Božidar Filipović-Grčić

High-Frequency Model of the Power Transformer Based on Frequency-Response Measurements

In this paper, a new high-frequency black-box model of the power transformer is presented for the calculation of transferred lightning overvoltages. The model is based on frequency-response analysis measurements and the application of four-terminal network theory. The computational verification of the presented model was successfully performed on a white-box transformer model in Electromagnetic Transients Program-Restructured Version software. The experimental verification was carried out on 130-kVA and 36-MVA three-phase power transformers. The presented calculation and measurement results confirm the validity of the proposed model for full and chopped lightning impulse voltages.

Artificial neural network approach for locating faults in power transmission system

This paper presents fault location recognition in transmission power system using artificial neural network (ANN). Single phase short circuit on 110 kV transmission line fed from both ends was analysed with various fault impedances, since it is the most common fault in power system. Load flow and short circuit calculations were performed with EMTP-RV software. Calculation results including currents and voltages at both line ends were used for training ANN in Matlab in order to obtain correct fault location and fault impedance, even for those cases that ANN has never encountered before. The network was trained with back propagation algorithm. Test results show that this approach provides robust and accurate location of faults for a variety of power system operating conditions and gives an accurate fault impedance assessment.

Influence of cables on power transmission network frequency response

Harmonic resonance is an important factor to be considered in a power transmission networks during connection of remote generation units with high-voltage cables (e.g. wind or solar power plants etc.). It is known that cable characteristics differs from characteristics of conventional overhead lines. Cable capacitance is far higher than capacitance of an equivalent overhead line, what can potentially lead to the low resonant frequencies which may be triggered by various switching events, such as transformer or shunt reactor energization etc. In this paper, possible consequences of power plant connection to transmission network with long HVAC cable are analyzed, with regard to harmonic resonance and frequency response of the network. The research has been conducted on developed model of the power transmission network in the software for calculation of electromagnetic transients EMTP-RV.

Leader progression model application for calculation of lightning critical flashover voltage of overhead transmission line insulators

The paper presents a method for calculation of lightning critical flashover voltage (CFO) of overhead transmission insulators. The method is based on the application of leader progression model (LPM). CFO was calculated and measured in high voltage laboratory for different polymer and glass insulator strings equipped with arcing horns and grading rings fittings. Comparison of laboratory measurements and calculation results showed that CFO can be determined with good accuracy by using the presented method.