No abstract

Investigations of the electromagnetic interference indicate that disconnecting switching of the off-loaded busbars is one of the most important sources of electromagnetic interference in the secondary circuits of a power station. Disconnector's contacts in air-insulated substations (AIS) move slowly causing numerous strikes and restrikes between contacts. Every strike causes high-frequency currents (from a few hundred kHz to a few MHz) tending to equalize potentials at the contacts. These travelling current and voltage waves are the most important sources of electromagnetic coupling to the secondary circuits of instrument transformers, on whose ends high-speed and lowpower electronic devices are connected. During disconnector switching malfunctioning of auxiliary circuits can occurred. In this paper results of measurements of overvoltages in the secondary circuits in the AIS Grabovica (Hydro Power Plant -HPP Grabovica) and AIS Kakanj are presented. In order to reduce overvoltages in secondary circuits, measures for mitigation of electromagnetic interference are presented.Index Terms-Switching, overvoltages, air insulated substation (AIS), disconnector, electromagnetic interference (EMI), disconnecting circuit breaker (DCB), secondary circuits.

There are numerous practical problems for which we need to know the spatial distribution of artificialy created electromagnetic fields, generated by the human due to advances in technology and widespread use of electrical devices. Low frequency electromagnetic fields around power transmission and distribution networks are time-varying quasistatic electromagnetic fields that have a conservative (non swirling) component of low frequency electric field caused by charges and low frequency swirling component of the magnetic field caused by currents. Compactization of power facilities or devices, reducing the mass of the conductors, the calculation of swirling currents or induced electromotive forces in low frequency circuits, designing of structures for a human protection from electromagnetic fields as well as designing of the facility itself, are only some of the practical issues where the knowledge about time changing of spatial distribution of electromagnetic field is essential. This paper elaborates the results of three-dimensional calculation of stationary, sinus variable low frequency electromagnetic fields of the wind turbine, with complex configuration of elements, consisting of 7 wind aggregates, rated power 1.5MW, type LTW77-1.5, the manufacturer Leitwind, in the software package EFC-400. Analyzing of these calculation results is necessary to point at possible weak spots and give a proposal for measures for elimination of the electromagnetic influences or reducing them to acceptable level.