Miszaina Osman

Analysis of Programme Outcomes achievement for Electrical Engineering programmes in UNITEN

In Outcome-Based Education approach, Programme Outcomes (PO) is a series of technical and non-technical skills that a graduate from an institution should acquire prior to graduation. The qualities in the PO are usually closely related to the training that the student has gone through. The attainment of PO must be tracked at every semester and corrective actions must be implemented if the attainment does not meet the performance criterion that has been set. This implies a need for a continuous quality improvement (CQI) process for PO attainment. This paper presents the analysis of PO achievement based on students achievement in formal assessments for core subjects in the Bachelor of Electrical Power Engineering (BEPE) and Bachelor of Electrical and Electronics Engineering (BEEE) programmes in UNITEN for four semesters from Semester 1, 2007/2008 to Semester 2, 2008/2009. In general, all POs are attained by both programmes. However, it was observed that with the current performance criteria a decline in soft skills PO achievement was observed. Hence, a new PO attainment strategy was devised and a new performance criterion has been set. This paper aims to highlight the CQI processes in place to analyze the BEPE and BEEE Programme Outcomes attainment.

Design of distribution substation earth grid in high resistivity soil using CDEGS

Design of distribution substation earthing grid can be very challenging in high resistivity soils especially in two layer soils where the top layer resistivity is lower than the bottom layer. This paper presents the design of a distribution substation earth grid using Current Distribution Electromagnetic Field Grounding Soil Structure Analysis Software (CDEGS). Soil resistivity measurement was carried out at the substation site using a 4-pole Megger earth tester based on Wenner method. The soil structure was determined using RESAP module, while the design was implemented using SESCAD and executed by MALT module. Results indicated a slight reduction of earth grid resistance, 0.6%, 5.8% and 6.5%, respectively as the grid burial depth was varied from 0.5m to 1.5m in steps of 0.5m. The touch and step voltages were found to be lower when surface layer material was not applied and higher when surface layer materials of 3000Q-m and 5000Q-m resistivity were interchangeably applied on the grid surface. It was also found that, the calculated earth grid resistance from IEEE Std. 80-2000 equation was lower than the grid resistance computed by MALT.

Case study on impact of seasonal variations of soil resistivities on substation grounding systems safety in tropical country

It is important to evaluate the validity and safety of the substation earthing system since over time the physical and electrical properties or requirements of the substation earthing can change in many ways. A research study focused on safety assessment of substation earthing systems due to variations of soil resistivities values which dependent on tropical rainfall variations was carried out on a 132kV substation. Actual earthing resistances and soil resistivities values were measured at a regular interval for a period of 18-months as input to the simulation process. The study used CDEGS™ software for modeling and assessment of substations earthing system safety. From the initial desktop simulation calculation based on the above models, it was found that the substation have its touch and step voltages exceeded the allowable limits as per IEEE 80–2000 Standard (IEEE Guide for Safety in AC Substation Grounding) for some period throughout the duration of the study.

Impact of split factor value on the safe design of distribution substation earth grid

Split factor is a fundamental consideration when designing a distribution substation earth grid. Arbitrary choice of split factor in earth grid design process may lead to technical and economic implications resulting in underestimated or overestimated designs. In this paper, a distribution substation earth grid was designed using SESCAD and executed in MALT module of CDEGS. The energization current was varied by 100%, 75%, 50% and 25% of the short circuit current available at the secondary terminals of the upstream transformer to determine the impact on safety criteria of the earth grid. Results indicated that, the EPR for 100% fault current was higher, whereas the step and touch voltages were lower. It was also revealed that, there was no difference in step and touch voltages when energization current was set at 75%, 50% and 25%.

Effect of earth grid conductor spacing on the safety criteria of substation earthing

Site dependent parameters such as soil resistivity, maximum grid current, fault duration, shock duration, surface layer material resistivity, and grid geometry have substantial impact on the design and performance of an earth grid. The grid geometry, i.e. the area occupied by the grid system, conductor spacing and the depth of burial of earth grid specifically have much impact on the mesh, step, touch voltage and earth potential rise, while parameters such as the conductor diameter and the thickness of the surfacing material have less impact on the safety criteria. In this paper, a distribution substation earth grid was designed using the CDEGS software by varying the spacing between grid conductors (compression ratio) from 1 to 0.5 in steps of 0.1. The safety criteria were studied under three scenarios, without surface layer material, with surface layer material of resistivity 3000Ω-m, and surface layer material of resistivity 5000Ω-m. Results indicated that the grid resistance and earth potential rise were lower for a compression ratio 0.9, while the step and touch voltages were found to be similar for each case of surface layer material.

Impact of energization current on the safe design of distribution substation earth grid

Energization current is a fundamental consideration in designing of distribution substation earth grid. Arbitrary choice of energization current in earth grid design process may lead to technical and economic implications resulting in underestimated or overestimated designs. In this paper, a distribution substation earth grid was designed using SESCAD and executed in MALT module of CDEGS. The energization current was varied by 100, 75, 50 and 25% of the short circuit current available at the secondary terminals of the upstream transformer to determine the impact on safety criteria of the earth grid. Results indicated that, the EPR for 100% fault current was higher, whereas the step and touch voltages were lower. Also, compared to the other cases of short circuit currents, there was no difference in step and touch voltages when the energization currents were varied at 75, 50 and 25%.