The Paper comprises research about influential parameters on test circuits which are used for exploring impulse grounding characteristics. On the basis of conducted experimental research on horizontal grounding, using atmospheric discharge currents, amplitudes of 2.5 kA and 2.3 kA, front time of 4 μs, obtained the impulse characteristics of these grounding electrodes length 10 and 20 m, respectively. For specific test circuit a computer model was formed and it was based on the well known ATP-EMTP which gave a good comparison of the results. Using this approach computational studies of influential components of concentrated grounding test circuits were performed.

High voltage transmission network in Bosnia and Herzegovina registered significant values of power frequency overvoltages which lasted quite long. This paper identified levels of temporary overvoltages on the basis of measurement results in an annual period during 2010 in specific points of 220 kV and 400 kV network. Measurements were made that exceeded upper voltage limits in relation to referential voltages and their duration for the considered measurement time. In order to indicate the problem of overvoltages in the transmission network additional voltage measurements were made during 2011 in a specific point Mostar 4, on the 440 kV side and in a point Prijedor 2, on the 220 kV side. For specific 220 kV and 400 kV overhead lines overvoltage calculations were made by using ATP-EMTP. Comparison with the measured values indicated good correlation of the measurement results and the calculation. The paper indicates the need for new methods of implementation in order to reduce overvoltages since the existing methods are not sufficient.

Abstract This article presents the results of investigating switching overvoltages caused by the operation of disconnectors in air-insulated substations rated at 220 kV. Measurements of switching overvoltages were performed in air-insulated substations at the Hydro Power Plant Grabovica on the River Neretva and at the Thermo Power Plant Kakanj. These power plants are of great importance to the operation of the electric power system in Bosnia and Herzegovina. Operation of air disconnectors was investigated in order to determine the switching overvoltages' shapes and levels in primary and secondary circuits, which could cause malfunctioning of signaling devices or burning of protection relays' supply units. Results of computer simulations using an electromagnetic transients program are presented. Comparison of measured and calculated overvoltage values confirms their concordance. These comparisons proved computer calculation to be useful for investigating transient overvoltages due to disconnector switching. Furthermore, experimental and computing investigations on the 220-kV switchyard of the Hydro Power Plant Grabovica demonstrate an influence of substation's elements on the waveform of switching overvoltages.

In this paper, switching overvoltages due to disconnector switching in air-insulated substations (AISs) are presented. Measurements of these switching overvoltages were performed in the AIS Grabovica (Hydro Power Plant-HPP Grabovica) on River Neretva and the AIS Kakanj (Thermo Power Plant-TPP Kakanj). These power plants are important objects for operation of Bosnia and Herzegovina's electric power system. Investigations of operating of air-disconnector-type centre break was performed in order to determine switching-overvoltage levels on primary and secondary circuits that can lead to relay tripping in AIS Grabovica and AIS Kakanj. During operations of disconnector (synchronization or disconnecting of generator from network), malfunctions of signaling devices and burning of supply units of protection relays appeared. At the same time, sparking between primary terminals of the instrument current transformer occurred. The influence of resistance of electric arc between the contacts of the disconnector is analyzed. Computer simulations by means of alternative transients program-electromagnetic transients program are performed. Differences between the measured and the calculated values were under 4.52% for overvoltage factor and under 2.56% for overvoltage wave frequency. Comparison of the transient computer simulations with the field measurements showed that calculations could be used for the assessment of the transient overvoltages caused by disconnector switching.

Switching overvoltages due to disconnector switching in air-insulated substations (AIS) are presented. Analysis of shape and levels of switching overvoltages by means of experimental and computing investigations on 220 kV switchyards of Thermo Power Plant (TPP) Kakanj are presented. Computer simulations by means of EMTP-ATP [1] are performed.

Switching overvoltages due to disconnector switching in air-insulated substations are presented. Shapes and levels of switching overvoltages by means of experimental and computing investigations on 220 kV switchyards of Public Enterprise Elektroprivreda Bill are presented. The influence of resistance of electric arc between the contacts of disconnector is analysed. Computer simulations by means of EMTP-ATP are performed. Differences between the measured and the calculated values were under 4.52% for overvoltage factor, and under 2.56% for overvoltage wave frequency. Comparison of the transient computer simulations with the field measurements showed that calculations could be used for assessment of the transient overvoltages caused by disconnector switching.