A method for calculating vibration of a transformer during a sudden short circuit

Abstract

The application discloses a kind of transformer burst short-circuit vibration calculation method, comprising the following steps: input transformer electrical parameter and structure parameter;Calculate short-circuit impulse current, establish mirror leakage magnetic field calculation model, calculate leakage magnetic field and winding stress;Establish winding axial dynamics model, calculate winding mass, initial stiffness;According to winding stiffness, use Runge-Kutta method to calculate winding vibration displacement after Δt step;According to winding vibration displacement, the equivalent stiffness of spacer between winding is calculated;After reaching the set time length, the displacement data of winding in T time is obtained.The technical scheme of the application considers that the winding coil displacement is large under short-circuit impulse current, and there is a situation that the coil is separated from the spacer, so the calculation of winding vibration under burst short-circuit is more accurate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power transformer simulation calculation, in particular to a vibration calculation method for transformer sudden short circuit. BACKGROUND

[0002] Power transformer is one of the most important and expensive devices in power system. Its operation condition not only affects its own safety, but also affects the stability and reliability of the whole power system. For a long time, the safe and reliable operation of power transformer has been paid attention by power operation and management department, which is also an important index for system safety, stability and economic operation. With the rapid development of national economy, people's demand for electricity is increasing, and the role of power transformer is becoming more and more important, and it is developing towards higher voltage level and larger capacity.

[0003] With the increase of power transmission system and single transformer capacity, the leakage magnetic field of large transformer during short circuit is also significantly enhanced. Excessive leakage magnetic field will cause a series of adverse problems such as local overheating of transformer structural parts (such as clamps, oil tank, etc.), increase of eddy current loss, and huge short circuit electric force in winding. Therefore, many scholars at home and abroad pay great attention to the calculation of leakage magnetic field and short circuit electric force of large transformer, and have done a lot of work and achieved certain results. In order to calculate the short circuit electric force of transformer winding, the mirror method or two-dimensional transformer winding is established in the finite element software to calculate the leakage magnetic field of transformer under short circuit impulse current, as shown in the attached Figure 1-2 , and then the stress is obtained.

[0004] Then the winding dynamics model shown in the attached Figure 3 is used for calculation, K0-K N is the equivalent stiffness of end plate; C0-C n is the equivalent damping of end plate; m1-m n is the equivalent mass of coil at different positions of winding; K1-K n-1 is the equivalent stiffness of cushion block and insulation paper; C1-C n-1 is the equivalent viscous damping of winding vibration. The dynamic equation can be established by the model

[0005]

[0006] In the formula: M is the mass matrix of winding coil; x is the acceleration, speed and dynamic displacement matrix of coil, x s is the static displacement matrix of coil; C is the damping coefficient matrix; K is the stiffness coefficient matrix; F is the electromagnetic force matrix; g is the gravity acceleration; F c is the compression force of winding.

[0007] The spring in the model is obtained by equivalent to the cushion and insulating material between the transformer windings, and the out-of-plane direction of the insulating paperboard presents strong nonlinear mechanical properties, the elastic modulus increases with the increase of stress, and the elastic modulus E and equivalent stiffness k of the cushion can be represented as:

[0008]

[0009]

[0010] In the formula, ε n represents the stress and strain of the cushion of the nth layer coil from the top to the bottom of the winding; a and b represent constants related to the mechanical properties of the paperboard.

[0011] However, the prior art has the following defects: (1) when calculating vibration and stress, it is considered that the winding and the cushion are in direct contact, but when the transformer winding occurs short-circuit impact, the current and electromagnetic force in the winding are much larger than those in the normal working state, the winding vibration displacement is large, and the winding coil and the cushion component exist, and the vibration result and the stress are more complex; (2) when the mirror method is used to calculate the leakage magnetic field, the multiple wire cakes separated from the winding are calculated as a whole as a homogeneous conductor, and the magnetic field intensity obtained is continuously smooth in the whole region, but in fact the magnetic field intensity varies differently in the winding conductor part and the conductor coil part, and the obtained magnetic field result also has differences. SUMMARY

[0012] The purpose of the present application is to provide a vibration calculation method for a transformer in a sudden short circuit, which considers that the winding coil displacement is large under the short-circuit impact current, and the coil and the cushion are separated, and the calculation of the winding vibration under the sudden short circuit is more accurate.

[0013] TECHNICAL SCHEME The vibration calculation method for a transformer in a sudden short circuit of the present application comprises the following steps:

[0014] (1) inputting the electrical parameters and structural parameters of the transformer;

[0015] (2) calculating the short-circuit impact current, performing a mirror image on the transformer core interface according to the inner and outer radii of the winding, the winding height, and the cushion height, establishing a multi-winding wire cake mirror image model, calculating the leakage magnetic field, and calculating the electromagnetic force of each cake winding by using the formula F=BIL, wherein B represents the average magnetic field strength in each cake winding; I represents the current of each cake winding; and L represents the circumferential length of each cake winding;

[0016] (3) Establishing the winding axial dynamics model, calculating the winding mass according to the wire material density p and the wire volume V of each pie, calculating the stress s of the wire according to the pressing force at both ends of the winding and the area of the pad, and then calculating the initial strain e of the pad according to the stress s of the wire, and further calculating the initial stiffness k;

[0017] (4) Setting the total solving time T, Δt = T / n, Δt is the solving step length of the Runge-Kutta method, and n is the total solving step number; according to the initial displacement X t0 = 0, the initial stiffness and damping, the Runge-Kutta method is used to solve the calculation formula of the vibration displacement of each pie winding, and the displacement X1 of each pie winding after the step length Δt is calculated;

[0018] (5) According to X1, the equivalent stiffness of the pad between the windings is recalculated, and the equivalent stiffness of the pad between the windings is used to calculate the displacement X t1 of the winding after the next time step Δt on the basis of the displacement X t2 , and the above process is repeated to obtain X t3 , X t4 , …, X tn , and finally the total displacement change X of the winding within T time is obtained.

[0019] In step (2), the calculation formula of the short-circuit impulse current i Hk is as follows:

[0020]

[0021] In the formula, i Hk represents the steady-state short-circuit current of the high-voltage winding; ω = 2πf, f represents the frequency of the transformer current, and a represents the current phase at the time of short-circuit; R k represents the short-circuit resistance; L k represents the short-circuit reactance; and t represents time.

[0022] In step (2), the leakage magnetic field is calculated, and the details are as follows:

[0023] It is assumed that the direction of the z-axis of the rectangular coordinate is out of the paper, the directions of the x-axis and the y-axis are right-hand helical relationship with the z-axis, all conductor sections are parallel or perpendicular to the coordinate axes, and the current density of the nth conductor is J n , then the magnetic vector potential at any point (x, y) in the window is:

[0024]

[0025] Δx = x - x nk (4)

[0026] Δy = y - y nk (5)

[0027] where x nk , y nk are the horizontal and vertical coordinates of the nth current carrier at the kth vertex, respectively, and C is an integral constant.

[0028] From B = ∇ × A, we have:

[0029]

[0030] where B x is the x-component of the magnetic induction at (x, y).

[0031] In step (3), the establishment of the winding axial dynamics model is specifically: the winding of the pie-type transformer is divided into winding coils in the axial direction by the axial oil duct and a plurality of pads, according to the winding structure, the wires of the same coil are regarded as concentrated equivalent mass blocks, and the stiffness and damping of each insulating material are regarded as equivalent springs and viscous pots respectively, so as to establish a dynamics model for characterizing the axial vibration of the winding.

[0032] In step (4), the calculation formula of the vibration displacement of each pie winding is as follows:

[0033]

[0034] where x1~x n represent the vibration displacement of each pie winding; m T represents the mass of the upper pressing plate of the winding; m B represents the mass of the upper and lower pressing plates of the winding; m1~m n represent the mass of each pie winding; k c represents the equivalent stiffness of the upper clamp; k s represents the equivalent stiffness of the lower clamp; k T represents the equivalent stiffness between the upper pressing plate and the winding; k B represents the equivalent stiffness between the lower pressing plate and the winding; k1~k n-1 represents the equivalent stiffness of the pads and insulating materials between the windings; c c , c s , c T , c B and c1~c n-1 represent the damping of each equivalent viscous in parallel with the spring; F c represents the winding pressing force; f1~f n represents the electromagnetic force borne by each pie winding; the damping c is taken as 10 -4 times the parallel spring stiffness.

[0035] In step (5), the calculation formula of the equivalent stiffness k of the pads between the windings is as follows:

[0036]

[0037]

[0038] In the formula, x n+1 and x n represent the displacement of the n+1th pancake and the nth pancake coil; a and b are constants, a=1.05x10 3 kg / cm 2 , b=1.75x10 3 kg / cm 2 ; L0 represents the initial thickness of the pad; epsilon 0 represents the static strain of the pad; A represents the total area of a layer of the pad; L represents the thickness of the pad; and E represents the elastic modulus of the pad.

[0039] When (x n+1 -x n ) / L0+epsilon 0<0, it indicates that the pad is separated from the winding coil, and at this time, the force between the spring and the wire pancake mass in the vibration model disappears.

[0040] Beneficial effects: compared with the prior art, the technical scheme of the present application has the beneficial effects that (1) the displacement of the winding coil under the short-circuit impact current is considered to be large, and the separation of the coil and the pad exists, so that the calculation of the winding vibration under the sudden short-circuit condition is more accurate; (2) the leakage magnetic field is calculated by using the first mirror method for multiple winding wire pancakes, so that the distribution of the magnetic field between the winding and the gap can be accurately calculated, and the result is more accurate. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 It is a schematic diagram of the mirror method calculation adopted by the prior art;

[0042] Figure 2 It is a two-dimensional finite element model adopted by the prior art;

[0043] Figure 3 It is a pancake winding mass-spring-damping model diagram adopted by the prior art;

[0044] Figure 4 It is a flowchart of the present application;

[0045] Figure 5 It is a mirror image of the multiple winding wire pancakes of the present application;

[0046] Figure 6 It is a mirror image model diagram of the multiple winding wire pancakes of the present application;

[0047] Figure 7 It is a winding axial dynamics model diagram of the present application;

[0048] Figure 8 It is a mirror image leakage magnetic field calculation model diagram of the present application;

[0049] Figure 9 Fig. 2 is a schematic diagram of the transverse magnetic field distribution of the winding of the present application;

[0050] Figure 10 Fig. 3 is a curve diagram of the vibration displacement and force of the winding of the present application changing with time;

[0051] Figure 11 Fig. 4 is a curve diagram of the compression force of the cushion block between the upper pressing plate and the first pancake coil changing with time in the present application. DETAILED DESCRIPTION

[0052] The technical solutions of the present application will be described in detail below in combination with the specific embodiments and the accompanying drawings of the specification. As shown in the drawings, the vibration calculation method of the transformer in the event of a sudden short circuit of the present application comprises the following steps: Figure 4

[0053] (1) Input the electrical parameters and structural parameters of the transformer; in this embodiment, the S11-5000 / 35, 35±2×2.5% / 0.69kV Dyn11 17Hz low-frequency transformer parameters used for calculation are shown in Table 1:

[0054] Table 1 Transformer parameters

[0055]

[0056]

[0057] According to the load loss and short-circuit impedance of the transformer, the short-circuit inductance and short-circuit resistance of the transformer can be obtained as follows:

[0058]

[0059] I 1NP is the phase current of the high-voltage winding, U k is the load test voltage, U k is the short-circuit impedance, U 1NP is the phase voltage of the high-voltage winding, z k is the size of the short-circuit impedance, p k is the load loss, R k is the short-circuit resistance, X k is the short-circuit reactance, L k is the short-circuit inductance, ω is the angular frequency.

[0060] (2) Calculate the short-circuit impulse current, according to the inner and outer radii of the winding, the winding height, and the cushion block height, perform a mirror image on the transformer core interface, establish a multi-winding line pancake mirror image model, calculate the leakage magnetic field, and use the formula F=BIL (which is a modification of formula (7)) to calculate the electromagnetic force on each pancake winding, wherein B represents the average magnetic field strength in each pancake winding; I represents the current of each pancake winding; L represents the circumferential length of each pancake winding; and the specific calculation is as follows:​

[0061] The short-circuit impact current of the high-voltage winding is:

[0062]

[0063] Based on the inner and outer radii of the windings, the winding height, and the height of the spacer blocks, the transformer core interface is mirrored once to establish a multi-winding piece mirror model, as detailed below:

[0064] Based on Table 1, the following parameters are obtained: high voltage winding height Hh, high voltage winding pad thickness d1, conductor height Hh1 per coil, width Hd (subtraction of inner and outer radii), and core interface; low voltage winding height Lh, low voltage winding spacing d2, and low voltage winding thickness per turn Ld; high and low voltage winding inner diameters Hr and Lr, respectively; core window height H; and left and lower parts of the core window as the y and x axes, respectively.

[0065] The coordinates of the four vertices of the i-th (i = 1, 2, 3, 4) disc winding from bottom to top of the high-voltage winding are:

[0066] (Hr,H / 2-Hh / 2+(Hh1+d1)×(i-1)), (Hr+Hd,H / 2-Hh / 2+(Hh1+d1)×(i-1)),

[0067] (Hr+Hd,H / 2-Hh / 2+Hh1+(Hh1+d1)×(i-1)),

[0068] (Hr,H / 2-Hh / 2+Hh1+(Hh1+d1)×(i-1))

[0069] The coordinates of the four vertices of the i-th (i = 1, 2, 3, 4) turn of the low-voltage winding from left to right are:

[0070] (Lr+(Ld+d2)×(i-1),H / 2-Lh / 2), (Lr+d2+(Ld+d2)×(i-1),H / 2-Lh / 2),

[0071] (Lr+d2+(Ld+d2)×(i-1),H / 2+Lh / 2), (Lr+(Ld+d2)×(i-1),H / 2+Lh / 2);

[0072] Obtain the original image, such as Figure 7 As shown; then mirroring the y-axis yields a multi-winding pie model with a single mirror image, as shown. Figure 8 As shown in the figure, from left to right, the windings are low voltage winding, high voltage winding, mirror high voltage winding, and mirror low voltage winding.

[0073] The leakage magnetic field is calculated using a formula based on the conductor current and winding coordinates, as follows:

[0074] Assuming the z-axis of the rectangular coordinate system extends beyond the paper, and the x and y axes are in a right-handed spiral relationship with the z-axis, and the sides of all conductor cross-sections are parallel or perpendicular to the coordinate axes, the current density in the nth conductor is J. n Then the magnetic vector potential at any point (x, y) in the window is:

[0075]

[0076] Δx=xx nk (4)

[0077] Δy=yy nk (5)

[0078] In the formula, x nk y nk and are the x and y coordinates of the kth vertex of the nth fluid carrier, respectively; C is the integration constant.

[0079] From B = ▽ × A, we can obtain:

[0080]

[0081] In the formula B x Let x be the x-component of the magnetic flux density at (x,y).

[0082] Therefore, the electromagnetic force acting on the coil can be obtained by the integral form of the Biot-Sawa law, that is:

[0083]

[0084] The variation of the transverse magnetic field strength in the middle of the high-voltage winding, calculated using the first-order mirror method of a multi-winding disc model, is as follows: Figure 10 As shown, Figure 10 The figure shows the transverse leakage magnetic field strength from bottom to top in the middle of the high-voltage winding. As can be seen from the figure, the change of magnetic field at the winding coil is different from that at the gap between the coil pads. The magnetic field distribution is not a continuous and smooth curve. Therefore, the multi-winding coil model is more accurate in calculating the magnetic field in the winding coil.

[0085] (3) Establish the axial dynamic model of the winding. Calculate the winding mass based on the conductor material density ρ and the volume V of each conductor coil. The volume V of each conductor coil is obtained from the conductor height and inner and outer radii. Calculate the stress σ on the conductor based on the clamping force at both ends of the winding and the area of ​​the pads. σ = aε + bε 3 (, a = 1.05 x 10 3 kg / cm 2 b = 1.75 x 10 3 kg / cm 2According to the stress σ of the wire, the initial strain ε of the cushion block is calculated, and the initial stiffness k is further calculated according to formula (9);

[0086] The winding of the pie-type transformer is divided into winding coils in the axial direction by the axial oil duct and a plurality of cushion blocks. According to the winding structure, the wires of the same coil are regarded as concentrated equivalent mass blocks, and the stiffness and damping of the insulating materials such as the pressing plate, the fastener, the coil and the cushion block are regarded as equivalent springs and viscous pots respectively, so that a discrete dynamic model for characterizing the axial vibration of the winding as shown in the table can be established. Figure 5

[0087] The initial stiffness of the winding cushion block obtained according to formula (9) is shown in Table 2, the initial strain ε of the cushion block is 0.024, a is 1.05×10 8 , and b is 1.75×10 9 .

[0088] Table 2 Initial parameters of the axial vibration model

[0089]

[0090] (4) Set the total solving time T, Δt=T / n, Δt is the solving step length of the Runge-Kutta method, and n is the total solving step number; according to the initial displacement X t0 =0 of the winding, the initial stiffness, damping and the like, the Runge-Kutta method is used to solve the calculation formula of the vibration displacement of each pie winding after the step length Δt, and the displacement X1 of each pie winding after the step length Δt is calculated as follows:

[0091] Taking the weight direction as the negative direction, the dynamic equation is obtained:

[0092]

[0093] In the formula, x1-x n represent the displacement of each pie winding; m T represents the mass of the upper pressing plate of the winding; m B represents the mass of the upper and lower pressing plates of the winding; m1-m n represent the mass of each pie winding; k c represents the equivalent stiffness of the upper clamp; k s represents the equivalent stiffness of the lower clamp; k T represents the equivalent stiffness between the upper pressing plate and the winding; k B represents the equivalent stiffness between the lower pressing plate and the winding; k1-k n-1 are the equivalent stiffness of the cushion blocks and the insulating materials between the windings; c c , c s , c T , c B and c1-c n-1 represent the damping of each equivalent viscous in parallel with the spring; F c ​Indicates the winding clamping force; f1~f n This represents the electromagnetic force on each winding; the damping c is taken as 10 times the stiffness of the parallel spring. -4 .

[0094] (5) Based on X1, recalculate the equivalent stiffness of the inter-winding spacer. Using the newly calculated equivalent stiffness of the inter-winding spacer, at displacement X... t1 Based on this, calculate the winding displacement X after the next time step Δt. t2 Repeat the above process to obtain X. t3 X t4 , ..., X tn Finally, the total displacement change X of the winding over time T is obtained.

[0095] The calculation process for the equivalent stiffness k of the inter-winding spacer is as follows:

[0096]

[0097] In the formula, x n+1 and x n This represents the displacement of the (n+1)th disc and the coil of the nth disc; a and b are constants, where a = 1.05 x 10^2. 3 kg / cm 2 b = 1.75 x 10 3 kg / cm 2 L0 represents the initial thickness of the pad; ε0 represents the static strain of the pad; A represents the total area of ​​one layer of pads; L represents the thickness of the pad; E represents the elastic modulus of the pad.

[0098] When (x) n+1 -x n When ) / L0+ε0<0, it indicates that the pad block is detached from the winding coil, and at this time the force between the spring and the coil mass block in the vibration model disappears.

[0099] The alternating electrodynamic forces borne by each winding coil obtained by the mirror method are substituted into equation (8), and the Runge-Kutta method is used for solution. The time step is 10... -5 The vibration response of the winding is calculated when the short circuit lasts for 0.2 s. The electromagnetic force and vibration displacement of the first winding of the high-voltage winding are calculated, such as... Figure 11 As shown in the figure, the variation law of the winding displacement is basically the same as the variation law of the electromagnetic force. The maximum electromagnetic force on the first coil is 84kN and the maximum displacement is 3.87mm.

[0100] Equation (8) is solved using the Runge-Kutta method. After each calculation, the stiffness of the inter-coil spacer is recalculated based on the obtained winding coil displacement. When (x i+1 -x i) / L0+ε0<0, the stiffness of the pad is set to zero. Then the winding vibration signal is solved.

[0101] Affected by the pad separation, the compression force of the pad between the upper pressing plate and the first pancake coil is as shown in Figure 10 Figure 10 The dynamic compression force of the pad between the winding top pressing plate and the winding pancake is shown in the figure. Since the top winding is subjected to the maximum force and vibration displacement, there is a component between the winding and the top pressing plate. At this time, the force on the top pressing plate is 0.

[0102] The present scheme solves the dynamic equation step by step by Runge-Kutta method. After each step, the winding stiffness is recalculated, and it is judged whether separation occurs. After separation, the stiffness is set to zero.

[0103] The mirror method calculates the transformer leakage magnetic field using the winding pancake model, and only one mirror is performed on one medium interface.​

Claims

1. A method for calculating vibration during a sudden short circuit in a transformer, characterized in that, Includes the following steps: (1) Input the electrical and structural parameters of the transformer, set the calculation time to T, and the initial displacement to 0; (2) Calculate the short-circuit impact current. Based on the inner and outer radii of the winding, the winding height, and the height of the pad, perform a mirror image of the transformer core interface. Establish a multi-winding disc mirror model and calculate the leakage magnetic field. Calculate the electromagnetic force on each disc winding using the formula F = BIL, where B represents the average magnetic field strength in each disc winding; I represents the current in each disc winding; and L represents the circumferential length of each disc winding. (3) Establish the axial dynamic model of the winding, calculate the winding mass based on the conductor material density ρ and the volume V of each conductor cake, calculate the stress σ on the conductor based on the clamping force at both ends of the winding and the area of ​​the pad, and then calculate the initial strain ε of the pad based on the obtained stress σ on the conductor, and further calculate the initial stiffness k. (4) Set the total solution time T, Δt = T / n, where Δt is the solution step size of the Runge-Kutta method, and n is the total number of solution steps; based on the initial displacement X of the winding... t0 =0, initial stiffness, damping, use the Runge-Kutta method to solve the calculation formula of the vibration displacement of each disc winding, and calculate the displacement X1 of each disc winding after Δt step size; (5) Based on X1, recalculate the equivalent stiffness of the inter-winding spacer. Using the newly calculated equivalent stiffness of the inter-winding spacer, at displacement X... t1 Based on this, calculate the winding displacement X after the next time step Δt. t2 Repeat the above process to obtain X. t3 X t4 , ..., X tn Finally, the total displacement change X of the winding over time T is obtained.

2. The vibration calculation method for a transformer during a sudden short circuit according to claim 1, characterized in that, In step (2), the short-circuit impact current i Hk The calculation formula is as follows: In the formula, i Hk Represents the steady-state short-circuit current of the high-voltage winding; ω = 2πf, where f represents the transformer current frequency, and α represents the current phase at the moment of short-circuit occurrence; R k Indicates short-circuit resistance; L k t represents short-circuit reactance; t represents time.

3. The vibration calculation method for a transformer during a sudden short circuit according to claim 1, characterized in that: In step (2), the leakage magnetic field is calculated as follows: Assuming the z-axis of the rectangular coordinate system extends beyond the paper, and the x and y axes are in a right-handed spiral relationship with the z-axis, and the sides of all conductor cross-sections are parallel or perpendicular to the coordinate axes, the current density in the nth conductor is J. n Then the magnetic vector potential at any point (x, y) in the window is: Δx=x-x nk (4) Δy=yy nk (5) In the formula, x nk y nk and are the x and y coordinates of the kth vertex of the nth fluid carrier, respectively; C is the integration constant. From B = ▽ × A, we can obtain: In the formula B x Let x be the x-component of the magnetic flux density at (x,y).

4. The vibration calculation method for a transformer during a sudden short circuit according to claim 1, characterized in that: In step (3), the establishment of the winding axial dynamic model is specifically as follows: the pancake transformer winding is divided into winding coils by axial oil channels and several pads in the axial direction. According to the winding structure, the conductors of the same coil are regarded as concentrated equivalent mass blocks, and the stiffness and damping of each insulating material are regarded as equivalent springs and glue pots, respectively, thereby establishing a dynamic model characterizing the axial vibration of the winding.

5. The vibration calculation method for a transformer during a sudden short circuit according to claim 1, characterized in that, In step (4), the calculation formula for the vibration displacement of each disc winding is as follows: In the formula, x1~x n Indicates the vibration displacement of each disc winding; m T Indicates the mass of the pressure plate on the winding; m B Indicates the mass of the upper and lower pressure plates of the winding; m1~m n Indicates the mass of each disc winding; k c Indicates the equivalent stiffness of the upper clamp; k s Indicates the equivalent stiffness of the lower clamp; k T Indicates the equivalent stiffness between the upper pressure plate and the winding; k B This indicates the equivalent stiffness between the pressure plate and the winding; k1~k n-1 c is the equivalent stiffness of the spacers and insulation material between windings; c c s c T c B and c1~c n-1 F represents the damping of each equivalent viscous component connected in parallel with the spring; c Indicates the winding clamping force; f1~f n This represents the electromagnetic force on each winding; the damping c is taken as 10 times the stiffness of the parallel spring. -4 .

6. The vibration calculation method for a transformer during a sudden short circuit according to claim 1, characterized in that, In step (5), the formula for calculating the equivalent stiffness k of the inter-winding spacer is as follows: In the formula, x n+1 and x n This represents the displacement of the (n+1)th disc and the coil of the nth disc; a and b are constants, where a = 1.05 x 10^2. 3 kg / cm 2 b = 1.75 x 10 3 kg / cm 2 L0 represents the initial thickness of the pad; ε0 represents the static strain of the pad; A represents the total area of ​​one layer of pads; L represents the thickness of the pads; E represents the elastic modulus of the pads.

7. The vibration calculation method for a transformer during a sudden short circuit according to claim 6, characterized in that: When (x) n+1 -x n When ) / L0+ε0<0, it indicates that the pad block is detached from the winding coil, and at this time the force between the spring and the coil mass block in the vibration model disappears.

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