Analysis of Network Observability of Phasor Measurement Unit Under Contingency Scenario

Abstract

Currently, rapid growth of power demands, disproportionate growth of power generation and transmission systems, power system restructuring, and other factors have overloaded the existing electrical networks and subsequently decreased the stability margin of these networks. In such circumstances, to ensure the stable and proper operation of the system, a precise measurement and monitoring of the system states are required. This monitoring was conventionally performed by utilizing the Supervisory Control and Data Acquisition (SCADA) system, in which state estimation is derived based on measurements that are not usually synchronized. To overcome this limitation in the SCADA, the wide-area monitoring, protection and control (WAMPAC) system has been employed, in which Phasor Measurement Units are placed at different locations in power network. These units, which are time synchronized with clock signals from global positioning system (GPS) satellites, are able to provide synchronized phasor measurements. To install optimal number of PMUs in a system network is an important task. The complete observability of the system is a prerequisite to the state estimation to achieve the same with economical considerations generally certain minimum number of appropriately distributed PMUs. The complete observability of the power system, using phasor measurements, implies that each bus of the network must have one voltage phasor measurement or a voltage phasor pseudo-measurement. The observability of power system is defined in terms of numerical observability as well as topological observability of the system. A network is said to be topological observable if it contains a spanning tree of full rank. When the measurement Jacobian is of full rank, the network is said to be numerically observable. To achieve full network observability, both topological and numerical observability is needed and for this optimal PMU placement is needed. The proposed method for network observability is tested for different standard test systems considering contingencies such as loss of single PMU, single line outage and communication constraints. Thus the optimal placement problem (OPP) is formulated such that minimizing the number of PMU installations for full network observability.