The paper presents a methodology with a new simplified approach, as a set of procedures, aiming to optimize the insulation level when compacting 400-kV overhead transmission lines (OTLs) in order to increase their operational reliability. The procedure initiates from presupposed requirements for compaction, as it is becoming increasingly more difficult to carry out reconstruction, revitalization, or construction of new OTLs while keeping the original design criteria. The main purpose of this approach is to reduce transients on the insulation, which are caused by direct lightning strikes to the tower top, and influence switching overvoltages using an additional shield wire on OTLs. The insulation leader progression model E 50% and the dynamic ionization model E ion for grounding with the constant ratio between the tower grounding resistance R g and specific ground resistivity ρ g are used to evaluate the lightning transients. For the analysis, the switching overvoltages phase domain transmission line model is used, where OTLs are divided into a number of short segments. For the purpose of this investigation, a mathematical model of a double-circuit compact OTL is implemented.

No abstract

The reliability of operation of a nuclear power plant substantially depends on the reliability of its individual components. Electric cables, particularly medium-voltage cables, represent an important constituent of the nuclear island as well as of the balance of the plant. It cannot be considered as satisfactory that the redundancy of a particular subsystem is ensured. For this purpose, it is important to check the cable insulation condition, which is supposed to be carried out during the overhaul activities. The lifetime of medium-voltage cables is estimated to attain somewhere around 40 years. However, due to electrical, thermal, and mechanical stresses, it may be significantly reduced. In order to avoid its likely failures and following outages, the insulation must be tested regularly. Based on obtained testing results, the condition of a cable or cable termination can be assessed and repaired or a replacement made, if necessary. The paper presents some of the most important nondestructive diagnostic measurements on cable connections recommended to be done during the overhaul of a nuclear power plant following a good practice of asset maintenance management.

No abstract

No abstract