CN105259486A - Aging site rapid diagnosis method for 10 kV XLPE cable based on polarization current measurement - Google Patents

Abstract

The invention discloses a 10kV based on polarization current measurement? XLPE cable aging field rapid diagnosis method, by improving the Harmon approximation algorithm when the relaxation current fitting parameter n is 0<n≤0.3 or 1.2≤n<2, expands the application range of the Harmon approximation algorithm, and can be based on The frequency range of the dielectric loss factor tanδ actually required on site greatly shortens the measurement time of the polarization current, and the dielectric loss factor tanδ at the corresponding frequency can be obtained quickly and intuitively through the improved Harmon approximation algorithm, so that according to the dielectric loss factor at the corresponding frequency The size of tanδ judges the cable aging condition. Therefore, the present invention provides a 10kV? The on-site rapid diagnosis method of XLPE cable aging can quickly diagnose the cable aging state on the spot, and has a wider application range. It can not only accurately reflect the aging state of the cable, but also meet the requirements of on-site measurement time.

Description

A Rapid Field Diagnosis Method for 10kV XLPE Cable Aging Based on Polarization Current Measurement

technical field

The invention relates to the field of aging assessment methods for insulating materials, and more particularly relates to a method for quickly evaluating the insulation of cross-linked polyethylene medium-voltage cables on site by using a polarization current method.

Background technique

Crosslinked Polyethylene (XLPE) cables are widely used in power transmission lines due to their excellent mechanical and electrical properties. The aging condition and remaining life of the cable insulation directly affect the stability of the power system, so the development of XLPE cable insulation diagnosis technology is of great significance for improving the stability of the power system.

At present, a lot of research has been done on cable insulation diagnosis methods at home and abroad. Among them, the PDC (Polarization and Depolarization Current, PDC) method is an effective test method for detecting the aging of electrical equipment. It has the advantages of simple measurement circuit, small power supply capacity, and non-destructive testing. And it can deeply reflect the aging information of the equipment from the level of aging mechanism.

However, the measurement time of the current PDC method is generally thousands of seconds, or even up to 10,000 seconds, which is not suitable for on-site diagnosis of cable status. The classical Harmon approximation algorithm is only applicable when the relaxation current fitting parameter n is 0.3<n<1.2, and the relaxation current fitting n value of the actual running cable may not be within this range, which has limitations.

Contents of the invention

Aiming at the above defects or improvement needs of the prior art, the present invention provides a rapid on-site diagnosis method for 10kVXLPE cable aging based on polarization current measurement. The measurement time is measured, and the polarization current is quickly and intuitively converted into the dielectric loss factor tanδ at the corresponding frequency through the improved Harmon approximation algorithm, so as to judge the insulation condition of the cable according to the dielectric loss factor tanδ at the required frequency. In the prior art, due to the long measurement time of the polarization current, the process of converting the polarization current into the dielectric loss factor tanδ at the corresponding frequency is complicated, which makes it difficult for the PDC method to quickly diagnose the cable on site.

The present invention provides a kind of 10kVXLPE cable aging field rapid diagnosis method based on polarization current measurement, comprising the following steps:

(1) Determine the polarization current measurement time according to the frequency range of the dielectric loss factor tanδ that is actually required on site, and measure the polarization current within the polarization current measurement time;

(2) Transform the polarization current into the dielectric loss factor tanδ at the corresponding frequency through the improved Harmon approximation algorithm;

(3) Judging the cable aging status according to the dielectric loss factor tanδ at the corresponding frequency.

The invention measures the polarization current in a short time, and according to the improved Harmon approximation theory, quickly converts the polarization current into the dielectric loss factor tanδ at the corresponding frequency. The on-site rapid diagnosis method for 10kVXLPE cable aging based on the polarization current measurement provided by the present invention has a wider application range, can greatly shorten the polarization current measurement time, and can quickly diagnose the cable on site. It can not only accurately reflect the aging state of the cable, but also meet the requirements of on-site measurement time.

Further, it is characterized in that, the method for determining the measurement time of the polarization current according to the frequency range of the dielectric loss factor tanδ that is actually needed in the step (1) is:

Assuming that the polarization current measurement time is T, and the sampling frequency of the current measurement module is f _sam , then theoretically the range of the frequency f of the dielectric loss factor tanδ can be obtained as:

Determine the polarization current measurement time T according to the frequency range of the dielectric loss factor tanδ that is actually required on site.

Further, it is characterized in that, the relation between the polarization current described in step (2) and the dielectric loss factor tanδ at the corresponding frequency is:

When 0.3<n<1.2, the corresponding relationship between the polarization current time point t and the frequency f of the dielectric loss factor tanδ is: t=0.1/f, and the relationship between the time-domain polarization current and the frequency-domain dielectric loss factor tanδ is: $ta\mathrm{no}\mathrm{\&delta;}\left(f\right)=\frac{i(0.1/f)}{2{\mathrm{\&pi;fC}}_{0}u};$

When 0<n≤0.3 or 1.2≤n<2, the corresponding relationship between the polarization current time point t and the frequency f of the dielectric loss factor tanδ is: t=A/2πf; the time-domain polarization current and the frequency-domain dielectric loss factor The relationship of tanδ is: $ta\mathrm{no}\mathrm{\&delta;}\left(f\right)=\frac{i(A/2\mathrm{\&pi;}f)}{2{\mathrm{\&pi;fC}}_{0}u};$

Among them, n is the relaxation current fitting parameter, f is the frequency of the dielectric loss factor tanδ, i(t) is the total current flowing through the cable, C ₀ is the bulk capacitance of the cable, U is the step wave voltage applied to the sample amplitude, $A={\&lsqb;\mathrm{\&Gamma;}(1-\mathrm{no})co\mathrm{the\; s}\frac{\mathrm{no}\mathrm{\&pi;}}{2}\&rsqb;}^{-\frac{1}{\mathrm{no}}}.$

In the present invention, the time-domain polarization current is converted into the dielectric loss factor tanδ at the corresponding frequency according to the improved Harmon approximation theory, and the polarization current can be quickly and intuitively converted into the dielectric loss factor tanδ at the corresponding frequency, and compared with The classic Harmon approximation algorithm has a wider range of application. The relaxation current is fitted by the empirical formula Φ(t)=βC ₀ t ^-n (C ₀ is the bulk capacitance of the dielectric, β and n are the fitting parameters), and according to the value of the fitting parameter n, the The polarization current of is converted into the dielectric loss factor tanδ at the corresponding frequency. According to the improved Harmon approximation algorithm, the polarization current at any time can be intuitively converted into the dielectric loss factor tanδ at the corresponding frequency.

Furthermore, in step (3), the relationship between the dielectric loss factor tanδ and the cable aging condition is: the larger the dielectric loss factor tanδ, the more serious the aging degree of the cable.

The invention can quickly diagnose the cable on the spot by shortening the measuring time of the polarization current, can accurately reflect the aging state of the cable, and can meet the requirement of the measuring time on the spot. According to the frequency range of the dielectric loss factor tanδ selected according to the actual site, the polarization current measurement time is shortened, and the polarization current is quickly converted into the dielectric loss factor tanδ at the corresponding frequency according to the improved Harmon approximation theory, and the XLPE cable is evaluated. insulation state. The measurement time of the polarization current is determined according to the frequency range of the dielectric loss factor tanδ that is actually required on site. If a higher frequency dielectric loss factor tanδ is selected to judge the cable condition, the measurement time can be shortened. Assuming that the polarization current measurement time is T, and the sampling frequency of the current measurement module is f _sam , then theoretically the range of the frequency f of the dielectric loss factor tanδ can be obtained as: Therefore, the shorter the measurement time, the smaller the frequency range of the dielectric loss factor tanδ that can be selected as the cable aging diagnosis criterion. The measurement time of the polarization current can be shortened according to the frequency range of the dielectric loss factor tanδ that is actually required on site.

At the same time, the invention is provided with a DC high-voltage power supply, a cable sample, a current measurement module and an anti-leakage ring. The high-voltage output end of the DC high-voltage power supply is connected to the conductor core of the cable sample to generate a polarization current. The anti-leakage rings at both ends are connected to each other so that the leakage current along the surface flows directly back to the power supply side without passing through the current measurement module, so as to avoid the influence of the leakage current along the surface on the measurement of the polarization current. The current measurement module measures the polarization current.

Therefore, the 10kVXLPE cable aging field rapid diagnosis method based on polarization current measurement provided by the present invention, by improving the Harmon approximation algorithm when the relaxation current fitting parameter n is located at 0<n≤0.3 or 1.2≤n<2, expands The application range of the Harmon approximation algorithm is widened, and the polarization current measurement time can be greatly shortened according to the frequency range of the dielectric loss factor tanδ that is actually required on site, and the medium at the corresponding frequency can be obtained quickly and intuitively through the improved Harmon approximation algorithm The loss factor tanδ, so as to judge the aging status of the cable according to the dielectric loss factor tanδ at the corresponding frequency. Therefore the present invention provides, a kind of 10kVXLPE cable aging on-the-spot rapid diagnosis method based on polarization current measurement can carry out rapid diagnosis to the cable aging state on the spot, and the scope of application is wider, can accurately reflect the aging state of the cable, can meet again On-site measurement time requirements.

Description of drawings

Fig. 1 is the schematic diagram of the polarization current measurement of the XLPE cable that the embodiment of the present invention provides;

Fig. 2 is the implementation flowchart of the 10kVXLPE cable aging site rapid diagnosis method based on the polarization current measurement provided by the embodiment of the present invention;

Fig. 3 is the polarization current diagram of cables with different aging degrees provided by the embodiment of the present invention;

Fig. 4 is the dielectric loss factor tanδ spectrum of cross-linked polyethylene cable samples with different aging degrees provided by the embodiment of the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

The present invention provides a rapid on-site diagnosis method for 10kVXLPE cable aging based on polarization current measurement, based on the classic Harmon approximation, for the Harmon approximation when the fitting parameter n is 0<n≤0.3 or 1.2≤n<2 The algorithm has been improved, and the applicable range of Harmon's approximation algorithm has been expanded. On this basis, the polarization current measurement time can be shortened according to the frequency range of the dielectric loss factor tanδ that is actually required on site, the polarization current can be measured, and the polarization current can be directly converted into the medium at the corresponding frequency through the improved Harmon approximation algorithm Loss factor tanδ, to judge the cable aging condition.

Therefore, a kind of 10kVXLPE cable aging field rapid diagnosis method based on polarization current measurement provided by the present invention improves the Harmon approximation algorithm when the relaxation current fitting parameter n is located at 0<n≤0.3 or 1.2≤n<2, The application range of the Harmon approximation algorithm is expanded, and the polarization current measurement time can be greatly shortened according to the frequency range of the dielectric loss factor tanδ that is actually required on site, and the corresponding frequency can be obtained quickly and intuitively through the improved Harmon approximation algorithm. The dielectric loss factor tanδ, so as to judge the aging status of the cable according to the size of the dielectric loss factor tanδ at the corresponding frequency.

Therefore, a kind of 10kVXLPE cable aging on-site rapid diagnosis method based on polarization current measurement provided by the present invention can quickly diagnose the cable aging state on the spot, and has a wider application range, which can not only accurately reflect the aging state of the cable, but also satisfy the on-site Measurement time requirements.

According to the classical Harmon approximation theory, the relaxation current is fitted through the empirical formula Φ(t)=βC ₀ t ^-n (C ₀ is the bulk capacitance of the dielectric, β and n are the fitting parameters), according to the fitting parameter n The value of can convert the polarization current at any moment into tanδ at the corresponding frequency. Among them, when 0.3<n<1.2, the polarization current moment t has the following relationship with the angular frequency ω:

$\mathrm{<span\; class="notranslate">\; \&omega;</span>}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; \&Gamma;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\frac{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&rsqb;</span>}^{<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; \&ap;</span>\mathrm{<span\; class="notranslate">\; 0.63</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Then the corresponding relationship between the polarization current time point t and the frequency f of the dielectric loss factor tanδ is:

$\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; \&ap;</span>\frac{\mathrm{<span\; class="notranslate">\; 0.63</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 0.1</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

The relationship between the polarization current in the time domain and the dielectric loss factor tanδ in the frequency domain is:

$\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0.1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&pi;fC</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

The classic Harmon approximation algorithm is only applicable when the relaxation current fitting parameter n is 0.3<n<1.2, but the relaxation current fitting n value of the actual running cable may not be within this range, which has obvious limitations. Based on the classical Harmon approximation, the invention improves the Harmon approximation algorithm when the relaxation current fitting parameters are 0<n≤0.3 or 1.2≤n<2. That is, when 0<n≤0.3 or 1.2≤n<2, if A is still taken as 0.63, it will cause a large error. At this time, the actual value of A can be taken to calculate the dielectric loss factor tanδ, then the corresponding relationship between the polarization current time point t and the frequency f of the dielectric loss factor tanδ is:

t=A/2πf(9) The relationship between time-domain polarization current and frequency-domain dielectric loss factor tanδ is:

$\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&pi;fC</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

Therefore, according to the improved Harmon approximation algorithm, the polarization current at any time can be intuitively converted into tanδ at the corresponding frequency.

The measurement time of the polarization current is determined according to the frequency range of the dielectric loss factor tanδ that is actually required on site. If the higher frequency dielectric loss factor tanδ is selected to judge the cable condition, the measurement time can be greatly shortened. Assuming that the polarization current measurement time is T, and the sampling frequency of the current measurement module is f _sam , then the range of the frequency f of the dielectric loss factor tanδ that can be theoretically obtained is:

The shorter the measurement time, the smaller the frequency range of the dielectric loss factor tanδ that can be selected as the cable aging diagnosis criterion. Therefore, the polarization current measurement time can be shortened according to the frequency range of the dielectric loss factor tanδ that is actually required on site.

Use the polarization current measurement principle circuit shown in Figure 1 to measure the cable polarization current. The high-voltage output end of the DC high-voltage power supply is connected to the conductor core of the cable sample to generate a polarization current. The anti-leakage rings at both ends are connected to each other so that the leakage current along the surface flows directly back to the power supply side without passing through the current measurement module, so as to avoid the influence of the leakage current along the surface on the polarization current measurement. The current measurement module measures the polarization current.

Therefore, a kind of 10kVXLPE cable aging field rapid diagnosis method based on polarization current measurement provided by the present invention improves the Harmon approximation algorithm when the relaxation current fitting parameter n is located at 0<n≤0.3 or 1.2≤n<2, The application range of the Harmon approximation algorithm is expanded, and the polarization current measurement time can be greatly shortened according to the frequency range of the dielectric loss factor tanδ that is actually required on site, and the corresponding frequency can be obtained quickly and intuitively through the improved Harmon approximation algorithm. The dielectric loss factor tanδ, so as to judge the aging status of the cable according to the size of the dielectric loss factor tanδ at the corresponding frequency. Therefore, a kind of 10kVXLPE cable aging on-site rapid diagnosis method based on polarization current measurement provided by the present invention can quickly diagnose the cable aging state on the spot, and has a wider application range, which can not only accurately reflect the aging state of the cable, but also satisfy the on-site Measurement time requirements.

The on-site rapid diagnosis method for 10kVXLPE cable aging based on polarization current measurement provided by the present invention, the implementation steps include: determining the polarization current measurement time according to the frequency range of the dielectric loss factor tanδ actually required on site, measuring the polarization current, and using the improved Ha The Mongolian approximation algorithm converts the polarization current into the dielectric loss factor tanδ at the corresponding frequency, and judges the aging status of the cable according to the dielectric loss factor tanδ at the corresponding frequency. This method can quickly diagnose the cable on site, which can not only accurately reflect the aging state of the cable, but also meet the requirements of on-site measurement time.

Assuming that the polarization current measurement time is T, and the sampling frequency of the current measurement module is f _sam , then the range of the frequency f of the dielectric loss factor tanδ that can be theoretically obtained is:

Therefore, the shorter the measurement time, the smaller the frequency range of the dielectric loss factor tanδ that can be selected as the cable aging diagnosis criterion. The measurement time of the polarization current can be shortened according to the frequency range of the dielectric loss factor tanδ that is actually required on site.

In an embodiment of the present invention, Fig. 1 shows a schematic diagram of measuring polarization currents on different aged cable samples; the high voltage output end of the DC high voltage power supply is connected to the conductor core of the cable samples to generate a polarization current. The anti-leakage rings at both ends are connected to each other so that the leakage current along the surface flows directly back to the power supply side without passing through the current measurement module, so as to avoid the influence of the leakage current along the surface on the polarization current measurement. The current measurement module measures the polarization current.

In the embodiment of the present invention, Fig. 2 shows a flow chart of the implementation of the on-site rapid diagnosis method for 10kVXLPE cable aging based on polarization current measurement provided by the present invention.

In the embodiment of the present invention, FIG. 3 shows a schematic diagram of polarization currents of cables with different aging degrees; the actual aging degree of cables: P1<P2. It can be seen from Figure 3 that with the increase of the cable aging degree, the polarization current increases obviously, and the curve shifts upward as a whole with the increase of the aging degree.

In the embodiment of the present invention, Fig. 4 shows frequency domain loss factor spectra of cable samples with different aging degrees. The relaxation current of the cable is separated from the polarization current in Figure 3, and fitted by the empirical formula Φ(t)=βC ₀ t ^-n (C ₀ is the bulk capacitance of the dielectric, β and n are the fitting parameters), according to The value of the fitting parameter n can convert the polarization current at any moment into tanδ at the corresponding frequency.

Among them, when 0.3<n<1.2, the corresponding relationship between the polarization current time point t and the frequency f of the dielectric loss factor tanδ is: t=0.1/f, and the relationship between the time-domain polarization current and the frequency-domain dielectric loss factor tanδ is : When 0<n≤0.3 or 1.2≤n<2, the corresponding relationship between the polarization current time point t and the frequency f of the dielectric loss factor tanδ is: t=A/2πf, the time-domain polarization current and the frequency-domain dielectric loss factor The relationship of tanδ is: Therefore, according to the improved Harmon approximation algorithm, the polarization current at any time can be intuitively converted into the dielectric loss factor tanδ at the corresponding frequency, so that the aging status of the cable can be judged according to the dielectric loss factor tanδ at the corresponding frequency. It can be seen from Figure 4 that with the increase of cable aging, the overall curve of the loss factor spectrum increases significantly, so the loss factor spectrum obtained by the improved Harmon approximation algorithm can be used to characterize the aging degree of XLPE cables.

A 10kVXLPE cable aging field rapid diagnosis method based on polarization current measurement provided by the example of the present invention improves the Harmon approximation algorithm when the relaxation current fitting parameter n is located at 0<n≤0.3 or 1.2≤n<2, and expands The application range of the Harmon approximation algorithm is widened, and the polarization current measurement time can be greatly shortened according to the frequency range of the dielectric loss factor tanδ that is actually required on site, and the medium at the corresponding frequency can be obtained quickly and intuitively through the improved Harmon approximation algorithm The loss factor tanδ, so as to judge the aging status of the cable according to the dielectric loss factor tanδ at the corresponding frequency. Therefore, a kind of 10kVXLPE cable aging on-site rapid diagnosis method based on polarization current measurement provided by the present invention can quickly diagnose the cable aging state on the spot, and has a wider application range, which can not only accurately reflect the aging state of the cable, but also satisfy the on-site Measurement time requirements.

Those skilled in the art can easily understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (4)

1. a kind of 10kVXLPE cable aging field rapid diagnosis method based on polarization current measurement, is characterized in that, comprises the following steps: (1) Determine the polarization current measurement time according to the frequency range of the dielectric loss factor tanδ that is actually required on site, and measure the polarization current within the polarization current measurement time; (2) Transform the polarization current into the dielectric loss factor tanδ at the corresponding frequency through the improved Harmon approximation algorithm; (3) Judging the cable aging status according to the dielectric loss factor tanδ at the corresponding frequency. 2. cable aging field rapid diagnosis method as claimed in claim 1, is characterized in that, the relation between the polarization current described in the step (2) and the dielectric loss factor tan δ under the corresponding frequency is: When 0.3<n<1.2, the corresponding relationship between the polarization current time point t and the frequency f of the dielectric loss factor tanδ is: t=0.1/f, and the relationship between the time-domain polarization current and the frequency-domain dielectric loss factor tanδ is: $ta\mathrm{no}\mathrm{\&delta;}\left(f\right)=\frac{i(0.1/f)}{2{\mathrm{\&pi;fC}}_{0}u};$ When 0<n≤0.3 or 1.2≤n<2, the corresponding relationship between the polarization current time point t and the frequency f of the dielectric loss factor tanδ is: t=A/2πf; the time-domain polarization current and the frequency-domain dielectric loss factor The relationship of tanδ is: $ta\mathrm{no}\mathrm{\&delta;}\left(f\right)=\frac{i(A/2\mathrm{\&pi;}f)}{2{\mathrm{\&pi;fC}}_{0}u};$ Among them, n is the relaxation current fitting parameter, f is the frequency of the dielectric loss factor tanδ, i(t) is the total current flowing through the cable, C ₀ is the bulk capacitance of the cable, U is the step wave voltage applied to the sample amplitude, $A={\&lsqb;\mathrm{\&Gamma;}(1-\mathrm{no})co\mathrm{the\; s}\frac{\mathrm{no}\mathrm{\&pi;}}{2}\&rsqb;}^{-\frac{1}{\mathrm{no}}}.$ 3. cable aging rapid diagnosis method as claimed in claim 1, is characterized in that, in step (1), the method for determining the polarization current measurement time according to the frequency range of the dielectric loss factor tan δ of on-site actual needs is: Assuming that the polarization current measurement time is T, and the sampling frequency of the current measurement module is f _sam , then theoretically the range of the frequency f of the dielectric loss factor tanδ can be obtained as: $\frac{0.1}{T}<f<\frac{f_{\mathrm{the\; s}am}}{2},$ (0.3<n<1.2) $\frac{A}{2\mathrm{\&pi;}T}<f<\frac{f_{\mathrm{the\; s}am}}{2},$ (0<n≤0.3 or 1.2≤n<2) Determine the polarization current measurement time T according to the frequency range of the dielectric loss factor tanδ that is actually required on site. 4. as claimed in claim 1 or 2, the on-the-spot rapid diagnosis method of cable aging is characterized in that, in step (3), the relation between the size of dielectric loss factor tan δ and the cable aging condition is: said dielectric loss factor tan δ The bigger it is, the more serious the aging degree of the cable is.