Smiths Power (United States)

Current methods of topology estimation rely on breaker statuses to obtain accurate results. However, due to the lack of availability of time stamped breaker status data in many electric systems, as well as the errors associated with this data, these methods are very limited in their current scope. Additionally, synchrophasor measurements can be used to supplement information on the connectivity between two nodes. The state of a breaker is correlated to the vector difference between the voltage phasors on either side of the breaker. The methodology presented in this paper calculates a voltage angle deviation threshold to determine topology inside a substation. The algorithm calculates the voltage phasor deviations for each possible set of breaker configurations. The threshold is then determined, such that the threshold is correct for a statistically significant portion of cases, while remaining a realistic value considering the Total Vector Error among the voltage phasor measurements.

The continuing success of synchrophasors has ushered in new subdomains of power system applications for real-time situational awareness, online decision support, and robust system control. In this paper, an adaptive decision-tree-based systematic method for open-loop regional voltage control is developed. This approach employs voltage security assessment method to generate voltage secure and insecure operating conditions for decision tree learning. Parallel decision trees corresponding to a set of control combinations are trained. To guarantee the robustness of decision trees and its capability of tracking the system condition after topology changes, the resulting trained trees are updated periodically in real time using an online boosting method. The performance of this approach is evaluated using IEEE 118 bus system.

In this paper we discuss the impact of PV on dynamic voltage stability. The power system becomes more vulnerable as we add PV and displace conventional generation, and consequently inertia and VAR support. While PV inverters have the capability to provide reactive power, the fact that most PVs are connected at lower voltage levels limits its usefulness. We use the Dominion Virginia Power's system with different PV scenarios to show how dynamic voltage stability of the system was significantly affected. The purpose of this paper is to increase the awareness to the dynamic voltage stability issues the in case of significant PVs connected to the system.

The exe-Guard Project is an alliance between Dominion Virginia Power (DVP), Sandia National Laboratories (SNL), Dartmouth University, and Schweitzer Engineering Laboratories (SEL). SEL is primary recipient on this project. The exe-Guard project was selected for award under DE-FOA-0000359 with CFDA number 81.122 to address Topic Area of Interest 4: Hardened platforms and Systems. The exe-Guard project developed an antivirus solution for control system embedded devices to prevent the execution of unauthorized code and maintain settings and configuration integrity. This project created a white list antivirus solution for control systems capable of running on embedded Linux® operating systems. White list antivirus methods allow only credible programs to run through the use of digital signatures and hash functions. Once a system’s secure state is baselined, white list antivirus software denies deviations from that state because of the installation of malicious code as this changes hash results. Black list antivirus software has been effective in traditional IT environments but has negative implications for control systems. Black list antivirus uses pattern matching and behavioral analysis to identify system threats while relying on regular updates to the signature file and recurrent system scanning. Black list antivirus is vulnerable to zero day exploits which have not yet been incorporated into a signature file update. System scans hamper the performance of high availability applications, as revealed in NIST special publication 1058 which summarizes the impact of blacklist antivirus on control systems: Manual or “on-demand” scanning has a major effect on control processes in that they take CPU time needed by the control process (Sometimes close to 100% of CPU time). Minimizing the antivirus software throttle setting will reduce but not eliminate this effect. Signature updates can also take up to 100% of CPU time, but for a much shorter period than a typical manual scanning process. Control systems are vulnerable to performance losses if off-the-shelf blacklist antivirus solutions aren’t implemented with care. This investment in configuration in addition to constant decommissioning to perform manual signature file updates is unprecedented and impractical. Additionally, control systems are often disconnected or islanded from the network making the delivery of signature updates difficult. Exe-Guard project developed a white list antivirus solution that mitigated the above drawbacks and allows control systems to cost-effectively apply malware protection while maintaining high reliability. The application of security patches can also be minimized since white listing maintains constant defense against unauthorized code execution. Security patches can instead be applied in less frequent intervals where system decommissioning can be scheduled and planned for. Since control systems are less dynamic than IT environments, the feasibility of maintaining a secure baselined state is more practical. Because upgrades are performed in infrequent, calculated intervals, it allows a new security baseline to be established before the system is returned to service. Exe-Guard built on the efforts of SNL under the Code Seal project. SNL demonstrated prototype Trust Anchors on the project which are independent monitoring and control devices that can be integrated into untrustworthy components. The exe-Guard team started with the lessons learned under this project then designed commercial solution for white list malware protection. Malware is a real threat, even on islanded or un-networked installations, since operators can unintentionally install infected files, plug in infected mass storage devices, or infect a piece of equipment on the islanded local area network that can then spread to other connected equipment. Protection at the device level is one of the last layers of defense in a security-in-depth defense model before an asset becomes compromised. This project provided non-destructive intrusion, isolation and automated response solution, achieving a goal of the Department of Energy (DOE) Roadmap to Secure Control Systems. It also addressed CIP-007-R4 which requires asset owners to employ malicious software prevention tools on assets within the electronic security perimeter. In addition, the CIP-007-R3 requirement for security patch management is minimized because white listing narrows the impact of vulnerabilities and patch releases. The exe-Guard Project completed all tasks identified in the statement of project objective and identified additional tasks within scope that were performed and completed within the original budget. The cost share was met and all deliverables were successfully completed and submitted on time. Most importantly the technology developed and commercialized under this project has been adopted by the Energy sector and thousands of devices with exe-Guard technology integrated in them have now been deployed and are protecting our power systems today

Transient stability is of essential concern in power systems. This paper provides a graphical method with high-order derivatives of voltage phase angle dynamics for transient stability analysis. Using a Single Machine Infinite Bus system, criteria are defined for determining unstable equilibrium points using the first, second, and third order derivatives of phase angle difference. To intuitively show stability characteristics, a new phase plane is defined with the first and second order derivatives. With measurement data from phasor measurement units, bus voltage phase angle and frequency dynamics are used for field application. Applications of the proposed method for transient stability evaluation and prediction are discussed. Simulations show that the proposed method provides an intuitive approach for transient stability analysis and is useful in field applications.

A fast islanding detection tool can help power dispatchers monitor and control power system operations. Frequency monitoring network (FNET) is a low cost and quickly deployable wide-area phasor measurement system at the distribution system level. The frequency disturbance recorder (FDR) in FNET is actually a single-phase phasor measurement unit (PMU) installed at ordinary 120 V outlets in the sense that it measures the voltage phase angle, amplitude, and frequency from a single-phase voltage source. Based on the data collected by the FDRs deployed in the North American power grid, two islanding detection methods, the frequency difference method and the change of angle difference method, are proposed. The nine real cases recorded, including islanding cases, generation trip cases, load shedding cases and oscillation cases, are presented to verify the proposed methods of islanding detection. Sensitivity analysis on the thresholds of the frequency deviation and angle deviation is done based on the real measurement data for obtaining the insensitive interval of two thresholds. The results show that the proposed methods can correctly detect power system islanding, and will not be falsely triggered by generation trips, load shedding and system oscillations.

Power systems measurements are often performed with current and voltage signals derived from instrument transformer secondary circuits. Errors introduced by these transformers are a recognized component of input data errors in supervisory control and data acquisition and phasor measurements. Correcting these errors by {in situ} calibration is an expensive option; hence, it is seldom employed except in a few special cases. This article proposes a new method for calibrating instrument transformers utilizing phasor measurements by estimating instrument transformers' ratio correction factors and phase angle correction factors. The method focuses on the fundamental frequency component of phasor measurements, and, in contrast with some of the techniques proposed in the literature, it does not require accurate instrument transformer models and can be executed as often as needed to keep the calibration up to date. Two alternative calibration techniques are introduced along with the simulation results to prove the feasibility.

This paper briefly describes Dominion's use of pseudo-measurements for the enhancement of its state estimator solution. Beyond providing a basic definition of pseudo-measurements and their usefulness, this paper highlights the specific integration of pseudo-measurements into Dominion's EMS platform. The paper concludes with a brief caution on the use of pseudo-measurements and highlights possible areas for further integration and treatment of pseudo-measurements.

Geomagnetic storms caused by solar activity can induce geomagnetic-induced current (GIC) in the power grids. The flow of GIC in the power transformer winding can cause half-cycle saturation of transformer. This saturation can cause distorted exciting current, transformer overheat, and some additional power system problems. There will also be more leakage flux leaving the core and entering into the tank due to GIC. This will cause large tank loss and overheat the transformer. Besides GIC, the leakage flux is also related to the transformer load current. This paper presents a 2D finite-element transformer model. Based on the finite element model, the transformer leakage flux and the tank loss caused by GIC with different transformer load current are studied. As a consequence of GIC, the transformer power factor and the magnitude of transformers load current have an important effect on the leakage flux of transformer. Copyright © 2010 John Wiley & Sons, Ltd.

Overhead distribution conductors move as a result of short-circuit conditions. In some cases, this motion can lead to conductors swinging together closer to the source. The subsequent fault causes higher stresses on the substation transformer and causes a backup overcurrent protective device to operate, having a negative impact on reliability. This paper reports on an investigation involving conductor motion on Dominion Virginia Power's overhead distribution system. It builds upon prior work dealing with compact overhead transmission lines. The author extends the model to typical overhead distribution lines and provides guidance to the distribution engineer as to when conductor swinging might become a problem. The characteristics of the most vulnerable spans led to the development of time-current curves depicting regions where spans are likely to have problems from short-circuit forces. The resulting critical clearing time curves have been adopted by the author's company to minimize problems from swinging conductors.