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Ferroresonance occurrence is a source of damage, causing overvoltage on voltage transformer (VT) and isolators of the grid equipment. Some solutions are available to protect VTs from the ferroresonance overvoltage. However, they just act after the ferroresonance occurrence. In this letter, to prevent the occurrence of ferroresonance, a dc reactor-based protection device is introduced. Analytical studies and simulations by MATLAB/Simulink and Maxwell ANSYS demonstrate the capability of the proposed protection device as a VT ferroresonance inhibitor. Experimental results from a scaled-down laboratory prototype are also provided to verify the proposed solution. [ABSTRACT FROM AUTHOR]

This study presents a novel DC reactor‐based ferroresonance and fault current limiter (DRFFCL) for stabilising ferroresonance oscillations of potential transformer (PT) in 33 kV distribution network and decreasing the amplitude of the fault current to an acceptable level. At first, the ferroresonance overvoltage is introduced and various types of overvoltage in the PT are studied. Then, the effects of the suggested DRFFCL on these oscillations are investigated. It is shown that the proposed DRFFCL not only can control the ferroresonance oscillations, but also can decrease the fault current amplitude in the case of short‐circuit faults occurrence. The DRFFCL performance is simulated using MATLAB software and a scaled‐down laboratory prototype is implemented and tested for the simulation results validation. The measured results are in agreement with the simulation results and clearly show the ability of the DRFFCL for controlling both the ferroresonance overvoltage and fault current. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Ferroresonance is a non-conventional electrical phenomenon which may cause overvoltages in the electrical power system endangers the system reliability. This paper studies the effect of circuit breaker shunt resistance, Metal Oxide Surge Arrester (MOSA) and neutral earth resistance on controlling chaotic ferroresonance in a potential transformer while transformer core losses is modeled as a nonlinear resistance which hysteresis and eddy current losses are included. It is expected that neutral earth resistance can control ferroresonance better than MOSA and circuit breaker air gap resistance. For confirmation this aspect, simulation has been done on a one phase potential transformer rated 100VA, 275kV. Simulation results show that considering shunt resistance on the circuit breaker and MOSA in parallel to the transformer, exhibits a great mitigating effect on ferroresonance oscillations, but these resistances cannot control these phenomena for wide variation of the power system parameters. By applying neutral earth resistance to the system grounding, ferroresonance is controlled and its amplitude has been damped for all parameters values. [ABSTRACT FROM AUTHOR]