Analyzing the Principle of Medical Withstand Voltage Tester from Electrical Equipment
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- High-voltage electrical equipment must maintain good insulation during operation, so a series of insulation tests should be carried out from the beginning of equipment manufacturing. These tests include: raw material testing during the manufacturing process, intermediate testing during manufacturing, product qualification and factory testing, handover testing after installation at the use site, and insulation preventive testing for maintenance and operation during use. The handover test and preventive test of electrical equipment are the two most important tests. The People's Republic of China electric power industry standards and national standards: DL/T 596-1996 "Regulations for Preventive Testing of Electric Power Equipment" and GB 50150-91 "Standard for Handover Test of Electrical Equipment" detail the content and standards of each test.
2. Insulation Preventive Test
The preventive insulation test of electrical equipment is an important measure to ensure the safe operation of equipment. Through testing, the insulation condition of the equipment can be grasped, hidden dangers in insulation can be discovered in time, and eliminated through maintenance. If serious problems occur, the equipment must be replaced to avoid irreparable losses, such as power outages or equipment damage caused by insulation failures during operation.
Insulation preventive tests can be divided into two categories: one is non-destructive test or insulation characteristic test, which refers to measuring various characteristic parameters at low voltage or by other methods that will not damage insulation, mainly including measuring insulation resistance, leakage current, dielectric loss tangent, etc. Thereby judging whether the insulation has any defects. Experiments show that this method is effective, but it cannot yet be used to reliably judge the electrical strength of insulation. The other is destructive test or withstand voltage test. The voltage applied in the test is higher than the working voltage of the equipment, and the requirements for insulation testing are very strict, especially exposing concentrated defects with greater risk, and ensuring that the insulation has a certain electrical strength, mainly including DC withstand voltage, AC withstand voltage, etc. The disadvantage of the withstand voltage test is that it will cause some damage to the insulation.
3. Electrical Equipment Handover Test
In order to meet the needs of electrical installation projects and electrical equipment handover tests, and to promote the promotion and application of new technologies for electrical equipment handover tests, the national standard GB 50150-91 "Standard for Handover Test of Electrical Equipment" details the content and standards of various tests. In addition to some insulation preventive tests, electrical equipment handover tests also include other characteristic tests, such as transformer DC resistance and ratio tests, circuit breaker loop resistance tests, etc.
4. Basic Principles of Insulation Preventive Test
4.1 Insulation Resistance Test Insulation resistance test is the most widely used and convenient item in insulation testing of electrical equipment. The value of insulation resistance can effectively reflect insulation defects, such as overall moisture, dirt, severe overheating and aging. The most commonly used instrument for testing insulation resistance is the insulation resistance tester (insulation resistance tester).
Insulation resistance testers (isolation resistance tester) usually have types of 100V, 250V, 500V, 1000V, 2500V, 5000V, etc. The insulation resistance tester should be used according to DL/T596 "Regulations for Preventive Testing of Electric Power Equipment".
4.2 Leakage Current Test
The voltage of a general DC insulation resistance tester is lower than 2.5KV, which is far lower than the working voltage of some electrical equipment. If it is considered that the measurement voltage of the insulation resistance tester is too low, the leakage current of electrical equipment can be measured by increasing DC high voltage. Common equipment for measuring leakage current includes high-voltage test transformers and DC high-voltage generators. When the equipment has defects, the leakage current at high voltage is much greater than that at low voltage, that is, the insulation resistance at high voltage is much smaller than that at low voltage.
The medical withstand voltage tester measures the leakage current of equipment, which is essentially not much different from insulation resistance, but leakage current measurement has the following characteristics:
(1) The test voltage is much higher than that of the insulation resistance tester, so defects in the insulation itself are easily exposed, and some concentrated defects that have not yet penetrated can be found.
(2) Measuring the relationship between leakage current and applied voltage helps to analyze the type of insulation defects.
(3) The microammeter used for leakage current measurement is more accurate than the insulation resistance tester.
4.3 DC Withstand Voltage Test
The DC withstand voltage test has a higher
AC withstand voltage test sometimes makes some weaknesses in insulation more prominent. Therefore, before the test, insulation resistance, absorption ratio, leakage current, dielectric loss and other test items must be carried out. If the test results are qualified, AC withstand voltage test can be carried out. Otherwise, it should be handled in time, and after all indicators are qualified, AC withstand voltage test should be carried out to avoid unnecessary insulation damage.
4.5 Dielectric Loss Factor tgδ Test
Dielectric loss factor tgδ is one of the basic indicators reflecting insulation performance. The dielectric loss factor tgδ reflects the characteristic parameters of insulation loss. It can sensitively detect overall insulation of electrical equipment affected by moisture, deterioration and degradation, as well as local defects of small-volume equipment.
Compared with insulation resistance and leakage current tests, the medical withstand voltage tester has obvious advantages in dielectric loss factor tgδ. It is independent of factors such as test voltage and test sample size, making it easier to judge the insulation changes of electrical equipment. Therefore, dielectric loss factor tgδ is one of the most basic tests for insulation testing of high-voltage electrical equipment.
The dielectric loss factor tgδ can effectively find the following insulation defects:
(1) Moisture; (2) Penetrating conductive channels; (3) Insulation contains free bubbles, insulation delamination, shelling; (4) Insulation is dirty, deteriorated, and aged.
Medical Withstand Voltage Tester
Note: The above information and technical parameters are compiled and released by Yangzhou Dali Electric Co., Ltd.
