Power cable fault distance problems in testing and processing & # 65288; The fourth stage & # 65289; Cable accessories
in the previous paper, AnWei power company small make up after years of power cable accessories production experience summarizes problems and handling of power cable fault distance test, a lot of friends reaction problem statement is overmuch, solution is less, want to directly see problem solution problem statement rather than a long paragraph, small make up for this response to the request, the rest of the series will be in a more detailed content analysis to friends, hope to be of help. Welcome to click on the portal of the previous period, the problems and processing of power cable fault distance test ( The third phase) 》
( 1) Old type joint failure
point of failure occurred in the ontology, cable is usually easy to judge, whether the low voltage pulse method is adopted, or direct flash or make flash, acquisition to relatively typical test waveform. However, if the point of failure occurred in the middle of the oil impregnated paper power cable of the old type head or terminal, usually happens judgment is difficult, but also could be some strange phenomenon is not easy to understand.
there are five common cable joint, joint joint, asphalt, oil filled epoxy resin joint, heat shrinkable joint and cold joint. The joint epoxy resin and asphalt joints is very common. Often due to exist for poor process and make the joint to joint harmful impurity, air bubble, crack and cause accidents. Even if it is hot, cold joint, ground wire process, wire core insulation stripping process and joint encapsulation process a slight negligence, can cause accidents. The change of environmental temperature, humidity, and long-term overload operation and is likely to be formed when the preventive test failure. Cable head ( Connector, terminal head) Malfunctioned, testing the following phenomena may occur.
1) coarse, the start point of failure resistance is low, because of not on dc and disable direct flash method, high impact after high pressure, more and more high insulation resistance, often do not have a fault point on the measured waveform reflected wave, is the point of failure has not been ionization breakdown.
(2) the impact flash method is used to test, the ball discharge gap are loud and clear, crisp seems to point of failure has been the breakdown, but observation point of failure reflected pulse wave.
3. Do preventive pressure test, leakage current, particularly large and in the impact of the high voltage ( Around 35 kv) , trouble-free reflected pulse wave.
the measured, if appear afore-mentioned abnormal phenomenon, should consider to junction point of failure occurred in the old type, the processing method is to increase the capacity of energy storage capacitor or improve impulse voltage.
( 2) Flashover sex high impedance fault transient flash process
the method of direct lightning waveform comparison with simple, small change, obvious characteristics of the inflection point, the advantages of small measurement error, so the test flashover sexual high impedance fault is the preferred way to direct flash method. But in actual test work, a significant number of flashover high impedance fault, there are only a few times and temporary flash process, if the master is bad, often makes direct flash test failure. Temporary flash process usually has the following three conditions.
1) several times after the flashover failure point into leakage resistance fault in either high or low resistance fault. Then direct flash test, should immediately stop use flash or low voltage pulse method test. From this aspect, when testing the direct flash method, with current meter detection cable leakage current is very necessary.
(2) several times after the flashover failure point leakage into high resistance fault. To blunt method after the test, the ideal has not yet been measured waveform, fault point flashover discharge disappeared, and high impedance fault flashover, so change again and again.
(3) after the temporary flash process, fault point is 'disappear', after a period of time after the temporary flash process starts all over again. To this kind of relatively special fault, should be straight flash method is used to test, especially in higher dc voltage is applied, But shall not be higher than the standard values of dc withstand voltage) Until the point of failure flashover discharge. This type of fault generally appear in the old type of oil in the joint.
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