Method for acquiring activation energy of dry-type insulating equipment based on equal conversion rate method
Technical Field
The invention relates to the technical field of transformer operation and test, in particular to a dry-type insulation equipment activation energy obtaining method based on an equal conversion rate method.
Background
Dry-type insulation equipment such as dry-type transformers, dry-type reactors and the like are important electrical equipment in power systems, undertake the tasks of converting voltage, distributing and transmitting electric energy and the like, and the operation state of the dry-type insulation equipment directly influences the safe and stable operation of the whole power grid. The dry type transformer has the advantages of good fireproof performance, strong heat resistance and short circuit resistance, safety, environmental protection and the like, but the main insulation of the dry type equipment is cast and molded by adopting an epoxy resin material, so that the insulation performance, the insulation aging degree and the residual life of the dry type equipment are difficult to detect and evaluate, and the effect of the existing method for detecting the macroscopic electrical parameters such as the local discharge, the dielectric performance and the like of the insulation monitoring of the dry type insulation equipment is poor.
The activation energy is a parameter capable of measuring the difficulty of a chemical reaction and has important significance in the chemical reaction. By accurately acquiring the activation energy of the dry type insulation device, the aging degree of the dry type insulation device can be detected from the nature of the insulation material. Through search, no activation energy acquisition method applicable to dry insulation equipment exists at present. The patent provides a dry-type insulation equipment activation energy obtaining method based on an equal conversion rate method, so that the activation energy is accurately measured, and a foundation is laid for evaluating the aging state of the dry-type insulation equipment.
Disclosure of Invention
In order to meet the requirement for obtaining the activation energy of the dry-type insulation equipment in the prior art, the invention aims to provide a method for obtaining the activation energy of the dry-type insulation equipment based on an equal conversion rate method.
In order to achieve the purpose of the invention, the invention provides a dry type insulation equipment activation energy obtaining method based on an equal conversion rate method, which comprises the following steps:
the method comprises the following steps: preparing an epoxy resin sample;
step two: carrying out a thermal weight loss test to obtain thermal weight loss curves TG and first-order differential curves DTG of a plurality of groups of epoxy resin samples;
step three: calculation of activation energy
The activation energy is defined by the Arrhenius equation for chemical reactions, as follows:
in formula (1), k represents a chemical reaction rate; a is called that the pre-factor has the same factor as k, and can be regarded as the limit value of k at high temperature; r is a universal gas constant; t is the absolute temperature; eaThe energy factor is the activation energy of the chemical reaction;
in the thermal ageing reaction of dry insulation equipment, the assumption exists that the epoxy polymer reaction process depends only on the conversion α and the temperature T, which are independent of each other, and the kinetic equation of the heterogeneous reaction at an indefinite temperature can be expressed in the form:
in the formula (2), t is time, k (T) is a temperature relation of rate constant, f (α) is a function of reaction mechanism, and the formula (1) can be converted into the following by converting temperature and time at the time of linear temperature rise:
β -dT/dT is the rate of temperature rise;
the heterogeneous system obtained by substituting the formula (1) into the formula (3) has a common kinetic equation under a non-constant temperature condition, such as the formula (5);
selecting one α in the TG plot1It is taken as a horizontal line, and the horizontal line intersects the curve at an intersection point (α)1,T11)(α1,T12) …, the ramp rates corresponding to them are β1、β2…, and selecting another α2Repeating the above process, another set of data (α) is obtained2,T21)、(α2,T22) …, their corresponding ramp rates are still β1、β2…;
Formula (5) can be modified as follows:
at α1~α2In the range of β1The two-sided integration of equation (6) can be obtained
For β2The two-sided integration of equation (6) can be obtained
Subtracting the above two equations can obtain:
the dry type can be obtained by solving the formula (9)Activation energy E of insulating devicea。
Compared with the prior art, the invention has the advantages that,
the method can be used for quantitatively calculating the activation energy of the insulating material of the dry-type insulating equipment on the basis of the thermal weight loss test.
In addition, the equal conversion method has the following advantages in calculating the chemical reaction activation energy of the dry insulating material:
1. the method is insensitive to the stage of the chemical reaction, and particularly can accurately calculate the activation energy at the initial stage of the chemical reaction;
2. the influence of different sample quality differences can be eliminated, and the calculation accuracy is high.
Drawings
FIG. 1 is a schematic representation of an epoxy resin sample of the present application;
FIG. 2 is a graph of TG of the present application;
fig. 3 is a graph showing the DTG of the present application.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
Examples
The embodiment of the invention relates to a method for acquiring activation energy of dry type insulation equipment based on equal conversion rate, which mainly comprises the following steps:
the method comprises the following steps: preparation of epoxy resin samples
And (3) punching and slicing the epoxy resin insulating material poured and cured in the same batch and process of the dry-type insulating equipment to prepare a plurality of epoxy resin slices, and forming a sample group for thermal weight loss test. A typical sample is shown in figure 1.
Step two: carrying out a thermal weight loss test
Heating the sample to be tested in a high-purity nitrogen atmosphere by using a synchronous thermal analysis combination instrument, setting the heating rates of 5K/min, 10K/min, 15K/min, 20K/min and 25K/min respectively, raising the temperature in the furnace to 800 ℃, and recording the change data of the sample mass along with the temperature by using a computer to obtain the thermogravimetric curves TG and the first-order differential curves DTG of the curves of the multiple groups of epoxy resin samples. Typical TG curves and DTG curves are shown in fig. 2 and 3.
Step three: calculation of activation energy
The activation energy can be defined by the Arrhenius equation for chemical reactions, as follows:
in formula (1), k represents a chemical reaction rate; a is called a pre-factor (or called a frequency factor) and has the same factor as k, and can be considered as the limit value of k at high temperature; r is a universal gas constant; t is the absolute temperature; eaHas an energy factor, namely the activation energy of the chemical reaction.
In the thermal ageing reaction of dry insulation equipment, the assumption exists that the epoxy polymer reaction process depends only on the conversion α and the temperature T, which are independent of each other, and the kinetic equation of the heterogeneous reaction at an indefinite temperature can be expressed in the form:
in formula (2), t is time, k (T) is a temperature relation of rate constant, f (α) is a function of reaction mechanism, and formula (1) can be converted into a reaction product by converting temperature and time at linear temperature rise
β -dT/dT is the rate of temperature rise, which is a constant value in most experiments.
The heterogeneous system obtained by substituting the formula (1) into the formula (3) has a common kinetic equation under the non-constant temperature condition, such as the formula (5):
selecting one α in TG plot 21It is taken as a horizontal line, and the horizontal line intersects the curve at an intersection point (α)1,T11)(α1,T12) …, the ramp rates corresponding to them are β1、β2…, and selecting another α2Repeating the above process, another set of data (α) is obtained2,T21)、(α2,T22) …, their corresponding ramp rates are still β1、β2…;
Formula (5) can be modified as follows:
at α1~α2In the range of β1The two-sided integration of equation (6) can be obtained
For β2The two-sided integration of equation (6) can be obtained
Subtracting the above two equations can obtain:
solving the formula (9) to obtain the activation energy E of the dry-type insulation equipmenta。
In the thermal weight loss test of the insulating material of the dry type insulating equipment, different chemical reaction stages may exist, so that the reflection rate of each stage is different, and different wave troughs appear on the DTG curve chart 3. in the activation energy acquisition method based on the equal conversion rate method, α1As a starting point for the calculation section, it is decided which stage of the activation energy is calculated for the activation energy of the insulating material, e.g., α1And α2Can span the whole process of the thermal weight loss test, and the E obtained at the momentaα is the activation energy of new epoxy resin insulating material1And α2May be selected only in the vicinity of the second trough, in which case E is obtainedaThe activation energy is the activation energy of the dry-type insulation equipment which has been subjected to secondary curing after a period of time and in a certain aging state in normal operation.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.