Development Of Testing System For Harmonic Component In Loss Current

Cross-linked polyethylene (XLPE) power cable has outstanding performance. Since appearred it has been rapid development, with a trend of comprehensive alternative to traditional oil-paper insulated cables in electric transmission lines at all voltage levels. But water tree in XLPE cable insulation is the main factor that will affect security and reliability of XLPE cable. Therefore, it is highly important to research diagnosis of water tree for XLPE cable which has important theory and application value in maintenance of reliable operation of power cables. This thesis develop a equipment which can test the condition of water tree aged for cable insulation under laboratory conditions and on site based on measurement of harmonic component in loss current.First, this thesis reviewed the development state of water tree aged detection technology for XLPE power cable at home and abroad, and on this basis, focused on analyzing the testing principles of harmonic component in loss current.In the design of the test system as a whole, the paper presents a design scheme of using the combination of high-voltage current-comparator bridges and high-voltage coaxial cable insulation technology. High-voltage current-comparator bridges can balance out the capacitive current of test products, which greatly improve the precision of loss current testing. And using high-voltage coaxial cable insulation technology, on the one hand to get loss current in high-voltage side, namely, to test ground test products; on the other hand to eliminate the impact of lead cables and terminal of measured cable to test with shield of lead cable grounding.The test system in the paper is transformation base on QS30A type high-voltage current-comparator bridges, focusing on describing the core components of the test system which current comparator design and shielding measures etc.In order to verify the validity of developed test device, the paper tested a number of samples which included loss tangent standards, new cable, water tree aged 3800 hours cable and simulation samples of non-linear and linear insulating composite insulation. The test results of loss tangent standards show that test system has the testing capabilities of testing items capacitance, loss tangent and loss current waveform, which reached the design goals. The test results of before and after aged XLPE cables show that harmonic component in loss current was able to reflect the extent of water tree aged cable, and more sensitive. The test results of simulation samples show that when the test voltage increased of water tree aged, the loss tangent and the third harmonic in loss current of the sample showed super-linear increase. Therefore, the paper suggested that in addition to test the loss tangent and the harmonic component in loss current of the cable in determining the voltage, should observe the laws of loss tangent and harmonic component in loss current with the change of voltage to change two or three voltage level, and evaluation the degree of water tree aged for cable with the law.The test system of harmonic component in loss current in the paper, to meet the test of harmonic component in loss current at the same time could test loss tangent and capacitance of the sample, has a strong practical value in engineering.