Hussein Ahmad

A scheme for controlled islanding to prevent subsequent blackout

The power systems operated by the utilities in developing countries suffer from a large gap between demand and generation, inadequate transmission capacity, and nonuniform location of the load centers and generating stations. Occurrences of faults in such systems, in most of the cases, end up with the worst consequences, i. e., complete blackout. This paper illustrates the way a blackout can be prevented in real-time through controlled segregation of a system into a number of viable islands together with generation and/or load shedding. The nature and location of any fault that warrants such islanding can be ascertained in real-time through monitoring the active power (MW) flows at both ends of a number of prespecified lines. The blackout of 20 June 1998 in the Bangladesh Power Development Board system is used as an example. The philosophy of the proposed islanding scheme may be considered for implementation in other power systems also.

A novel method for ATC computations in a large-scale power system

In a restructured power system, it is the responsibility of the independent system operator (ISO) to control the power transactions and avoid overloading of the transmission lines beyond their thermal loading megavolt-ampere (MVA) limits. For this, ISO has to update periodically a real-time index termed available transfer capability (ATC). The methods reported to date for ATC determination are unable to cater to either the accuracy or the online CPU time requirements when the system is a large one. This paper proposes a novel method with the full details for determining ATC in a large power system from only three input variables through fuzzy modeling. The method is validated through extensive simulation tests on the standard IEEE 24-bus reliability test system (RTS), and comparison with an ac load flow-based conventional method using the same array of transactions, base cases, and generation/line outages.

Partial discharge characteristics of XLPE cable joint and interfacial phenomena with artificial defects

This paper deals with partial discharge (PD) causing degradation of XLPE cable joint and interfacial phenomena of XLPE/EPR interface due to artificial defects such as metal particles, needle-like void and fiber soaked with water. We measured aging time dependence of phase-resolved PD (phi-q-n) patterns and PD statistic parameters when such kinds of defects were placed at XLPE/EPR interface. As a result, phi-q-n patterns were found to depend upon the defect type varying with aging time. In order to grasp the degradation mechanisms, we compared a practical XLPE cable joint with a model sample to simulate the real one. Moreover, electron spectroscopy for chemical analysis (ESCA) was also carried out to interpret the degradation mechanism.

Prediction of salt contamination on high voltage insulators in rainy season using regression technique

The severity of contamination on the high voltage insulator surfaces is the significant factor in determining the level of outdoor insulation and in choosing the types of insulators. In the equatorial region, the most dangerous kind of contamination is salt contamination. A regression technique has been used to develop a modified equivalent salt deposit density (ESDD) mathematical model with respect to meteorological conditions. This model provides a useful way for predicting contamination level and for determining frequency of washing the insulators in a given contaminated area.

Modeling of various meteorological effects on contamination level for suspension type of high voltage insulators using ANN

The performance of polluted insulators is very much dependent on the degree of contamination. For the high voltage insulators to be installed in areas especially near the coast, determination of the contamination level becomes the major task to design the insulators appropriately. The aim of this paper is to obtain accurate information about the degree of contamination which the high voltage insulators are exposed to when they are installed in coastal areas. Regression technique has been used successfully in estimating the level of contamination on high voltage insulators surfaces in terms of equivalent salt deposit density (ESDD). This paper has also used artificial neural network algorithm to model ESDD as a function of various meteorological parameters. A comparative analysis has also been carried out between the two methods in this work.

Diagnosis of XLPE Cable using the Recovery Voltage Measurement Method

This paper presents a preliminary investigation on the evaluation of ageing in 11 kV XLPE cable using return voltage measurement (RVM) method. Accelerated ageing using AC voltage was performed on new XLPE cable samples. Within the period of ageing, the state of insulation was investigated and assessed. The result of the diagnosis using the RVM showed a good correlation between aging time and the return voltage initial slopes (dU,/dt) of the aged XLPE cables, indicating the samples have undergone thermal ageing. The RVM technique, which was initially proposed for diagnosis of oil-paper insulation systems, was found to be able to detect ageing in XLPE cables, and thus insulation diagnosis using this technique could be extended to extruded-polymeric insulation systems.

Shielding failure analysis of 132 kV transmission line shielded by surge arresters associated with multiple strokes lightning

Analysis of shielding failure is carried out to observe flashover of insulators parallel with phase conductors of a transmission line associated with a lightning strike on phase conductor. Peak current of different magnitude have been used to represent the multiple strokes lightning (MSL). This paper aims to simulate the worst case due to transmission shielding failure with three direct strikes to a line phase conductor of magnitudes 25 kA, 35kA, 50kA, 65 kA and 80kA per strike respectively. Insulators where flashover had occurred with respect to MSL were identified. Installation of an arrester on a phase insulator where a flashover has occurred proven to be useful mitigation technique thatch could prevent flashover of the insulator and also improves lighnting performance of the line.

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.

Statistical study on tree inception voltage of silicone rubber and epoxy resin

Weibull distribution has been used widely by many researches around the world especially in the analysis of high voltage experimental data. Unfortunately, most of the experimental data analysis was not following the accurate statistical technique. Thus in this paper, a statistical study on the tree inception voltage of silicone rubber and epoxy resin is presented. The tree inception voltage of silicone rubber and epoxy resin was measured via camera-equipped online monitoring system. The leaf-like specimen was used as test sample. The experiment was performed based on IEC 1072:1991 “Methods of Test for Evaluating the Resistance of Insulating Materials against the Initiation of Electrical Trees”. The obtained results were analysed statistically by using fitting method. Anderson-Darling goodness-of-fit test was performed in order to obtain the best fitting distribution. Comparison exercise was made between the fitted distribution and Weibull distribution. Based on Anderson-Darling tests, the tree inception voltage of silicone rubber and epoxy resin was best fitted with Johnson SB distribution. Based on this fitted distribution, the value of tree inception voltage for silicone rubber and epoxy resin was calculated and equalled to 3.1529 kV and 4.6528 kV respectively. Thus, it was found that, the fitting method by means of Anderson-Darling goodness-of-fit test was successful to recognize the best fitted distribution for the value of tree inception voltage for silicone rubber and epoxy resin.

Effects of Moisture Contents in Soil and Impulse Polarity of Earth Electrode Under High Impulse Conditions

The study on the physics of discharges in soil and performance of earthing networks subjected and obtain better electrical models of earthing systems. In this study, the characteristics of medium grain size sand of different moisture contents and impulse polarity are investigated. The soil characteristics of various moisture contents under high impulse currents have been well studied in previous work. Until today, no publication has been made on the dry soil characteristics and no direct comparisons has been made between the characteristics of dry and wet soils under impulse conditions. This paper is therefore aimed to observe the characteristics of dry and wet soil under both impulse polarities. The results were discussed based on its voltage and current traces, impulse resistances and breakdown characteristics of the cylindrical test cell