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Protective measures of epoxy board
2020-09-26

When the electric field strength of the epoxy board applied to the insulating material is higher than the critical value, the current through the insulating material will increase sharply, the insulating material will be broken or decomposed, and the insulation performance will be completely lost. This phenomenon is called insulation breakdown. The voltage at which breakdown occurs is called breakdown voltage, and the electric field strength during breakdown is called breakdown strength. The unit is kV/m. The breakdown of solid insulating materials can be roughly divided into electrical breakdown, thermal breakdown, and discharge breakdown. Kind of form. Under the action of a strong electric field, the electric particles inside the insulating material move violently, causing collision ionization, destroying the molecular structure, increasing the conductance, and finally breaking down, called electric breakdown; under the action of a strong electric field, the inside of the insulating material occurs due to dielectric loss If the heat is too late to dissipate, it will increase the internal temperature of the insulating material, leading to breakdown of the molecular structure and breakdown, which is called thermal breakdown; under the action of a strong electric field, the bubbles contained in the insulating material first undergo collision ionization and discharge The impurity is also vaporized by the electric field heating, and the impurity vaporizes and generates bubbles, so the bubble discharge further develops, resulting in the breakdown of the entire material, which is called the discharge breakdown breakdown voltage, which is in the continuous boost test, in the specified test Under conditions, the voltage at which the sample breaks down.

Epoxy board refers to the quotient of the breakdown voltage and the distance between the two electrodes of the applied voltage under the specified test conditions. The electrical strength test result can be used to detect the change or deviation of the performance from the normal value due to process changes, aging conditions or other manufacturing or environmental conditions. Flashover refers to the gas or liquid medium surrounding the sample and the electrode under electrical stress. When the insulation performance is lost, the test circuit current caused by this will prompt the corresponding circuit breaker to operate. The appearance of the carbonized channel or the breakdown of the penetrating sample can be used to distinguish whether the test is breakdown or flashover. In fact, the breakdown of the insulation structure often occurs in multiple forms such as electricity, heat, and discharge, and it is difficult to separate them completely. Generally speaking, when the material has poor heat resistance, high working temperature, and poor heat dissipation conditions, the possibility of thermal breakdown is greater. The electrical breakdown strength of solid insulating materials is higher than the thermal breakdown strength, while the discharge breakdown strength depends on bubbles and impurities. Therefore, the breakdown strength fluctuates greatly. The breakdown strength decreases as the ambient temperature increases. In a uniform electric field, the breakdown voltage is proportional to its thickness, that is, the breakdown strength does not change. In practice, the electric field distribution is generally uneven. The electric field strength at a certain point in the insulating material first reaches a critical value and then breaks down first, causing the entire insulation Breakdown of materials. Therefore, in actual use, the breakdown voltage of the insulating material is not proportional to the thickness. The methods that can be used to improve the breakdown strength of the insulating material are: keep it clean, without harmful impurities in the material; make the entire insulating material have a dense overall structure , Use reasonable impregnation or other methods to eradicate pores or bubbles in the insulating material; improve the electric field distribution to make it as uniform as possible.

Epoxy board reasonably selects materials and constitutes an insulating structure so that each part can reasonably assume the role of electric field strength and prevent breakdown caused by partial discharge; improve the environmental conditions of the insulating material and adopt protective measures such as casting and surface coating. In order to enhance heat dissipation, reduce vibration and protect the main insulation structure from direct contact with moisture, ozone and other harmful gases. The test method and standard for measuring the breakdown voltage is GB/T1408, which specifies the test method for measuring the short-term electrical strength of solid insulating materials (power frequency (48~62Hz)), which is used as the surrounding medium for the test of solid insulating materials. , But not suitable for liquid and gas tests.


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