High Voltage Connector- Insulation Resistance Test
Whether it is a high-voltage electrical connectors, or low-voltage electrical connectors, insulation resistance, dielectric strength (also known as electrical strength) and contact resistance are to ensure that the electrical connectors can work properly and reliably the most basic electrical parameters. Usually in the technical conditions of the electrical connector product quality consistency inspection A, B group of conventional delivery inspection projects are listed in the clear technical specifications and test methods. These three tests are also an important basis for users to identify the quality and reliability of electrical connectors.
In addition, with the rapid development of electronic information technology, a new generation of multi-functional automatic testers are gradually replacing the original single-parameter tester. The application of these new test instruments will certainly greatly improve the speed, efficiency and accuracy and reliability of electrical performance testing.
This paper begins with the insulation resistance, mainly divided into three parts: the principle of action, factors affecting and discussion of the problem.
1. Operating Principle
Insulation resistance is the resistance value presented by applying a voltage to the insulating part of the connector so that a leakage current is generated on the surface or inside the insulating part. That is, insulation resistance (MΩ) = the voltage applied to the insulator (V) / leakage current (μA). The insulation resistance test determines whether the insulation performance of the connector can meet the requirements of the circuit design. Or whether the insulation resistance meets the provisions of the relevant technical conditions when subjected to environmental stresses such as high temperature and humidity.
Insulation resistance is a limiting factor for designing high-impedance circuits. Low insulation resistance means high leakage current, which will destroy the circuit and normal operation. If a feedback loop is formed, the heat and DC electrolysis from excessive leakage current will destroy the insulation or deteriorate the electrical properties of the connector.
2. Influencing Factors
Mainly affected by insulation materials, temperature, humidity, fouling, test voltage and continuous application of test voltage duration and other factors.
Insulation Material
Design of electrical connectors when the choice of which insulation material is very important, it often affects the product insulation resistance can be stable and qualified. If you use phenolic glass fiber plastic and reinforced nylon and other materials to make the insulator, these materials contain polar genes, moisture absorption is large. Insulation performance at room temperature can meet the product requirements, while at high temperature and humidity, the insulation performance is not qualified.
But the use of special engineering plastics PES (polyphenylene ether sulfone) material, the product by 200 ℃, 1000h and 240h moisture test, insulation resistance change is small, still in 105 MΩ or more, no abnormal changes.
Temperature
High temperature can destroy the insulation material, causing a reduction in insulation resistance and voltage resistance. For metal shell, high temperature can make the contact parts lose elasticity, accelerate oxidation and occurrence of coating deterioration. Such as GJB598 production of environmentally resistant fast separation of electrical connector series II products, insulation resistance of 25 ℃ should be not less than 5000MΩ, while 200 ℃, it is reduced to not less than 500MΩ.
Humidity
Humid environment causes the attraction and diffusion of water vapor on the surface of the insulator, which easily reduces the insulation resistance to below MΩ level. Long-term high temperature environment will cause physical deformation of the insulator, decomposition, etc., creating a breathing effect and electrolytic corrosion or cracking. Such as the production of ribbon cable electrical connectors according to GJB2281, the insulation resistance value under standard atmospheric conditions should be not less than 5000MΩ, and by 90% to 95% relative humidity, temperature 40 ± 2 ℃, 96h damp heat test after the insulation resistance down to not less than 1000MΩ.
Fouling
The cleanliness of the insulator's interior and surface has a significant impact on the insulation resistance. As a result of injection molding insulator with the powder or gluing the upper and lower insulation mounting plate mixed with impurities in the adhesive material. Or due to repeated plugging and unplugging wear residual metal chips and solder termination residual flux seeped into the insulator surface, will significantly reduce the insulation resistance.
Test Voltage
The test voltage applied during the insulation resistance test is highly relevant to the test results. Because the test voltage increases, and the increase in leakage current is not a linear relationship. The rate of increase in current is greater than the rate of increase in voltage, so the test voltage increases when the measured insulation resistance value will drop. Electrical connector product technical conditions referenced in the test method, the test voltage are clearly defined, usually specified as 500 V. Therefore, you can not use the general ohmmeter, DC bridge and other resistance measuring instruments to measure insulation resistance.
Duration (reading time)
As the electrical connector under test has a certain capacitance between the measuring poles, the power supply should first charge the capacitance at the beginning of the measurement. Therefore, during the test there is often a gradual increase in the resistance value indicated on the insulation resistance tester, which is a normal phenomenon. Many electrical connectors test methods clearly specify that the reading on the insulation resistance tester must be read after the voltage is applied for 1min.
3. Discussion of the Problem
Inspection of Environmental Temperature and Humidity
Electrical connector technical conditions usually provide for the use of product environmental temperature and humidity, such as temperature -55 ~ 125 ℃, humidity of 40 ± 2 ℃, 95% ± 3%. Technical conditions specify that the product can be used in the above temperature and humidity environment, does not mean that the production plant in the above conditions of use of the insulation resistance should be tested to meet the normal atmospheric pressure under the assessment of the indicators.
If there is an upper limit of the use of temperature 125 ℃ and 40 ± 2 ℃, 93% ± 3% of the hot and humid environment conditions to measure insulation resistance, should be specified in the technical conditions of high temperature and hot and humid environment test assessment indicators for assessment, and should not be assessed by the assessment of the normal atmospheric pressure indicators for assessment.
The same batch of products in the northern climate under drier conditions (humidity <50%) factory inspection of insulation resistance greater than 1000MΩ, is qualified; but the products shipped to the southern use of the plant, in a more humid environment (humidity > 80%) retest, the insulation resistance of only 100MΩ ~ 200MΩ, is unqualified. In this case, sometimes after cleaning and drying with alcohol, just take out the test is qualified. But placed to the next day and then retest failed.
To this end, it is recommended that the manufacturer in the product acceptance test, insulation resistance should be controlled above a specified value of an appropriate level, to maintain a certain margin; do not barely reach the specified value of the product in a dry environment is judged to be qualified, so as to avoid the supply and demand sides due to the inspection of different climatic and environmental conditions resulting in inconsistent test results and cause controversy.
In order to clarify the requirements of the test environment temperature and humidity, some test methods now provide for both the test environment temperature and humidity (relatively wide range), but also provides for the emergence of divergent arbitration temperature and humidity requirements (relative to take the middle limit of a narrower range). Such as GJB1217-91 "electrical connector test method" provides: test the standard atmospheric conditions, temperature 15 ~ 35 ℃, humidity 20% ~ 80%, air pressure 73 ~ 103kPa. Arbitration test of the standard atmospheric conditions, the temperature 25 ± 1 ℃, humidity 50% ± 2%, air pressure 86 ~ 106kPa.
The Impact of Inspection Tooling
Electrical connector technical conditions, electrical connectors between all contact parts and all contact parts and the insulation resistance between the shell should be in line with the specified value; also provides for the duration of the applied voltage to be more than 1min. Therefore, many electrical connectors produced by the production of each type of specification products are equipped with the corresponding 2 to 3 different arrangements for the connection of the inspection tooling (head hole with seat pin tooling or head pin with seat hole tooling ).
By applying test voltage in parallel between contact points and points, between rows and rows and between all contacts and shells to check whether its insulation resistance is qualified. This test tooling in parallel with the voltage applied than a single contact between the voltage applied to harsh conditions.
Therefore, if the test tooling test found that the insulation resistance is not qualified, it is allowed to use the tooling directly to apply voltage between the single point for retesting. But the existing part of the production plant and the vast majority of the use of units do not use the inspection tooling, but directly with the insulation resistance tester connected to the two test table stick, between each contact or contact between the shell lap, test its insulation resistance is qualified.
This method of different inspection tooling has the following shortcomings:
First, the randomness is very large, it is very likely to produce leakage;
Second, each contact is not possible as there is inspection tooling, you can stay 1min after reading.
So it is possible to cause misjudgment, the reliability of the test is poor.
Of course, even if the use of inspection tooling, before the test must first ensure that the tooling qualified, to ensure that the tooling clean and dry, its own insulation resistance must be qualified, and leave a sufficient margin.
*Metabee high voltage connectors conform to all test requirements, please contact us if you have any request.
