What is withstand voltage test
Withstand voltage test generally refers to withstand voltage test, which is one of the main methods to test the ability of electrical appliances, electrical equipment, electrical devices, electrical circuits and electrical safety equipment to withstand overvoltage. It is divided into two types: power frequency withstand voltage test and DC withstand voltage test. The test voltage of the power frequency withstand voltage test is more than one to several times the rated voltage of the equipment under test, and is not less than 1000V. The pressurization time is: 1 minute for equipment with porcelain and liquid as the main insulation, 5 minutes for equipment with organic solids as the main insulation, 3 minutes for voltage transformers, and 10 minutes for oil-immersed power cables. The DC withstand voltage test can draw the leakage current-voltage characteristic curve based on the leakage current values at different test voltages. The withstand voltage test of electrical equipment can reveal local defects, moisture and aging of the insulation.
Basic principles of withstand voltage testing
A higher than normal operating voltage is applied to the insulator of the device under test for a specified period of time. If the insulation is good enough, the applied voltage will only produce a small leakage current. If the leakage current of the insulator of a device under test remains within the specified range within a specified period of time, it can be determined that the device under test can operate safely under normal operating conditions.
Pressure test method
1. Hydraulic test
1) During the test, an exhaust port should be provided on the top of the container, and the air in the container should be exhausted when filling. During the test, the outer surface of the container should be kept dry.
2) Pressurization can only occur when the wall temperature of the pressure vessel is approximately the same as the liquid temperature.
3) The pressure should rise slowly during the test. After reaching the specified test pressure, the pressure holding time is generally not less than 30 minutes, and then the pressure is reduced to 80% of the specified test pressure, and maintained long enough to test all welded joints and connecting parts. Check. If there is leakage, repair it and retest.
4) The pressure should remain unchanged during the inspection, and continuous pressurization should not be used to maintain the pressure constant. During the hydraulic test, it is not allowed to tighten bolts under pressure or apply external force to pressure components.
5) For spherical storage tanks, the hydraulic test method should comply with the requirements of 8.10.4.4 in GB 12337-1998.
2. Air pressure test
1) There should be safety measures for air pressure testing, which must be approved by the technical director of the testing unit. During the air pressure test, the safety department of the test unit shall conduct on-site supervision of the implementation of safety measures.
2) The pressure should rise slowly during the test. When it reaches 10% of the specified test pressure and does not exceed 0.05MPa, the pressure should be maintained for 5 minutes. All welded joints and connection parts should be inspected for initial leakage with soap solution or other leak detection fluid. If there is any leakage, , retest after repairing. After passing the initial leakage inspection, slowly increase the pressure to 50% of the specified test pressure. If there are no abnormal phenomena, then increase the pressure step by step at 10% of the specified test pressure for each level until the specified test pressure. After maintaining the pressure for 30 minutes, reduce the pressure to 87% of the specified test pressure and maintain it for a long enough time. Check all welded joints and connecting parts for leaks again. If there is a leak, repair it and then retest according to the above regulations.
3) The pressure should remain unchanged during the inspection, and continuous pressurization should not be used to maintain the test pressure unchanged. During the air pressure test, it is strictly prohibited to tighten bolts under pressure and apply external force to pressure components.
4) For spherical storage tanks, the air pressure test method should also comply with the requirements of 8.10.5.5 in GB 12337-1998.
The purpose of pressure test
All products have default voltage/current tolerances at the beginning of design. The withstand voltage test evaluates the insulation capability of the product by applying a high voltage to the product far beyond normal conditions and measuring the leakage current. When the leakage current exceeds a certain level, it will cause harm to the operator and even endanger life safety. Therefore, the withstand voltage test is a common but important electronic safety test.
The withstand voltage test is to apply a higher test voltage to the test product, and then maintain it for a period of time and then drop it to zero. Different products apply voltage for different times, ranging from 2S-5min, which is determined according to the different requirements of different test products. , there are also some things that need to be paid attention to during the withstand voltage test. Grounding measures are required for the withstand voltage test. During the test, you must stand on an insulating pad or sit on a stool padded with insulating material. You cannot touch the metal parts of the instrument with your hands, because The test voltage of the instrument is tens of kilovolts, which may cause personal safety. The withstand voltage tester cannot be tested in an overtime environment because the humid air will turn into a conductor, and breakdown will occur during the test, causing the test The results are inaccurate.
The withstand voltage test includes long-term test and field test. The long-term test is a test with high requirements. The factory test is widely used. Generally, the test time is within 5S. If the detected overvoltage meets the specified value, it is qualified. The withstand voltage Factory testing is widely used in insulation materials, switch factories, wire and cable material factories and other industries, and has become one of the indispensable tests.
Measurement standards for withstand voltage testing
When performing a withstand voltage test, the test products with different technical specifications will have different measurement standards. For general equipment under test, the withstand voltage test is to measure the leakage current value between the live wire and the chassis. The basic rule is: use twice the working voltage of the object under test plus 1000V as the standard voltage for the test. The test voltage of some products may be higher than this specified value. According to the provisions of IEC61010, the test voltage must gradually rise to the required test voltage value (such as 5kV, etc.) within 5s to ensure that the test voltage value is stably applied to the insulator under test for no less than 5s. At this time, the leakage of the circuit under test By comparing the current value with the leakage current threshold specified in the standard, it can be judged whether the insulation performance of the product under test meets the standard.
After the test is completed, the test voltage must gradually decrease to zero within the specified time. When performing a withstand voltage test, the test products with different technical specifications will have different measurement standards. For general equipment under test, the withstand voltage test is to measure the leakage current value between the live wire and the chassis. The basic rule is: use twice the working voltage of the object under test plus 1000V as the standard voltage for the test. The test voltage of some products may be higher than this specified value. According to the provisions of IEC61010, the test voltage must gradually rise to the required test voltage value (such as 5kV, etc.) within 5s to ensure that the test voltage value is stably applied to the insulator under test for no less than 5s. At this time, the leakage of the circuit under test By comparing the current value with the leakage current threshold specified in the standard, it can be judged whether the insulation performance of the product under test meets the standard. After the test is completed, the test voltage must gradually decrease to zero within the specified time.
A test that determines whether the insulation material and spacing of the equipment meet the requirements by giving the equipment a voltage higher than its rated voltage and maintaining it for a certain period of time. Withstand voltage testing is an important part of electrical safety standards and is used to discover local defects, moisture and aging of product insulation.
The original withstand voltage tester was just a simple transformer and voltage regulator, which converted the mains power into the required test voltage and applied it to the sample being tested. However, due to the fluctuation of the mains power, people sometimes have to adjust the output voltage to a degree greater than 20% of the actual required value to prevent possible fluctuations in the input voltage. At the same time, many safety standards specifically require that the withstand voltage tester used has a capacity of more than 500VA. This is to ensure that the withstand voltage tester still has a large enough output voltage when the sample has a large leakage current.
However, with the development of technology, this requirement has become outdated. New withstand voltage testers all have sufficient source voltage regulation and load regulation, and only some old safety standards still have this requirement. In fact, many new standards no longer include 500VA capacity in the requirements for withstand voltage testers. From the user's perspective, the 500VA capacity of the withstand voltage tester is a threat to the operator. Due to different testing standards, mass testing of assembly lines and people's increasing awareness of the safety performance of electrical appliances, the functions of withstand voltage testing devices are required to be improved accordingly. The functions of voltage regulator-type withstand voltage testing instruments are limited and full electronic program control technology is used. New withstand voltage testers based on power electronics technology are becoming popular.
At present, this type of voltage withstand test instrument is mainly divided into two types: one uses a single-chip microcomputer as the monitoring center and digital waveform synthesis technology + linear power amplifier as the test source; the other uses a single-chip microcomputer as the monitoring center and SPWM (sinusoidal pulse width modulation) Pulse generator + IGBT (Insulated Gate Bipolar Transistor) pulse power amplifier is used as the test source.
The structure of this withstand voltage tester is relatively complex. Its anti-interference ability and reliability depend on the design of the whole machine and the quality of electronic components. The output waveform distortion is small, the output frequency is variable (50Hz/60Hz), and the output voltage adjustment range is wide. The control accuracy is high, the output voltage is stable within the power range, and is not affected by load changes. The output power of the test source can generally reach 500W. The instrument can automatically protect when outputting over power. The output voltage setting is performed without voltage output. It has good safety, and it is easy to detect potential hazards in the insulation performance of the test product such as arc, creepage, flashover, etc. The voltage output mode can meet various standard requirements through software, such as segmented voltage boost, timed voltage boost, Fixed-speed voltage boosting, etc., can conduct breakdown point analysis, fast breakdown protection, and leakage current display resolution up to nanoampere level, which is very suitable for high-standard electrical appliances or component testing. There is little interference to the power grid during operation. The calibration of the instrument is carried out through buttons or communication interfaces, which facilitates the completion of test statistics and sorting work with the computer network, and can continuously test the tested products.
The withstand voltage tester is mainly composed of an AC (DC) high-voltage power supply, a timing controller, a detection circuit, an indication circuit and an alarm circuit. The basic working principle is: the instrument under test is generated under the test high voltage output by the withstand voltage tester. Compare the leakage current with the preset judgment current. If the detected leakage current is less than the preset value, the instrument passes the test. When the detected leakage current is greater than the judgment current, the test voltage is instantly cut off and an audible and visual alarm is issued, thereby Determine the compressive strength of the part under test.
The technical indicators of the withstand voltage tester mainly include its output AC and DC voltage and preset cut-off current. Analog indicating voltage withstand testers usually express their maximum allowable voltage error in the form of quoted errors.
Withstand voltage test, also known as Hipot Test or Dielectric Test, is probably the most familiar and used product process safety test. Its importance is demonstrated by the fact that it is referenced in virtually every safety standard.
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