N. A. Othman

Measurement of surface charge distribution on glass insulator using steel mesh

This paper studies the charge distribution on the transmission line glass insulator surfaces under two different ac voltages viz. 28 kV and 33 kV. A string of four insulator units under dry and clean conditions is taken as the main research object. An attempt to capture the accumulated charge has been made by using radially shaped stainless steel mesh placed axially at a distance of 2 cm from each glass insulator circumference. Results show that the distribution of charge across each glass of insulator in the string is uneven, and the value of surface charge increases with the increment of applied voltage.

Heat distribution pattern of oil-filled transformer at different hottest spot temperature locations

Sustained high temperature on transformer insulation systems is one of the main causes of its accelerated degeneration. Continuous monitoring of transformer heat distribution could provide useful information on intensity and location estimation for hottest spot temperature (HST) development. Furthermore, faults will aggravate the formation of HST inside the transformer tank. However, there is difficulty in measuring and locating HST in many aged in-service transformer because there are no in-tank sensors installed. Thus HST can be monitored by observing the heat distribution pattern in the transformer. Therefore, this paper aims to investigate the effect of HST on the overall transformer temperature distribution and the heat distribution pattern associated with HST. The focus is on the effect of this heat distribution to the surface of transformer tank for condition monitoring purposes. Simulation of mineral oil-filled distribution transformer (ONAN type) was done by using Finite Element Method Magnetism (FEMM) 4.2 where particular interest was on the transformer cross section. Changes of heat dissipation at the inner and outer transformer body tank were analyzed. The results show that the continuous presence of HST increases oil temperatures as well as inner and outer tank surface temperatures. The existence of HST affects the whole temperature distribution pattern inside the transformer. Thus, the transformer HST can be used as indication of potential inside the transformer. The changes of surface heat near to the HST may also be useful in in-service monitoring the transformer condition.

Potential and Electric Field Characteristics of Broken Porcelain Insulator

A new type of leaky-wave antenna (LWA) using half-mode substrate integrated waveguide (HMSIW) as the base structure is proposed in this paper. The structure consists of an array of slot, antenna designed to operate in X band applications from 8 to 12 GHz. HMSIW preserves nearly all the advantages of SIW whereas its size is nearly reduced by half. The antenna radiates one main beam that can be steered from the backward to the forward direction by changing frequency.Internet of things (IoT) has described a future vision of internet where users, computing system, and everyday objects possessing sensing and actuating capabilities are part of distributed applications and required to support standard internet communication with more powerful device or internet hosts. This vision necessitates the security mechanisms for end-to-end communication. A key management protocol is critical to ensuring the secure exchange of data between interconnecting entities, but due to the nature of this communication system where a high resource constrained node may be communicating with node with high energy makes the application of existing key management protocols impossible. In this paper, we propose a new lightweight key management protocol that allows the constrained node in 6loWPAN network to transmit captured data to internet host in secure channel. This protocol is based on cooperation of selected 6loWPAN routers to participate in computation of highly consuming cryptographic primitives. Our protocol is assessed with AVISPA tool, the results show that our scheme ensured security properties.

Electric Field and Current Density Performance Analysis of Sf6, C4f8 and CO2 Gases As An Insulation

SF6 gases are not only widely used as an insulating component in electric power industry but also as an arc extinguishing performance in high voltage (HV) gas-insulated circuit breaker (GCB). SF6 gases is generally used in the production of semiconductor materials and devices. Though these gasses is widely used in many application, the presences of temperature hotspot in the insulations may affect the insulation characteristics particularly electric field and current density. Therefore, it is important to determine the relationship between electric field and current density of gasses used in the insulator in the presence of hotspot. In this paper, three types of gases in particular Sulphur Hexafluoride (SF6), Octafluorocylobutane (C4F8), and Carbon Dioxide (CO2) was used in the insulator for gas insulation with the presence of two hotspots. These two hotspost were detected by referring the rising temperature in the insulator which are 1000 and 2000 Kelvin temperature for hotspot 1 and hotspot 2, respectively. From the simulation results, it can be concluded that Sulphur Hexafluoride (SF6) is the best choice for gas insulation since it had the lowest current density and electric field compared to Octafluorocylobutane (C4F8), and Carbon Dioxide (CO2). It is observed that the maximum current density and electric field for SF6 during normal condition are 358.94 x 103 V/m and 0.643 x 109 A/m2, respectively. Meanwhile, during temperature rising at hotspot 1 and hotspot 2, SF6 also had lowest current density and electric field compared to the other gasses where the results for Emax and Jmax at hotspot 1 are 322.34 x 103 V/m and 1.934 x 109 A/m2, respectively; While, Emax and Jmax at hotspot 2 are 259.77 x 103 V/m and 2.824 x 109 A/m2. The results of this analysis can be used to find the best choices of gas that can be used in the insulator.

Leakage current and trapped charge characteristics for glass insulator string under contaminated conditions

This paper reports a study on leakage current (LC) and trapped charge characteristics for contaminated glass insulator string. Four units of glass insulators recently removed from service were contaminated according to IEC 60507. The measurement of trapped charge distribution was made by a radially shaped stainless steel mesh surrounding each insulator while LC was measured using 100 Q shunt resistor. The results revealed that as the contamination levels increase, the amplitude of LC increases; but the amplitude of trapped charge decreases.