Pressboard

About: Pressboard is a research topic. Over the lifetime, 1123 publications have been published within this topic receiving 9089 citations.

A fast and reliable dielectric diagnostic method to determine moisture in power transformers

Abstract: This paper describes a novel dielectric diagnostic method ldquoDIRANArdquo which features a fast measurement methodology and an improved analysis algorithm for determining moisture in pressboard and paper of oil-paper-insulated transformers. Dielectric response methods provide substantial advantages compared to moisture determination by conventional equilibrium diagrams, for example it is unnecessary to wait for moisture equilibrium. For the new approach, combination of time and frequency domain measurements substantially shortens the measurement time, typically to 25 % compared to a pure frequency domain measurement. The data analysis algorithm compares the measured dielectric properties of the actual power transformer to modeled dielectric properties. The software features a compensation for the influences of conductive aging byproducts. Conductive aging byproducts have similar dielectric properties as water; without compensation the analyzed moisture content will be too high, leading to unnecessary actions like drying. This paper also includes examples of practical onsite measurements in comparison to other measurement methods and a guide for assessing the obtained moisture content.

A review of the techniques used by utilities to measure the water content of transformer insulation paper

Abstract: Cellulosic insulation materials are very widely used in power transformers, in designs up to 1,500 MVA [1]. Cellulosic insulation is formed of either wood, pressboard, or Kraft paper. The wood and thick sections of pressboard are used to manufacture the base of the transformer; pressboard is also used for the spacers and barriers of the windings, and the paper is wrapped around the current carrying conductors. The water content of this cellulosic insulation must be monitored, because if it becomes too high, a transformer can fail on overload, and will reach the end of its functional life sooner because the paper insulation will age faster [2]. Eventually, the paper will become brittle, and will either tear or lift off the conductor. The water content of paper (WCP) is the ratio of the mass of adsorbed water to the mass of dry paper, usually expressed as a percentage. Water can migrate out of the wood and pressboard and around the system, eventually increasing the WCP. If the WCP becomes too high, the transformer may be dried out by the relevant utility [3].

Dielectric Properties of Natural Esters and their Influence on Transformer Insulation System Design and Performance

Abstract: There is considerable knowledge of transformer insulation system design based on the use of cellulose insulation used in conjunction with mineral oil. This knowledge is based on over 100 years of transformer design and manufacture. Insulation design is based on the stress distribution between the solid insulation, in this case Kraft, and the fluid. In power and distribution transformers the stress is distributed in accordance with the permittivity of the various insulation components. The insulation designer must determine the stress in the fluid, in the solid insulation and along the interface. Design curves have been established for mineral oil, which give limits to the allowable stress at each of these critical areas. Considerable work has been done and is in progress to establish these criteria for Kraft insulation in natural ester fluids. The permittivity of natural ester fluid and various Kraft insulation materials including diamond pattern paper (DPP), low density pressboard and high density pressboard impregnated with natural ester is presented. A test program to determine the design criteria for interfacial stress (creep stress) is presented

Application of relaxation current measurements to on-site diagnosis of power transformers

Abstract: Results of relaxation current measurements on impregnated pressboard samples and on multi-layer arrangements of pressboards in series with oil ducts are presented. The measurements have been performed dependent on the material properties of oil and pressboard and the volume ratio of these materials. Calculated values of related dielectric quantities such as tan/spl delta/ versus frequency, based on equivalent circuits obtained from relaxation currents are also shown. The relaxation currents of multi-layer test objects are calculated from the dielectric properties of the individual components and their geometrical capacitances. Finally, it is shown that relaxation currents of power transformers can easily be measured and their evolution can be described well by basic relations of linear dielectric theory.

Experimental evaluation on dielectric and thermal characteristics of nano filler added transformer oil

Abstract: Liquid dielectrics play a major role in the insulation system used in high voltage equipments. The most commonly used liquid dielectric is transformer oil which serves the dual purpose as insulation and a coolant. It also acts as insulation between the conductingparts and as an arc quenching medium. Moreover the breakdown strength of the paper and the pressboard insulation depends on the properties of the oil in which it is impregnated. Therefore investigations have been attracted towards the development of nano fluids with better thermal and dielectric properties. In this work, ceramic nano particles are chosen because of their electrical insulating property. Because of higher relative permittivity Zirconia(ZrO2) and Titania(TiO2) nano particles are used here. The dielectric and thermal properties are measured for different concentrations of nanofillers. AC and Impulse breakdown voltage measurements were performed as per IS 6792:1972 and IS 11697:1986 respectively. The specific resistivity and the dielectric dissipation factor measurement were carried with reference to IS 6103:1971 and IS 6262:1971. The kinematic viscosity and flash point are measured as per IS 1448 Part-25:1970 and IS 1448 Part-21:1970 respectively.