WDM Local-Area Networks

WDM-based broadcast-and-select transmission over optical passive-star topology can significantly enhance the speed of optical LANs/MANs. This type of optical LAN/MAN (or simply WDM LAN) can function using a variety of network architectures. In particular, WDM LANs can transmit packets between two nodes using direct or single-hop transmission or through intermediate nodes using multihop transmission, leading to broadly two types of network architectures: single-hop and multihop. The nodes in WDM LANs can employ two types of transmitters and receivers: tunable transmitter (TT) or fixed transmitter (FT) and tunable receiver (TR) or fixed receiver (FR), giving four types of WDM transceiver configurations: TT-TR, TT-FR, FT-TR, and FT-FR. Of the four configurations, the first three can realize single-hop communication, while the fourth generally leads to multihop networks. In this chapter, we describe various types of passive-star-based WDM LANs and examine their salient performance features. (141 words)

Remote testing for defects in service high-voltage insalators

On the basis of the two-channel remote measurement method previously developed at the Department of PES KGEU, a set of characteristics of the PD with the simultaneous use of electromagnetic and acoustic sensors, which allows you to remotely measure and evaluate the technical condition of high-voltage insulators (HVI). The article presents the results of developments in the development of the previously proposed method, which allowed to determine not only the type and location of the defect, but also its size and the degree of influence on the working condition of the VI. Particular attention is paid to the evolution of defects under the influence of overvoltage and other electrophysical processes in operating conditions. In particular, the generation of ultra-large PDs that can create erosion of the dielectric surfaces of defects was recently discovered, and the technical condition of highvoltage polymer insulators was examined. All measurements were performed on an experimental bench by non-contact receiving pulse signals of the PD by an electromagnetic tunable receiver in the range of 50-600 MHz. Their indication and computer processing were carried out in order to determine in each of the discrete intervals of the phase voltage the average values of the number and intensity of PD pulses, which either do not exceed the allowable threshold for the occurrence of defects and their development, in comparison with the reference HVI, or exceed it. Based on the results of preliminary bench tests on model specimens and real HVIs under operating conditions, and the obtained set of PD parameters, diagnostic signs were established that made it possible to determine the type, location of the most dangerous defects and the degree of their influence on the HVI working capacity. At the same time, the presence of the most dangerous defects is determined by the expansion of the phase intervals of PD radiation, a sharp increase in PD in negative half-periods of high voltage compared with positive half-periods, and also by a significant difference in the width and shape of single PD pulses.