A.H.A. Bakar

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.

Flashover voltage of insulator string under various conditions

Porcelain insulator has been slowly replaced by composite insulator in power grid nowadays. However, flashover fault still occurs on this insulator type. Under certain conditions, partial discharges may occur on the insulator and lead to a complete flashover. The flashover can cause the breakdown and damage the whole power system. Therefore, this paper reports on the flashover voltage of 11kV composite insulator under different conditions. They are pollution methods, insulator surface condition, water content, operating orientations and the ambient temperature. It was found that the flashover voltage can be improved by using 0° operating orientation angle of the insulator, at lower temperature, dry condition, less insulator surface roughness and no pollution on the insulator. Therefore, a better understanding of flashover voltage under different pollution conditions may be attained from this work.

Modelling of partial discharge pulses in high voltage cable insulation using finite element analysis software

Measurement of partial discharge (PD) in high voltage equipment is widely used in condition assessment and performance maintenance of the insulation system. One of the methods to evaluate PD data from condition monitoring activities is by analysing PD signals captured from the PD detection equipment. In high voltage power cable, PD pulses originated from defect sites within cable insulation can propagate along the insulation. A better understanding of PD pulse propagation along cable insulation can be attained through simulation work. Therefore, in this paper, the propagation of PD pulses within cable insulation was simulated using finite element analysis (FEA) software and its velocity of propagation was calculated. The result was compared with the theoretical value and simulation results using PSCAD software. The effect of cable insulation parameters on the PD pulse propagation was also studied through the FEA model; these include variation of the permittivity and conductivity of the insulation material.

Electric field distribution in 132 kV one piece premolded cable joint structures

Defect in a cable joint is one of the main reasons of a power system being faulty. A defect can cause the electric field in the cable joint to become higher than the material surrounding the defect. This may result in partial discharge (PD) activity to occur within the defect site. When PD is repeating at the defect site, the material surrounding the defect will be affected, where PD may extend its path in the material. This may result in a breakdown at cable joint and consequently causes breakdown on the whole system. Therefore, the purpose of this research is to study the electric field distribution in 132 kV one piece premolded cable joint with and without the presence of defects. A better understanding of the electric field distribution at a cable joint can be attained by modelling the cable joint structure using finite element analysis (FEA) method. Through modelling and simulation results obtained in this work, an understanding of the electric field distribution in defects within cable joint structure can be enhanced.

Corona discharges under various types of electrodes

Partial discharge (PD) is the most unwanted phenomenon in high voltage insulation system. One of the wellknown types of PD in high voltage insulation is corona discharge. In this work, the characteristics of corona discharges from different types of electrodes (sharp, flat and sphere electrodes) were studied to enhance the understanding of corona discharges. The electrical field distribution for all types of the electrodes was also simulated to study the influence of the field on the PD characteristics. The results show that the characteristics of corona discharges and its electric field distribution are heavily influenced by the shape of the electrodes under high voltage stress.

Electric field distribution in 132 kV XLPE cable termination model from finite element method

High voltage cable terminations are widely used in power system networks. A proper design of cable termination is essential in reducing the electric field distribution around the end of high voltage cable. However, if there are defects exist at cable termination structure, the electric field can be enhanced significantly and can be the source of electrical discharges. Therefore, it is important to understand the effect of defects on the electric field distribution at cable terminations. In this work, a 132 kV XLPE outdoor cable termination has been modelled using finite element analysis (FEA) method. The model has been used to simulate the electric field distribution in the cable termination in the presence of defects. Defects that have been considered are void defect in porcelain, stress cone and fluid, sharp pin on the porcelain surface and delamination defect between the insulator and the stress cone. The effect of different void location, material dielectric constant and porcelain radius on the electric field magnitude at cable termination have also been investigated. From the results obtained in this work, a better understanding of the electric field distribution at the cable termination with defects can be attained.

Distribution of electric field in medium voltage cable joint geometry

Cable joint is used to connect different sections of cable because a cable section is limited to a certain length. The design of a cable joint mainly depends on the cable type, the applied voltage and the cores. These factors contribute to the way of how electric field stress is distributed at the cable joint. If there are defects exist within the cable joint insulation material, the electric field at that region is altered. The alteration may cause electrical discharges to occur within the defects if the electric field magnitude is larger than the breakdown strength at the defect sites. Therefore, this paper investigates the electric field distribution in a medium voltage cable joint in the presence of defects. The investigation was done through modelling a medium voltage (MV) cable joint using finite element analysis (FEA) software. Several parameters such as the defect size and location, insulation material dielectric constant and insulation thickness have been studied of their effects on the electric field distribution at the cable joint. The results obtained may be able to help in the designing of cable joint structures which can reduce the electric field stress.

An efficient constraint handling approach for economic load dispatch problem with non-smooth cost function

Increasing of the power demand and fuel cost in power generation required an advanced algorithm for scheduling the output of generating unit in economical manner. The economic load dispatch problem (ELD) problem consists several operational and system constraints such as prohibited operating zones (POZs) and ramp-rate limit that need to handle wisely by optimization algorithm. Previously, the penalty function is widely used to satisfy the power balance and other constraints by augmenting the objective function with the penalized function. However, it required a proper penalty factor tuning and depends on the size of problem. This paper proposes an efficient constraint handling based on the repairing or adjusting infeasible solution into feasible solution in every iterative process. The simulation results show that the proposed constraints handling approach is better than penalty function approach in term of convergence characteristic and robustness.

Condition monitoring of discharged ZnO surge arrester on temperature distribution under various design conditions

Surge arrester is a device for protecting electrical power system from harmful effect of lightning. There are many types of surge arrester in the world, which are categorised by different sizes, voltage ratings, varistors and housing material. In this work, the influence of various parameters in a 132 kV surge arrester design on its thermal distribution has been studied using finite element analysis software, which is COMSOL Multiphysics software. A 132 kV surge arrester model was developed and used to simulate the thermal distribution under normal condition and overvoltage condition using different surge arrester parameters. The surge arrester considered was a Zinc Oxide type. The parameters of surge arrester design that were varied include the arrester length, bushing thermal conductivity, bushing width, glass width and ZnO width. It was found that these parameters affect the thermal distribution within the surge arrester model that has been developed. From the simulation results, understanding on thermal distribution for various parameters of surge arrester can be enhanced. This study may also help in condition monitoring on surge arresters as the effect of different surge arrester designs can be evaluated.