D G Fernando - Academia.edu (original) (raw)
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Papers by D G Fernando
Engineer: Journal of the Institution of Engineers, Sri Lanka, 2020
The irregularity of particle motions during quasi-static deformation is investigated using discre... more The irregularity of particle motions during quasi-static deformation is investigated using discrete element (DEM) simulations of of sphere and sphere-cluster assemblies. Three types of inter-particle movements are analyzed: relative motions of particle centers, relative motions of material points of two particles at their contact, and the traversal of contacts across the surfaces of particles. Motions are a complex combination of rolling, sliding, and elastic distortion at the contacts, and all motions are highly irregular and variant, qualities that increase with increasing strain. The relative motions of particle centers diverges greatly from those of an affine displacement of the particles. The motions of the non-convex sphere-cluster particles was more regular that those of spheres. The paper also investigates the effect of the distance between two remote particles and their pair-wise relative displacements. Even for particle-pairs separated by more than 6 intermediate particles, the relative motions do not conform with the mean deformation (affine) field. Force chains are shown to be transient features, which survive only briefly across elapsed strains.
Engineer: Journal of the Institution of Engineers, 2020
Fast Valving (FV) mechanism of steam turbines is considered to be one of the most effective actio... more Fast Valving (FV) mechanism of steam turbines is considered to be one of the most effective actions for enhancing the security of a power system subsequent to disturbances. It plays a significant role in mitigating the impact of severe disturbances by instantly decreasing steam turbine power, thus ensuring the power system stability. There is a direct relationship between the settings of Over-Speed Protection Control (OPC) unit of steam turbines and the control functions of FV. This paper proposes a generalized simulation-based procedure to determine the optimum intermediate valve actuation timings of the FV control action. A coal-fired thermal power plant has been used as the case study and the accuracy of the settings made using the proposed approach has been demonstrated using actually happened contingencies in a real power system. Finally, it is concluded that the proper selection of actuation timings of intermediate valves for FV scheme has a significant effect on enhancing fre...
Contamination-driven insulator failure is a problem that incessantly plagues distribution systems... more Contamination-driven insulator failure is a problem that incessantly plagues distribution systems. Contamination levels can continue to grow unless abated by natural cleaning or if not taken measures to wash insulators at the distribution level in a preventative maintenance mode. In order to assess the pollution behavior, 33kV pin type insulator was selected as a sample insulator and been subjected for natural pollution at three selected localities (zone 1, 2 and 3) for considerable period. The naturally polluted insulators have been subjected for conductivity test and by which the equivalent salt deposit density (ESDD) is calculated. Subsequently, artificially contaminated insulators of different pollution severities were tested for power frequency and impulse test in the High Voltage Laboratory of University of Moratuwa. Finally, it is recommended that insulators in Zone 1 have to be treated after 8 months from the date of last treatment and those in Zone 2 & 3 to be treated after...
Engineer: Journal of the Institution of Engineers, Sri Lanka
Contamination-driven insulator failure is a problem that incessantly plagues distribution systems... more Contamination-driven insulator failure is a problem that incessantly plagues distribution systems. Contamination levels can continue to grow unless abated by natural cleaning or if not taken measures to wash insulators at the distribution level in a preventative maintenance mode. In order to assess the pollution behavior, 33kV pin type insulator was selected as a sample insulator and been subjected for natural pollution at three selected localities (zone 1, 2 and 3) for considerable period. The naturally polluted insulators have been subjected for conductivity test and by which the equivalent salt deposit density (ESDD) is calculated. Subsequently, artificially contaminated insulators of different pollution severities were tested for power frequency and impulse test in the High Voltage Laboratory of University of Moratuwa. Finally, it is recommended that insulators in Zone 1 have to be treated after 8 months from the date of last treatment and those in Zone 2 & 3 to be treated after 18 months under preventive maintenance to get away from flashover. It is also recommended to review the required specific creepage distance (SCD) of insulators installed in non-polluted areas due to the fact that the current practice of insulators placement in most of the places are with SCD of 25mm/kV which is recommended for high polluted zones as per IEC regulation.
Engineer: Journal of the Institution of Engineers, Sri Lanka, 2020
The irregularity of particle motions during quasi-static deformation is investigated using discre... more The irregularity of particle motions during quasi-static deformation is investigated using discrete element (DEM) simulations of of sphere and sphere-cluster assemblies. Three types of inter-particle movements are analyzed: relative motions of particle centers, relative motions of material points of two particles at their contact, and the traversal of contacts across the surfaces of particles. Motions are a complex combination of rolling, sliding, and elastic distortion at the contacts, and all motions are highly irregular and variant, qualities that increase with increasing strain. The relative motions of particle centers diverges greatly from those of an affine displacement of the particles. The motions of the non-convex sphere-cluster particles was more regular that those of spheres. The paper also investigates the effect of the distance between two remote particles and their pair-wise relative displacements. Even for particle-pairs separated by more than 6 intermediate particles, the relative motions do not conform with the mean deformation (affine) field. Force chains are shown to be transient features, which survive only briefly across elapsed strains.
Engineer: Journal of the Institution of Engineers, 2020
Fast Valving (FV) mechanism of steam turbines is considered to be one of the most effective actio... more Fast Valving (FV) mechanism of steam turbines is considered to be one of the most effective actions for enhancing the security of a power system subsequent to disturbances. It plays a significant role in mitigating the impact of severe disturbances by instantly decreasing steam turbine power, thus ensuring the power system stability. There is a direct relationship between the settings of Over-Speed Protection Control (OPC) unit of steam turbines and the control functions of FV. This paper proposes a generalized simulation-based procedure to determine the optimum intermediate valve actuation timings of the FV control action. A coal-fired thermal power plant has been used as the case study and the accuracy of the settings made using the proposed approach has been demonstrated using actually happened contingencies in a real power system. Finally, it is concluded that the proper selection of actuation timings of intermediate valves for FV scheme has a significant effect on enhancing fre...
Contamination-driven insulator failure is a problem that incessantly plagues distribution systems... more Contamination-driven insulator failure is a problem that incessantly plagues distribution systems. Contamination levels can continue to grow unless abated by natural cleaning or if not taken measures to wash insulators at the distribution level in a preventative maintenance mode. In order to assess the pollution behavior, 33kV pin type insulator was selected as a sample insulator and been subjected for natural pollution at three selected localities (zone 1, 2 and 3) for considerable period. The naturally polluted insulators have been subjected for conductivity test and by which the equivalent salt deposit density (ESDD) is calculated. Subsequently, artificially contaminated insulators of different pollution severities were tested for power frequency and impulse test in the High Voltage Laboratory of University of Moratuwa. Finally, it is recommended that insulators in Zone 1 have to be treated after 8 months from the date of last treatment and those in Zone 2 & 3 to be treated after...
Engineer: Journal of the Institution of Engineers, Sri Lanka
Contamination-driven insulator failure is a problem that incessantly plagues distribution systems... more Contamination-driven insulator failure is a problem that incessantly plagues distribution systems. Contamination levels can continue to grow unless abated by natural cleaning or if not taken measures to wash insulators at the distribution level in a preventative maintenance mode. In order to assess the pollution behavior, 33kV pin type insulator was selected as a sample insulator and been subjected for natural pollution at three selected localities (zone 1, 2 and 3) for considerable period. The naturally polluted insulators have been subjected for conductivity test and by which the equivalent salt deposit density (ESDD) is calculated. Subsequently, artificially contaminated insulators of different pollution severities were tested for power frequency and impulse test in the High Voltage Laboratory of University of Moratuwa. Finally, it is recommended that insulators in Zone 1 have to be treated after 8 months from the date of last treatment and those in Zone 2 & 3 to be treated after 18 months under preventive maintenance to get away from flashover. It is also recommended to review the required specific creepage distance (SCD) of insulators installed in non-polluted areas due to the fact that the current practice of insulators placement in most of the places are with SCD of 25mm/kV which is recommended for high polluted zones as per IEC regulation.