30 classic questions about safety withstand voltage and leakage current!

QWhy do products need to be tested for electrical safety?
A This is a question that many product manufacturers want to ask. Of course, the general answer is "because there are regulations in the safety standards." If you have a deep understanding of the background of electrical safety regulations, you will find the hidden responsibilities and responsibilities behind it. significance. Although electrical safety testing takes up a little time on the production line, it allows you to reduce the risk of product recycling due to electrical hazards. Doing it right next time is the right way to reduce costs and maintain goodwill.
Q What is electrical shock (Electrical Shock)?
A There are many factors that cause electrical damage. The main one is electrical damage caused by the current passing through the human body. This type of electrical injury has a direct impact on humans, and the severity of the injury varies depending on the size of the electrical energy, humidity, and contact area. Imagine that when you take a bath in the bathtub, the hair dryer that is in operation suddenly falls into the bathtub. This situation causes the current to flow from the hair dryer to the ground through your body. At this time, your heart has irregular palpitations and a drop in blood pressure, causing an irreversible tragedy.
Q What are Type I and Type II products?
AClassⅠ equipment refers to the contactable conductor parts connected to the grounding protective conductor; when the basic insulation fails, the grounding protective conductor must be able to withstand the failure error current, that is, when the basic insulation fails, the accessible parts cannot become active parts. Simply put, equipment with a grounding pin on the power cord is a Class I equipment. ClassⅡ equipment not only relies on "basic insulation" to prevent electric fouling, but also provides other safety precautions, such as "double insulation" or "reinforced insulation". There are no requirements for the reliability of protective grounding or installation conditions.
Q What are the main tests for electrical damage?
A electrical damage tests are mainly divided into the following four types:
Withstand Hipot Test (Dielectric Withstand Hipot Test): Withstand voltage test applies a high voltage to the power and ground circuits of the product and measures its collapse state.
Insulation Resistance Test (Isolation Resistance Test): Measure the electrical insulation state of the product.
Leakage Current Test: Check whether the leakage current of the AC/DC power supply to the ground terminal exceeds the standard.
Protective Ground: Check whether the accessible metal mechanism and other parts are actually grounded.
Q Does the safety standard have special requirements for the withstand voltage test environment?
A. For the safety of testers in manufacturers or test laboratories, it has been practiced in Europe for many years. Whether it is manufacturers and testers of electronic appliances, information technology products, household appliances, mechanical tools or other equipment, they are in various safety Regulations and regulations have chapters to stipulate, whether it is UL, IEC, EN, including test area marking (personnel location, instrument location, DUT location), equipment labeling (clearly labeling "danger" or items under test) ), the grounding status of equipment workbenches and other related facilities, and the electrical insulation capacity of each test equipment (IEC 61010).
Q What is withstand voltage test?
A withstand voltage test or high voltage test (HIPOT test), is used to verify the quality and electrical safety characteristics of the product (such as JSI, CSA, BSI, UL, IEC, TUV and other standards required by international safety agencies) 100 % Of production line testing is also a production line safety test that many people know and often perform. The HIPOT test is a non-destructive test to determine that the electronic insulating material is sufficient to withstand instantaneous high voltage. It is a high-voltage test suitable for all equipment to ensure that the insulating material is sufficient. The other reason for the HIPOT test is that it can detect possible defects such as insufficient leakage distance and electrical clearance caused during the manufacturing process.
Q Why do I need to do a withstand voltage test?
A Under normal circumstances, the voltage waveform in the power system is a sine wave. During the operation of the power system, due to lightning strikes, operations, faults, or improper coordination of electrical equipment parameters, the voltage of some parts of the system suddenly rises, greatly exceeding its rated voltage, which is an overvoltage. Overvoltages can be divided into two categories according to their causes. One is the overvoltage caused by direct lightning strikes or lightning induction, which is called external overvoltage. The amplitude of lightning impulse current and impulse voltage is very large, and the duration is very short, and it is extremely destructive. However, because the overhead lines of 3-10kV and below in towns and general industrial enterprises are shielded and protected by factories or tall buildings, the probability of being directly struck by lightning is small and relatively safe. What's more, what is discussed here is for civil electrical appliances, which is not within the above range, so we won't discuss it further. The other type is caused by energy conversion or parameter changes within the power system, such as closing no-load lines, cutting off no-load transformers, and single-phase arc grounding in the system, which are called internal overvoltages. Internal overvoltage is the main basis for determining the normal insulation level of various electrical equipment in the power system. In other words, the design of the insulation structure of the product must consider not only the rated voltage but also the internal overvoltage of the product's use environment. Withstand voltage test is to detect whether the insulation structure of the product can withstand the internal overvoltage of the power system.
What are the advantages of QAC withstand voltage test?
A Generally, AC withstand voltage test is easier to be accepted by safety agencies than DC withstand voltage test. The main reason is that most of the tested items will work under AC voltage, and the AC withstand voltage test provides two extreme advantages for applying pressure to the insulation, which is closer to the pressure that the product will encounter in actual use. Since the AC test will not charge the capacitive load, the current reading remains consistent from the beginning of the voltage application to the end of the test. Therefore, since there is no stabilization problem required for monitoring current readings, there is no need to gradually increase the voltage. This means that unless the product under test senses a sudden applied voltage, the operator can immediately apply the full voltage and read the current without waiting. Since the AC voltage will not charge the load, there is no need to discharge the device under test after the test.
What are the disadvantages of QAC withstand voltage test?
A When testing a capacitive load, the total current is composed of reactive current and leakage current. When the reactive current is much larger than the true leakage current, it may be difficult to detect products with excessive leakage current. When testing large capacitive loads, the total current required is much greater than the leakage current itself. Since the operator faces a larger current, this may be a greater danger.
What are the advantages of QDC withstand voltage test?
A When the device under test (DUT) is fully charged, only real leakage current flows. This enables the DC withstand voltage tester to clearly show the true leakage current of the product under test. Since the charging current is short, the power requirement of a DC withstand voltage tester can usually be much smaller than that of an AC withstand voltage tester used to test the same product.
What are the disadvantages of the QDC withstand voltage tester?
A Since the DC withstand voltage test does charge the DUT, in order to eliminate the risk of electric shock for the operator who handles the DUT after the withstand voltage test, the DUT must be charged after the test Discharge. The DC test will charge the capacitor. If the DUT actually uses AC power, the DC method does not simulate the actual situation.
The difference between QAC withstand voltage test and DC withstand voltage test
There are two types of 　　A withstand voltage test: AC withstand voltage test and DC withstand voltage test. Due to the characteristics of the insulating material, the breakdown mechanism of AC and DC voltage is different. Most insulating materials and systems contain a series of different media. When an AC test voltage is applied to it, the voltage will be distributed according to the ratio of the dielectric constant and size of the material. The DC voltage only distributes the voltage in proportion to the resistance of the material. In fact, when the insulation structure is broken down, multiple forms such as electrical breakdown, thermal breakdown, and electric discharge are often present at the same time, and it is difficult to separate them completely. The AC voltage increases the possibility of thermal breakdown compared to the DC voltage. Therefore, we believe that the AC withstand voltage test is more stringent than the DC withstand voltage test. In actual operation, when the withstand voltage test is performed, if DC is used for the withstand voltage test, the test voltage is required to be higher than the AC power frequency test voltage. Generally, the test voltage of the DC withstand voltage test is by multiplying the effective value of the AC test voltage by a constant K. Through comparative tests, we have the following results: wire and cable products, the constant K is 3; for the aviation industry, the constant K is 1.6 to 1.7; CSA generally uses 1.414 for civil products.
Q How to determine the test voltage used in the withstand voltage test?
A The test voltage that determines the withstand voltage test depends on the market your product will be put into. You must comply with the safety standards or regulations that are part of the country's import control regulations. The safety standard specifies the test voltage and test time for the withstand voltage test. The ideal situation is to ask your customers to give you relevant test requirements. The test voltage of the general withstand voltage test is as follows: For the working voltage between 42V and 1000V, the test voltage is twice the working voltage plus 1000V. This test voltage is applied for 1 minute. For example, for a product that works at 230V, the test voltage is 1460V. If the time for applying the voltage is shortened, the test voltage must be increased.
Q What is the capacity of the withstand voltage test and how to calculate it?
The capacity of 　　A withstand voltage tester refers to its power output. The capacity of the withstand voltage tester is determined by the output current x output voltage. For example: 5000Vx100mA=500VA
Q Why is the leakage current measured by the AC withstand voltage test and the DC withstand voltage test different?
A The stray capacitance of the test object is the main reason for the difference between the measured values of AC and DC withstand voltage tests. When using AC test, these stray capacitances may not be fully charged, and there will be a continuous current flowing through these stray capacitances. With the DC test, once the stray capacitance on the test object is fully charged, what is left is the actual leakage current of the test object. Therefore, the leakage current measured by the AC withstand voltage test and the DC withstand voltage test will have different.
Q What is the leakage current of the withstand voltage test
A insulator is non-conductive, but in fact almost no insulating material is non-conductive. Any kind of insulating material, when a voltage is applied to its two ends, there will always be a certain amount of current passing through. The active component of this current is called leakage current, and this phenomenon is also called leakage of insulators. For electrical appliances testing, leakage current refers to the current formed through the surrounding medium or insulating surface between metal parts that are insulated from each other, or between live parts and grounded parts, when there is no fault and voltage is applied. Is the leakage current. According to the American UL standard, the leakage current is the current that can be conducted from the accessible part of the household appliance, including the capacitive coupling current. Leakage current consists of two parts, one part is the conduction current I1 through the insulation resistance; the other part is the displacement current I2 through the distributed capacitance. The capacitive reactance of the latter is XC=1/2pfc and is inversely proportional to the power supply frequency. The distributed capacitance current increases with frequency. And increase, so the leakage current increases as the power frequency increases. For example: using SCR to supply power, its harmonic components increase the leakage current.
What is the difference between the leakage current of the Q withstand voltage test and the power supply leakage current (touch current)?
A Withstand voltage test is to detect the leakage current flowing through the insulation system of the object under test and apply a voltage higher than the working voltage to the insulation system; while the leakage current of the power supply (contact current) is under normal operation of the object under test. An unfavorable condition (voltage, frequency) measures the leakage current of the measured object. Simply put, the leakage current of the withstand voltage test is the leakage current measured under no working power supply, and the power supply leakage current (touch current) is the leakage current measured under normal operation.
Q Classification of contact current
A. For electronic products with different structures, the measurement of contact current also has different requirements, but in general, the contact current can be divided into Ground Leakage Current, Surface to Line Leakage Current, and Surface to Line Leakage Current. There are three types of Surface to Surface Leakage Current tests.
QWhy do contact current tests need to be done?
A The accessible metal parts or enclosures of the electronic products of Class I equipment should also have a good grounding circuit as a protection against electric shock in addition to basic insulation. But [size=+0] we often encounter some users who use Class I equipment as Class II equipment at will, or directly unplug the ground terminal (GND) from the power input of Class I equipment, so that there is a certain amount of Security risks. Even so, as a manufacturer, it is obligated to avoid the danger to users caused by this situation. This is why the purpose of the touch current test is.
Q Why is there no standard for the leakage current in the withstand voltage test?
A In the AC withstand voltage test, there is no standard due to the different types of tested objects, and there will be stray capacitances in the tested objects, and different test voltages will have different leakage currents.
How does Q determine the test voltage?
A The method of determining the test voltage is to set it according to the specifications required for the test. Generally speaking, we will set the test voltage based on 2 times the working voltage plus 1000V. For example, if the working voltage of a product is 115VAC, we use 2 x 115 + 1000 = 1230 Volt as the test voltage. Of course, the test voltage will also have different settings depending on the level of the insulating layer.
What is the difference between QDielectric Voltage Withstand Testing, High Potential Testing, Hipot Testing?
A These three nouns all have the same meaning, but they are often used interchangeably in the testing industry.
Q What is the insulation resistance (IR) test?
A Insulation resistance test and withstand voltage test are very similar. Apply a DC voltage up to 1000V to the two points that need to be tested. The IR test usually gives the resistance value in megohms, not the Pass / Fail expression obtained from the withstand voltage test. Generally, the test voltage is 500V DC, and the value of insulation resistance (IR) should not be less than a few megohms. The insulation resistance test is a non-destructive test and can detect whether the insulation is good or not. In some specifications, the insulation resistance test is performed first and then the withstand voltage test. When the insulation resistance test fails, the withstand voltage test often fails.
Q What is the ground bond test?
A ground connection test, some people call ground continuity (Ground Continuity) test, which measures the impedance between the frame of the DUT and the ground post. The ground connection test determines whether the protection circuit of the DUT can handle the fault current adequately if the product is broken. The ground connection tester will generate 30A DC current or AC root-mean-square current (CSA requires 40A measurement) through the grounding circuit to determine the impedance of the grounding circuit, which is generally below 0.1 ohm.
There is a difference between Q withstand voltage test and insulation resistance test
What's the difference?
AIR test is a qualitative test, which gives an indication of the relative quality of the insulation system. Usually 500V or 1000V DC voltage is used for testing, and the result is measured with megohm resistance. The withstand voltage test also applies high voltage to the object under test (DUT), but the applied voltage is higher than that of the IR test. It can be performed under AC or DC voltage. The result is measured in milliamperes or microamperes. In some specifications, IR test is performed first, followed by withstand voltage test. If a device under test (DUT) fails the IR test, the device under test (DUT) cannot pass the withstand voltage test performed at a higher voltage.
Q Why is there an open circuit voltage limit for the ground impedance test? Why is it recommended to use alternating current (AC) current?
The purpose of the 　　A grounding impedance test is to ensure that when an abnormal condition occurs in the equipment product, the protective grounding wire can be allowed to withstand the flow of fault current to ensure the safety of the user. The safety standard test voltage requires that the open circuit voltage value cannot exceed the limit of 12V, which is based on the user's safety considerations. Once the test failure occurs, the operator can reduce the risk of electric shock. The general standard requires the grounding resistance to be less than 0.1ohm. It is recommended to use an AC current test with a frequency of 50Hz or 60Hz to meet the actual working environment of the product.
What is the difference between the leakage current measured by the Q withstand voltage test and the power leakage test?
There are some differences between 　　A withstand voltage test and power leakage test, but generally speaking, these differences can be summarized as follows. Withstand voltage test is to use high voltage to pressurize the insulation of the product to determine whether the insulation strength of the product is sufficient to prevent excessive leakage current. Leakage current test is to measure the amount of leakage current that flows through the product under normal and single power supply failure conditions when the product is in use.
Q How to determine the discharge time of capacitive load during DC withstand voltage test?
A The difference in discharge time depends on the capacitance of the test object and the discharge circuit of the withstand voltage tester. The larger the capacitance, the longer the discharge time required.
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