertia matrix, and k is the kinetic energy;

[0018] S2-2. Conduct dynamic calculations on each key component to satisfy the following theoretical calculation equations:

[0019]

[0020] In the formula, M and J are the torque and moment of inertia of the cam, F 1 is the closing spring force, F 2 is the force exerted by the roller on the cam under the action of the opening spring and the buffer spring, is the cam rotation angle, r 1 is the equivalent radius of the cam, v 3 is the velocity of the moving contact, and s is the displacement of the moving contact;

[0021] S2-3. Calculate the pressure change in the inner cavity of the oil buffer: According to the rigid body dynamics calculation, obtain the force change from the rocker arm to the connecting rod to the piston. Assume that the pressure at any position in the inner cavity is equal at any time, and obtain the inner cavity pressure at any piston displacement through the following formula:

[0022] P(t) = F(t) / S 活塞表面 (3)

[0023] In the formula, P is the internal pressure of the oil buffer, F is the force on the piston, and S is the bottom surface area of the piston.

[0024] As a further technical improvement, for the static solid mechanics calculation described in step S5, all components of the oil buffer satisfy the following equations:

[0025] The axial stress is the ratio of the axial force F to the corresponding cross-sectional area A:

[0026]

[0027] The axial strain is the ratio of the elongation Δ to the length L in the elongation direction:

[0028]

[0029] The two constitute the constitutive relationship:

[0030] σ xx = Eε xx (6)

[0031] Where E is the Young's modulus of the material;

[0032] The ratio between stress and strain or force and displacement is called Hooke's law; the stiffness relationship of the material is:

[0033]

[0034] The relationship between the transverse strain and the axial strain is given by the Poisson's ratio:

[0035] ε yy =ε zz = - νε xx (8)

[0036] The stress and strain distributions of the oil buffer at each calculation position are obtained by calculating from the above equations.

[0037] As a further technical improvement, for the fatigue life analysis of the oil buffer during the operation process in step S6, for each calculation position, it specifically includes the following steps:

[0038] The process of the degradation of material strength with the attenuation of the number of load cycles is represented by the S - N curve, and the cyclic load is the cycle between the actual pressure and one atmospheric pressure:

[0039] σ a =f SN (N) (9)

[0040] If a component undergoes fatigue damage under the action of a cyclic constant amplitude stress S and endures N cyclic loads, then the damage quantification value D when it endures n cycles is shown in Equation (10):

[0041] D = n / N (10)

[0042] Assume that a component undergoes damage D i when it endures n i cycles under the action of a stress level S i =n i / N i . If a single load history endured by the component includes the action of k stress levels S i (i = 1, 2, 3,..., k), and each stress level S i includes n i cycles, then the total damage under a single load history can be defined as shown in Equation (11):

[0043]

[0044] Where: n i is the number of cycles under the action of S i , determined by the load spectrum; Ni For S i The fatigue life under the action of S is determined by the S-N curve.

[0045] As a further technical improvement, by comparing the calculation results of each calculation position in step S6, the position with the minimum number of fatigue cycles is the weakest position of the oil buffer; and the fatigue life distribution of each position of the oil buffer at each critical moment can be obtained.

[0046] As a further technical improvement, the three-dimensional model of the operating mechanism established in step S1 includes closing and opening springs, cams, ratchets, crank arms, various detents, oil buffers, and fixing shafts, plates, and frames.

[0047] Compared with the prior art, the present invention has the following beneficial technical effects:

[0048] The present invention realizes a more comprehensive calculation of SF 6 The stress-strain and cyclic fatigue life of the oil buffer used in the circuit breaker operating mechanism during the action process, effectively obtaining the most vulnerable points of the oil buffer, providing theoretical support for the design optimization or condition monitoring of the oil buffer of the circuit breaker operating mechanism. Brief Description of the Drawings

[0049] In order to more clearly illustrate the embodiments of the present invention, the drawings required for the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0050] Figure 1 is the flowchart of the simulation method of the present invention.

[0051] Figure 2 is the simulation model diagram of the present invention.

[0052] Reference Signs in the Drawings: 1 - piston rod, 2 - piston, 3 - oil cylinder, 4 - oil cylinder base, 5 - damping hole. Detailed Embodiments

[0053] The embodiments of the present disclosure will be described in detail below with reference to the drawings.

[0054] The following describes the embodiments of the present disclosure through specific examples, and those skilled in the art can easily understand the other advantages and effects of the present disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. The present disclosure can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present disclosure. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present disclosure without creative efforts belong to the scope of protection of the present disclosure.

[0055] Embodiment:

[0056] As shown in the attached Figure 1-2 figure, this embodiment provides a method for analyzing the fatigue life of an oil buffer for a breaker operating mechanism, which is characterized by including the following steps: 6 The method for analyzing the fatigue life of an oil buffer for a breaker operating mechanism is characterized by including the following steps:

[0057] S1. Establish a simulation model: According to the actual structural dimensions of the breaker operating mechanism, establish a three-dimensional model of the operating mechanism, including closing and opening springs, cams, ratchets, crank arms, various pawls, oil buffers, and fixing shafts, plates, and frames. The ultimate goal of establishing the simulation model is to calculate the force change of the oil buffer piston rod during closing and opening. Since the closing and opening springs are the power sources of the operating mechanism, the model needs to consider the power source, transmission fittings, fixed constraint fittings, and oil buffers. Therefore, the established three-dimensional model needs to include closing and opening springs, cams, ratchets, crank arms, various pawls, oil buffers, and fixing shafts, plates, and frames. S2. Calculate the force change of the piston of the oil buffer during the action process: Set relevant constraint and load conditions according to the actual assembly, and calculate the force change of the piston during closing and opening based on the rigid body dynamics equation and the force of each fitting; the specific steps are as follows:

[0058] S2-1. The motion of all fittings satisfies the rigid body dynamics equation:

[0059]

[0060] In the formula, M is the generalized mass matrix, J is the generalized moment of inertia matrix, and k is the kinetic energy;

[0061] S2-2. Conduct dynamic calculations on each key fitting to satisfy the following theoretical calculation equations:

[0062]

[0063] In the formula, M and J are the torque and moment of inertia of the cam, F 1is the closing spring force, F 2 is the force exerted by the roller on the cam under the action of the opening spring and the buffer spring, is the rotational angle of the cam, r 1 is the equivalent radius of the cam, v 3 is the velocity of the moving contact, and s is the displacement of the moving contact;

[0064] S2-3. Calculate the pressure change in the inner cavity of the oil buffer: Calculate the force change from the rocker arm to the connecting rod to the piston according to rigid body dynamics. Assuming that the pressure at any position in the inner cavity is equal at any time, the inner cavity pressure at any piston displacement can be obtained through the following formula:

[0065] P(t) = F(t) / S 活塞表面 (3)

[0066] In the formula, P is the internal pressure of the oil buffer, F is the force on the piston, and S is the bottom surface area of the piston.

[0067] S3. Select typical piston displacement positions: After obtaining the force change of the piston through the static simulation of the oil buffer, select the pressure mutation point and the position where the piston moves to the edge of the damping hole as the typical key calculation positions; considering that the stress concentration point is often near the oil discharge damping hole, so select the position where the piston moves above or below a certain damping hole as a characteristic point; at the same time, supplement the mutation point of the piston force;

[0068] S4. Set the calculation boundary conditions. Set the load on the wall surface of the lower inner cavity of the piston and the damping hole to P; set the load on the wall surface of the upper inner cavity of the piston, the damping hole wall surface, and the outer cavity wall surface to one atmospheric pressure; set the external piston rod and the oil cylinder seat of the cylinder body to fixed constraints;

[0069] S5. Static solid mechanics calculation. Based on the basic parameters such as material density, Young's modulus, and Poisson's ratio, calculate the stress and strain distribution of the oil cylinder during the opening and closing processes based on Hooke's law; further, in the static solid mechanics calculation described in step S5, all components of the oil buffer satisfy the following equations:

[0070] The axial stress is the ratio of the axial force F to the cross-sectional area A corresponding to the axial force:

[0071]

[0072] The axial strain is the ratio of the elongation Δ to the length L in the elongation direction:

[0073]

[0074] The two constitute a constitutive relationship:

[0075] σ xx = Eε xx (6)

[0076] where E is the Young's modulus of the material;

[0077] The ratio between stress and strain, or force and displacement, is known as Hooke's law; the stiffness relationship of the material is:

[0078]

[0079] The relationship between the transverse strain and the axial strain is given by Poisson's ratio:

[0080] ε yy = ε zz = -νε xx (8)

[0081] The stress and strain distributions of the oil buffer at each calculation position are obtained by calculating from the above equations.

[0082] S6. Fatigue life analysis of the oil buffer during operation, based on the material S-N curve and stress life, calculate the change in the failure cycle life of the oil buffer during operation, and find the weak points (the most vulnerable points) of the buffer;

[0083] Specifically, for the fatigue life analysis of the oil buffer during operation in step S6, for each calculation position, it specifically includes the following steps: use the S-N curve to represent the process of material strength degradation with the attenuation of the number of load cycles, and the cyclic load is the cycle between the actual pressure and one atmosphere:

[0084] σ a = f SN (N) (9)

[0085] If a component suffers fatigue damage under the action of a cyclic constant amplitude stress S and undergoes N cyclic loads, then the damage quantification value D when it undergoes n cycles is shown in Equation (10):

[0086] D = n / N (10)

[0087] Assume that a component under the stress level S i suffers damage D i when it undergoes n i = n i / N i . If a single load history of a component includes the action of k stress levels S i (i = 1, 2, 3,..., k), and each stress level S i includes n i cycles, then the total damage under a single load history can be defined as shown in Equation (11):

[0088]

[0089] In the formula: ni is the number of cycles under the action of S, which is determined by the load spectrum; N i is the fatigue life under the action of S, which is determined by the S-N curve. i is S i is the fatigue life under the action of S, which is determined by the S-N curve.

[0090] Compare the calculation results of each calculation position in step S6, and the position with the minimum fatigue cycle number is the weakest position of the oil buffer; and the fatigue life distribution of each position of the oil buffer at each critical moment can be obtained.

[0091] Figure 2 It represents a schematic diagram of the simulation model, which means that when the piston moves to different positions, the load of P is set on the inner cavity wall of the lower part of the piston and the damping hole; the load of one atmospheric pressure is set on the inner cavity wall of the upper part of the piston, the damping hole wall and the outer cavity wall; the piston rod outside the cylinder block and the oil cylinder seat are set as fixed constraints. Based on this, static and fatigue life calculations are carried out.

[0092] The above is only a preferred and feasible embodiment of the present invention, and does not limit the scope of the rights of the present invention. For those of ordinary skill in the art, without departing from the principle described in the present invention, several improvements and refinements can be made. Any equivalent changes made by using the content of the specification and drawings of the present invention are included in the scope of the rights of the present invention.

Claims

1. A kind of SF 6 Fatigue life analysis method for oil buffer of breaker operating mechanism It is characterized in that it includes the following steps: S1. Establish a simulation model: Establish a three-dimensional model of the operating mechanism according to the structural dimensions of the actual circuit breaker operating mechanism. S2. Calculate the change in the force on the piston during the operation of the oil buffer: Set relevant constraints and load conditions according to the actual assembly, and calculate the change in the force on the piston during opening and closing based on the rigid body dynamics equation and the forces on each fitting. S3. Select typical piston displacement positions, and select the pressure mutation point and the position where the piston moves to the edge of the damping hole as typical key calculation positions. S4. Set the calculation boundary conditions, set the load on the wall surface of the lower inner cavity of the piston and the damping hole to P; set the load on the wall surface of the upper inner cavity of the piston, the damping hole wall surface, and the outer cavity wall surface to one atmospheric pressure; set the piston rod outside the cylinder body and the oil cylinder seat to fixed constraints. S5. Perform static solid mechanics calculations, and calculate the stress and strain distributions of the oil cylinder during opening and closing based on the basic parameters of material density, Young's modulus, and Poisson's ratio, and based on Hooke's law. S6. Analyze the fatigue life during the operation of the oil buffer, and calculate the change in the failure cycle life during the operation of the oil buffer based on the material S-N curve and stress life, and find the weak points of the buffer. In step S6, the fatigue life analysis during the operation of the oil buffer, for each calculation position, specifically includes the following steps: Use the S-N curve to represent the process of material strength degradation with the attenuation of the number of load cycles. The cyclic load is the cycle between the actual pressure and one atmospheric pressure. σ a = f SN (N) If a component suffers fatigue damage under the action of a cyclic constant amplitude stress S and withstands N cyclic loads, then the damage quantification value D when it withstands n cycles is shown by the following formula: D = n / N Assume that the damage of the component under the stress level S i is D when it undergoes n i cycles, where D i = n i / N i ; If a single load history of the component includes the action of k stress levels S i , where i = 1, 2, 3, …, k, and each stress level S i includes n i cycles, then the total damage under a single load history can be defined as shown in Equation (11): Where: n i is the number of cycles under the action of S i and is determined by the load spectrum; N i is the fatigue life under the action of S i and is determined by the S-N curve.

2. The SF according to claim 1 6 Fatigue life analysis method for oil buffer of breaker operating mechanism It is characterized in that step S2 specifically includes the following steps: S2-1. The motion of all fittings satisfies the rigid body dynamics equation: where M is the generalized mass matrix, J is the generalized moment of inertia matrix, and k is the kinetic energy. S2-2. Carry out dynamics calculations on each key fitting, satisfying the following theoretical calculation equations: where M and J are the torque and moment of inertia of the cam, and F 1 is the closing spring force, and F 2 is the force exerted by the roller on the cam under the action of the opening spring and buffer spring, is the rotational angle of the cam, r 1 is the equivalent radius of the cam, v 3 is the velocity of the moving contact, and s is the displacement of the moving contact; S2-3. Calculate the pressure change in the inner cavity of the oil buffer: According to the force change from the toggle arm to the connecting rod to the piston obtained by rigid body dynamics calculation, assuming that the pressure at any time and any position in the inner cavity is equal, the inner cavity pressure at any piston displacement is obtained through the following formula: P(t) = F(t) / S 活塞表面 where P is the internal pressure of the oil buffer, F is the force on the piston, and S is the bottom surface area of the piston.

3. The SF according to claim 1 6 Fatigue life analysis method for oil buffer of circuit breaker operating mechanism It is characterized in that in the static solid mechanics calculation described in step S5, all components of the oil buffer satisfy the following equations: The axial stress is the ratio of the axial force F to the cross-sectional area A corresponding to the axial force: The axial strain is the ratio of the elongation Δ to the length L in the elongation direction: The two constitute a constitutive relationship: σ xx = Eε xx where E is the Young's modulus of the material; The ratio between stress and strain or force and displacement is called Hooke's law; the stiffness relationship of the material is: The relationship between the transverse strain and the axial strain is given by Poisson's ratio: ε yy = ε zz = -νε xx The stress and strain distributions of the oil buffer at each calculation position are obtained by calculating the above equations.

4. The SF according to claim 1 6 Fatigue life analysis method for oil buffer of breaker operating mechanism It is characterized in that , comparing the calculation results of each calculation position in step S6, the position with the minimum number of fatigue cycles is the weakest position of the oil buffer; and the fatigue life distribution of each position of the oil buffer at each critical moment can be obtained.

5. The SF according to claim 1 6 Fatigue life analysis method for oil buffer of breaker operating mechanism It is characterized in that , The establishment of the three-dimensional model of the operating mechanism described in step S1 includes closing and opening springs, cams, ratchets, crank arms, various pawls, oil buffers, and fixing shafts, plates, and frames.

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