What is the difference between DC withstand voltage and AC withstand voltage? Wuhan UHV specializes in producing AC voltage withstand testers with a wide range of product options. When looking for an AC voltage withstand tester, choose Wuhan UHV.    

Voltage withstand testing, also known as high voltage testing or dielectric strength testing, may be the most familiar and commonly used in product process safety testing. Voltage withstand test is a non-destructive test used to test the insulation capability of products under frequent transient high voltages. It applies high voltage to the tested equipment for a certain period of time to ensure that the insulation performance of the equipment is strong enough.         

Insulation preventive tests can be divided into two categories:

One type is non-destructive testing, also known as insulation characteristic testing, which measures various characteristic parameters at lower voltages or using other methods that will not damage the insulation. It mainly includes measuring insulation resistance, leakage current, dielectric loss tangent value, etc., in order to determine whether there are defects inside the insulation. Experimental results have shown that this method is effective, but currently it cannot be relied solely on to reliably determine the electrical strength of insulation.         

The other type is destructive testing, also known as withstand voltage testing. The voltage applied in the test is higher than the operating voltage of the equipment, and the insulation test is very strict, especially to expose concentrated defects with high danger and ensure that the insulation has a certain electrical strength, mainly including DC withstand voltage, AC withstand voltage, etc. The disadvantage of voltage withstand test is that it may cause certain damage to the insulation.  

AC voltage

The AC withstand voltage test is the most effective and direct method for evaluating the insulation strength of power equipment. During the operation of power equipment, insulation will gradually deteriorate due to the long-term effects of electric fields, temperature, and mechanical vibrations, including overall deterioration and the formation of defects. For example, local defects may exist due to concentrated electric fields or fragile insulation in certain areas. Various preventive testing methods have their own strengths and can detect some defects, reflecting the condition of insulation. However, the testing voltage of other testing methods is often lower than the working voltage of power equipment, and the guarantee for safe operation is not strong enough. Although the DC withstand voltage test has a relatively high test voltage and can detect some insulation weaknesses, due to the fact that most insulation of power equipment is composed of composite dielectrics, the voltage is distributed according to resistance under the action of DC voltage. Therefore, the weaknesses of AC power equipment under AC electric field may not be detected by using DC for testing. The AC withstand voltage test is in line with the electrical conditions that power equipment can withstand during operation. At the same time, the AC withstand voltage test is generally higher than the operating voltage. Therefore, after passing the test, the equipment has a large safety margin. Therefore, this test has become an important means to ensure safe operation.

However, due to the fact that the test voltage used in the AC withstand voltage test is much higher than the operating voltage, excessively high voltage can increase insulation medium loss, heat generation, discharge, and accelerate the discovery of insulation defects. Therefore, in a sense, the AC withstand voltage test is a destructive test.  

Before conducting the AC withstand voltage test, various non-destructive tests must be carried out, such as measuring insulation resistance, absorption ratio, dielectric loss factor tg δ, DC leakage current, etc. The comprehensive analysis of the test results is conducted to determine whether the equipment is damp or contains defects. If problems are found, they need to be dealt with in advance. After the defects are eliminated, the AC withstand voltage test can be carried out to avoid insulation breakdown, expansion of insulation defects, extension of maintenance time, and increase in maintenance workload during the AC withstand voltage test process.

DC Voltage

Testing voltage, most safety standards allow the use of AC or DC voltage in withstand voltage testing. If an AC test voltage is used, when the voltage peak is reached, whether it is a positive or negative peak, the tested insulator will withstand the maximum pressure. Therefore, if choosing to use DC voltage testing, it is necessary to ensure that the DC test voltage is N times the AC test voltage, so that the DC voltage can be equivalent to the peak value of the AC voltage.         

One of the benefits of using DC test voltage is that in DC mode, the current flowing through the alarm current measuring device of the withstand voltage tester is the actual current flowing through the sample. Another advantage of using DC testing is that the voltage can be gradually applied. By monitoring the current flowing through the sample as the voltage increases, the operator can detect it before breakdown occurs. It should be noted that when using a DC withstand voltage tester, due to the charging of capacitors in the circuit, the sample must be discharged after the test is completed. In fact, regardless of the testing voltage or product characteristics, it is beneficial to discharge the product before operating it.        

The drawback of DC withstand voltage testing is that it can only apply test voltage in one direction and cannot apply electrical stress in two polarities like AC testing, which is why most electronic products work under AC power supply. In addition, due to the difficulty in generating DC test voltage, the cost of DC testing is higher than that of AC testing.