Transformer winding damage quantitative evaluation method considering short-circuit impact cumulative effect

Abstract

A transformer winding is an important component in a power transformer and undertakes electric energy conversion and transmission tasks, the invention discloses a transformer winding damage quantitative evaluation method considering a short circuit impact accumulation effect, and the method comprises the following steps: firstly, obtaining a transformer winding short circuit current through a transformer winding nameplate; the method comprises the steps that firstly, a multi-physics field coupling simulation system is established, then data of the transformer winding under short-circuit impact is obtained, finally, a transformer winding accumulative damage model is constructed based on characteristic parameters, and the method can effectively evaluate the transformer winding damage.

Description

Technical Field

[0001] The present invention belongs to the field of transformer damage status assessment, and in particular relates to a transformer winding damage quantitative assessment method taking into account the cumulative effect of short-circuit impact. Background Art

[0002] As the core equipment of the power system, large transformers undertake the key functions of power transmission and voltage conversion. Their operational reliability directly affects the security of the power grid and social and economic stability. Studies have shown that transformer windings are subjected to the multi-field coupling of electromagnetic forces and mechanical vibrations for a long time under complex working conditions, and frequent short-circuit shocks (such as power grid failures or lightning strikes) can cause plastic deformation of the winding structure, displacement of the conductors, and even fracture of the insulation layer. According to statistics, about 35% of transformer mechanical failures are caused by cumulative damage caused by multiple short-circuit shocks. However, traditional assessment methods only focus on the instantaneous mechanical response under a single short circuit and cannot quantify the material fatigue degradation and damage superposition effects caused by multiple shocks. Therefore, an accurate transformer winding damage quantitative assessment method that takes into account the cumulative effect of short-circuit shocks is needed. Summary of the Invention

[0003] In order to accurately assess the damage status of transformer windings, the present invention provides a method for quantitatively assessing transformer winding damage taking into account the cumulative effect of short-circuit impact, comprising the following steps:

[0004] 1. A method for quantitatively assessing transformer winding damage taking into account the cumulative effect of short-circuit shocks, comprising the following steps:

[0005] Step 1: Obtain the short-circuit current of the transformer winding

[0006] The rated capacity S of the transformer winding can be obtained from the transformer winding nameplate. N , rated voltage U N , short-circuit impedance percentage Z K , calculate the transformer winding short-circuit current as follows:

[0007] Transformer winding rated current:

[0008]

[0009] Effective value of the periodic component of the transformer winding short-circuit current:

[0010]

[0011] Ignoring the attenuation of the periodic component of the transformer winding short-circuit current, the instantaneous value of the full current is:

[0012]

[0013] Where: ω is the angular frequency, ω = 2Πf, f is generally 50Hz; is the initial phase angle, which determines the initial phase of the current. e is the natural logarithm; T is the time constant, which is 0.2;

[0014] Step 2: Establish a multi-physics coupling simulation system

[0015] In the process of establishing a multi-physics field coupling simulation system, a high-precision transient magnetic field model is first constructed using finite element simulation software based on the geometric parameters of the transformer winding. The winding is encrypted using manual partitioning technology, and the conductivity of the copper conductor is set. At the same time, the instantaneous value of the full short-circuit current is loaded into the model as a transient excitation source to solve the electromagnetic force distribution. The transient magnetic field is coupled with the transient structural field, and then the mechanical properties of the transformer winding material are assigned, including density D, elastic modulus E, Poisson's ratio, and stress-strain relationship curve. The load value (short-circuit impact electromagnetic force) is then mapped to the transient structural field to solve the dynamic deformation, stress distribution, and plastic strain of the winding under short-circuit impact.

[0016] Step 3: Obtain data on transformer windings under short-circuit impact

[0017] The maximum deformation of the winding during the short-circuit impact process and the plastic strain after the short-circuit impact are obtained according to the number of short-circuit impacts. When the number of short-circuit impacts is 1, 2, ..., i, ..., the maximum deformation during the short-circuit impact process is d1, d2, ..., d i , ..., the plastic strains after short-circuit impact are h1, h2, ..., h i , ..., after experiencing multiple short-circuit shocks, the plastic strain tends to be stable and there is a maximum plastic strain increment Δh max , the plastic strain increment Δh generated by each short-circuit impact is used as the damage parameter, and the plastic strain increments are Δh1, Δh2, ..., Δh i ,……;

[0018] Step 4: Constructing a transformer winding cumulative damage model

[0019] Establishing the plastic strain increment Δh i The nonlinear function Q i :

[0020]

[0021] by As the dependent variable, the plastic strain increment Δh is established i The damage factor H i :

[0022]

[0023] Establish the maximum deformation d during the short-circuit impact process i The nonlinear function P i :

[0024]

[0025] by As the dependent variable, the maximum deformation d during the short-circuit impact process is established. i The damage factor D i :

[0026]

[0027] The total cumulative damage factor L of the nonlinear superposition fitting of impact damage total :

[0028] L total =η(H i -1)+(1-η)D i (8)

[0029] Total cumulative damage factor L total The weight coefficient η:

[0030]

[0031] When L total When the value is ≤0.2, the transformer winding will issue an early warning and limit the load. If necessary, the transformer needs to be forced to shut down for maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Flowchart for quantitative assessment of transformer winding damage taking into account the cumulative effects of short-circuit surges. DETAILED DESCRIPTION

[0033] The implementation process of the present invention is further described in detail below with reference to the accompanying drawings and examples.

[0034] 1. A method for quantitatively assessing transformer winding damage taking into account the cumulative effect of short-circuit shocks, comprising the following steps:

[0035] Step 1: Obtain the short-circuit current of the transformer winding

[0036] The rated capacity S of the transformer winding can be obtained from the transformer winding nameplate. N , rated voltage U N , short-circuit impedance percentage Z K , calculate the transformer winding short-circuit current as follows:

[0037] Transformer winding rated current:

[0038]

[0039] Transformer winding short-circuit current periodic component effective value:

[0040]

[0041] Full current instantaneous value ignoring attenuation of transformer winding short-circuit current periodic component:

[0042]

[0043] In the formula: ω is the angular frequency, ω = 2Πf, f is generally taken as 50Hz; is the initial phase angle, which determines the initial phase of the current, let e is the natural logarithm; T is the time constant, taken as 0.2;

[0044] Second step: Establishing a multi-physical field coupling simulation system

[0045] In the process of establishing the multi-physical field coupling simulation system, first, based on the geometric parameters of the transformer winding, a high-precision transient magnetic field model is constructed through the finite element simulation software, the winding is encrypted by manual partitioning technology, and the conductivity of the copper conductor is set. At the same time, the short-circuit full current instantaneous value is loaded into the model as a transient excitation source to solve the electromagnetic force distribution; the transient magnetic field and the transient structure field are coupled, and then the mechanical properties of the transformer winding material are given, including density D, elastic modulus E, Poisson's ratio, stress-strain relationship curve, and then the load value (short-circuit impact electromagnetic force) is mapped to the transient structure field to solve the dynamic deformation, stress distribution and plastic strain of the winding under short-circuit impact;

[0046] Third step: Obtaining data of transformer winding under short-circuit impact

[0047] According to the number of short-circuit impacts, the maximum deformation of the winding during the short-circuit impact process and the plastic strain after the short-circuit impact are obtained. When the number of short-circuit impacts is 1, 2, …, i, …, the maximum deformation during the short-circuit impact process is d1, d2, …, di, …, and the plastic strain after the short-circuit impact is h1, h2, …, hi, …, After experiencing multiple short-circuit impacts, the plastic strain tends to be stable and there is a maximum plastic strain increment Δh i , …, the plastic strain increment generated by each short-circuit impact is Δh1, Δh2, …, Δhi, …; i max i

[0048] Fourth step: Building a cumulative damage model of transformer winding

[0049] ​​​Establishing the plastic strain increment Δh i The nonlinear function Q i :

[0050]

[0051] by As the dependent variable, the plastic strain increment Δh is established i The damage factor H i :

[0052]

[0053] Establish the maximum deformation d during the short-circuit impact process i The nonlinear function P i :

[0054]

[0055] by As the dependent variable, the maximum deformation d during the short-circuit impact process is established. i The damage factor D i :

[0056]

[0057] The total cumulative damage factor L of the nonlinear superposition fitting of impact damage total :

[0058] L total =η(H i -1)+(1-η)D i (8)

[0059] Total cumulative damage factor L total The weight coefficient η:

[0060]

[0061] When L total When the value is ≤0.2, the transformer winding will issue an early warning and limit the load. If necessary, the transformer needs to be forced to shut down for maintenance.

Claims

1. A method for quantitatively assessing transformer winding damage taking into account the cumulative effect of short-circuit shocks, characterized in that: The following steps are involved: Step 1: Obtain the short-circuit current of the transformer winding The rated capacity S of the transformer winding can be obtained from the transformer winding nameplate. N , rated voltage U N , short-circuit impedance percentage Z K , calculate the transformer winding short-circuit current as follows: Transformer winding rated current: Effective value of the periodic component of the transformer winding short-circuit current: Ignoring the attenuation of the periodic component of the transformer winding short-circuit current, the instantaneous value of the full current is: Where: ω is the angular frequency, ω = 2Πf, f is generally 50Hz; is the initial phase angle, which determines the initial phase of the current. e is the natural logarithm; T is the time constant, which is 0.2; Step 2: Establish a multi-physics coupling simulation system In the process of establishing a multi-physics field coupling simulation system, a high-precision transient magnetic field model is first constructed using finite element simulation software based on the geometric parameters of the transformer winding. The winding is encrypted using manual partitioning technology, and the conductivity of the copper conductor is set. At the same time, the instantaneous value of the full short-circuit current is loaded into the model as a transient excitation source to solve the electromagnetic force distribution. The transient magnetic field is coupled with the transient structural field, and then the mechanical properties of the transformer winding material are assigned, including density D, elastic modulus E, Poisson's ratio, and stress-strain relationship curve. The load value (short-circuit impact electromagnetic force) is then mapped to the transient structural field to solve the dynamic deformation, stress distribution, and plastic strain of the winding under short-circuit impact. Step 3: Obtain data on transformer windings under short-circuit impact The maximum deformation of the winding during the short-circuit impact process and the plastic strain after the short-circuit impact are obtained according to the number of short-circuit impacts. When the number of short-circuit impacts is 1, 2, ..., i, ..., the maximum deformation during the short-circuit impact process is d1, d2, ..., d i , ..., the plastic strains after short-circuit impact are h1, h2, ..., h i , ..., after experiencing multiple short-circuit shocks, the plastic strain tends to be stable and there is a maximum plastic strain increment Δh max , the plastic strain increment Δh generated by each short-circuit impact is used as the damage parameter, and the plastic strain increments are Δh1, Δh2, ..., Δh i ,……; Step 4: Constructing a transformer winding cumulative damage model Establish a plastic strain increment Δh i The nonlinear function Q i : by As the dependent variable, the plastic strain increment Δh is established i The damage factor H i : Establish the maximum deformation d during the short-circuit impact process i The nonlinear function P i : by As the dependent variable, the maximum deformation d during the short-circuit impact process is established. i The damage factor D i : The total cumulative damage factor L of the nonlinear superposition fitting of impact damage total : L total =η·(H i -1)+(1-η)·D i (8) Total cumulative damage factor L total The weight coefficient η: When L total When the value is ≤0.2, the transformer winding will issue an early warning and limit the load. If necessary, the transformer needs to be forced to shut down for maintenance.

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