The VLF hipot tester under Wuhan UHV can help many power workers conduct various power tests more conveniently.
In insulation testing of power systems, withstand voltage testing is an important means to ensure the safe operation of equipment. Although traditional power frequency withstand voltage tests are widely used, for capacitive equipment such as cables, generators, GIS, etc., the test current is large, the equipment is bulky, and the energy consumption is high. With the development of technology, ultra-low frequency withstand voltage testing technology (VLF) has gradually replaced traditional methods and become the mainstream solution for insulation testing of medium and high voltage cables and large capacity electrical equipment. As the core of this technology, the VLF hipot tester is widely used in on-site inspection and equipment handover testing of power systems due to its advantages of small size, low energy consumption, and accurate testing.
The main function of the VLF hipot tester is to conduct insulation withstand voltage tests, which means applying extremely low frequency (usually 0.1Hz, 0.05Hz, or 0.02Hz) AC high voltage to the test sample and maintaining it for a specified time to test the insulation withstand voltage capability. When the equipment does not experience breakdown or flashover during the testing process, its insulation performance can be judged as qualified. This project is applicable to equipment such as power cables, cable joints, generators, motor stators, transformers, and GIS, and is used to verify whether the insulation layer is damp, aged, or has potential partial discharge hazards.
During the withstand voltage test, the VLF hipot tester can also synchronously monitor the leakage current, and determine the absorption characteristics and loss of the insulation medium by recording the current changes in real time. Excessive leakage current often indicates insulation defects or moisture issues, therefore leakage current testing is also an important indicator for insulation health assessment. Some high-end models can also draw voltage current characteristic curves to analyze insulation aging trends or moisture levels, providing data support for equipment maintenance.
In addition, the VLF hipot tester can also be used for insulation aging assessment and status detection of electrical equipment. For equipment that has been in operation for many years or has been out of service for a long time, the degree of insulation degradation can be determined through withstand voltage testing and current monitoring, potential hazards can be detected in advance, and faults can be avoided during operation. Compared with power frequency withstand voltage, VLF testing can complete the test with less energy under the same electrical stress, which can truly reflect the insulation condition without causing damage to aging equipment. Therefore, it is very suitable for pre operation or preventive testing of equipment.
Some models of VLF hipot testers also support online use with partial discharge detection systems, which can monitor and analyze discharge signals while applying high voltage, thereby determining whether there are small defects inside the insulation. This "withstand voltage+partial discharge" joint testing method has become an important means of insulation diagnosis for cables and large motors, which can effectively improve the accuracy and reliability of testing.
In the installation, operation, and maintenance of power system equipment, VLF hipot testers are also commonly used equipment for handover and preventive testing. According to national standards, medium and high voltage cables must undergo ultra-low frequency withstand voltage testing before being put into operation to verify whether the construction process and insulation quality meet the standards. Through experiments, not only can we confirm whether the cable has safe operating conditions, but we can also avoid operational accidents caused by potential insulation defects.
In general, the main testing items that can be completed by the VLF hipot tester include insulation withstand voltage test, leakage current test, insulation aging evaluation, partial discharge trend detection, as well as cable and equipment handover and preventive testing. It can not only comprehensively evaluate the insulation health status of equipment, but also help operation and maintenance personnel detect potential faults in advance.