Ahmad Qisti Ramli

Detection of acoustic emission signals from partial discharge sources in oil-pressboard insulation system

Partial Discharges are major source of insulation failure in power transformers. Therefore, partial discharge (PD) measurement has been commonly carried out to detect and monitor PD activity in insulation in order to avoid from any catastrophic failure. In this research work, acoustic emission (AE) detection system is used to detect PD in an experimental tank filled with transformer oil. Three different types of PD sources to generate PD in the experimental tank are created from pressboards which are the plain pressboard, the floating metal in the pressboard and the bubble in pressboard. The AE signals due to the occurrence of PD from these sources are captured and recorded. Due to the large number of AE signals to be recorded by the Data Acquisition System, some of these signals may not be stored correctly in the system. Some of these signals may also be affected by the reflection and refraction phenomena, interference and attenuation of the AE signals. Hence, the preprocessing and validation of the acquired AE signals from the experimental setup are also explored in this paper. Finally, the valid AE signals due to three different types of PD sources are identified for further analysis.

A novel design of DC-AC electrical machine rotary converter for hybrid solar and wind energy applications

This paper proposes the design of a new bi-directional DC-AC rotary converter machine to convert a d.c. voltage to three-phase voltage and vice-versa using a two-stage energy conversion machine. The rotary converter consists of two main stages which are combined into single frame. These two stages are constructed from three main electromagnetic components. The first inner electromagnetic component represents the input stage that enables the DC power generated by solar energy from photo-voltaic cells to be transformed by the second and third components electro-magnetically to produce multi-phase voltages at the output stage. At the same time, extra kinetic energy from wind, which is sufficiently available, can be added to existing torque on the second electromagnetic component. Both of these input energies will add up to the final energy generated at the output terminals. Therefore, the machine will be able to convert solar and wind energies to the output terminals simultaneously. If the solar energy is low, the available wind energy will be able to provide energy to the output terminals and at the same time charges the batteries which are connected as backup system. At this moment, the machine behaves as wind turbine. The energy output from the machine benefits from two energy sources which are solar and wind. At night when the solar energy is not available and also the load is low, the wind energy is able to charge the batteries and at the same time provides output electrical power to the remaining the load. Therefore, the proposed system will have high usage of available renewable energy as compared to separated wind or solar systems. MATLAB codes are used to calculate the required dimensions, the magnetic and electrical circuits parameters to design of the new bi-directional rotary converter machine.