Haziah Abdul Hamid

Many studies have demonstrated that a reduction in ground impedance value occurs under high-impulse current magnitudes, due to the ionisation process in soil. The degree of the ionisation process was found to be influenced by several factors, such as soil resistivity, the ground electrode’s configuration/size, impulse polarity, voltage/current magnitudes and impulse polarity, while in several publications, there was no clear influence of these factors on the ionisation process in soil. Given the uncertainty in the characterisations of grounding systems under high-impulse conditions, it can be difficult to relate the impulse characteristics to the design of grounding systems. This, however, may be possible to achieve if adequate data is obtained, with more tests and analytical studies being performed. Furthermore, as the use of enhancement materials (EMs) has been shown to reduce ground resistance values, the relevant data, which have been found to be limited, are the impulse characteristics of EMs. The effectiveness of these EMs is mostly presented at low-voltage and low-frequency currents, and so far, there is limited available data on their performance with various water contents (WCs) subjected to high-impulse currents. This paper aims to provide the impulse characteristics of soil mixed with various EMs and WCs. Three types of EM were used, and the initial results show that the performance of EMA has an advantage over the others, due to having the lowest Z_imp, current rise and discharge times, and breakdown voltage and times in comparison to other EMs tested in this work.

Regarding the installation of grounding systems, it is not common for the installation site to be re-located due to high soil resistivity. Enhancement materials have been widely used for their known advantages, including their ability to reduce the resistivity of soil. Although some studies have been conducted on the characterization of EMs under AC of various frequencies, limited studies can be found on their performance when mixed with various percentages of water content (WC) and soil. In this work, sand mixed with controlled percentages of enhancement materials (EM 1, EM 2 and EM 3) and controlled amounts of water content was placed on a parallel plate and tested under AC of various frequencies to obtain the resistivity and permittivity. It was found that dry sand–EM mixtures can be represented by an R-C parallel circuit, while wet sand–EM mixtures can be represented by a nonlinear R. These new test data providing the soil resistivity and permittivity of various sand–EM mixtures are important in selecting suitable EMs to be used in grounding systems.

The system voltage may be negatively impacted by the transformer’s energisation which draws a large value of magnetising inrush current for a few seconds. During the transformer’s energisation process, it experiences an unexpected saturation. When the transformer is saturated, the growth of magnetising inrush current, sympathetic inrush current and voltage sags are a few issues that are appear. Numerous variables that affect the inrush current and the resulting voltage sags were taken into consideration. This is due to the fact that the energisation of a large power transformer may result in a high voltage sag which relies on a value of parameters, including the duration of the circuit breaker closing time. One of the most essential objectives for power quality is the research of voltage sags that appear in a network. The goal of this project is to investigate sympathetic and inrush currents as well as to assess the voltage sag that occurs during transformer energisation and how severe it is. In this paper, the voltage sags are analysed by modelling 100kVA, 11kV/415V of wye-delta of single line (circles) transformer and using PSCAD software. It is expected to observe the magnitude, the duration and the percentage of voltage sags in order to make a comparison result between single connected transformer, two parallel-connected transformers and three parallel-connected transformers. To predict the severity of the sympathetic inrush current, the effects of voltage sags and their assessment is developed. As a result, it has been shown that the more energisation of the transformers, the peak of inrush current increases causing the higher magnitude and the longer duration of voltage sags. In conclusion, the voltage sags also become severe and persists for a longer duration when the number of transformers in operation are increased.

Differential equation fault location algorithm with harmonic effects in power system

Three types of Rogowski coils were designed and constructed by utilising 3D printing technology: RC1, RC2, and RC3, with the sensors having the same geometrical dimensions but varying number of turns: 20, 50, and 100 respectively. To verify the feasibility and effectiveness of the proposed sensors, a series arc fault generator was set up and high voltage of up to 3-kV was injected. The analysis of the Fast Fourier Transform (FFT) was done by using MATLAB to determine frequency and voltage amplitude. From the analysis, it was determined that the higher the number of turns, the greater the sensitivity. The resonance frequency (MHz) dropped significantly as the number of turns increased. Furthermore, sensor features such as frequency bandwidth and sensitivity are affected by the number of turns, which was thoroughly investigated in this study. The Rogowski coil was created to detect the high frequency component of the series arc fault signal. All the designed sensors reliably detect the series arc fault signal, according to the experimental results.