It consists of a variable frequency power supply, an excitation transformer, high-voltage reactors, and a capacitive voltage divider. The capacitance of the test object and the reactor form a series resonance connection; the voltage divider is connected in parallel with the test object to measure the resonance voltage on the test object and serve as an overvoltage protection signal; the frequency-modulated power output is coupled to the series resonance circuit through the excitation transformer, providing the excitation power for series resonance. Shanghai Dafan specializes in R&D and production, adopting a split-component design to greatly reduce labor intensity.
Current Situation Analysis
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 gained increasingly widespread use both domestically and internationally 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, significant progress has been made. Compared with oil-filled cables, XLPE cables are more convenient to lay and install, simpler to operate and maintain, and do not have the problem of oil leakage. However, recent years of operation and research have shown that the insulation of XLPE cables is prone to treeing discharge during operation, causing insulation aging and damage, which seriously affects the service life of XLPE insulated power cables. Therefore, fully understanding the insulation characteristics of XLPE cables and effectively detecting and preventing certain defects in the insulation in a timely manner is of great significance for ensuring the safe operation of equipment and even the entire system. This paper elaborates on the main factors affecting XLPE cable insulation and the principles of cable commissioning tests, and believes that it is necessary and feasible to conduct AC withstand voltage tests on XLPE cables on site. To ensure the safe and reliable operation of cables, relevant international standards have clearly stipulated various tests for 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 detecting defects in the insulation. However, recent test and operation experience both domestically and internationally has proven that DC withstand voltage tests cannot effectively detect insulation defects in XLPE cables and may even cause insulation hazards. In Germany, Sechiswag Company experienced 87 faults 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 faults occurring. Domestically, cable accidents have also occurred multiple times, and a considerable number of cable faults are caused by the negative effects of frequent DC withstand voltage tests. Therefore, relevant departments both domestically and internationally widely recommend using AC withstand voltage to replace 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. Starting from the late 1990s, regions in China such as Guangdong, Beijing, Shanghai, Zhejiang, and Shandong issued interim regulations for conducting AC tests on XLPE cables. The national standard GB50150-2006 "Standard for Handover Test of Electrical Equipment Installation Engineering" recommends the use of variable frequency series resonance withstand voltage method.
Product Features
1. One of the few in the country to pass the strict type test appraisal by the national authoritative department - the Electric Power Industry Electrical Equipment Quality Inspection and Testing Center (Wuhan High Voltage Research Institute), with reliable quality, ensuring the safety of test personnel, test objects, and the test equipment itself;
2. In the 2008 national equipment competition organized by Northeast Electric Power Research Institute, it passed all test items in one go, being the only one to meet all national standard requirements including the 60-minute temperature rise, and ranked among the top again in the competition results;
* With excellent quality and professional service, it has gained the recognition of many professional customers (such as Guangxi Electric Power Research Institute, Hulunbuir Electric Power Bureau, Qiqihar Electric Power Bureau, China Water Conservancy and Hydropower Sixteenth Engineering Bureau, China Chemical Group, etc.)
* Small size, light weight, especially suitable for on-site use;
* All major components are imported from world-renowned enterprises, including Texas Instruments, Intel, Siemens, Schneider, Toshiba, Fuji, etc., ensuring stable and reliable performance;
* Comprehensive and reliable overvoltage, overcurrent, discharge, overheating, and zero-start protection, with an action time of 1 microsecond;
* The equipment comes with a built-in micro printer, which can promptly print and save test data;
* Designed with military-standard anti-vibration and dustproof features, resistant to long-distance transportation and harsh usage environments;
* One-key mouse-style knob "foolproof" operation, with a large-screen LCD display;
* Unique software calibration function, convenient for users to calibrate meters, ensuring the accuracy of high voltage values;
* German Rittal-designed all-aluminum alloy chassis, usable both vertically and horizontally, lightweight and beautiful, greatly facilitating on-site use;
* Keep promises, provide professional and timely service, and strive to meet customer needs to the greatest extent;
* The product is stable and reliable, with a three-year warranty (ten-year warranty for the main unit) and lifelong maintenance;
Product Principle
We know that when the circuit frequency f=1/2π√LC, the circuit resonates, and at this time the voltage on the test object is Q times the output voltage at the high-voltage end of the excitation transformer. Q is the quality factor of the system, i.e., the voltage resonance multiple, generally ranging from tens to over a hundred. First, adjust the output frequency of the variable frequency power supply to make the circuit resonate in series, then, under the condition of circuit resonance, adjust the output voltage of the variable frequency power supply to make the voltage on the test object reach the test value. Due to the resonance of the circuit, a relatively small output voltage from the variable frequency power supply can generate a high test voltage on the test object CX.
Shanghai Dafan Schematic Diagram
Main Technical Parameters of the Equipment
* Working power supply: 220V/380V, 50HZ * Test capacity: 30-30000KVA
*(Test voltage: 1000KV and below * Resonance frequency range: 20-300Hz
* Test voltage waveform: sine wave, with waveform distortion rate less than or equal to 0.3%
* Test voltage accuracy: Class 1
* Frequency adjustment: 0.01Hz * Protection response time: less than 1 microsecond
* The system has overvoltage protection, overcurrent protection, discharge protection, breakdown trip protection, and overheating protection.
Product Aliases
Variable frequency series resonance AC withstand voltage test device, variable frequency series resonance, variable frequency series resonance, series resonance, frequency-modulated series resonance, series resonance withstand voltage test device, series resonance test equipment, cable withstand voltage test device, power frequency withstand voltage test device, high-voltage XLPE cable AC withstand voltage test equipment, AC withstand voltage test device, frequency-modulated resonance, frequency-modulated series resonance 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.
