Applied Mechanics and Materials Vol. 785

Abstract: Vertical-Axis Wind Turbines (VAWTs) are known as the most suitable wind turbine for small-scale electrical generation. There are many types of VAWTs and each of it has different performances and efficiency. In this work, three types of VAWT systems (Savo-B2, Savo-B4 and Giro-B3) were designed, constructed and tested to investigate the amount of electrical power that could be generated under several constant wind speeds. The blade rotors were designed and built using 2 mm thickness of aluminum plate. The tip speed ratios, power coefficients, blade rotations for each blade rotor and the simplicity of the proposed designs were studied via an experimental setup. The experimental work demonstrates that Savo-B2 provides the highest power coefficient which is up to 0.32. Meanwhile, Giro-B3 offers the fastest rotational blade speed, up to 20.53 rad/s, among the three designs.

Abstract: Insulation is one of the most important parts in the power transformer. Palm oil impregnated paper is investigated to replace the mineral oil impregnated paper due to the high viscosity of palm oil compared to the viscosity of the mineral oil. This paper discussed on ultrasonic radiation technique that was used to reduce the viscosity of the vegetable oil (palm oil) for transformer insulation application. The ultrasonic equipment produces 500W heating power, 240W ultrasonic power at a fixed frequency of 40 kHz. Ultrasonic radiation was applied on oil samples at 30 °C, 50 °C and 75 °C by using the sonicator water bath for several periods of time. The results show up to 42.6 % reduction from the original viscosity of palm oil and proved to have a long term effect on the viscosity of palm oil. The cavitation bubbles that occur in the sample during radiation is one of the mechanism in viscosity reduction.

Abstract: The properties of Palm Oil (PO) and Coconut Oil (CO) offer the potential for transformers with non-toxicity, high fire and flash points and better environmental compatibility while compared with those filled with Mineral Oil (MO). This potential has led to intensive studies of electrical performance of biodegradable oil especially in evaluating the electrical performance under lightning impulse voltage in recent years. This paper presents the investigation on the impulse breakdown voltage of PO and CO in such a uniform field. The PO used in this study is Refined, Bleached and Deodorized Palm Oil (RBDPO) Olein type. Two testing methods, rising-voltage and up-and-down are considered for both oils with different gap distances (2.0 mm and 3.8 mm). Testing methods including rising-voltage method and up-and-down method have no notable influence on the breakdown voltages of RBDPOs and CO compared to MO.

Abstract: Polymeric nanocomposites are widely used for high voltage outdoor insulating application due to their good electrical performance. Recently, SiO₂, TiO₂ and MMT nanofillers are being used as filler because there are listed as main nanofiller commonly used in electrical engineering. Natural rubber (NR) was used because the nature of the interphase is found to affect viscoelasticity and it develops several interphases with the Linear Low-Density Polyethylene (LLDPE) matrix. One of the problems associated with outdoor polymeric insulators is tracking of the surface which can directly influence the reliability of the insulator. This paper presents the outcome of an experimental study to determine the conductivity level of the LLDPE-NR compound, filled with different amount of SiO2, TiO2 and MMT nanofiller using Polarization and Depolarization Current (PDC) measurement technique. LLDPE and NR with the ratio composition of 80:20 were selected as a base polymer. Results show that different compositions as well as the surface physical conditions affect the PDC measurement results.

Abstract: The idea of using circuit breaker profile as a part of initial assessment on switchgear is introduced as early as in 1996. Subsequently, there is a requirement to establish a systematical and analytical approach in managing and interpreting profile data. This paper aims to elaborate implementing Expert Rule Analysis (ERA) as part of a method in assessing performance of circuit breaker profile.

Abstract: Travelling wave method is commonly used for partial discharge (PD) location since the past. However, for a long cable, the attenuation of PD pulse propagation could be significant. This is due to more energy loss during the propagation of pulse, which can affect the sensitivity of the PD source location within cable insulation. In this work, PD pulse propagation along cable insulation from the defect site was modelled using finite element analysis (FEA). The model was used to simulate the electric field distribution in the cable insulation due to the PD pulse propagation and to calculate the attenuation constant. The effect of cable length and PD source location in the cable insulation on the attenuation constant was also studied. Through this work, a better understanding of PD pulse propagation and attenuation constant using the FEA model geometry that has been developed can be attained.

Abstract: This paper presents a computationally accurate technique used to determine the critical clearing time using the one machine infinite bus equivalent system based on the equal area criterion. The critical clearing time is the maximum time interval by which the fault must be cleared in order to preserve the system stability. The computation of critical clearing time involves an intrinsic mathematical formulation derived from the pre-fault, during fault and post-fault conditions. The value of critical clearing time becomes significantly less when transient instability is induced by a three phase fault occurred at the bus bar closest to the substation connected with a sensitive generator. By setting the protection relay with the obtained value of critical clearing time, it is adequate to sustain the transient stability even though fault happened at the other locations. During the occurrence of fault, a circuit breaker which is operating earlier than the smallest critical clearing time will not agitate to a transient instability. The IEEE Reliability Test System 1979 (RTS-79) is used to verify the robustness of the methodology in a determining the critical clearing time.

Abstract: Leakage current is known to be directly related to the degree of degradation of arrester. Leakage current is commonly flow across arrester under non-conducting condition. In this work, a two-dimensional (2D) axial-symmetrical 11kV surge arrester model was developed and used to simulate the leakage current under normal condition. The influence of insulator shed widths, housing materials and sizes of ZnO in an 11kV ZnO surge arrester design on its leakage current was studied using finite element method (FEM) software, which is COMSOL Multiphysics. The simulation results show that leakage current is mostly affected by the sizes of the ZnO and material of the housing. From this work, an understanding on the leakage current behaviors in a ZnO surge arrester can be enhanced. This study may also help in improving the design of surge arresters in reducing leakage current.

Abstract: In this paper, a novel fault location algorithm in distribution networks based on combination of impedance based method is presented. The voltage sag and current swell from the measurement node are used as input data to estimate the fault distance. To improve the accuracy of the proposed method, the voltage sag and current swell in the un-faulted phase also considered. Test results using a large scale distribution network from Malaysia confirms the accuracy of the proposed method. A comparison is made with the existing method which shows that the proposed method gives more accurate fault distance.

Abstract: The existing distance relay is accommodated with starting function to detect short-circuits in power system. However, this function proves vulnerable to distance relay operation as it could falsely send a tripping signal during power swing. Hence, it is important to introduce an adaptive concept to the distance protection to prevent such false tripping. This paper presents a simple and effective adaptive protection algorithm for power swing prevention based on Under Impedance Fault Detector (UIFD) characteristics, in which capable to identify the power swing condition and adjusting the relay setting accordingly to avoid system mal-operation.