WO2014075584A1 - Method for in-situ detection of partial discharge of damped oscillation wave of large-length ultrahigh-voltage crosslinked cable - Google Patents

Abstract

Provided is a method for in-situ detection of the partial discharge of a damped oscillation wave of a large-length ultrahigh voltage crosslinked cable. The method employs a damped oscillation wave voltage having an attenuation period of 300 mS to replace power-frequency sine-wave voltage as an excitation voltage for testing partial discharge in a cable line having a potential insulation defect; during a voltage boosting process, the partial discharge detection method is changed from off-line single-ended fixation measurement to charged detection or distributed monitoring of the middle connectors along the line; for signal pickup, a high-frequency pulse current coupling sensor, instead of a coupling capacitor and a detection impeder connected to a cable terminal in parallel, is clamped on a metal sheathed cable lead line; for data processing, a PD quantity value is calculated by using a pulse current frequency domain integration method. The method provides technical support for troubleshooting of high-voltage and ultrahigh-voltage crosslinked cables, and evaluation of the condition of cable insulation, and further diversifies and improves cable status testing means of cable operation and maintenance units, thus providing strong support for improving the reliability of cable line operation.

Description

 Field detection method for damped oscillation wave partial discharge of large length ultra-high voltage cross-linked cable

 The invention belongs to the technical field of power cable state detection, and relates to a method for detecting partial discharge of a large-length high-voltage and ultra-high-voltage cross-linked cable line, which is applicable to a voltage level of 110 (66) kV~500 kV. Background technique

With the continuous transformation of China's urban power grid, XLPE (hereinafter referred to as cross-linked) cable has been widely used as the mainstream product of power cable engineering in urban power transmission and distribution lines. In the past decade, the length of the laying loop of cross-linked cables has steadily increased with an average annual growth rate of more than 15%. The high-voltage and ultra-high-voltage cross-linked cable lines have become an important part of China's power grid, and the large length (the longest domestic 220kV cable line is 17.77km) and the large section (the conductor core core cross-sectional area is 3000mm ² ). It is found that Partial Discharge (PD) is the main form of early insulation failure of cable lines. It is not only the main cause of insulation aging, but also the main characteristic parameter of insulation condition.

 The PD live detection/on-line monitoring technology under the operating voltage of high-voltage and ultra-high-voltage cross-linked cables in the power grid is a hot technology focus at home and abroad. Although the PD trend can be obtained under operating conditions, there are also PD test data. Accurate quantification of IEC standards causes measurement difficulties and quantification criteria to be inconsistent. A single detection voltage is not easy to find insulation defects of a smaller size. It is technically difficult to handle background noise, and the metal sheath of the line is connected to the copper row by cross-transposition interconnection. Prominent problems such as the difficulty in accurately locating the partial discharge signal.

The AC voltage method is recommended for on-site diagnostic tests of cross-linked cables, mainly including power frequency voltage, ultra-low frequency voltage and variable frequency voltage test. The voltage frequency of the cross-linked cable in the power grid is the power frequency. The voltage generated by the power frequency voltage test system is ideal from both waveform and frequency. However, due to the large capacitance of the cross-linked cable itself, especially the high-voltage and ultra-high voltage cable sites. The test requires a large capacity of the test system, resulting in an excessively large volume and weight of the system equipment, which is difficult to implement on site. The validity of the ultra-low frequency voltage test and the power frequency voltage test is still inconclusive, and the upper limit of the output voltage of the test system is low. Currently, it is only applicable to the distribution network cable test. The variable frequency voltage test device generates a test voltage close to the power frequency through frequency modulation or modulating resonance, and has the best equivalence with the power frequency voltage. The volume of the power frequency voltage system is reduced and the weight is reduced, but the high voltage and ultra high voltage cable field test The volume and weight of the inverter device are still large, the power supply capacity requirement is high, and it is also limited by the operating site. Inconvenience in running and lifting equipment.

 Conventional Damping AC (hereinafter referred to as DAC) The PD is mainly used for off-line single-ended fixed measurement, that is, the test voltage generating device and the PD detecting device are combined into a complete system. The secondary test system is only connected to one end of the cable line, and the voltage excitation and PD signal acquisition are performed at the end position. The results of many scholars in the Netherlands, Japan, Germany and China have shown that the DAC voltage is equivalent to the power frequency sine wave voltage and can be used as the excitation voltage for the PD test. Partial discharge detection of high-voltage cross-linked cable line under DAC voltage has the requirements of IEC standard calibration (detection band is 10kHz~500kHz), the discharge level is accurately quantified, the discharge value is pC as the effective unit, and the discharge pulse and voltage phase are clearly correlated, test data The comparability is strong, and it is convenient to unify the evaluation criteria. Compared with the power frequency and variable frequency voltage generating device, the DAC voltage generating device is small in size, light in weight, and small in power demand, and is convenient for on-site handling and arrangement.

 Cable lines have significant distributed characteristics over their length compared to power devices with unitary structural features such as transformers and transformers. When the distributed parameter transmission line characteristics of the cross-linked cable line cause its internal PD signal to propagate along the cable, the amplitude of the signal is exponentially attenuated, and the waveform is significantly distorted, no longer having steep rising and falling edges. The longer the line, the attenuation and distortion of the discharge pulse at the discharge source far from the test end is severe. When the line length exceeds 3km, the effectiveness and applicability of the off-line single-ended fixed PD detection method based on IEC60270 standard under DAC voltage has been It is difficult to meet the requirements of insulation performance testing and evaluation. It is very difficult to capture the weak PD signal generated by the power supply of several kilometers away by the single-ended fixed PD detection method under the conventional DAC voltage.

 Chinese invention patent "Detection device and method for partial oscillation and fault location of cable oscillation wave" (application number: 201210205908.7) proposes a device and method for detecting partial discharge and fault location of cable oscillation wave, and the system power control host automatically finds system resonance Frequency, and adjust the output voltage to the initial set test voltage value of the system, the user can carry out the cable withstand voltage test or the damped oscillation wave partial discharge detection test according to the demand, the system passes the collected partial discharge signal of the cable, and analyzes, diagnoses and locates the fault. position. However, the invention still has the above drawbacks, and it is impossible to solve the detection requirements under a large length.

In view of this, the present invention provides a method for detecting a partial discharge of a damped wave in a large-length ultra-high voltage cross-linked cable to solve the above problem. Summary of the invention

 The object of the present invention is to overcome the shortcomings of the field detection method for the partial discharge of large-length high-voltage and ultra-high-voltage cross-linked cable lines under DAC voltage, and to fill the technical blank of the state detection of large-length high-voltage and ultra-high-voltage cross-linked cable lines in China, and propose a large length. The partial discharge on-site detection method for high-voltage and ultra-high-voltage cross-linked cable lines can detect the PD signals of cables and accessories under the condition that the line length exceeds 3km, and is suitable for voltage levels of 110 (66) kV~ 500kV.

 The technical solution of the present invention is: a method for detecting a partial discharge of a damped wave in a large-length ultra-high voltage cross-linked cable, which is characterized in that it comprises the following steps:

 The first step, before the test, the three phases of the tested cable lines A, B, and C are separated from the power grid; the second step is to replace the copper in the metal sleeve of the insulated joint of the B, C, and C three-phase cables. The row is changed from cross-connected to split-phase direct connection;

 In the third step, the terminal of the tested cable line A on the test site side is connected to the oscillating wave voltage generating device and the voltage divider, and the measured cable line A phase is remotely suspended, and the tested cable line is not on both sides of the test phase. Terminals are relatively shorted;

 The fourth step is to install a high-frequency pulse current-coupled sensor on the A-phase direct copper busbar in the grounding lead-out line on both sides of the tested cable line A and all the grounding boxes in the grounding box or the cross-connecting box, and connect the signal Output line

 The fifth step is to inject a calibration signal from the terminal A phase of the cable to be tested using a standard pulse generator; in this step, a portable high frequency partial discharge detector can be used, and the sensor is collected from the near end to the terminal and the connector along the cable line. The output signal is measured and calibrated; or a distributed high-frequency partial discharge monitoring system is adopted, and one pre-stage acquisition unit is installed near each terminal or joint, and the output signal of each sensor is synchronously collected along the cable line for measurement and calibration;

 In the sixth step, the voltage generating device uses a stepped boosting method to output a damped oscillating wave voltage with an attenuation period of 300 mS, the starting voltage is 0.5 times of the rated phase voltage U0 of the cable, and the boosting voltage is 10 kV per stage; the seventh step, the pressurization process If the PD signal is detected, the current DAC test voltage is continuously applied for N cycles, N is an integer greater than or equal to 10; if the PD signal is not detected, the step boost is continued until 1.4 U0;

The eighth step, during the pressurization process, whether using a portable high-frequency PD detector, collecting the output PD pulse current signal of the sensor from the near end and the connector along the cable line, or adopting distributed The high-frequency partial discharge monitoring system synchronously collects the output pulse current signal of each sensor along the cable line, and simultaneously uses the oscilloscope to simultaneously collect the output test voltage small signal of the voltage divider;

 In the ninth step, after the end of the N voltage cycles, the discharge pulse current signals collected by each sensor are subjected to frequency domain integration processing, the PD magnitude is calculated, and the PD characteristic statistical distribution spectrum is plotted;

 In the tenth step, steps 3 to 9 are repeated on the B-phase and C-phase cables of the cable to be tested.

 The above-mentioned large-length ultra-high voltage cross-linked cable damped wave partial discharge field detection method is characterized in that: the damped oscillating wave voltage with a decay period of 300 mS is used instead of the power frequency sine wave voltage as the excitation voltage for the partial discharge test of the cable line. .

 The above-mentioned method for detecting the partial discharge of the oscillating wave partial discharge of the large-length ultrahigh-voltage cross-linked cable is characterized in that: the PD value is calculated by the pulse current frequency domain integration method, and the frequency domain range is from 10 kHz to 500 kHz, and pC is a unit of measurement.

 The method for detecting the partial discharge of the oscillating wave of the large-length ultra-high voltage cross-linked cable as described above is characterized in that: the characteristic distribution spectrum of the PD characteristic adopts three parameters of the PD quantity, the number of pulses and the test voltage phase in N periods. draw.

 The method for detecting the partial discharge of the oscillating wave of the large-length ultrahigh-voltage cross-linked cable as described above is characterized in that: the value of N is 20.

 The invention has the beneficial effects that the invention can overcome the deficiencies of the field detection method for the partial discharge of the large-length high-voltage and ultra-high-voltage cross-linked cable lines under the DAC voltage, and fill the technical blank for the state detection of the large-length high-voltage and ultra-high-voltage cross-linked cable lines in China. The PD signal of the cable and accessories can be detected under the condition that the line length exceeds 3km, and it is suitable for 110 (66) kV~ 500kV voltage level. This method can provide technical support for the diagnosis of high-voltage and ultra-high-voltage cross-linked cable line defects and cable insulation health assessment, further enrich and improve the cable operation and maintenance unit cable state detection means, and provide strong protection for improving the reliability of cable line operation. DRAWINGS

1 is a flow chart of a method for detecting partial discharge of a large-length ultra-high voltage cross-linked cable line according to the present invention. 2 is a schematic view showing a partial discharge charging detection method for a large-length ultrahigh-voltage cross-linked cable line under damped oscillating wave voltage according to the present invention.

Figure 3 is a partial discharge distribution of a large-length ultra-high voltage cross-linked cable line under the oscillating oscillating wave voltage of the present invention Schematic diagram of the monitoring method. detailed description

 In order to better understand the present invention, the contents of the present invention will be further clarified below with reference to the embodiments, but the contents of the present invention are not limited to the following embodiments. A person skilled in the art can make various changes or modifications to the invention, and such equivalents are also within the scope of the appended claims.

 Marked in the figure, 1-DC excitation oscillating voltage generator, 2-resistive-capacity voltage divider, 3-cable line terminal, 4-terminal grounding wire, 5-cable line intermediate connector, 6-connector phase separation Straight copper busbar, 7- cable line cable body, 8-high frequency pulse current coupling sensor, 9-portable high frequency PD detector, 10- oscilloscope, 11-distributed high frequency PD monitor system (including pre-stage acquisition) unit).

 The method for detecting partial discharge of a large-length high-voltage and ultra-high-voltage cross-linked cable line provided by the embodiment of the present invention is as follows:

 The first step: Before the test, the tested cable lines, B, C three phases are separated from the grid.

 The second step: A, B, C three-phase cable insulation joints in the metal sleeve cross-connected box inside the swap copper row from cross-connected way to split-phase direct connection.

 The third step: the cable line to be tested is located at the end of the test site (near end). The conductor lead-out rod is connected to the high-voltage lead of the DC-excited oscillating voltage generating device and the voltage divider, and the distal conductor lead-out rod is suspended. Terminals on both sides of the non-test phase are shorted to ground with metal leads.

 Step 4: Install a high-frequency pulse current-coupled sensor on the A-phase direct-connected copper busbar on the terminal grounding lead-out line on both sides of the A-phase cable and all the grounding boxes or cross-connecting boxes at the joint, and connect the signal output line.

 Step 5: Before the boost, the calibration signal is injected from the Phase A terminal using a standard pulse generator. Test equipment conditions General cable operation and maintenance unit, it is recommended to use portable high-frequency partial discharge detector, from the near end of the cable line to the terminal and the output signal of the joint acquisition sensor for measurement and calibration; test equipment with good condition, cable operation and maintenance unit, It is recommended to use a distributed high-frequency PD monitor system. Each terminal or connector is installed with a pre-stage acquisition unit nearby, and the output signal of each sensor is synchronously collected along the cable line for measurement and calibration.

The sixth step: the voltage generating device adopts a step-up boosting method to output a damped oscillating wave voltage with an attenuation period of 300 mS, the starting voltage is 0.5 times of the rated phase voltage U _Q of the cable, and the boosting voltage is 10 kV per stage until PD Starting voltage (PDIV) or 1.4U ₀ .

Step 7: During the pressurization process, if the PD signal is detected, the current DAC test voltage is continuously applied for 20 cycles; if the PD signal is not detected, the step boost is continued until 1.4 U _Q .

 The eighth step: During the pressurization process, whether using the portable high-frequency PD detector, the output PD pulse current signal of the sensor is collected from the near end and the connector along the cable line, or the distributed high-frequency PD monitor system is adopted. Simultaneously collect the output pulse current signal of each sensor along the cable line, and simultaneously use the oscilloscope to simultaneously collect the output test voltage small signal of the voltage divider.

 The ninth step: After the end of the 20 voltage cycles, the discharge pulse current signal collected by each sensor is subjected to frequency domain integration processing to calculate the PD value. The discharge statistical distribution spectrum was drawn by taking three parameters of PD value, number of pulses and phase of test voltage in 20 cycles.

 Step 10: Repeat steps 3 through 9 on the Phase B and Phase C cables, respectively.

 In this embodiment, the parameters of 20 cycles are continuously taken. In actual operation, the number of cycles of continuous pressurization can be flexibly adjusted, and generally 10 or more cycles should be taken.

 The method for detecting partial discharge of large-length high-voltage and ultra-high-voltage cross-linked cable lines provided by the present invention has the main difference from the prior art: the use of a damped oscillating wave voltage with an attenuation period of 300 mS instead of the power frequency sine wave voltage as a potential in the cable line The excitation voltage for the partial discharge test of the insulation defect; the partial discharge detection method during the pressurization process is changed from the off-line single-ended fixed measurement to the live detection or distributed monitoring along the line intermediate joint; on the signal pick-up, the cable metal sleeve is used on the lead-out line The card is equipped with a high-frequency pulse current-coupled sensor to replace the coupling capacitor and the detection impedance in parallel with the cable terminal. For data processing, the PD value is calculated by the pulse current frequency domain integration method, and the frequency domain range is from 10 kHz to 500 kHz, and the measurement unit is pC. In terms of data analysis, the PD characteristic statistical distribution spectrum is drawn by using three parameters of PD quantity, number of pulses and test voltage phase in 20 cycles. The contents not described in detail in the present specification belong to the prior art well known to those skilled in the art.

Claims

Rights request

1. An on-site detection method for damped oscillating wave partial discharge of large-length ultra-high voltage cross-linked cables, which is characterized by including the following steps:

The first step is to disconnect the three phases A, B and C of the cable line under test from the power grid before the test; the second step is to replace the metal sleeves at the insulated joints of the three-phase cables B and C with copper in the cross interconnection box. The platoon is changed from cross-connection mode to split-phase direct connection mode;

The third step is to connect the terminal of phase A of the cable line under test located on the side of the test site to the oscillating wave voltage generating device and voltage divider. The far end of phase A of the cable line under test is suspended, and the cable line under test is on both sides of the non-test phase. terminals are shorted relative to ground;

The fourth step is to install a high-frequency pulse current coupling sensor on the terminal grounding leads on both sides of phase A of the cable line under test and on the phase A direct-connected copper bars in all grounding boxes or cross-interconnection boxes at the joints, and connect the signals output line;

The fifth step is to use a standard pulse generator to inject the calibration signal from the A-phase terminal of the cable line under test; in this step, a portable high-frequency partial discharge detector can be used to collect sensors from the near end along the cable line one by one at the terminals and connectors. The output signal of the sensor can be measured and calibrated; or a distributed high-frequency partial discharge monitoring system can be used, with a front-end acquisition unit installed nearby each terminal or connector, and the output signal of each sensor can be synchronously collected along the cable line for measurement and calibration;

The sixth step is to use a voltage generating device to use a stepped voltage boosting method to output a damped oscillation wave voltage with a decay period of 300mS. The starting voltage is 0.5 times the rated phase voltage U _Q of the cable, and each step is boosted by 10kV; the seventh step is to pressurize. During the process, if a PD signal is detected, the current DAC test voltage is continuously applied for N cycles, where N is an integer greater than or equal to 10; if a PD signal is not detected, the stepwise voltage boosting is continued until 1.4U ₀ ;

The eighth step is during the pressurization process, whether using a portable high-frequency partial discharge detector to collect the output PD pulse current signal of the sensor along the cable line one by one from the near end to the terminals and joints, or using a distributed high-frequency partial discharge monitoring system. To simultaneously collect the output pulse current signal of each sensor along the cable line, an oscilloscope must be used to simultaneously collect the output test voltage small signal of the voltage divider;

In the ninth step, after N voltage cycles, the discharge pulse current signal collected by each sensor is subjected to frequency domain integration processing, the PD value is calculated, and the PD characteristic statistical distribution spectrum is drawn;

Step 10: Repeat steps three to nine on the B-phase and C-phase cables of the cable line under test.

2. The on-site detection method of damped oscillating wave partial discharge of large-length ultra-high voltage cross-linked cables according to claim 1, characterized in that: a damped oscillating wave voltage with a decay period of 300 mS is used as the local part of the cable line instead of the power frequency sine wave voltage. Excitation voltage for discharge testing.

3. The on-site detection method of damped oscillating wave partial discharge of long-length ultra-high voltage cross-linked cables according to claim 1, characterized in that: the PD value is calculated using the pulse current frequency domain integration method, and the frequency domain range is 10kHz~500kHz, with pC is the unit of measurement.

4. The on-site detection method of damped oscillating wave partial discharge of large-length ultra-high voltage cross-linked cables according to claim 1, characterized in that: the PD characteristic statistical distribution spectrum adopts the PD magnitude, the number of pulses and the test voltage within N cycles Phase 3 parameters to draw.

5. The on-site detection method of damped oscillatory wave partial discharge of large-length ultra-high voltage cross-linked cables according to claim 1, characterized in that: the value of N is 20.