Fig. 3 shows the block diagram of the proposed control method. Note that the d-axis controller is not shown for simplicity. The block diagram consists of the full state-feedback controller and the proposed inrush current mitigation technique. The feedback control, feed forward control, and decoupling control are explained as follows.
4.5 Use of a point-on-wave (POW) controlled switching This method uses synchronised switching but requires independent-pole operated circuit breakers and knowledge of residual fluxes to achieve optimal energisation. If no POW controller is applied, the energisation of the transformer may occur at any time on the sinusoidal wave resulting in high inrushcurrents particularly if the transformer core is moved into saturation . It is generally observed that POW would not entirely eliminate inrushcurrents because of the effects of residual flux. The authors note that there are equipment vendors who offer a POW switching solution that reduces the effects of residual flux. The authors made contacts with two manufacturers offering solutions to limit possible transformerinrushcurrents but did not receive further details. In the absence of such information, this option was not further investigated.
At the time of transformer energization, a high current will be drawn by the transformer. The mentioned current is called transient inrush current and it may rise to ten times the nominal full load current of transformer during operation. Transformerinrushcurrents can be divided into three categories, energization inrush, recovery inrush and sympathetic inrush. The first, energization inrush results from reapplication of system voltage to a transformer which has been previously de-energized. The second, recovery inrush occurs when transformer voltage is restored after having been reduced by a nearby short circuit on system. The third, sympathetic inrush can occur when two or more transformers are operated in parallel.
Abstract- Recognition of Power-Transformer Protection is a veryimportant task for the power system operation. In this work, a hybrid of wavelet transform and neural network (WNN) approach is introduced for PTP (Power- Transformer Protection) events classification.The PT(Power Transformer) waveform is first decomposed by four levels Daubechies-4(db4) waveletanalysis and the decomposed waveforms then be processed by the NN for PTP event classification. (4) By utilizing the WNN, the PTP event recognition system can be implemented with minimum neurons and produces maximum attainment. Furthermore, this technique can accommodate maximum training patterns automaticallyreconsider the ANN system. The proposed approach is implemented in a simulation program to verify the validation and classification accuracy.
Power system transients including inrushcurrents, over voltages, and lightning impulse stresses can be harmful to the power and distribution transformers. Even though this sudden change in the system cannot be eliminated in total, it can possibly be reduced to a safe state. Malfunctioning of the system due to the high inrush current can occur in many ways such as voltage dips, sympathetic inrush, harmonic resonance over-voltages and also excessive mechanical and electrical stresses. All these can further result in protection malfunctioning, system equipment damage and power quality problems.
Abstract: It is well understood that induction motors draw higher currents during their starting operations than is the case under full load running conditions. Since the early days of induction motor availability, starting methods other than Direct-on-Line have been used, and in some cases mandated by Utilities, to reduce the effect of these high starting currents on the electrical distribution network. What is generally not recognized is the existence of short duration inrushcurrents, which greatly exceed these starting currents. Furthermore, the introduction of complex starting methods to reduce starting currents is often compromised by other unanticipated inrushcurrents introduced by the starting system itself, unless special precautions are taken. This paper implements a device that protects three phase induction motor from inrushcurrents on the distribution system, as well as on the motor protection components using PIC16F84A Microcontroller.
Abstract — Three phase power Transformers are key equipment in power systems and power plants.Security,power quality and stability of three phase transformers are both important and necessary to system operation Energization of unloaded transformer results in magnetizing inrush current very often with high amplitude ,harmonic rich currents generated when transformer cores are driven into saturation .These currents have many unfavorable effects, including operation failure of transformer differential protection, deterioration of the insulation and mechanical support structure of windings and reduced power quality of the system. The inrushcurrents are always unbalanced among three phases. The amplitude of the magnetizing current depends mainly on two factors; the residual flux in the magnetic core and the transient flux produced by the integral of the sinusoidal supply voltage. To satisfy the principle of the flux steadiness, it is necessary to build an equalizing flux with the same magnitude, but opposite polarity to the prospective flux. Inrushcurrents from transformer and reactor energization have always been concern in power industry. So it is needed to find simpler and low cost scheme to limit these currents. Independent power producers are especially interested in such techniques. Different methods are used for minimizing the transient current. In this Simultaneous closing of circuit breaker and sequential closing of circuit breakers are used for reduce this large current Electric utilities and end users of electrical power are becoming increasingly concerned about the quality of electric power. A neutral resistor could provide some damping to the currents. The idea is further improved by introducing controlled energization of each phase of the transformer. The performance and characteristics of the proposed scheme is investigated using MAT LAB simulations.
The power transformer is one of most important equipment in electrical power system. Due to its immense importance its protection is also very important. Relays currently used for protection of power transformer are differential current based and uses filters to restrain the second harmonic component and sometimes even fifth harmonic component for avoiding false tripping against the magnetizing currents . However harmonic component can be reduced by using proper magnetic material for manufacturing transformer core . Some researchers have used artificial-neural-network (ANN) based protection technique to differentiate between magnetizing inrush from internal faults in power transformers . Also large number of training data samples, slow convergence during training, and a tendency to over fit data are the limitations of ANN-based schemes.  Proposed a decision making method based on wavelet transform for discriminating internal faults from inrushcurrents but over excitation conditions have not considered by them.
WARNING: MAKE SURE THAT THE TOTAL AVERAGE CURRENT, TOTAL PEAK CURRENT AND TOTAL INRUSH CURRENT REQUIRED BY ALL APPLIANCES THAT ARE CONNECTED TO THE SYSTEM’S PRIMARY AND SECONDARY POWER SOURCES, NAC CIRCUITS, SM AND DSM SYNC MODULES DO NOT EXCEED THE POWER SOURCES’ RATED CAPACITY OR THE CURRENT RATINGS OF ANY FUSES ON THE CIRCUITS TO WHICH THESE APPLIANCES ARE WIRED. OVERLOADING POWER SOURCES OR EXCEEDING FUSE RATINGS COULD RESULT IN LOSS OF POWER AND FAILURE TO ALERT OCCUPANTS DURING AN EMERGENCY, WHICH COULD RESULT IN PROPERTY DAMAGE AND SERIOUS INJURY OR DEATH TO YOU AND/OR OTHERS.
In this study a new approach was presented in order to recognize and distinguish fault signal from Inrush current. Wavelet transforms splits off the signal energy in time-frequency domain whereas Fourier transformer does not have this capability. With this kind of analysis, these two currents can be separated simply since the distribution of energy in time and frequency domain for inrush and fault current is very different. Because of the existence of DC component and even harmonics in inrush current and regarding the sampling frequency (64 samples per cycle) the energy of zero, third and fourth levels can be a proper criteria for recognition.
The plant is getting main power supply from the state utility at 132kV level. Afterward, it is stepped down to 6.6kV via two (2) nos 35MVA transformer. There are three different 6.6kV switchgears for HP Plant, DP plant and CHH Plant. HP plant is connected with DP and CHH plant at 6.6kV via tie lines. During normal operation one transformer is connected at HP plant and another is connected with DP pant. CHH plant is connected with HP plant through the tie cable of 6.6kV. The tie between HP and DP plant remains open in normal condition.
used to discriminate magnetizing inrush from internal faults in power transformers. Most of them follow a deterministic approach, i.e. they rely on an index and fixed threshold. This article proposes for Identification of Inrush Current & Internal Fault Current power transformer for proper protection scheme. In the proposed algorithm, is Feed Forward Back Propagation Network (BPN) are used as a classifier and address the challenging task of detecting magnetizing inrush & internal fault current . Medium & large power transformers are very important and vital component of electric power systems. Due to its importance and cost, its protection needs to be addressed properly. The protection should be fast and reliable. Proper continuous monitoring of power transformer can provide early
The paper is concerned with whether CT transient saturation, which caused by sympathetic inrush, is the direct reason for mal-operation of transformer differential relays. In order to analyze transforming characteristics of saturated CT, the gain of each harmonic current transforming from primary winding to secondary winding of transient saturation CT is calculated. Based on the fact that series sympathetic inrush is easier to lead differential relay mal-operation than parallel sympathetic inrush, the effect of CT saturation on differential relay in the case of both parallel sympathetic inrush and series sympathetic inrush are investigated respectively. Theory analysis and simulation show that higher harmonic will be transferred by saturated CT more easily than lower harmonic, and then the second harmonic proportion of CT sec- ondary side is higher than that of CT primary side. Thus CT transient saturation itself is not essential reason for differ- ential relay mal-operation. Parallel sympathetic inrush and series sympathetic inrush will lead to different location CT saturated. Parallel sympathetic inrush will lead to CT located system side saturated; second harmonic ratio of differen- tial current increase and dead angle is large. Series sympathetic inrush will lead to CT located load side saturated; sec- ond harmonic ratio of differential current decrease and dead angle is small.
Abstract: The inrush current is a transient current that results from a sudden change in the exciting voltage across a transformer’s windings. It may cause inadvertent operation of the protective relay system and necessitate strengthening of the transformer’s mechanical structure. Many methods were reported in the literatures for reduction and mitigation of trans- former inrushcurrents. This paper represents a study of techniques that have been proposed for transformerinrush current mitigation. A new, simple and low cost technique to reduce inrushcurrents caused by transformer energization is presented here. In this method, a controlled switching approach with a grounding resistor connected to transformer neutral point and a magnetic flux shunt is used. By energizing each phase of the transformer in sequence, the neutral resistor behaves as a se- ries-inserted resistor and thereby significantly reduces the inrushcurrents. The dimensions of the magnetic flux shunts are chosen such that the inrush current amplitude is further reduced. The proposed method has been tested by computer simula- tion using 2-D FEM (two-dimensional finite element method) by Maxwell software. The obtained results show that the proposed method is efficient in reduction of transformerinrush current and is much less expensive since there is only one resistor involved and the resistor carries only a small neutral current in steady-state.
WARNING: MAKE SURE THAT THE TOTAL AVERAGE CURRENT, TOTAL PEAK CURRENT AND TOTAL INRUSH CURRENT REQUIRED BY ALL APPLIANCES THAT ARE CONNECTED TO THE SYSTEM’S PRIMARY AND SECONDARY POWER SOURCES, NAC CIRCUITS, SM, DSM SYNC MODULES OR PS-12/24-8 POWER SUPPLY DO NOT EXCEED THE POWER SOURCES’ RATED CAPACITY OR THE CURRENT RATINGS OF ANY FUSES ON THE CIRCUITS TO WHICH THESE APPLIANCES ARE WIRED. OVERLOADING POWER SOURCES OR EXCEEDING FUSE RATINGS COULD RESULT IN LOSS OF POWER AND FAILURE TO ALERT OCCUPANTS DURING AN EMERGENCY, WHICH COULD RESULT IN PROPERTY DAMAGE AND SERIOUS INJURY OR DEATH TO YOU AND/OR OTHERS.
The output voltages of all four types of transformer connections are fed to the five phase induction motor and observe the torque, speed and stator currents of the motor are obtained by using MATLAB. Here the induction motor is tested for both balanced and unbalanced supply conditions -.unbalanced applied voltages to the motor is done to simulate fault conditions.
The power electronics based devices have been used to overcome the major power quality problems .In order to reduce the power quality problems present in the 3P4W system, the Unified Power Quality Conditioner (UPQC) is one of the best solutions to compensate both current and voltage related problems. As the UPQC is a combination of series and shunt active power filters (APF’s).The series active power filter (APF) suppresses and isolates voltage-based distortions, whereas the shunt active power filter (APF) cancels current based distortions. At the same time, the shunt active power filter (APF) compensates the reactive current of the load and improves power factor-.A 3P4Wdistribution system is generally realized by providing a neutral conductor along with the three power lines from substation or by utilizing a delta–star transformer at the distribution level. The neutral of series transformer used as the series part of UPQC, is considered as a neutral for 3P4W system. Thus, even if the power supplied by utility is 3P3W an easy expansion to 3P4W system can be achieved in UPQC based applications that is by adding a fourth leg to the existing 3P3W UPQC.Ensure that the neutral current flowing toward transformer neutral point should be zero. Thus, the transformer neutral point can be maintained at virtual zero potential .The unbalanced load currents are very common in 3P4W distribution system can be reduced by injecting the currents using shunt active power filter (APF) .
The occurrence of strong GICs is often associated with strong auroral electrojet currents at geomagnetically high latitudes (Thomson et al. 2011; Pulkkinen et al. 2012). Japan is located at a geomagnetically lower lati- tude compared to its geographical latitude. It is believed that the possibility of power grid problems caused by GICs is lower because of the country’s location at geo- magnetically low latitude. However, it was reported that long distance telegraph lines between Tokyo and the re- gions outside Tokyo (the Tokyo-Yokkaichi line, the Tokyo-Matsumoto line, the Tokyo-Ogasawara line, the Tokyo-Guam line, and so on) were affected by GICs caused by a geomagnetic storm on September 25, 1909 in Japan (Uchida 1909). Kappenman (2004) noted that
catalyst for the energy revolution of the 20 th century. Charles Fortescue's paper demonstrating that unbalanced phasors could be expressed as a symmetrical set of balanced phasors was the match that lit the fire of this energy revolution. This paper is regarded as the one of the most important papers written in the 20 th century and it has laid the foundation for how every single utility in the world performs fault analysis. The underlying assumptions in this analysis are that the faulted system is linear, which means sources can be represented by a Thevenin model. And secondly, load currents can be neglected compared with fault currents. However, times are changing, and so must our methods of fault analysis.
During geomagnetic storm periods (GMS), the geomag- netically induced currents (GIC) are flowing into high- voltage power grids and high-voltage power transformer windings with dead-earthed neutral, which in turns create asymmetric saturation of magnetic system and multiple increase of nonsinusoidal magnetizing current [1,2]. As a result, power transformer becomes a powerful source of high order current harmonics, which impact on all power consumers of power distribution circuit [3,4]. Electrical motor load is the most sensitive to supply voltage quality degradation, especially high-voltage synchronous motors (SM) with direct connection to power distribution circuit 6 (10) kV. High order currents in stator SM windings result into additional power loss and additional electro- magnetic torque constituents appearing.