Markham, ON, Canada. {zhihan.xu, ilia.voloh}@ge.com. AbstractâAccurate fault location in distribution network of power system is an essential technology, yet ...
Enhanced Distribution System Fault Location Zhilin Wu, Lihan He
Zhihan Xu, Ilia Voloh
General Electric, Global Research Center Shanghai, China {zhilin.wu, lihan.he}@ge.com
General Electric, Digital Energy Markham, ON, Canada {zhihan.xu, ilia.voloh}@ge.com
Abstract—Accurate fault location in distribution network of power system is an essential technology, yet less studied compared to transmission systems, that enables utility companies in maintaining service reliability to reduce SAIDI (System Average Interruption Duration Index). This study develops novel methods for feeder fault location with current/voltage sensors sparsely deployed in the network. The voltages and currents measured in the substation and sensors are utilized in this study. Depending on the available sensor locations relative to fault, such as both upstream/downstream or upstream only, and the lateral conditions, the algorithm searches every possible path and calculates the fault distance and fault resistance. Eight scenarios are identified for all possible situations. Theoretical analysis and simulation experiments are performed to verify the proposed methods. High fault location accuracy has been achieved in various network and fault conditions.
Key words -- fault location, power system, distribution network, feeder, and sensor.
I.
INTRODUCTION
Accurate fault location is an essential technology that enables utility companies in maintaining service reliability to reduce SAIDI (System Average Interruption Duration Index) [1]. When a fault occurs, particularly for a permanent fault, immediate actions have to be taken to reduce the impacted areas and customers. In this condition, fault location must be accurately detected and then the fault can be removed from the power system. At presence, automatic fault location is mostly performed in transmission lines, where the lines are long without laterals. In such applications, a few major technical solutions have been developed. One solution is the impedance based method [2][3], which utilizes fault current and voltage to calculate the apparent impedance of the line and hence determine the fault location. This method is low cost, but relatively low accuracy. Another major solution is the traveling wave based method [4]. This method can be passive or active. The passive approach measures the time delay between the fault signal arrival and its echo from the ground position. The active approach measures the time delay between the injected signal and the echo signal from the fault point. With known
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electricity propagation speed, the fault distance can be calculated from the echo time. In practice, the traveling wave based method is often performed along with manual line check (the active approach) to find the shorted line position. There are growing needs for fault location in distribution systems [5][6], as the distribution systems directly connect to the end customers. Although the fault location methods in transmission lines are widely used and are relatively mature, the methods face huge challenges in distribution systems. In practice, fault location in distribution systems still heavily relies on manual line check. Research result accuracies are mostly around km [7]. One major challenge is that the distribution systems have a large number of laterals. In such a scenario, the impedance based method lacks the fundamental assumption of uniform line figure, which makes the method invalid. For traveling wave based method, echoes from multiple laterals confound the fault echo detection and make it difficult to locate the fault. With multiple laterals in the complex system, the sensing information is highly limited. In the distribution systems, there is usually no sensing device except at substation. For the application of fault location, a fault recorder is available at the substation to collect information of voltage and current. Yet, this limited information at a single point can hardly help solving the problem. It is natural to think about adding more sensing devices to collect information from every lateral. Yet, the cost would be unacceptable due to the large number of laterals in the distribution system. Even the cost for a single sensor may be low, the cost for a full network deployment is huge. In this study, novel and automatic fault location methods are developed to utilize current/voltage sensors in the distribution systems. With the help of only a few sensors sparsely deployed in a complex distribution system, fault location can be determined with the proposed algorithms. Results show that the proposed methods provide high fault location accuracy for different levels of fault resistance and long lines. As single phase line to ground fault counts for about 90% of all faults, this type of fault is targeted in this study. The proposed method can be easily extended to other types of fault, such as line to line fault, etc.
II.
SENSING AND NETWORK
A.
Sensors The proposed method is originally based on FMC-Tech sensor system [8], which consists of line-mounted sensors with built-in radio communications, as shown in Figure 1. The sensor measures the line current, both amplitude and phase, and forwards the data to a locally mounted controller. The data is then forwarded by GPRS to a server from the controller. The line sensors are powered by the magnetic field of the line, and the local controller is powered by a solar panel. The FMC current sensor has GPS time stamp in the communication system. Thus, measurements from multiple sensors in the system are synchronized. The sensing system has been validated in some power systems. In this study, all data from sensors are considered as already time aligned. The proposed method applies the sensing data for fault location; hence it does not rely on any specific sensing system. Here, FMC system serves as an example.
Figure 1. FMC sensing system
B. IEEE 34-node Test Feeder In this study, IEEE 34 node test feeder is selected for simulations. This test feeder is a real network served as one of the standard feeder networks. Detailed parameters are available from IEEE for reference [9]. This test feeder covers the most important features, including 3-phase lines, singlephase lines, transformer, regulators, balanced and unbalanced loads. For simplicity, the transformer and regulators are not considered in this study. In practice, the regulators can be modeled to adjust the sensed voltage and current. The transformers can be modeled by T model with symmetric component method for fault current/voltage analysis. They do not affect the proposed methods. Figure 2 shows the feeder system topology, where the transformer is still shown. Two sensors are deployed at node 812 and 830.
III.
ENHANCED FAULT LOCATION ALGORITHM
The impedance based methods have already been used in transmission line fault location. However, it is quite difficult to borrow the same idea in distribution networks. This is because the distribution systems have many laterals, nonuniform lines and distributed loads, which increase the complexity of the systems, introduce the uncertainty, and make the assumptions used in transmission systems invalid. This section introduces the proposed algorithm with framework and theoretical analysis. A. Algorithm Framework In this study, it is assumed that only one fault occurs at a time in the network. It is widely accepted that the fault is resistive, thus without reactance part. Moreover, we focus on the low impedance fault, i.e., the fault resistance RF
