With the development of urban construction, the proportion of power cables in urban power supply is increasing. In some cities, urban transmission lines have gradually replaced overhead transmission lines with the number of cables and the extension of running time. It is also more and more frequent due to the concealment 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 properly select fault test equipment, find cables accurately and quickly. Faults, shortening the time of power failure and becoming a concern of cable operators. This paper introduces the current 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 their nature. Fault and parallel (short circuit) faults, the latter according to whether there is metal sheath or shield outside the main insulation can be divided into main insulation fault (external metal sheath or shield) and outer sheath (outer sheath) fault (no metal Jacket or shield) main insulation fault according to the test method, according to the insulation resistance Rf of the fault point For 1 metal short circuit (low resistance) fault, different instruments and methods choose Rf different, generally Rf<10Z. (Z. is cable impedance); 2 high resistance fault; 3 intermittent (flashover) fault 3 is not absolute The boundary is mainly determined by the field test method, and is related to the capacity and internal resistance of the equipment. 2 Cable fault test method Comparison of cable fault test steps are: 1 diagnosis fault, 2 fault pre-positioning; 3 fault fixed point (fine positioning) The faults and their corresponding test methods are shown in Table 1. Table 1 Power cable faults and detection methods Fault type Pre-positioning method Fine positioning method Broken-line fault Lu low-voltage pulse reflection method ▲ Bridge method Acoustic-magnetic synchronization method Low-resistance fault Lu low-voltage pulse reflection Method ▲ bridge method ★ audio induction method ★ sound and magnetic synchronization method, current direction method secondary pulse method (SIM) ▲ flashing method main high resistance fault ★ high voltage bridge method sound method magnetic and magnetic synchronous method fault secondary Pulse method (DC resistance to intermittent fault (flashover) after voltage breakdown) ▲ attenuation method ▲ DC flash method acoustic and magnetic synchronization method outer sheath failure high voltage bridge method ▲ acoustic magnetic synchronous method pressure drop Faro step Voltage law note Recommended for use; ★ is conditional; ▲ is available; test method for 3 power cables is not recommended. Before 1970, power cable faults were usually tested using bridge method and low voltage pulse reflection method. Very accurate, but not applicable to high resistance faults. Later, DC flash and impact flashing methods were used to test intermittent faults and high-impedance faults, both of which can be divided into current and voltage flashing methods. The voltage method can measure high rate, the waveform is clear and easy to judge, and the blind area is twice as small as the current method, but the wiring is complicated. When the partial pressure is too large, it is dangerous to people and instruments; the current law is opposite. The current two methods are domestic high-resistance fault test. The mainstream method of the instrument basically solves the problem of high-resistance fault test of the cable, but the instrument has a blind zone, and the waveform is sometimes not obvious enough. By human judgment, the instrument error is relatively large. 1990s, the foreign invention of the second pulse method, that is, combined with the impact of the high-voltage generator The flashover technology triggers the emission of a low-voltage pulse through the internal device at the moment of the arcing of the fault point. This pulse is short-circuited at the flash point of the fault point (the resistance value of the arc is very low), and is memorized in the instrument. After the arc is extinguished, Recurrence-measurement pulse passes through the fault to the end of the cable and an open-circuit reflection occurs. Comparing the two low-voltage pulse waveforms (see) can easily determine the position of the fault point (breakdown point). It is the most advanced basic test method based on the second pulse. The method has the Austrian high voltage technology to emphasize the arcing and the trigger pulse, and the internal communication device dampens the inrush current. The impact width of the inrush current is added; Seba uses an arc-stabilizer to emphasize the extended arc time and ensure that the low-voltage pulse reaches the Baur company's precision cable fault test during the arcing. The principle of the system is shown in the device and the domestic current or voltage method tester. Compared with the following advantages: the secondary pulse schematic diagram is compact in structure, simple in wiring, easy to switch, safe and reliable, automatic matching and automatic judgment, and can be printed or saved. "tm* test can eliminate the blind zone and pre-test the pulse wave to reach the lead through the instrument. The end time "tm* value is entered into the system. In the same method, *tm* is a fixed value, regardless of the wave speed selection. The tm time point of the measured waveform is the high precision of the measured cable. The sampling frequency is 200MHz, and the accuracy is up to 0. 4m. The cable status and the automatic positioning test with the fault during operation will be the cable GIS (Geographic Information System) and GPS ( Global Positioning System) for joint application, real-time, dynamic online monitoring and will be the future development trend. At present, some important cable lines in Japan are equipped with an online monitoring and fault testing system. The monitoring system will automatically detect the fault location of the cable and transmit it to the satellite system. The user terminal can know the actual location of the fault and realize fully automated management. 4 Configuration cable fault test equipment The consideration of high-performance equipment is high, but when the service scope reaches a certain scale, the loss of power failure is far greater than the price of the instrument.
In order to cope with all possible cable faults, test single-test instrument, pre-positioning equipment (including bridge, echo reflectometer, supporting high-voltage device and signal generator) fine locator (step voltage method, acousto-magnetic synchronization method) , audio locator) and so on. The path tester is especially important for direct buried cable faults that do not know the path, but it is disturbed by underground parallel metal pipelines in the actual measurement, and the damage is large. Seba's new products use double induction coils to superimpose the inverted wave of the largest normal wave minimum method. It can solve the interference problem. The capacitor C in the high-voltage impact generator is related to the cable test. The foreign instruments mostly use 2PF or 4PF capacitors. However, for longer cable lines, intermittent fault insulation resistance, or low-voltage cable fault test, the waveform impact energy CU2 is often not obtained. Considering the adverse effects on the main insulation and the volume limitation of the instrument, U should not be too large (not Exceeding the pre-test voltage of 5 (%~70%), only the increase of the capacitance, the impact energy is increased, so that the fault point has a long arcing time, the discharge is thorough, and the test waveform is easy to obtain, especially for the low-voltage cable. The arc-extending device or widening the shock pulse extends the arc-starting time function, and the triggering pulse is well matched, and the capacitance 4 F is sufficient. The domestic equipment configuration should select a larger capacitor, but increasing the capacitance makes the instrument bulky and also changes the instrument. Matching equipment with high sampling frequency to ensure high positioning accuracy.
For faults or intermittent faults of high voltage cables of 110kV and above, high voltage class equipment should be selected and tested by attenuation method.
5 The main experience of cable fault test application Tested nearly 30 insulation faults with Baur and Seba cable fault test and positioning equipment, the success rate reached 100%, and the fault points were determined within 12h. The main experience of the test is: the cable must be required to provide complete cable data (length, path reserved, joint position, etc.). The main insulation fault pre-positioning is easier and more difficult to locate; on the contrary, the outer sheath fault pre-position Difficult and precise positioning (step voltage method) is very accurate and easy. In special cases (when the insulation and outer sheath faults are common), the two can be combined to make the grounding connection of the low-voltage cable joints not standardized. When testing, pay attention to the cable grounding and grounding. When no obvious waveform is detected at one end of the cable, change the other end or increase the arcing current and measure again. A good waveform can be obtained. When the measured cable is long and the waveform is not detected at the predetermined position, the surge voltage can be increased. Adjust the trigger delay to get the waveform. For intermittent faults, when the surge voltage cannot be broken down, it can be broken down by the conventional DC withstand voltage test.
The position should be equipped with test equipment, such as electric å‘—J path test è¤“å« H.AU h post down to the first page of the page) bookmark1 pre-positioning error includes: a. instrument error, constant; b. measurement error, greater impact Should pay attention to whether there are reserved loops at both ends of the cable; c. Improper error of wave speed value should be calculated by cable length; d. Waveform judgment error depends on instrument performance and tester experience intermediate rise, £1 I splitter Due to its high weight and low mobility, the frequency conversion power supply is mainly used in the laboratory frequency conversion resonance test system, which not only meets the pressure requirements of 110kV XLPE cable, but also has the advantages of light weight and good mobility, and is suitable for field test.
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 frequency modulation. The frequency adjustment range is 30~300Hz. In accordance with GIGREWG21.03 recommended AC frequency and approximate power frequency (30 ~ 300Hz) AC voltage requirements This AC voltage test can reproduce the field strength similar to the operating conditions, practice has proved to be an effective method.
3 On-site acceptance test example The Shandong Power Grid conducted a field AC withstand voltage acceptance test on a 110kV XLPE cable using a variable frequency resonant test device. The model number is YJLW03; the rated voltage is 64/110kV; the conductor size is 1 claw seven <300 claw 2 copper conductor; the capacitance is 0.1391 corpse / 1
Custom Curtains,Tab Top Curtains,Grommet Curtains,Jacquard Grommet Curtain
SHAOXING NINGBO DECORATTION FABRIC FACTORY , https://www.curtaincushion.com