CN114910703A - Dielectric spectrum-based monitoring method for precooling process of superconducting cable - Google Patents
Dielectric spectrum-based monitoring method for precooling process of superconducting cable Download PDFInfo
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Abstract
The invention relates to a monitoring method for a precooling process of a superconducting cable based on a dielectric spectrum, which comprises the following steps: before cooling, the superconducting cable is vacuumized and purged; the superconducting cable is cooled by injecting low-temperature nitrogen and low-temperature liquid nitrogen in sequence and starting a refrigerating machine, and the precooling speed is controlled; performing a dielectric spectrum test on the superconducting cable in the blowing and cooling processes to obtain dielectric loss of the superconducting cable insulation medium under different frequency excitation voltages in the blowing stage and the cooling stage; and analyzing to obtain the internal state change information in the precooling process of the superconducting cable according to dielectric loss of the superconducting cable insulating medium under different frequency excitation voltages in the purging stage and the cooling stage. Compared with the prior art, the method can comprehensively and truly reflect the internal state change of the superconducting cable in the precooling process, ensure that the superconducting cable can realize stable temperature transition in the precooling process, effectively prevent the cable from being damaged due to severe temperature change and ensure that the precooling can be completely finished.
Description
Technical Field
The invention relates to the technical field of superconducting cable detection, in particular to a monitoring method for a superconducting cable precooling process based on a dielectric spectrum.
Background
The High-Temperature Superconducting (HTS) cable is a power facility which adopts an unobstructed Superconducting material capable of transmitting High current density as a conductor and can transmit large current, has the advantages of compact structure, low loss and large transmission capacity, and can realize low-loss and large-capacity power transmission. At present, the related experiments and operation experiences of the high-temperature superconducting cable at home and abroad are very few, and the whole technology is in the stage of network hanging demonstration and a small amount of commercial application in the global range.
The superconducting cable system consists of four main parts, namely a cable body, cable accessories, a refrigeration system and a detection protection system, and the high-temperature superconducting cable generally uses liquid nitrogen (77K, namely-196 ℃) as a cooling medium and an insulating medium. Inside the high temperature superconducting cable, on the flexible cable frame, there are no-gap spirally wound multiple layers of high temperature superconducting tapes to form the superconducting conductor layer, which is the conducting part for transmitting current; an insulating layer and a shielding layer are wound outside the superconductor; in order to keep the liquid nitrogen in the cable at the critical temperature of the superconductor (77K), it is necessary to have a thermal insulation tube with excellent thermal insulation properties. Therefore, the high temperature superconducting cable is generally composed of a superconductor layer, an insulating layer, a shield layer, a heat insulating pipe, and the like, the insulating layer being formed by winding a 7mm polypropylene laminated paper (PPLP) around the outside of the superconductor. The PPLP is formed by pressing a porous pulp material and a polypropylene (PP) film, has good impregnation performance, and can effectively prevent air gaps from being generated so as to reduce the occurrence of partial discharge; and the PP film has higher electrical strength and good mechanical property at low temperature.
The process from the normal temperature state to the superconducting state (liquid nitrogen temperature) of the superconducting cable system is called system precooling, and precooling is a process which must be carried out before the cable is put into operation, and is used for removing impurities in the system on one hand and testing the sealing performance of the system on the other hand. In the precooling process of the superconducting cable, the corresponding part of the cable is contracted due to temperature change, wherein the deformation of the cable core is maximum, the expansion rate can reach 0.3 percent, and mechanical stress is easily generated on the local part of the cable. At present, when cables are laid, certain offset (telescopic arc) needs to be preset according to different positions of conductors and insulating materials, the longitudinal offset and the transverse offset of the cables need to be measured in a precooling process, and the offset (telescopic arc) of the cables is adjusted manually so as to avoid the generation of larger mechanical stress, so that the damage of thermal stress and mechanical stress of components caused by severe temperature change is prevented.
After the pre-cooling is finished, performing a handover test on the superconducting cable according to related technical standards, wherein the handover test comprises a high voltage test and a high current test; after the test is qualified, the cable can be put into operation. That is to say, when precooling is finished, the cable conductor and the insulation should be in a stable and uniform low-temperature environment, and the whole superconducting cable refrigerating system reaches the standby state of a power grid, so that liquid nitrogen in the whole refrigerating circulation pipeline is ensured not to generate phase change. If the liquid nitrogen is solidified, the circulation of the system is blocked, and efficient heat exchange cannot be carried out; if the liquid nitrogen is vaporized, a two-phase flow will be produced in the circulation system, as shown in FIG. 1. The resulting effects are: (1) the flow resistance increases; (2) the heat exchange efficiency is reduced (the convection heat exchange coefficient of liquid nitrogen is far larger than that of nitrogen); (3) the dielectric strength decreases (the nitrogen dielectric strength is 1/2 for liquid nitrogen); (4) the two-phase flow will generate elastic vibration in the pipe and will damage the mechanical properties of the pipe in long-term operation.
With the increase of the length of the superconducting cable, the precooling time is correspondingly increased, the construction period of a project is necessarily influenced by the overlong precooling time, the safe operation of the cable is endangered by the insufficient precooling and the existence of gas-phase nitrogen in the cable, and the cable is damaged by the untimely release of stress caused by the too fast precooling. Therefore, besides the non-electric quantity (temperature, pressure, flow, liquid level, telescopic displacement and the like) monitoring, the electric quantity of the superconducting cable in the precooling process is necessarily monitored so as to comprehensively and truly reflect the internal state change of the superconducting cable in the precooling process, thereby ensuring that the superconducting cable can realize stable transition of temperature in the precooling process and avoiding cable damage; the precooling can be completely completed, so that the superconducting cable can be safely put into operation.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a method for monitoring the precooling process of a superconducting cable based on a dielectric spectrum, which can comprehensively and truly reflect the internal state change of the superconducting cable in precooling by developing a dielectric spectrum test, ensure that the superconducting cable can realize stable temperature transition in the precooling process and ensure that the precooling can be completely finished.
The purpose of the invention can be realized by the following technical scheme: a superconducting cable precooling process monitoring method based on a dielectric spectrum comprises the following steps:
s1, before cooling, vacuumizing and purging the superconducting cable;
in the process, dielectric spectrum test is carried out on the superconducting cable to obtain dielectric loss of the superconducting cable insulating medium under different frequency excitation voltages in the purging stage;
s2, cooling the superconducting cable by sequentially injecting low-temperature nitrogen and low-temperature liquid nitrogen and starting a refrigerator, and simultaneously controlling the precooling speed;
in the process, dielectric spectrum test is carried out on the superconducting cable to obtain dielectric loss of the superconducting cable insulating medium under different frequency excitation voltages in the cooling stage;
and S3, analyzing and obtaining the internal state change information in the precooling process of the superconducting cable according to dielectric loss of the superconducting cable insulating medium under different frequency excitation voltages in the purging stage and the cooling stage.
Further, the specific process of performing the vacuum-pumping and purging process on the superconducting cable in the step S1 is as follows:
s11, carrying out vacuum-pumping replacement on the superconducting cable;
and S12, blowing the cable system by using dry nitrogen with the temperature difference between the dry nitrogen and the room temperature being less than or equal to the set temperature difference threshold value so as to blow impurities.
Further, the specific process of cooling the superconducting cable in step S2 is as follows:
s21, injecting low-temperature nitrogen for slow cooling;
s22, when the temperature of the system is smaller than or equal to the set first temperature threshold value, injecting low-temperature liquid nitrogen for cooling;
and S23, when the temperature of the system is less than or equal to the set second temperature threshold, starting the refrigerating machine to continue supercooling the circulating liquid nitrogen until the temperature of the system is less than or equal to the set third temperature threshold, and keeping the supercooling circulation of the liquid nitrogen for the set cooling time.
Further, the third temperature threshold is less than a second temperature threshold, which is less than the first temperature threshold.
Further, in the step S2, the pre-cooling speed is controlled to decrease the system temperature from the ambient temperature in sequence by a set gradient, and each gradient temperature is maintained for several tens to several hundreds of hours, so that the temperature of the head end and the tail end of the superconducting cable is balanced and can reach the set value of the temperature.
Further, the steps S1 and S2 are to perform the dielectric spectrum test on the superconducting cable at different frequencies for a plurality of times in the purging stage and the cooling stage respectively according to the set monitoring time interval.
Further, the steps S1 and S2 are specifically to perform a dielectric spectrum test on the superconducting cable by using a dielectric spectrum tester, and the frequency of the dielectric spectrum test is 0.1Hz to 1000 Hz.
Further, the dielectric spectrum tester is specifically an IDAX series automatic dielectric loss frequency characteristic tester.
Further, the specific process of performing the dielectric spectrum test on the superconducting cable in the steps S1 and S2 is as follows:
directly grounding a grounding wire and a low-voltage lead of the dielectric spectrum tester, connecting a high-voltage lead of the dielectric spectrum tester to an inner lead of one phase of the superconducting cable, and keeping the other two phases of the superconducting cable grounded;
setting the frequency of the dielectric spectrum tester to the required frequency, and carrying out dielectric spectrum test on one phase of the superconducting cable according to the set test voltage;
and according to the steps, sequentially carrying out medium spectrum test on the other two phases of the superconducting cable to finally obtain dielectric loss values of the superconducting cable insulation medium under different frequencies.
Further, the set effective value of the test voltage is less than 200V.
Further, the step S3 specifically includes the following steps:
s31, performing curve fitting on the dielectric loss values corresponding to different frequencies to obtain a dielectric loss-frequency curve;
and S32, analyzing according to the dielectric loss-frequency curve to obtain the internal state change result in the process of precooling the superconducting cable.
Further, the step S32 is to analyze and obtain the change result of moisture, phase state and temperature inside the superconducting cable, where the phase state includes a gas state and a liquid state.
Compared with the prior art, the invention provides a monitoring method based on the dielectric spectrum aiming at the precooling process of the superconducting cable, and the method can obtain richer monitoring information by carrying out data detection and analysis on dielectric loss of the superconducting cable under different frequencies, can comprehensively and reliably determine the internal state change of the superconducting cable in the precooling process, is favorable for ensuring the stable transition of the temperature of the superconducting cable in the precooling process, and effectively prevents the thermal stress and the mechanical stress damage of parts caused by severe temperature change;
according to the invention, the moisture, the phase state and the temperature in the superconducting cable are analyzed according to the dielectric loss-frequency change curve, so that the progress condition of the superconducting cable during precooling can be comprehensively and really reflected, the abnormality generated in the precooling process can be found in time, the precooling can be completely finished, and meanwhile, the optimal precooling speed can be determined in the follow-up process.
The invention is tested based on the dielectric spectrum, the effective voltage value is less than 200V during testing, and the invention is safer and more convenient during practical application.
Drawings
FIG. 1 is a schematic view of a two-phase flow in a superconducting cable circulation system;
FIG. 2 is a schematic flow diagram of the process of the present invention;
FIG. 3 is a diagram illustrating the effect of controlling the pre-cooling rate;
FIG. 4 is a schematic diagram of the connection of the superconducting cable for the dielectric spectrum test in the embodiment;
FIG. 5 is a schematic temperature curve of a pre-cooling process in an embodiment;
FIG. 6 is a dielectric spectrum curve of the superconducting cable at low temperature and normal temperature in the example;
FIG. 7 is a comparison graph of the medium spectrum curves corresponding to the pre-cooling period of 220Hz and 1Hz in the example;
FIG. 8 is a comparison graph of the medium spectrum curves corresponding to 0.1Hz and 1Hz in the late stage of precooling in the example.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Examples
As shown in fig. 2, a method for monitoring a pre-cooling process of a superconducting cable based on a dielectric spectrum includes the following steps:
s1, before cooling, vacuumizing and blowing the superconducting cable;
in the process, dielectric spectrum test is carried out on the superconducting cable to obtain dielectric loss of the superconducting cable insulating medium under different frequency excitation voltages in the purging stage;
wherein, the specific processes of vacuumizing and purging treatment are as follows:
s11, carrying out vacuum-pumping replacement on the superconducting cable;
s12, purging the cable system by using dry nitrogen with the temperature difference between the dry nitrogen and the room temperature being less than or equal to a set temperature difference threshold value to purge impurities;
s2, cooling the superconducting cable by sequentially injecting low-temperature nitrogen and low-temperature liquid nitrogen and starting a refrigerator, and simultaneously controlling the precooling speed;
in the process, dielectric spectrum test is carried out on the superconducting cable to obtain dielectric loss of the superconducting cable insulating medium under different frequency excitation voltages in the cooling stage;
wherein, the specific process of the cooling treatment comprises the following steps:
firstly, injecting low-temperature nitrogen for slow cooling;
when the temperature of the system is less than or equal to a set first temperature threshold, injecting low-temperature liquid nitrogen for cooling;
when the temperature of the system is less than or equal to the set second temperature threshold, starting the refrigerating machine to continuously supercool the circulating liquid nitrogen until the temperature of the system is less than or equal to the set third temperature threshold, and keeping the supercooled circulation by the liquid nitrogen for the set cooling time;
the set third temperature threshold is smaller than the second temperature threshold, and the second temperature threshold is smaller than the first temperature threshold;
in addition, in order to avoid the performance damage of the superconducting cable joint and the superconducting strip caused by the stress generated by the excessively fast cooling of the superconducting cable, the precooling speed must be controlled, so that the system temperature is sequentially reduced from the environmental temperature by a set gradient, and each gradient temperature is kept for tens to hundreds of hours, so that the temperature of the head end and the tail end of the superconducting cable is balanced and can reach a set value of the temperature, as shown in fig. 3;
and S3, analyzing and obtaining the internal state change information in the precooling process of the superconducting cable according to dielectric loss of the superconducting cable insulating medium under different frequency excitation voltages in the purging stage and the cooling stage.
It should be noted that, in steps S1 and S2, the superconducting cable is subjected to a dielectric spectrum test at different frequencies for multiple times in the purging stage and the cooling stage according to the set monitoring time interval, in this embodiment, a dielectric spectrum tester (specifically, an IDAX series automatic dielectric loss frequency characteristic tester) is used to perform the dielectric spectrum test on the superconducting cable, the frequency of the dielectric spectrum test is 0.1Hz to 1000Hz, and the specific process of performing the dielectric spectrum test is as follows:
as shown in fig. 4, first, both the ground wire and the low voltage lead of the dielectric spectrum tester are directly grounded, the high voltage lead of the dielectric spectrum tester is connected to the inner lead of one phase of the superconducting cable, and the other two phases of the superconducting cable are kept grounded;
then, setting the frequency of the dielectric spectrum tester to the required frequency, and performing dielectric spectrum test on one phase of the superconducting cable according to the set test voltage (in the embodiment, the effective value of the test voltage is 140V);
and according to the two steps, sequentially carrying out dielectric spectrum test on the other two phases of the superconducting cable to finally obtain dielectric loss values of the superconducting cable insulating medium under different frequencies.
Step S3, firstly, curve fitting is carried out on the dielectric loss values corresponding to different frequencies to obtain a dielectric loss-frequency curve;
and analyzing to obtain the internal state change results in the precooling process of the superconducting cable according to the dielectric loss-frequency curve, wherein the internal state change results comprise the change results of the internal moisture, the phase states (gas state and liquid state) and the temperature of the superconducting cable.
The insulation structure of the HTS cable under low temperature (operation condition) is solid-liquid composite insulation of liquid nitrogen impregnated PPLP (polypropylene laminated paper); before the low temperature state is not reached, the composite insulation of solid gas and solid gas is realized.
Relative dielectric constant ε of liquid nitrogen r 1.43, epsilon of air r Is 1, epsilon of nitrogen r Is 1.00058. Epsilon of PPLP at Normal temperature according to relevant laboratory data r And dielectric loss tan δ both decrease with increasing frequency; epsilon r Less variation, epsilon at 10Hz r About 80% at 0.1 Hz; the tan delta varied widely, with tan delta at 10Hz being only 30% at 0.1 Hz.
The calculation formula of the capacitance value of the superconducting cable insulating medium is as follows:
C＝2*π*ε r *ε/ln(R 2 /R 1 )
wherein ε is a vacuum dielectric constant, R 2 Radius of cable shield, R 1 Is the cable conductor radius; the above equation regards the cable insulation as a whole, and if each layer of insulation medium is analyzed, the cable insulation consists of a number of layers of PPLP and nitrogen in series. The partial pressure of 0.1 Hz-1000 Hz alternating voltage on PPLP and nitrogen (liquid or gas) in the dielectric mass spectrometry test is mainly determined by capacitance values of the PPLP and the nitrogen, and the capacitance value and epsilon r Closely related,. epsilon r And to frequency and phase. Therefore, the partial pressure is uneven and variable, and the contribution of each layer of insulation to the total dielectric loss at different frequencies is also variable; the insulation layer with large voltage bearing capacity contributes more to the total dielectric loss.
Above analyze epsilon r The influence on the tan δ of the entire cable, in addition to the influence, the tan δ of the PPLP itself varies with temperature, and is large from normal temperature to low temperature in the superconducting cableUnder the temperature difference, the change of tan delta is considerable, and the change law of tan delta is different at different frequencies.
The embodiment applies the technical scheme and is implemented on the Shanghai kilometer-level superconducting cable demonstration project. The Shanghai kilometer level superconducting cable demonstration project is an AC 35kV three-phase system cable, and a cable shielding layer is grounded and not led out inside the cable. When the dielectric mass spectrometry is carried out in the precooling process, the lower the frequency is, the longer the time for completing one test is, and the on-site time is limited, so that the frequency of the dielectric mass spectrometry is 0.1 Hz-1000 Hz, about 20 minutes is needed for completing one test by a three-phase cable, and the effective value of the test voltage is 140V.
The main process of implementation comprises:
(1) purging
In order to prevent impurities inside the superconducting cable system from blocking pipes or affecting the performance of some components when the system operates at low temperature, the superconducting cable must be evacuated and blown before cooling.
1) Carrying out vacuum-pumping replacement on the cable system;
2) the cable system was purged with dry, near room temperature nitrogen.
(2) Cooling down
Firstly, injecting low-temperature nitrogen; after reaching a certain temperature, injecting low-temperature liquid nitrogen; and after the whole cable is filled with liquid nitrogen, starting a refrigerator to circularly supercool the liquid nitrogen. In order to avoid the damage of the performance of the superconducting cable joint and the superconducting strip caused by the stress generated by the excessively fast cooling of the superconducting cable, the pre-cooling speed must be controlled.
For example, precooling is performed on a certain 100m, 35kV/1kA three-phase ac high-temperature superconducting cable: in the pre-cooling process, the superconducting cable is not suitable for quick cooling, so that low-temperature nitrogen is introduced for slow cooling, when the temperature of the system is less than or equal to 200K, liquid nitrogen is introduced for cooling the system, when the temperature is reduced to 100K, a refrigerating machine is started for supercooling the circulating liquid nitrogen until the temperature is reduced to less than or equal to 70K, the liquid nitrogen keeps a supercooling cycle, the whole process lasts for one week, and the pre-cooling temperature curve in the pre-cooling process is shown in figure 5.
In the purging stage and cold respectivelyThe dielectric spectrum test is carried out at the cooling stage, and the epsilon of each layer of material in the solid-liquid composite insulation is carried out in the precooling process of the superconducting cable from normal temperature to low temperature r The polarization characteristics and tan δ were changed. In the process, dielectric mass spectrometry is carried out, the tan delta of the detected superconducting cable under different frequencies also changes, and the change of the internal state of the superconducting cable in precooling is reflected from the electrical parameters.
From the experimental data of the superconducting cable demonstration project, at normal temperature, the tan delta of the superconducting cable insulation (consisting of PPLP and air without liquid nitrogen) decreases with the increase of frequency, and the tan delta at 10Hz is only 1.5% at 0.1 Hz. At low temperature (77K), the tan delta of liquid nitrogen impregnated PPLP insulation increases with increasing frequency, with tan delta at 0.1Hz being about 40% at 10Hz and tan delta at 10Hz being about 3.5% at 1000Hz, as shown in FIG. 6.
From the spectrum data of the medium, in the whole precooling process, the characteristics of dielectric loss at low frequency (1Hz and below), at power frequency of 50Hz and at high frequency (220Hz and above) are very different:
1) in the precooling process, the variation amplitude of the power frequency 50Hz dielectric loss is about 4 times; the variation range of 0.1Hz dielectric loss can reach 1000 times, the variation range of 220Hz dielectric loss can reach 40 times, and the variation range is far greater than the power frequency;
furthermore, the pre-cooling is divided into two stages, purging and cooling. In the purge stage, the moist air inside the cable is replaced by nitrogen and the impurities are purged. In the process, dielectric loss near the power frequency (such as 40Hz and 70Hz) in the medium spectrum data is obviously reduced, the temperature is not changed, and the reason of the reduction of the dielectric loss is the reduction of the moisture in the paper insulation. Therefore, the effect of moisture removal can be evaluated by analyzing the dielectric spectrum.
2) In the early stage of precooling (the temperature is relatively high), as shown in fig. 7, the high-frequency dielectric loss value is small, the fluctuation is also small, and the fluctuation amplitude of the low-frequency (for example, 0.1Hz) dielectric loss is large; during this period, the high-frequency dielectric loss value is small and stable, and if the data is taken as background noise, the signal-to-noise ratio is high, so that the data is suitable for observing abnormal signals, and therefore, the high-frequency dielectric loss is suitable for monitoring in the early stage of precooling.
3) In the late stage of precooling (low temperature), as shown in fig. 8, the high frequency dielectric loss fluctuates greatly, while the low frequency (e.g. 0.1Hz) data is reduced to the minimum and remains stable, during which the low frequency dielectric loss data is stable, and the signal-to-noise ratio is high when the data is regarded as background noise, which is suitable for observing abnormal signals; for example, if liquid nitrogen is gasified and the temperature is increased, the low-frequency dielectric loss is obviously increased, so that the low-frequency dielectric loss is suitable for monitoring and analyzing in the late stage of precooling.
In summary, dielectric losses at different frequencies all show different characteristics throughout the pre-cooling process. The dielectric loss-frequency curve is obtained by measuring the dielectric loss of the insulating medium under the excitation voltages with different frequencies by the dielectric spectrum, and the dielectric loss-frequency curve has one dimension more than the conventional power frequency dielectric loss, so that the cable has better resolution, the dielectric loss with different frequencies is comprehensively analyzed, the state in the cable in the precooling process can be more comprehensively and accurately mastered, and if the precooling is completely finished or not, the characteristics of low-frequency dielectric loss are more obvious.
In practical application, for example, before large-scale superconducting cable engineering is implemented, short superconducting cables with the same structure can be manufactured, a precooling experiment is carried out in a laboratory, and non-electric quantity (temperature, pressure, flow, liquid level and cold-contraction displacement) and electric quantity (medium spectrum data obtained by adopting the technical scheme) in a precooling process are collected at the same time, so that fingerprint data of cable precooling are obtained, and a precooling database of multidimensional state quantity of the superconducting cables is formed; in addition, the precooling speed of a laboratory can be changed, and the change of each state quantity of the cable can be monitored so as to obtain the optimal precooling speed.
When precooling is carried out on an engineering site, interpolation fitting comparison is carried out on the measured electric quantity and non-electric quantity of the superconducting cable system by using a mathematical tool and data in a precooling database, so that the current internal state of the cable is grasped, and whether the precooling process is smooth or not is judged.
In addition, in practical application, monitoring data comparison between three-phase single-core cables can be carried out, and the abnormal condition can be immediately analyzed.
Claims (10)
1. A superconducting cable precooling process monitoring method based on a dielectric spectrum is characterized by comprising the following steps:
s1, before cooling, vacuumizing and purging the superconducting cable;
in the process, dielectric spectrum test is carried out on the superconducting cable to obtain dielectric loss of the superconducting cable insulating medium under different frequency excitation voltages in the purging stage;
s2, cooling the superconducting cable by sequentially injecting low-temperature nitrogen and low-temperature liquid nitrogen and starting a refrigerator, and simultaneously controlling the precooling speed;
in the process, dielectric spectrum test is carried out on the superconducting cable to obtain dielectric loss of the superconducting cable insulating medium under different frequency excitation voltages in the cooling stage;
and S3, analyzing and obtaining the internal state change information in the precooling process of the superconducting cable according to dielectric loss of the superconducting cable insulating medium under different frequency excitation voltages in the purging stage and the cooling stage.
2. The method for monitoring the pre-cooling process of the superconducting cable based on the dielectric spectrometer as claimed in claim 1, wherein the specific processes of vacuumizing and purging the superconducting cable in the step S1 are as follows:
s11, carrying out vacuum-pumping replacement on the superconducting cable;
and S12, blowing the cable system by using dry nitrogen with the temperature difference between the dry nitrogen and the room temperature being less than or equal to the set temperature difference threshold value so as to blow impurities.
3. The method for monitoring the pre-cooling process of the superconducting cable based on the dielectric spectroscopy spectrum as claimed in claim 1, wherein the specific process of cooling the superconducting cable in the step S2 is as follows:
s21, injecting low-temperature nitrogen for slow cooling;
s22, when the temperature of the system is less than or equal to a set first temperature threshold, injecting low-temperature liquid nitrogen for cooling;
s23, when the temperature of the system is smaller than or equal to the set second temperature threshold, starting the refrigerator to continuously supercool the circulating liquid nitrogen until the temperature of the system is smaller than or equal to the set third temperature threshold, and keeping the supercooled circulation by the liquid nitrogen for the set cooling time;
wherein the third temperature threshold is less than a second temperature threshold, the second temperature threshold being less than the first temperature threshold.
4. The method for monitoring a superconducting cable precooling process based on the dielectric spectrum as claimed in claim 1, wherein the precooling speed is controlled in step S2 to make the system temperature decrease from the ambient temperature in sequence by a set gradient, and each gradient temperature is maintained for tens to hundreds of hours, so that the temperature at the head end and the tail end of the superconducting cable are balanced and can reach a set temperature value.
5. The method for monitoring the pre-cooling process of the superconducting cable based on the dielectric spectrum of claim 1, wherein the steps S1 and S2 are performed for the superconducting cable at a plurality of times of dielectric spectrum tests under different frequencies respectively in a purging stage and a cooling stage according to a set monitoring time interval.
6. The method for monitoring the pre-cooling process of the superconducting cable based on the dielectric spectrum spectrometer as claimed in claim 5, wherein the steps S1 and S2 are to perform a dielectric spectrum test on the superconducting cable by using a dielectric spectrum tester, and the frequency of the dielectric spectrum test is 0.1Hz to 1000 Hz.
7. The method for monitoring the precooling process of the superconducting cable based on the dielectric spectroscopy spectrum as claimed in claim 6, wherein the specific processes of performing the dielectric spectroscopy test on the superconducting cable in the steps S1 and S2 are as follows:
directly grounding a grounding wire and a low-voltage lead of the dielectric spectrum tester, connecting a high-voltage lead of the dielectric spectrum tester to an inner lead of one phase of the superconducting cable, and keeping the other two phases of the superconducting cable grounded;
setting the frequency of the dielectric spectrum tester to the required frequency, and carrying out dielectric spectrum test on one phase of the superconducting cable according to the set test voltage;
according to the steps, the dielectric spectrum test is carried out on the other two phases of the superconducting cable in sequence, and dielectric loss values of the superconducting cable insulating medium under different frequencies are finally obtained.
8. The method for monitoring the precooling process of the superconducting cable based on the dielectric spectrometer as claimed in claim 7, wherein the effective value of the set test voltage is less than 200V.
9. The method for monitoring the pre-cooling process of the superconducting cable based on the dielectric spectroscopy spectrum as claimed in claim 7, wherein the step S3 specifically includes the following steps:
s31, performing curve fitting on the dielectric loss values corresponding to different frequencies to obtain a dielectric loss-frequency curve;
and S32, analyzing according to the dielectric loss-frequency curve to obtain the internal state change result in the process of precooling the superconducting cable.
10. The method for monitoring the pre-cooling process of the superconducting cable based on the dielectric spectrometer as claimed in claim 9, wherein the step S32 is to analyze the change results of the moisture, the phase state and the temperature in the superconducting cable, where the phase state includes a gas state and a liquid state.
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006078461A (en) * | 2004-06-28 | 2006-03-23 | Sumitomo Electric Ind Ltd | Withstand voltage test method for superconductive cable |
| CN101036062A (en) * | 2005-01-07 | 2007-09-12 | 住友电气工业株式会社 | Superconductive cable withstand voltage test method |
| CN110208662A (en) * | 2019-06-24 | 2019-09-06 | 国网上海市电力公司 | Based on mass spectrographic hyperconductive cable PPLP insulation detecting method and the system of being situated between |
-
2022
- 2022-03-28 CN CN202210317281.8A patent/CN114910703A/en active Pending
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006078461A (en) * | 2004-06-28 | 2006-03-23 | Sumitomo Electric Ind Ltd | Withstand voltage test method for superconductive cable |
| CN101036062A (en) * | 2005-01-07 | 2007-09-12 | 住友电气工业株式会社 | Superconductive cable withstand voltage test method |
| US20080039334A1 (en) * | 2005-01-07 | 2008-02-14 | Sumitomo Electric Industries, Ltd. | Dielectric Strength Test Method of Superconducting Cable |
| CN110208662A (en) * | 2019-06-24 | 2019-09-06 | 国网上海市电力公司 | Based on mass spectrographic hyperconductive cable PPLP insulation detecting method and the system of being situated between |
| WO2020258835A1 (en) * | 2019-06-24 | 2020-12-30 | 国网上海市电力公司 | Detection method and system for pplp insulation aging degree of superconducting cable |
Non-Patent Citations (2)
| Title |
|---|
| 宁政, 林玉宝, 高智远, 戴少涛, 徐励, 惠东, 林良真, 肖立业: "高温超导电缆实时监测系统及试验", 高技术通讯, no. 09, 28 September 2004 (2004-09-28) * |
| 永;文华;席海霞;任安林;李锐海;陈宇民;曹敏;信赢: "中国第一组超导电缆并网运行试验", 低温物理学报, 28 November 2005 (2005-11-28), pages 2 - 4 * |
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