my country has become the world's largest production base for household appliances and electronic and electrical products, and its export volume continues to increase. Together with consumers' product safety, in line with relevant worldwide laws and regulations, manufacturers continue to improve product safety standards. In addition, the manufacturer also pays great attention to the safe inspection of the product before leaving the factory. In the meantime, the safety of the electrical functions of the product, perhaps the safety against electric shock, is a very important check item in the meantime.
In order to understand the product's insulation function, the product planning, structure, and insulation materials have corresponding specifications or specifications. Generally, manufacturers will use different methods to check or test. However, for electrical products, there is a kind of test that must be carried out, that is-Dielectric Withstand Test, sometimes referred to as Hipot Test or Hipot Test, High Voltage Test, Electric Strength Test, etc. The insulation function of general products is good or bad; it can be reflected by the electrical strength test.
There are many kinds of withstand voltage testers on the market nowadays. As far as manufacturers are concerned, how to save capital investment and their own needs to purchase useful withstand voltage testers has become more and more important.
1. Type of withstand voltage test (communication or DC)
The production line withstand voltage test, the so-called Routine Test (Routine Test), according to different products, there are communication withstand voltage test and DC withstand voltage test. Obviously, the communication withstand voltage test must consider whether the frequency of the withstand voltage test is consistent with the operating frequency of the tested object; therefore, the ability to flexibly select the type of test voltage and the flexible selection of the communication voltage frequency are the fundamental functions of the withstand voltage tester. .
2. Test voltage scale
Generally, the output scale of the test voltage of the communication withstand voltage tester is 3KV, 5KV, 10KV, 20KV, and even higher, and the output voltage of the DC withstand voltage tester is 5KV, 6KV or even higher than 12KV. How does the user choose the appropriate voltage scale for his application? According to different product categories, the test voltage of the product has corresponding safety regulations. For example, in IEC60335-1:2001 (GB4706.1), the withstand voltage test at the operating temperature has a test value for the withstand voltage. In IEC60950-1:2001 (GB4943), the test voltage of different types of insulation is also pointed out.
According to the product type and the corresponding specifications, the test voltage is also different. Regarding the general manufacturer’s choice of 5KV and DC 6KV withstand voltage testers, it can basically meet the needs, but about some special testing organizations or manufacturers In order to respond to different product specifications, it may be necessary to select products that use 10KV and 20KV communication or DC. Therefore, being able to arbitrarily regulate the output voltage is also the fundamental requirement of the withstand voltage tester.
3. Quiz time
According to product specifications, the general withstand voltage test requires 60 seconds at the time. This must be strictly implemented in safety inspection organizations and factory laboratories. However, such a test is almost impossible to be implemented on the production line at the time. The main focus is on production speed and production efficiency, so long-term tests cannot satisfy practical needs. Fortunately, many organizations now allow selection to shorten the test time and increase the test voltage. In addition, some new safety regulations also clearly state the test time. For example, in Appendix A of IEC60335-1, IEC60950-1 and other specifications, it is said that the routine test (Routine Test) time is 1sec. Therefore, the setting of the test time is also a necessary function of the withstand voltage tester.
Fourth, the voltage slow rise function
Many safety regulations, such as IEC60950-1, describe the output characteristics of the test voltage as follows: "The test voltage applied to the insulation under test should be gradually increased from zero to the regular voltage value..."; IEC60335-1 The description in: "At the beginning of the experiment, the applied voltage did not exceed half of the regular voltage value, and then gradually increased to the full value." Other safety regulations also have similar requirements, that is, the voltage cannot be suddenly applied to the measured object, and there must be a slow rise process. Although the specification does not quantify the detailed time requirements for this slow rise in detail, its intention is to prevent sudden changes. High voltage may damage the insulation function of the measured object.
We know that the withstand voltage test should not be a destructive experiment, but a means of checking product defects. Therefore, the withstand voltage tester must have a slow rise function. Of course, if an abnormality is found during the slow rise process, the instrument should be able to immediately stop the output, so that the test combination makes the function more vivid.
Five, the selection of test current
From the above requirements, we can find that, in fact, the requirements of the safety regulations regarding the withstand voltage tester basically give clearer requirements. However, another consideration in choosing a withstand voltage tester is the scale of leakage current measurement. Before the experiment, it is necessary to set the experiment voltage, experiment time and the determined current (the upper limit of leakage current). The current withstand voltage testers on the market take communication current as an example. The maximum leakage current that can be measured is roughly from 3mA to 100mA. Of course, the higher the scale of leakage current measurement, the higher the relative price. Of course, here we temporarily consider the current measurement accuracy and resolution at the same level! So, how to choose an instrument that suits you? Here, we also look for some answers from the specifications.
From the following specifications, we can see how the withstand voltage test is determined in the specifications:
Specification title The expression in the specification to determine the occurrence of breakdown
"Safety requirements for audio, video and similar electronic equipment" 10.3.2...... During the electric strength test, if there is no flashover or breakdown, the equipment is deemed to meet the requirements.
IEC60335-1: 2001 (GB4706.1)
"Safety of household and similar electrical appliances Part 1: General requirements" 13.3 During the experiment, there should be no breakdown.
"Safety of Information Technology Equipment" 5.2.1 During the experiment, the insulation should not be broken down.
IEC60598-1: 1999 (GB7000.1)
"General safety requirements and experiments for lamps and lanterns" 10.2.2... During the experiment, no flashover or breakdown shall occur.
It can be seen from Table 1 that in fact, in these specifications, there is no clear quantitative data to determine whether the insulation is invalid. In other words, it does not tell you how many current products are qualified or unqualified. Of course, there are relevant rules regarding the maximum limit of the determined current and the capacity requirements of the withstand voltage tester in the specification; the maximum limit of the determined current is to make the overload protector (in the withstand voltage tester) act to indicate the occurrence of breakdown The current, also known as the trip current. The description of this limit in different specifications is shown in Table 2.
Specification title Maximum rated current (trip current) Short-circuit current
"Safety requirements for audio, video and similar electronic equipment" 10.3.2...... When the output current is less than 100mA, the overcurrent device should not be disconnected. The test voltage should be provided by the power supply. The power supply should be planned to ensure that when the test voltage is adjusted to the corresponding level and the output terminal is short-circuited, the output current should be at least 200mA.
IEC60335-1: 2001 (GB4706.1)
"Safety of household and similar electrical appliances Part 1: General requirements" 13.3: Trip current Ir Short-circuit current Is
<4000 Ir=100mA 200mA
≧4000 and <10000 Ir=40mA 80mA
≧10000 and≦20000 Ir=20mA 40mA
"Safety of Information Technology Equipment" Not clearly stated Not clearly stated
IEC60598-1: 1999 (GB7000.1-2002)
"General safety requirements and experiments of lamps and lanterns" 10.2.2...... When the output current is less than 100mA, the overcurrent relay should not be disconnected. For the high voltage transformer used in the experiment, when the output voltage is adjusted to the corresponding experimental voltage and the output is short-circuited, the output current is at least 200mA
How to set the correct value of leakage current
From the above safety regulations, many manufacturers will have questions. How much should the leakage current set in practice be chosen? In the early stage, we clearly stated that the capacity of the withstand voltage tester needs to be 500VA. If the test voltage is 5KV, then the leakage current must be 100mA. Now it seems that the capacity requirement of 800VA to 1000VA is even needed. But does the general application manufacturer have this need? Since we know that the larger the capacity, the higher the cost of the equipment invested, and it is also very dangerous to the operator. The selection of the instrument must fully consider the matching relationship between the specification requirements and the instrument range.
In fact, during the production line testing process of many manufacturers, the upper limit of the leakage current generally uses several typical determined current values: such as 5mA, 8mA, 10mA, 20mA, 30mA to 100mA. Moreover, experience tells us that the actual measured values and the requirements of these limits are actually far from each other. However, it is recommended that when selecting a suitable withstand voltage tester, it is better to verify with the specifications of the product.
Correctly choose withstand voltage test equipment
Generally, when selecting a withstand voltage tester, there may be a mistake in knowing and understanding the safety regulations. According to the general safety regulations, the trip current is 100mA, and the short-circuit current needs to reach 200mA. If it is directly explained as a so-called The 200mA withstand voltage tester is a serious fault. As we know, when the output withstand voltage is 5KV; if the output current is 100mA, the withstand voltage tester has an output capacity of 500VA (5KV X 100mA). When the current output is 200mA, it needs to double the output capacity to 1000VA. Such a fault explanation will result in a cost burden on the purchase of equipment. If the budget is limited; originally able to purchase two instruments, due to the fault of the explanation, only one can be purchased. Therefore, from the above clarification, it can be found that the manufacturer actually chooses the withstand voltage tester. Whether to choose a large-capacity and wide-range instrument depends on the characteristics of the product and the requirements of the specification. If you choose a wide-range instrument and equipment , It will be a very big waste, the basic principle is that if it is enough, it is the most economical.
Of course, due to the complex production line testing situation, the test results are greatly affected by factors such as man-made and environmental factors, which will directly affect the test results, and these factors have a direct impact on the defective rate of the product. Choose a good withstand voltage tester, grasp the above key points, and trust that you will be able to choose a withstand voltage tester suitable for your company's products. As for how to prevent and lower the misjudgment, it is also an important part of the pressure test.