Occurrence Of Ferroresonance Research Articles

Study and comparison of the effect of conventional, low losses and amorphous transformers on the ferroresonance occurrence in electric distribution networks

Study and comparison of the effect of conventional, low losses and amorphous transformers on the ferroresonance occurrence in electric distribution networks

Elimination of Chaotic Ferroresonant Oscillations Originated from TCSC in the Capacitor Voltage Transformer

ABSTRACTFerroresonance is one of the complex phenomena, which occurs in power network. This can create thermal and insulation problems in the power system equipments. It can also cause chaotic oscillations in the power network. The magnitude of the power system capacitor is one of the important factors that lead to ferroresonance in capacitor voltage transformers (CVTs).Thyristor controlled series capacitors (TCSCs) are applied for series compensation in the transmission line of power system. In normal operation, these equipments have capacitance magnitude up to three times of fixed capacitor such that the increased value of transmission line capacitor, which is one of the reasons for ferroresonance occurrence, is provided. This paper studies and investigates the effects of TCSCs on the ferroresonance in the CVTs. Because of nonlinear dynamics of ferroresonance, bifurcation theory is utilized in this paper. Using this theory, variation of system parameters that cause chaotic ferroresonant oscillations can be efficiently analyzed. By using bifurcation and phase plane diagrams, behavioral variations of the system with TCSC can be easily reviewed in this case. The results show that TCSCs raise ferroresonance occurrence in CVT. Since thermal and insulation problems may happen during the occurrence of ferroresonance in CVT and TCSC, a device is used to limit and remove these chaotic oscillations; literally called ferroresonance limiter. Obtained results strongly and efficiently show effectiveness of using this method for restricting ferroresonant oscillations.

Ferroresonance Characteristics on Capacitive Voltage Transformer Under Lightning Impulse Voltage

Nowadays, more papers explain about the occurrence of ferroresonance due to the switching operation. Indeed, the switching operation is more possible to occurr on system respect to other transient disturbances, such as lightning stroke. However, lightning stroke which is always characterized by a high impulse current is also able to initiate the ferroresonance on the system. In this paper, the effect of ferroresonance due to the lightning stroke on capacitive voltage transformer (CVT) is simulated and investigated. The ferroresonance causes an overvoltage as well as on overcurrent on CVT. ATP/EMTP is utilized to simulate and analyze the ferroresonace phenomena. In this study, Heidler’s lightning model is used to describe the lightning condition on the system. Lightning impulse parameters such as its amplitude and duration, including its front time (ts) and tail time (tr) are varied. The effect of these lightning parameters on peak voltage and peak current on the primary side of CVT is investigated. The simulation results show that the peak voltage increases to about 267.5% of its normal peak voltage while peak current increases up to about 266.1% of its normal current. These peak values increase linearly with the amplitude and they increase non-linearly with the duration of the lightning impulse. However, the front time almost does not affect the peak values of voltage and current. Therefore, it can be concluded that lightning impulse characteristics affect the occurrence of ferroresonance on CVT.

Wrażliwość sieci potrzeb własnych elektrowni na możliwość wystąpienia ferrorezonansu

Implementation of the new class of 1000 MW power units to a power system creates new problems associated with the operation of its individual components and circuits. One such issue is the phenomenon of ferroresonance in the internal load network. This is not a new problem but it requires examination due to the higher level of supply voltage (10 kV). This paper examines the possibility of ferroresonance occurrence and its character depending on the extent of the network, voltage transformers’ load, the effect of grounding resistors in the star point of the power transformer and the presence of varistor surge arresters. The results are presented in the form of ferroresonance maps. They allow assessing the impact of various parameters on the phenomenon, explaining the reasons for possible failure and properly programming the network conditions in order to avoid the risk of ferroresonance.

A new approach to eliminating of chaotic ferroresonant oscillations in power transformer

Abstract Ferroresonance is a complex phenomenon, which can result in thermal and electrical stresses on power system equipments. It can also cause chaotic oscillations in power system. In this paper, a new method is proposed to restrict and damp ferroresonant oscillations, which is based on a new of fault current limiter (FCL). In this method in order to restrict chaotic ferroresonance oscillations, a kind of fault current limiters (FCL) is used which has been used to restrict unwanted high current flow in power system before. To study the ferroresonance nonlinear dynamics, in this paper, the chaos theory is used. By using this theory, the changes in system parameters which can cause chaotic ferroresonant oscillations, can be reviewed and analyzed in details. The behavior of the system during ferroresonance occurrence, with and without using proposed FCL, is discussed in bifurcation and phase plane diagrams. By using these diagrams, the behavioral changes of the system can be easily seen in two cases. The simulation results strongly show the effectiveness of using the proposed FCL for restricting the ferroresonant oscillations.

Effect of TCSC on Chaotic Ferroresonant Oscillations in Voltage Transformer

ABSTRACTFerroresonance is one of the complex phenomena that occur in power system. This can create thermal and insulation problems for power system equipment. It can also cause chaotic oscillations in the power system. One of the factors that influences on the occurrence of ferroresonance in the capacitor voltage transformers (CVTs) is the magnitude of transmission line capacitor. To study the ferroresonance nonlinear dynamics, in this paper, the chaos theory is used. By using this theory, changes in system parameters which cause chaotic ferroresonant oscillations can be better reviewed and analysed. Thyristor-controlled series capacitors (TCSCs) are used for series compensation in the transmission line. Behaviour of the system in ferroresonance occurrence, with TCSC, is shown in bifurcation and phase plane diagrams. By using these diagrams, behavioural changes of the system can be easily seen in this case. The results show that TCSCs lead increasing of ferroresonance in CVT.

Research on Ferroresonance Detection in Small Current Neutral Grounding System

A novel method to detect ferroresonance was proposed based on the drastic characteristics of the electromagnetic voltage transformer (PT) current rate. This scheme takes current rate which is greater than a threshold value as starting signal and judges the occurrence of resonance by detecting duty ratio of the peaks and interval angles. Then, it identifies the periods and patterns established on the interval time of spikes. Through simulation testing of MATLAB, it can distinguish the occurrence and types of ferroresonance accurately, which verifies the validity of the detection method.

Relation analysis for ferroresonance of bus potential transformer and circuit breaker grading capacitance

This paper presents a methodology to reduce the ferroresonance between a bus potential transformer and circuit breaker grading capacitance. It starts with the investigation of the relations between ferroresonance of a bus potential transformer and circuit breaker grading capacitance, where different resistors are simulated to add in the secondary side of bus potential transformers, anticipating that the ferroresonance occurrence can be better comprehended. In the study, both the driving force factor and the ratio of system-to-ground capacitance and inductance are assessed. In order to confirm the feasibility of the proposed strategy, a ferroresonance-suppression device has been developed and several scenarios have been examined through digital simulations, laboratory analyses, and field validations. Test results support this proposed approach for its ferroresonance-suppression application that is considered.

Chaotic oscillations control in the voltage transformer including nonlinear core loss model by a nonlinear robust adaptive controller

In this paper, control of chaos is done in presence of ferroresonant oscillations in a voltage transformer with nonlinear model of core losses. In order to control the chaotic oscillations, nonlinear adaptive approach is employed. Moreover, a Time Delay Feedback Controller (TDFC) is implemented to stabilize Unstable Periodic Orbits (UPOs). Also multiple scales method to analyze chaotic behavior and types of fixed points in ferroresonance occurrence at voltage transformers considering different types of core loss models is applied. In the literature ferroresonance phenomenon in voltage transformers is proved to be classified in chaotic dynamics systems. In this contribution, chaos occurs in the system from a sequence of Period Doubling Bifurcation (PDB). This phenomenon consists of different types of bifurcations such as Period Doubling Bifurcation (PDB), Saddle Node Bifurcation (SNB), Hopf Bifurcation (HB) and chaos. Dynamic analysis of ferroresonant circuit is performed using bifurcation theory. bifurcation diagrams and phase plane diagrams are illustrated using a continuation method for linear and nonlinear core loss models. For analyzing ferroresonance phenomenon, Lyapunov exponents are calculated using multiple scales method and feigenbaum numbers are obtained. Bifurcation diagrams illustrate variation of parameter control and as a result chaos is created and increased in the system.

CCVT Failure due to Improper Design of Auxiliary Voltage Transformers

In-situ tests of coupling capacitor voltage transformers (CCVTs) in some of the high-voltage substations indicate that the ratio error of a considerable number of CCVTs has increased to more than 5%. Experimental analyses reveal that the CCVTs excessive ratio error is mainly due to the short-circuited capacitor elements of CCVTs. Comprehensive tests and investigations indicate that the occurrence of ferroresonance due to saturation of the auxiliary voltage transformers (AVTs) is one of the main reasons for this problem. These small transformers are usually utilized inside the protective relays and control and measuring equipment or are connected to the secondary side of CCVTs as an interface between the CCVT and the equipment. Imposed stress on CCVT components and the voltage oscillations' effect on transmission-line distance relay are also scrutinized in this paper. Finally, appropriate specifications for AVTs are recommended to prevent undesirable CCVT overvoltages and distance relay maloperation.

Analysis of Ferroresonance Modes in Power Transformers Using Preisach-Type Hysteretic Magnetizing Inductance

The magnetic hysteresis phenomenon plays an important role in the ferroresonance behavior of a transformer. However, most existing transformer models for the analysis of the ferroresonance phenomenon either ignore the hysteresis effects or represent it based on the hysteresis major loop and scale it for lower current levels. Such a modeling approach does not reflect the actual physical behavior of the magnetic core with respect to the ferroresonance phenomenon. This paper, based on Preisach theory, introduces an accurate model of hysteretic inductor to represent a single-phase transformer for the investigation of the ferroresonance phenomenon. Based on the developed model, time-domain simulation studies show that even in the case of a single-phase transformer where no magnetic coupling exists between the three-phases, all known types of ferroresonance, including fundamental, sub-harmonic, quasi-periodic and chaotic modes, may occur. The effects of hysteresis and its initial conditions, grading capacitors and transformer winding capacitance on occurrence of ferroresonance and its change of mode are also discussed

Characterization of ferroresonant modes in HV substation with CB grading capacitors

This paper reports a ferroresonant experience involving inductive voltage transformers (VT's) in a 400 kV substation equipped with circuit breaker grading capacitors. Field measurements are presented and compared with ATP/EMTP simulation results, showing very good agreement. A parametric analysis has been performed to investigate the effect of the substation capacitance on the occurrence of ferroresonance. Fundamental frequency and sub-harmonic ferroresonant modes have been identified and compiled in a bifurcation diagram. The methodology presented can be used to create risk maps of avoidable switching operations or substation configurations.

Damping circuit design for ferroresonance in floating power systems

AbstractPractical countermeasures to prevent the occurrence of ferroresonance in floating systems are compared. Most attention is paid to the design of practical damping circuits. Existing criteria to determine the necessary ohmic load are evaluated and a new mathematical tool based on harmonic balance is presented. As the damping resistor can cause thermal overload of the voltage transformers, the use of a non‐linear damping circuit is advocated in some cases. Therefore, the proposed calculation method is extended to include the effect of non‐linear damping.

Studying ferroresonance in actual power systems by bifurcation diagram

An approach for finding ferroresonance occurrence domains has been developed. The steady state solutions are calculated by the Galerkin method and a bifurcation diagram is created using a continuation method. By using the proposed approach, continuous and well defined domains can be found. A study of two actual systems is introduced and experimental and computational results are shown.

Series ferroresonance in power systems

Nonlinear oscillations in power systems involving the excitation of nonlinear inductance with a linear capacitance in series have been termed ferroresonant oscillations, Such oscillations are unpredictable and their occurrence is of serious concern predominantly because of possible damage to equipment such as transformers. The probability of system disruption due to the occurrence of ferroresonance has increased with improvements in the characteristics of transformer steel and the use of higher and higher voltages for transmission of bulk power. Conditions that lead to the occurrence of ferroresonant oscillation, given a system, therefore, need to be known. It will be shown that for any disturbance the autonomous form of the nonlinear differential equation representing the system with two-degrees of freedom deca ys to a point attractor; that is, it is always stable. The non-autonomous form of the system's equation, however, exhibits the possibility of occurrence of a cyclic fold bifurcation which causes ferroresonant oscillations with two stable states to co-exist. Each stable state can, however, be either harmonic, periodic, subharmonic or aperiodic. Aperiodic oscillations occur when satisfactory conditions for the occurrence of subharmonic cascade exist.

Ferroresonance and Loading Relationships for DSG Installations

Self-excitation of induction generators or small synchronous generators connected to distribution feeders is analyzed during the transient period following the islanding of a generator on the feeder. The relationship of feeder load after separation and the occurrence of ferro-resonance with an isolated induction, synchronous or single-phase generator are developed. The results indicate that an isolated distribution system generator (DSG) can theoretically support as much as three times the generator's rated power output in a ferroresonant mode provided the prime mover has the needed inertia or torque available at the abnormal isolated speed. The abnormal voltage and frequency operation during separation modifies load, generator, and prime mover characteristics and may result in an energy balance, although such balance is not obvious before separation.

An analytical investigation of a ferroresonant circuit

An analytical approach, based on harmonic balance techniques, is presented to study ferroresonance circuits with an arbitrary degree of nonlinearity. This approach is then employed to investigate the effect of the different circuit parameters and forcing frequency on the occurrence of ferroresonant jumps. In particular, it is shown that increasing either the forcing frequency or the capacitance makes the circuit more vulnerable to ferroresonance. This explains the frequent occurrence of ferroresonance in distribution networks during light loading periods. An example is given to illustrate the feasibility of the technique.

Magnetic transport properties of dipolar conducting liquids at ambient temperature

Ferromagnetic liquids at ambient temperature are characterized as dipolar, possessing magnetic properties that could be investigated through classical as well as quantum theories. Classical analysis identified the dipolar ions as loose enough to be considered freely rotating within the liquid continum while the quantum basical approach recognized the limited degrees of gyromagnetization with respect to the total angular momentum quantum number. Experimental work supported with rigorous analytical treatment identified the occurrence of ferroresonance for the gyromagnetic energy absorbed by the dipolar fluid at a unified level of magnetic field intensity, sudden and sharp reversal in the polarity of the dipole moment per unit volume at resonance, and the impulsive singularity nature for the magnetic susceptibility. Energy levels for Bloch walls distribution across a longitudinal channel of the dipolar liquid indicate reversible as well as irreversible locations.

Some new solutions to ferroresonance problem in power system

A parametric equation of the envelope on the G?1(jw) plane for the general polynomial-type nonlinearity is derived. An analytical method has been suggested for the evaluation of threshold frequency for the occurrence of ferroresonance. Mathematical equations have been deduced for computing the jump-to points for quintic nonlinearity. A generalised equation for asymptotic values of percentage unstable zone for various types of nonlinearities has been derived. New definitions for jump-up severity and jump-down severity are introduced. A system due to Swift has been analaysed for the purposes of illustration.

Ferroresonance on Rural Distribution Systems

The conditions under which ferroresonant overvoltages can occur on rural distribution systems are reviewed. A brief description of the phenomenon of ferroresonance is given, and the reasons for the increasingly frequent occurrence of ferroresonance on modern systems are enumerated. Preventive or corrective measures that have been proposed are reviewed and evaluated. A guide for the selection of corrective or preventive measures on rural systems is presented.