This paper reveals that the impedance match (or the Thevenin circuit) based voltage stability monitoring techniques have problems to predict voltage stability limits when applied to multi-load power systems. Power system loads are nonlinear and dynamic. They cannot be simply represented as Thevenin circuit parameters for impedance match analysis. To overcome these difficulties, a new concept called "coupled single-port circuit" is proposed in this paper. The concept decouples a meshed network into individual single generator versus single bus network and, as a result, a modified version of the impedance match theorem can be used. This leads to a real-time voltage stability monitoring scheme without the need to estimate Thevenin parameters. The scheme can estimate voltage stability margin and identify weak areas in a system based on the SCADA and PMU data. Case studies conducted on several test systems have verified the validity of the proposed method.

Distribution systems are undergoing many enhancements and developments to enable the future smart grid, and distribution system state estimation (DSSE) provides the control centers with the information necessary for several of its applications and operational functions. However, the quality of DSSE typically suffers from a lack of adequate/accurate measurements. Recently, many electric utilities have started to install fairly accurate smart meters throughout their distribution networks, which create an opportunity to achieve higher quality DSSE. However, the signals provided by smart meters are generally not synchronized and the difference between the measurement times of smart meters can be significant. Therefore, a complete snapshot of the entire distribution system may not be available. This paper proposes a method to deal with the issue of nonsynchronized measurements coming from smart meters based on the credibility of each available measurement and appropriately adjusting the variance of the measurement devices. To illustrate the effectiveness of the proposed method, two IEEE benchmark systems are used. The results show that the proposed method is robust and improves the accuracy of DSSE compared with the traditional DSSE approach.

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Traditionally Security Constrained Optimal Power Flow and VAr planning methods consider static security observing voltage profile and flow constraints under normal and post contingency conditions. Ideally, these formulations should be extended to consider dynamic security. This paper reports on a B.C. Hydro/CEPEL joint effort establishing a Dynamic Security Constrained OPF/VAr planning tool which considers simultaneously static constraints as well as voltage stability constraints. This paper covers the details of formulation and implementation of the tool together with the test results on a large scale North American utility system and a reduced Brazilian system.

The objective of contingency screening and ranking function is to shortlist a specified number of critical contingencies from a large list of credible contingencies and rank them according to their severity. This paper summarizes the work conducted as part of the EPRIA3.C. Hydro on-line voltage stability project in developing a Contingency Screening and Ranking (CS&R) module. The two methods of Reactive Support Index (RSI) and Iterative Filtering are derived in this paper and tested on the large scale systems of B.C. Hydro and another Major Unnamed Utility. The results obtained indicate that RSI on its own or in combination with the Iterative Filtering method can be used for CS&R depending on the acceptable level of misranking. The RSI method is a very fast and powerful CS&R method and is suggested for systems where some misclassification of contingencies can be tolerated. On the other hand, for systems where an exact list of critical contingencies is intended, then the Iterative Filtering method can be used for screening complemented with another method like RSI for ranking. The latter technique is being integrated in the EPRU6.C. Hydro On-line Voltage Stability tool.

In this paper, qualitative and quantitative differences between nonlinear and linear modal simulations in stressed power system are presented. For the first time in the literature, timedomain nonlinear simulation is used to validate the accuracy of the second order modal model, obtained by using modal series. Furthermore three new selective indices are defined and used to explain and predict the differences between nonlinear and linear modal simulations. These indices also explain the under or over damping results being experienced when a linear system theory designed controller is applied to a nonlinear system.

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