Hamid Radmanesh

Bridge-Type Solid-State Fault Current Limiter Based on AC/DC Reactor

This paper proposes a novel bridge-type solid-state fault current limiter (BSSFCL) based on one series reactor which operates in ac and dc modes. The proposed BSSFCL includes a rectifier bridge with a reactor. This reactor is used as a dc reactor in normal operation mode and as an ac reactor in fault conditions. The advantages of the proposed BSSFCL over the existing dc reactor-type FCLs are its negligible impedance in normal operation mode and its high impedance during a fault interval using simple and novel switching. In other words, during the normal operation mode, the proposed BSSFCL operates in dc mode and in the fault interval, its topology is changed to the ac mode. This switching decreases the switching transient recovery voltage and introduces considerable impedance during the fault period. MATLAB/Simulink software is used for simulations and a prototype is designed and tested for results verification, and to show the performance of the proposed BSSFCL.

Series Transformer-Based Solid State Fault Current Limiter

This paper studies a novel transformer-based solid state fault current limiter (TBSSFCL) for radial distribution network applications. The proposed TBSSFCL is capable of controlling the magnitude of fault current. In order to control the fault current, primary winding of an isolating transformer is connected in series with the line and the secondary side is connected to a reactor, paralleled with a bypass switch which is made of anti-parallel insulated gate bipolar transistors. By controlling the magnitude of ac reactor current, the fault current is reduced and voltage of the point of common coupling is kept at an acceptable level. Also, by this TBSSFCL, switching overvoltage is reduced significantly. The proposed TBSSFCL can improve the power quality factors and also, due to its simple structure, the cost is relatively low. Laboratory results are also presented to verify the simulation and theoretical studies. It is shown that this TBSSFCL can limit the fault current with negligible delay, smooth the fault current waveform, and improve the power quality.

A Novel Solid-State Fault Current-Limiting Circuit Breaker for Medium-Voltage Network Applications

In this paper, a novel solid-state fault current-limiting circuit breaker (SSFCLCB) based on a series resonance LC tank is proposed. Since the series configuration of the resonance structure (a capacitor and a reactor) of the SSFCLCB is invisible during normal operation mode, it shows negligible impedance in the line. In fault conditions, the SSFCLCB topology changes to a rectifier bridge and feeds the resonance structure with rectified ac voltage. With the rectified voltage, the series capacitor is charged and, as a result, the faulty line is opened and the fault current is seized. Hence, the suggested SSFCLCB cannot only limit the fault current but can also open the faulty line and acts as a circuit breaker. For confirmation of these aspects, simulations are performed using MATLAB software. Also, a prototype structure is designed and built for results confirmation. This experimental setup is established to prove that SSFCLCB has excellent performance in its startup, normal operation, and current-limiting/breaking conditions. The results show that the SSFCLCB has the ability to improve distribution network reliability and it can decrease the network fault current level successfully.

Ferroresonance of Power Transformers Considering Non-linear Core Losses and Metal Oxide Surge Arrester Effects

Abstract In this article, a simple case of ferroresonance in a three-phase transformer is used to study the effect of a metal oxide surge arrester on the control of chaotic ferroresonance and duration of chaotic transient in a power transformer including non-linear core losses. The time-domain simulations are derived using MATLAB (The MathWorks, Natick, Massachusetts, USA) for a three-phase 50-MVA, 635.1-kV power transformers while one of its phases is opened. The magnetization characteristic of the power transformer is modeled by a single-value two-term polynomial. The non-linear core losses are modeled by a third-order power series in terms of voltage, and the core losses non-linearities are considered as well. The simulation results show that connecting the metal oxide surge arrester to the transformer exhibits a great suppressing effect on occurred ferroresonance over-voltage.

Analyzing ferroresonance phenomena in power transformers including zinc oxide arrester and neutral resistance effect

This paper studies the effect of zinc oxide arrester (ZnO) and neutral earth resistance on controlling nonconventional oscillations of the unloaded power transformer. At first, ferroresonance overvoltage in the power system including ZnO is investigated. It is shown this nonlinear resistance can limit the ferroresonance oscillations but it cannot successfully control these phenomena. Because of the temperature dissipation of ZnO, it can withstand against overvoltage in a short period and after that ferroresonance causes ZnO failure. By applying neutral earth resistance to the system configuration, mitigating ferroresonance has been increased and chaotic overvoltage has been changed to the smoother behavior such as fundamental resonance and periodic oscillation. The simulation results show that connecting the neutral resistance exhibits a great mitigating effect on nonlinear overvoltage.

Series transformer based diode-bridge-type solid state fault current limiter

We propose a novel series transformer based diode-bridge-type solid state fault current limiter (SSFCL). To control the fault current, a series RLC branch is connected to the secondary side of an isolation series transformer. Based on this RLC branch, two current limiting modes are created. In the first mode, R and C are bypassed via a paralleled power electronic switch (insulated-gate bipolar transistor, IGBT) and L remains connected to the secondary side of the transformer as a DC reactor. In the second mode, the series reactor impedance is not enough to limit the fault current. In this case, the fault current can be controlled by selecting a proper on-off duration of the parallel IGBT, across the series damping resistor (R. and capacitor, which inserts high impedance into the line to limit the fault current. Then, by controlling the magnitude of the DC reactor current, the fault current is reduced and the voltage of the point of common coupling (PCC) is kept at an acceptable level. In addition, in the new SSFCL, the series RC branch, connected in parallel with the IGBT, serves as a snubber circuit for decreasing the transient recovery voltage (TRV) of the IGBT during on-off states. Therefore, the power quality indices can be improved. The measurement results of a built prototype are presented to support the simulation and theoretical studies. The proposed SSFCL can limit the fault current without any delay and successfully smooth the fault current waveform.

Harmonic study in electromagnetic voltage transformers

Ferroresonance is a complex electrical phenomenon which may cause overvoltages and overcurrents in electrical power system disturbing the system reliability and continuous safe operating. The ability to predict or confirm ferroresonance depends primarily on the accuracy of the voltage transformer model used in the computer simulation. In this study, at first an overview of the subject in the literature is provided. Then, occurrence of ferroresonance and the resulting harmonics in a voltage transformer are simulated. The effect of iron core saturation characteristic on the occurrence of harmonic modes has been studied. The system under study has a voltage transformer rated 100VA, 275 kV. The nonlinear magnetization cure index of the autotransformer is chosen with q=7. The linear core loss of the transformer core is modeled with linear resistance. Harmonic modes in the proposed power system are analyzed using MATLAB software. The results show that harmonics are produced in the considered substation and causes great effect on voltage transformer failure.

Distribution Network Protection Using Smart Dual Functional Series Resonance-Based Fault Current and Ferroresonance Overvoltage Limiter

This paper proposes a smart dual function series resonance ferroresonance overvoltage and fault current limiter (SRFFCL) for distribution networks. The studied network has potential transformers (PTs) with a typically low thermal capacity and high accuracy. The PT core losses are assumed to be constant during ferroresonance oscillation. The MATLAB software is used for simulation of the novel SRFFCL in distribution network, to study the PT ferroresonance overvoltage and fault current. Also, experimental results are obtained using a laboratory prototype. Both the simulation and experimental results, which are in good agreement with each other, show that the suggested SRFFCL can not only control the fault current but also adequately decrease the ferroresonance oscillation of the PT.

Aircraft electrical power distribution system protection using smart circuit breaker

In some aircraft with traditional distribution electrical systems, the sources, distribution, and electrical loads are fully coupled. The control surfaces in traditional aircraft are based on cables and hydraulic actuators. Furthermore, the system stability mainly related to the hydraulic system and a small portion of it is related to the electrical system reliability. However, for aircraft like A380 and B787, the flight system is based on fly by wire (FBW) technology and more electric aircraft (MEA) have drawn the attention of aircraft designers. In addition, more hydraulic actuators change to the electrical actuator, which leads to more electrical generation usage. The availability of electrical energy to the loads is only ensured through overdesign, system reconfiguration, and protection. Power electronic converters are starting to be used to fully decouple the dynamics between sources, distribution systems, and loads.

Thyristor-Controlled AC Reactor Based Fault Current Limiter for Distribution Network Stability Enhancement

Recently, various types of Solid State Fault Current Limiters (SSFCLs) have been proposed. These SSFCLs can improve the voltage quality, decrease the transmission losses, and also can enhance the distribution network stability but there are some practical problems with these FCLs. This paper proposes a modified FCL with focusing on the components optimization, efficiency improvement and reducing the cost. The suggested FCL uses a series AC reactor with controllable power electronic switches named Thyristor-Controlled AC Reactor (TCAR) which is connected in series with the feeder to limit the fault current and avoid fault current problems, which impairs overall distribution network reliability. The influence of TCAR on the fault current is analyzed using analytical, simulation and laboratory tests. The performance of the proposed TCAR in the simple distribution network is examined. The simulation and experimental results are in a good agreement with together and show the proper operation of the proposed TCAR during the normal and fault operation modes.