CHESF

Abstract: It is noted that the occurrence of fires under transmission lines is responsible for a great number of line outages in many countries. The insulation requirements for lines of several voltage levels were established on the basis of field investigations and laboratory tests under fire conditions. The results obtained and the statistics presented indicate that for actual AC transmission lines with rated voltage up to 500 kV, faults are mainly due to conductor-to-ground short circuit at midspan or phase-to-phase short circuit, depending on line configuration. Another problem arising from the burning is the contamination of the insulators due to the accumulation of particles (soot, dust) on their surface. Pollution severity in terms of ESDD (equivalent salt deposit density) measured on insulators coming from regions of sugar cane fields in Brazil has shown values of up to 0.1 mg/cm/sup 2/. >

Abstract: Limnoperna fortunei (Dunker, 1857) is a small mytilid native to Southeast Asia. It was introduced in South America in early 1990 and has dispersed from Argentina to central Brazil, and until 2014 has been restricted mainly to the Parana and Uruguay river basins. The present note reports the occurrence of Limnoperna fortunei for the first time in the Sao Francisco River basin in northeastern Brazil. The establishment of L. fortunei in these regions will require close attention from the government and also by society.

Abstract: This paper describes the design and development of a sensor system network for remote monitoring of the state of pollution on high-voltage insulators, its deployment among four states in Northeast Brazil and preliminary analysis of the data gathered by the system. Six monitoring units, each composed by leakage current, humidity, and temperature sensors, an electronic processing module, and a satellite-communication link, were built and installed on 230- and 500-kV transmission towers. Measured data are sent by the different systems via satellite to a database controlled by a web-based graphical user interface, incorporated into the supervision-management system of the electric utility company. Sample field results on one of the sensor systems, both for short- and long-term measurements, show a direct correlation of the activity recorded by the system with the pollution level expected to occur near the corresponding monitoring point.

Abstract: The authors describe the dynamic performance of a radial weak, heavily shunt-compensated power system, with three static VAr (volt-ampere reactive) compensators (SVCs) of relatively large rating installed at short distances from one another. Dynamic interactions between the SVC control systems and between them and the network are analyzed by using eigenvalues and frequency-response techniques. Some noteworthy effects concerning the SVCs' regulator stability that can arise in such systems are described. These effects, revealed in the eigenvalue analysis, were confirmed in TNA simulations. A brief description of the mathematical formulation and the complete system data is also included. Among other results, it is shown that the operation of SVCs with low values of ESCR can exhibit oscillation mode frequencies above 5 Hz, depending substantially on SVC regulator gain. In such cases, the representation of both network dynamics and thyristor time delay is crucial in the analysis if the SVC regulator stability limits. >