After the overall assembly of the factory is completed, adjustments are carried out using GIS. Once the test is passed, the units are transported to the site for installation. During the transportation process, mechanical vibrations, impacts, etc. may cause the original components or fasteners in the assembly to loosen or shift relative to each other. During the installation process, there are mistakes in the connection and sealing processes, resulting in scratches on the electrode surface or installation misalignment, causing defects on the electrode surface. Dust, conductive particle impurities and burrs suspended in the air are difficult to be thoroughly cleaned at the installation site and are also difficult to detect, which can trigger insulation accidents. Due to the limitations of the test equipment and conditions, most of the early GIS products did not undergo strict on-site withstand voltage tests.
The accident statistics show that although it cannot be guaranteed that GIS that have undergone on-site pressure tests will not have insulation accidents during operation, most of the GIS that did not undergo on-site AC pressure tests have experienced accidents. Therefore, on-site pressure tests must be conducted for GIS.
The on-site withstand voltage test of GIS is conducted using test devices such as AC voltage, oscillating operation impulse voltage, and oscillating lightning impulse voltage. The AC withstand voltage test is a common method in the on-site withstand voltage test of GIS, as it can effectively detect abnormal electric field structures (such as electrode damage). Currently, due to the limitations of test equipment and conditions, on-site tests generally only include AC withstand voltage tests.
(1) Requirements for the experiment:
① The GIS should be fully installed, with SF6 gas charged to the rated density. The main circuit resistance measurement, tests for all components, as well as the tests for the micro-water content and leak detection of SF6 gas have been completed. All secondary windings of current transformers are grounded, while the secondary windings of voltage transformers are open-circuited and grounded.
② Before conducting the AC withstand voltage test, the following equipment should be isolated from the GIS: high-voltage cables and busbars; power transformers and most electromagnetic voltage transformers; arresters and protective spark gaps.
③ For each new installation site of GIS, a withstand voltage test should be conducted. Meanwhile, when conducting a withstand voltage test for the expansion part, the original parts of adjacent equipment should be disconnected from power and grounded. Otherwise, a sudden breakdown could have adverse effects on the original equipment.
The method for applying the test voltage for insulation withstand capability:
The test voltage is applied between each phase conductor and the enclosure. The test is conducted separately for each phase, while the other non-tested phases are connected to the enclosure for grounding. The voltage is applied from the inlet and outlet bushings of each phase. During the test, each component of the GIS should be subjected to the test voltage at least once. At the same time, to avoid insulation aging caused by repeated exposure to voltage at the same location, the test voltage should be applied to several locations as much as possible. Generally, only relative ground AC withstand voltage is performed on-site. If the disconnect switch of the circuit breaker is damaged during transportation or installation, or has been disassembled, port AC withstand voltage should be conducted. The withstand voltage value should be the same as the relative ground AC withstand voltage value. If the overall capacitance of the GIS is large, the withstand test can be conducted in sections.
Communication withstand voltage test procedure
The stage of on-site GIS withstand voltage test is called “aging purification”, whose purpose is to remove any conductive or non-conductive particles that may exist inside the GIS. These particles could be those left uncleaned during installation due to contamination, metal debris generated after multiple operations, or cutting debris from fasteners and burrs on the electrode surface. “Aging purification” enables the conductive particles to move to the low electric field area or particle traps and ablate the burrs on the electrode surface, thus eliminating their insulation hazards. The voltage value for “aging purification” should be lower than the withstand voltage value, and the duration can be several minutes. The second stage is the withstand voltage test, which is conducted after the “aging purification” process is completed, lasting for 1 minute.
The judgment of the results from the on-site pressure test
(1) Only when each component of the GIS has withstood the prescribed test voltage according to the selected complete test procedure without any breakdown discharge, can it be considered that the entire GIS has passed the test.
(2) During the test process, if breakdown discharge occurs, a comprehensive judgment should be made based on the discharge energy and various discharge effects such as sounds, lights, electricity, and chemical reactions caused by the discharge, as well as the test results provided by other fault diagnosis techniques during the withstand voltage test. In case of discharge, the following steps can be taken:
Apply the prescribed voltage and conduct repeated tests. If the equipment or gas barrier can still withstand it, this discharge is a self-recovery discharge. If the voltage reaches the set value and the specified time during the repeated tests, the test sample is considered qualified; otherwise, proceed with the following steps.
② Disassemble the equipment, open the electrical isolation, and carefully inspect the insulation condition. After taking the necessary restoration measures, the next prescribed withstand voltage test can be carried out.
The method for locating the fault in GIS withstand voltage test breakdown: If the withstand voltage test is conducted after the GIS is segmented and there are many intervals between the incoming and outgoing lines, and if non-self-recovery discharge or breakdown occurs during the test, it is difficult to determine the exact location of the fault by merely listening with the human ear. Such a method is prone to incorrect judgments and wastes manpower, material resources, and causes unnecessary damage to the equipment. If a fault locator based on the principle of the shock wave generated by discharge causing the vibration wave of the enclosure is developed on-site, the discharge interval can be determined. Before each withstand voltage test, the sensors should be installed separately on the tested parts, especially on the insulation bushings of the circuit breakers, disconnectors, busbars, and the connection parts between each interval. If the discharge or breakdown occurs unpredictably due to the limited number of sensors, then after reducing the voltage and cutting off the power supply, the sensors should be moved and the voltage should be increased again until the location of the discharge or breakdown is found.
Post time: Jul-21-2026