Common ones include ratedvoltage,current, active power, reactive power, resistance, capacitance, inductance,conductance.
Semiconductors cover a broader range, such as DC current gain,AC current gain, rectified current, reverse breakdown voltage, forward conduction voltage, junction capacitance,noise figure, characteristic frequency, cutoff frequency, power dissipation, etc.
ICs also have many, such as maximum operating voltage, slewrate of op-amps,bandwidth, distortion factor, conversion rate of ADCs, conversion accuracy, resolution, etc.
The main electrical properties of electrical performance connectors include contact resistance, insulation resistance, and dielectric strength. ① Contact resistance: High-quality electrical connectors should have low and stable contact resistance. The contact resistance of connectors ranges from a few milliohms to tens of milliohms. ② Insulation resistance: An index to measure the insulation performance between contacts and between contacts and the shell of electrical connectors, with magnitudes ranging from hundreds of megohms to thousands of megohms. ③ Dielectric strength, also known as voltage withstand or dielectric voltage withstand, characterizes the ability of connectors to withstand the rated test voltage between contacts or between contacts and the shell.
Influence;
To study the influencing factors of charge accumulation process in epoxy insulating materials and reduce the surface charge accumulation effect, a high resistance meter was used to measure key electrical properties such as volume resistivity and surface resistivity of epoxy insulating materials at different time points under DC voltage, and a DC test device was used to measure surface charge under DC high voltage using the capacitive probe method. Through related theoretical research, the relationship between resistivity of epoxy insulating materials and DC voltage application time was obtained, the relationship between electrical properties and charge accumulation of epoxy insulating materials was established, and improvement measures for electrical properties of epoxy insulating materials were clarified, which is of practical significance for reducing surface charge accumulation on epoxy insulating materials under DC voltage and improving the operational reliability of DC insulators in power transmission and transformation equipment.
Theory of charge accumulation process
For charge to dissipate from the surface, it needs to migrate from the interior to the surface, which will lead to a further decrease in freely movable charges inside the epoxy insulating material. At this time, the migration rate is relatively high, and since the surface charge is small, there is almost no dissipation from the surface to the interior, and charge gradually accumulates on the material surface; then, due to the limited amount of free charge inside the epoxy insulating material, the charge migration rate gradually decreases, while the dissipation of charge along the interior gradually increases. At a certain moment, a maximum value of volume resistivity appears. Subsequently, the charge migration rate further decreases, and since the dissipation along the interior is still increasing at this time, the volume resistivity shows a slight decline until both migration and internal dissipation eventually tend to stabilize, and the volume resistivity also tends to stabilize. This process is the special electrical saturation process under DC electric field.
Improvement of electrical properties of epoxy insulating materials
In terms of volume resistivity. Increasing the initial volume resistivity is beneficial to reduce the charge migration rate and migration current density, but since the increase in volume resistivity also prolongs the duration of stage 1, in addition, increasing the initial volume resistivity will also increase the time constant of charge dissipation along the interior. Therefore, the volume resistivity can only be appropriately increased.
In terms of surface resistivity. The smaller the surface resistivity of epoxy insulating materials, the faster the dissipation speed after surface charge accumulation, that is, if the surface resistivity is reduced, the charge accumulation density will be reduced. However, since under a certain tangential field strength, the reduction of surface resistivity will increase the surface conduction current density, thereby increasing the risk of flashover. The charge density of insulator #3 is relatively large, while the surface resistivity is relatively small, and the surface conduction current is too large, causing flashover. Therefore, the surface resistivity can only be appropriately reduced. In addition, there is a certain matching characteristic between surface resistivity and volume resistivity. When a material has excessively high volume resistivity and excessively low surface resistivity, since the migration current density of internal charge to the surface is small, the migration rate is also small, the surface accumulated charge is small, and the growth rate is small. The surface tangential field strength mainly comes from the component of the applied electric field. At this time, the field strength is relatively large, and because the surface resistivity is too small, the generated charge quickly moves to the electrode loading area, forming an excessive surface conduction current, resulting in flashover. The difference between volume resistivity and surface resistivity of insulator #9 is large, and although the charge amount is small, flashover still occurs. Therefore, there should be a certain difference relationship between surface resistivity and volume resistivity. For example, when the volume resistivity is on the order of 1014Ω·m, the surface resistivity should be on the order of 1011Ω.
Microstructure;
The relationship between the microstructure of oil-impregnated insulating paper and its electrical properties during partial discharge damage was studied. Using material analysis methods such as atomic force microscopy and X-ray diffractometry combined with electrical analysis methods such as dielectric spectroscopy, high resistance meter, and rod-rod electrodes, the molecular chain structure, aggregation structure, dielectric constant, dielectric loss factor, volume conductivity, and electrical strength of oil-impregnated insulating paper during the damage process were analyzed. The results show that during the damage process, the crystalline region of insulating paper is more susceptible to partial discharge damage than the amorphous region; the crystallinity shows an upward trend and the grain orientation is strengthened, but the grain size, crystal type, and two-phase coexistence structure do not change; the increase in crystallinity and grain orientation causes a downward trend in dielectric constant, volume conductivity, and dielectric loss factor, but an upward trend in electrical strength; crystallization and orientation change the mobility of molecules, ions, and electrons, which is an important reason for the changes in electrical properties.
Electrical performance measurement;
At 20°C, the Concept80 broadband dielectric spectroscopy test system (novocontrol GmbH) was used to measure the frequency-domain dielectric spectrum, frequency-domain dielectric loss spectrum, and frequency-domain volume conductivity of oil-impregnated insulating paper during the damage process; at the same time, according to IEC60093 and IEC60243-1 standards, the DC volume conductivity and power-frequency electrical strength of oil-impregnated insulating paper were measured respectively.
To make the measurement results of electrical properties more representative and effectively reflect the changes in the material's microstructure, that is, the electrical performance measurement is not affected by moisture and other damage products, 5 test samples were taken for each measurement, and before measurement, the samples were cleaned with acetone, vacuum dried, and oil-impregnated. The average value of the 5 test samples was taken as the measurement result.
Changes in electrical properties;
There is an inherent correlation between structure and performance, among which the aggregation structure is an important factor directly affecting material performance. During the partial discharge damage process, the heat generated by partial discharge leads to an increase in crystallinity and orientation degree that characterize the aggregation structure of oil-impregnated insulating paper, which will inevitably cause changes in its electrical properties.
Polarization, conduction, loss, and breakdown are the four basic electrical properties of insulating dielectric materials. Polarization includes instantaneous polarization and relaxation polarization, etc. The dielectric constant (or relative permittivity) is a macroscopic parameter describing the polarization of the medium, divided into real and imaginary parts. The real part is proportional to the reactive current caused by instantaneous polarization and relaxation polarization, while the imaginary part, when conduction is not considered, is proportional to the active current caused by relaxation polarization; conduction includes electronic conduction and ionic conduction, etc. Conductivity is a macroscopic parameter characterizing the conduction performance of the medium. Loss is mainly caused by conduction and relaxation polarization, and its characteristics can be characterized by the dielectric loss factor tanδ, whose value is calculated when the conduction current is not considered. Breakdown represents the
