Direct current integral charge measuring device and method for high-voltage cable
Technical Field
The invention belongs to the technical field of electrical equipment insulation, and particularly relates to a direct-current integral charge measuring device and method for a high-voltage cable.
Background
The insulating material is affected by multiple stress effects such as electricity, heat, mechanical force and the like in the operation process to age, so that the insulating property is reduced, and finally breakdown occurs. The aging of insulation is inevitable, and the realization of rapid and nondestructive detection of the aging state of insulation still faces huge challenges, so that the problem of solving the aging state is an urgent need for the development of the future industry.
At present, the service life of the cable made of the insulating material is mostly based on qualitative analysis, and the service life of the cable cannot be effectively and quantitatively analyzed.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a direct current integral charge measuring device and method for a high-voltage cable.
The technical problem to be solved by the invention is realized by the following technical scheme:
a dc integrated charge measurement device for a high voltage cable, characterized by: including cable core, cable shielding layer, constant voltage power supply, skin ampere meter protection module and digital skin ampere meter, the cable core outside is provided with the cable shielding layer, constant voltage power supply is connected to cable core, the cable shielding layer is connected to through skin ampere meter protection module digital skin ampere meter, constant voltage power supply, skin ampere meter protection module and digital skin ampere meter all are connected to ground electrode, be provided with the needle electrode on the cable core.
Moreover, the output voltage of the direct current stabilized power supply is constant to 1kV, and the stability of insulation leakage current in the cable is ensured.
And the picoampere meter protection module is composed of a current-limiting resistor and a bidirectional transient diode, the cable shielding layer is connected to the digital picoampere meter through the current-limiting resistor, and the bidirectional transient diode and the digital picoampere meter are connected in parallel to protect the normal operation of the system.
Furthermore, the model number of the digital pico-meter is B2983A, the minimum measuring range is 2pA, and the maximum reading speed is 20000 readings/second.
A direct current integral charge measurement method for a high-voltage cable is characterized by comprising the following steps: the method comprises the following steps:
1) turning on a power switch of the digital pico-meter, adjusting the pico-meter to a charge measurement file, setting the digital pico-meter to be in an automatic trigger mode, and turning on a measurement switch of the digital pico-meter;
2) turning on a switch of the direct current stabilized power supply, and rotating a voltage regulating knob of the direct current stabilized power supply;
3) keeping the voltage stable, and measuring the integral charge of the cable shielding layer for 10 min;
4) and closing a measuring switch of the digital pico-meter, reading the measurement data of the pico-meter, processing the measurement data and evaluating the insulation state of the cable.
In step 2), the knob needs to be turned rapidly to ensure that the boosting time does not exceed 5s,
an insulation state evaluation method for direct current integrated charge of a high-voltage cable is characterized by comprising the following steps of:
1) taking a plurality of sections of direct current cables, respectively inserting different numbers of pin electrodes into the same cross section at equal intervals, ensuring that the distance between the pin tips of the pin electrodes and the core of the cable is 2mm, and commonly grounding all the pin electrodes;
2) applying the same level voltage to each group of cable cores, taking different time nodes to measure direct current integral charges, and recording experimental data;
3) and calculating the slope of a fitting curve by using the least square method according to the integrated charge-time scatter data of each group of cables, wherein the slope is used as an index for evaluating the insulation state of the cables.
Furthermore, in step 1), the number of the inserted needle electrodes is adjusted to simulate the size of the electric tree branch growing region. The equal interval insertion of the same section of the needle electrode is ensured to ensure that the field intensity of the needle point of the needle electrode is equal, and the curvature radius of the needle point is 3.5 mu m +/-0.3 mu m.
And in the step 2), the voltage applied to the wire core is 8kV, the set voltage is larger than the tree starting voltage of the pin-cable wire core electrode, the time node is set to be 30min, 1h and 2h, and different stages of the growth of the electric tree are simulated.
And in the step 3), the data processing software is Labview, the slope of the fitting curve corresponds to the insulation leakage current in the cable, and the increase of the slope of the direct current integral charge curve indicates the degradation of the insulation state of the cable.
The invention has the advantages and beneficial effects that:
1. the invention provides an experimental device for measuring the integral charge of a cable, which can be used for measuring the integral charge variation of a high-voltage cable within 10min, and a power supply is determined to be a 1kV high-voltage stabilized power supply. The test voltage is stable, the test result is less affected by the power supply, and the feasibility of the test method is ensured.
2. The high-voltage cable direct-current integral charge measuring method provided by the invention has the advantages that the device is simple in structure and easy to operate, after the test is finished, the data of the digital pico-ampere meter can be timely transmitted to a computer, the data processing and display functions of the computer are strong, and the slope of curves in different time periods can be quickly obtained by matching Labview software with a front panel which is easy to operate. The insulation performance of the cables with different aging degrees can be accurately evaluated.
3. Compared with the prior art, the device has the advantages of simple structure, low cost, stable test result and short measurement time, can quickly measure the direct-current integral charge quantity of the cable, and improves the research approach for quickly evaluating the insulation condition of the cable, thereby having important significance for verifying and perfecting the theoretical research of aging mechanisms of high-voltage cable branches and the like.
Drawings
FIG. 1 is a schematic diagram of a DC integrated charge measurement device according to the present invention;
fig. 2 is a dc integrated charge plot of a cable sample at various time nodes according to the present invention.
Description of the reference numerals
1-needle electrode; 2-a current limiting resistor; 3-Pian watch protection module; 4-bidirectional transient diodes; 5-digital pico ampere meter; 6-cable shielding layer; 7-a cable core; 8-a direct current stabilized power supply; 9-ground electrode.
Detailed Description
The present invention is further illustrated by the following specific examples, which are intended to be illustrative, not limiting and are not intended to limit the scope of the invention.
A direct current integral charge measuring device for a high-voltage cable is characterized in that: including cable core 7, cable shielding layer 6, direct current constant voltage power supply 8, skin ampere meter protection module 3 and digital skin ampere meter 5, the cable core outside is provided with the cable shielding layer, direct current constant voltage power supply is connected to cable core, the cable shielding layer is connected to through skin ampere meter protection module digital skin ampere meter, direct current constant voltage power supply, skin ampere meter protection module and digital skin ampere meter all are connected to ground electrode 9, be provided with the needle electrode on the cable core.
The output voltage of the direct current stabilized power supply is constant to be 1kV, and the stability of insulation leakage current in the cable is ensured.
And the picoampere meter protection module is composed of a current-limiting resistor 2 and a bidirectional transient diode 4, a cable shielding layer is connected to the digital picoampere meter through the current-limiting resistor, and the bidirectional transient diode and the digital picoampere meter are connected in parallel to protect the normal operation of a system.
The digital piranha meter is model B2983A, the minimum range is 2pA, and the maximum reading rate is 20000 readings/second.
The integrated charge is measured by a digital picoampere meter, while the resistor and the bi-directional transient diode mainly play a role in protecting the picoampere meter.
A direct current integral charge measurement method for a high-voltage cable comprises the following steps:
1) turning on a power switch of the digital pico-meter, adjusting the pico-meter to a charge measurement file, setting the pico-meter to be in an automatic trigger mode, and turning on a measurement switch of the pico-meter;
2) starting a switch of the DC stabilized power supply, rapidly rotating a voltage regulating knob of the DC stabilized power supply, and ensuring that the boosting time does not exceed 5s
3) Keeping the voltage stable, and measuring the integral charge of the cable shielding layer for 10 min;
4) and closing a measurement switch of the pico-ampere meter, reading the measurement data of the pico-ampere meter, processing the measurement data, and evaluating the insulation state of the cable.
Through the device structure shown in fig. 1, the specific steps of the test according to the method for measuring the direct-current integrated charge of the high-voltage cable of the invention are as follows:
the prepared aging cable sample is inserted into the pin electrodes 1 with different numbers at equal intervals on the same section, the distance between the pin tips of the pin electrodes and the core of the cable is 2mm, and all the pin electrodes are grounded together. The equal interval insertion of the same section of the needle electrode is ensured to ensure that the field intensities of the needle points of the needle electrode are equal. The radius of curvature of the needle tip is 3.5 μm + -0.3 μm.
And applying 8kV voltage to each group of cable cores, taking time nodes for 30min, 1h and 2h to perform direct-current integral charge measurement, and recording experimental data.
And calculating the slope of a fitting curve by using Labview software and the integrated charge-time scatter data of each group of cables by using a least square method, wherein the slope is used as an index for cable insulation state evaluation.
The measurement results shown in fig. 2 illustrate that as the aging time increases, the slope of the dc integrated charge curve also increases, and the present invention can achieve the effect of cable aging evaluation.
The invention provides a direct current integral charge experimental device and a measurement method for a high-voltage cable, aiming at solving the problems that other insulation evaluation methods introduce new defects into a system and the evaluation precision is insufficient. Related research has indicated that electrical dendrites are induced in cables by local electric field concentrations due to defects within the insulation or improper design of the insulation structure. For cable insulation evaluation, an ultralow frequency dielectric loss measurement method and a partial discharge online monitoring method are available. However, the voltage applied to the former is high, and there is a certain probability that new damage is generated to the cable insulation. The latter is susceptible to interference from the surrounding environment and the test accuracy is insufficient. The direct current integral charge experimental device and the direct current integral charge measurement method for the high-voltage cable can be used for carrying out nondestructive measurement on the defects of the cable, obtaining the insulation state of the cable insulation in real time, laying a foundation for verifying and perfecting a cable electrical tree growth theoretical model, and having important significance for preventing and treating the insulation breakdown disasters of the power grid cable.
Although the embodiments of the present invention and the accompanying drawings are disclosed for illustrative purposes, those skilled in the art will appreciate that: various substitutions, changes and modifications are possible without departing from the spirit and scope of the invention and the appended claims, and therefore the scope of the invention is not limited to the disclosure of the embodiments and the accompanying drawings.