The Measurement Of Loss Current Harmonics Of XLPE CableInsulation Under The Variable Frequency Power Supply

XLPE power cable lines have become the city’s main power distribution lines. To ensure the safety of the city power supply, the development of insulation diagnostic technique, test equipments, and operating guidelines or standards for XLPE power cables are urgent need for power system in city.Water-tree degradation is the dominant mode for XLPE power cable insulation. It influences operation reliability of power cable directly from long term view. Effective diagnosis of water-tree degradation condition of XLPE cable is the premise of assuring XLPE cable operating safely. Water tree aged XLPE insulation has characters of nonlinear conductance. Under standard pure sinus voltage, loss current of XLPE insulation will include harmonic components. Harmonic components method can diagnose water-tree degradation extent of XLPE power cable.First of all, according to the actual situation of loss current measurement, the measurement system was improved and perfected. In the hardware aspect micro current amplifier was applied, in terms of software the loss current amplitude and phase analysis function was applied, and thus more effective loss current information was extracted. Second, in the proving test, it is confirmed that the developed loss current harmonic component test device can test loss current and harmonic components, at the same time,it can measure the test product’s equivalent capacitance and loss factor, which has the good consistency. Those index have reached the expected developmental target.The experiments confirm that the used for cable lines withstand voltage test of the series with variable frequency resonant high voltage power supply can be used for medium loss current harmonic components, which can replace the foreign expensive standard sine wave power supply under the variable frequency power supply.Verification test were conducted on the cable lines in Zhenjiang, Changzhou, Wuxi and other power supply8cable lines, total test cable back in23, we found that2cable lines had the phenomenon of water-tree degradation, and this phenomenon exists in the three phase of cable. Taking field sampling of aged cables which are detected with water tree and making physico-chemical analyses of samples, we found that the cable insulation were in a large number of butterfly-shaped water tree. The other6lines were in good condition, which is still in normal operation. Thus it confirms that the measurement of loss current harmonics of XLPE cable insulation under the variable frequency power supply in the aspect of diagnosing XLPE power cable insulation water-tree degradation degree is feasible and effective.Compared with the Japanese technology, the cost of the test system and equipment weight were greatly reduced, and the harmonic method was promoted to practical application and popularization. It built up a solid foundation for the research and development for the latter part of a higher voltage vehicle-mounted on-site diagnostic system, it also contributed to diagnostic techniques and standards which based on loss factor, loss current harmonics component of water tree aging of cable insulation.