Modeling PV for unbalanced, dynamic and quasistatic distribution system analysis

To be cost‐effective, a process hazards analysis effort should concentrate on those areas where there is the greatest potential for risk reduction. The level of detail of the analysis is a factor which affects the magnitude of effort and the completeness of the results. Often, there is an opportunity to combine components together to be analyzed as a single entity, in order to increase the efficiency of the hazard identification process. Issues arise concerning how to combine components, and what should be the appropriate level of detail for consideration. For instance, a level of detail shown on piping and instrumentation diagrams which has proven convenient for process design may not be sufficient or optimal for hazard identification. To resolve such issues, some guidelines are proposed for determining the appropriate level of detail. These guidelines have been deduced from the intent of the analysis and the basic assumptions of the methodology.

In this paper we are presenting a novel approach for rendering large datasets in a view-dependent manner. In a typical view-dependent rendering framework, an appropriate level of detail is selected and sent to the graphics hardware for rendering at each frame. In our approach, we have successfully managed to speed up the selection of the level of detail as well as the rendering of the selected levels. We have accelerated the selection of the appropriate level of detail by not scanning active nodes that do not contribute to the incremental update of the selected level of detail. Our idea is based on imposing a spatial subdivision over the view-dependence trees data-structure, which allows spatial tree cells to refine and merge in real-time rendering to comply with the changes in the active nodes list. The rendering of the selected level of detail is accelerated by using vertex arrays. To overcome the dynamic changes in the selected levels of detail we use multiple small vertex arrays whose sizes depend on the memory on the graphics hardware. These multiple vertex arrays are attached to the active cells of the spatial tree and represent the active nodes of these cells. These vertex arrays, which are sent to the graphics hardware at each frame, merge and split with respect to the changes in the cells of the spatial tree.

The safe use of electricity underwater by the working diver can increase the complexity of the tasks he can complete. By using a multiple-faceted safety program of education, preventive maintenance and specialized ground fault systems underwater electrical safety can be achieved. The Naval Civil Engineering Laboratory (NCEL) has developed a family of ground fault current detection and shutdown systems for loads from 2.5 KVA to 25 KVA. An underwater electric field detects has also been developed to prevent the diver from swimming into an electric field created by faults in equipment not equipped with ground fault protection. INTRODUCTION Electrical power has been used successfully by divers to provide lighting, vehicle propulsion, electric arc welding, and more recently, television and underwater inspection equipment. Fortunately, reported accidents due to these uses of electricity underwater have been limited to minor shocks; the number of such reports has been small when compared with diving accidents due to other causes. However, as the demand for use of electricity grows and the system power levels increase, the potential hazard of using electrical power underwater must be addressed. This increased demand for electrical power can be safely met by the use of properly designed ground fault protection systems. To help meet this need, NCEL, under the sponsorship of the Naval Facilities Engineering Command and the Naval Sea Systems Command, has developed improved ground fault detection (GFD) and shutdown systems and an underwater electric field detector. The GFD system protects the diver from electrical shock hazards originating from ground faults in the power system at the dive site. The field detector detects and warns the diver of stray electric fields originating from electrical, faults in systems not equipped with GFD or from, powered cathodic protection systems. BACKGROUND Electricity can be used safely underwater provided the diver is protected from electrical shock hazards, but the use of electric power underwater involves hazards to humans not present in overland uses. Reduction in skin contact resistance caused by water absorption is of primary importance; a nominal dry skin resistance of 3,500 ohms may drop to 250 ohms when the skin is saturated with seawater. This decrease in skin resistance reduces the voltage across the body required to create a fatal current flow. The voltage gradient can be applied to the diver directly by physical contact with an energized circuit or by the presence of a strong electric field in the water. In either case, it is important that protection circuits on the power system exceed requirements of overland use and that a means is provided for warning a diver inadvertently swimming into an electric field. The effect of electric shock on the human body has been studied by many researchers and is well documented for the case of electric shock in air, How these results apply to the diver who has lost the protection of skin contact resistance and whose body may be saturated with mixed breathing gases is unknown.

In industrial facilities with on-site generation, there are two major approaches to connect generators to the main distribution busbar. One is to connect generators through step-up delta-wye transformers with low-resistance grounded wye on the busbar side. The second common method is to connect generators directly to the main distribution busbar and use low-resistance grounding or hybrid grounding in the generator neutral. A grounding resistor in the step-up transformer’s wye side neutral or in the generator neutral will limit the ground fault in the main distribution system. When busbar differential protection is used on the main busbar, sensitivity for bus ground faults has to be evaluated to ensure detection of limited low-level ground faults. While step-up transformer grounding resistors can be selected to allow ground faults of higher magnitudes detectable by bus differential protection, the choice of grounding resistor is more complex when generators are connected directly to the main busbar. In such systems, a grounding resistor in the generator neutral limits the generator fault to protect the alternator core from excessive damage. At the same time, busbar differential protection needs to detect a limited low-magnitude ground fault on the bus. This paper discusses considerations to select the main distribution busbar differential protection type, CTs, and relaying scheme to enable detection of busbar ground faults limited by the generator low-resistance grounding resistor.

Until recently, TriMet traction power substations (TPSs) utilized a low resistance grounding system for the dc switchgear and rectifier equipment enclosures. The TPS negative bus was connected to a dc ground mat through a grounding diode. In addition to the basic dc overcurrent and rate-of-rise relays, each substation is provided with a low resistance frame fault current relay (device 64 C) and a negative-to-ground potential relay (device 64 V). Recently, TriMet has conducted several field tests: a) bolted frame fault tests, by applying 750 Vdc to the dc switchgear enclosure with the grounding diode connected and then with the grounding diode removed, b) ground fault tests, by connecting the OCS contact wire to an OCS pole ground rod (the ground fault tests were done with and without the diode), c) ground fault tests simulating an arcing ground fault, with a 9 ohm resistor inserted in series between the OCS contact wire and the OCS pole ground rod. This paper provides the test data and discusses the results of these frame fault and ground fault field tests. Technical analysis including personnel safety considerations are performed for various test configurations. The analysis will be focused on ground fault detection since most ground faults are undetected because of the very low ground fault current magnitudes, which are normally not detected by the rate-of-rise relay.

Until recently, TriMet traction power substations (TPSs) utilized a low resistance grounding system for the dc switchgear and rectifier equipment enclosures. The TPS negative bus was connected to a dc ground mat through a grounding diode. In addition to the basic dc overcurrent and rate-of-rise relays, each substation is provided with a low resistance frame fault current relay (device 64 C) and a negative-to-ground potential relay (device 64 V). Recently, TriMet has conducted several field tests: a) bolted frame fault tests, by applying 750 Vdc to the dc switchgear enclosure with the grounding diode connected and then with the grounding diode removed, b) ground fault tests, by connecting the OCS contact wire to an OCS pole ground rod (the ground fault tests were done with and without the diode), c) ground fault tests simulating an arcing ground fault, with a 9 ohm resistor inserted in series between the OCS contact wire and the OCS pole ground rod. This paper provides the test data and discusses the results of these frame fault and ground fault field tests. Technical analysis including personnel safety considerations are performed for various test configurations. The analysis will be focused on ground fault detection since most ground faults are undetected because of the very low ground fault current magnitudes, which are normally not detected by the rate-of-rise relay.

The growing adoption of electric vehicles has recently attracted increasing attention of scientists and brought about pioneering research studies from various fields. Safety concerns particularly those regarding ground faults detection and protection, have extensively been addressed. Ground faults occur quite frequently in electric vehicles and they may be due to severe operation conditions, such as vibrations, twists or even crashes. Generally, the first ground fault is not dangerous, since the powertrain systems, namely, the dc bus where the batteries are connected, the power inverter and one or more ac machines, are generally ungrounded. The second ground fault, however, can produce malfunction in some systems, power loss or even serious damages. Locating the fault has often proved hard and time consuming. For this reason, the present study focuses on developing a ground-fault detection method for electric vehicles capable of determining on which side, the dc or the ac, the ground fault is located. The method is based on the analysis of the voltage in a grounding resistor connected between the midpoint of the battery pack and ground. Based on the polarity and harmonics, it is possible to locate the ground fault. This method has been verified excellent results have been achieved using computer simulations and experimental tests in a 140-kW electronic power inverter fed by a 480 Vdc battery.

In this paper we are presenting a novel approach that enables rendering large-shared datasets at interactive rates on a remote inexpensive workstations. Our algorithm is based on view-dependent rendering and client-server technologies. In our approach, servers host large datasets and manage the selection of the various levels of detail, while clients receive blocks of update operations which are used to generate the appropriate level of detail in an incremental fashion. We assume that servers are capable machines in term of storage capacity and computational power while clients are inexpensive workstation that have limited 3D rendering capabilities. To avoid network latency we have introduced two powerful mechanisms that cache the adapt operation blocks on the clients' side and predict the future view-parameters of clients based on their recent behavior history. Our approach dramatically reduces the amount of memory needed by each client and the entire computing system since the dataset is stored only once in the local memory of the server. In addition, it decreases the load on the network as a result of the incremental update contributed by view-dependent rendering.

Photovoltaic ground fault detection recommendations for array safety and operation

The detection of ground faults in the rotor of brushless synchronous machines is usually a difficult task due to the absence of available measurements. This paper presents a new on-line rotor ground fault location method for brushless synchronous machines. The proposed method is able to detect and locate a ground fault in the excitation system without removing the rotor for testing. The method is based on the measurement of the exciter field current and on the analysis of a voltage. This voltage is measured at a high ohmic grounding resistor installed between the neutral of the exciter armature and ground through a slip ring. The method has been validated by computer simulations and by experimental tests using a special laboratory setup, obtaining excellent results.

A fault protection and location method for ungrounded dc traction power systems is presented in this paper. Many dc traction power systems have an ungrounded power circuit to increase the leakage path resistance. Although ungrounded systems can continue operating with a single ground contact, unlike solid- or low-resistance grounded systems, because of the very low fault current, a second ground fault in another pole will result in a line-to-line fault that could cause significant system damage. However, it is difficult to detect the first ground contact due to the low ground current and even harder to locate because it can be seen by many detectors in the network. The proposed scheme in this paper uses a probe unit to detect and locate the first single ground fault in ungrounded traction power systems. The probe unit applies probe voltage to detect the fault and, once the fault is detected, analyzes the response to dc or swept-frequency ac probe voltage to locate the fault. The proposed concepts have been verified with computer simulations and hardware experiments and demonstrated a successful performance.

The “Parametric Prototype” has been developed as a tool for integrated parametric and physical shape representation to optimize styling and design. This tool will be applied in the early phases of the product development process at an appropriate level of detail, e.g. for the fast visualization of car parameters and proportions of the exterior car body. The development comprises a method that converses changes in the product model in a CAD system and the physical model bidirectional. Further the implementation of an interface between the physical shape presentation and the computer based representation has been realized.

Megastructures: use of CFD turbulence models for the evaluation of wind-induced fatigue loads

El Programa para la Evaluación Internacional de Alumnos (PISA) proporciona un marco en el que más de 80 países colaboran para construir métricas globales avanzadas para explorar los conocimientos, habilidades y atributos del estudiantado. El diseño de las evaluaciones plantea importantes desafíos conceptuales y técnicos, como el éxito del aprendizaje. Más allá de una base conceptual sólida, PISA necesita cumplir una serie de exigencias a veces contradictorios. Los/as administradores de escuelas, autoridades normativas y los docentes deben ser capaces de utilizar esta información de la evaluación para determinar cómo crear mejores oportunidades para el aprendizaje de los estudiantes. Las evaluaciones también deben proporcionar retroalimentación productiva, con niveles apropiados de detalle, para potenciar las decisiones de mejora y rendición de cuentas, en todos los niveles educativos. De hecho, además de evaluar la lectura, las matemáticas y la ciencia como competencias clave, PISA va incorporando progresivamente también algunas de las competencias cognitivas más amplias, sociales y emocionales.

We describe the design of a system to augment a light striping camera for three dimensional scanning with a photometric system to capture bump maps and approximate reflectances. In contrast with scanning an object with very high spatial resolution, this allows the relatively efficient and inexpensive acquistion of input for high quality rendering. This system is being used in a project to digitize a Michelangelo Pietà in Florence, Italy.