Viktor Milardić

Selection of Surge Protective Devices for Low-Voltage Systems Connected to Overhead Line

This paper presents a procedure of choosing an appropriate surge protective device for low-voltage systems connected to an overhead line. For a typical surge protection application, an appropriate Electromagnetic Transients Program model is devised. The energy overload is calculated for a surge protective device following a simulation of the lightning effect. This way, it is possible to determine the required class for the surge protective device in question. The procedure has been tested on some typical overhead low-voltage networks. The results of these calculations, as well as very good service experiences, demonstrate that the use of Class II surge protective devices seems to be appropriate for service entrances in buildings that have no lightning protection systems.

Study of time correlation between lightning data recorded by LLS and relay protection

Paper deals with the time correlation between lightning strokes and protection relay pickups. On a line fault, the relay pickup is the first action registered by the protection relay. For this, the pickup time is taken for correlation with lightning data available from the lightning locating system (LLS). The conducted studies have shown the time differences between a lightning stroke and a relay pickup to be up to 28 ms in 85% of the observed cases.

Surge protection of generators directly connected to a medium voltage network

The paper presents the results of the surge protection study of a generator in a small hydro power plant that is directly connected to the overhead network. Overhead lines pass through to the area of high isoceraunic activity with high specific resistance of soil. Lightning striking overhead lines produce voltage transients that can harm insulation of a generator winding. The parameters for the generator model were obtained by calculation and measurement. The simulation model is presented, and results of the simulations are given. The improvement of surge protection is achieved by installation of additional surge arresters connected to generator terminals and at neutral point. It is recommended to conduct surge protection analysis for each generator which is designed to be directly connected to the overhead line.