1. Preparation and processing of sample for dielectric strength testing machine Samples are prepared by molding or machining according to the test product specifications and test requirements. The two surfaces of the sample in contact with the electrode shall be parallel and shall be as smooth and smooth as possible. The thickness of the sample is generally not more than 3 mm. When the thickness is greater than 3 mm, the single surface is (3 ± 0.2) mm, and the unmachined surface should be in contact with the high voltage electrode. . Note: The results for samples of different thicknesses cannot be compared. For tests perpendicular to the surface of the material, the specimen is required to have a large enough area to prevent flashover during the test. (Note: Flashover: When the gas or liquid coal around the sample and the electrode is subjected to electrical stress, its insulation performance is lost, and the resulting test loop current causes the corresponding circuit breaker to operate) The geometry of the sample is shown in the table below, and the number of samples in each group shall not be less than three. Sample pretreatment should be carried out in accordance with the product specifications of the test materials. If there is no special requirement, the sample is not less than 24 hours at a temperature of (23 ± 2) ° C and a relative humidity of (50 ± 5)%. 2. The dielectric strength of the dielectric breakdown strength tester is calculated according to equation (5-15). Eb=Ub/d 5-15 Where: Eb-breakdown strength, KV/mm; Ub-breakdown voltage, KV, taking the arithmetic mean of each experiment as the experimental result, taking three significant figures; D-sample thickness, mm. Taking the average of 5 experiments as the experimental result, three significant figures were taken. If the relative error of the individual experimental values ​​to the average exceeds 15%, another sample is taken for 5 experiments, and the experimental results are calculated from the arithmetic mean of 10 experiments. 3. How to judge what the voltage breakdown test results should be? During electrical breakdown, the current in the loop increases and the voltage across the sample drops, causing the circuit breaker to trip or the fuse to blow. The sample has traces such as through holes, cracks or burns along the direction and position of the applied voltage. If the trace is unclear, it can be judged by repeatedly applying the test voltage. 4. Voltage breakdown test terminology explanation of chamfer r The angle of the radius r formed by the electrode contacting the plane edge of the sample is called chamfering. When the electrode area does not change much, the dielectric strength does not change much. When the electrode becomes a semi-spherical shape (r is large), the dielectric strength changes greatly. The edge effect is a phenomenon in which the field strength at the edge is very large. Due to the edge effect, the medium between the edges of the electrodes is easily broken down. The magnitude of the field strength at the edge is related to the chamfering r. Generally, r is small and the field strength is large. Therefore, r=2.5 mm is specified in the standard method. 5. What is the dielectric strength and the withstand voltage of the plastic? Dielectric strength refers to the highest voltage that an insulating material per unit thickness can withstand before breakdown, that is, the maximum electric field strength in kV/mm. Including plastics, films, etc. If you want to test the dielectric breakdown strength of plastics and films, we can use our voltage breakdown tester model KP8009. The instrument is equipped with a withstand voltage test function, so customers can buy more than one insulation withstand voltage tester. 6. Dielectric strength terminology and basic principle of voltage breakdown tester Generally, the higher the dielectric strength, the better the insulation quality of the material. The main performance of plastic breakdown The insulation performance is destroyed, an arc is generated at the breakdown point, the material is perforated, melted, zoomed, burned, and the like. In a solid medium, there are always some free electrons that are accelerated by an external electric field to strike a neutral atom, causing the atoms to ionize, eventually causing material breakdown. Polymer breakdown is usually related to temperature When below a certain temperature, the boundary strength is independent of temperature - electrical breakdown Above this temperature, the boundary strength decreases as the temperature increases. Polymer materials are often accompanied by thermal breakdown in the event of electrical breakdown. Thermal breakdown, the dielectric strength decreases rapidly with increasing temperature. Plastic breakdown features: The breakdown process of plastic materials is usually accompanied by thermal breakdown and electrical breakdown. It is difficult to say that the breakdown is some kind of breakdown. In general, materials with high operating temperatures, poor heat dissipation conditions, and large dielectric conductance and loss have a high probability of thermal breakdown. Principle of thermal breakdown The plastic medium generates more heat in the electric field than it can dissipate, causing its internal temperature to rise. When the temperature rises, the resistance decreases, the current flowing through the sample increases, and the heat generated is more, so the cycle is reversed, causing the medium to transform into another aggregation state, losing the withstand voltage capability and the material being destroyed. External performance of thermal breakdown: The dielectric strength decreases rapidly with increasing temperature; Thermal breakdown is related to the length of the voltage; It has little relationship with electric field distortion and electrical properties of surrounding medium; The breakdown point occurs mostly inside the electrode. Dressing Table,Makeup Dressing Table,Vanity Dressing Table,Mirrored Dressing Table Set DUOBUY TECHNOLOGY SHANDONG CO., LTD. , https://www.doubuytech.com
December 28, 2022