Medium Voltage Distribution Lines Research Articles

Deriving the Signal-to-Noise Ratio Probability of Error and Performance Measure Matrices for Distribution Line Carrier Signals Propagation (Using Bus Impedance Approach)

The automated distribution system using distribution line carrier (DLC) needs a two way communication between the various controlled terminals and the main substation. Digital data should be transmitted over the distribution power lines from the main substation to the transceivers in the distribution system and vice versa. The distribution system is a hostile medium for data transmission [i.e., high noise levels and standing wave patterns with low voltage nodes (as a result of signal reflections in the system)]. This hostility leads to low signal-to-noise ratio (SNR) locations and subsequently to high probability of bit error at these locations. The bus impedance matrix was developed for medium voltage distribution system. An actual medium voltage distribution line was tested. The actual measurements of the tested line verified the validity of the derived equations. The above mentioned line with the addition of a branch is used as an example in this paper. This paper derives (SNR) probability of bit error and performance measure transfer rate of information bits (TRIB) matrices of any DLC system starting from the bus impedance matrix.

New Technologies, Standards, and Maintenance Methods in Spacer Cable Systems

The overhead distribution lines with bare conductors for medium-and low-voltage circuits are being substituted due to their failure rate and security level, particularly in adverse areas i.e., heavy trees and high isokeraunic levels. The failure rate in CEMIG's medium-voltage overhead distribution lines, in urban areas, is 0.9 failure/km-year. More and more customers ask for better services and lower costs. These types of systems are greatly influenced by external causes such as lightning, rain, trees, collision, and vandalism. In Brazil, based on U.S. experience, the Aerial Spacer Cable System has been shown as the best system to improve its reliability. The low-maintenance cost, easy operation, high security level, and the attractive cost benefits have justified its use, mainly in urban areas, by CEMIG, a Brazilian utility. In the MV Spacer Cable System were included other technologies, such as the CSP transformer, SF6 switch, medium-and low-voltage polymeric arresters, low-voltage multiplex cable, and wedge and piercing connectors. The CEMIG's Spacer Cable System has been performing at an average failure rate of 0.04 failure/km-year. This paper describes the line design, equipment, standards, and maintenance methods in live-line and field experiences of Spacer Cable System in our company, with the technical support of Hendrix Wire & Cable, USA, and Wirex Cable, Brazil. Other utilities in Brazil are now using this system, to meet one of the government's requirements of improved reliability. It is a great alternative for companies searching for high reliability for their distribution electrical system.

Probabilistic derivation of overstress for overhead distribution in-line structures

This paper shows how probability techniques can be applied to low and medium voltage distribution and high voltage sub-transmission lines which use self-supporting single-pole structures. The probabilistic concept uses overlapping distributions in which the randomized stress induced by wind pressure is matched to the resisting strength of a pole structure. In this way a risk load is evaluated which optimizes structural strength and enhances the economic utility of the asset. Specific to the work is the inclusion of the degeneration of pole strength with age. This is important in distribution systems where wood is the most common construction material. The modeling uses Monte Carlo simulation to establish a failure risk of a line structure within a design return period and a life. Input to the model involves the static load imposed by line conductors and their ancillaries, random gust wind pressures (modeled by a Gumbel distribution), and a 3-parameter Weibull distribution to describe the dispersion of strength and degradation of the material. The pole overturning (wind) moment is compared to the degrading resisting (strength) bending-moment over daily or monthly intervals related to a designated life time. The work, for a large electric utility, analyzes treated hardwood and steel-reinforced concrete poles for new works, with emphasis on urban and semi-urban area construction. In the context of an urban and semi-rural environment, cost reductions in the order of 10% to 15% can be achieved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>