Abstract
A high-density electrical pressboard plays a significant role in maintaining the safe and stable operation of power equipment. In response to concerns about finding an evaluation method based on the dielectric performance of the pressboard, this study set up a measurement platform to capture data for three key dielectric properties, namely, relative permittivity, volume resistivity, and surface resistivity. Five kinds of pressboards obtained from representative insulating materials manufacturers were chosen as test samples, and the effects of temperature and moisture content of the pressboards on their dielectric properties were quantitatively investigated. The results indicated that (1) with increasing temperature and moisture content of the pressboards, there was an increase in the relative permittivity, with a maximum increase of 55.85%; (2) the higher the temperature and moisture content of the pressboards, the lower the volume and surface resistivity, and the maximum reduction was as much as 98.25%; (3) significant differences exist in the dielectric properties of different batches of pressboards from the same manufacturer; and (4) the results of tests of conventional physical and chemical properties of pressboards could help explain the differences in dielectric properties between different types of pressboards. Finally, based on the variation in dielectric properties for different test conditions, a method for evaluating the performance of pressboards is proposed. Using this method, the dielectric properties of different insulating pressboard products can be compared horizontally, which will provide data support and technical reference for the design of insulation structures and the selection of insulating materials for different applications.
Highlights
With the rapid development of high voltage direct current (HVDC) transmission projects, the capacity of power grids continues to increase and the operating voltage levels of converter transformers are continually increasing
In response to concerns about finding an evaluation method based on the dielectric performance of the pressboard, this study set up a measurement platform to capture data for three key dielectric properties, namely, relative permittivity, volume resistivity, and surface resistivity
The results indicated that (1) with increasing temperature and moisture content of the pressboards, there was an increase in the relative permittivity, with a maximum increase of 55.85%; (2) the higher the temperature and moisture content of the pressboards, the lower the volume and surface resistivity, and the maximum reduction was as much as 98.25%; (3) significant differences exist in the dielectric properties of different batches of pressboards from the same manufacturer; and (4) the results of tests of conventional physical and chemical properties of pressboards could help explain the differences in dielectric properties between different types of pressboards
Summary
With the rapid development of high voltage direct current (HVDC) transmission projects, the capacity of power grids continues to increase and the operating voltage levels of converter transformers are continually increasing. The main insulating structure of a converter transformer is a typical oil–pressboard composite insulation composed of transformer oil and a high-density pressboard for electrical purposes.. The main insulating structure of a converter transformer is a typical oil–pressboard composite insulation composed of transformer oil and a high-density pressboard for electrical purposes.3 The latter (referred to as “pressboard” in the following) is made of natural vegetable fibers, mineral fibers, synthetic fibers, and other admixtures. During the installation or maintenance processes carried out on transformers, the pressboard can encounter external ingress of moisture, and the aging process of pressboard or transformer oil can produce additional quantities of moisture Both these conditions would exert significant moisture-dependent effects on the pressboard.. Both these conditions would exert significant moisture-dependent effects on the pressboard. the key dielectric properties of the pressboard and their variation with external conditions such as temperature and moisture will directly or indirectly affect the operational reliability, safety, and service life of related power equipment
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