Ferroresonance Suppression Circuits Research Articles

Probabilistic framework for vulnerability analysis of coupling capacitor voltage transformer to ferroresonance phenomenon

The performance of measurement transformers especially in transient phenomena affects the monitoring, control and protective devices. Coupling capacitor voltage transformer (CCVT) is a measurement transformer that may experience ferroresonance phenomenon due to the presence of capacitors and non-linear reactors. This study provides a probabilistic framework for investigation of ferroresonance phenomenon in CCVT. The aim of this investigation is to find out the area of the power system in which a CCVT is highly prone to experience ferroresonance phenomenon. Also through this framework the behaviour of the different types of ferroresonance suppression circuits and possible solutions to avoid or reduce the chance of ferroresonance will be discussed. The effects of several factors such as switching moment, different fault type and the fault inception angle are investigated. The investigation will be conducted considering the effects of single-pole auto-reclosing, three-pole auto-reclosing and capacitor failure in the CCVT. As shown in the simulation results, the presented framework can provide some useful information regarding the exposure level and severity of CCVT ferroresonance in the system.

Parameters of Passive Ferroresonance Suppression Circuit (FSC) Affecting Ferroresonance Damping and Normal Operating Voltage and Current of Capacitive Voltage Transformer (CVT)

This paper discusses the effect of parameters of passive Ferroresonance Suppression Circuit (FSC) on Capacitive Voltage Transformer (CVT) in not only the mitigation of ferroresonance oscillation, but also the normal operating voltage and current of CVT. The passive FSC composed of a resistor paralleled with a saturable reactor that has been a series circuit of a resistor and a saturable inductor. In this study, the resistance values have been varied. Then, one of the resistance variations has been used to damp the ferroresonance oscillation during the simulation with load variation of CVT. The opening and the reclosing of the circuit breaker have been utilized to initiate the ferroresonance on CVT. The results have showed that the existence of passive FSC with the given parameter values could effectively suppress the highly distorted overvoltage and overcurrent of ferroresonance oscillation, but the normal operating voltage and current of CVT have been increased during FSC resistor variation and have been decreased during saturable reactor resistor variation. The resistance value of FSC has been linear with the peak voltage and the ripple of waveform, whereas the resistance value of saturable reactor has been opposite with the peak voltage and the ripple of waveform. Furthermore, the load variation of CVT affected the ferroresonance behaviour and the peak voltage and current of CVT. Regarding those results, the electrical engineer should be able to choose the design of FSC appropriately in order to not only get the effective ferroresonance mitigation, but also to maintain the normal operating conditions of CVT in the future.

A new control unit for electronic ferroresonance suppression circuit in capacitor voltage transformers

Ferroresonance suppression circuit (FSC) as an important portion of capacitor voltage transformer (CVT) has a vital role in the prevention of overvoltages. There are three types of FSC: active, passive and electronic type. In this paper, a new control unit is proposed for electronic FSC (EFSC) to damp out oscillations and overvoltages of ferroresonance as quickly as possible. The proposed control unit is installed at the secondary side of the CVT and takes samples from the output voltage and then switches on the silicon-controlled rectifier (SCR) according to the overvoltages level. In the proposed control unit, the SCRs are switched off automatically after the disappearance of overvoltages. Thus, a separate command circuit is not required for generation of negative pulses to switch off SCRs. In addition, phase detector unit, firing circuit and separate source for SCRs triggering are omitted from the control unit. All simulation studies are conducted in the Multisim software environment. The obtained results show that the designed control unit has very fast response and desirable stability in different operation conditions. Moreover, frequency response and CVT transient response are not affected by the proposed electronic control unit.

English

Capacitive Voltage Transformers (CVTs) are widely used as source of voltage signals for monitoring, protection relays and control application at transmission and sub transmission voltage level. The main component of the CVT are the capacitive voltage divider, a tuning reactor, a step down voltage transformer, a Ferro-resonance suppression circuit and the burden made by the relay. CVT are used for protection of high voltage lines, substations and transmission of high frequency signals. These applications required low voltage signal, which is given by output of CVT. The CVT applications require fast and secure protection. The energy storage elements like inductors & capacitors cause CVTs to exhibit transient behaviour. Further the performance of protection devices is also affected by the transient of CVTs. In steady state, the secondary voltage of a capacitor voltage transformer mirrors the primary voltage. Because of the energy-storage elements used, the transient output, caused by sudden change in primary voltage, is no longer a replica of the primary. Transient over voltages, which exceed insulation ratings can stress electrical insulation, leading to abrupt failure or gradual breakdown of the dielectric of electrical component. This paper attempts to study the effects of changes in capacitor values on the transient response of the CVT. Furthermore, the various method which affects the transient response are discussed by simulating the mathematical model using MATLAB

Mitigating Ferroresonance in Capacitive and Inductive Voltage Transformers with Ferroresonance Suppressing Methods

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.

Estimation of Electronic Suppression Circuit Resistance for Protective Relaying Applications

The transient response of instrument transformers affects the performance of high-speed relays, particularly speed and overreach in case of distance protection. Transient response of a capacitive voltage transformer depends on the type of ferro-resonance suppression circuit (FSC), i.e., active, passive, or electronic, provided in the secondary to damp the ferro-resonant oscillations. The objective of this article is not to estimate optimum resistance but to provide a systematic approach instead of the trial-and-error approach to estimate damping resistance for the electronic ferro-resonance suppression circuit used in the: capacitive voltage transformer for protective relaying application. The performance of the numerical distance relay for the: capacitive voltage transformer with estimated damping resistance in the electronic ferro- resonance suppression circuit is tested and validated in real time using a field programmable gate array.

Performance assessment of distance protection fed by capacitor voltage transformer with electronic ferro-resonance suppression circuit

Distance relay may over-reach when the voltage information is delivered from capacitor voltage transformer (CVT) and when source to line reach impedance (SIR) is high. A technique adopted recently involves attacking the CVT transient problem from source side itself, i.e., by using electronic ferro-resonance suppression circuit (FSC), rather than allowing the transients and tackling this issue in the relay by providing adaptive zone 1 reach, providing a fixed time delay or using a narrow band pass filter which increases the total fault clearing time by the local relay. The work in this paper investigates the performance of CVT with electronic FSC for different fault, loading and SIR conditions.

Stabilizing Ferroresonance Oscillations in Voltage Transformers Using Limiter Circuit

This paper employs the multiple scales method and chaos theory for analyzing chaotic behavior of the voltage transformer (VT) with linear core loss model. It is shown that ferroresonance phenomenon in VTs can be classified as chaotic dynamics, including a sequence of bifurcations such as period doubling bifurcation (PDB), saddle node bifurcation (SNB), Hopf Bifurcation (HB) and chaos. Bifurcation diagrams and phase plane diagrams are drawn using a continuation method for linear core loss model and lyapunov exponents are obtained using the multiple scales method. At first an overview of the subject in the literature is provided. Then, ferroresonance phenomenon is introduced and its various types in a VT are simulated. Finally the effects of ferroresonance suppression circuit on stabilizing these oscillations are studied. The proposed approach is implemented using MATLAB, and simulation results are presented. The results show connecting the ferroresonance suppression circuit to the system configuration, causes great controlling effect on ferroresonance overvoltage.

Analysis and Suppression of the Coupling Capacitor Voltage Transformer Ferroresonance Phenomenon

This paper provides a detailed core model for the step-down transformer (SDT) of the coupling capacitor voltage transformer (CCVT) to investigate the CCVT transients and ferroresonance behavior. The core model represents hysteresis symmetric and asymmetric minor loops, remnant flux, and the eddy current effects. Based on the developed model, the impacts of passive and active ferroresonance suppression circuits (PFSC and AFSC) and overvoltage protection devices (OPDs) for fast suppression of the CCVT ferroresonance phenomenon are also studied. This paper also presents a generalized methodology to select the AFSC parameters. The simulation results, in the PSCAD/EMTDC environment, indicate that the hysteresis and eddy current effects of the SDT core significantly influence the CCVT ferroresonance behavior. The study results also show that: 1) in both the presence and the absence of arresters and spark gaps, the AFSC can mitigate the phenomenon faster than the PFSC, i.e., in about two cycles and 2) the output fidelity of the AFSC-based CCVT is less dependent on the burden as compared with that of the PFSC.

Fast and Perfect Damping Circuit for Ferroresonance Phenomena in Coupling Capacitor Voltage Transformers

This article investigates the effect of a few types of ferroresonance suppression circuits on suppression of the phenomenon of ferroresonance in coupling capacitor voltage transformers. A novel technique is proposed for damping of dangerous overvoltages due to ferroresonance. In this technique, by using power electronic devices, a damping resistance is switched to the secondary side of the system transformer during dangerous oscillations. This technique leads to important cost and damping-time reductions when compared with conventional alternatives. Additional devices, such as surge arresters, may be added to improve the performance of the ferroresonance suppression circuit. The technique proposed in this article is a “novel but classic” technique. The prediction of ferroresonance is achieved by detailed modeling using a digital computer transient analysis program such as the EMTP/ATP.

Coupling capacitor voltage transformer: A model for electromagnetic transient studies

In this work, an accurate coupling capacitor voltage transformer (CCVT) model for electromagnetic transient studies is presented. The model takes into account linear and nonlinear elements. A support routine was developed to compute the linear 230 kV CCVT parameters (resistances, inductances and capacitances) from frequency response data. The magnetic core and surge arrester nonlinear characteristics were estimated from laboratory measurements as well. The model is used in connection with the electromagnetic transients program (EMTP) to predict the CCVT performance when it is submitted to transient overvoltages, as are the cases of voltages due to the ferroresonance phenomenon and circuit breaker switching. The difference between simulated and measured results is fairly small. Simulations had shown that transient overvoltages produced inside the CCVT, when a short circuit is cleared at the CCVT secondary side, are effectively damped out by the ferroresonance suppression circuit and the protection circuit.