Winding deformation in power transformers can be measured externally using a new frequency response analysis (FRA) method Field experience since 1975, on five separate transformers up to 550 MVA rating, 230kVclassindicatesthatthismethod hasadvantagesover the low voltage impulse (LVI) method as a practical maintenance tool. Results on suspect transformers indicate that benchmark reference data is not always necessary to identify certain kinds of mechanical damage.

Transformer Diagnostic Testing by Frequuency Response Analysis

A complete, three phase transformer model for the calculation of electromagnetic transients is presented. The model consists of a set of state equations solved with the trapezoidal rule of integration in order to obtain an equivalent Norton circuit at the transformer terminals. Thus the transformer model can be easily interfaced with an electromagnetic transients program. Its main features are: (a) the basic elements for the winding model are the turns; (b) the complete model includes the losses due to eddy currents in the windings and in the iron core; and (c) the solution of the state equations is obtained in decoupled iterations. For validation, the frequency response of the model is compared with tests on several transformers. Applications to the calculation of transients are given for illustration. >

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Complete transformer model for electromagnetic transients

This paper presents a method for calculating terminal and internal impedance versus frequency for a lumped parameter model of a transformer The transformer's total frequency response can be accurately determined from this impedance data directly, ie, the terminal resonance and anti-resonance and internal amplification factor characteristic can be calculated for a single or three-phase transformer model Since most equipment associated with power system operation can be accurately modeled with lumped parameter networks, this method also provides an accurate, straightforward method for determining the resonance characteristic of those systems An additional significance of this method is that the accuracy of the calculation is limited only by the user's ability to represent the equipment or system Heretofore, the accuracy of this calculation was limited by the simplifying assumptions required of the network model by each solution method This paper presents the definitions and mathematical theory underlying the method Two examples are presented in which comparisons are made between measured and calculated values for a helical air core coil and a 200 MVA single-phase autotransformer The agreement is excellent

A general method for determining resonances in transformer windings

This paper presents a detailed model for simulation of a Superconducting Magnetic Energy Storage (SMES) system. SMES technology has the potential to bring real power storage characteristic to the utility transmission and distribution systems. The principle of SMES system operation is reviewed in this paper. To understand transient and dynamic performance of a SMES system, a detailed SMES system benchmark model is given with extensive simulation results. This system is demonstrated using an electromagnetic transient program-PSCAD/EMTDC.

Detailed modeling of superconducting magnetic energy storage (SMES) system

This paper presents the application of a combined adaptive Fourier filtering technique and fault detector to fast distance protection of transmission lines. The filtering technique is extended from the Fourier filters and can be applied under arbitrary data window length. The proposed filtering technique possesses the advantage of recursive computing, and a decaying dc offset component is removed from fault signals by using an adaptive compensation method. A variable data window scheme is embedded in the technique to adaptively speed up its transient response under various system and fault conditions. A fault detector is developed to initiate the process of the technique. For the sake of speed and security, two phasor estimation methods based on the proposed technique are designed to achieve fast distance protection. An algorithm consisting of the two methods is used to detect internal faults by "OR" logic. Extensive simulation studies show that the algorithm significantly reduces tripping time of a distance relay and provides better protection performance than that of the conventional filters with fixed data windows.

Application of combined adaptive Fourier filtering technique and fault detector to fast distance protection

Some recent transformer failures have been attributed to part-winding resonances excited by a form of switching surge voltage pulse which produced internal overvoltages. This paper takes a tutorial approach to relate a transformer winding to an equivalent electrical network which can exhibit resonant effects both at its terminals and internally. The relationship between the resonance phenomenon and pulse response is explained and illustrated with practical examples for the standard test waveforms. A proposed alternative switching surge waveform is examined for its effect on the internal response of transformer windings. The material presented should promote the understanding required for consideration of changes in standard test waveforms.

Response of Transformer Windings to System Transient Voltages

Recent investigations of systems involving vacuum switching have forced a reappraisal of the traditional protection methods necessitating major changes in protection philosophy. The new philosophy has been developed on industrial systems supplying are furnace transformers where the exceedingly large number of switchings makes such systems particularly sensitive. This paper discusses a new transient voltage protection system which has been developed in response to these recent investigations. In support of the development of the new protection system, transient voltage measurements have been made on 14 are furnace systems at various locations within the United States and abroad. This paper also documents the instrumentation used to monitor transients on these systems and describes its application. Typical oscillographic records are presented as indications of the performance of the system with and without the new transient voltage protection system.

T. J. Blalock

Papers

Response of Transformer Windings to System Transient Voltages

Extensive field measurements support new approach to protection of arc furnace transformers against switching transients