Muhammad Saufi Kamarudin

Study on the performance of underground XLPE cables in service based on tan delta and capacitance measurements

Performance of underground XLPE cables in service is critical because of ageing mechanisms influences. One of the techniques to evaluate performance of aged and unaged underground XLPE cables is based on tan delta and capacitance measurements of the cable insulations. This study focuses on underground XLPE cables which rated at 11 kV and 22 kV for both 1-core and 3-core types. Tan delta and capacitance data of underground XLPE cables are obtained using a Schering bridge instrument. Tan delta and capacitance measurements are performed at ambient temperature (about 27degC) and 50 Hz power frequency. The analysis of data show that tan delta values increased in proportion to the aging time of the cables. Meanwhile the data analysis of the capacitance measurement shows that the values of capacitance inconsistent. Nevertheless, tan delta measurement is more accurate and appropriate parameter for evaluating performance of underground XLPE cables as compared to capacitance parameter. Therefore, the finding of this study shows that aging mechanisms contributes the deteriorations of underground XLPE cable insulations in service and consequently the value of tan delta increases with aging time of the cables.

Potential of CF3I gas mixture as an insulation medium in gas-insulated equipment

SF6 is a widely used gas medium in gas-insulated equipment. Due to the high global warming potential and long atmospheric lifetime of SF6, there has been research into a new environmentally friendly replacement gas. This paper describes the research carried out at Cardiff University on CF3I gas and its mixture as a substitute insulation medium for SF6 in gas-insulated lines (GIL). A reduced-scale coaxial test system having the electric field properties of a full-scale 400 kV GIL system was fabricated. The design of the reduced-scale coaxial test system was simulated to ensure that the highest electric field would be along the center of the conductor. The coaxial prototype was then tested under a standard lightning impulse (1.2/50) in order to determine the 50% breakdown voltage for such a system when insulated with CF3I gas mixture. It was found that CF3I has the potential to replace SF6 as an insulation medium in GIL. A full-scale short length GIL demonstrator is being assembled in the laboratory to evaluate further the feasibility of using a CF3I gas mixture as an insulation medium.

Breakdown of CF3I gas and its mixtures under lightning impulse in coaxial-gil geometry

SF₆ is widely used in modern transmission and distribution networks because of its outstanding dual qualities: arc quenching and dielectric insulation. As a gas medium, SF₆ is chemically inert, non-toxic, and non-flammable, which makes possible the construction of compact SF₆ switchgear. One major known disadvantage of the gas is that it has a global warming potential which is 23,900 times higher than CO₂. This has led to research into alternative gases with a much lower environmental impact, and one of the emerging candidates is CF₃I. The high boiling temperature of CF₃I means that it has to be used as part of a mixture inside gas-insulated equipment. To carry out the investigation on CF₃I, a scaled-down coaxial system that replicates the maximum electric field of a 400 kV GIL system was designed and fabricated. The insulation performances of CF3I/CO₂ and CF₃I/N₂ gas mixtures were then examined by measuring the 50% breakdown voltage, U₅₀, using a standard lightning impulse waveform (1.2/50) under absolute pressures of 1 to 4 bar. The experimental results show that CF₃I gas mixtures have promising potential as an insulation medium for application in gasinsulated lines.

Development of Test Vessel for Gas Insulation Breakdown Test

Efficiency, reliability, high power quality and continuous operation are important aspects in electric vehicle attraction system. Therefore, quick fault detection, isolation and enhanced fault-tolerant control for open-switches faults in inverter driving systems become more and more required in this filed. However, fault detection and localization algorithms have been known to have many performance limitations due to speed variations such as wrong decision making of fault occurrence. Those weaknesses are investigated and solved in this paper using currents magnitudes fault indices, current direct component fault indices and a decision system. A simulation model and experimental setup are utilized to validate the proposed concept. Many simulation and experimental results are carried out to show the effectiveness of the proposed fault detection approach.The inverter with critical loads should be able to provide critical loads with a stable and seamless voltage during control mode change as well as clearing time. The indirect current control has been proposed for providing stable voltage with critical load during clearing time and seamless control mode transfer of inverters. However, the islanding detection is difficult since with the indirect current control the magnitude and frequency of voltage do not change when the islanding occurs. The conventional anti-islanding method based on the magnitude and frequency of voltage variation cannot apply to the indirect current control. This paper proposes an islanding detection method for the indirect current control. The proposed islanding detection method can detect the islanding using reactive power perturbation and observation when the frequency and magnitude of voltage don’t vary during clearing time. In order to verify the proposed anti-islanding method, the experimental results of a 600W three-phase inverter are provided.

Finite Element Analysis of Maximum Electric Field for Air Breakdown under Various Electrode Configurations

Zarina Mohd Noh*, Abdul Rahman Ramli, Marsyita Hanafi, M Iqbal Saripan, Ridza Azri Ramlee 1,2,3,4 Department of Computer and Communication Systems Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia 1,5 Fakulti Kejuruteraan Elektronik dan Kejuruteraan Komputer, Universiti Teknikal Malaysia Melaka (UTeM), Hang Tuah Jaya, 75450 Durian Tunggal, Melaka, Malaysia

Breakdown Characteristic Analysis of Paper- Oil Insulation under AC and DC Voltage

This paper presents the study of breakdown characteristic of Kraft paper insulated with two different types of insulating fluid, which are Palm oil and Coconut oil. Palm oil and Coconut oil are chosen as the alternative fluid to the transformer oil because it has high potential and environmentally-friendly. The Segezha Kraft papers with various thicknesses (65.5 gsm, 75 gsm, 85gsm, 90 gsm) have been used in this research. High Voltage Direct Current (HVDC), High Voltage Alternating Current (HVAC) and carbon track and severity analysis is conducted to observe the sample of aging Kraft paper. These samples have been immersed using Palm oil and Coconut oil up to 90 days to observe the absorption rate. All samples started to reach saturation level at 70 days of immersion. HVDC and HVAC breakdown experiments have been done after the samples had reached the saturation level based on normal condition, immersed in Palm oil and immersed in Coconut oil. All samples immersed in liquid show different breakdown voltage reading compared to normal condition. The analysis of carbon track and severity on surface has been done using Analytical Scanning Electron Microscope (SEM) Analysis. The results of the experiment show that the sample of Kraft paper immersed in Palm oil was better than Coconut oil immersed sample. Therefore the sample condition was the main factor that determines the value of breakdown voltage test. Introduction

Dynamic modelling of polluted outdoor insulator under wet weather conditions

This paper proposes a dynamic pollution modelling for evaluating electric field distribution over the composite insulator surface. Axial-symmetric insulator profile under wet contaminated conditions was developed and analysed using Finite Element Method (FEM) software. A nonlinear field-dependent conductivity with simplified assumptions was established to characterise the electrical properties of the pollution layer. Comparative studies showed that simulation of the proposed pollution model results in a more realistic electric field profile, offering better understanding on how the electric field behaves under various wet and contaminated conditions.

Purpose-built test rig for gas insulation breakdown tests under lightning impulse

A new test rig has been developed specifically for gas research work, which includes a pressure chamber, control measures, and a recovery system of the gas. The air-tight pressure chamber was designed and tested to withstand pressures of up to 5 bar (abs). Through help from a reliable sealing gland, wires were passed through the pressurized gas inside the vessel to the outside to provide a means of controlling the gap length of the electrodes, without the need of removing the gas. Other control measures include humidity, temperature, and pressure readings. The humidity and temperature are read wirelessly and from the readings, the necessary atmospheric corrections can be made according to standards. Safety measures are equally important and were achieved by using a pressure relief valve. The valve is set to release the gas at 6 bar. A recovery system of the gas mixture was used so that after each test, the gas was properly stored in cylinder bottles and not being released into the atmosphere. As it is important to study the ‘deteriorated’ gas for future works, this recovery process provided a means of obtaining the deteriorated gas to be investigated. From initial tests on air breakdown, it was found that U50 increases with pressure. Rod-plane configuration provides lowest U50 values due to its electrode geometry, followed by R12-plane and plane-plane configurations.

Performance of multi-column MOVs for C class protection of AC power circuits

High voltage protection for low voltage AC power circuits is very important to minimize the damage of electrical equipment. Unfortunately, review of performance and safety features in commercially-available surge suppressors has shown that sometimes they cannot deliver the proper protection to withstand the high voltage surges. This paper reviews the performance of multi-column surge suppressors. Metal oxide varistors (MOVs) are used as the test objects of this. Some configurations of MOVs have been tested to show the difference in protection capabilities. Experiments involving a wide range of high voltage surges revealed that a multi-column MOVs provides increased in peak current and energy-handling capabilities for a given application.