CN112147467B - Cable insulation branch degradation detection method based on leakage current integral charge - Google Patents
Cable insulation branch degradation detection method based on leakage current integral charge Download PDFInfo
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- 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 invention discloses a method for detecting the degradation of an insulated cable branch based on leakage current integral charge, which comprises the following steps: building an electric tree detection circuit based on a leakage current integral charge technology; acquiring a capacitance voltage variation curve along with time based on the circuit, and reversely deducing a capacitance charge quantity variation curve along with time through a capacitance value; performing linear fitting on the capacitance charge data sampled for 500-600 seconds to obtain a fitting function; judging a time demarcation point at which the deviation of the electric charge quantity and the fitting function is more than or equal to 5%, and calculating the slope k of the electric charge to the time between the time demarcation point and 600 seconds; when k is 10 or more‑10Judging generation of branches with electricity, otherwise, judging generation of branches without electricity; when the value of k is between 10‑10And 10‑9When k is more than 10, the deterioration level of electrical tree branches is low‑9When the water is used, the electrical tree is seriously degraded.
Description
Technical Field
The invention relates to the field of degradation detection of power cable insulating materials, in particular to a cable insulating electrical branch degradation detection method based on leakage current integral charges.
Background
The power cable is a key electrical device in a new energy grid-connected and urban power supply system, and in the service process of the power cable, the aging, the deterioration and the breakdown of the cable insulation under complex working conditions are important factors influencing the reliable operation of the power cable. Under the action of a long-term electric heating field, a dendritic discharge channel can be formed between a semi-conducting layer and an insulating layer in the cable, and a series of chemical and physical reactions caused by partial discharge in micropores or channels can continuously degrade surrounding materials, maintain the continuous development of the dendritic channel and seriously influence the safe and stable operation of the cable. How to accurately evaluate the degradation characteristics of the cable insulation, and identifying the insulation aging state are important contents for the operation and maintenance of the power cable.
At present, the evolution of dielectric and physical and chemical properties of the power cable in an electrothermal composite field is widely researched by researchers, and becomes a theoretical basis for evaluating the operation reliability of the power cable. The traditional test method is mainly used for laboratory analysis and research, is greatly influenced by the interference of field and environmental conditions under the actual cable operation working condition, and seriously influences the accuracy of the power cable insulation state evaluation. The real aging state of the insulation is determined by the partial discharge characteristic parameters, long-term online monitoring is needed, and the diagnosis accuracy is limited depending on the analysis means of the characteristic parameters and the development state of the electrical branch. Therefore, future power cable insulation requires more advanced and accurate detection and diagnostic techniques to accommodate the large-scale application of future power cables.
Disclosure of Invention
The invention provides a cable insulation electrical tree degradation detection method based on leakage current integral charge, which comprises the following steps of connecting a power cable or an accessory into a leakage current integral charge circuit, applying direct-current high voltage to the cable/accessory, reflecting the dynamic evolution of charge by utilizing an integral capacitor, and estimating the development state of an insulation layer electrical tree through the dynamic evolution characteristic of the charge, so as to evaluate the electrical tree degradation level of the power cable or the accessory, which is described in detail in the following description:
a method for detecting degradation of an insulated electrical branch of a cable based on integrating charge with leakage current, the method comprising:
building an electric branch detection device based on a leakage current integral charge technology, acquiring a capacitance voltage change curve based on the device, and performing linear fitting on capacitance charge data sampled for 500-600 seconds according to the capacitance voltage change curve and the change of capacitance reverse calculation charge quantity to obtain a fitting function; judging a time boundary point of which the deviation of the charge quantity and the fitting function is more than or equal to 5%, calculating the slope k of the charge to the time between the time boundary point and 600 seconds, and when the k is more than or equal to 10-10And judging generation of the branches with electricity, otherwise, judging generation of the branches without electricity. When the value of k is between 10-10And 10-9When k is more than 10, the deterioration level of electrical tree branches is low-9When the water is used, the electrical tree is seriously degraded.
Wherein, electric branch detection device includes: the high-voltage end of the high-voltage direct-current power supply is connected with the integrating capacitor and the protective resistor in series in an insulated manner with the cable/accessory; the sampling device is composed of an operational amplifier, an analog-to-digital converter and a processing chip/signal transmitter, and is connected with the integrating capacitor in parallel and used for representing the voltage at two ends of the capacitor.
The cable is an alternating current cable or accessory with the voltage grade of 35kV or above or a direct current cable or accessory with the voltage grade of 100kV or above, and the cable insulation material is cross-linked polyethylene, polypropylene or modified polymer insulation taking the three materials as matrixes; the cable accessory insulating material is ethylene propylene rubber, silicon rubber or other solid polymer insulating materials.
Furthermore, the voltage sampling time is 5-20 minutes, and the sampling rate of the voltmeter is not lower than 1 Hz.
The technical scheme provided by the invention has the beneficial effects that:
according to the invention, the cable/accessory to be tested is tested through the self-built test circuit based on the leakage current charge integration, the insulated electrical treeing state of the cable can be effectively detected, and the convenient, nondestructive and accurate detection of the degradation level of the electrical treeing is realized.
Drawings
FIG. 1 is a schematic circuit diagram of a high voltage cable insulation electrical treeing detection test;
FIG. 2 is a schematic circuit diagram of an electrical treeing test for cable accessories;
FIG. 3 is a flow chart of a data processing algorithm;
FIG. 4 is a graph of the charge dynamics of different electrical dendron insulations in the test case;
fig. 5 is a schematic diagram of the actual growth state of the electrical tree in the test case.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in further detail below.
A brief summary of the invention is provided below to provide a basic understanding of some aspects of the invention. The invention provides a test device and a test method for treeing detection of insulated electric cables/accessories, which comprise a device, an experimental method and a data processing part.
The testing device of the detection method comprises a high-voltage direct-current power supply, an integrating capacitor, a sampling device, a protective resistor and a transient diode, and the principle of the main circuit is shown in figure 1 or figure 2. Fig. 1 is a schematic diagram of a method for detecting the deterioration of an insulated electrical branch of a high-voltage cable, and fig. 2 is a schematic diagram of a method for detecting the deterioration of an electrical branch of a cable accessory. The high-voltage direct-current power supply is mainly characterized by a direct-current high-voltage generating device with the capability of outputting direct-current high voltage. The high-voltage end, the integrating capacitor and the protection resistor are connected with the cable/accessory in series in an insulating mode, and the current flowing through the integrating capacitor is the same as the current flowing through the to-be-tested insulation. The transient diode is connected with the integrating capacitor in parallel, and the transient diode is quickly conducted when the voltage values at two ends of the integrating capacitor are overlarge, so that the integrating capacitor and the operational amplifier are protected from being damaged by high voltage. When current flows through the integrating capacitor, the integral of the current with respect to time is the charge accumulated by the capacitor. The voltage signals at the two ends of the capacitor can be obtained through the sampling devices connected in parallel at the two ends of the capacitor. The sampling device consists of an operational amplifier, an analog-to-digital converter and a processing chip/signal emitter, wherein the operational amplifier can obtain the voltage change of the integrating capacitor, thereby inverting the dynamic change of the charge. The signal output by the operational amplifier is converted into a digital signal for processing and transmission through an analog-to-digital converter, so that the data can be further analyzed, processed and transmitted.
The experimental method comprises the following steps:
(1) circuit construction: and connecting the cable/accessory to be tested into the test circuit, connecting the conductor with the protective resistor, grounding the outer shielding layer and checking whether the circuit connection is correct.
(2) Voltage application: and turning on the high-voltage direct-current power supply, and slowly adjusting the voltage knob until the voltage reaches a set voltage value.
(3) Voltage sampling: and opening a voltmeter to acquire voltage value change data of the integral capacitor, and recording a voltage change curve of the integral capacitor.
(4) And (4) finishing the test: and (3) closing the data acquisition function of the voltmeter, slowly reducing the high-voltage direct-current power supply to 0, taking out the cable/accessory to be tested from the circuit, disconnecting the test power supply, and processing and recording data.
Wherein, the voltage sampling time is 5-20 minutes, and the sampling rate of the voltmeter is not lower than 1 Hz.
Further, the series connection sequence of the circuits is not limited to the connection sequence of the circuits shown in fig. 1 or fig. 2, and the integration capacitor, the protection resistor and the cable/accessory to be tested can be replaced arbitrarily.
The cable to be tested is an alternating current cable and accessories with the voltage class of 35kV or above and a direct current cable or accessories with the voltage class of 100kV or above. The cable insulation material is cross-linked polyethylene, polypropylene or modified polymer insulation taking the three materials as a matrix, and the cable accessory insulation material is ethylene propylene rubber, silicon rubber or other solid polymer insulation.
The data processing method of the invention comprises the following steps:
(1) voltage signal inversion charge variation: and multiplying the acquired voltage signal by the integral capacitance to obtain integral capacitance charge amount evolution data.
(2) And (3) charge component decomposition: and performing linear fitting on the data sampled from 500 seconds to 600 seconds to obtain a fitting function, and judging a time demarcation point with deviation of more than or equal to 5% between the previous stage and the fitting function, so that the charge change curve is divided into two parts of absorbed charge and leaked charge at the time demarcation point.
(3) The leakage current value is calculated. The corresponding electric charge amount at the time demarcation point is the absorbed electric charge amount, and the slope k of a fitting curve after the time demarcation point is the leakage current value. The slope k of the charge versus time between the offset time point and 600 seconds is calculated. When k is 10 or more-10And judging generation of the branches with electricity, otherwise, judging generation of the branches without electricity. When the value of k is between 10-10And 10-9When k is more than 10, the deterioration level of the electrical tree branches is low-9In time, electrical tree degradation is severe.
The voltage obtained by the operational amplifier is used to reverse the charge variation of the capacitor with the time variation data. When a voltage is applied to the cable/accessory under test, the resulting current includes both sinking and leakage currents. The absorption current is generated by a capacitive equivalent circuit in the circuit, the leakage current generated by the conductance becomes a main component of current integration along with the reduction of the capacitive current, and finally the slope of the integration gradually approaches to the leakage current value. And judging the degradation level of the cable/accessory insulation according to the rate of charge change, thereby realizing the detection and diagnosis of electrical treeing.
A typical application case of electrical dendronization detection based on the method is as follows:
a circuit is built according to the diagram shown in figure 1, a sample to be tested is connected into the circuit, the output voltage of a direct current voltage source is 3kV, and the pressurizing time is 10 minutes. And recording the reading change of the voltmeter within 10 minutes, and calculating the change of the charge quantity of the capacitor through the capacitance value to obtain the dynamic change of the charge quantity along with the pressurization time. The resulting charge dynamics of the different electrical dendrons are shown in figure 4. The leakage current value k corresponding to the samples (a), (b), (c), (d) and (e) was calculated to be 3.04x10 by the data processing means-10、2.80x10-10、6.01x10-10、1.08x10-9And 1.17x10-9A。
The actual growth state of the electrical tree is shown in fig. 5. It can be seen that as the electrical tree damage is more severe, the leakage current of the sample to be tested increases and the rate of charge increase is more rapid. When the value of k is between 10-10And 10-9When k is more than 10, the deterioration level of the electrical tree branches is low-9In time, electrical tree degradation is severe.
Compared with the existing electric tree detection method, the electric tree detection method has the following advantages:
(1) the method is a non-destructive method, the applied voltage and the pressurizing time are shorter, new space charge accumulation cannot be introduced into the cable insulation, and the original insulation state of the cable cannot be damaged;
(2) the current integration method adopted by the method is less influenced by environmental interference, the testing method is simple and high in sensitivity, and the method can be conveniently used for full-size cables and accessories.
In the embodiment of the present invention, except for the specific description of the model of each device, the model of other devices is not limited, as long as the device can perform the above functions.
Those skilled in the art will appreciate that the drawings are only schematic illustrations of preferred embodiments, and the above-described embodiments of the present invention are merely provided for description and do not represent the merits of the embodiments.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (4)
1. A method for detecting degradation of an insulated electrical branch of a cable based on integrated charge of leakage current, the method comprising:
building an electric branch detection circuit based on a leakage current integral charge technology, wherein an integral capacitor is connected with a cable to be detected in series, and the current flowing through the integral capacitor is the same as the current flowing through the cable to be detected;
acquiring a capacitance voltage variation curve along with time based on the circuit, and inversely calculating the variation of capacitance charge quantity along with time by combining a capacitance value;
performing linear fitting on the 500-600 second data of the sampled charge quantity to obtain a fitting function;
judging the time demarcation point of the deviation value of the charge quantity curve and the fitting function which is more than or equal to 5%, calculating the slope k of the charge to the time between the deviation time point and 600 seconds, and when the k is more than or equal to 10-10Judging generation of branches with electricity, otherwise, judging generation of branches without electricity;
when the value of k is between 10-10And 10-9When k is more than 10, the deterioration level of electrical tree branches is low-9When the water is used, the electrical tree is seriously degraded.
2. The method for detecting the electrical branch degradation of the cable insulation based on the integrated leakage current charge according to claim 1, wherein the electrical branch detection circuit comprises: the high-voltage direct-current power supply, the integrating capacitor, the sampling device, the protective resistor and the transient diode;
the high-voltage end of the high-voltage direct-current power supply, the integrating capacitor and the protective resistor are connected with the cable/accessory in series in an insulating way; the sampling device is composed of an operational amplifier, an analog-to-digital converter and a processing chip/signal transmitter, and is connected with the integrating capacitor in parallel and used for representing the voltage at two ends of the capacitor.
3. The method for detecting the branch degradation of the cable insulation based on the leakage current and the integrated charge according to claim 1, wherein the cable is an alternating current cable or an accessory with a voltage class of 35kV or more or a direct current cable or an accessory with a voltage class of 100kV or more, the cable insulation material is crosslinked polyethylene, polypropylene or modified polymer insulation using the three materials as a matrix; the cable accessory insulating material is ethylene propylene rubber, silicon rubber or other solid polymer insulating materials.
4. The method for detecting the branch degradation of the cable insulation based on the leakage current and the integrated charge according to claim 1, wherein the voltage sampling time is 5-20 minutes, and the sampling rate of a voltmeter is not lower than 1 Hz.
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| CN112989596B (en) * | 2021-03-09 | 2022-03-01 | 天津大学 | Electric tree degradation analysis method under mechanical stress action based on driving energy |
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| CN114113790A (en) * | 2021-11-29 | 2022-03-01 | 云南电网有限责任公司电力科学研究院 | Multi-parameter cable insulation state diagnosis method and device based on electric charge quantity |
| CN114167755B (en) * | 2021-12-13 | 2023-06-30 | 华北电力大学（保定） | Method for establishing polymer electric branch development digital twin model |
| CN114217146A (en) * | 2021-12-14 | 2022-03-22 | 国网江苏省电力有限公司泰州供电分公司 | Direct-current integral charge measurement method for analyzing distribution network cable water branch degradation stage judgment |
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