What Are Electrical Properties?

Common ones are rated voltage, current, active power, reactive power, resistance, capacitance, inductance, and conductance.

In order to study the influencing factors of the charge accumulation process of epoxy insulation materials and reduce the surface charge accumulation effect of materials, high resistance meters were used to measure the key electrical properties of epoxy insulation materials at different points in time under DC voltage. A DC test device is used to measure the surface charge under DC high voltage with the help of a capacitance probe method. Through the related theoretical research, the relationship between the resistivity of epoxy insulating materials and the time of DC voltage is obtained, the relationship between the electrical properties of epoxy insulating materials and the accumulation of charges is established, and the improvement measures of the electrical properties of epoxy insulating materials are clarified Under DC voltage, the surface charge of epoxy insulation material accumulates, and it has practical significance to improve the operation reliability of DC insulators of power transmission and transformation equipment. ^[1]

The microstructure of oil-impregnated insulating paper and its relationship with electrical properties during partial discharge damage were studied. Using atomic force microscope and X-ray diffractometer and other materials analysis methods combined with electrical analysis methods such as dielectric spectrometer, high resistance meter and column-column electrode, to analyze the molecular chain structure, aggregate structure and structure of oil-impregnated insulating paper during damage Dielectric constant, dielectric loss factor, volume conductivity, and electrical strength. The results show that during the damage process, the crystalline region of the insulating paper is more susceptible to partial discharge damage than the amorphous region; the crystallinity is increasing and the grain orientation is strengthened, but the grain size, crystal type and two-phase coexisting structure are not changed; the crystallinity Increasing and grain orientation strengthening cause the dielectric constant, volume conductivity, and dielectric loss factor to decrease, but the electrical strength is increasing; crystallization and orientation change the mobility of molecules, ions, and electrons, which causes changes in electrical properties important reason. ^[2]

Electrical performance measurement

At 20 ° C, the Concept80 broadband dielectric spectrum test system (novocontrol GmbH) was used to measure the frequency-domain dielectric spectrum, frequency-domain dielectric loss spectrum, and volume conductivity in the frequency domain of the oil-impregnated insulating paper during damage; meanwhile, according to IEC60093 and The IEC60243-1 standard measures the DC volume conductivity and power frequency electrical strength of oil-impregnated insulation paper, respectively.

In order to make the electrical performance measurement results more representative and effectively reflect the changes in the microstructure of the material, that is, the electrical performance measurement is not affected by moisture and other damage products, take out 5 samples for each measurement. Cleaned with acetone, dried under vacuum and immersed in oil. The average of the five test samples was taken as the measurement result. ^[2]

Electrical performance changes

There is an inherent correlation between structure and performance. The aggregate structure is an important factor that directly affects the performance of materials. In the process of partial discharge damage, the heat generated by the partial discharge leads to an increase in crystallinity and an increase in the degree of orientation that characterize the aggregated structural characteristics of the oil-impregnated insulating paper, which will also cause its electrical properties to change.

Polarization, conductivity, loss and breakdown are the four basic electrical properties of insulating dielectric materials. Polarization includes forms such as instantaneous polarization and relaxed polarization. The dielectric constant (or relative permittivity) is a macro parameter that describes the polarization of a medium. It is divided into real and imaginary parts. It is proportional to the reactive current caused by the change. The imaginary part is directly proportional to the active current caused by relaxed polarization when the conductance is not considered; conductance includes electronic conductance and ionic conductance. Conductivity is a macro parameter that characterizes the conductance of the medium. The loss is mainly caused by conductance and relaxed polarization, and its characteristics can be characterized by the dielectric loss factor tan, which is calculated when the electrical conduction current is not considered. Breakdown characterizes the ultimate ability of the medium under the action of an electric field, and electrical strength characterizes this ability of the medium, which is a characteristic parameter of the medium. ^[2]

Relative dielectric constant of oil-immersed insulating paper changes with frequency

During partial discharge damage, after the oil-impregnated insulating paper was cleaned, vacuum dried, and oil-impregnated, the water content was less than 0.1817%, and the composition of the oil-impregnated insulating paper was basically the same. As the grain size increases, the grain orientation strengthens. At the same time, its dielectric constant, volume conductivity, dielectric loss factor, and electrical strength are measured.

After the oil-impregnated insulating paper is cleaned, vacuum-dried, and oil-impregnated, the real part of the dielectric constant increases with decreasing frequency, but the imaginary part decreases first and then increases with decreasing frequency, with a minimum value. With the increase of the damage time, both the real and imaginary frequency-domain spectral lines move downward, but the shape of the spectral line remains basically unchanged; in the low-frequency region, the spectral line decreases faster and the minimum value of the imaginary part moves to the left. This indicates that the dielectric constant of oil-impregnated insulating paper decreases with increasing crystallinity and grain orientation. ^[2]

Volume conductivity of oil-impregnated insulation paper measured at DC

The volume conductivity of oil-impregnated insulation paper measured under AC and DC conditions is described. After the oil-impregnated insulating paper is cleaned, vacuum-dried, and oil-immersed, its volume conductivity decreases with decreasing frequency; as the damage time increases, the frequency-domain spectral line of volume conductivity also moves downward, but its The shape of the spectral line is basically unchanged, and the decline rate of the spectral line is fast in the low frequency region; when the frequency is reduced to its minimum limit value, the voltage source displays a DC characteristic. The measured volume conductivity under DC conditions also shows a downward trend with increasing damage time. It can be seen that with the increase of crystallinity and grain orientation, the volume conductivity of oil-impregnated insulating paper shows a downward trend. ^[2]

Dielectric loss factor of oil-immersed insulating paper varies with frequency

With the change of the dielectric constant and volume conductivity, the dielectric loss factor will change accordingly. After the oil-immersed insulating paper is cleaned, vacuum-dried, and oil-immersed, the change of the dielectric loss factor in the frequency domain is similar to the law of the imaginary part of the dielectric constant, that is, it decreases first and then increases as the frequency decreases. A minimum value appears; as the damage time increases, the spectral line of the dielectric loss factor moves downward, but the shape of the spectral line is basically unchanged, and the minimum value shifts to the left. This shows that as the crystallinity increases and the grain orientation strengthens, the dielectric loss factor of oil-impregnated insulating paper shows a downward trend. ^[2]

Electrical strength of oil-impregnated insulation paper

During the damage process, the electrical strength measured after the oil-impregnated insulating paper was cleaned, vacuum dried, and oil-impregnated. It can be seen that with the increase of the damage time, the electrical strength of oil-impregnated insulating paper is generally on the rise. In other words, as the crystallinity increases and the grain orientation strengthens, the electrical strength of oil-impregnated insulating paper is on the rise.

In short, as the crystallinity increases and the grain orientation strengthens, the dielectric constant, volumetric conductivity, and dielectric loss factor of oil-impregnated insulating paper all show a downward trend, but their electrical strength generally increases. ^[2]