This paper deals with investigation of the impulse characteristics of transmission line tower grounding. Investigations of the impulse characteristics of transmission lines tower grounding in this paper are based on experimental analysis conducted on type “A” grounding of transmission line tower. Firstly, paper describes the problem of back-flashover and impact of transmission lines tower grounding impedance on it. Also, experimental investigation of impulse characteristics with different rise time of current wave front on real type “A” grounding are given. Finally, detail analysis of experimental data is given.

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.

Investigations of electric and magnetic fields on 400 kV transmission lines Tuzla-Visegrad, Sarajevo 10-Sarajevo 20, Tuzla-Ugljevik and 220 kV transmission line Kakanj-Zenica are performed. These transmission lines are important objects for operation of electric power system of Bosnia and Herzegovina. In the paper measurements of extra low frequency (ELF) electric and magnetic fields (EMF) of single 220 and 400 kV overhead transmission lines with flat conductor arrangement but with different horizontal distances between phases and different heights above ground are presented. These electric and magnetic field measurements are also compared with calculations results performed with two software programs (one commercially available and one developed by authors on the base of a solver). Also, in the paper the parameters influencing electric and magnetic fields measurements are investigated.

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.

Very fast electromagnetic transients (VFT) in air insulated substations (AIS) and gas insulated substations (GIS) caused by switching operation of disconnectors are investigated. Results obtained from very extensive field tests and from digital simulations as well as a comparison between field tests and calculation results of VFT in AIS and GIS due to disconnector switching are presented. Field tests of disconnector switching in 220 kV air insulated substations Grabovica and Kakanj as well as test circuit of 110 kV GIS section are performed. Digital simulation of VFT for different models of power network are performed using EMTP-ATP.

In the paper are presented results of switching overvoltages investigations, produced by operations of air disconnector rated voltage 220 kV. Measurements of these switching overvoltages are performed in the air-insulated substation HPP Grabovica on River Neretva, which is an important object for operation of electric power system of Bosnia and Herzegovina. Investigations of operating of air disconnector type Centre-Break were performed in order to determine switching overvoltage levels that can lead to relay tripping in HPP Grabovica. During operations of disconnector (synchronization or disconnecting of generator from network) malfunctions of signalling devices and burning of supply units of protection relays were appeared. Also, results of computer simulations using EMTP-ATP [1] are presented.