Virtual Instrument for Lightning Impulse Tests

Frequency domain correlation technique for PD location in transformer winding

Abstract: Partial discharge (PD) is one of the sources of insulation failures in Power transformers. Knowledge of the PD source locations are important for transformer maintenance and repair. Due to the complex structure of the transformer, it is very difficult to locate the PD accurately in transformer winding. Correlation methods are applied to locate the PD source across the winding. The PD across parts of the winding are simulated by applying voltage pulse across the sections. The winding response for a reference PD impulse across transformer sections are taken as base for correlation and correlated with winding response of PD impulse across any section with different PD pulse widths. In this paper the limitation of time domain correlation method in locating PD in transformer windings is found out. To overcome the limitation of time domain correlation method, frequency domain correlation with Gram Schmidt orthogonalization is proposed. Simulation and experiments are performed on layer, continuous disc and interleaved windings to prove the feasibility of the proposed method.

Real-Time Techniques to Measure Winding Displacement in Transformers During Short-Circuit Tests

Abstract: The ability of a transformer to withstand the dynamic effects of a short circuit test is conventionally evaluated by a measurement of short circuit reactance before and after the test. We propose new techniques for fault detection based on continual assessment during the test. The methods are based on the comparative null method for accuracy measurement in instrument transformers. They include voltage comparison, current comparison and real/reactive power measurements. High resolution sampling based acquisition systems are used to compute changes on a cycle-to-cycle basis. The proposed methods are validated on a number of models including a voltage transformer and a distribution transformer winding. They would be useful for designers in assessing events leading to failure in a more transparent manner.

Comparison of Impulse Wave and Sweep Frequency Response Analysis Methods for Diagnosis of Transformer Winding Faults

Abstract: Monitoring of winding faults is the most important item used to determine the maintenance status of a transformer. Commonly used methods for winding-fault diagnosis require the transformer to exit operation before testing and an external exciting signal, whether the transformer is malfunctioning or not. However, if an overvoltage signal can be regarded as a broadband excitation source for fault diagnosis, then the interference caused by signal injection can be eliminated without the need for additional pulse or impulse signals. In this paper, a tapped transformer is designed and test platforms are built to compare winding diagnoses using the impulse wave and sweep frequency response analysis methods by recording voltage responses on both the high- and low-voltage sides and calculating the respective transfer functions. Based on comparison of statistical indicators, it is found that the sensitivities of both methods are similar for detecting conditions of winding-ground and winding-interlayer short circuits. It is concluded that it is feasible to use a transient overvoltage monitoring system for winding-fault diagnosis.

Statistical Techniques for Partial-Discharge Location in Transformer Windings

Abstract: To locate the partial discharge in transformer windings, statistical techniques are proposed. The experimental studies are performed on a 22-kV prototype interleaved winding to prove the feasibility of the methods.

A technique based on an archimedean copula for the localization of partial discharge in a transformer winding

Abstract: Precise localization of a Partial Discharge (PD) source inside a winding is one of the important tasks for early detection and prevention of catastrophic failure of a transformer. However, due to the highly complex structures of the windings and statistical nature of PD, the exact location of a PD source is quite difficult to discover. In this paper, a technique based on an Archimedean copula is proposed to find the location of a PD source in a transformer winding. The winding responses to the PD signals of known pulse-widths applied at all the sections are taken as reference data. Further, the winding responses, obtained from the PD pulses of random shapes and magnitudes applied across various sections of the winding, are taken as test data. To predict the location of the test signals, the best-fit copula and its parameters are established using the reference and test data. The maximum value of log-likelihood between the reference data and the test signal indicates the location of the PD source. Firstly, simulation case-studies are conducted to demonstrate how the proposed approach can be implemented to locate the PD source. The results of the proposed method are then compared with the time-domain and frequency-domain based correlation techniques. Finally, the proposed method is tested with experimental data acquired from a laboratory scale model of the transformer winding. The simulation and experimental results demonstrate that the proposed approach is capable of achieving an accurate prediction of the location of the PD source.

Design with Operational Amplifiers and Analog Integrated Circuits

Abstract: Franco's "Design with Operational Amplifiers and Analog Integrated Circuits, 3e" is intended for a design-oriented course in applications with operational amplifiers and analog ICs. It also serves as a comprehensive reference for practicing engineers. This new edition includes enhanced pedagogy (additional problems, more in-depth coverage of negative feedback, more effective layout), updated technology (current-feedback and folded-cascode amplifiers, and low-voltage amplifiers), and increased topical coverage (current-feedback amplifiers, switching regulators and phase-locked loops). Table of contents 1 Operational Amplifier Fundamentals 2 Circuits with Resistive Feedback 3 Active Filters: Part I 4 Active Filters: Part II 5 Static Op Amp Limitations 6 Dynamic Op Amp Limitations 7 Noise 8 Stability 9 Nonlinear Circuits 10 Signal Generators 11 Voltage References and Regulators 12 D-A and A-D Converters 13 Nonlinear Amplifiers and Phase-Locked Loops

Transformer Engineering: Design and Practice

Abstract: This reference illustrates the interaction and operation of transformer and system components and spans more than two decades of technological advancement to provide an updated perspective on the increasing demands and requirements of the modern transformer industry. Guiding engineers through everyday design challenges and difficulties such as stray loss estimation and control, prediction of winding hot spots, and calculation of various stress levels and performance figures, the book propagates the use of advanced computational tools for the optimization and quality enhancement of power system transformers and encompasses every key aspect of transformer function, design, and engineering.

Large Power Transformers

Abstract: 1. The Physical Background of Transformer Operation. 2. The Core. 3. The Windings. 4. Stray-Field Losses in Structural Parts of Transformers. 5. Transformer Insulation. 6. Temperature Rise and Cooling of Transformers. 7. Constructional Parts of the Transformer. Subject Index.

Impulse testing of power transformers using the transfer function method

Abstract: The transfer function of a transformer winding is deconvoluted in the frequency domain from the digitally recorded neutral current and high voltage applied during impulse tests. The integrity of the winding insulation is determined by comparing the transfer function obtained at full and reduced test voltage. Differences between the transfer function plots reveal local breakdowns in the winding that can be dissociated from partial discharges. Thus the method permits unambiguous acceptance or rejection if the transformer and, since the transfer function is theoretically immune to changes in the applied impulse, also allows evaluation of the chopped-impulse test. Some 100 windings of large HV power transformers have been tested using the transfer function method, which on several occasions has revealed transformer faults as well a test setup problems that would have been missed or misinterpreted by conventional techniques. >