Jens Tepper

Simulation and Measurement of Lightning-Impulse Voltage Distributions Over Transformer Windings

This paper presents: 1) a novel method for accurate high-frequency modeling of dry-type transformer windings based on magnetic and electric field simulations for parameter extraction of the detailed equivalent circuit of the entire winding system; 2) a method for fast and accurate transient solution of the circuit differential equations that describe the voltage distribution over the winding system; 3) an efficient, cheap, and nondestructive low-voltage measurement system based on a self-developed lightning-impulse generator; and 4) verification of the simulation results by comparison with measurement.

A novel current limitation principle basedon application of liquid metals

In this paper, a new current limiting principle based on the application of liquid metals is proposed. This principle takes advantage of the arcless commutation of currents to a gradually increasing parallel resistance and makes it possible to realize a current-controlled resistor for very high currents, which can be used to limit the fault currents in power networks. The conditions for the arcless current commutation are investigated theoretically and the optimum profile for the parallel resistor is derived. An experimental setup is constructed to investigate the behavior of the separating contacts under different current amplitudes, different current steepnesses, and different resistance profiles. The experimental results relating to the commutation phase are compared to the theoretical limits

On the arcless commutation of currents higher than 1 kA

A new current limiting principle based on the application of liquid metals is proposed. This principle takes advantage of the arcless commutation of currents to a gradually increasing parallel resistance and makes it possible to realize a current-controlled resistor for very high currents, which can be used to limit the fault currents in power networks. The conditions for the arcless current commutation are investigated theoretically and the optimum profile for the parallel resistor is derived. An experimental set-up is constructed to investigate the behaviour of the separating contacts under different current amplitudes, different current steepnesses and different resistance profiles. The experimental results relating to the commutation phase are compared to the theoretical limits.

Computational and Experimental Investigation of Distribution Transformers Under Differential and Common Mode Transient Conditions

Electromagnetic (EM) modeling of transformers is crucial for the prediction of critical behavior (short-circuit, overvoltage etc.) of the entire system. Time domain simulations and measurements have been performed in order to model the behavior of dry-type transformers under transient overvoltages in Common and Differential Mode configurations. This analysis and the developed method allow investigations of possible means of protection (or their possible redundancy) of the transformer against uncommon transients experienced in real circumstances that might exceed the dielectric stresses the transformer was designed for. For this purpose, an existing, detailed computational model [1] has been further developed, and the results have been benchmarked against measurements.

Computational and experimental investigation of distribution transformers under differential and common mode transient conditions

Electromagnetic modeling of transformers is of paramount importance for the prediction of the transient behavior of the entire system during atmospheric overvoltages and switching transients. Time domain simulations and measurements have been performed to model the behavior of dry-type transformers under transient overvoltages in different configurations. This analysis and the developed method allow investigations of possible means of protection (or their possible redundancy) of the transformer against uncommon transients experienced in real circumstances that might exceed the dielectric stresses the transformer was designed for. For this purpose, an existing, detailed computational model has been further developed, and the results have been benchmarked against measurements.