A：This is a question that many product manufacturers want to ask, and of course the most common answer is "because the safety standard stipulates it." If you can deeply understand the background of electrical safety regulations, you will find the responsibility behind it. with meaning. 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. Getting it right the first time is the right way to reduce costs and maintain goodwill.
A：The electrical damage test is mainly divided into the following four types: Dielectric Withstand / Hipot Test: The withstand voltage test applies a high voltage to the power and ground circuits of the product and measures its breakdown state. Isolation Resistance Test: Measure the electrical insulation state of the product. Leakage Current Test: Detect whether the leakage current of the AC/DC power supply to the ground terminal exceeds the standard. Protective Ground: Test whether the accessible metal structures are properly grounded.
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, in various safety regulations There are chapters in the regulations, whether it is UL, IEC, EN, which include test area marking (personnel location, instrument location, DUT location), equipment marking (clearly marked "danger" or items under test) , the grounding state of the equipment workbench and other related facilities, and the electrical insulation capability of each test equipment (IEC 61010).
A：Withstand voltage test or high voltage test (HIPOT test) is a 100% standard used to verify the quality and electrical safety characteristics of products (such as those required by JSI, CSA, BSI, UL, IEC, TUV, etc. international safety agencies) It is also the most well-known and frequently performed production line safety test. The HIPOT test is a non-destructive test to determine that electrical insulating materials are sufficiently resistant to transient high voltages, and is a high-voltage test that is applicable to all equipment to ensure that the insulating material is adequate. Other reasons to perform HIPOT testing is that it can detect possible defects such as insufficient creepage distances and clearances caused during the manufacturing process.
A：Normally, the voltage waveform in a power system is a sine wave. During the operation of the power system, due to lightning strikes, operation, faults or improper parameter matching of electrical equipment, the voltage of some parts of the system suddenly rises and greatly exceeds its rated voltage, which is overvoltage. Overvoltage can be divided into two categories according to its causes. One is the overvoltage caused by direct lightning strike or lightning induction, which is called external overvoltage. The magnitude of lightning impulse current and impulse voltage are large, and the duration is very short, which is extremely destructive. However, because the overhead lines of 3-10kV and below in towns and general industrial enterprises are shielded by workshops or tall buildings, the probability of being directly struck by lightning is very small, which is relatively safe. Moreover, what is discussed here is household electrical appliances, which is not within the above-mentioned scope, and will not be discussed further. The other type is caused by energy conversion or parameter changes inside the power system, such as fitting the no-load line, cutting off the no-load transformer, and single-phase arc grounding in the system, which is called internal overvoltage. Internal overvoltage is the main basis for determining the normal insulation level of various electrical equipment in the power system. That is to say, the design of the insulation structure of the product should consider not only the rated voltage but also the internal overvoltage of the product use environment. The withstand voltage test is to detect whether the insulation structure of the product can withstand the internal overvoltage of the power system.
A：Usually the AC withstand voltage test is more acceptable to safety agencies than the DC withstand voltage test. The main reason is that most items under test will operate under AC voltage, and the AC withstand voltage test offers the advantage of alternating two polarities to stress the insulation, which is closer to the stress the product will encounter in actual use. Since the AC test does not charge the capacitive load, the current reading remains the same from the start of the voltage application to the end of the test. Therefore, there is no need to ramp up the voltage since there are no stabilization issues required to monitor current readings. This means that unless the product under test senses a suddenly applied voltage, the operator can immediately apply full voltage and read the current without waiting. Since the AC voltage does not charge the load, there is no need to discharge the device under test after the test.
A：When testing capacitive loads, the total current consists of reactive and leakage currents. When the amount of 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. This may be a greater hazard as the operator is exposed to higher currents
A：When the device under test (DUT) is fully charged, only true leakage current flows. This enables the DC Hipot Tester to clearly display the true leakage current of the product under test. Because the charging current is short-lived, the power requirements of a DC withstand voltage tester can often be much less than that of an AC withstand voltage tester used to test the same product.
A：Since the DC withstand voltage test does charge the DUT, in order to eliminate the risk of electric shock for the operator handling the DUT after the withstand voltage test, the DUT must be discharged after the test . The DC test charges the capacitor. If the DUT actually uses AC power, the DC method does not simulate the actual situation.
A：There are two types of withstand voltage tests: AC withstand voltage test and DC withstand voltage test. Due to the characteristics of insulating materials, the breakdown mechanisms of AC and DC voltages are different. Most insulating materials and systems contain a range of different media. When an AC test voltage is applied to it, the voltage will be distributed in proportion to parameters such as the dielectric constant and dimensions of the material. Whereas DC voltage only distributes the voltage in proportion to the resistance of the material. And in fact, the breakdown of the insulating structure is often caused by electrical breakdown, thermal breakdown, discharge and other forms at the same time, and it is difficult to separate them completely. And AC voltage increases the possibility of thermal breakdown over DC voltage. Therefore, we believe that the AC withstand voltage test is more stringent than the DC withstand voltage test. In actual operation, when carrying out the withstand voltage test, if DC is used for the withstand voltage test, the test voltage is required to be higher than the test voltage of the AC power frequency. The test voltage of the general DC withstand voltage test is multiplied by a constant K by the effective value of the AC test voltage. Through comparative tests, we have the following results: for 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 civilian products.
A：The test voltage that determines the withstand voltage test depends on the market your product will be put into, and you must comply with safety standards or regulations that are part of the country's import control regulations. The test voltage and test time of the withstand voltage test are specified in the safety standard. The ideal situation is to ask your client to give you relevant test requirements. The test voltage of the general withstand voltage test is as follows: if the working voltage is 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 operating at 230V, the test voltage is 1460V. If the voltage application time is shortened, the test voltage must be increased. For example, the production line test conditions in UL 935:
Application time (seconds)
|1000V + （2 x V）|
|1200V + （2.4 x V）|
|V=maximum rated voltage|
A：The capacity of a Hipot Tester refers to its power output. The capacity of the withstand voltage tester is determined by the maximum output current x the maximum output voltage. E.g:5000Vx100mA=500VA
A: The stray capacitance of the tested object is the main reason for the difference between the measured values of AC and DC withstand voltage tests. These stray capacitances may not be fully charged when testing with AC, and there will be a continuous current flowing through these stray capacitances. With the DC test, once the stray capacitance on the DUT is fully charged, what remains is the actual leakage current of the DUT. Therefore, the leakage current value measured by the AC withstand voltage test and the DC withstand voltage test will have different.
A: Insulators are non-conductive, but in fact almost no insulating material is absolutely non-conductive. For any insulating material, when a voltage is applied across it, a certain current will always flow through. The active component of this current is called leakage current, and this phenomenon is also called leakage of the insulator. For the test of electrical appliances, leakage current refers to the current formed by the surrounding medium or insulating surface between metal parts with mutual insulation, or between live parts and grounded parts in the absence of fault applied voltage. is the leakage current. According to the US UL standard, leakage current is the current that can be conducted from the accessible parts of household appliances, including capacitively coupled currents. The leakage current includes 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 latter capacitive reactance is XC=1/2pfc and is inversely proportional to the power supply frequency, and the distributed capacitance current increases with the frequency. increase, so the leakage current increases with the frequency of the power supply. For example: using thyristor for power supply, its harmonic components increase the leakage current.
A: The 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 power leakage current (contact current) is to detect the leakage current of the object under test under normal operation. Measure the leakage current of the measured object under the most unfavorable condition (voltage, frequency). Simply put, the leakage current of the withstand voltage test is the leakage current measured under no working power supply, and the power leakage current (contact current) is the leakage current measured under normal operation.
A: For electronic products of different structures, the measurement of touch current also has different requirements, but in general, touch current can be divided into ground contact current Ground Leakage Current, surface-to-ground contact current Surface to Line Leakage Current and surface-to-line Leakage Current Three touch current Surface to Surface Leakage Current tests
A: The accessible metal parts or enclosures of electronic products of Class I equipment should also have a good grounding circuit as a protection measure against electric shock other than basic insulation. However, we often encounter some users who arbitrarily use Class I equipment as Class II equipment, or directly unplug the ground terminal (GND) at the power input end of the Class I equipment, so there are certain security risks. Even so, it is the responsibility of the manufacturer to avoid the danger to the user caused by this situation. This is why a touch current test is done.
A: During the AC withstand voltage test, there is no standard due to the different types of the tested objects, the existence of stray capacitances in the tested objects, and the different test voltages, so there is no standard.
A: The best way to determine the test voltage is to set it according to the specifications required for the test. Generally speaking, we will set the test voltage according to 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 due to the different grades of insulating layers.
A: These three terms all have the same meaning, but are often used interchangeably in the testing industry.
A: Insulation resistance test and withstand voltage test are very similar. Apply a DC voltage of up to 1000V to the two points to be tested. The IR test usually gives the resistance value in megohms, not the Pass/Fail representation from the Hipot test. Typically, the test voltage is 500V DC, and the insulation resistance (IR) value 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. 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.
A: The ground connection test, some people call it ground continuity (Ground Continuity) test, measures the impedance between the DUT rack and the ground post. The ground bond test determines whether the DUT's protection circuitry can adequately handle the fault current if the product fails. The ground bond tester will generate a maximum of 30A DC current or AC rms current (CSA requires 40A measurement) through the ground circuit to determine the impedance of the ground circuit, which is generally below 0.1 ohms.
A: The IR test is a qualitative test that gives an indication of the relative quality of the insulation system. It is usually tested with a DC voltage of 500V or 1000V, and the result is measured with a megohm resistance. The withstand voltage test also applies a high voltage to the device under test (DUT), but the applied voltage is higher than that of the IR test. It can be done at AC or DC voltage. Results are measured in milliamps or microamps. In some specifications, the IR test is performed first, followed by the withstand voltage test. If a device under test (DUT) fails the IR test, the device under test (DUT) also fails the withstand voltage test at a higher voltage.
A: The purpose of the grounding impedance test is to ensure that the protective grounding wire can withstand the flow of fault current to ensure the safety of users when an abnormal condition occurs in the equipment product. The safety standard test voltage requires that the maximum open-circuit voltage should not exceed the limit of 12V, which is based on the user's safety considerations. Once the test failure occurs, the operator can be reduced to the risk of electric shock. The general standard requires that the grounding resistance should 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.
A: There are some differences between the withstand voltage test and the power leakage test, but in general, these differences can be summarized as follows. The 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. The leakage current test is to measure the leakage current that flows through the product under normal and single-fault states of the power supply when the product is in use.
A: The difference in discharge time depends on the capacitance of the tested object and the discharge circuit of the withstand voltage tester. The higher the capacitance, the longer the discharge time required.
A: Class I equipment means that the accessible conductor parts are connected to the grounding protective conductor; when the basic insulation fails, the grounding protective conductor must be able to withstand the fault current, that is, when the basic insulation fails, the accessible parts cannot become live electrical parts . Simply put, the equipment with the grounding pin of the power cord is a Class I equipment. Class II equipment not only relies on "Basic Insulation" to protect against electricity, but also provides other safety precautions such as "Double Insulation" or "Reinforced Insulation". There are no conditions regarding the reliability of protective earthing or installation conditions.