Mohsin Ali Tunio

Determination of partial discharge time lag in void using physical model approach

Repetition of partial discharge (PD) activities within a dielectric insulation of high voltage equipment may lead to dielectric breakdown, eventually resulting in failure of the whole equipment. Thus, PD measurement is essential in high voltage insulation system. Modeling of PD activity may increase an understanding of PD phenomenon. One of the parameters which can be determined from PD modeling is the statistical time lag. In this work, a physical model of PD using finite element analysis (FEA) method has been developed to determine the relationship of statistical time lag with different applied stresses; these include different applied voltage, frequency and temperature. The statistical time lag as a function of different applied stresses was determined through comparison between measurement and simulation results. The proposed experimental-modeling approach may increase an understanding on the physical explanation about the statistical time lag.

Partial discharges within two spherical voids in an epoxy resin

A void in a dielectric insulation material may exist due to imperfection in the insulation manufacturing or long term stressing. Voids have been identified as one of the common sources of partial discharge (PD) activity within an insulation system, such as in cable insulation and power transformers. Therefore, it is important to study PD phenomenon within void cavities in insulation. In this work, a model of PD activity within two spherical voids in a homogeneous dielectric material has been developed using finite element analysis software to study the parameters affecting PD behaviour. The parameters that have been taken into account are the void surface conductivity, electron generation rate and the inception and extinction fields. Measurements of PD activity within two spherical voids in an epoxy resin under ac sinusoidal applied voltage have also been performed. The simulation results have been compared with the measurement data to validate the model and to identify the parameters affecting PD behaviour. Comparison between measurements of PD activity within single and two voids in a dielectric material have also been made to observe the difference of the results under both conditions.

Partial discharge phenomena within an artificial void in cable insulation geometry: experimental validation and simulation

In the presence of void in cable insulation, repetition of partial discharge (PD) occurrences is one of the main sources of insulation degradation, which may lead to complete breakdown. Therefore, it is important to monitor the condition of cable insulation through PD measurement. Replicating PD measurement on a test object with the presence of a void within cable insulation may help a better understanding of PD characteristics within cable insulation to be achieved. Therefore, in this work, test samples of cable insulation geometry containing an artificial void were prepared in the laboratory for PD experiment. The PD measurements were done as a function of void size and applied voltage. A physical model of PD activities within an artificial void in cable insulation geometry was also designed using finite element analysis method. The model was developed by considering PD occurrences within non-uniform electric field distribution in the void and charge movement along the void surface. The model was applied for simulation of PDs within the void in cable insulation geometry to increase the understanding on PD physical phenomena. This includes the impact of distribution of void surface charge on the distribution of the electric field within the void through comparison with the captured measurement results.

Measurement and simulation of partial discharge activity within a void cavity in a polymeric power cable model

In high voltage power cable, partial discharge (PD) phenomenon may occur within defects that exist in its insulation system. The insulation is normally made of a dielectric material, typically polymeric materials. Repetition of PD activity at the defect site may cause insulation breakdown when the defect grows until it bridges the electrodes between the insulation. Consequently, breakdown of the whole cable will occur. Thus, measurement of PD activity within cable insulation system has been extensively used to monitor the condition of power cables in service. A void cavity is one of the most common PD sources when a cable insulation is stressed under high electric field. In this work, measurements of PD activity within an artificial cylindrical void in the insulation layer of a 22 kV cross-linked polyethylene (XLPE) cable was performed. A two-dimensional model of a cable insulation geometry with a void was also developed using finite element analysis (FEA) software. The model was used to calculate the electric field magnitude in the void within the cable insulation under different conditions of voids and insulation. From this work, an understanding on PD phenomenon within a cylindrical void in a power cable insulation can be enhanced.

Experiment and modeling of void discharges within dielectric insulation material under impulse voltage

The presence of cavity in motor insulation fed by variable speed drive is one of the sources of partial discharge (PD) occurrence, especially under impulse voltage. This is a serious problem as PD can accelerate degradation of the motor insulation. Therefore, it is important to prevent void discharges from occurring in motor insulation under impulse voltage. In this work, the characteristics of void discharges within dielectric insulation material under impulse voltage were investigated through experiment and modeling. The test object consists of a rectangular void within a polyethylene material. The test object was stressed with different peak magnitude, front time and tail time of the applied impulse voltage. The experimental results were reproduced by simulation results from a void discharge model in insulation material. From the model that was developed, a better understanding on physical parameters that influence the characteristics of void discharges within dielectric material under impulse voltage can be attained.

Surface Discharge Characteristics on HDPE, LDPE and PP

The degradation of polymer insulation is affected by many factors. One of the main factors is surface discharge. In this work, the characteristics of surface discharge on different types of polymer insulation material under different types of electrode shapes were studied. The insulation materials used were high density polyethylene (HDPE), low density polyethylene (LDPE) and polypropylene (PP). Different types of electrode shape used were sharp, flat and sphere electrodes. From the experiments that have been performed, surface discharge characteristics were found to be influenced by the type of insulation material and the electrode shape. Hence, a better understanding on the characteristics of surface discharges may be attained.

Simulation of partial discharge within a void under square waveform applied voltage

Partial discharge (PD) activity within a void in a dielectric material is influenced by many factors. One of the factors is the applied voltage waveform on the material. In this paper, a two-dimensional (2D) model of a cylindrical void in polyethylene layers has been developed using finite element analysis (FEA) software. The model was used to simulate PD activity in the void under square waveform applied voltage. The obtained simulation results were compared with the measurement results from literature. It was found that both results are within reasonable agreement but with only slight disagreement. From comparison, critical parameters from the model affecting PD activity under square waveform applied voltage were identified; they include the inception and extinction voltages and electron generation rate. This finding may increase an understanding of PD behaviour within a void in a dielectric material under square waveform applied voltage.