Aberdeen University, UK, School of Engineering
Ali A. Razi-Kazemi received the PhD degree in Electrical Engineering from the Sharif University of Technology, Iran and Research Attachment at Aalto University, Espoo, Finland, in 2013.
Dr. Razi-Kazemi is the Associate Professor in the Department of Electrical Engineering at K. N. Toosi University of Technology. He has been elevated to IEEE Senior member since 2019. He was also a member of CIGRE A3.43 working group 2019. He is a member of IEEE PES Switchgear Committee since 2020
Aberdeen University, UK, School of Engineering
K.N. Toosi University of Technology, Department of Electrical Engineering
K.N. Toosi University of Technology, Department of Electrical Engineering
Ph.D. in Electrical engineering-Power System
Sharif University of Technology, Tehran, Iran
M.Sc. in Electrical engineering-Power System
Tehran University, Tehran, Iran
B.Sc. in Electrical engineering
K.N. Toosi University of Technology, Tehran, Iran
My main interests are related to high-voltage and high-current technology topics, which can be categorized into three groups as follows:
The first one is dealt with the online monitoring of power system components especially high voltage circuit breakers. My researches in this issue focus on two different viewpoints, i.e. power system and component. The former is dealt with investigations on related concerns such as priority assessment, maintenance modeling, etc. The center of attention of the later is to explore the physics of various CBs and designs.
My other concentration is pulsed power technologies. By way of illustration, researches on energy storage systems such as compact Marx generators, opening switches, closing switches and so on.
Finally, my last research topic is transients phenomena in power systems such as transient modeling of power components, insulation coordination and so on.
Noteworthy is that I have some personal interest beyond my main research topics such as green houses, clean energy, etc.
Hard working,  Hope and   Success
The Supervisory Team: Dr.Niayesh (Tehran University) and Dr. Razi-Kazemi (K.N.Toosi University).
Students, who are interested in this issue, can contact with me.
Money won't buy happiness, but it will pay the salaries of a large research staff to study the problem. Bill Vaughan
High voltage direct current (HVDC) systems have been increasingly employed to provide a connection amongst various energy sources, especially renewable energies. In order to switch the load current in these systems, the passive resonance breaker (PRB) is employed as a transfer switch. The interruption capability of the PRBs is highly dependent on the dynamic behavior of the arc in this system. Accordingly, this article presents a black-box high-degree of freedom arc-model based on Schwarz and the genetic algorithm as a heuristic optimization to follow the characteristics of the static and quasi-static arc regarding the oscillation frequency of the interruption current. The model has been verified by the published experiments. Subsequently, the PRB operation has been quantified based on the state-space approach along with an accurate dynamic arc model to follow in a wide frequency range of the arc current. The results are indicated that the amplification coefficient alone is insufficient to determine the interruption capability of these protection tools. Therefore, this article attempts to quantitatively determine the interruption capability curve by introducing criteria, such as Δt PZ (peak to zero time-interval), diarc/dtCZ- and duarc/dtCZ+ to obtain the origins of the interruption failure probabilities and dimensioning of the PRBs with respect to the interruption limits for gas blast CBs.
Condition assessment of circuit breakers (CBs) based on the installation of online monitoring systems (OLMs) is increasingly demanded by utilities. However, equipping all CBs with OLMs is neither technically nor economically feasible in a large power system. Therefore, the prioritization of the CBs is very important to identify critical components for equipping with such expensive tools (OLMs). The limited information along with the large size of power systems result in the inapplicability of the conventional ranking methods, in practice. To cope with this problem, this paper proposes a simple yet effective method based on the analytic hierarchy process (AHP) for organizing the experts’ knowledge. The prioritization of the CBs has been solved as a multi-criteria decision-making problem (MCDM). The proper criteria have been defined to incorporate the practical concerns and reliability points regarding the limited data in a large scale system. In addition, in order to avoid the inconsistency of the decision matrix, the problem has been divided into three-level, i.e. ranking of substations, CBs in each substation, and CBs in the network. The applicability of the approach has been verified through successful implementation in a large-scale power transmission network to determine the critical substations and CBs for equipping with OLMs.
Gas-insulated substations (GISs) are widely used in power systems due to high reliability, convenient maintenance, and small area occupation. Transient enclosure voltage (TEV) is a consequent effect of very fast transient overvoltage (VFTO) during the switching operations in GISs. It can lead to insulation degradation, damage to the secondary equipment connected with the shell of GIS, and harm to the working staff. This paper presents a correlation between a lumped-circuit model based on transmission line theory (TLT) for purpose of the simulation and an analytical approach based on the scattering matrix for the evaluation of TEVs. Furthermore, a frequency-dependent model is proposed to quantify the transient grounding impedance (TGIM) against the waves with high-frequency content such as TEVs. The interaction between the TEV and the grounding system has been investigated analytically, and experimentally based on the field measurements in other efforts. The comparisons indicate that the modified wide-band TGIM results in an improvement in comparison with the other works to track both the front and tail of a measured voltage-wave within acceptable accuracy. Furthermore, the role of the ground strap as a damping structure using a modified model on TEV profile has been scrutinized regarding the grounding system model and the rising rate of TEVs. It is indicated that considering frequency-dependent TGIM could lead to a 25% variation in the estimation of amplitude of TEVs.
Pulsed power sources provide high-power waves with high frequency (HF) content for a wide range of applications. Conventionally, a simple resistance is employed for the most prevalent pulsed power loads. However, the load model can highly affect the efficiency of source design. This paper contributes to fill this gap by considering the HF behavior of the loads. Accordingly, a new approach has been proposed to present a general HF lumped-circuit model for pulsed power loads. The frequency response of the loads is identified using the Finite Integration Technique (FIT). Subsequently, an equivalent circuit model is established based on the vector fitting (VF) algorithm. The applicability of the approach has been verified by comparison with two experiments, i.e. Vircator and coaxial reactor as the loads. It is indicated that the HF-based model can significantly improve the simulation results to be in good agreement with experiments. The results present that while a pure-resistive load model could lead to about 30% error in the estimation of the characteristics of output voltage, it is about less than 5% in the case of the proposed HF load model.
Wind energy as an affordable and clean source has increasingly penetrated power networks. Vacuum circuit breaker (VCB) owing to high-rated operation-frequency, long service life, and the fast operation speed is of the main protection options in wind farms. Several incidents such as prestrike, restrike, and current chopping happening over the lifetime of VCBs might cause erosion in the contacts or a change in the pressure. This paper presents the applicability of a hybrid-approach on real-time assessment of the erosion and pressure in VCB based on the field emission current level and restrike frequency in a standard three-phase network including wind turbines. Interaction amongst the prominent parameters such as field emission current, arc voltage, vacuum pressure, and erosion rate is scrutinized in a three-phase mode associated with a healthy and a defective VCB. The results reemphasize the applicability of the approach in online condition monitoring of VCBs in a real network. It is indicated that one phase evaluation could result in an imprecise estimation of the diagnostic features. It has been revealed that the worst deterioration rate is dealt with in the first interrupted phase. While the erosion rate of the first clearing pole is twice as high as the other phases in a healthy breaker, it would be eight times in a defective VCB. Furthermore, it is deduced that a VCB with a high operation frequency and subject to more restrikes is more likely to be aged. It is deduced that the erosion leads to a decrease in the interruption capability of high-frequency current, and a lengthier interruption. In addition, it is comprehended that VCBs connected to wind turbines are aged faster than what we expect in conventional networks.
This paper presents a hybrid-approach based on the establishment of a relationship between diagnostic signals, vacuum pressure and contact erosion of vacuum circuit breakers (VCBs). The signals used for this real-time diagnosis comprise of the level of chopped-current, dielectric strength, and the field emission current. The proposed approach has been verified against authentic experiments and the results indicate an acceptable agreement between the estimated values by approach and experiments.
Spark-gaps surrounding with high-pressure gas are widely applied as the closing switches in the pulsed-power technologies (PPT). The stochastic closure time delay and jitter in these closing switches can lead to a significant impact on the characteristics of output pulses. This paper aims to model a high-pressure gas spark-gap through COMSOL Multiphysics to quantify the correlation amongst prominent factors such as gas pressure, gas mixture, and the rate of rising of the applied-voltage (RRV) on the stochastic behavior of the closing operation. The comparison of the results obtained by the model with results presented in the other reports indicates a satisfactory agreement. Besides, it is indicated that increasing the gas pressure increases both the statistical time lag and jitter. In addition, in the case of alternatives, it is obtained that 30-atm and 70-atm lead to the lowest and highest statistical time characteristics, respectively. Moreover, it is deduced that the outputs in PPT might be more robust in the faster rising-rate voltage waves. Finally, the correlations between time delay and jitter with gas pressure and RRV have been quantified and employed in a three-stage compact Marx generator (CMG) to clarify the interactions.
High voltage circuit breakers (HVCBs) play a critical role on providing the desired reliability, and resiliency in power systems. In order to extend their lifetime and predict the failures, various maintenance policies could be applied on these critical components. Amongst these strategies, condition-based maintenance (CBM) provides a satisfactory agreement with future smart environment. This paper aims to provide an insight into the relevant developments in this subject and to explore the viable visions compatible with future research stream. Accordingly, three directions, i.e. diagnostic signals, intelligent modelling and using monitoring data in asset management have been addressed in this paper. It presents challenges dealing with real-time assessment of the diagnostic signals relating to measurements, and analyses. Subsequently, the issues associated with using artificial intelligent (AI) and Machine learning for providing intelligent algorithms have been discussed. Finally, the connection between the monitoring data and the asset management approach is investigated. The latter is looking for the subjects including remaining lifetime estimation, prioritization, and health index definitions. This paper has attempted to make a bridge from past to future research trends in the failure diagnosis of HVCBs.
Ultrafast disconnector (UFD) is a key component of hybrid DC circuit breakers and it is also studied as the main switch in some DC grid topologies. A UFD model suitable for DC grid studies and considering both normal operation and failure mode is presented. The dynamic motion of contacts is analysed in detail and it is concluded that Thomson coil inductances including parasitic parameters play important role and it is recommended to use finite element modelling. The arcing mode of UFD is repressed using a variable resistance in series with an ideal switch. The variable resistance is calculated analytically based on instantaneous position of contacts and the circuit conditions. Two different arc models are recommended: for the air insulated UFD and SF6 UFD, and in each case two operating regimes should be considered: high and low currents. The UFD model is verified for both normal operation and failure mode using measurements on a 5kV laboratory UFD and the results show very good matching. The 320kV SF6 UFD model is evaluated using limited reported results from manufacturers.
One of the phenomena affecting the insulation coordination of power distribution systems is indirect lightning. This article aims to investigate the impacts of stratification of the soil along with the characteristics of the lightning current, i.e., peak, current time-derivative, striking distance to overhead lines on quantification of the lightning indirect overvoltage (LIOV). Accordingly, comprehensive analyses have been established based on the finite integration technique. The flexibility of the method and the simulation results have been compared with the other finite element method and well-known formula, i.e., Rusck and Darveniza. It is also demonstrated that the Darveniza's formula cannot be relied upon as a precise approach in nonuniform grounds. It is revealed that more resistivity of the lower layer results in the increase of LIOV peak in a two-layer soil. It is comprehended that the increase in the number of layers could highly affect LIOVs. Furthermore, the results indicate that the nonuniformity of the ground increases the sensitivity of LIOV to the characteristics of lightning strokes. Finally, an intelligent package is introduced to assess the characteristics of the indirect lightning-induced overvoltage in the complex situation within acceptable accuracy and computation time based on an equivalent resistivity of the soil.
Compact Marx generators (CMGs) are commonly used to provide high-power and high-voltage pulses. Generally, CMGs are composed of spark gaps, charging capacitors, resistors, connections, and a metal body. The stray capacitances between spark gaps and the body could play a significant role in the performance of these generators. This article presents modifications in the conventional structure of a ten-stage CMG to generate various voltage profiles through variations in stray capacitances. These capacitances have been calculated numerically for six reconfigured structures with COMSOL. Eventually, the modified CMGs have been simulated in MATLAB to statistically investigate the impacts of various modified structures on the features of the output voltage such as the voltage peak, the pulsewidth, and the rise time in comparison with the conventional structure. In light of the presented results, the proper and applicable structure would be utilized based on the type of the load.
Lifetime of oil-immersed transformers is highly dependent on condition of paper insulation. This contribution is aimed to quantify the deterioration and ageing process of the paper insulation of distribution transformers based on degree of polymerization (DP). The proposed approach involves real operating conditions of a transformer such as variable ambient temperature, load factor, and moisture content of the paper insulation through calculation of hot-spot temperature to estimate remaining lifetime of the transformers. The results indicate that a DP profile obtained based on actual conditions is completely different to that usually discussed in other researches under completely constant conditions. Consequently, the proposed dynamic DP model could predict lifetime of the transformers more precisely based on real-time measurable quantities. In addition to the remnant lifetime estimation, the proposed dynamic DP profile is utilized to suggest the optimum time for implementing reductions in moisture content of the paper insulation through three scenarios regarding the practical limitations. Finally, reliability of the transformer is evaluated based on statistical data.
Vacuum circuit breakers (VCBs) are increasingly used in power systems. During the operation of a circuit breaker (CB), several incidents such as prestrike, restrike and current chopping might happen which cause erosion in the contacts of the CB and high frequency inrush current. The evaluation of these transients are highly important due to their influence on the switching overvoltage, as well as their dependency to the statistical behavior of the dielectrics. Accordingly, this paper presents a new realistic model for VCBs with respect to the three factors as follows: I-probabilistic breakdown voltage, II-probabilistic operation-velocity and III-nonlinear movement of the contacts. The results based on the proposed model have been compared with other published-experiments and those obtained based on the conventional model in the Helmer circuit. The results are indicated that ignoring the probabilistic behavior of the parameters or linear consideration for breakdown voltage led to the imprecise estimation of transient parameters such as transient recovery voltage (TRV), rate of rise of recovery voltage (RRRV) and the number of breakdowns. The results indicated that using the improved model led to a 60% and 20% change in TRV peak and RRRV, respectively.
Employing online monitoring (OLM) of circuit breakers (CBs) is increasing continuously due to its compatibility with future smart grids. The proper and reliable operation of CBs directly affects the resiliency, reliability and continuity of power systems. Since there is a large number of CBs in power systems, installation of OLM systems to all CBs is not economically justifiable. Consequently, an effective prioritization framework to find the critical CBs to be monitored online is essential. This paper provides a sensible correlation between failure rate and the deterioration process of the CBs through the combination of the discrete Markov model and signal processing of diagnostic features. To prove its feasibility, the proposed approach is applied to a real utility substation using Monte Carlo method based on real monitoring data. The CBs have been prioritized from both reliability and financial viewpoints. In addition, sensitivity analyses results interestingly indicate that, old CBs are not optimistic choice all the time due to the dependency of the problem to the important parameters such as deterioration process, failure rates, operation frequency and the location of the CBs in the power system. The proposed approach enables us to find the optimum choice in such complex environment.
High voltage circuit breakers (HVCBs) play a substantial protection role in power networks. This paper focuses on coil current (CC) and contact travel (CT) waveforms as significant signals that bear helpful information about the fault occurrence for a typical EDF, 72.5kV, SF6 HVCB. Healthy and faulty signals simulated based on Michael Stanek's HVCB model in Matlab, with performing some modifications in the actuating coil and operating mechanism. In the first step, to arrange efficient fault recognition system, Neural Network and Support Vector Machine (SVM) have been designed using information of 475 simulated healthy and faulty HVCBs and verified for 200 new samples. In the second step, to improve the classification results, an additional distinction algorithm has been recommended for the cases in which two failure modes detected by the classifier. Since any failure modes impact on the selected features is different, the proposed diagnostic method makes a decision, between two classes of faults, based on the extracted pattern of each failure mode. The recommended method, which is a combination of commonly used classification techniques and the defined algorithm, leads to the more accurate diagnosis.p>
Moving and fixed main and arc contacts used in circuit breakers (CBs) are prone to erosion with time and usage. Static resistance measurement and dynamic resistance measurement (DRM) are well-known noninvasive methods for the condition assessment of the contacts. Practically, the implementation of various failures on contacts of the CB is so difficult due to their placement in a high-pressure interruption chamber. This paper investigates the impacts of common failure modes such as erosion, disconnection, and misalignment of contacts on DRM profile through 3-D multiphysical simulation of the interruption chamber in the finite-element analysis software COMSOL. The model has been verified against experiments conducted on a 24-kV, SF? CB with a high-resolution scope. The measured profiles indicate that DRM exhibits specific behavior with respect to each failure, e.g., the arc contact erosion leads to a change in the commutation point in DRM. The results have been organized into an intelligent failure diagnosis algorithm based on a set of DRM-based features. In the end, the performance of the proposed algorithm which could be suitable for smart grids is evaluated in the case of an experiment.
o avoid failures in circuit breakers (CBs) and to extend the lifetime of these critical components, condition-based-maintenance has been increasingly requested by utilities to enable them to efficiently manage their assets. The origin of the most failures in CBs is the operating mechanism. Travel curve (TC) could effectively reveal the condition of the operating mechanism. However, the measurement of a TC profile is not simple in all CBs. This paper presents the impacts of common failure modes of CBs on TC profiles, and proposes a new model-aided approach to simulate the behavior of the operating mechanism with coupling the model-based and rule-based approaches. The simulation results along with experiments conducted on 72.5 kV SF6 CBs are organized into a fuzzy-probabilistic approach through maximum likelihood and interacting multiple models (IMM) to precisely predict the condition of CB and to detect intelligently the cause of the failure.The CB condition has been categorized into three modes based on its operating speed: normal, faulty-1 and faulty-2. The mode variations of the CB have been estimated via IMM in each operation. The proposed approach in prediction of the failures and cause(s) prior to their occurrence has been verified against experime
The behavior of grounding systems against waves with high-frequency content such as lightning or very fast transient over voltages is completely different from the steady state. This paper presents more flexible model of grounding system with respect to frequency dependency of electrical parameters of soil and moisture variations using finite integration technique (FIT). The applicability and accuracy of the FIT have been verified against experiments as well as conventional methods such as method of moments (MoM), finite-difference time-domain (FDTD) method, and partial element equivalent circuit (PEEC). In addition, the impacts of moisture variations of soil on resistivity and permeability have been quantified through Weibull distributions. The obtained probabilistic parameters of soil resulting from moisture uncertainty have been involved in the model to provide more realistic model. The probabilistic ground potential rise (GPR) indicated that the grounding system can be optimized up to 50 percent by accepting low-rate of risk depending on the soil moisture level. The provided insight into is a beneficial approach especially for gas insulation substation (GIS) where the available space is limited for grounding system.
Maintenance and repair of circuit breakers (CBs) due to their protective role in the power systems is the centre of attention and assessing their condition is tremendously important. The interruption chamber of the CBs including main contacts is highly subjected to erosion over time due to friction, and excessive heat produced by an arc during the interruption of the currents. This study presents a new high-frequency (HF) non-intrusive diagnostic technique for the deterioration of contacts used in high-voltage CBs. The most striking result to emerge from the investigations is that the resonance frequency highly relies on the condition of contacts. The proposed approach is implemented in Computer Simulation Technology Studio Suite software and compared with the measured data obtained through the static resistance measurement. In addition, a HF model based on the transmission line theory has been developed for the interruption chamber of CBs. The comparison of the obtained results via a novel HF-based approach with the experimental data validates the feasibility and accuracy of this approach in analysing the ablation of contacts used in the interruption chamber of CBs.
Nowadays, reliability of power system is of great importance. Therefore, the condition of transformers as the expensive and critical components of a power system should be monitored and assessed. The dominant factor that causes limitation in transformers lifetime is the paper insulation. This paper aims to investigate the conspicuous influence of moisture content, especially in low oxygen and temperature on lifetime estimation under constant conditions, based on the results of previous experiments. Degree of polymerization (DP) is employed to quantify the effects of detrimental parameters with respect to their time-varying nature. This paper proposes a novel lifetime estimation-approach considering a yearly moisture growth for transformers. The results indicate different trend of DP profiles, which lead to an accurate lifetime estimation in comparison with DP obtained through ideal conditions. Furthermore, oscillations in the hot-spot temperature of transformers are demonstrated to have a negative effect on the lifetime.
Lifetime management of circuit breakers (CBs) compared with the other components in power system is dependent not only on the natural age but also on the number of operation, applications, and maintenance scheduling. In addition, condition?monitoring systems (CMSs) are widely used to extend lifetime and improve the quality of maintenance. However, the employing CMSs for CBs are faced with economical and technical challenges. This paper presents a new probabilistic aging failure model for CBs equipped with CMS. The proposed model improves the conventional approach for the assessment of efficiency of maintenance strategies using available filed data and coupling some weighting factors. The model is based on the state diagram along with Monte Carlo simulations to provide more flexibility in quantification of practical concerns. The model helps us to compare all maintenance strategies within 1 framework to select the best policy with respect to working situation of CBs. The approach has been compared and verified with the conventional aging model. Moreover, it is numerically applied to 2 common types of CBs, that is, SF6 and minimum oil based on the field data to reveal the results of considering the real aging and dynamic behavior of CBs on cost/benefits of maintenance policies. The results of applying the proposed approach to CBs indicate that ignoring the realistic situation of CBs results in a significant underestimation or overestimation of reliability and consequently making a wrong decision on installation of CMS or even in selection of the optimum inspection time.
Circuit breaker (CB) as the key element in power system requires regular maintenance. Nowadays, online condition assessment has been requested increasingly in smart environment. The interruption chamber as the most critical part of the CBs plays an important role in the proper operation of the CBs. Online assessment of this part is difficult from technical point of view due to high noise level and presence of transient recovery voltage. This paper proposes a set up for online measurement of arc voltage of the CBs during trip/close operations. In addition, a method has been proposed to evaluate the remaining useful lifetime (RUL) of interruption chamber based on the measured arc voltage and current. The setup and the proposed approach are verified through the experimental results.
Circuit breaker (CB) is a component providing significant electrical protection for power transmission and distribution systems. Hence, an effective condition monitoring system for the CBs is of imminent importance. This paper presents a fuzzy probabilistic based condition assessment algorithm to assess the CB operation performance by monitoring its trip/close coil current (C.C.), and suggests a simple yet effective condition assessment tool. The C.C. patterns are acquired by measurements carried out on sixty CBs (72.5 kV, SF6) under faulty and normal conditions. To intelligently assess the CB s operating state (i.e.; normal, alarm, emergency), in terms of its reliability, the optimum C.C. features with minimum interdependence were obtained. Furthermore, a fuzzy-probabilistic method is proposed based on the results of the statistical analyses of the features. The feasibility and applicability of the proposed method in CB condition assessment is verified against the experimental measured data.
Circuit breaker (CB) due to its important roles in protection of power system has been recognized as a critical component. In order to assess the condition of CBs, a prevalent and conventional diagnosis method is time measurement of the mechanical operations (called timing test) through the travel curve (T.C.). However, it is an inappropriate technique for the online assessment. The major objective of this paper is to reveal the correlation between the T.C. and auxiliary contacts (A.Cs) of CB. On the basis the results, timing of A.Cs is proposed as easy-to-access, easy-to-measure, and non-invasive diagnosis parameters in online condition assessment of mechanism of CBs. The investigations are established upon measurements carried out on sixty CBs (72.5 kV, SF6) under healthy and faulty conditions. The new approach is conducted through an adaptive neuro-fuzzy inference system (ANFIS). The feasibility and applicability of the proposed method in CB condition assessment is verified against the experimental measured data.
The 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 24-kV rating voltages, having SF6 insulation medium, and are equipped with a spring-drive mechanism.
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 the CBs CBM planning in this power system. This paper employs some qualitative and quantitative criteria to develop this method. While, the former criterion is deals with through assessing the condition of CBs through fuzzy sets theory. And the latter criterion is dealt with through the evaluation of CBs' influence on the overall system reliability (through introduced indices). This method is applied on a sample transmission substation with a breaker-and-a-half configuration. Numerical analysis of this simulation results demonstrates how this method can be employed to prioritize the CBs for OLM.
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 includes 32 CBs. The impacts of interest rate and load interruption cost variations as well as nonoptimum selection of CBs for monitoring on the results are also discussed in this paper. The results of numerical analyses of the case study presented in this paper demonstrate how the proposed method can be employed for maintenance management of power system CBs.
The Compact Marx Generators (CMG) are widely used as portable pulse generators in different applications. They are of great importance anywhere that pulses with rise times on the order of tens of nanoseconds are needed such as nanosecond-pulse breakdown. Considering the fact that the breakdown of a spark gap is a statistical process, the delay times of the closing switches are also statistical and voltage dependent parameters. In this paper, a generalized state space-based model for compact Marx generators is proposed. It can be useful in investigating the impacts of statistical behavior of the breakdown process in spark gaps and closing switch time delays on nanosecond-pulse breakdown rod-plate gaps in nitrogen. Moreover, to increase the transferred current and energy to load, CMGs are used in parallel. The simulation results indicate that in this case, it is more important to have output voltages pulses with temporal low jitter. Discharges were modeled by a nonlinear load using a Rompe-Weizel model to calculate the time-dependent resistances of the spark gaps. The stray capacitances were calculated using electrostatic simulations.
Compact Marx generators are widely used as portable pulse generator in different industrial applications, where high power pulses with rise times of order of some tens of nanoseconds are needed. For those applications, closing switches with very short delay and jitter times have to be used. Considering the fact that the breakdown of spark gap is a statistical process, the delay times of the closing switches are statistical voltage dependent parameters. As a result, the characteristics of the output voltage of the Marx generator, i.e. its amplitude and rise time, are also statistical parameters. In this paper, taking the statistical behaviour of the breakdown process in spark gaps into consideration, the statistical characteristics of the output voltage have been studied in detail.
Supervisory control and data acquisition (SCADA) infrastructures have so far been brought into the huge amount of focus since the need for a more reliable power system accosting with the catastrophic events of interruptions has been raised. Hence, Benefiting from an automation technology which can remotely monitor and coordinate commands to enable immediate response and switching are obviously inevitable. This paper outlines an implementable method in response to the goal of placement of remote terminal units (RTUs) which are in charge for data acquisition and control in a power distribution system. In this light, a new practical methodology based on the robust decision making (DM) method, analytical hierarchical process (AHP), is proposed to simply and at the same time profoundly exploit some practical aspects which have not been considered before in the cases of placements. The proposed method investigates both qualitative and quantitative aspects interrelated with the placement problem. Fuzzy sets are then involved to overcome the existent uncertainty and judgment vagueness. The optimum number of RTUs to be located in the previous-step obtained candidates is determined through reliability cost/worth analysis. Having the belief practically implemented on a real distribution test feeder of Iran s power grid, the efficacy and accuracy of the proposed methodology are satisfactorily confirmed. .
Confronted with the power system restructuring trend reforming the past-regulated power systems, the need for a narrower insight on the costly maintenance strategies seems imperative. It falls within the realm of reliability centered maintenance to enhance the cost effectiveness of power distribution maintenance policies. From a practical point of view, this paper devises a novel approach on the basis of the analytical hierarchical process (AHP) accompanied by fuzzy sets theory to determine the most critical component types of distribution power systems to be prioritized in maintenance scheduling. In the presence of many qualitative and quantitative attributes, fuzzy sets can effectively help to deal with the existent uncertainty and judgment vagueness. As demonstrated in a practical case study, the proposed fuzzy AHP method introduces its applicability and efficiency in the asset management procedure.
So far, the need for power systems to be control automated has been approached. Moreover, the advent of smart technological infrastructures calls for a more systematic and well-designed schemes for data acquisition process. Hence, Remote Terminal Units (RTUs) are going to be considered as a crucial part of smart grid puzzle in power distribution systems. This paper aims to present a novel practical approach to have the RTU placement dilemma unraveled in power distribution systems. Practically approaching in this paper, some pragmatic factors of major importance in this respect are introduced. A framework with which the utility's experts' knowledge could be efficiently exploited is presented and handled through a robust decision making (DM) method referred to as Analytical Hierarchical Process (AHP). To overcome the existing inaccuracies associated with the experts knowledge and to effectively deal with the existent uncertainties and imprecision in the conventional AHP approach, fuzzy sets theory is incorporated to reach the most reliable and optimal substations as the RTU placement candidates. The efforts are focused on the pragmatic aspects interrelated with the procedure. Being applied to a real distribution power system of Iran's power grid, the applicability and practicality of the proposed fuzzy AHP (FAHP) method is well approved.
This paper investigates a reliability-centered approach for the placement procedure of remote terminal units (RTUs) in power distribution systems. Entire attempt is contributed to incorporate the practical aspects interrelated with the problem, e.g. the accessibility to the candidate substations, the load point criticality, as well as the load probabilistic behavior and consequently the inevitable variation in the electricity price. The placement process is done through an optimization problem wherein the common reliability indices, as the decisive factors in the placement process, are going to be minimized. The approach is successfully applied to a real power distribution feeder of Iran's power grid and well demonstrates its applicability accompanied by its accuracy in dealing with the practical planning concerns.
This In a practical power system, automating all the substations is neither affordable nor economically justifiable. On the other hand, the trend for electric power subsidies elimination in some regions, such as Iran, aggravates this situation. To enhance the cost effectiveness of distribution automation system, this paper proposes a novel applicable qualitative-quantitative method using analytical hierarchical process (AHP) to find the optimum placement of remote terminal units (RTU). Entire attempt is to contribute all the crucial technical and practical parameters related to this problem in order to find the most reliable solution. Optimum number of RTUs is determined using the concepts of reliability cost/worth taking into account the total cost of customer interruption and investment cost of RTUs. The effectiveness of the proposed technique is validated on a real distribution feeder of Iran's power grid.
Lightning strikes or flashovers of insulation can result in impulse voltages with very short front times of some tens of ns. Power apparatuses are exposed to these voltages. Steep-front square impulse voltage with high accuracy can be generated by applying advanced pulsed power technology. Nowadays, compact Marx generator (CMG) is used for achieving exact results in tests. Considering the fact that the breakdown of spark gap is a statistical process, the delay times of the closing switches are statistical and voltage-dependent parameters. In this paper, taking the statistical behaviour of the breakdown process in spark gaps into consideration, the statistical characteristics of the output voltage have been studied in detail and its effect on accuracy of insulation tests are described.
The desire to decrease electrical loading by using energy efficient lighting has resulted in a high level of attention to replacing conventional incandescent lamps with compact fluorescent lamps (CFL). In Iran from energy management point of view, people are encouraged by ministry of power to use CFLs. Also after elimination of subsidies, the substantial increase in electric energy price resulted in a high level of penetration of CFLs in electricity grid. CFL is a nonlinear load, therefore it injects harmonic to the network. In past, due to lower application of CFL, these harmonics were ignored, however today by the widespread application of CFLs; these small sources are combined and have high effect on power distribution networks. This paper presents the results of an investigation on the effect of widespread application of CFLs on a real power distribution system of Iran. CFL has some disadvantages that should rectify gradually. However at present great use of this component may cause adverse effects especially on the distribution network. Most of the CFL disadvantages are related to its high level of harmonics. In this paper the interference of the harmonics generated by CFLs to a real distribution network of Iran power grid will be simulated and studied. Since the CFL employed in these network have a relatively poor quality, in this study three samples of the brands which are in wider use in Iran market are selected. The characteristic current of these samples are experimentally determined. After that, CFLs are modeled with considering the attenuation effect. For harmonic mitigation, optimize capacitor placement is done and at the end, Simulation results are discussed.
With the expansion of electricity networks, increasing operational complexities, improved knowledge of the system operators, all with the subsidies elimination in some countries such as Iran and experiencing the real price of electricity by then, it necessitates a more reliable power to be delivered to the system customers. Power system automation is regarded as an efficient solution and the effective key to this problem. However, the great number of substations in power distribution systems has led to the fact that it is neither feasible nor economic to automate all of them. This calls for a comprehensive scheme on the placement of the distribution substations to be automated. In this paper, a practical glance is followed on the calculation of outage times which follows a practical approach for the substations placement. Some reliability-oriented indices are also proposed with which, together with their suitable fuzzy membership functions, the optimal location of substations for automation would be identified. The presented approach is finally applied to a real part of a distribution system in Tehran, Iran. And the results, as expected, show the applicability and effectiveness of the proposed algorithm.
In a distribution power system, vividly in a deregulated market and restructured environment, blind time based maintenance of all the distribution equipments is neither affordable nor economically justifiable. Moreover, an acceptable level of system reliability is an indispensable criterion for the successful operation of a power distribution system. To enhance the cost effectiveness o distribution maintenance policy and particularly from the asset management point of view, this paper proposes a new applicable qualitative-quantitative approach based on analytical hierarchical process (AHP) to determine the most critical equipments to be prioritized in maintenance scheduling. Entire attempt is to contribute all the major technical and practical parameters related to this problem to find the most optimized solution. The proposed method i applied to a practical distribution feeder of Iran's power grid to illustrate the applicability and effectiveness of the method.
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Room 206, Saturday 10:30-12:30
High voltage lab, Saturday-Monday 1:30-3:00.
High Voltage Lab, Tuesday 10:30-12:00.
Undergraduate course at Sharif University of Technology,Tehran, Iran.
Undergraduate course at KN Toosi University of Technology,Tehran, Iran.
Undergraduate course at KN Toosi University of Technology,Tehran, Iran.
Undergraduate course at KN Toosi University of Technology,Tehran, Iran.
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You can find me at my office located at K. N. Toosi University, Electrical Engineering department, fourth floor, Room 413.
I am at my office every day from 9:00 am until 5:00 pm, but you may consider a call or an email to fix an appointment.
You can find me at my Work located at K. N. Toosi University, Electrical Engineering department, High voltage Lab.
You can find me at my Work located at K. N. Toosi University, Electrical Engineering department, High voltage Lab.
I am at my office every day from 8:00 until 5:00 pm, but you may consider a call to fix an appointment.