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Judgement and treatment of failure of partial discharge test equipment for medium voltage cross-linked cables

Release time:2020-12-25 11:10:57Popularity:

After the partial discharge detection oscilloscope has a breakdown of the cable body during the cable test, a large instantaneous short-circuit impulse current in the ground wire flows through the amplifier inside the oscilloscope, causing damage to the internal electronic components of the amplifier. After damage, it often appears that the oscilloscope cannot receive the marking echo pulse on the oscilloscope's elliptical baseline after it is marked with no load, or the echo pulse pulse amplitude is significantly reduced compared with normal marking, and the oscilloscope no-load marking signal is abnormal, causing The test cannot be performed normally. In order to facilitate the partial discharge instrument oscilloscope to quickly find, judge and repair the cause of the instrument failure after the above-mentioned failure occurs, when the equipment is normal, the tester should mark the partial discharge instrument without load (without cable load) after marking the "calibration" of the oscilloscope layout The “output” switch position, the “gain” adjustment knob position, and the “attenuation” switch position correspond to the reading of the partial discharge digital display meter at that time, diligently record. In order to conduct a quick comparison and analysis when the oscilloscope has an abnormal situation, quickly narrow the fault search range, determine the fault location, quickly eliminate it, and restore the normal use of the equipment. Let's take the JF-2000 partial discharge detector for the partial discharge test system as an example. When the local discharge device is normal, we can use a coaxial cable to short the calibration square wave output on the rear panel of the partial discharge device and the partial discharge signal input. Connect, the calibration output is set to 1PC, the attenuation is in the second gear, and the gain is increased. At this time, the digital meter should display more than 50pC, which means that the partial amplifier itself is working normally, otherwise it means that the partial amplifier is malfunctioning. The timely recording and accumulation of the relevant parameters under normal use of the equipment will greatly reduce the troubleshooting time of the equipment.

       The reactor is the core component of the partial discharge test equipment. The internal coil core is frequently moved up and down for a long time or the vibration of the reactor noise during the test with a long cable length may cause some travel switches in the mechanical transmission part. The fixing screws at the bottom of the cable are loosened, causing the travel switch to malfunction, and making it difficult to switch between different gears of the internal windings of the reactor and the excitation transformer. We only need to find the corresponding "high voltage switch" switch on the top of the reactor as the corresponding travel switch, and fix the bottom of it, so that the above equipment failure can be eliminated in time.

       After the reactor was inspected and repaired due to various reasons, it was not dried, dehumidified and vacuumed in time, which caused no-load partial discharge during the actual application of the equipment, resulting in the equipment cannot be used normally. Therefore, the reactor part of the partial discharge test system is subjected to core lifting treatment. After the second reinstallation, it must be vacuumed, dehumidified and dried in time. At the same time, the no-load partial discharge test shall be carried out on the repaired equipment in time to assess the actual use performance of the equipment to ensure that the equipment can meet the needs of normal tests.

       False breakdown sometimes occurs during the test of equipment without load or with cable. One reason is that after long-term use of the equipment voltage regulator, the epoxy plane where the coil and the brush are in contact, and the carbon brushes on the exposed slide of the voltage regulator are more abraded, causing local sparks on the surface of the rail during the movement of the brush. Discharge phenomenon causes frequent spark discharge alarms in the test system during voltage regulation. Therefore, during the test, the surface of the sliding rail of the voltage regulator brush should be cleaned regularly. Transformer oil can be used to wipe the surface of the rail regularly. At the same time, the electrode carbon brush of the coil should be maintained and maintained in time to extend the voltage regulation. The normal service life of the device can improve the occurrence of false breakdown of equipment. The high-voltage bushing of the reactor part of the equipment, the coupling capacitor of the high-voltage filter part, the calibration capacitor, and the high-voltage connection lead ends between the inductance coils often cause loosening of the wire nose fixing screws due to maintenance movement, resulting in poor contact in the equipment circuit. Spark discharge occurs, causing frequent spark discharge alarms in the system. At this time, as long as you carefully check and tighten the high-voltage connection line of the high-voltage filter part of the equipment, the above phenomenon will be quickly improved.

       There are also many problems in the actual use of the quick connector of the high-voltage lead of the test system. In use, the 35KV cross-linked cable test oil cup is often too heavy, causing the pressure-equalizing shielded metal hose at the high-voltage lead quick connector to pull off, causing the system to cause a spark discharge alarm due to poor local contact of the test line. Long-term practical work experience shows that high-voltage leads need to be repaired and replaced regularly during actual use. At the same time, the joints of some coaxial cable signal lines of the test system sometimes have poor contact, which causes trouble for the test. Therefore, in our normal test process, we should reserve some coaxial cable signal wires and high-voltage leads that have been packaged at both ends, so that when the above problems occur, they can be quickly replaced to improve the efficiency and accuracy of the test. At the same time, repair the problematic coaxial cable signal line and high-voltage lead in time for the next use.

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