Fault Location Using Sparse Wide Area Measurements
Transmission line fault location allows quick repair of the damage caused by the fault and timely restoration of the line affected by the fault. Accuracy of the fault location is quite important since it affects repair crew’s ability to physically locate the damage part quickly. Typically, the desirable accuracy is to be able to locate a fault within a span of the transmission line towers. This paper presents a new fault location scheme which uses synchronized phasor measurements from different substations sparsely located near the region where the fault has occurred. When fault occurs different Intelligent Electronic Devices (IEDs) such as Phasor Measurement Units (PMUs) and Digital Fault Recorders (DFRs) connected to Global Positioning System (GPS) receivers and installed in some of the substations in the region will be automatically triggered by the change in monitored signals and will record corresponding current, voltage and status signals. Apart from these sparse measurements, the proposed method also uses SCADA PI Historian data which is utilized for tuning the power system model data with the pre-fault condition in real time information. The paper presents how the technique is implemented and shows test results using actual power system model as well as actual field data from a utility company that supported demonstration of the technique. The results are quite encouraging since the sparse measurement problem for such unique transmission line configurations does not allow any other known techniques to produce accurate and reliable results while the proposed technique produces satisfactory results.
The next Generation Ems Design
The concept of Supervisory Control and Data Acquisition (SCADA) system was introduced in the late sixties and subsequently the Energy Management System (EMS) solution with set of functionalities that relied on SCADA data was introduced in the seventies. This EMS design was based on the notion that power system goes through distinct states such as normal, alert, emergency and restorative, and hence the EMS functionalities need to support operators’ ability to monitor the system behaviour as it goes through various operating states and make decisions to steer it back to the normal state. As the time went by, many things have changed in the area of power systems: introduction of the electricity markets to accommodate competitive trading, the growth of the power system infrastructure to meet demands for renewable resources, EMS technology to improve computations, communications and visualization. Hence, almost 50 years after the initial proposals for the EMS solution as we know it today, the question whether we need a new EMS design and if so, how the next generation EMS design is going to look like may be raised. While this is a complex question requiring analysis well beyond what may be achieved through a discussion in a single paper, there are a few requirements of the next generation EMS design that are becoming rather obvious. They revolve around three simple questions: a) can the operator’s ability to monitor the system be improved and how, b) what are the requirements for the better decision-making tools for the operators and how such tools may be implemented, and c) how the design may evolve from the current legacy design to the stages of future EMS implementation. This paper is focused on trying to answer those three questions. The discussion is facilitated by using specific examples of the developments that the author was or is involved with. The examples include the discussion of spatial and temporal improvements in data management by merging operational and non-operational data, development of improved operator decision-making tools by better matching data and models, and introduction of a development and implementation strategy that relies on gradual transition from legacy to future design.
Effect of stress conditions on collapse deformation behavior of a rockfill material
A set of saturated and dry-saturated large-scale triaxial tests were conducted in order to explore the effects of stress conditions on the saturation-induced collapse deformation behavior of a rockfill material. Specimens were tested in different confining pressures and for dry-saturated tests the specimens were submerged in various shear stress levels. The results indicate that in all of the dry-saturated tests a sudden reduction in the volume of the specimens was observed during the submerging process. The ratio of the minimum axial strength of a submerged specimen (at the end of the saturation process) to the shear strength of the specimen before saturation is defined as the coefficient of stress recovery, Csr. Results of the dry-saturated tests showed that this ratio increases as the confining pressure increases and decreases by increasing the shear stress level. According to the results of dry-saturated tests the values of internal friction angle reduction caused by saturation (Δϕc), the ratio of the elasticity modulus of the material after saturation to its elasticity modulus in dry condition, i.e., Ewet/Edry, and also the saturation induced sudden volumetric strain (εvc) decrease as the confining pressure increases. However the shear stress level does not have any meaningful effect on the variation of Dfc, Ewet/Edry and (εvc).