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With the development of urban construction, the proportion of power cables in the power supply of urban networks is increasing. In some urban areas, overhead transmission lines have been gradually replaced. With the increase in the number of cables and the extension of the operating time, cable failures have occurred. Also more and more frequent Because of the hidden nature of cable lines, imperfect operating data of individual operating units, and limitations of test equipment, it is very difficult to find cable faults. How to reasonably select fault test equipment and accurately and quickly find cables? Failure, shortening the time of fault interruption, becoming a problem that cable operators are very concerned about This text introduces the new technology of cable fault testing at home and abroad and the experience of cable fault testing in this Council. 1 Power cable fault classification Power cable faults can be divided into series according to the nature (breaking ) Faults and parallel (short circuit) faults of two kinds, the latter according to whether the main insulation outside the metal sheath or shield can be divided into the main insulation fault (external metal sheath or shielding) and skin (outer sheath) fault (no metal Sheath or shield) main insulation fault According to the test method, according to the fault point insulation resistance Rf size For different metallographic short-circuit (low-resistance) faults, Rf is different for different instruments and methods. Generally, Rf is able to cope with all possible cable faults, test single tester, pre-positioning equipment (including bridge, echo reflectometer, supporting High-voltage device and signal generator) fine positioning instrument (step voltage method, sound and magnetic synchronization method, audio locator). The path tester is particularly important for buried cable faults where the path is not known, but in actual measurement, it is disturbed by underground parallel metal pipelines, and the damage is larger. Seba's new product uses double induction coils to superimpose the inverse wave of the largest normal wave method. Can solve the interference problem The capacitor C in the high-voltage impact generator is related to the cable test, and foreign instruments often use 2PF or 4PF capacitors. However, for longer cable lengths, intermittent faults with particularly high insulation resistance, or low-voltage cable failures, the waveform impact energy CU2 is often not obtained. Considering the adverse effects of the main insulation and being limited by the instrument volume, U cannot be too large (should not More than 5 (%~70%) of the pretest voltage, only increase the capacity, the impact energy only increases, so that the arcing point at the fault point is long, the discharge is thorough, and the test waveform is easily obtained. Especially for the low voltage cable, the foreign instrument is automatic. The extension arc device or widening the impact pulse to prolong the arcing time function, and the trigger pulse cooperate well, the capacity 4 F is enough.The domestic equipment configuration should choose a larger capacitance, but increase the capacitance to make the instrument cumbersome, but also to change the instrument Match the equipment with high sampling frequency to ensure high positioning accuracy.
For faults or intermittent faults of high-voltage cables of 110 kV and above, high-voltage rated equipment shall be selected and attenuation testing may be used.
5 Main experience of cable fault test application Nearly 30 insulation faults were tested with Baur and Seba's cable fault testing and positioning equipment. The success rate reached 100%, and the fault points were fixed within 12 hours. The main experience of the test is: When the cable is verified, it must be required to provide complete cable data (length, path is reserved, joint position, etc.) The main insulation fault pre-positioning is easier and precise positioning is difficult; on the contrary, the outer sheath fault pre-positioning The more difficult and precise positioning (step voltage method) is very accurate and easy. In special circumstances (when insulation and outer sheath faults are common), the combination of the two can make the connection of the ground wire during the construction of the low voltage cable joint not standardized, and the cable ground should be separated from the grounding during the test. When the end of the cable does not have a noticeable waveform, change to the other end or increase the arcing current before testing. A better waveform can be obtained. If the measured cable is longer and the waveform cannot be measured at the pre-position, increase the impulse voltage or Adjust the trigger delay to get the waveform. For intermittent faults, when the breakdown voltage cannot be used, the DC breakdown test can be used.
Bit should be equipped with test equipment, such as electrical routing, J path testing, chanting, H.AU h, mailing down, 1st forbidding, book1, pre-positioning error, including: a. instrument error, constant; b. measuring error, influential , should pay attention to whether the two ends of the cable reserved ring; c. improper value of the wave speed, should be calculated by the cable length; d. waveform judgment error, depending on the performance of the instrument and the tester in the middle of the increase, FM high voltage power supply technology, but because of the large weight, poor mobility, mainly used in laboratory frequency conversion resonance test system can not only meet the 110kVXLPE cable pressure requirements, but also has the advantages of light weight, good mobility, suitable for field testing.
Through investigation and demonstration, Shandong Electric Power Research Institute selected the frequency conversion resonance test device developed by Changsha Electric Power Test and Development Co., Ltd., which uses a fixed reactor as a resonant reactor to achieve resonance by means of frequency modulation. The frequency adjustment range is 30~300Hz. Compliance with GIGREWG 21.03 AC voltage requirements for the recommended power frequency and approximated industrial frequency (30 to 300 Hz) This AC voltage test can reproduce similar field strengths under operating conditions. Practice has proven to be an effective method.
3 Site Acceptance Test Examples Shandong Power Grid used an inverter resonance test device to conduct on-site AC withstand voltage acceptance tests on 110kV cross-linked polyethylene cables. Its test model is YJLW03; rated voltage is 64/110kV; conductor specification is 1 claw 7
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