G.C. Paap

Symmetrical components in the time domain and their application to power network calculations

Although the symmetrical component transformation has existed for 80 years, its application in the time-dependent form is practically restricted to the electric-machine theory. In the power systems field one uses the transformation applied to steady-state sinusoidal phasors in a nonunitary form for fault calculations. For time-domain calculations the real equivalent, 0, /spl alpha/, /spl beta/, is preferred, usually extended to 0, d, q-components. In network calculations, however, the application of time-dependent symmetrical components makes sense, since many net-component parameters are already available in this form. In this paper a short historical overview of the symmetrical-component transformation and the application of unitary and orthogonal transformations are presented. From these general transformations logic choices for base quantities necessary in per unit calculations are derived. The relations between real and complex transformations, steady-state phasors and well-known sequence networks are given and illustrated through the use of some examples with asymmetrical faults.

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.

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. >

On a hysteresis model for transient analysis

The letter describes an approach to a representation of transient behavior due to switching off complex nonlinear circuits. For this purpose the widely known Jiles model (JM) was implemented into the Alternative-Transient-Program (ATP). Calculations have been made on simplified transformer single-phase and three-phase circuits.

PES Digital Library

Surge arresters, which are used to protect transformers against overvoltages, are an important part of the power system. Overvoltages occur because of switching operations of nearby circuit breakers or as a result of lightning strokes. The behavior of the surge arrester during an overvoltage occurrence depends on the amplitude and the shape of the surge. Therefore, it is important to have an understanding of the behavior of the surge arrester when it is stressed by overvoltages with different shapes and amplitudes. The application of a simplified model of a surge arrester is presented. The behavior of the arrester based on its measured volt-ampere characteristic is examined according to the ANSI/IEEE C62.11-1993 standard. The residual voltage of the arrester is calculated for three different current impulses: 8/20 μs, 30/60 μs, and an impulse with a 0.5 μs front-of-wave. The application of the model is presented when it is used for protecting a distribution transformer exposed to voltage escalation and to low-frequency surges.

Unit commitment in multiple energy carrier systems

During the last decade there has been a strong development of energy applications that make use of multiple energy carriers. A new approach is necessary to tackle problems related to planning and operation of energy systems, since conventional techniques are mostly oriented to deal with independent energy carrier infrastructures only. The contribution of this paper is to offer a general unit commitment framework for energy systems that contain multiple energy carriers and to present illustrative examples on the topic. The unit commitment problem is solved using the optimization software AIMMS.

A technique for unit commitment in multiple energy carrier systems with storage

A new approach on the planning and operation of power systems is necessary in order to cope with the characteristics of energy systems with multiple energy carriers, as well as with the intensified integration of renewable energy sources and storage units. This paper proposes a technique to include storage as part of a general unit commitment framework for energy systems that contain multiple energy carriers.

Real-time simulation to study the impact of renewable energy in power systems

A real-time simulation tool, in our case a real-time digital simulator (RTDS), gives the opportunity to study the impact of renewable energy in power systems on a real-time base, driven by actual solar and wind data. In the first part of this paper, the real-time digital simulator (RTDS) is briefly introduced. The application of this analyzing tool is first demonstrated on a detailed model of a wind energy conversion system (WECS) whereas secondly the application on an autonomous power system is shown. Both applications demonstrate the capabilities of this simulator and the added value for power system analysis

The application of a fuel cell-electrolyzer arrangement as a power balancing set-up in autonomous renewable energy systems

Small-scale autonomous renewable energy systems have gained attention during the last years due to growing concerns in relation to an increasing world energy demand and to constraints in CO2 emissions. Polymer electrolyte membrane fuel cells (PEMFC), wind turbines and solar panels are promising zero-emission devices to be incorporated into these systems. In order to integrate them, appropriate control designs are necessary, among other aspects. This paper presents a configuration that allows a proper operation of the fuel cell while the system is able to handle the power fluctuations produced by the wind turbine and the load. An electrolyzer is used to take advantage of the power surplus. The system is designed to supply 10 households, but can be easily extended. The objective of this study is to evaluate the technical feasibility of implementing such a power balancing set-up in DENLab, a renewable energy laboratory at Delft University of Technology, the Netherlands.

Control strategy for an autonomous energy system with electricity and heat flows

This paper presents a control strategy for the operation of an autonomous distributed generation system (DGS) that includes multiple energy carries, storage devices and wind energy. The simulation is performed for the heat and electricity demand of 200 households. The proposed control strategy provides suitable performance results and improved energy efficiency for the system under study.