L. van der Sluis

Analysis of Very Fast Transients in Layer-Type Transformer Windings

This paper deals with the measurement, modeling, and simulation of very fast transient overvoltages in layer-type distribution transformer windings. Measurements were performed by applying a step impulse with 50-ns rise time on a single-phase test transformer equipped with measuring points along the winding. Voltages along the transformer windings were computed by applying multiconductor transmission-line theory for transformer layers and turns. Interturn voltage analysis has also been performed. Computations are performed by applying an inductance matrix determined in two different ways; by making use of the inverse capacitance matrix and by making use of the well known Maxwell formulas. The modeling of the transformer and the computations are verified by measurements

Adaptive distance protection of a double-circuit line

Serious power system disturbances are often caused by faults in a weakened power system. In these cases, over-tripping of relays and sympathy trips easily happen because of inappropriate settings. In this paper, the effects of inappropriate settings are shown by the simulation of the distance protection of a double-circuit transmission line. A strategy is presented in this paper for the implementation of artificial neural nets (ANN) in an automated substation keeping the settings of all distance relays in the substation appropriate. The required information and equipment are described. The strategy also serves as a guideline for the use of an ANN.

Stochastic Modeling of Power Demand Due to EVs Using Copula

The driving patterns characterizing electric vehicles (EVs) are stochastic and, as a consequence, the electrical load due to EVs inherits their randomness. This paper presents a Monte Carlo procedure for the derivation of load due to EVs based on a fully stochastic method for modeling transportation patterns. Under the uncontrolled domestic charging scenario three variables are found to be crucial: the time a vehicle leaves home, the time a vehicle arrives home, and the distance traveled in between. A detailed transportation dataset is used to derive marginal cumulative distribution functions of the variables of interest. Since the variables are statistically dependent, a joint distribution function is built using a copula function. Subsequently, simulated EV trips are combined with a typical charging profile so that the energy contribution to the system is computed. The procedure is applied to analyze the effect of the EV load on the national power demand of The Netherlands under different market penetration levels and day/night electricity tariff scenarios.

Computation of very fast transient overvoltages in transformer windings

The paper deals with the computation of very fast transient overvoltages (VFTO) in transformer windings. For this purpose an algorithm is developed. The applied algorithm uses a hybrid model, which is a combination of the multi-conductor transmission line model (MTLM) and the single-transmission line model (STLM). By means of the STLM, the voltages at the end of each coil are calculated. Then, these values are used in the MTLM to determine the distributed overvoltages along the turns. Also, this method significantly reduces the number of linear equations that needs to be solved for each frequency to determine the required voltages in frequency domain. The algorithm uses a modified continuous Fourier transformation that provides an accurate time domain computation. As an example, the inter-turn voltage distributions for two 500 kV auto-transformers are computed and compared with measurements provided by other publications.

Dynamic Stability of Power Systems with Power Electronic Interfaced DG

In this paper, the transient stability of power systems with a high penetration level of power electronic interfaced (converter connected) distributed generation is explored by means of computer simulations. Small 2 and 3 bus test systems are used. The converter is modeled as a three-phase full-bridge IGBT voltage source converter (VSC). The control setting is such that during the actual disturbance the converter connected DG stays connected to the system but with a current limiter. The simulations are performed by using MATLAB SimPowerSystems

Transient Stability Analysis of a Distribution Network With Distributed Generators

This letter describes the transient stability analysis of a 10-kV distribution network with wind generators, microturbines, and CHP plants. The network being modeled in Matlab/Simulink takes into account detailed dynamic models of the generators. Fault simulations at various locations are investigated. For the studied cases, the critical clearing times are calculated. Results obtained from several case studies are presented and discussed.

Adaptive Distance Protection of Double-Circuit Lines using Artificial Neural Networks

Because of the zero sequence mutual coupling of parallel transmission circuits, the distance calculation performed by a ground distance relay is incorrect. This error is influenced by the actual power system condition. Although accounted for by using a large safety margin in the zone boundaries, unexpected overreach can still occur and the operation speed is decreased. Adaptive protection offers an approach to compensate for the influence of the variable power system conditions. By adapting the relay settings to the actual power system condition, the relay will respond more accurately to power system faults. The selectivity of the protection system is increased, as is the power system reliability. In this paper, an adaptive distance relaying concept is presented. In order to minimize the required communication, local measurements are used to estimate the entire power system condition. An artificial neural network is used to estimate the actual power system condition and to calculate the appropriate tripping impedance. Application of this concept to the model of the Dutch 380 kV power system has resulted in an enormous increase in relaying accuracy. The relaying error is reduced substantially. Most importantly, the standard deviation, indicating the relays sensitivity to power system condition variations, is reduced to nearly zero. The zone boundary is kept nearly constant, which facilitates the relay coordination. The selectivity of the entire power system protection system is improved. It is shown that adaptive protection improves the protection system selectivity, and that artificial neural networks can very well be used to estimate the actual power system condition.

Investigating impacts of distributed generation on transmission system stability

Driven by the increasing environmental concerns and the increasing amount of new generation technologies, it is expected that many new generation technologies, including renewable generation, will be connected to the electrical power system. A lot of these new technologies will be connected at the distribution level. When the penetration of this distributed/dispersed generation (DG) is low, the impacts of the DC on the transmission system transient stability may be neglected. However, when the penetration of DG strongly increases, its impact is no longer restricted to the distribution network but begins to influence the whole system. In this paper the impact of DG on the transmission system transient stability is investigated by considering different types of DG technologies and various penetration levels. It is observed that both the types of DG technologies and the penetration levels of DG in the power system have a strong influence on the transmission system transient stability.

Overvoltages in power transformers caused by no-load switching

When an unloaded power transformer is switched on via a relatively long cable, sometimes extreme high voltages appear at the secondary side of the transformer. These overvoltages are caused by a resonant phenomenon that occurs when the resonant frequencies of the transformer and the cable match. The resonant frequency of the cable feeder is equal to the reciprocal of 4 times its travel time /spl tau/. The resonant frequency of the transformer is determined by its short-circuit inductance and the capacitance which is connected to the secondary winding. In this paper a model of this phenomenon is presented and an example of this resonant phenomenon, leading to the insulation breakdown at the secondary side of a power transformer, is given. >

Digital Metering of Power Components According to IEEE Standard 1459-2000 Using the Newton-Type Algorithm

In this paper, a new two-stage Newton-type algorithm for the measurement of power components according to the IEEE Standard 1459-2000 is presented. To estimate their spectra and fundamental frequency, in the first stage, the current and voltage signals are processed, whereas in the second stage, the power components are calculated based on the results obtained in the first stage. The algorithm considers the frequency as an unknown parameter and simultaneously estimates it with the input signal spectrum. Through this, the algorithm becomes insensitive to frequency changes and the problem becomes non-linear. The algorithm performance is tested using computer-simulated and laboratory tests.