Equipment Introduction
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It consists of a variable frequency power supply, an excitation transformer, a high-voltage reactor, and a capacitive voltage divider. The capacitance of the test object and the reactor form a series resonant connection; the voltage divider is connected in parallel with the test object to measure the resonant voltage on the test object and serve as an overvoltage protection signal; the frequency-modulated power output is coupled to the series resonant circuit through the excitation transformer, providing the excitation power for the series resonance. Shanghai Dafan specializes in R&D and production, adopting a modular design to greatly reduce labor intensity.
Product Aliases
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Variable frequency series resonant AC withstand voltage test device, variable frequency series resonance, variable frequency series resonance, series resonance, frequency-modulated series resonance, series resonant withstand voltage test device, series resonant test equipment, cable withstand voltage test device, power frequency withstand voltage test device, high-voltage cross-linked cable AC withstand voltage test equipment, AC withstand voltage test device, frequency-modulated resonance, frequency-modulated series resonant AC withstand voltage test device, AC series resonance, AC variable frequency series resonance, variable frequency resonance, variable frequency series resonance, series resonance test device, series resonance withstand voltage device, GIS AC withstand voltage test device, generator power frequency (AC) withstand voltage test device, motor power frequency (AC) withstand voltage test device, transformer power frequency (AC) withstand voltage test device, etc.
Current Status Analysis
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Why do relevant domestic and foreign departments widely recommend replacing DC withstand voltage with AC withstand voltage? With the development of the national economy and the increase in the voltage level of urban power supply, cross-linked polyethylene insulated power cables (XLPE) have been increasingly widely used at home and abroad due to their reasonable process and structure, excellent electrical performance, and safe and reliable operation characteristics. Especially in the field of high-voltage power transmission, great progress has been made. Compared with oil-filled cables, cross-linked cables are convenient to lay and install, simple to operate and maintain, and there is no oil leakage problem. However, in recent years, operation and research have shown that the insulation of cross-linked polyethylene cables is prone to tree-like discharge during operation, causing insulation aging and damage, which seriously affects the service life of cross-linked polyethylene insulated power cables. Therefore, fully understanding the insulation characteristics of cross-linked cables and timely and effectively discovering and preventing certain defects in the insulation are of great significance for ensuring the safe operation of equipment and even the system. This article elaborates on the main factors affecting the insulation of cross-linked cables and the principle of cable handover tests, and believes that it is necessary and feasible to implement AC withstand voltage tests on cross-linked cables on site. In order to ensure the safe and reliable operation of cables, relevant international standards have made clear provisions for various tests on cables. The main test items include: measuring insulation resistance, DC withstand voltage, and leakage current. Among them, measuring insulation resistance is mainly to check whether the cable insulation is aged, damp, or has insulation defects exposed during the withstand voltage test. The DC withstand voltage and leakage current tests are carried out simultaneously, with the purpose of discovering defects in the insulation. However, in recent years, domestic and foreign test and operation experience has proven that DC withstand voltage tests cannot effectively discover insulation defects in cross-linked cables, and may even cause insulation hazards in cables. In Germany, Sechiswag Company had 87 failures in 41 circuits of 10 kV XLPE cables from 1978 to 1980; in Sweden, more than 9,000 km of 3 kV to 24.5 kV XLPE cables were put into operation, with 107 failures. Domestically, cable accidents have also occurred many times, and a considerable number of cable faults are caused by the negative effects of frequent DC withstand voltage tests. Therefore, relevant domestic and foreign departments widely recommend using AC withstand voltage to replace the traditional DC withstand voltage. From the 1980s to the mid-1990s, advanced countries such as Canada, Germany, and the United States formulated corresponding AC withstand voltage test standards and promoted their application. Since the late 1990s, regions in China such as Guangdong, Beijing, Shanghai, Zhejiang, and Shandong have issued interim regulations for AC testing of XLPE cables. The national standard GB50150-2006 "Standard for Handover Test of Electrical Equipment Installation Engineering" recommends the use of variable frequency series resonant withstand voltage method.
