1128 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 21, NO. 3, JULY2006 Transmission Network Fault Location Observability With Minimal PMU Placement Kai-Ping Lien, Student Member, IEEE, Chih-Wen Liu, Senior Member, IEEE, Chi-Shan Yu, Member, IEEE, and Joe-Air Jiang, Member, IEEE Abstract—This paper presents a concept of fault-location ob- servability and a new fault-location scheme for transmission net- works based on synchronized phasor measurement units (PMUs). Using the proposed scheme, minimal PMUs are installed in existing power transmission networks so that the fault, if it occurs, can be located correctly in the network. The scheme combines the fault-lo- cation algorithm and the fault-side selector. Extensive simulation results verify the proposed scheme. Index Terms—Fault location, phasor measurement unit (PMU), transmission network. I. INTRODUCTION A CCURATE estimate of the fault location is critical to in- spection, maintenance, and repair of transmission lines [1]–[8]. Several two-terminal fault-location algorithms based on phasor measurement units (PMUs) techniques have been pro- posed [9]–[13] recently. These PMU-based algorithms propose the calculation of fault location using synchronized voltage and current phasors. While they can achieve high accuracy in fault location, they are limited to locate faults in a transmission net- work installed by PMUs on every bus. Considering the installa- tion cost of PMUs, it is important to investigate the placement scheme of the PMUs at minimal locations on the network in the sense that the fault-location observability can be achieved over the entire network. By borrowing from the concept of network state observability, which means that the entire steady-state bus voltage phasors can be estimated using the installed meter mea- surements, we define the fault-location observability as that if a fault occurs on the network, then it can be located exactly using the installed digital fault recorders such as PMUs. Based on the topology of the power system, this paper first proposes a minimal placement strategy of PMUs, and then develops an innovative fault-location algorithm for the trans- mission network. Using installed PMUs, the new fault-location scheme can enhance the protection function of the network. In the proposed scheme, every line section in transmission networks only needs one-side PMU installation. The proposed Manuscript received February 3, 2005; revised May 26, 2005. This work was supported by the National Science Council of Taiwan, R.O.C., under Contract NSC-93-2213-E-002-054. Paper no. TPWRD-00067-2005. K.-P. Lien and C.-W. Liu are with the Department of Electrical En- gineering, National Taiwan University, Taipei 106, Taiwan (e-mail: f89921115@ntu.edu.tw, cwliu@cc.ee.ntu.edu.tw). C.-S. Yu is with the National Defense University, Chung-Cheng Institute of Technology, Taoyuan 335, Taiwan (e-mail: chsyu@ccit.edu.tw). J.-A. Jiang is with the Department of Bio-Industrial Mechatronics Engi- neering, National Taiwan University, Taipei 106, Taiwan, R.O.C. (e-mail: jajiang@ntu.edu.tw). Digital Object Identifier 10.1109/TPWRD.2005.858806 Fig. 1. IEEE-14 test buses. fault-location scheme can accurately and quickly determine a fault point no matter where it occurs on the power grid. Meanwhile, the prefault transmission network models are not necessary in this approach. The proposed algorithm is more appropriate to practical applications. II. MINIMAL PMU PLACEMENT STRATEGY Based on the purpose of this work, this section will present a simple but minimal PMU placement strategy such that the fault- location observability can be achieved. The PMUs placement proceeds with the following steps. Step 1) PMUs are placed on the buses with the largest number of connected branches and with the second largest number of connected branches. Step 2) PMUs are placeed on the buses by the so-called “one-bus spaced deployment strategy,” which means that every two PMUs are spaced by one bus as pos- sible as that the minimal PMUs are achieved and the proposed fault-location scheme can work. Step 3) Prune PMUs deployment after the above two steps and eliminate the redundant PMUs until it violates the one-bus-spaced deployment strategy. Notably, the selection of PMU’s placement location is not unique in Step 2). The criterion for the proposed fault-location scheme can work properly in that every line section in the pro- tected network needs at least one-side PMU installation. We illustrate the placement strategy with Fig. 1, which is the IEEE 14-bus system. The sample network shown in Fig. 1 can 0885-8977/$20.00 © 2006 IEEE Authorized licensed use limited to: National Taiwan University. Downloaded on March 9, 2009 at 05:16 from IEEE Xplore. Restrictions apply.