Chapter 9. Constant-Voltage Transformers

Chapter 9. Constant-Voltage Transformers - 9...

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9 Constant-Voltage Transformers Arindam Maitra Anish Gaikwad Arshad Mansoor Douglas Dorr Electric Power Research Institute Ralph Ferraro Ferraro, Oliver and Associates 9.1 Background. ......................................................................... 9 -1 History of Constant-Voltage Transformers . What Is a Constant-Voltage Transformer? . The Working of a Constant-Voltage Transformer . Voltage Regulation on the Customer Side . What Constant-Voltage Transformers Can and Cannot Do 9.2 Applications . ........................................................................ 9 -8 Application Considerations—Sizing Guidelines . Application Considerations—Output Performance under Varying Supply Conditions . Application Considerations—Output Performance under Dynamic Supply Conditions . Application Considerations—CVT Electrical Characteristics during Linear and Nonlinear Loading . Application Considerations—Using Three-Phase Input 9.3 Procurement Considerations. ........................................... 9 -17 What to Look for When Purchasing a Constant-Voltage Transformer 9.4 Typical Service, Storage, and Shipment Conditions . ..... 9 -20 9.5 Nameplate Data and Nomenclature . ............................... 9 -21 9.6 New Technology Advancements. ...................................... 9 -21 9.7 Addendum . ........................................................................ 9 -21 9.1 Background Constant-voltage transformers (CVT) have been used for many years, primarily as a noise-isolation device. Recently, they have found value when applied as a voltage-sag protection device for industrial and commercial facilities. The purpose of this section in the handbook is to give power-system engineers and facility engineers who are unfamiliar with the CVT technology (also known as ferroresonant transformers) the insights and information necessary to determine the types of electric-service-supply events that CVTs can mitigate. Items covered in this chapter include operation, characteristics, appli- cations, specifications, and sizing guidelines of CVTs. The goal here is not to duplicate information currently available but, rather, to collect information into a single location and then supplement it to provide: . Adequate information and procedures to applications personnel in effectively selecting CVTs for voltage-sag ride-through protection . Application notes to demonstrate how CVTs can improve process voltage-sag ride-through ß 2006 by Taylor & Francis Group, LLC.
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9.1.1 History of Constant-Voltage Transformers The industrial use of constant-voltage transformers (also called CVTs and ferroresonant transformers) goes back to the early 1940s. Living in the U.S. during the 1930s, Joseph G. Sola, a German-born engineer, discovered the CVT technology [1,2] based on a single transformer rather than an arrangement of transformers, separate filters, and capacitors. This innovation provides several important advantages: its inherent robustness (CVT consists of just three or four windings and a high-reliability capacitor), its imperviousness to continuous short circuits (whether it is turned on into a short circuit or from full load), and its capability to maintain output-voltage stabilization on a cycle-to-cycle basis for signifi- cantly large overvoltages and undervoltages.
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Chapter 9. Constant-Voltage Transformers - 9...

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