Saeed Shahabi - Academia.edu (original) (raw)

Papers by Saeed Shahabi

International Journal of Engineering, 2015

In order to restrain ferroresonance in coupling capacitor voltage transformers (CCVT), three kind... more In order to restrain ferroresonance in coupling capacitor voltage transformers (CCVT), three kinds of ferroresonance suppression circuits (FSCs) have been presented. The resonant type, the fast-saturation reactor type and electronic type which are connected to secondary side of CCVTs, are proposed in this paper. Frequency domain analyses, for voltage ratio magnitude, are carried out for CCVTs to obtain preferable FSC. Furthermore, using surge suppressors such as metal oxide varistors (MOV) to improve the performance of the FSCs is investigated. Time domain simulations demonstrate that ferroresonance can be cleared in few cycles in presence of FSCs. In addition, to mitigate ferroresonanse in inductive transformers (VTs), we connect the damping resistor to the open-delta-arranged auxiliary winding.

TURKISH JOURNAL OF ELECTRICAL ENGINEERING & COMPUTER SCIENCES, 2017

This paper presents a theoretical dynamic model based on the Hampton criterion and Mayr's equatio... more This paper presents a theoretical dynamic model based on the Hampton criterion and Mayr's equation for predicting the critical values of flashover on the surface of nonuniformly polluted cap and pin porcelain insulators. The nonuniform pollution layer on the surface of the insulator, the number of disk insulator units, and the geometry of the insulator such as diameter and ribs are the important factors used for prediction. Two types of pollution layer configuration, linear and graded, are introduced as nonuniform pollution layers. The influences of the nonuniform pollution layer on critical flashover voltage are investigated. Furthermore, a random value is added to the surface discharge length during propagation in order to consider the effects of the wind and thermal convection on surface discharge length. The specifications of a real porcelain disk insulator are used in the model. Finally, the estimated results of the proposed model are compared with the measured data of the tests in order to validate the proposed model.

The transient electromagnetic fields during switching operation in gas-insulated substations (GIS... more The transient electromagnetic fields during switching operation in gas-insulated substations (GIS) have rise times of nanoseconds. These fields leak into the external environment through the discontinuities of gas-insulated modules and affect on control cables and lead to induce transient voltage in cables which result in malfunctioning of equipment. Amplitudes of the electrical and magnetic fields could be a few tens of kilovolts per meter and a few hundreds of amperes per meter according to layout of gas-insulated substations, respectively.In this paper, the induced voltage in a control cable and induced current in its sheath in a gas-insulated substation with rated voltage of 245 kilovolts were calculated. Also, the effect of cable's length and type of cable sheath grounding on the induced current will be calculated.

CIGRE, 2015

One of the major problems in electric power transmission and distribution systems is the flashove... more One of the major problems in electric power transmission and distribution systems is the flashover caused by polluted insulators. This type of flashover is known as temporary fault that can turn into a permanent fault, causing sustained interruption [1]. Cost of power interruptions is highly significant for consumers and utility companies. For example, U.S. electric power interruptions, cost $135 billion per year [2]. Polluted insulators also contribute to the leakage current in a transmission line system. The dissipation of power due to leakage current is significant. The leakage current increases with pollution conductivity, and result in rapid extension of partial arcs [3, 4]. It is important to evaluate the contamination level of energized insulators to prevent unexpected pollution flashover and improve the reliability of the system. When the pollution level of in-service insulators are identified, the appropriate decision can be made about period of washing the insulators. In this study, a leakage current waveform characteristics is used in order to predict the severity of the contamination on the surface of insulators. The phase angle difference, total harmonic distortion (THD), and rate of rise of THD are the leakage current characteristics used for monitoring the pollution level. The values of the phase angle difference () between applied voltage and the fundamental frequency of the leakage current are computed while the pollution conductivity increases. When the pollution conductivity is low, the leakage current is capacitive. On the other hand, the leakage current becomes resistive when the pollution conductivity is high enough. The total harmonic distortion (THD) of leakage current is used for detection of contamination severity. The high frequency components of the leakage current increase with pollution conductivity and affect the THD level. Furthermore, the harmonic level variation of the leakage current over time results in THD variation. The rate of rise of THD (RRTHD) is introduced as an effective parameter to find the pollution level. These details provide a good correlation between the state of pollution and the leakage current. Therefore, phase angle difference (), THD, and RRTHD are used as the characteristic parameters of leakage current in order to find the contamination level.

2009 4th IEEE Conference on Industrial Electronics and Applications, 2009

In order to restrain ferroresonance in coupling capacitor voltage transformers (CCVT), three kind... more In order to restrain ferroresonance in coupling capacitor voltage transformers (CCVT), three kinds of ferroresonance suppression circuits (FSCs): the resonant type, the fast-saturation reactor type and electronic type which are connected to secondary side of CCVTs, are proposed in this paper. Frequency domain analyses, for voltage ratio magnitude, are carried out for CCVTs to obtain preferable FSC. Furthermore, using surge suppressors such as metal oxide varistors (MOV) to improve the performance of the FSCs is investigated. Time domain simulations demonstrate that ferroresonance can be cleared in few cycles in presence of FSCs. The Electromagnetic Transients Program (EMTP) is used for modeling and fine-tuning the FSCs.

2014 Ieee Pes General Meeting Conference Exposition, Jul 1, 2014

Lightning surge overvoltages are generally related to two cases, direct lightning stroke and back... more Lightning surge overvoltages are generally related to two cases, direct lightning stroke and back-flashovers. Lightning overvoltage waves travel on the transmission line and then enter a substation. High voltage equipment in a substation can be affected by transient overvoltage. This paper investigates the influences of lightning surge with fast front wave on Siahbishe 400 kV Gas Insulated Substation (GIS) located in the north of Iran. The fast transient overvoltages induced in major parts of GIS are investigated due to the first and subsequent direct lightning strokes and back-flashovers. We also show the relationship between the lightning surge current and the overvoltage induced at the entrance of the substation. In addition, the proper arc distance value for 400 kV transmission line string insulators is obtained. Index Terms--Gas insulated, direct stroke, back-flashover, fast transient, arc distance I.

Flashover on polluted insulator is a major problem for the safe operation of transmission lines a... more Flashover on polluted insulator is a major problem for the safe operation of transmission lines and the design of external insulation. It initiates when the current flows through the conductive pollution layer on the surface of an insulator and create dry bands are created. The performance of insulators under polluted conditions is an important factor in the design and dimensioning of insulators in power transmission lines. Therefore, many researchers have studied the modeling of polluted insulators and predicting the flashover voltage, e.g.

IEEE EUROCON 2009, 2009

This paper deals with the effect of distorted overvoltage and current on a transformer terminated... more This paper deals with the effect of distorted overvoltage and current on a transformer terminated at a transmission line through a cable that caused by striking of lightening on transmission line. Also the effect of harmonic current on transformer losses that cause overheating and aging of insulation is discussed. And then the hot spot and top oil temperature under the harmonic conditions using thermal model will be predicted. The thermal model is introduced by heat transfer principles including oil-to-air heat transfer and winding to oil heat transfer. And also the increase of harmonic current decline transformer life time. In addition, transient simulation is performed using EMTP software will show the longer cable the less amplitude of distorted operating conditions on the terminal of the transformer.

2014 IEEE PES General Meeting | Conference & Exposition, 2014

IEEE EUROCON 2009, 2009

In order to restrain ferroresonance in coupling capacitor voltage transformers (CCVT), two kinds ... more In order to restrain ferroresonance in coupling capacitor voltage transformers (CCVT), two kinds of ferroresonance suppression circuits (FSCs), are proposed in this paper: the resonant type, the fast-saturation reactor type which are connected to secondary side of CCVTs. Frequency domain analyses, for voltage ratio magnitude, are carried out for CCVTs to obtain preferable FSC. Furthermore, using surge suppressors such as

IEEE EUROCON 2009, 2009

This paper investigates the problem of controlling and modulating power flow in a transmission li... more This paper investigates the problem of controlling and modulating power flow in a transmission line using a Synchronous Static Series Compensator (SSSC). The studies, which include detailed techniques of twelvepulse and PWM controlled SSSC, are conducted and the control circuits are presented. The developed control strategies for both twelve-pulse and PWM-controlled SSSC use direct manipulations of control variables instead of typical d-q transformations. The complete digital simulation of the SSSC within the power system is performed in the MATLAB/Simulink environment using the Power System Blockset (PSB). Simulation results validate that Voltage and Power Oscillation can be damped properly using of Synchronous Static Series Compensator (SSSC).

IEEJ Transactions on Electrical and Electronic Engineering, 2013

The transient electromagnetic fields during switching operation in gas-insulated substations (GIS... more The transient electromagnetic fields during switching operation in gas-insulated substations (GISs) have rise times on the order of nanoseconds. These fields leak into the external environment through the discontinuities of gas-insulated modules and affect the control cables and induce the transient voltage on cables, which results in malfunctioning of the equipment. The amplitudes of the electric and magnetic fields could be a few tens of kilovolts per meter and a few hundred amperes per meter according to layout of GIS, respectively. In this work, the induced voltage in the central conductor of a control cable and the induced current in its sheath, which is parallel to bus duct in a GIS with rated voltage of 230 kV, are calculated. Influence of the sheath material on the induced voltage and the type of its grounding on the induced current are analyzed. Furthermore, the impact of installing ferrite rings over the control cable sheath in mitigating the induced voltage and current is investigated.

… and Applications, 2009 …, Jan 1, 2009

International Journal of Engineering, 2015

TURKISH JOURNAL OF ELECTRICAL ENGINEERING & COMPUTER SCIENCES, 2017

CIGRE, 2015

2009 4th IEEE Conference on Industrial Electronics and Applications, 2009

In order to restrain ferroresonance in coupling capacitor voltage transformers (CCVT), three kind... more In order to restrain ferroresonance in coupling capacitor voltage transformers (CCVT), three kinds of ferroresonance suppression circuits (FSCs): the resonant type, the fast-saturation reactor type and electronic type which are connected to secondary side of CCVTs, are proposed in this paper. Frequency domain analyses, for voltage ratio magnitude, are carried out for CCVTs to obtain preferable FSC. Furthermore, using surge suppressors such as metal oxide varistors (MOV) to improve the performance of the FSCs is investigated. Time domain simulations demonstrate that ferroresonance can be cleared in few cycles in presence of FSCs. The Electromagnetic Transients Program (EMTP) is used for modeling and fine-tuning the FSCs.

2014 Ieee Pes General Meeting Conference Exposition, Jul 1, 2014

IEEE EUROCON 2009, 2009

2014 IEEE PES General Meeting | Conference & Exposition, 2014

IEEE EUROCON 2009, 2009

IEEJ Transactions on Electrical and Electronic Engineering, 2013

The transient electromagnetic fields during switching operation in gas-insulated substations (GIS... more The transient electromagnetic fields during switching operation in gas-insulated substations (GISs) have rise times on the order of nanoseconds. These fields leak into the external environment through the discontinuities of gas-insulated modules and affect the control cables and induce the transient voltage on cables, which results in malfunctioning of the equipment. The amplitudes of the electric and magnetic fields could be a few tens of kilovolts per meter and a few hundred amperes per meter according to layout of GIS, respectively. In this work, the induced voltage in the central conductor of a control cable and the induced current in its sheath, which is parallel to bus duct in a GIS with rated voltage of 230 kV, are calculated. Influence of the sheath material on the induced voltage and the type of its grounding on the induced current are analyzed. Furthermore, the impact of installing ferrite rings over the control cable sheath in mitigating the induced voltage and current is investigated.

… and Applications, 2009 …, Jan 1, 2009