Alen Bernadić

Transient analysis of coupled non-uniform transmission line using finite element method

This paper presents a finite element time domain model for a numerical solution of a coupled non-uniform transmission line problem. On the basis of the finite element method, a novel numerical procedure for the solution of a system of the non-uniform multi-conductor transmission line equations in the time domain is presented. The results obtained by the proposed method have been compared with the solution obtained using the finite difference time domain method, and an excellent correlation has been demonstrated. Copyright

Determining of fault location with Hilbert - Huang transformation on XLPE cables between land and offshore substations

Using of mathematical transformations and digital signal processing (DSP) methods of recorded voltage and currents in power systems in order to extract important informations about physical processes is already known. Higher measuring resolutions and massive introduction of PMU devices in the power systems allows appliance of DSP - based fault location methods in complex power networks. High availability of power systems is required in the modern societies. Fast fault location algorithms and consequent fast repairing of faults is necessary condition for high availability of power networks. Here represented numerical procedure for fault location is testing of method already introduced in scientific papers on complex configuration of power network consists of XLPE underground submarine and land cables between land and offshore substation connecting large wind park with main power system.

Impact of characteristics of block-transformers on inrush currents and voltage distortions at the connection point of wind parks

In the procedure of connecting large wind parks (WP) to the external power grid, TSOs or DSOs request is that WPs in operation do not excessively affect the power quality in the connection point. In the process of determining WP operating procedures it is necessary to include switching operations in the WP main feeder. The transformers connected near the wind generator units are then energized and a transformer inrush current appears, followed usually by voltage distortions. Those currents may cause nuisance tripping of protection devices and power quality problems in the WP connection point. For illustration, the connection to a real power grid of a large WP with twelve generators and block transformers is simulated. Considered network short circuit power is comparable to typical parameters of the transmission or distribution medium-voltage networks. Simulated inrush currents depend on the characteristics of connected devices in the network. Results of our study can be useful for correct protection relay device setting and determining optimal WP exploitation procedures.

Selection of HV equipment for large wind parks connections with power system as stability parameter and direction for network planning

The most important parameter in estimations and calculations of technical adequacy of wind park (WP) connection is short-circuit power in the Point of Common Connection (PCC). Design and planning of wind park substations can be important factor in fulfillment of transmission or distribution system operator (TSO, DSO) grid code. Likewise, selection of high-voltage equipment such as power transformer, power underground cables or overhead lines can have a considerable effect on connection terms. Typical large WP collector substation is considered. Short-circuit power dependence from high-voltage equipment characteristics in Connection Points (CP) of WP is especially examined. Detail computer simulations are elaborated for chosen substation design. The graphs quantifying the most important wind park connection parameters in relation with chosen high voltage equipment and overhead/underground option for interconnection feeder are presented.

Time-Domain Finite Element Method Analysis of Frequency-Dependent Transmission Lines

This paper presents the finite element (FE) time-domain model for numerical solution of frequency-dependent transmission lines (TLs) problem. Based on the finite element method (FEM) and the generalized trapezoidal rule applied to frequency-dependent TL equations, a novel numerical procedure for a solution of a system of the telegraph equations in time domain is presented. The principles of the proposed method, for the sake of simplicity, have been shown to the case of two-conductor TL where frequency-dependent per-unit length TL parameters have been incorporated into the FE local system of equations by the direct convolution algorithm. The proposed numerical method has been tested and compared to the solutions available in the literature, and a good correlation has been demonstrated.