Ferroresonance Conditions Research Articles

Application of Superconductors to Suppress Ferroresonance Overvoltage in DFIG-WECS

While much attention was given in the literature to improve the fault ride through (FRT) capability of a doubly-fed induction generator (DFIG)-based wind energy conversion system (WECS) during various faults at the grid side, not much attention was given to investigate and improve the performance of the DFIG-WECS under ferroresonance conditions. This paper investigates the impact of ferroresonance on the overall performance of a DFIG-WECS. The paper also presents a new technique to improve the high voltage ride through capability of the investigated system under such condition. The proposed technique relies on incorporating a superconducting coil within the dc-link of the DFIG grid-side and rotor-side converters. Energy exchange between the coil and the system is controlled through regulating the duty cycle of the dc-chopper interfacing the coil with the dc-link. In this regard, a simple but yet effective proportional-integral (PI) controller is employed to regulate the dc-chopper duty cycle. Parameters of the PI controller are optimized using elephant herding optimization algorithm. Simulation results verify the effectiveness of the proposed controller in improving the overall performance of a DFIG-WECS during ferroresonance events.

Impacts of ferroresonance and inrush current forces on transformer windings

Deformation of the windings is one of the main causes of the power transformers failure. Here, for the first time, the electromagnetic forces exerted on the windings are computed in ferroresonance condition and compared with that of the inrush current for a typical power transformer. In both cases, the magnetic core of the transformer saturates and the leakage flux around the windings increases, which leads to large forces on the windings carrying high currents. Therefore, precise modelling of the transformer core is required to calculate the forces inside the transformer. For this purpose, the Jiles–Atherton vector hysteresis model is employed in conjunction with finite element method (FEM) to simulate the laminated grain-oriented steel core, and then the radial and axial forces inflicted on the windings are estimated.

Analisis Karakteristik Arus dan Tegangan pada Inisiasi Feroresonansi Transformator Tegangan Rendah

Ferroresonance is an interaction phenomenon between non-linear inductance and capacitance that initiates abnormal waveform of current and voltage. This phenomenon is very sensitive to system parameter and initial condition. In this paper, ferroresonance initiation involved a basic circuit of series ferroresonance with variation of source voltage magnitude on a single phase low voltage transformer. The scheme of experiment was based on the case of transformer energizing. The trends of current and voltage waveform on the primary windings were investigated and transformed by using Fast Fourier Transform (FFT). The harmonics spectrum was then employed to identify the feroresonance mode and calculate the Total Harmonics Distortion (THD) of current and voltage. The experimental results showed that the higher source voltage magnitude caused the ferroresonance responses to be seen more clearly. It was indicated by the more distorted waveform, the higher odd harmonics frequency amplitude especially for 150 Hz, and the greater THD. Based on the harmonics spectrum and wave period, the ferroresonance responses were identified as fundamental mode. The effects of initial conditions, such as residual flux of transformer and capacitor charge, were also seen on the distorted wave peak during transient condition. In addition, the difference of waveform between normal and ferroresonance condition could be more easily observed on the voltage than the current. The waveforms of current and voltage during experiment had been verified by using simulation.

Ferroresonance conditions in wind parks

Wind parks are made up of a large number of saturable inductances (power transformers, inductive voltage transformers (IVTs)), as well as capacitors (cables, wind turbine harmonic filters, capacitor voltage transformers (CVTs), voltage grading capacitors in circuit-breakers). Therefore, they may present scenarios in which ferroresonance occurs. This paper presents the scenarios that can lead to ferroresonant circuits in doubly fed induction generator (DFIG) based wind parks. Ferroresonance conditions and their consequences are demonstrated by simulating the detailed model of the wind park in EMTP-RV. The wind park simulation model includes detailed models of wind turbines, medium voltage (MV) collector grid, high voltage/medium voltage (HV/MV) wind park substation, overvoltage, overcurrent and differential current protections, current transformers (CTs), IVTs and CVTs.

Challenges of Power Converter Operation and Control Under Ferroresonance Conditions

This paper presents the challenges that the power converters with $dq$ -frame-based control confront when subjected to ferroresonance. This is mainly due to two main properties of the widely used $dq$ -frame control systems. It is demonstrated in this paper that regardless of the phase-to-ground or phase-to-phase voltage measurement, the $dq$ -frame control only responds to phase-to-phase voltage variations. Furthermore, the PI controllers, which are employed in conjunction with the $dq$ reference frame, can inherently only track dc references and reject dc disturbances. Consequently, a $dq$ -based PI controller can only respond to the positive-sequence phase-to-phase voltage variations, effectively. This, in turn, limits the disturbance mitigation capability of the power converter. This study investigates the impacts of the ferroresonance phenomenon on the control system response and the operating conditions of the power converters. Based on a droop-based $dq$ frame controller, the behavior of an electronically interfaced distribution generation system is studied, under various transient conditions. In spite of a promising performance under the load change and islanding scenarios, the $dq$ -frame-based controller of the power converter fails to detect and respond to the voltage fluctuation and excessive overvoltages as a result of ferroresonance.

Time‐domain finite‐element technique for quantifying the effect of sustained ferroresonance on power transformer core bolts

Detailed investigation of the effects of ferroresonance on power transformers requires a method that is able to quantitatively and topologically assess the core saturation and the stray fields attributed to flux redistribution. This study describes a time-domain finite-element approach to model a ferroresonance condition and quantify its effect. More specifically the model generates sustained ferroresonance waveforms and, crucially, also allows examination of the effect of the resulting high core fluxes on the transformer core clamping bolts. Two benchmarking concepts are used to aid this: (i) the space-averaged permeability variation and (ii) a topological calculation of flux variation within the core.

Hysteresis and eddy current effects in ferroresonant LCR circuits

Ferroresonance conditions are analyzed in a LCR circuit including nonlinear inductor. The effect of the ferromagnetic model (single valued curve, static hysteresis, dynamic hysteresis) and of the eddy currents are deepened by means of a coupled circuit-field equations. It is found that all the dissipative effects reduce or avoid ferroresonance and, in this paper, this influence is quantified and discussed, making reference to different material models.