Arc suppression and insulation design method for on-load tap-changer of phase-shifting transformer

Abstract

The invention discloses an arc suppression and insulation design method for an on-load tap-changer of a phase-shifting transformer. In the aspect of arc suppression, the grading ring is additionally arranged on the moving contact of the on-load tap-changer of the phase-shifting transformer, the electric field distribution is improved, and the arc discharge probability of the moving contact and the static contact is reduced; in the aspect of insulation design, the interelectrode barrier is added between the static contacts of the tap switch, an arc discharge path is blocked, and the adjacent discharge probability of an arc is reduced. The grading rings are additionally arranged on the moving contacts of the on-load tap-changer, and the inter-electrode barriers are additionally arranged between the static contacts, so that the development of electric arcs is inhibited, and the electric arc discharge probability of the tap-changer is reduced. The service life of transformer oil can be prolonged, and stable operation of a power system is guaranteed.

Description

Technical Field

[0001] The invention relates to an arc suppression and insulation design method for an on-load tap changer of a phase-shifting transformer, and belongs to the field of transformers. Background Art

[0002] As a typical power flow control device, the phase-shifting transformer can be used to meet the power flow regulation and new energy consumption of a large number of new energy sources such as photovoltaic power generation connected to the distribution network. Its on-load tap changer needs to be switched frequently to cope with the intermittent and uncertain nature of new energy power generation. Each phase of the on-load tap changer consists of a set of moving contacts and multiple sets of side-by-side static contacts, and each static contact corresponds to a different ratio of the transformer coil. The on-load tap changer is usually switched multiple times a day, which may cause frequent arc discharge in the tap changer, thereby accelerating the deterioration of the transformer oil, which is not conducive to the stable operation of the power system. Therefore, it is necessary to carry out special arc suppression and insulation design for the on-load tap changer contacts to extend the service life of the transformer oil and ensure the stable operation of the power system. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the present invention provides a design method for an on-load tap changer of a phase-shifting transformer, which reduces the probability of arc discharge of the tap changer.

[0004] In order to achieve the above-mentioned purpose, the technical solution proposed in the present invention is: a method for designing arc suppression and insulation of an on-load tap changer of a phase-shifting transformer, wherein the on-load tap changer of the phase-shifting transformer comprises a moving contact and a plurality of side-by-side stationary contacts; the method comprises a grading ring sleeved on the moving contact; and a pole barrier is arranged between adjacent stationary contacts.

[0005] A further design of the above technical solution is that the size design of the pressure equalizing ring includes the following steps:

[0006] Given the radius of the moving contact and the installation height of the grading ring;

[0007] The initial values ​​of the pressure equalizing ring dimensions are given, including the radius and width of the pressure equalizing ring;

[0008] Calculate the electric field strength distribution at the moving contact after installing the grading ring, and set the maximum electric field strength;

[0009] If the maximum electric field strength at the moving contact (the maximum electric field strength is located on the lower surface of the moving contact) exceeds the requirement, increase the radius and width of the grading ring, and repeat the steps to calculate the electric field strength distribution until the maximum electric field strength meets the requirement.

[0010] The electric field intensity distribution at the moving contact is calculated by the Laplace equation, which is as follows:

[0011]

[0012] In the formula, is the electric potential, ε is the dielectric constant, is the electric field strength, and x, y, and z represent the X, Y, and Z coordinates of the position in three-dimensional space.

[0013] The boundary conditions for calculating the electric field intensity distribution include:

[0014] (1) The electric potential at infinity is 0 boundary condition:

[0015]

[0016] (2) Known conditions for the potential of the moving contact and the static contact:

[0017]

[0018] (3) Known conditions for the potential of the grading ring:

[0019]

[0020] In the formula, are the potentials of the moving contact and the static contact respectively; Γ D , Γ S Respectively represent the metal surfaces of the moving contact and the stationary contact; Γ R is the surface boundary of the pressure equalizing ring.

[0021] A further design of the above technical solution is that the height design of the inter-pole barrier between the static contacts includes the following steps:

[0022] Using the random walk arc simulation model, multiple arc trajectory simulations were performed on static contacts without inter-pole barriers, and all arc trajectories where breakdown occurred between adjacent static contacts were obtained.

[0023] The distance from the highest point of the arc trajectory where breakdown occurs to the top of the stationary contact is used as the distance of the inter-pole barrier above the top of the stationary contact, and the inter-pole barrier height is set.

[0024] The electric field calculation in the random walk arc simulation model is simplified to a two-dimensional model and calculated using the variable step-size finite difference method.

[0025] In the random walk arc simulation model, the probability of the arc development direction can be calculated by the following formula:

[0026]

[0027] Where n is the number of possible arc development directions, P(i) is the probability of the arc developing in the i-th direction, and E i is the electric field strength along the ith direction, E c is the breakdown field strength of transformer oil, and τ(·) is a step function.

[0028] The direction of arc development is determined by generating a random number. The value range of the generated random number rand is 0 to 1. For the i-th development direction, if rand falls within this range:

[0029]

[0030] At the same time, satisfy E i ≥E c Condition, the arc develops in the i-th direction.

[0031] The electric field strength in the random walk arc simulation model is calculated by the Laplace equation, and the boundary conditions of the calculation include:

[0032] (1) The electric potential at infinity is 0 boundary condition:

[0033]

[0034] (2) Known conditions for static contact potential:

[0035]

[0036]

[0037] In the formula, is the potential of two adjacent static contacts; Γ S1 , Γ S2 Respectively represent the metal surfaces of the two static contacts.

[0038] (3) The arc path potential is known under the following conditions:

[0039]

[0040] In the formula, E A is the arc voltage drop per unit length, l A It is the length from a certain position on the arc to the root of the arc.

[0041] The variable step finite difference method is calculated, and its difference format is

[0042]

[0043] In the formula, Δh i-1 , Δh i , Δh j-1 , Δh j is the step size for the finite difference meshing.

[0044] The beneficial effects of the present invention are:

[0045] In terms of arc suppression, the present invention adds a grading ring to the moving contact of the on-load tap changer of the phase-shifting transformer to improve the electric field distribution and reduce the probability of arc discharge between the moving and static contacts; in terms of insulation design, an inter-pole barrier is added between the static contacts of the tap changer to block the arc discharge path and reduce the probability of arc discharge between adjacent static contacts, thereby extending the service life of the transformer oil and ensuring the stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a structural diagram of the on-load tap changer contacts, grading ring and inter-pole barrier.

[0047] Figure 2 Schematic diagram of the dimensions of the grading ring and the inter-electrode barrier.

[0048] Figure 3 Schematic diagram of electric field calculation and boundary conditions near the moving contact and grading ring.

[0049] Figure 4 This is the electric field distribution cloud map after the voltage grading ring is installed.

[0050] Figure 5 Schematic diagram of the arc path with breakdown and without breakdown.

[0051] Figure 6 Schematic diagram of random walk simulation of arc discharge.

[0052] Figure 7 Schematic diagram of electric field calculation and boundary conditions near the static contact and inter-pole barrier.

[0053] Figure 8 Schematic diagram of grid division using variable step-size finite difference method.

[0054] Fig. 9 Schematic diagram of the step size between the central node and adjacent nodes of the variable step size finite difference method.

[0055] Fig.10 Schematic diagram of the relationship between the selection of inter-electrode barrier height and the breakdown arc trajectory.

[0056] Fig.11 This is the arc path simulation result diagram. DETAILED DESCRIPTION

[0057] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0058] Embodiment 1

[0059] like Figure 1 As shown in the figure, the on-load tap changer consists of a moving contact and a stationary contact. Both the moving contact and the stationary contact are cylindrical, with radii r and r respectively. D and r S , the distance between the moving and static contacts is hC The specific values ​​are shown in Table 1.

[0060] Table 1 Dimensions of moving contact and stationary contact

[0061]

[0062] like Figure 2 As shown, the arc suppression and insulation design method of the on-load tap changer of the phase-shifting transformer in this embodiment is to set a grading ring on the moving contact of the on-load tap changer of the phase-shifting transformer to improve the electric field distribution and reduce the probability of arc discharge between the moving and static contacts; and to set an inter-pole barrier between adjacent static contacts of the tap changer to block the arc discharge path and reduce the probability of arc discharge in adjacent static contacts.

[0063] The size selection of the grading ring of the moving contact of the on-load tap-changer includes the following steps:

[0064] S101: Given the radius r of the moving contact of the tap changer D and installation height h R The installation height of the pressure equalizing ring is 5mm.

[0065] S102: Give an initial value of the size of the pressure equalizing ring, including the radius r of the pressure equalizing ring R and ring width d R .

[0066] The dimensions of the moving contact and the initial dimensions and installation height of the grading ring in steps S101 and S102 are shown in Table 2.

[0067] Table 2 Initial dimensions of the pressure equalizing ring

[0068]

[0069] S103: Figure 3 As shown, the electric field intensity distribution near the moving contact after the voltage grading ring is installed is calculated. The electric field distribution is calculated using the Laplace equation, and its specific form is as follows:

[0070]

[0071] In the formula, is the electric potential, ε is the dielectric constant, E is the electric field strength; x, y, z represent the X, Y, and Z axis coordinates of any position in three-dimensional space.

[0072] At the same time, the Laplace equation is applicable to the calculation of the electric field of any size of the grading ring. However, the Laplace equation cannot be used alone and must be accompanied by some boundary conditions. Different boundary conditions (including boundary shape, potential magnitude on the boundary, etc.) will result in different electric field calculation results. The size of the grading ring affects the shape of the boundary conditions, and thus affects the electric field distribution.

[0073] Therefore, the boundary conditions for the electric field calculation in this embodiment include:

[0074] (1) The electric potential at infinity is zero boundary condition

[0075]

[0076] (2) The potential of the moving contact and the static contact is known

[0077]

[0078] (3) Known conditions for the potential of the grading ring:

[0079]

[0080] In the formula, Γ R is the surface boundary of the voltage-equalizing ring. Since the voltage-equalizing ring is connected to the moving contact, the potential of the voltage-equalizing ring is equal to the potential of the moving contact. By changing the size of the voltage-equalizing ring, Γ R It also changes accordingly, and the calculated electric field distribution is also different accordingly.

[0081] In the formula, are the potentials of the moving contact and the static contact respectively, and the specific values ​​are shown in Table 3. Since the grading ring is connected to the moving contact, the potential of the grading ring is also Γ D , Γ S Represent the metal surfaces of the moving contact and the static contact respectively.

[0082] Table 3 Potential of moving contact and static contact

[0083]

[0084] S104: If the maximum electric field strength near the contact exceeds the requirement, increase the ring radius and ring width by Δr R , Δd R , repeat step S103 until the maximum electric field strength meets the requirements. R and Δd R The maximum allowable value of the electric field strength in this embodiment is the breakdown electric field strength of transformer oil, 8kV / mm.

[0085] Through steps S101 to S104, the dimensions of the pressure equalizing ring are shown in Table 4. The radius of the pressure equalizing ring r R The ring width is 19mm, R is 10mm. The electric field distribution is as follows Figure 4 As shown, the maximum electric field strength is 4.05kV / mm, which meets the requirements.

[0086] Table 4 Selection of pressure equalizing ring size

[0087]

[0088] The selection of the height of the interpolar barrier between the stationary contacts includes the following steps:

[0089] S201: First, simulate the arc discharge of the static contact without the inter-pole barrier installed to obtain all arc trajectories where breakdown occurs.

[0090] like Figure 5 As shown in the figure, because the arc path is random, part of the arc can reach the adjacent static contact from one static contact, causing breakdown; the other part of the arc track will gradually move away from the static contact and extinguish before reaching the adjacent static contact. When selecting the inter-pole barrier degree, only the arc track with breakdown is used as a reference.

[0091] like Figure 6 As shown, in the random walk arc simulation model, the probability of the arc development direction can be calculated by the following formula

[0092]

[0093] Where n is the number of possible arc development directions, P(i) is the probability of the arc developing in the i-th direction, and E i is the electric field strength along the ith direction, E c is the breakdown field strength of transformer oil, which is 8 kV / mm. τ(·) is the step function:

[0094]

[0095] In order to reflect the randomness of the arc discharge path, random numbers are generated to determine the direction of arc development.

[0096] The value range of the generated random number rand is from 0 to 1, that is,

[0097] 0≤rand≤1 (8)

[0098] For the i-th development direction, if rand falls within this range:

[0099]

[0100] At the same time, satisfy E i ≥E c Condition, the arc develops in the i-th direction.

[0101] like Figure 7 As shown, the electric field is calculated by Laplace equation, and the formula is the same as equations (1) and (2) in step S103.

[0102] The boundary conditions for the electric field calculation include:

[0103] (1) The electric potential at infinity is 0 boundary condition:

[0104]

[0105] (2) Known conditions for static contact potential:

[0106]

[0107] In the formula, is the potential of two adjacent static contacts, the specific value is shown in Table 5; Γ S1 , Γ S2 Respectively represent the metal surfaces of the two static contacts.

[0108] (3) The potential of the arc path is known. The arc itself also has a voltage drop, so the potential at different points of the arc track is different. The longer the arc length, the lower the potential:

[0109]

[0110] In the formula, E A is the arc voltage drop per unit length, l A It is the length from a certain position on the arc to the root of the arc.

[0111] Table 5 Boundary condition values ​​for arc discharge simulation calculation

[0112]

[0113]

[0114] In the random walk arc simulation model, since the maximum height that the arc path can reach is mainly considered, the electric field calculation is simplified to a two-dimensional field, and the variable step-size finite difference method is used to reduce the amount of calculation.

[0115] like Figure 8 As shown in the figure, when the variable step finite difference method is applied, the variable step size grid is used to divide the calculation area. Since the arc trajectory between two adjacent static contacts is the main concern, the area between the two static contacts is divided into dense grids with a step size of Δh. dense Smaller; other areas are divided into sparse grids with a step size of Δh sparse The step size selection in the simulation is shown in Table 6.

[0116] Table 6 Grid division size

[0117]

[0118] After meshing, a series of discrete nodes are obtained, and the nodes are located at the grid lines. Fig. 9 As shown, for the (i,j)th node, its differential format is

[0119]

[0120] In the formula, is the potential of the (i,j)th node (central node), The potentials of the (i-1,j), (i+1,j), (i,j-1), and (i,j+1) nodes (adjacent nodes), Δh i-1 , Δh i , Δh j-1 , Δh j is the spatial step length between the center node and each adjacent node.

[0121] S202: Fig.10 As shown, according to the distance from the highest point in all arc trajectories in step S201 to the top of the static contact, the distance of the top of the inter-pole barrier above the top of the static contact, that is, the height h of the inter-pole barrier B . Fig.11 The simulation results of the arc path are shown. The arcs in the figure are all arcs where adjacent static contacts break down. According to the simulation results, the maximum height reached by the arc is 1.4 mm higher than the top of the static contact. The height h of the inter-pole barrier is set at this distance. B In this embodiment, from the perspective of leaving a certain margin, the height of the inter-electrode barrier h can also be B Select 2mm.

[0122] The technical solutions of the present invention are not limited to the above-mentioned embodiments, and any technical solutions obtained by equivalent replacement methods fall within the scope of protection required by the present invention.

Claims

1. A method for arc suppression and insulation design of an on-load tap changer of a phase-shifting transformer, wherein the on-load tap changer of the phase-shifting transformer comprises a moving contact and a plurality of side-by-side stationary contacts, characterized in that: A pressure equalizing ring is sleeved on the moving contact; An interpolar barrier is provided between adjacent stationary contacts.

2. The arc suppression and insulation design method for the on-load tap changer of the phase-shifting transformer according to claim 1 is characterized by: The size design of the pressure equalizing ring includes the following steps: Given the radius of the moving contact and the installation height of the grading ring; The initial values ​​of the pressure equalizing ring dimensions are given, including the radius and width of the pressure equalizing ring; Calculate the electric field strength distribution at the moving contact after installing the grading ring, and set the maximum electric field strength; If the maximum electric field strength at the moving contact exceeds the requirement, increase the radius and width of the grading ring, and repeat the steps to calculate the electric field strength distribution until the maximum electric field strength meets the requirement.

3. The arc suppression and insulation design method for the phase-shifting transformer on-load tap changer according to claim 2 is characterized in that: The electric field intensity distribution at the moving contact is calculated by the Laplace equation, which is as follows: In the formula, is the electric potential, ε is the dielectric constant, is the electric field strength, and x, y, and z represent the X, Y, and Z coordinates of the position in three-dimensional space.

4. The arc suppression and insulation design method for the on-load tap changer of the phase-shifting transformer according to claim 3 is characterized by: The boundary conditions for calculating the electric field intensity distribution include: (1) The electric potential at infinity is 0 boundary condition: (2) Known conditions for the potential of the moving contact and the static contact: (3) Known conditions for the potential of the grading ring: In the formula, are the potentials of the moving contact and the static contact respectively; Γ D , Γ S Respectively represent the metal surfaces of the moving contact and the stationary contact; Γ R is the surface boundary of the pressure equalizing ring.

5. The arc suppression and insulation design method for the on-load tap changer of the phase-shifting transformer according to claim 1 is characterized by: The height design of the inter-pole barrier between the static contacts comprises the following steps: Using the random walk arc simulation model, multiple arc trajectory simulations were performed on static contacts without inter-pole barriers, and all arc trajectories where breakdown occurred between adjacent static contacts were obtained. The distance from the highest point of the arc trajectory where breakdown occurs to the top of the stationary contact is used as the distance of the inter-pole barrier above the top of the stationary contact, and the inter-pole barrier height is set.

6. The arc suppression and insulation design method for the on-load tap changer of the phase-shifting transformer according to claim 5 is characterized by: The electric field calculation in the random walk arc simulation model is simplified to a two-dimensional model and calculated using the variable step-size finite difference method.

7. The arc suppression and insulation design method for the on-load tap changer of the phase-shifting transformer according to claim 6 is characterized by: In the random walk arc simulation model, the probability of the arc development direction can be calculated by the following formula: Where n is the number of possible arc development directions, P(i) is the probability of the arc developing in the i-th direction, and E i is the electric field strength along the ith direction, E c is the breakdown field strength of transformer oil, and τ(·) is a step function.

8. The arc suppression and insulation design method for the on-load tap changer of the phase-shifting transformer according to claim 7 is characterized in that: The direction of arc development is determined by generating a random number. The value range of the generated random number rand is 0 to 1. For the i-th development direction, if rand falls within this range: At the same time, satisfy E i ≥E c Condition, the arc develops in the i-th direction.

9. The arc suppression and insulation design method for the on-load tap changer of the phase-shifting transformer according to claim 8 is characterized in that: The electric field strength in the random walk arc simulation model is calculated by the Laplace equation, and the boundary conditions of the calculation include: (1) The electric potential at infinity is 0 boundary condition: (2) Known conditions for static contact potential: In the formula, is the potential of two adjacent static contacts; Γ S1 , Γ S2 Respectively represent the metal surfaces of the two static contacts. (3) The arc path potential is known under the following conditions: In the formula, E A is the arc voltage drop per unit length, l A It is the length from a certain position on the arc to the root of the arc.

10. The arc suppression and insulation design method for the on-load tap changer of the phase-shifting transformer according to claim 9 is characterized in that: The variable step finite difference method is calculated, and its difference format is In the formula, Δh i-1 , Δh i , Δh j-1 , Δh j is the step size for the finite difference meshing.

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