Application of variable frequency resonance high voltage test device in GIS system

1 Variable frequency series resonance withstand voltage test advantages

The variable frequency series resonance withstand voltage test is to use the inductance of the reactor and the capacitor of the test object to achieve capacitive resonance, and obtain high voltage and high current on the test object. It is a new method and trend of current high voltage tests. Has been widely used.

Frequency conversion series resonance is a resonant current filter circuit, which can improve the distortion of the power supply waveform, obtain a better sinusoidal voltage waveform, and effectively prevent the peak of the harmonic from erroneous breakdown of the test object. The variable frequency series resonance works in a resonance state. When the insulation point of the test object is broken down, the current is immediately detuned, and the loop current quickly drops to one tenth of the normal test current. When flashover breakdown occurs, due to the loss of resonance conditions, in addition to the short-circuit current immediately falling, the high voltage also disappears immediately, and the arc can be extinguished. The process of re-establishing the recovery voltage is very long, and it is easy to disconnect the power supply when the flashover voltage is reached again, so it is suitable for the insulation withstand voltage test of high-voltage and large-capacity power equipment, such as: GIS substations, high-voltage cross-linked power Cables, generators, large transformers, disconnectors, transformers, etc.

2 Application of variable frequency resonance high voltage test device in GIS system

The GIS is adjusted and tested after the entire assembly of the factory is completed. After passing the test, the GIS is transported to the site for installation by means of a transport unit. Mechanical vibration and impact during transportation may cause loosening or relative displacement of fasteners in the original GIS or assembly. During the installation process, there were errors in the process of connection and sealing, which caused the electrode surface to be scratched or misplaced, resulting in electrode surface defects. The dust, conductive particles, and burrs suspended in the air were difficult to completely clean at the installation site. Checking it out will cause an insulation accident. Due to limited test equipment and conditions, most early GIS products did not undergo rigorous field withstand voltage tests. Accident statistics show that although there is no guarantee that an GIS that has undergone a field withstand voltage test will not have an insulation accident during operation, most GIS that has not undergone an on-site AC withstand test has an accident, so GIS must undergo an on-site withstand voltage test.

The on-site withstand voltage of GIS is carried out by using test equipment such as AC voltage and oscillating lightning impulse voltage of oscillating operation impulse voltage. AC withstand voltage test is a common method in GIS on-site withstand voltage test, which can effectively check abnormal electric field structures (such as electrodes damage). At present, due to the limitations of test equipment and conditions, only AC withstand voltage tests are generally performed on site.

(1) Test requirements:

① The GIS should be completely installed, and the SF6 gas should be inflated to the rated density. The main circuit resistance measurement, the test of each component, and the SF6 gas micro-water content and leak detection test have been completed. The secondary windings of all current transformers are grounded, and the secondary windings of voltage transformers are open and grounded.

② Before AC withstand voltage test, the following equipment should be isolated from GIS: high-voltage cables and bus bars; power transformers and most electromagnetic voltage transformers; lightning arresters and protection of spark gaps.

③ Each new installation part of GIS should be subjected to a withstand voltage test. At the same time, when an extension part is subjected to a withstand voltage test, the original parts of adjacent equipment should be powered off and grounded. Otherwise, the sudden breakdown will have an adverse effect on the original equipment.

(2) Method of increasing test voltage:

The test voltage is applied between each phase of the conductor and the shell. The test is performed in phases. The other non-test phases are connected to the shell and grounded. The inlet and outlet sleeves of each phase are pressurized. During the test, each part of the GIS should be tested at least once Voltage. At the same time, in order to avoid insulation aging due to multiple voltages at the same location, the test voltage should be applied in as many locations as possible. Generally, only the relative AC withstand voltage is used on the site. If the disconnector of the circuit breaker is damaged during transportation or installation, or has been disassembled, the AC withstand voltage of the port should be used. The withstand voltage is consistent with the relative AC withstand voltage. The overall capacitance of GIS is large, and the withstand voltage test can be carried out in stages.

3 AC withstand voltage test procedure

The first stage of the GIS field AC withstand voltage test is "sophisticated purification", whose purpose is to remove conductive or non-conductive particles that may exist in the GIS. These particles may be formed due to inadequate cleaning when brought in during installation, or metal debris generated after multiple operations, or cutting debris from fasteners and burrs on the electrode surface. "Sophisticated purification" can make conductive particles move to low electric field areas or particle traps and ablate the burrs on the electrode surface, making it less harmful to insulation. "Sophisticated purification" voltage value should be lower than the voltage value, the time can take several minutes. The second stage is the pressure test, that is, the pressure test is performed after the "sophisticated purification" process is completed, and the time is 1 minute.

4 判断 Judgment of the results of the on-site pressure test

(1) If each component of the GIS has withstood the specified test voltage without breakdown discharge in accordance with the selected complete test procedure, the entire GIS is considered to have passed the test.

(2) If a breakdown discharge occurs during the test, the test shall be based on the discharge energy and various acoustic, optical, electrical, chemical and other discharge effects caused by the discharge, and other fault diagnosis techniques performed during the withstand voltage test. The results are comprehensively judged. In case of discharge, the following steps can be taken:

① Repeat the test by applying the specified voltage. If the equipment or air barrier can withstand the discharge, the discharge is a self-recovery discharge. If the repeated test voltage reaches the set value and the specified time, the test sample is considered to be qualified, otherwise it is performed as follows.

② Disassemble the equipment, open the discharge gas barrier, and check the insulation carefully. After the necessary recovery measures are taken, the next specified pressure test can be carried out.

5 GIS fault location method

If the interval between the input and output lines of the withstand voltage test after GIS segmentation is large, and non-self-recovery discharge or breakdown occurs during the test, it is difficult to determine the exact location of the failure only by human ear monitoring, and it is easy to misjudge and waste. Human, material and unnecessary damage to equipment. If a fault locator developed based on the principle of shock waves generated by the discharge that causes the shell to vibrate is used on site, the discharge interval can be determined. Before each withstand voltage test, install the sensors on the tested parts, especially the circuit breakers, disconnectors, busbars and the connection housings of the insulators at the connection points of each interval. If the discharge or breakdown is unpredicted due to the limited number of sensors, the sensor should be moved after voltage reduction and power down according to the monitoring of the discharge, and the voltage will be increased again until the discharge or breakdown location is found.

AC voltage withstand resonance device for electrical equipment of substations produced by Wuhan Xinchunda Power Equipment Co., Ltd., product stability, high reliability, powerful auto-tuning function, support for multiple test modes, friendly human-computer interaction interface, perfect protection function