Zdenka Benesova

New approach to surge phenomena analysis in transformer winding

The paper deals with very fast transient phenomena in a transformer winding connected to a transmission line. The model of this system is created as a circuit with distributed parameters and it is solved numerically using FDTD method in time domain. It results in the time-space distribution of voltage and current waves along the transmission line and the transformer winding. An influence of the line length and rate of surge wave shape was studied. The obtained results provide a deeper insight into very fast transients in the transformer winding and can be used for more advanced design of insulation and a protection system.

Origin of the circulating currents on the quadrupple EHV/VHV transmission line during the specific operation

This paper is focused on an analysis of mutual influence between the circuits of different voltage level located on the same pylon. The significant consequence of these mutual couplings between all conductors including earth wires is a voltage induced into conductors which results in current asymmetry not only during a specific operations but also during standard operations. In the case, that some circuits are switched-off, the switched-on circuits induce voltage via inductive couplings to the switched-off circuits, which brings some problems for instance the circulating currents in the unloaded line. This phenomenon has been analysed on the quadruple EHV/VHV non-transposed transmission line and the capacitive couplings were neglected.

Modelling of the transients on the multi-circuit EHV/HV overhead transmission lines

This paper describes a method for a common transient analysis for the multi-circuit overhead transmission line. The presented algorithm is based on two-port approach, where the phase conductors and earth wires are modelled by inductive and capacitive coupled cascades of two-ports. For a considered network model, a system of ordinary differential equations (ODE) has been formulated and it has been solved in MATLAB. Obtained results provide the time distribution of currents and voltages in all conductors. In this paper a system with four three-phase system of two voltage levels (EHV and HV) has been analysed. The performed calculations deal with short circuits and the necessary switching. The optimization of the creation of the two-port model has been discussed.

Influence of transmission line wave properties on surge voltage wave propagation

The paper deals with an analysis of transmission line wave properties and their influence on the voltage wave propagation in the system EHV/UHV consisting of a transmission line and a grid transformer where a gas-insulated switchgear (GIS) are set up. Switching on/off operations in the GIS generate pulses with very short rise time it results in travelling wave phenomena which are depending on the type of the line-connection and wave properties of both the line and the transformer. The analysis of the system transmission line-grid transformer was carried-out numerically in time domain and an algorithm based on FDTD has been developed. It provides the time and space distribution of voltage and current waves along the line and the transformer windings.

Surge phenomena in system of transmission line and transformer winding

This paper deals with surge phenomena in the transformer winding which are caused by switching-on processes or by the lightning stroke into the overhead line. In both cases the surge voltage or the current wave propagating via the transmission line into the transformer winding are considered and influence of the transmission lines on a travelling surge wave is studied. The model of the whole system is based on the circuits with distributed parameters and is described with the system of partial differential equations. The mathematical model is solved numerically by FDTD method it results in the time-space distribution of the voltage and the current. It enables to determine the most dangerous points at the winding and to improve a design of the isolation system and system of protections. Some illustrative examples are solved and interesting results are presented.