Chapter 20. Transient-Voltage Response

Chapter 20. Transient-Voltage Response - 20...

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20 Transient-Voltage Response Robert C. Degeneff Rensselaer Polytechnic Institute 20.1 Transient-Voltage Concerns. ........................................... 20 -1 Normal System Operation . Sources and Ty pes of Transient-Voltage Excitation . Addressing Transient-Voltage Performance . Complex Issue to Predict 20.2 Surges in Windings . ........................................................ 20 -3 Response of a Simple Coil . Initial Voltage Distribution . Steady-State Voltage Distribution . Transient-Voltage Distribution 20.3 Determining Transient Response. .................................. 20 -6 Histor y . Lumped-Parameter Model . Frequency-Domain Solution . Solution in the Time Domain . Accuracy versus Complexity 20.4 Resonant Frequency Characteristic. ............................... 20 -9 Definitions . Impedance versus Frequency . Amplification Factor 20.5 Inductance Model. ......................................................... 20 -11 Definition of Inductance . Transformer Inductance Model . Inductance Model Validity 20.6 Capacitance Model. ....................................................... 20 -13 Definition of Capacitance . Series and Shunt Capacitance . Equivalent Capacitance for Disk Windings . Initial Voltage Distribution 20.7 Loss Model. .................................................................... 20 -16 Copper Losses . Core Losses . Dielectric Losses 20.8 Winding Construction Strategies. ................................ 20 -19 Design . Core Form . Shell Form . Proof of Design Concept . Standard Winding Tests . Design Margin . Insulation Coordination . Additional System Considerations 20.9 Models for System Studies . .......................................... 20 -24 Model Requirements . Reduced-Order Model 20.1 Transient-Voltage Concerns 20.1.1 Normal System Operation Transformers are normally used in systems to change power from one voltage (or current) to another. This is often driven by a desire to optimize the overall system characteristics, e.g., economics, reliability, ß 2006 by Taylor & Francis Group, LLC.
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or performance. To achieve these system goals, a purchaser must specify—and a designer must configure—the transformer to meet a desired impedance, voltage rating, power rating, thermal charac- teristic, short-circuit strength, sound level, physical size, and voltage-withstand capability. Obviously, many of these goals will produce requirements that are in conflict, and prudent compromise will be required. Failure to achieve an acceptable characteristic for any of these goals will make the overall transformer design unacceptable. Transformer characteristics and the concomitant design process are outlined in the literature [1–4]. Normally, a transformer operates under steady-state voltage excitation. Occasionally, a transformer (in fact all electrical equipment) experiences a dynamic or transient overvoltage. Often, it is these infrequent transient voltages that establish design constraints for the insulation system of the transformer. These constraints can have a far-reaching effect on the overall equipment design. The transformer must be configured to withstand any abnormal voltages covered in the design specification and realistically expected in service. Often, these constraints have great impact on other design issues and, as such, have significant effect on the overall transformer cost, performance, and configuration. In recent years, engineers have explored the adverse effect of transient voltages on the reliability of transformers [5–7] and found them to be a major cause of transformer failure.
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This note was uploaded on 10/19/2010 for the course ENGINEERIN ELEC121 taught by Professor Tang during the Spring '10 term at University of Liverpool.

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Chapter 20. Transient-Voltage Response - 20...

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