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Even with the expeditious progress in global Photovoltaic (PV) power generation, faults occurring in PV systems pose excessive challenges to the productivity and reliability of PV installations. Though specific installation standards have been developed for the protection of PV systems, the compatibility of these standards to cope with the unique operating characteristics of PV generating systems is questionable and hence, needs critical evaluation. Therefore, this paper briefly analyzes the standards available for the protection of PV systems, investigates the protection challenges and inspects the compatibility of latest National Electric Code (NEC) standards to protect PV arrays against Line-Line (LL) and Line-Ground (LG) fault occurrences. In particular, this article conducts a detailed behavioral study on LL and LG faults and evaluates the compatibility of NEC standards in the context of: (1) Varying mismatch levels, (2) Impact of Maximum Power Point Trackers (MPPTs) and (3) Changing irradiation levels. Detailed simulations as well as experimental analysis have been carried out to clearly portray the challenges in LL/LG fault detection despite by following new NEC recommendations. Further, based on the implications attained, some suggestions for reliable fault detection have also been presented that are expected to enhance the reliability of LL/LG fault detection in PV systems.

Arc faults can produce very high temperatures and can easily ignite combustible materials; thus, they represent one of the most important causes of electrical fires. The application of arc fault detection, as an emerging early fire detection technology, is required by the National Electrical Code to reduce the occurrence of electrical fires. However, the concealment, randomness and diversity of arc faults make them difficult to detect. To improve the accuracy of arc fault detection, a novel arc fault detector (AFD) is developed in this study. First, an experimental arc fault platform is built to study electrical fires. A high-frequency transducer and a current transducer are used to measure typical load signals of arc faults and normal states. After the common features of these signals are studied, high-frequency energy and current variations are extracted as an input eigenvector for use by an arc fault detection algorithm. Then, the detection algorithm based on a weighted least squares support vector machine is designed and successfully applied in a microprocessor. Finally, an AFD is developed. The test results show that the AFD can detect arc faults in a timely manner and interrupt the circuit power supply before electrical fires can occur. The AFD is not influenced by cross talk or transient processes, and the detection accuracy is very high. Hence, the AFD can be installed in low-voltage circuits to monitor circuit states in real-time to facilitate the early detection of electrical fires.

The worldwide global market requires electrical en- gineers to have a deep understanding of the bonding and earthing practices adopted in different countries around the world. This knowledge is essential to obtain effective designs and high safety standards and can promote the elimination of technical obstacles that can still create market barriers. The full comprehension of the "grounding" theory requires the command of key technical con- cepts regarding the earthing methods, which may cause confusion when used in the North American technical realm rather than in the International Electrotechnical Commission (IEC) world. This issue is further worsened by the lack of literature in this matter, as well as of harmonization documents between national codes and international standards. This paper, by analyzing the protection against indirect contact in ac (50/60-Hz) low-voltage power sys- tems by automatic disconnection of supply, seeks to clarify both the terminologies and each type of grounding system adopted in IEC standards, with the intent to create a common reference for practicing engineers in the matter of bonding and earthing of power systems. Major differences encountered between sizing procedures adopted in IEC standards and the North American National Electrical Code are also examined. Index Terms—Direct contact, earth, exposed conductive part (ECP), extraneous conductive part (EXCP), ground, indirect contact, Isolation Terre (IT) systems, protective conductors (PEs), single-phase line-to-ground (SLG) fault, Terre-Neutral (TN) systems, Terre-Terre (TT) systems.

The growing gap between sustained and peak performance for scientific applications is a well-known problem in high end computing. The recent development of parallel vector systems offers the potential to bridge this gap for many computational science codes and deliver a substantial increase in computing capabilities. This paper examines the intranode performance of the NEC SX-6 vector processor and the cache-based IBM Power3/4 superscalar architectures across a number of scientific computing areas. First, we present the performance of a microbenchmark suite that examines low-level machine characteristics. Next, we study the behavior of the NAS Parallel Benchmarks. Finally, we evaluate the performance of several scientific computing codes. Results demonstrate that the SX-6 achieves high performance on a large fraction of our applications and often significantly out performs the cache-based architectures. However, certain applications are not easily amenable to vectorization and would require extensive algorithm and implementation reengineering to utilize the SX-6 effectively.

Electrical safety requires a combination of standards and enforcement processes that must be carefully integrated so they work together. Two main standards are used to provide electrical safety in facilities: the Internationale Electrical Technical Commission (IEC) system in Europe and the National Electrical Code (NEC). These two systems provide electrical safety when used separately, but using a mix of the two raises many technical issues that are complex and not obvious to most users. This paper examines some of them, showing some similarities and differences while looking at related product issues.

We compare several approaches and their tradeoffs to achieving terabit/s transmission in SMF with 40 km and/or 80 km repeater spacing. Capacity and maximum transmission distances in multiple low-loss windows are discussed.