AUTOMATED FAULT LOCATION SYSTEM in PRIMARY DISTRIBUTION NETWORKS
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AUTOMATED FAULT LOCATION.docx (Size: 357.72 KB / Downloads: 212) PRESENTED BY P.RAMAMOHAN T.MUNI PRAKASH RAJIV GANDHI MEMORIAL COLLEGE OF ENGINEERING AND TECHNOLOGY . NANDYAL . KURNOOL (DIST). ABSTRACT In this paper is presented a new method of AUTOMATED FAULT LOCATION SYSTEM in PRIMARY DISTRIBUTION NETWORKS based on measurements provided by intelligent electronic devices (IEDs) with built in oscillography functions, installed only at the substation level .This system can identify the most probable fault locations in a fast and accurate way using a database that stores information about the network topology and its electrical parameters. The method is based on an algorithm which combines the information about both the fault type and load rejection for better estimation of fault location .This algorithm is robust in nature and is also least influenced by errors in load distribution. This is because of the fact that magnitude of load current is much smaller than that of the fault current. This procedure excels the traditional ones which assume that measurements from local terminals of the faulted distribution lines are available. It is a powerful tool to operate and maintain the distribution network efficiently and locate the faults ver y far from the substation. When the fault resistance is greater, the error in estimation of the fault rises to a higher level. A part of my contribution : a novel approach is proposed to minimize the error in such cases. The approach increases the accuracy of estimation and also improves the stability of the system. INTRODUCTION : A Power system is said to be well designed if it gives a good quality and reliable supply. Good quality means maintaining flat voltage profile. Reliable supply means having stability. The reliability of a system is affected because of short circuit fault occurrences which represent one of the most extreme conditions of the power systems. The causes of the faults must be determined and eliminated. The process can be expedited only if f ault location can be determined quickly and reliably. Since the deregulation process has started , most of the research on power distribution systems is focused on delivering power in an efficient way , i.e. ,in terms of quality , reliability and end user price. PROBLEM DEFINED: An accurate estimation of fault location in power systems presents a challenging task. Several authors have researched on this topic and have proposed valuable methods. Most of the proposed methods assume that measurements from the local terminals of faulted line are available. As most of the power systems are equipped by sparsely located instrumentation, the number of measured quantities is rather small. The problem is compounded by the presence of measuring noise. Despite the advances and wide spread use of intelligent electronic devices and need for performance improvements, the fault location process employed nowadays 1 is still based on trouble calls from the affected customers. Besides, when a transient fault occurs, the operation centre will not receive any phone call and prevention of these transient faults from becoming permanent ones is difficult. FAULT LOCATION ALGORITHMS IN VOGUE : Most of the proposed fault location algorithms were developed for power transmission systems. A few methods were proposed for distribution networks due to the following reasons: i. Variety of conductors and structures ii. Lateral branches iii. Load distributed along the feeder iv. Modifications in feeder configurations Most of the proposed algorithms are based on fault detectors installed along the feeders and can only be applied to balanced networks. As a result, these methods will estimate a fault location far from the actual one. AUTOMATED FAULT LOCATION SYSTEM : The automated fault location system proposed in this paper combines information provided by IEDs located only at the substations with knowledge of the distribution systemâ„¢s topology and its electrical parameters. Whenever an over current event occurs, the system automatically provides the most probable fault locations to the operators, at the operation center . Let us examine the substation ar rangement depicted in fig.1. An IED, connected to each mediumvoltage feeder, is responsible for monitoring voltage and current signals .It also records transient data whenever an over current event occurs. A computer, located at the substation, is connected to the array of IEDs and to the computer at the operation centre via a communication channel such as dial phone line, dedicated line, radio link, and tie to corporate local area network (LAN). This fault location system consists of eight software modules. These software modularities enable future software upgrades with out the need for changing the whole system. A part of these modules is installed at the substations whereas the rest are installed at the operation centre as illustrated in fig.2. The decision of installing 2 the fault location modules at the substations and at the operation centre was based on the following reasons. D U : The fault location system uses information stored in ATABASE PDATE database, which must be periodically updated in order to reflect possible modifications in the distribution networks. Therefore, this database and software modules that have access to it should be located at the operation centre computers. C C O : Transferring all transient data COMMUNICATION CHANNEL OVERFLOW recorded by the IEDs to operation centre would probably overflow the communication channel that connects the substationsâ„¢ computers to the operation centre computer. Therefore it is convenient to preprocess the transient data and extract only the information located by the fault location system, which is transmitted to the operation centre. S S M : SUBSTATION SOFTWARE MODULES M M : Responsible for scheduling and storing data acquisition . It AIN ODULE also coordinates and monitors all data transfers among other modules. IED I M : Converts the transient data recorded by the IEDs NTERFACE ODULE into COMTRADE format. This format is desirable to make the fault location system independent of the recording equipment in such a way that future IEDs changes will not imply in major software upgrades. The information sets included in the COMTRADE file are as follows: i. Detailed oscillography of the fault: phase voltages and line currents; ii. Additional measurements: Prefault and post fault measurements (active and reactive powers, voltages and currents),circuitbreaker operation time, etc. D S P (DSP) M : Preprocesses the transient IGITAL IGNAL ROCESSING ODULE data stored in COMTRADE file. This software module performs the tasks described below and stores the results in an ASCII file, which is less than 1 KB and much smaller than the COMTRADE file. Determination of the fault occurrence instant : The algorithm 3 developed to perform this task is based on digital signal processing techniques, which can identif y signal transition instants . Estimation of prefault and f ault phasor quantities : The DSP module places two data windows(one at the present fault region and other at the fault region) after the fault occurrence instant is determined and estimates the phasor quantities using the discrete fourier transform method (DFT). Fault type and phases involved : The algorithm developed to perform this task is based on the analysis of the super imposed sequence components of the currents. The DSP module compares the magnitudes and phases of the positive, negative and zero sequence components to determine whether the fault is single line to ground (AN, BN, or CN), lineline faults (AB, BC, or CA) double line to ground (ABN, BCN, or CAN), or three phase. Estimation of load rejection : The DSP module estimates the pre fault and post fault active power to determine the amount of load rejection. This information is used to classify the fault. Fault classification : Using the information about the circuit breaker status, after the fault clearance , and the amount of load rejection , the algorithm can classify the fault as : Permanent faults isolated by breaker operation : When the circuit breaker remains closed after the over current event Permanent faults isolated by the fuse operation: When the circuit breaker remains closed after the overcurrent event and there is load rejection (the prefault active power is bigger than the active power measured after the fault clearance). Transient faults : When the circuit breaker remains closed after the event and there is no load rejection. C (COMM) : Responsible for automatically sending OMMUNICATION MODULE the ASCII file produced by the DSP module to the operation centre. O C M : PERATION ENTRE ODULES M : Responsible for scheduling and storing data acquisition data AIN MODULE transfer among the other modules. COMM M : Responsible for receiving the data sent by the sub station ODULE computer and scheduling its processing priority. WEB B I : Provides graphical results of the fault location ASED NTERFACE procedure. The decision of using this kind of Interface was based on its flexibility and widespread use of web based tools. Besides, the results 4 provided by the system can not only be accessed f rom computers connected to the utilityâ„¢s intranet, but also from the computers at the operation center. Fault location module : Performs the fault location procedure, based on the algorithm detailed in the next item, and provides the results to the web based interface. D ATABASE The fault location system has access to the database that stores the information about the topology and electrical parameters of the feeders. This data base is obtained and periodically updated from the electricity utilityâ„¢s corporate database and contains the following information. T : The distribution feeders are described using the universal OPOLOGY transverse mercator coor dinates (UTM) . Therefore, it is possible to integrate information provided by the fault location system to any geographic information systems ( GIS) system ; E : Cable types and feeder geometry such as overhead, LECTRICAL PARAMETERS spacer, twisted, and underground, are used to calculate the line impedances, nominal power of the distribution transformers and connection schemes, etc. FAULT LOCATION ALGORITHM Primary distribution feeders are radial networks with several lateral branches. This means that faults at different locations may result in the same voltage and current signals recorded at the substation. Therefore, the algorithm should investigate all line sections in order to determine the possible fault locations. Consider the feeder illustrated in figure 3, where a starting and ending node identify each line section. The procedure adopted to determine whether the k th line section, generically delimited by nodes p and q , has a possible fault location, consists of estimating the fault distance(D) from node p , where a fault would produce the same voltage and current signals recorded at the substation. If the estimated distance is less than the sectionâ„¢s length ( L ), the k th line section has a possible fault location. K The methodology used to estimate the fault distance is described later. It is based on a set of equations that depends on the fault type, and on the following phasor quantities: 5 V I p pq a a V = and I = P pq (1) V I p pq b b V I p pq c c V I are the phasor quantities at node p , during the fault, and the Where p and pq currents at line section k ,during the fault. Assuming that the fault current (I fault ) and the load currents during the fault ( I j , j =1 to n) are known, V and I can be calculated using a three phase power flow P pq algorithm. Since it is impossible to correctly calculate the load currents during the fault using data available only at the substation, a procedure was developed to estimate them. This procedure consists of estimating the prefault complex power at each node , then using it to calculate the prefault voltage and current phasor quantities(using a three phase power flow algorithm), and finally calculating the complex power at each node during the fault by means of modeling its behaviour according to the voltage variation. Symbols used in the block diagram and in following equations are: Ëœmâ„¢ total number of nodes at the feeder ËœS â„¢ Prefault complex power at the ps sbstn. ËœS â„¢ Nominal power of transformers j n connected to node j ËœS â„¢ prefault complex power at node j pj ËœS â„¢ complex power at node j during j the fault ËœV â„¢ prefault voltage at node j pj ËœV â„¢ voltage at node j during the fault j ËœI â„¢ load current at node j during fault j ËœV â„¢ voltage at sbstn. during fault s ËœI â„¢ current at sbstn. during fault s ËœI â„¢ fault current phasor m Ëœnâ„¢ load model used by the algorithm Ëœz â„¢ line and mutual impedances( ) / km i j Fault location algorithm logic diagram 6 Fault Types The fault location algorithm is recursive, which means that a new fault distance D is calculated at each step .With this distance, the voltage and current phasor quantities during the fault are recalculated (considering the fault to have occurred at the new distance). The block diagram depicted in fig.4, presents the procedure developed to locate the possible fault points. E O T P C P STIMATION F HE REFAULT OMPLEX OWER The first methodology used to determine the prefault complex power at each node consists of aggregating the representative load curves of all consumers connected to each node of the feeder. Preliminary tests indicate that minor errors in the load estimation have not considerably affected the algorithmâ„¢s accuracy and, since this methodology uses a large amount of data to determine the complex power at each bus, a simplified methodology was developed. It consists of assuming that all distribution transformers connected to the feeder operate proportionally to their nominal apparent power. Consequently, the total complex power measured at the substation is distributed at each node according to S their nominal power as in S = S x (2) t pj ps m S t j 1 P P F REFAULT OWER LOW The prefault load currents and voltages at each node are estimated using a three phase power flow .The implemented power flow algorithm explains the fact that distribution networks are almost always radial .Therefore, it does not use the admittance matrix. I A L S : NVESTIGATION OF LL INE ECTIONS After estimating the prefault voltage and current phasor quantities, the algorithm starts investigating all line sections in order to determine all possible fault points. First, the algorithm assumes that the load currents and node voltages, during the fault are equal to the prefault ones, and the f ault distances are zero (i.e., the fault occurred at the beginning of the investigated line section). E STIMATION OF THE FAULT CURRENT The fault cur rent is estimated by subtracting the fault current phasor quantities (measured at the substation) from the load currents at the feeder, during the fault, as in m I = I  I (3) f s j j 1 7 P OWER FLOW DURING THE FAULT In this item the load currents are calculated using the following procedure. First the complex load power at each node during every fault is calculated assuming that the loads connected to each node depend on voltage. n V S = S (4) j j pj V pj Then the load currents at each node can be calculated using the complex power previously calculated, and the voltage phasor quantities at each node are calculated. S I = (5) j j V j n 2 V From 4 and 5, I = (S ) * * V (6) j j pj j n V pj Once the load currents during the fault, are known, the voltages at each node can be calculated. D : ISTANCE CALCULATION The algorithm presented in this paper is based on solution of (7) that describes the fault condition.Fig.5 and table 1 illustrate all possible fault types occurring in the line section delimited by nodes p and q. TABLE I RESISTANCE VALUES FOR ALL FAULT TYPES Fault Type R R R R af bf cf f AN 0 Unknown BN 0 Unknown CN 0 Unknown AB Unknown Unknown BC Unknown Unknown CA Unknown Unknown ABN Unknown Unknown Unknown BCN Unknown Unknown Unknown CAN Unknown Unknown Unknown ABC Unknown Unknown Unknown ABCN Unknown Unknown Unknown Unknown Z Z Z V I R R R R I p pq f f + aa ab ac a a a f f f a = D . Z Z Z . x (7) V I R R R R I p pq f f ba bb bc b b f b f f b Z Z Z V I R R R R I p pq f f ca cb cc c c f f c f c Based on fault type and phases involved equations are written. Using (7) as example consider ABN fault now equation (7) can be written resulting in 8 and 9 as + + follows = D . Z . I . ( + ) (8) V pq R I R I I p f f f f ai i a a a f a b i a , b , c 8 + + = D . Z . I . ( + ) (9) pq V R I R I I p f f f f bi i b b b f a b i a , b , c The fault distance (D) and fault resistances can be calculated by separating 9 and 8 into real and imaginary parts and then solving the resulting linear system R A P F L : ANKING LL OSSIBLE AULT OCATIONS The fault location algorithm provides more than one possible fault point. In order to exactly estimate fault location, the algorithm combines information about the fault type and load rejection (provided by the DSP module) with the feederâ„¢s topology and electrical parameter s (stored in data base) to rank them by the most probable ones. Basically, the algorithm follows the rules described below: i> When the fault is permanent, isolated by breaker operation, the algorithm verifies which located points are protected by fuses and ranks them as the less probable ones. ii> When the fault is permanent isolated by fuse operation, the algorithm verifies which located points are not protected by fuses and ranks them as the less probable ones. Among those who are protected by fuses the algorithm ranks as the most probable one the point that is protected by a fuse whose opening would cause an amount of load rejection comparable to the load rejection measured by the IEDs. INFLUENCE OF LOAD DISTRIBUTION The fault location algorithm estimates the load currents by proportionally distributing the total apparent power measured at the substation to each node, according to their nominal apparent power. However, the load distribution may not be proportional to nominal installed load. The error caused due to this estimation does not influence significantly the algorithmâ„¢s accuracy due to the fact that in most cases the magnitude of load currents is much smaller than that of the fault current. ADDITIONAL SIMPLIFICATION TO THE GIVEN ALGORITHM An additional simplification reducing the algorithmâ„¢s computational burden consists of replacing the power â€œflow algorithm by a simple equation removing the iterative process. This is done by considering the voltage phasor quantities at each node, during the fault, equal to the voltage phasor quantities measured at the substation also during the fault. The error level is based on the fact that, the bigger the fault resistance becomes, the smaller becomes the magnitude of the fault current. When the magnitude of fault current is comparable to that of the load current , the error level increases greatly. However, large fault resistances (>20 ohms) will not trigger the digital meter oscillography function resulting in large errors while estimating the fault. M C T T P : Y ONTRIBUTION O HE APER As mentioned in this presentation, when the fault resistance is greater than 20 ohms, the error in the estimation of fault rises to a greater value. As a part of my contribution, a novel approach is proposed to minimize the error in such cases. Considering the operation of the circuit shown in fig. 6, when a fault occurs, the pulse transformer through the rectifiers forces the thyristors to turn ON(due to high fault cur rents).Therefore, a shunt path across the load with effective resistance (<20 ohms) is obtained. This decreases the error in estimation. As it can be observed, the circuit is activated only when a fault occurs. 9 (1) Pulse Transformer (2) Rectifiers with Filters (3) Thyristor Controller (4) Shunt Resistance (< 1ohm) (5) Fault Resistance Fig. 6 T A O T A A : HE DVANTAGES F HIS PPROACH RE i. Accurate estimation of fault by considerable minimization of error. This accurate estimation helps especially in the case of underground cables. ii. When a fault occurs, a considerable part of the fault current is shunted through the circuit and hence the effect of fault on other loads is reduced. Consequently, stability of the system increases. CONCLUSION The most important benefits provided by the fault location system for primary distribution networks are as follows: Downtime reduction: Decrease in time spent by maintenance crews to locate faults. Operation costs get reduced. No. of maintenance crews on standby is reduced. Higher profits and increase in electricity supply Consumer satisfaction due to faster system restoration Identification of, transient faults which do not cause permanent breaker Operation or fuse blowing. Identification of areas with high no. of transient f aults resulting in reduced maintenance. BIBLOGRAPHY Eduardo Cesar Senger ,Giovanni Manassero, Clovis Goldemberg ,Automated fault location system for primary distribution networks, IEEE Trans.Power Del., vol20,No.2,April2005. Power system analysis by Hadi Sadat Computer analysis of power systems by J.Arrilage and C.P.Arnold. 10 Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion



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