Voltage withstand test for inverters is a high voltage test performed on inverters to evaluate their insulation and voltage withstand capability. The test is designed to determine the insulation capability of the inverter under normal operation and abnormal conditions to ensure its safe and reliable operation.
I. Why do inverters need to be tested for withstand voltage?
Under normal circumstances, the voltage waveform of the power system is sinusoidal. Power system in operation due to lightning strikes, operations, faults or electrical equipment parameters with improper reasons, causing some parts of the system voltage suddenly rise, greatly exceeding the rated voltage, which is overvoltage.
Overvoltage can be divided into two categories according to the reason for its occurrence:
- Overvoltage caused by direct lightning strike or lightning induction, known as external overvoltage. Lightning impact current and the amplitude of the impact voltage are very large, and the maintenance time is very short, very destructive.
- Because of energy conversion or parameter changes within the power system, such as: cut off the no-load line, cut off the no-load transformer, single-phase arcing grounding within the system, etc., known as internal overvoltage.Internal overvoltage is to determine the normal insulation level of various electrical equipment in the power system is the main basis. That is to say, the design of the product insulation structure should not only consider the rated voltage, but also to consider the product in the use of the environment of the internal overvoltage. Withstand voltage test is to detect whether the product insulation structure can withstand the internal overvoltage of the power system.
II. Differences in Withstand Voltage Testing
There are two types of withstand voltage tests:
- AC frequency withstand voltage test;
- DC withstand voltage test.
Due to the properties of the insulating materials, the breakdown principles for AC and DC voltages are different. Most materials and systems contain a range of different dielectrics.
When an AC test voltage is applied to them, the voltage will be distributed in proportion to the material’s parameters such as dielectric constant and dimensions. DC voltages, on the other hand, only distribute the voltage in proportion to the resistance of the material. And in fact, the breakdown of the insulation structure occurs, often electrical breakdown, thermal breakdown, discharge and other forms exist at the same time, it is difficult to separate. And AC voltage increases the possibility of thermal breakdown than DC voltage, so AC voltage withstand test is considered more stringent than DC voltage withstand test.
In practice, when conducting the withstand voltage test, if DC is to be used for the withstand voltage test, the test voltage requirement is higher than the test voltage of the industrial frequency. General DC withstand voltage test by multiplying the RMS value of the AC test voltage by a constant K. Through comparative testing, there are the following empirical results:
(a) wire and cable products, the constant K selected 3;
(b) For the aviation industry, the constant K is 1.6-1.7;
(c) CSA for civilian products generally use 1.414.
III. Formal test and factory test
Form testing is used to determine whether the design of a product’s insulation structure is suitable for actual use, and is usually performed immediately after temperature rise testing, moisture testing, anomaly testing, and some other tests, generally by applying a test voltage to the product for one minute.
Factory testing is used to detect production defects in the manufacturing process, not to test whether the insulation structure is designed properly. It is usually performed after the product is completed and before it is ready to be packaged. Defects in the insulation structure of the product are usually found as follows:
- sharp parts damaging the wire insulation;
- between connecting wires – ground;
- short-circuiting of electronic components between primary and secondary;
- poorly soldered or detached soldering points on the wire;
- the creepage distance is reduced
- insulation damage in the transformer, etc.
In order to adapt to mass production, the factory test can also increase the test voltage by 20% and shorten the test time from 1min to 1s.
IV. Voltage withstand test and breakdown test
The specific voltage value for the test is specified in the standard. After the voltage withstand test, the intelligence indicates that the insulating structure of the product can withstand high enough voltage. If it is necessary to determine the insulation strength in the application research of insulating materials and the design of electrical equipment, it is necessary to carry out the breakdown test, the breakdown test is to test the voltage when the dielectric is broken down.
When the electric field strength exceeds a certain limit, the relationship between the current through the dielectric and the voltage applied to the dielectric does not conform to Ohm’s law, but increases suddenly. At this point, the insulating material is destroyed and loses its insulating properties.
For an electrical product, if the insulation breaks down, it loses its operational function. This result is completely different from a voltage test. A voltage test is a test to ensure that a product is free of defects and can work safely and normally, proving that the product is safe, reliable and effective.
In the factory review, some factories in order to show that their products are good, the voltage of the withstand voltage test is particularly high, and some even increased to twice the required, which is detrimental but not beneficial.
First: this reduces the pass rate of the product;
Second: although through the test, but may damage part of the insulation structure, making the product safety reduced;
Third: there is a possibility of damage to some components, so that the quality of the product is reduced, the life expectancy is shortened.
Often people mention: how much leakage current is considered to be voltage breakdown?
This leakage current is difficult to determine accurately. Because when the high voltage is applied to the product, it will produce a stable and tiny leakage current between the insulations. This leakage current varies depending on the complexity of each product and the construction of the insulation. When the insulation gives way, the leakage current increases rapidly. Generally, it is sufficient to set the overcurrent relay of the tester to operate at a current (i.e., leakage current) that is slightly higher than the leakage current that would be generated if the product’s normal applied voltage were high.
Note: The leakage current here is essentially the same as the leakage current in the leakage current test, which is a very small current generated by the insulation system under the action of voltage. The difference is that the leakage current in the Withstand Voltage Test is generated under high voltage, while the leakage current in the Leakage Current Test is generated under rated voltage.
V. Advantages of Conducting a Withstand Voltage Test
Ensures product safety: The withstand voltage test assesses the insulation performance and voltage withstand capability of the frequency inverter, ensuring that the product operates safely and reliably under normal and abnormal conditions.
Reduces electrical failure risks: By conducting the withstand voltage test, potential insulation faults and defects can be identified, preventing accidents or damage caused by electrical failures during operation.
Compliance with standards and regulations: The withstand voltage test is often part of product certification and compliance evaluation, meeting the requirements of relevant standards and regulations, thereby enhancing the product’s market competitiveness.
VI.Disadvantages of not conducting a withstand voltage test:
Increased safety risks: Without a withstand voltage test, the insulation performance and voltage withstand capability of the frequency inverter cannot be comprehensively assessed, posing risks of electrical failures that may lead to safety accidents or equipment damage.
Potential issues not meeting requirements: Frequency inverters that have not undergone a withstand voltage test may contain insulation faults or defects, which may gradually manifest during actual usage, resulting in performance degradation and increased failure rates.
Lack of market recognition: The withstand voltage test is often part of product compliance and certification. The absence of a withstand voltage test may lead to a lack of market recognition, reducing competitiveness.
In summary, conducting a withstand voltage test ensures product safety and reliability, reduces electrical failure risks, and meets the requirements of relevant standards and regulations. Not conducting a withstand voltage test may increase safety risks, contain potential faults and defects, and lack market recognition. Therefore, it is recommended for frequency inverter manufacturers to conduct a withstand voltage test to ensure product quality and safety.
About GTAKE
GTAKE is a manufacturer specializing in the design and production of innovative inverters using advanced control algorithms and cutting-edge technology to provide optimal performance and reliability for industrial automation and new energy applications.If you need to purchase a frequency inverter or have any questions about frequency inverters, please feel free to contact GTAKE and our experts will work out the best solution for you on a case-by-case basis.
