Observability analysis and measurement placement for systems with PMUs

Observability analysis and measurement placement for systems with PMUs

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1 Abstract —This paper is concerned about the analysis of network observability and phasor measurement unit (PMU) placement when using a mixed measurement set. The measurements will include conventional power flows and injections as well as phasor measurements for voltages and line currents provided by phasor measurement units. The observability analysis is followed by an optimal meter placement strategy for the PMUs. Index Terms —State estimation, network observability, meter placement, phasor measurement units. I. INTRODUCTION Secure operation of power systems requires close monitoring of the system operating conditions. This is traditionally accomplished by the state estimator which resides in the control center computer and has access to the measurements received from numerous substations in the monitored system. These measurements are commonly provided by the remote terminal units (RTU) at the substations and include real/reactive power flows, power injections, and magnitudes of bus voltages and branch currents. More recently, synchronized phasor measurements have started to become available at selected substations in the system. Phasor measurement units (PMU) are devices, which use synchronization signals from the global positioning system (GPS) satellites and provide the positive sequence phasor voltages and currents measured at a given substation. These types of measurements will in turn improve the performance of the state estimators. Pioneering work in PMU development and utilization is done by Phadke et al. [1-2]. It is argued that the use of PMUs at each bus will lead to a simplified linear state estimator. This requirement is later relaxed in [3] due to the fact that each PMU can measure not only the bus voltage but also the currents along all the lines incident to the bus. Hence, furnishing a selected subset of buses with PMUs can make the entire system observable. This will only be possible by proper placement of PMUs among the system buses. This problem is formulated and solved using graph theoretic observability analysis and an optimization method based on Simulated Annealing in [3]. In this paper, a different formulation which is numerical and uses integer programming will be presented. This formulation allows easy analysis of network observability for mixed measurement sets, which may include conventional power flow and injection measurements in addition to the PMUs. Determination of optimal locations of PMUs with or without existing conventional measurements is also accomplished using the same formulation. II. PMU PLACEMENT PROBLEM FORMULATION A PMU placed at a given bus is capable of measuring the voltage phasor of the bus as well as the phasor currents for all lines incident to that bus. Thus, the entire system can be made observable by placing PMUs at strategic buses in the system. The objective of the PMU placement problem is to accomplish this task by using a minimum number of PMUs. In this paper, the problem is formulated and solved as an
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This note was uploaded on 01/29/2011 for the course ENGR 52 taught by Professor Mcmillan during the Spring '10 term at Baylor Med.

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Observability analysis and measurement placement for systems with PMUs

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