A modified Maxwell model for characterization of relaxation processes within insulation system having non-uniform aging due to temperature gradient

Abstract

Modeling of dielectric relaxation function φ(t) by a distribution of exponential decay functions is advantageous due to its monotonically decreasing property which ensures that φ(t) is integrable over any period of time. Several equivalent circuits based on simple combination of energy storing and dissipating elements are available in literature which are capable of modeling φ(t). One of the widely used two-parameter equivalent circuit for dielectric response modeling of various polymeric dielectric as well as oil-paper insulation is the Maxwell ladder structure. In this paper it is shown that for more accurate modeling and better understanding of the dielectric response of complex insulation system like oil-paper insulation of high voltage equipments operating under temperature gradient, modification of Maxwell model is necessary. The proposed model, similar to the classic Maxwell circuit, is also composed of a number of parallel branches, but unlike the former, the proposed model considers each of the parallel branches to be composed of not just one but a number of exponential functions. He has published about 140 research papers, has authored a book, edited three books and developed three online courses. His current fields of interest are numerical field computation, computer aided design and optimization of insulation system and condition monitoring of transformers.

Condition assessment of cellulosic part in power transformer insulation using transfer function zero of modified debye model

“…Therefore, it can be understood that a single RC branch has limited capability to fully describe the behavior of a dipole groups distributed throughout the insulation [7]. Though the effect of measurement temperature has been analyzed to a significant extent by CIGRE TF.D1.0109 [4] and other researchers [8], few literature are available that address the effect of non-linear aging and its subsequent effect on insulation model parameters. The authors have shown that the Modified Debye Model shown in Figure 6 is capable of modeling this non-linear aging [7] and hence provides a better representation of the insulation.…”

“…It is reported in [8][9] that with the passage of time, cellulosic parts of transformer insulation undergoes nonuniform aging. It is further reported in [8] that unlike Modified Debye Model (MDM), CDM is incapable of modeling the effect of such non-uniform aging.…”

“…It is further reported in [8] that unlike Modified Debye Model (MDM), CDM is incapable of modeling the effect of such non-uniform aging. Though the effect of temperature (at the time of measurement) on dielectric response of insulation has been analyzed to a significant level by CIGRE TF.D1.0109 [4] and other researchers [10], few literature are available that address the effect of non-linear aging and its subsequent effect on dielectric response and insulation model parameters.…”

Prediction of moisture present in cellulosic part of power transformer insulation using transfer function of modified debye model

“…When the insulation shown in Figure 2 is approximated by Figure 3, the insulation model (shown in Figure 1) can be represented in the form shown in Figure 4. It is shown in [8] that unlike CDM, the Modified Debye Model (MDM) shown in Figure 4 is capable of taking into account the effect of the non-uniform aging in cellulosic parts and hence is a better representation of the overall insulation. It should be mentioned here that effect of non-uniform aging on dielectric response is difficult to study using scaled down physical model due to reduced volume of cellulosic material and lower power rating.…”

“…Though the effect of measurement temperature on dielectric response of insulation has been analyzed to a significant level by CIGRE TF.D1.0109 [1] and other researchers [7], only few papers are available that analyzes the effect of non-uniform aging on dielectric response and hence on insulation model parameters. It is shown in [8] that Modified Debye Model, a modification of CDM, is capable of modeling the non-linear aging of cellulosic parts in insulation.…”