CN107622150B - Transformer short-circuit resistance assessment method based on winding deformation state diagnosis - Google Patents
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Abstract
The invention discloses a transformer short-circuit resistance evaluation method based on winding deformation state diagnosis, which comprises the following steps of: constructing a deformed transformer winding model; calculating the hoop tensile stress sigma of the transformer winding according to the deformed transformer winding modeltHoop compressive stress sigmacAnd a safety coefficient K, and then according to the hoop tensile stress sigma of the transformer windingtHoop compressive stress sigmacAnd evaluating the short-circuit resistance of the transformer winding when the three-phase symmetrical short circuit occurs again by using the safety coefficient K, and finishing the evaluation of the short-circuit resistance of the transformer based on the winding deformation state diagnosis.
Description
Technical Field
The invention belongs to the technical field of power transformers, and relates to a transformer short-circuit resistance evaluation method based on winding deformation state diagnosis.
Background
The transformer is one of the core devices in the power system, and takes charge of the electric energy conversion task at each node of the power grid, and once the transformer is shut down due to a fault, immeasurable loss is brought to each department of the power grid and national economy. With the improvement of the capacity and the voltage grade of a power grid, the short-circuit accidents of the transformer are increased continuously, according to related researches, the windings, the leads and the like of the transformer are main parts of the transformer which are damaged due to faults, wherein more than 80% of the faults are caused by large-current impact, and therefore, the detection and evaluation of the short-circuit resistance of the transformer have great significance for the safe and stable operation of the transformer. At present, a method for evaluating the short-circuit resistance of a transformer is mainly performed on a transformer without winding deformation or displacement, and is used for accurately mastering the deformation state of the transformer subjected to short-circuit impact and evaluating the capability of the slightly deformed winding for bearing next three-phase symmetrical short-circuit impact on the basis of the deformation state, so that unnecessary core hanging inspection or repair is avoided, the safe and economic operation of the transformer is ensured, however, no related open technology exists in the current stage, and therefore, a method for evaluating the short-circuit resistance of the transformer based on winding deformation state diagnosis is necessary to be researched to evaluate the short-circuit resistance of the transformer winding when three-phase symmetrical short-circuit occurs again.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a transformer short-circuit resistance evaluation method based on winding deformation state diagnosis, which can evaluate the short-circuit resistance of a transformer winding when three-phase symmetrical short circuit occurs again.
In order to achieve the above purpose, the method for evaluating the short-circuit resistance of the transformer based on the winding deformation state diagnosis comprises the following steps:
1) carrying out frequency response analysis detection and short-circuit impedance detection on the short-circuited transformer winding to obtain a frequency response curve and a short-circuit impedance value of the short-circuited transformer winding, and calculating a frequency response curve correlation coefficient of the short-circuited transformer winding before and after according to the frequency response curve of the short-circuited transformer winding and the frequency response curve of the short-circuited transformer winding before and after; meanwhile, the short-circuit impedance value of the transformer winding before short circuit is obtained according to the operation maintenance historical data before the short circuit of the transformer, and then the impedance variation of the transformer winding before and after short circuit is calculated according to the short-circuit impedance value of the transformer winding before and after short circuit;
2) judging whether the transformer winding is seriously deformed or not according to the impedance variation of the transformer winding before and after short circuit and the frequency response curve correlation coefficient of the transformer winding before and after short circuit, and checking and maintaining the transformer winding when the transformer winding is seriously deformed; when the transformer winding is not seriously deformed, reversely solving the inductance variation and the capacitance variation of the equivalent circuit of the transformer winding before and after short circuit by adopting a model correction method according to the frequency response curve variation of the transformer winding before and after short circuit, then calculating the corresponding relation between the deformation and the deformation type of the transformer winding and the inductance variation and the capacitance variation of the equivalent circuit of the transformer winding by adopting a finite element method, diagnosing the deformation and the deformation type of the transformer winding through the frequency response curve deviation, and then constructing a deformed transformer winding model according to the deformation and the deformation type of the transformer winding;
3) calculating the hoop tensile stress sigma of the transformer winding according to the deformed transformer winding modeltHoop compressive stress sigmacAnd a safety coefficient K, and then according to the hoop tensile stress sigma of the transformer windingtHoop compressive stress sigmacAnd evaluating the short-circuit resistance of the transformer winding when the three-phase symmetrical short circuit occurs again by using the safety coefficient K, and finishing the evaluation of the short-circuit resistance of the transformer based on the winding deformation state diagnosis.
Calculating the hoop tensile stress sigma of the transformer winding according to the deformed transformer winding model in the step 3)tHoop compressive stress sigmacAnd the specific operation of the safety coefficient K is as follows:
31) calculating the short-circuit current of the transformer winding according to the deformed transformer winding model, calculating the leakage magnetic field distribution of the transformer winding according to the short-circuit current of the transformer winding, and calculating the axial electromagnetic force and the radial electromagnetic force of the transformer winding according to the leakage magnetic field distribution of the transformer winding;
32) calculating the dynamic displacement, dynamic force and radial pressure of the transformer winding according to the axial electromagnetic force and radial electromagnetic force of the transformer winding, and calculating the hoop stress [ sigma ] of the transformer winding according to the dynamic displacement, dynamic force and radial pressure of the transformer windingt]Axial force FcAnd axial strength Ft；
33) According to axial force F of transformer windingcAnd axial strength FtCalculating the safety coefficient K of the transformer winding and then according to the hoop stress [ sigma ] of the transformer windingt]Calculating to obtain the maximum hoop tensile stress sigma of the transformer windingtAnd maximum circumferential directionCompressive stress sigmac。
When the safety coefficient K of the transformer winding is larger, the short-circuit resistance of the transformer winding is stronger when three-phase symmetrical short circuit occurs again.
The expression of the safety coefficient K of the transformer winding is as follows:
K＝Ft/Fc。
hoop tensile stress sigma of transformer windingt≤0.9·σ0.2And the hoop compressive stress sigma of the transformer windingc≤0.35·σ0.2The short-circuit resistance of the transformer winding is qualified when the three-phase symmetrical short circuit occurs again, wherein sigma0.2The allowable stress after the strength of the transformer winding wire is degraded is obtained.
When the transformer winding wire is a copper wire, the short-circuit resistance of the transformer winding is qualified when the three-phase symmetric short circuit occurs again when the safety coefficient K of the transformer winding is more than or equal to 1.25.
The invention has the following beneficial effects:
during specific operation, according to the frequency response curve change of the transformer winding before and after short circuit, the method of model correction is adopted to reversely solve the inductance variation and the capacitance variation of the equivalent circuit of the transformer winding before and after short circuit, then the corresponding relation between the deformation amount and the deformation type of the transformer winding and the inductance variation and the capacitance variation of the equivalent circuit of the transformer winding is calculated by adopting a finite element method, then the deformed transformer winding model is constructed according to the deformation amount and the deformation type of the transformer winding, and the hoop tensile stress sigma of the transformer winding is calculated according to the deformed transformer winding modeltHoop compressive stress sigmacAnd a safety factor K, and according to the hoop tensile stress sigma of the transformer windingtHoop compressive stress sigmacAnd the safety coefficient K evaluates the short-circuit resistance of the transformer winding when the three-phase symmetrical short circuit occurs again, thereby effectively improving the safety and reliability of the transformer winding in the use process and being the short-circuit impact resistance of the transformer windingThe detection of the force provides powerful technical support and has strong practicability.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a flow chart of the calculation of mechanical strength degradation of the winding material;
FIG. 3 is a graph of fatigue life of a copper wire;
FIG. 4 is a flow chart of the calculation of the short-circuit resistance of the transformer;
FIG. 5 is a graph of stress-strain relationship for an insulating spacer;
FIG. 6 is a graph of stress-strain relationship of a copper wire;
FIG. 7 is a waveform diagram of short-circuit current of high and low voltage windings;
FIG. 8 is a distribution diagram of a leakage magnetic field during radial deformation;
FIG. 9 is a high-pressure axial electromagnetic force plot;
FIG. 10 is a graph of low-pressure axial electromagnetic force;
FIG. 11 is a graph of high pressure radial electromagnetic force, radial pressure and hoop stress;
FIG. 12 is a graph of low pressure radial electromagnetic force, radial pressure and hoop stress;
FIG. 13 is a 40 th cake dynamic force profile for the high voltage winding;
FIG. 14 is a graph of the 40 th cake displacement of the high voltage winding;
FIG. 15 is a graph of wire stress at short circuit fault;
fig. 16 is a graph of wire stress during normal operation.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
referring to fig. 1, the method for evaluating the short-circuit resistance of a transformer based on winding deformation state diagnosis according to the present invention includes the following steps:
1) carrying out frequency response analysis detection and short-circuit impedance detection on the short-circuited transformer winding to obtain a frequency response curve and a short-circuit impedance value of the short-circuited transformer winding, and calculating a frequency response curve correlation coefficient of the short-circuited transformer winding before and after according to the frequency response curve of the short-circuited transformer winding and the frequency response curve of the short-circuited transformer winding before and after; meanwhile, the short-circuit impedance value of the transformer winding before short circuit is obtained according to the operation maintenance historical data before the short circuit of the transformer, and then the impedance variation of the transformer winding before and after short circuit is calculated according to the short-circuit impedance value of the transformer winding before and after short circuit;
2) judging whether the transformer winding is seriously deformed or not according to the impedance variation of the transformer winding before and after short circuit and the frequency response curve correlation coefficient of the transformer winding before and after short circuit, and checking and maintaining the transformer winding when the transformer winding is seriously deformed; when the transformer winding is not seriously deformed, reversely solving the inductance variation and the capacitance variation of the equivalent circuit of the transformer winding before and after short circuit by adopting a model correction method according to the frequency response curve variation of the transformer winding before and after short circuit, then calculating the corresponding relation between the deformation and the deformation type of the transformer winding and the inductance variation and the capacitance variation of the equivalent circuit of the transformer winding by adopting a finite element method, diagnosing the deformation and the deformation type of the transformer winding through the frequency response curve deviation, and then constructing a deformed transformer winding model according to the deformation and the deformation type of the transformer winding;
3) calculating the hoop tensile stress sigma of the transformer winding according to the deformed transformer winding modeltHoop compressive stress sigmacAnd a safety coefficient K, and then according to the hoop tensile stress sigma of the transformer windingtHoop compressive stress sigmacAnd evaluating the short-circuit resistance of the transformer winding when the three-phase symmetrical short circuit occurs again by using the safety coefficient K, and finishing the evaluation of the short-circuit resistance of the transformer based on the winding deformation state diagnosis.
Calculating the maximum stress [ sigma ] of the transformer winding according to the deformed transformer winding model in the step 3)t]And the specific operation of the safety coefficient K is as follows:
31) calculating the short-circuit current of the transformer winding according to the deformed transformer winding model, calculating the leakage magnetic field distribution of the transformer winding according to the short-circuit current of the transformer winding, and calculating the axial electromagnetic force and the radial electromagnetic force of the transformer winding according to the floor magnetic field distribution of the transformer winding;
32) calculating the dynamic displacement, dynamic force and radial pressure of the transformer winding according to the axial electromagnetic force and radial electromagnetic force of the transformer winding, and calculating the hoop stress [ sigma ] of the transformer winding according to the dynamic displacement, dynamic force and radial pressure of the transformer windingt]Axial stress FcAnd axial strength Ft；
33) According to axial stress F of transformer windingcAnd axial strength FtCalculating the safety coefficient K of the transformer winding and then according to the hoop stress [ sigma ] of the transformer windingt]Calculating the hoop tensile stress sigma of the transformer windingtAnd hoop compressive stress sigmac。
When the safety coefficient K of the transformer winding is larger, the short-circuit resistance of the transformer winding is stronger when three-phase symmetrical short circuit occurs again.
The expression of the safety coefficient K of the transformer winding is as follows:
K＝Ft/Fc。
hoop tensile stress sigma of transformer windingt≤0.9·σ0.2And the hoop compressive stress sigma of the transformer windingc≤0.35·σ0.2The short-circuit resistance of the transformer winding is qualified when the three-phase symmetrical short circuit occurs again, wherein sigma0.2The allowable stress after the strength of the transformer winding wire is degraded is obtained.
When the transformer winding wire is a copper wire, the short-circuit resistance of the transformer winding is qualified when the three-phase symmetric short circuit occurs again when the safety coefficient K of the transformer winding is more than or equal to 1.25.
In addition, referring to fig. 2, the present invention further includes: calculating the maximum stress of the transformer winding according to the short-circuit electromagnetic force of the transformer winding after short circuit and the rated operation electromagnetic force of the transformer winding before short circuit, then calculating the fatigue accumulated damage coefficient of the transformer winding according to the maximum stress of the transformer winding and the fatigue life curve of the transformer winding material, judging whether the transformer winding is damaged or not according to the fatigue accumulated damage coefficient of the transformer winding, and calculating the allowable stress of the winding material after the mechanical strength of the transformer winding is degraded according to the fatigue accumulated damage coefficient of the transformer winding when the transformer winding is not damaged.
The invention also includes: and establishing a winding material fatigue accumulated damage model according to a fatigue life curve (S-N curve) of a winding wire of the transformer, establishing a transformer life evaluation model according to the winding material fatigue accumulated damage model, and evaluating the residual life of the transformer according to the transformer life evaluation model.
Specifically, under two working conditions of normal operation and short circuit impact of the transformer, the winding is under the action of electric force, when the winding material is not damaged under the action of alternating electric force for a plurality of times, namely the actual stress is smaller than the limit value, the transformer can still work normally, but the mechanical strength of the winding material is damaged and accumulated in the process, and the influence of the process on the mechanical strength of the winding material can be described by a linear fatigue accumulation damage theory.
The linear fatigue accumulated damage theory is that under the action of cyclic load, fatigue damage can be accumulated linearly, all stresses are independent and independent, when the accumulated damage reaches a certain value, a test piece or a component is subjected to fatigue damage, and the typical linear accumulated damage theory is the Miner theory.
Under constant amplitude load, the damage D caused by n cycles is as follows:
where N is the number of cycles the current load actually acts on, and N is the fatigue life corresponding to the current load level S.
Under variable amplitude load, damage D caused by n cycles is as follows:
wherein n isiNumber of cycles actually applied for the i-th load level, NiTo correspond to the current load level SiThe fatigue life of the steel.
The winding material is affected by fatigue damage due to electrodynamic forces, and the mechanical strength degradation model of the material can be represented by the following formula:
[σt]＝(1-D)·[σs]
wherein [ sigma ]t]Allowable stress after the material is subjected to strength degradation due to fatigue damage, [ sigma ]s]The initial allowable stress of the material, and D is the fatigue accumulated damage coefficient of the material.
Example one
Taking a certain transformer as an example, the normal operation time of the transformer is 10 years, 20 times of short circuit occurs in the 10 years, and the short circuit resistance after the short circuit occurs again is evaluated, wherein the evaluation steps are as follows:
1) the calculation of the short circuit resistance of the winding is shown in fig. 4.
Firstly, according to the winding deformation detection result after short circuit, determining that the radial deformation of the high-voltage winding of the transformer is 4%, then, according to the deformation state of the winding of the transformer and the geometric structure size of the winding, the iron core, the oil tank and accessories thereof, establishing a deformed winding model, and then, calculating the short-circuit current of the winding, the distribution of leakage magnetic fields, the axial and radial electromagnetic force distribution, wherein the waveform of the short-circuit current of the winding is shown in fig. 7, the distribution of leakage magnetic fields is shown in fig. 8, the axial electromagnetic force distribution of high-voltage winding and low-voltage winding is shown in fig. 9 and fig. 10, and the radial electromagnetic force distribution of high-.
Then calculating dynamic displacement, dynamic force, winding stress distribution, radial pressure, hoop stress, axial force and axial strength of the winding, and finally calculating the ratio of the axial strength and the axial force of the winding to obtain the result, namely the safety coefficient of the short circuit resistance of the winding; the dynamic force and the dynamic displacement of the high-voltage winding 40 cake are respectively shown in fig. 13 and 14; the radial pressure and hoop stress of the high and low voltage windings are shown in fig. 11 and 12, respectively; the axial force, axial strength and safety factor of each winding zone are shown in table 1.
2) Transformer short circuit resistance assessment
From the above calculation results, it can be seen that, in the event of a short-circuit fault, the axial electromagnetic forces at the two ends of the high-voltage winding and the low-voltage winding are large, as shown in fig. 9 and 10; the radial electromagnetic force of the wire cake in the middle of the high-voltage winding and the low-voltage winding is large, and the radial pressure and the hoop stress are also large, as shown in fig. 11 and 12 respectively. The dynamic force and the dynamic displacement of the high-low voltage winding oscillate with time and gradually become stable after reaching the peak value, as shown in fig. 13 to 14.
Establishing a finite element model of the transformer winding, calculating to obtain the distribution of the leakage magnetic field of the winding, and obtaining the stress distribution of the winding during the normal operation of the short-circuit fault and the transformer winding by using the magnetic-solid coupling calculation, wherein the stress distribution of the transformer wire during the normal operation of the short-circuit fault is shown in figures 15 and 16.
When the short circuit happens suddenly, the value of the short circuit electromagnetic force applied to the transformer winding is very small after the short circuit electromagnetic force is attenuated for 3 periods, so that the winding is considered to generate fatigue accumulation damage under the action of 3-cycle alternating stress at each short circuit fault. On the basis of the calculation of the stress of the copper conductor and the insulating material under the short-circuit fault, the accumulated damage value of the winding subjected to different short-circuit times can be obtained by applying a fatigue accumulated damage theory; in normal operation, the period of the electromagnetic force of the winding is 100Hz, namely the stress cycle times per second is 100, and the stress cycle times of normal operation for one year is 3.1104 multiplied by 109Secondly; on the basis of the calculation of the stress of the copper conductor and the insulating material under the normal operation working condition of the transformer, the accumulated damage values of the windings at different operation times are obtained by applying a fatigue accumulated damage theory.
When three-phase symmetrical short circuit occurs, the maximum stress of a winding copper conductor is 93.7MPa, a short circuit fault occurs, the number of times of the winding which is subjected to a load with the stress level of 93.7MPa is 3, and according to a fatigue life curve of the copper conductor, the number of stress cycles endured by the conductor under the stress level is 5662, and according to an accumulated damage formula, the damage value of the current short circuit to the transformer winding is 0.0006, namely the mechanical strength of the transformer winding copper conductor is reduced by 0.06%. At this short circuit current level, the mechanical strength of the transformer winding copper wire was reduced by 1.2% when the number of short circuits occurred was 20.
When in normal operation, the maximum stress on the winding copper wire is 0.07MPa,after 10 years of normal operation, the winding wire is applied with a load with a stress level of 0.07MPa for 3.1104 multiplied by 10 times10Next, according to the fatigue life curve of the copper wire, at this stress level, the wire withstood the number of stress cycles of 1.0054 × 1011Then, according to the accumulated damage formula, the damage value generated to the mechanical strength of the transformer winding copper wire in 10 years of normal operation is 0.3094, namely the mechanical strength of the transformer winding copper wire is reduced by 30.94%.
Therefore, when the transformer which normally runs for 10 years is subjected to 20 times of short circuits, the mechanical strength and the mechanical service life damage value of the transformer winding copper wire are 32.14 percent, and the factory allowable stress sigma of the transformer winding copper wire is0.2At 156MPa, the mechanical strength of the copper wire would drop from an initial value of 156MPa to 105.86MPa after the strength degradation. According to the stress distribution of the lead under the normal working condition and the fatigue accumulation damage model of the copper lead, under the normal operating current working condition, the residual mechanical life of the transformer is 13.2 years.
In the short-circuit process, the high-voltage winding is subjected to outward-expanded radial force due to the longitudinal leakage magnetic field, so that tensile stress is generated in the wire cake, and the low-voltage winding is subjected to inward extrusion, so that compressive stress is generated in the wire cake. As can be seen from fig. 11, the maximum value of the hoop tensile stress in the high-voltage winding cake is 4.2MPa, and as can be seen from fig. 12, the maximum value of the hoop compressive stress in the low-voltage winding cake is 7.8 MPa. According to the regulation of the circumferential tensile stress and the circumferential compressive stress in GB1094.5 'the capability of the power transformer to bear short circuit', the circumferential tensile stress sigma is ensuredt≤0.9·σ0.2Radial compressive stress σc≤0.35·σ0.2. Considering the strength degradation of the copper wire, 0.9. sigma. can be calculated according to the allowable stress of the copper wire of the transformer winding0.295.27MPa, 0.35. sigma0.237.05MPa, obviously 4.2MPa is less than or equal to 95.27MPa, and the hoop tensile stress of the high-voltage winding meets the requirement of short-circuit strength; 7.8MPa is less than or equal to 37.05MPa, and the hoop compressive stress of the low-voltage winding meets the requirement of short-circuit strength.
Table 1 shows the safety factor of the dynamic stability of a winding in short circuit at 4% radial deformation according to GB1094.5 power transformer withstanding short circuitAxial force F on winding in road capabilitycAnd axial strength FtTo qualify the dynamic stability of the short circuit of the winding, F should be ensuredc≤0.8·FtI.e. the safety factor K ═ Ft/Fc) Not less than 1.25. As can be seen from Table 1, the safety factors of the high-voltage winding and the low-voltage winding in each area are all larger than 1.25, so that the short-circuit dynamic stability bearing capacity of each section of the winding meets the requirement, and the safety factors of the two ends of the high-voltage winding and the low-voltage winding are lower and are the weakest parts, and special attention needs to be paid.
TABLE 1
Claims (6)
1. A transformer short-circuit resistance assessment method based on winding deformation state diagnosis is characterized by comprising the following steps:
1) carrying out frequency response analysis detection and short-circuit impedance detection on the short-circuited transformer winding to obtain a frequency response curve and a short-circuit impedance value of the short-circuited transformer winding, and calculating a frequency response curve correlation coefficient of the short-circuited transformer winding before and after according to the frequency response curve of the short-circuited transformer winding and the frequency response curve of the short-circuited transformer winding before and after; meanwhile, the short-circuit impedance value of the transformer winding before short circuit is obtained according to the operation maintenance historical data before the short circuit of the transformer, and then the impedance variation of the transformer winding before and after short circuit is calculated according to the short-circuit impedance value of the transformer winding before and after short circuit;
2) judging whether the transformer winding is seriously deformed or not according to the impedance variation of the transformer winding before and after short circuit and the frequency response curve correlation coefficient of the transformer winding before and after short circuit, and checking and maintaining the transformer winding when the transformer winding is seriously deformed; when the transformer winding is not seriously deformed, reversely solving the inductance variation and the capacitance variation of the equivalent circuit of the transformer winding before and after short circuit by adopting a model correction method according to the frequency response curve variation of the transformer winding before and after short circuit, then calculating the corresponding relation between the deformation and the deformation type of the transformer winding and the inductance variation and the capacitance variation of the equivalent circuit of the transformer winding by adopting a finite element method, diagnosing the deformation and the deformation type of the transformer winding through the frequency response curve deviation, and then constructing a deformed transformer winding model according to the deformation and the deformation type of the transformer winding;
3) calculating the hoop tensile stress sigma of the transformer winding according to the deformed transformer winding modeltHoop compressive stress sigmacAnd a safety coefficient K, and then according to the hoop tensile stress sigma of the transformer windingtHoop compressive stress sigmacAnd evaluating the short-circuit resistance of the transformer winding when the three-phase symmetrical short circuit occurs again by using the safety coefficient K, and finishing the evaluation of the short-circuit resistance of the transformer based on the winding deformation state diagnosis.
2. The method for evaluating short-circuit resistance of transformer based on winding deformation state diagnosis of claim 1, wherein in step 3), the hoop tensile stress σ of transformer winding is calculated according to the deformed transformer winding modeltAnd the specific operation of the safety coefficient K is as follows:
31) calculating the short-circuit current of the transformer winding according to the deformed transformer winding model, calculating the leakage magnetic field distribution of the transformer winding according to the short-circuit current of the transformer winding, and calculating the axial electromagnetic force and the radial electromagnetic force of the transformer winding according to the leakage magnetic field distribution of the transformer winding;
32) calculating the dynamic displacement, dynamic force and radial pressure of the transformer winding according to the axial electromagnetic force and radial electromagnetic force of the transformer winding, and calculating the hoop stress [ sigma ] of the transformer winding according to the dynamic displacement, dynamic force and radial pressure of the transformer windingt]Axial force FcAnd axial strength Ft；
33) According to axial force F of transformer windingcAnd axial strength FtCalculating the safety coefficient K of the transformer winding and then according to the hoop stress [ sigma ] of the transformer windingt]Calculating the hoop tensile stress sigma of the transformer windingtAnd hoop compressive stress sigmac。
3. The method for evaluating the short-circuit resistance of the transformer based on the winding deformation state diagnosis of claim 2, wherein the larger the safety factor K of the transformer winding, the stronger the short-circuit resistance of the transformer winding when three-phase symmetrical short-circuit occurs again.
4. The method for evaluating the short-circuit resistance of the transformer based on the winding deformation state diagnosis of claim 2, wherein the expression of the safety factor K of the transformer winding is as follows:
K＝Ft/Fc。
5. the method for evaluating short-circuit resistance of transformer based on winding deformation state diagnosis of claim 2, wherein hoop tensile stress σ of transformer winding ist≤0.9·σ0.2And the hoop compressive stress sigma of the transformer windingc≤0.35·σ0.2The short-circuit resistance of the transformer winding is qualified when the three-phase symmetrical short circuit occurs again, wherein sigma0.2The allowable stress after the strength of the transformer winding wire is degraded is obtained.
6. The method for evaluating the short-circuit resistance of the transformer based on the winding deformation state diagnosis of claim 2, wherein when the transformer winding wire is a copper wire, the short-circuit resistance of the transformer winding is qualified when the three-phase symmetric short circuit occurs again when the safety factor K of the transformer winding is greater than or equal to 1.25.
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| CN108872805B (en) * | 2018-05-09 | 2021-02-09 | 贵州电网有限责任公司 | Comprehensive management method for short-circuit resistance of transformer |
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| CN111781534B (en) * | 2020-06-04 | 2021-11-19 | 湖南大学 | Method and device for testing short-circuit resistance of transformer |
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