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In this study, we examined a typical high-voltage gas circuit breaker. The main goal of this study is to characterize arc plasma and to determine its behavior using the generalized Mayr-type equation model following the interruption of high-voltage circuit breakers according to a semi-empirical one, named conductance model. Here, we tried to evaluate some arc parameters that affect interrupting ability by performing a numerical analysis so that our model defines recorded experimental results of an actual test. © 2008 The Japan Society of Applied Physics  

The online condition assessment of circuit breakers (CBs) has been increasingly requested by power utilities in recent years. Trip and close coil current (CC) signature is an effective and noninvasive parameter in CB online condition monitoring. This paper gives an insight into the impacts of the various failures on the coil current waveform, as well as on the CB operation time. The failures and their causes are categorized based on the outcome of these investigations. Finally, a new algorithm using trip/close CC is proposed to detect the mode and cause of CB incipient failures. In this study, the CC patterns are acquired by measurements carried out on (healthy and faulty) CBs of 72.5-kV and... 

Circuit breakers, like price limits and trading suspensions, are used to reduce price volatility in security markets. When returns hit price limits or missed, observed returns deviate from equilibrium returns. This creates a challenge for predicting stock returns and modelling value at risk (VaR). In Tehran Stock Exchange (TSE), the circuit breakers are applied to control for the excess price volatilities. This paper intend to address which models and what methodology should be applied by risk analysts to calculate the VaR when the returns are unobservable. To this end, we extend Wei’s (2002) model, in the framework of Bayesian Censored and Missing-GARCH approach, to estimate VaR for a share... 

The proper and reliable operation of circuit breakers (CBs) directly affects the reliability and continuity of electricity services in a power systems. Condition-based maintenance (CBM) is the best economic CB maintenance strategy through its online monitoring (OLM) possibilities. Since there is a large number of CBs in a power system, to equip all CBs with OLM systems is not economically justifiable however. This paper, as the second part of a two-part paper, presents an effective optimization framework to find the optimal number of CBs to be monitored online as the kernel of CBM process. To prove its feasibility, the proposed approach is applied to the IEEE Roy Billinton Test System, which... 

Recognition of the circuit-breaker's (CB) vital role in reliable operation and protection of power systems (i.e., during energization, disconnecting loads, and clearing faults), helps to understand the requirement and importance of its maintenance management as well as maintenance scheduling. Condition-based maintenance (CBM), employing online monitoring (OLM) of CBs, has been long reported as the most practical maintenance policy on the power system CBs. There are a large number of CBs in a power system to be monitored; however, to address the financial limitations for OLM implementation (in utilities), a method will be proposed to find the most critical breakers for enforcing effectively... 

In puffer type Sulfur Hexafluoride (SF6) Circuit Breakers (CBs), the refill valve is the main inlet duct for the SF6 gas to enter the puffer volume. When the CB is closing and moving contacts and the nozzle are moving toward fixed contacts, the SF6 gas enters the puffer volume via the refill valve. Since changing the refill valve diameter can alter the direction of the SF6 gas motion in the closing operation of CBs, understanding its effects on CBs' function and performance may help to improve the CB design. This paper has focused on the effects of refill valve diameter on prestrike occurrence in the closing operation of puffer type SF6 CBs. In order to accurately study these effects, some... 

Achieving high-distribution reliability levels and concurrently minimizing capital costs can be considered as the main issues in distribution system optimization. Determination of the optimum number and location of switches in distribution system automation is an important issue from the reliability and economical points of view. In this paper, a novel three-state approach inspired from the discrete version of a powerful heuristic algorithm, particle swarm optimization, is developed and presented to determine the optimum number and locations of two types of switches (sectionalizers and breakers) in radial distribution systems. The novelty of the proposed algorithm is to simultaneously... 

During power system restoration, it is necessary to check the phase angle between two buses before closing circuit breakers to connect a line between them. These angles may occur across a tie line between two systems or between two connected subsystems within a system. In case of large Standing Phase Angle (SPA) difference the synchrocheck relay does not allow closing of the breaker for this line. Therefore, this excessive SPA has to be reduced before attempting to connect the line. In this paper a new and fast method for reducing SPA is presented. For this purpose, the standing phase angle difference between two specific buses is represented in terms of sensitivity factors associated with... 

Short circuit current is one of the major threats for power system stability. Power system should have the ability to detect and clear these faults within a specified time. The protection system can clear the faults only if the interruption capability of the circuit breakers is higher than the fault level. Expansion of the grid and installation of new power on the scale that is envisaged will require practical solutions to a number of technical challenges. One of the technical challenges is fault level management as system expansion often results in increased fault levels beyond the design limits of the existing switchgears. Replacing the old equipments particularly circuit breakers with the... 

Different methods are developed for mitigation of ferro-resonance in high-voltage gas insulated substations (GISs). The main components, which have impacts on probability of occurrence of ferro-resonance, are grading capacitance of circuit breakers (CBs) and internal loss of potential transformers (PTs). However, by using active or passive damping resistance in the secondary of PTs, the probability of occurrence of ferro-resonance can be decreased substantially. It is worth mentioning that the thermal limitations of PTs restrict us to dissipate a lot of energy in the damping resistance. Therefore, in this paper, both thermal and electrical aspects of ferro-resonance are considered and... 

Electricity companies have been under a great pressure to improve their technical and financial performances in order to survive and thrive in the deregulated environment. Therefore, these companies are seeking for innovative approaches to take the most out of the restricted resources. These approaches inherently concentrate the available budgets to the most critical components. In this regard, prioritizing the system components and identifying the most critical ones play a vital role in the planning and operation of the system. This paper presents a novel approach to prioritize power transmission system components. In the proposed methodology, a criticality factor is defined and implemented... 

The present paper studies the impact of dynamic interaction between high-voltage substation equipment on the response and vulnerability of substation equipment. The 3D numerical model is developed for four types of vulnerable equipment in the both unconnected and connected conditions. The bus slider-rigid bus assembly is utilized to establish the connection between the equipment. The incremental dynamic analysis is carried out in the developed systems to produce the fragility function for each equipment. Also, the Monte Carlo approach is employed to evaluate the accuracy of the generated functions. It is concluded that the incorporation of connection parts in the model can significantly... 

This paper presents a novel approach for evaluating the reliability of protective systems taking into account its components reliability. In this paper, a previously proposed extended model is used for a directional over- current scheme. In the extended model, the impacts of individual protective components are taken into account. An optimum routine test schedule is determined for each protective component as a separate unit. A comparison is made to show that the proposed approach has excellence over conventional routine test inspections. Impacts of factors such as circuit breaker inadvertent opening, required time for performing routine test inspections, human mistakes and self-checking and... 

An ideal steganographic technique embeds secret information into a carrier cover object with virtually imperceptible modification of the cover object. Steganalysis is a technique to discover the presence of hidden embedded information in a given object. Each steganalysis method is composed of feature extraction and feature classification components. Using features that are more sensitive to information hiding yields higher success in steganalysis. So far, several steganalysis methods have been presented which extract some features from DCT or wavelet coefficients of images. Multi-scale and time-frequency localization of an image is offered by wavelets. However, wavelets are not effective in... 

This paper presents a novel approach for evaluating the reliability of protective systems taking into account its components reliability. In this paper, a previously proposed extended model is used for Directional Overcurrent scheme. In the extended model, the impacts of individual protective components are taken into account. An optimum routine test schedule is determined for each protective component as a separate unit. A comparison is made to show that the proposed approach has excellence over conventional routine test inspections. Impacts of factors such as circuit breaker inadvertent opening, required time for performing routine test inspections, human mistakes and self-checking and...