CN-116165489-B - Ultra-short cable ultra-low frequency dielectric loss measurement platform and method

CN116165489BCN 116165489 BCN116165489 BCN 116165489BCN-116165489-B

Abstract

The invention relates to an ultra-short cable ultra-low frequency dielectric loss measurement platform which comprises an ultra-low frequency high-voltage power supply, a transmission cable, a measured cable, a voltage acquisition module, a current acquisition module, a dielectric loss measurement module and a calibration module. The invention also relates to an ultra-short cable ultra-low frequency dielectric loss measurement method which comprises the steps of S1, error calibration and S2, dielectric loss measurement. The invention has scientific and reasonable design, and can realize the ultralow-frequency dielectric loss measurement of the insulation of the high-voltage cable under a lower voltage level, thereby completing the state evaluation of the insulation of the cable. Compared with the existing complete set of ultra-low frequency dielectric loss measuring devices, the ultra-low frequency dielectric loss measuring device fills the blank of ultra-low frequency dielectric loss measuring equipment in the field of short sample cables, and can complete collection of extremely small resistive leakage current and shield external high-voltage interference.

Inventors

HUANG YOUCONG
XIE WENBING
XU JUN
HAN TAO
LI WENHAO
ZHENG ZHONGNAN
ZHANG YING
CHEN SHAOKANG
WANG QIONG
LIN ZIQI
Cheng Yunchu
WANG XIAOJIE
FANG CHAOYING

Assignees

国网福建省电力有限公司电力科学研究院
天津大学

Dates

Publication Date: 20260512
Application Date: 20221231

Claims (8)

1. The ultra-low frequency dielectric loss measurement platform for the ultra-short cable is characterized by comprising an ultra-low frequency high-voltage power supply, a transmission cable, a tested cable, a voltage acquisition module, a current acquisition module, a dielectric loss measurement module and a calibration module; the ultra-low frequency high voltage power supply, the transmission cable and the tested cable are sequentially connected, a shielding shell is arranged outside the tested cable, a first shielding electrode and a second shielding electrode at two sides of the tested cable are in short circuit and are in short circuit with the shielding shell, a current collection module comprises a current sampling resistor, a current signal voltage follower, a current signal low-pass filter and a current signal high-pass filter which are sequentially connected, the current sampling resistor is connected to the tested cable through a switch K1, the voltage collection module comprises a voltage sampling resistor R1, a voltage sampling resistor R2, a voltage signal voltage follower, a voltage signal low-pass filter and a voltage signal high-pass filter, the voltage sampling resistor R1 is connected with the voltage sampling resistor R2 in parallel and then is connected with the voltage signal voltage follower, the voltage signal low-pass filter and the voltage signal high-pass filter in series, the voltage sampling resistor R1 is connected to the first shielding electrode of the tested cable through the switch K2, the dielectric loss measurement module comprises a current signal zero-crossing comparator, a voltage signal zero-crossing comparator, an AND gate and a first oscilloscope, one end of the current signal zero-crossing comparator is connected with the current signal high-pass filter, the other end of the current signal zero-crossing comparator is connected with the AND gate through the switch K3, one end of the voltage signal zero-crossing comparator is connected with the voltage signal high-pass filter, the other end of the voltage signal zero-crossing comparator is connected with the AND gate through the switch K4, the AND gate is connected with the first oscilloscope, the calibration module comprises a signal generator and a second oscilloscope, the signal generator is connected to the tested cable through a switch K1, and the second oscilloscope is connected to the current signal zero-crossing comparator and the voltage signal zero-crossing comparator through switches K3 and K4 respectively.
2. The ultra-short cable ultra-low frequency dielectric loss measurement platform according to claim 1, wherein the frequency of the ultra-low frequency high voltage power supply is 0.01-0.1 Hz, the voltage is 0-80 kV, and the maximum load current is 40mA.
3. The ultra-short cable ultra-low frequency dielectric loss measurement platform according to claim 1, wherein the transmission cable is a power cable with the length of 50m and the voltage of 35kV, and the highest withstand voltage value is larger than 80kV.
4. The ultra-short cable ultra-low frequency dielectric loss measurement platform according to claim 1, wherein the length of the cable to be measured is 1-50 m, and the shielding shell is made of aluminum foil, copper foil or stainless steel.
5. The ultra-short cable ultra-low frequency dielectric loss measurement platform of claim 1, wherein the current sampling resistor is a noninductive resistor with a resistance value smaller than 1 Mohm, the current signal voltage follower adopts an integrated operational amplifier with an input resistance larger than 1 Gohm, the upper limit cut-off frequency of the current signal low-pass filter is 0.5Hz, and the lower limit cut-off frequency of the current signal high-pass filter is 0.005Hz.
6. The ultra-short cable ultra-low frequency dielectric loss measurement platform of claim 1, wherein the voltage sampling resistor R1 is a non-inductive resistor with a resistance value of 1G ohm, the voltage sampling resistor R2 is a non-inductive resistor with a resistance value of 1M ohm, the voltage signal voltage follower adopts an integrated operational amplifier with an input resistance of more than 1G ohm, the upper limit cutoff frequency of the voltage signal low-pass filter is 0.5Hz, and the lower limit cutoff frequency of the voltage signal high-pass filter is 0.005Hz.
7. The ultra-short cable ultra-low frequency dielectric loss measurement platform of claim 1, wherein the response time of the current signal voltage follower, the voltage signal zero-crossing comparator, the current signal zero-crossing comparator and the AND gate is less than 10ns.
8. The method for measuring the ultra-low frequency dielectric loss measurement platform of the ultra-short cable according to the claims 1-7 is characterized by comprising the following steps: S1, error calibration, namely dialing a switch K1 to 1, dialing a switch K2 to 1', dialing a switch K3 to 4, dialing a switch K4 to 4', turning on a signal generator to generate a sine wave signal of 0.1Hz to 0.01Hz, connecting the signal generator to a current acquisition module and a voltage acquisition module at the same time, connecting rectangular waves output by a current signal zero-crossing comparator and a voltage signal zero-crossing comparator to a second oscilloscope, and observing the time difference Deltat of the rising of the rectangular waves on the second oscilloscope; S2, dielectric loss measurement, namely dialing a switch K1 to 2, dialing a switch K2 to 2', dialing a switch K3 to 3 and dialing a switch K4 to 3', entering a dielectric loss measurement mode, respectively entering a current signal zero-crossing comparator and a voltage signal zero-crossing comparator, converting a sine wave signal into a rectangular wave digital signal, and then connecting two paths of rectangular wave signals into two input ends of an AND gate to generate a level comparison signal and displaying the level comparison signal on a first oscilloscope; Because of the existence of the capacitive current of the tested cable, the current signal leads the voltage signal, according to the signal observed on the first oscilloscope, the half period duration of the ultralow frequency signal is T, the high level duration of the rectangular wave output by the AND gate signal is T, the time of leading the current signal to the voltage signal is T-T, Therefore, the dielectric loss angle radian before correction is calculated as: after the calibration error is considered, the dielectric loss angle radian value is corrected as follows: the dielectric loss tangent is further determined to be tg delta.

Description

Ultra-short cable ultra-low frequency dielectric loss measurement platform and method Technical Field The invention belongs to the technical field of safe operation of cables, and particularly relates to an ultra-low frequency dielectric loss measurement platform and method for an ultra-short cable. Background With the continuous development of the economy in China, the town scale is larger and larger, the construction of power facilities is also continuously carried out, and the power cable is an important factor for determining the safety and stability of the power system. The Cross-linked polyethylene (Cross-linked polyethylene, XLPE) insulated power cable is invented by the universal electric company of the United states in about 50 th century, and compared with the traditional cable, the Cross-linked polyethylene insulated power cable has the advantages of 1) good electrical performance (high breakdown field strength, strong dielectric property and large insulation resistance), 2) good thermal and mechanical properties, high work allowable temperature and large current-carrying capacity, 3) convenient installation and maintenance, simple structure and small electric energy loss, and 4) can be widely applied to medium-low voltage transmission and distribution networks and also be applied to high-voltage and ultra-high voltage transmission systems. The cable runs in a strong electric field, high temperature and humid environment for a long time, and is subjected to the synergistic effect of factors such as electricity, heat, machinery, chemistry and the like, so that the insulation is subjected to physical and chemical changes, the degradation process of the cable insulation is accelerated, and finally, the cable breakdown and insulation failure are caused. Among them, heat aging is a key factor affecting the aging state of the cable, and many students study the aging state of the insulation by developing accelerated heat aging tests, but most of them adopt the test result characteristics of a single diagnostic mode to determine the state of the cable, and the test result is generally affected by various factors. Therefore, it is necessary to develop a cable insulation accelerated thermal ageing test, and comprehensive evaluation is performed on the cable state by using various characteristic parameters, so that the method has important significance for improving the safe and reliable operation of the power system. Conventional methods for detecting the operation state of a cable include non-electrical parameter methods and electrical parameter methods. The non-electrical parameter method realizes the operation state diagnosis by detecting the physical and chemical properties of the cable, and is mainly used for evaluating the whole aging life of the cable, such as the Elongation At Break (EAB) and compression modulus detection of the cable material. The cable electrical parameter detection method mainly comprises measurement of cable insulation resistance, withstand voltage test, leakage current test, dielectric loss detection and the like. However, the above-mentioned electrical method is currently popular mainly in distribution network cables, but is not applied to high-voltage cables. In recent years, the ultra-low frequency dielectric loss measurement method has a plurality of advantages of miniaturization, portability and the like, is widely popularized in the detection of the national distribution network cable, and promotes the daily operation and maintenance work of the 35kV and below voltage class cable in China. However, in practical operation, the current sampling mode of the ultralow frequency dielectric loss measurement device is current and voltage sampling at the high voltage side, and the minimum length (and the minimum load capacitance value) of the cable to be measured is definitely required, and the minimum measurement length of the main stream device is about 50 m. When the ultra-low frequency dielectric loss is used for measuring a short cable sample (below 10 m), the problems generally exist that (1) the capacitance value of the sample is insufficient, the ultra-low frequency voltage waveform cannot work normally, the output voltage waveform has a great error with a standard sine wave, and (2) the resistive current proportion in the current component is extremely low in the measuring process, so that the ultra-low frequency high voltage power supply noise is easy to influence, and the great measuring error is caused. Therefore, in order to meet the requirement of the cable state evaluation on the ultralow frequency dielectric loss measurement of the short sample cable, an ultralow frequency dielectric loss measurement platform needs to be developed aiming at the problem, and the ultralow frequency dielectric loss measurement of the cable sample with the minimum length of 1m is realized. Disclosure of Invention The invention aims to overcome the defects of the prior art, provides an