CN113009277B - Full-size cable activation energy analysis method and system - Google Patents
Full-size cable activation energy analysis method and system Download PDFInfo
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- CN113009277B CN113009277B CN202110241184.0A CN202110241184A CN113009277B CN 113009277 B CN113009277 B CN 113009277B CN 202110241184 A CN202110241184 A CN 202110241184A CN 113009277 B CN113009277 B CN 113009277B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/003—Environmental or reliability tests
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/083—Locating faults in cables, transmission lines, or networks according to type of conductors in cables, e.g. underground
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
- G01R31/1272—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of cable, line or wire insulation, e.g. using partial discharge measurements
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Abstract
The application discloses full-size cable activation energy analysis method and system, which are used for measuring the electric charge amount of a cable to be measured under the condition of multiple step temperatures and calculating the activation energy of the cable to be measured according to the measured electric charge amount. Connecting a cable to be tested with a current integrator, calibrating a charge quantity measuring system, and carrying out a charge quantity test to obtain a dynamic charge quantity; solving the charge quantity change rate, the relaxation time, the capacitance, the dielectric constant, the conductivity and the activation energy of the whole cable according to the dynamic charge quantity obtained by measurement; and analyzing the solved activation energy to obtain the rule that the activation energy of the cable to be tested changes along with the voltage under different temperature conditions, thereby realizing more complete service life evaluation of the XLPE cable. The method is based on the current integral charge quantity technology, can be applied to the whole cable activation energy test calculation, can realize the test under the low voltage condition (100V-4kV), can obtain stable conductivity, and provides accurate data basis for the activation energy calculation.
Description
Technical Field
The invention relates to the technical field of electrical equipment and electrical engineering, in particular to a full-size cable activation energy analysis method and system.
Background
XLPE power cables are widely used in power systems. However, in the actual working process, due to the influence of conditions such as heat, machinery, electricity, water and the like, the insulation is aged, faults are caused, even the whole cable is broken down, and the normal operation of the power system is influenced. Therefore, the aging problem of the XLPE cable arouses the attention at home and abroad.
At this stage, there are several ways to evaluate the aging of XLPE in the laboratory, such as fourier infrared spectroscopy analysis of carbonyl index of XLPE, DSC analysis of melting peak of XLPE, and TGA analysis of weight loss of XLPE under high temperature conditions. Combined with a large number of literature reports, aging of XLPE is closely related to activation energy, which is closely related to the service life of the material. In a laboratory, the weight loss rate, the elongation at break, the current and other parameters are related to the temperature, and the parameters conform to an Arrhenius empirical equation, and the activation energy of the material is calculated according to the empirical equation. However, the conventional experimental method is only suitable for XLPE thin sheet samples, and cannot directly detect full-size integral cables.
Disclosure of Invention
The application provides a full-size cable activation energy analysis method and system, which aim to solve the problem that the activation energy of a full-size whole cable cannot be directly detected and calculated in the prior art.
The application provides a full-scale cable activation energy analysis method, which comprises the following steps:
measuring the electric charge quantity of the cable to be measured under the condition of a plurality of step temperatures, and calculating the activation energy of the cable to be measured according to the measured electric charge quantity;
wherein the step of measuring the amount of charge comprises:
connecting a conductor of a cable to be tested with a high-voltage output end of a current integrator;
performing a non-pressurization test and an integral capacitance test of the current integrator, and calibrating the charge quantity measuring system;
carrying out a charge quantity test under a plurality of step temperature conditions to obtain a dynamic charge quantity, an instantaneous charge quantity and a charge quantity at the end of a pressurization time;
wherein the step of calculating the activation energy comprises:
solving the charge quantity change rate according to the measured instantaneous charge quantity and the charge quantity at the end of the pressurization time, and obtaining the relaxation time according to the solved change rate and the test time;
solving the capacitance of the whole cable according to the instantaneous charge quantity and the voltage, and calculating to obtain a dielectric constant according to the solved capacitance, the length of the cable to be tested, the diameter of the cable to be tested and the diameter of the copper core;
calculating according to the solved relaxation time and dielectric constant to obtain the conductivity;
calculating to obtain activation energy according to the solved electric conductivity meeting an Arrhenius empirical formula;
and analyzing the solved activation energy to obtain the rule that the activation energy changes along with the voltage under different temperature conditions of the cable to be tested.
In the embodiment of the present invention, the plurality of step temperature conditions include five temperature conditions of 30 ℃, 50 ℃, 70 ℃, 90 ℃ and 110 ℃;
when the electric charge quantity is tested under the condition of a plurality of step temperatures, the test voltage is 1kV to 4kV, the step length is 1kV, the pressurization time is 300s, and the sampling step length is 2 s;
the cable to be tested comprises an unaged full-size cable and a thermal aged full-size cable, and the unaged full-size cable and the thermal aged full-size cable are respectively connected with the current integrator for comparison test.
When the cable conductor is connected with the high-voltage output end of the current integrator, the outer shielding semi-conducting layers with certain lengths at the head end and the tail end of the cable to be tested are stripped, and the copper foil is wound outside and grounded.
The formula for calculating the relaxation time is:
wherein Q is 0 Is the instantaneous charge amount, nC; q (300s) is the amount of charge at the end of the pressurization time, nC; t is t m Is the test time, s; τ is the relaxation time, s;
the formula for calculating the dielectric constant is:
wherein epsilon 0 Dielectric constant in vacuum, 8.854 × e -12 ；ε r Is a relative dielectric constant; l is the length of the whole cable, mm; b is the diameter of the whole cable, mm; a is the diameter of the copper core of the cable, mm;
the formula for calculating conductivity is:
the formula for calculating activation energy is:
a is a constant; k is Boltzmann constant, 1.38X 10 -23 J/k; t is the thermodynamic temperature, K; ea is activation energy, J.
Calculating logarithms of two sides of the formula of the activation energy to obtain:
wherein, 1/T and ln gamma are approximately in linear relation, and the product of the absolute value of the slope and the boltzmann constant is the activation energy.
The application provides a full-size cable activation energy analysis system, which is applied to a full-size cable activation energy analysis method and comprises a current integrator, a temperature control oven, a high-voltage power supply, a controller and a data acquisition and processing module;
the input end of the current integrator is connected with the high-voltage power supply, and the output end of the current integrator is connected to a cable to be tested in the temperature control oven body through a high-voltage wire;
the data acquisition and processing module is connected to the current integrator through an Opt optical fiber;
the controller is connected with the high-voltage power supply.
Optionally, a resistor is connected in series between the current integrator and the cable to be tested.
Optionally, a heat-resistant insulating tape is wound at the connection between the high-voltage wire and the copper core of the cable to be tested and between the high-voltage wire and the current integrator.
According to the technical scheme, the application provides a full-size cable activation energy analysis method and system, the electric charge quantity of a cable to be tested under the condition of multiple step temperatures is measured, and the activation energy of the cable to be tested is calculated according to the measured electric charge quantity. Wherein the step of measuring the amount of charge comprises: connecting a conductor of a cable to be tested with a high-voltage output end of a current integrator; performing a non-pressurization test and an integral capacitance test of the current integrator, and calibrating the charge quantity measuring system; the charge amount test is performed under a plurality of stepped temperature conditions, and the dynamic charge amount, the instantaneous charge amount, and the charge amount at the end of the pressurization time are obtained. Wherein the step of calculating the activation energy comprises: solving the charge quantity change rate according to the measured instantaneous charge quantity and the charge quantity at the end of the pressurization time, and obtaining the relaxation time according to the solved change rate and the test time; solving the capacitance of the whole cable according to the instantaneous charge quantity and the voltage, and calculating the dielectric constant according to the solved capacitance, the length and the diameter of the cable to be tested and the diameter of the copper core; calculating according to the solved relaxation time and dielectric constant to obtain the conductivity; calculating to obtain activation energy according to the solved electric conductivity meeting an Arrhenius empirical formula; and analyzing the solved activation energy to obtain the rule that the activation energy changes along with the voltage under different temperature conditions of the cable to be tested. It can be seen that, compared with the conventional technical scheme which can only be used for a flat plate sample, the current integrator and the cable to be tested are separated based on the current integration charge quantity technology, the current integrator can be applied to the whole cable, the requirement of actual engineering is met, the current integrator is separated from the cable to be tested, the current integrator is prevented from being increased in error and even damaged due to high temperature influence, in addition, the current integration charge quantity technology is high in sensitivity, the test under the low voltage condition (100V-4kV) can be realized, and the electric conductivity is not obviously changed along with the electric field intensity in the range, so that stable electric conductivity can be obtained, and accurate data basis is provided for the calculation of activation energy.
Drawings
In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without any creative effort.
FIG. 1 is a schematic flow chart of a full-scale cable activation energy analysis method according to the present application;
FIG. 2 is a schematic flow chart of a full-scale cable charge measurement method according to the present application;
FIG. 3 is a schematic flow chart illustrating a method for calibrating a charge measurement system according to the present application;
FIG. 4 is a schematic flow chart of a full-scale cable activation energy calculation method according to the present application;
FIG. 5 is a graph showing the relationship between the rate of change of the amount of charge and the voltage at different temperatures for an unaged cable under test according to the present application;
FIG. 6 is a graph showing the relationship between the rate of change of the amount of charge and the voltage at different temperatures for a cable to be tested aged for 60 days at 150 ℃;
FIG. 7 is a graph showing the relationship between the conductivity and the voltage of an unaged cable under test according to the present application at different temperatures;
FIG. 8 is a graph showing the relationship between the conductivity and voltage at different temperatures for a cable to be tested aged for 60 days at 150 ℃ according to the present application;
FIG. 9 is a graph showing the variation of the activation energy of an unaged cable to be tested at different temperatures according to the present application;
FIG. 10 is a graph showing the variation of the activation energy of a cable to be tested aged at 150 ℃ for 60 days at different temperatures according to the present application;
fig. 11 is a schematic diagram of a full-scale cable activation energy analysis system according to the present application.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 1 is a schematic flow chart of a full-scale cable activation energy analysis method in an embodiment of the present application, and referring to fig. 1, the present application provides a full-scale cable activation energy analysis method, mainly for the activation energy of cable insulation crosslinked polyethylene (XLPE), taking a comparative test of an entire cable that is not aged and is thermally aged at 150 ℃ for 60 days as an example, but not limited to the above case. The method comprises the following steps:
s1, measuring the charge quantity of the cable to be measured under the condition of a plurality of step temperatures; selecting two proper cables as cables to be measured, preprocessing the cables to be measured, measuring basic parameters of the preprocessed cables, and measuring the charge quantity after debugging a charge quantity measuring system. The pretreatment comprises the following operations of carrying out heat aging on cables of a heat aging test group for 60 days at 150 ℃, removing outer shielding semi-conducting layers 5 cm from the head end and the tail end of the cable to be tested, winding copper foils outside the cable to be tested and the like; the basic parameters comprise the length of the cable to be measured, the diameter of the copper core of the cable to be measured and the like.
The outer shielding semi-conducting layers of 5 cm at the head end and the tail end of the cable to be measured are removed, so that the influence of the electric leakage phenomenon in pressurization on the measurement result can be effectively prevented; the cable insulation layer is grounded by winding a copper foil on the outside of the cable to be tested.
Fig. 2 is a schematic flow chart of a full-scale cable charge measurement method according to an embodiment of the present application, and referring to fig. 2, the present application provides a full-scale cable charge measurement method, including:
s11, connecting a conductor of the cable to be tested with a high-voltage output end of the current integrator; the copper core of a preprocessed cable to be measured is connected with the high-voltage output end of a current integrator of the charge quantity measuring system through a high-voltage wire, and a polytetrafluoroethylene heat-resistant insulating tape is wound at the joint of the high-voltage wire, the cable copper core and the current integrator, so that the influence of leakage current on a measuring result is prevented.
S12, performing a non-pressurization test and an integral capacitance test of the current integrator, and calibrating the charge quantity measuring system; fig. 3 is a schematic flow chart of a method for calibrating a charge measurement system according to an embodiment of the present disclosure, and referring to fig. 3, the present disclosure provides a method for calibrating a charge measurement system, the method including:
s121, after the connection between the cable to be tested and the current integrator is completed, carrying out non-pressurization test on the current integrator under the condition that the current integrator is not connected with a high-voltage power supply, wherein the time length is 60 seconds, and the sampling step length is 2 seconds;
s122, carrying out non-pressurization test on the integral capacitor, and clicking a capacitor test button under the condition of not applying voltage;
s123, carrying out an integral capacitor pressurization test, pressurizing two ends of the integral capacitor, and clicking a capacitor test button;
considering the influence of errors, the charge value obtained by sampling in the non-pressurization test of the current integrator is less than 1nC and basically does not change along with time, the acquired data in the non-pressurization test of the integrating capacitor shows a straight line with a slope, and under the condition that the integrated capacitance value obtained by data calculation after the pressurization test of the integrating capacitor is 20 seconds is compared with the theoretical capacitance value within an error range, the influence of internal faults, the faults of the integrating capacitor and other reasons of the current integrator on the charge measurement is eliminated, and the calibration of the charge measurement system is completed.
S13, carrying out a charge quantity test under a plurality of step temperature conditions to obtain a dynamic charge quantity, an instantaneous charge quantity and a charge quantity at the end of a pressurization time; the cable to be tested is integrally placed in a constant-temperature blast oven and is connected with a current integrator outside the oven through a high-voltage wire, so that the insulation distance between a wiring part, particularly a high-voltage end and a low-voltage end, and the ground potential is ensured; the charge amount test was performed under five temperature conditions of 30 ℃, 50 ℃, 70 ℃, 90 ℃ and 110 ℃. The test voltage starts from 1kV, the step length is 1kV till 4kV, the pressurizing time is 300s, and the sampling step length is 2 s.
Before testing, the cable to be tested is wiped by using sterile cotton cloth dipped with alcohol and preheated in an oven for 30 minutes, so that the whole insulating crosslinked polyethylene (XLPE) insulating layer of the cable to be tested is heated uniformly.
The current integration equipment is directly connected with a cable to be tested in series through a resistor with the resistance value of 1 Mohm for current limiting, current flows into an integration capacitor in a current integrator from a high-voltage power supply, then through the cable to be tested, the integration of the current on the integration capacitor to time is equal to the integration of the current on the cable to be tested to time, namely, the charge quantity information of cable insulation can be reflected through an external capacitor, and through testing voltage signals on the capacitor and signal processing, the dynamic charge quantity change information of the whole-size cable is obtained.
S2, calculating the activation energy of the cable to be measured according to the measured electric charge amount; under low voltage, the insulation conductivity of the cable to be tested is in a linear ohmic region, the conductivity does not change along with the change of an electric field, the insulation conductivity of the cable gradually increases along with the increase of the voltage and enters a conductivity region regulated by a trap, and the conductivity and the electric field intensity present a nonlinear relation. In this embodiment, the cable insulation activation energy is calculated by using the conductivity of the test analysis at low voltage. Fig. 4 is a schematic flow chart of a method for calculating activation energy of a full-scale cable according to an embodiment of the present application, where the activation energy calculation is performed according to the following steps based on measured basic parameters and charge amount:
s21, solving the charge quantity change rate according to the measured instantaneous charge quantity and the charge quantity at the end of the pressurization time, and obtaining the relaxation time according to the solved change rate and the test time; the calculation was performed using the following formula:
wherein Q is 0 Is the instantaneous charge amount, nC; q (300s) is the amount of charge at the end of the pressurization time, nC; t is t m Is the test time, s; τ is the relaxation time, s.
Using the rate of change of electric charge eta ═ Q (300s)/Q 0 The injection and accumulation degree of space charge is characterized. When k is approximately equal to 1, no space charge is injected and accumulated in the whole cable; when k is more than 1, the influence of insulated conductive current on space charge is increased along with the increase of k, and the electric conduction is realized when charge injection is neglected under a low electric fieldThe magnitude of the rate of change of the amount of the excess charge may reflect the magnitude of the conductance current. As shown in fig. 5 and 6, the relationship between the change rate of the charge amount and the voltage at different temperatures is shown for the unaged cable and the cable aged at 150 ℃ for 60 days.
S22, solving the capacitance of the whole cable according to the instantaneous charge quantity and the voltage, and calculating to obtain a dielectric constant according to the solved capacitance, the length and the diameter of the cable to be tested and the diameter of the copper core; the calculation was performed using the following formula:
wherein epsilon 0 Dielectric constant in vacuum, 8.854 × e -12 ；ε r Is a relative dielectric constant; l is the length of the whole cable, mm; b is the diameter of the whole cable, mm; a is the diameter of the copper core of the cable, mm;
fitting the initial charge and the applied voltage to obtain the capacitance of the whole cable, and further calculating to obtain the insulation dielectric constant epsilon 0 ε r 。
S23, calculating the conductivity according to the solved relaxation time and dielectric constant; the calculation was performed using the following formula:
the relaxation time is the ratio of the static dielectric constant of the cable insulation to the low field conductivity, and tau ═ epsilon 0 ε r And/gamma. The equations in the simultaneous steps S21 and S22 result in the insulation conductivity γ at different temperatures. As shown in fig. 7 and 8, the relationship between the conductivity and the voltage of the unaged cable and the cable aged at 150 ℃ for 60 days is shown.
S24, calculating according to the solved electric conductivity and the Allen-Wus empirical formula to obtain activation energy;
as can be seen from fig. 7 and 8, in the test voltage range, the relationship between the conductivity and the voltage is not large, but the conductivity is very sensitive to the temperature, and the conductivity rapidly increases with the increase of the temperature, which conforms to the empirical formula of arrhenius. The conductivity and the temperature of the insulating layer of the insulating cross-linked polyethylene (XLPE) of the cable to be tested meet the Allen-baus empirical formula:
wherein A is a constant; k is Boltzmann constant, 1.38X 10 -23 J/k; t is the thermodynamic temperature, K; ea is activation energy, J.
Taking logarithms at two sides of the above formula to obtain the formula:
wherein 1/T and ln gamma are approximately in a linear relation, and the logarithm of the conductivity and the reciprocal of the thermodynamic temperature are subjected to linear fitting to obtain the activation energy E of the full-size cable a The product of the absolute value of the slope and the boltzmann constant is the activation energy.
S25, analyzing the solved activation energy to obtain the rule that the activation energy changes along with the voltage under different temperature conditions of the cable to be tested;
and calculating the integral cable activation energy of the cable to be tested according to the steps. The activation energy reflects the energy required by the molecules to be converted from a normal state into an active state which is easy to turn, the thermodynamic characteristics of molecular chains in the insulating material are reflected, and the influence of thermal aging on the insulation of the whole cable is judged by comparing the sizes of the activation energy; after aging, the activation energy of the whole cable is reduced, and the service time is shortened. As shown in fig. 9 and 10, the change law of the activation energy of the unaged cable and the cable aged for 60 days at 150 ℃ at different temperatures is shown.
Fig. 11 is a schematic diagram of a full-scale cable activation energy analysis system according to an embodiment of the present application, and referring to fig. 11, the present application provides a full-scale cable activation energy analysis system. The analysis system includes:
the device comprises a current integrator 1, a temperature control oven 2, a high-voltage power supply 3, a controller 4 and a data acquisition processing module 5;
the input end of the current integrator 1 is connected with the high-voltage power supply 3, and the output end of the current integrator 1 is connected to a cable to be tested in the box body of the temperature control oven 2 through a high-voltage wire 6, and outputs voltage to the whole cable to be tested in the full size.
The data acquisition processing module 5 is connected to the current integrator 1 through an Opt optical fiber 7 to acquire charge information of the full-size integral cable; the traditional current integrator is wirelessly connected with the data acquisition module through a Zigbee communication technology. The Zigbee wireless signal is easily interfered by external conditions to affect the integrity of the test data. In the embodiment, Opt optical fiber connection is adopted, so that the stability of the testing process is enhanced.
The controller 4 is connected with the high-voltage power supply 3, and the controller 4 is used for controlling the voltage output of the high-voltage power supply 3.
Further, a resistor 8 is connected in series between the current integrator 1 and the cable to be tested to play a role in current limiting.
Furthermore, heat-resistant insulating tapes are wound at the joints of the high-voltage wire 6 and the copper core of the cable to be tested and the high-voltage wire 6 and the current integrator 1 so as to prevent the influence of leakage current.
Compared with the traditional technical scheme that the method can only be used for a flat-plate sample, the method is based on the current integration charge quantity technology, can be applied to the whole cable, and meets the requirements of actual engineering. The current integrator is separated from the cable to be tested, so that the current integrator is prevented from being influenced by high temperature to cause large errors and even damage. The current integration charge quantity technology has high sensitivity, can realize the test under the low voltage condition (100V-4kV), the conductivity does not obviously change along with the electric field intensity in the range, and can obtain stable conductivity. In the embodiment, the charge information of two integral cables with different aging degrees is acquired by using the series integration capacitors, and the electric conductivity under different temperature conditions is obtained by analysis. The relationship between the conductivity and the temperature is described by using an Arrhenius empirical equation, the activation energy of the whole cable is obtained through calculation, and the influence of thermal ageing on the whole cable is analyzed.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed invention. This application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
Claims (10)
1. A method of full-scale cable activation energy analysis, the method comprising:
measuring the electric charge quantity of the cable to be measured under the condition of a plurality of step temperatures, and calculating the activation energy of the cable to be measured according to the measured electric charge quantity;
wherein the step of measuring the amount of charge comprises:
connecting a conductor of a cable to be tested with a high-voltage output end of a current integrator;
performing a non-pressurization test and an integral capacitance test of the current integrator, and calibrating the charge quantity measuring system;
carrying out a charge quantity test under a plurality of step temperature conditions to obtain a dynamic charge quantity, an instantaneous charge quantity and a charge quantity at the end of a pressurization time;
wherein the step of calculating the activation energy comprises:
solving the charge quantity change rate according to the measured instantaneous charge quantity and the charge quantity at the end of the pressurization time, obtaining the relaxation time according to the solved change rate and the test time, and calculating the relaxation time according to the formula as follows:
wherein Q is 0 Is the instantaneous charge amount, nC; q (300s) is the amount of charge at the end of the pressurization time, nC; t is t m Test time, s; τ is the relaxation time, s;
solving the capacitance of the cable to be tested according to the instantaneous charge quantity and the voltage, and calculating the dielectric constant according to the solved capacitance, the length and the diameter of the cable to be tested and the diameter of the copper core;
and calculating the conductivity according to the solved relaxation time and the dielectric constant, wherein the formula for calculating the conductivity is as follows:
wherein epsilon 0 Dielectric constant in vacuum, 8.854 × e -12 ；ε r Is a relative dielectric constant;
calculating to obtain activation energy according to the solved electric conductivity meeting an Arrhenius empirical formula;
and analyzing the solved activation energy to obtain the rule that the activation energy changes along with the voltage under different temperature conditions of the cable to be tested.
2. The assay of claim 1, wherein the plurality of step temperature conditions comprises five temperature conditions of 30 ℃, 50 ℃, 70 ℃, 90 ℃ and 110 ℃.
3. The analysis method according to claim 1, wherein the test voltage is 1kV to 4kV, the step size is 1kV, the pressing time is 300s, and the sampling step size is 2s when the charge amount test is performed under the condition of a plurality of step temperatures.
4. The analysis method according to claim 1, wherein the cable to be tested comprises an unaged full-scale cable and a heat-aged full-scale cable, and the unaged full-scale cable and the heat-aged full-scale cable are respectively connected with the current integrator for comparison test.
5. The analysis method according to claim 1, wherein when the cable conductor is connected to the high voltage output end of the current integrator, the outer shielding semi-conducting layer is stripped from the head and tail ends of the cable to be tested by a certain length, and the copper foil is wound on the outer shielding semi-conducting layer and grounded.
6. The analytical method of claim 1, wherein the dielectric constant is calculated by the formula:
wherein L is the length of the whole cable, mm; b is the diameter of the whole cable, mm; a is the diameter of the copper core of the cable, mm;
the formula for calculating activation energy is:
a is a constant; k is Boltzmann constant, 1.38X 10 -23 J/k; t is the thermodynamic temperature, K; ea is activation energy, J.
7. The analytical method of claim 6, wherein the logarithm of both sides of the formula for calculating the activation energy is obtained by:
wherein, 1/T and ln gamma are approximately in linear relation, and the product of the absolute value of the slope and the boltzmann constant is the activation energy.
8. A full-scale cable activation energy analysis system applied to the method of any one of claims 1 to 7, characterized by comprising a current integrator (1), a temperature-controlled oven (2), a high-voltage power supply (3), a controller (4) and a data acquisition and processing module (5);
the input end of the current integrator (1) is connected with the high-voltage power supply (3), and the output end of the current integrator (1) is connected to a cable to be tested in the box body of the temperature control oven (2) through a high-voltage wire (6);
the data acquisition and processing module (5) is connected to the current integrator (1) through an Opt optical fiber (7);
the controller (4) is connected with the high-voltage power supply (3).
9. An analysis system according to claim 8, characterized in that a resistor (8) is connected in series between the current integrator (1) and the cable under test.
10. The analysis system according to claim 8, wherein the junction of the high voltage wire (6) and the copper core of the cable to be tested, and the high voltage wire (6) and the current integrator (1) is wound with a heat-resistant insulating tape.
Priority Applications (1)
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