Space Charge Properties Of Two Kinds Of Oil-paper Under DC Electric Field During The Process Of Thermal Aging

Transformer is one of the core equipment of energy conversion in power system, the reliability of its operation is related to the operation of power grid stability and security directly. During its normal operation of insulation paper in transformer, space charge will be generated to effect the field distribution of material when under the electric field. Paper will be also under the action of thermal stress and generate thermal degradation, and lead to deterioration of insulation. These phenomenen will impact the improvement of insulating paper life and limited service life of power transformers. Because people's understanding with the relationship between thermal aging of paper and space charge transport properties is still limited, it will impact the development of new anti-aging insulation material, and restrict the development of power transformer insulation to a certain extent.This paper analyzes the space charge characteristics between new synthetic fiber insulation paper named NOMEX and traditional plant cellulose insulation paper when under the action of DC electric field, and research the evolution of total charge amount in insulation paper when under the DC field and remove the field, and discuss the charge transport properties of inject, migrate, accumulate, decay in two insulation materials. Finally, the total space charge decay curves of plant cellulose insulation paper were fitted by using the total charge exponential decay model, and extract two characteristic parameters of decay time constantτand the half-life t1/2 to characterize the decay capability of the residual space charge in insulation paper under different thermal aging status.The mainly conclusions in this paper are as follows:①NOMEX paper have a higher threshold than cellulose paper. Thermal aging will influence the space charge characteristics of cellulose paper dramaticlly, the amount of charge injection increase and injection rate slowed down gradually, threshold of charge injection decreased. The differences of pace charge characteristics of insulating paper under thermal aging process are lower.②Early in the thermal aging, the amount and dissipation rate of residual charge in NOMEX paper are lower than cellulose paper. The amount and dissipation rate of residual charge in NOMEX paper dropped further under thermal aging, but the amount of residual charge in cellulose paper increase and dissipation rate solwed up significantlly.③The polarity of master charge in two insulation materials are changed observably in the process of thermal aging. Injection rate of master charge in cellulose paper is greater than NOMEX paper.④The distribution density and the depth of trap are enlaged but the charge mobility reduced in thermal aging. The capbility of charge mobility and transport in NOMEX paper are lower than cellulose paper.⑤total space charge decay curve of cellulose paper is submit to exponential function better, and decay time constantτand half-life t1/2 could characterize the decay capability of the total residual charge preferably.