Models for Design: Electrical Calculations for Industrial Plants PDF
Preview Models for Design: Electrical Calculations for Industrial Plants
Models for Design Electrical Calculations for Industrial Plants Models for Design Electrical Calculations for Industrial Plants Robert E. Henry, PE CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2018 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed on acid-free paper International Standard Book Number-13: 978-1-138-50468-4 (Hardback) International Standard Book Number-13: 978-1-315-14615-7 (eBook) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. 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Contents List of Figures .........................................................................................................xi List of Tables ........................................................................................................xiii Acknowledgments ................................................................................................xv Author ..................................................................................................................xvii 1. Introduction .....................................................................................................1 Fun Test .............................................................................................................4 Questions ......................................................................................................4 Answers ........................................................................................................5 Section I Plant Equipment 2. Using an Uninterruptible Power Supply to Feed a Variable-Speed Drive ..................................................................................9 Introduction ......................................................................................................9 Variable-Frequency Drives ...........................................................................11 Uninterruptible Power Supplies ..................................................................12 Harmonic Distortion .....................................................................................13 Torque .........................................................................................................14 Rotating Inertia ..........................................................................................14 Starting a Fan .............................................................................................17 Starting Ramp Time ..................................................................................18 Mechanical Resonance .............................................................................20 Response Time of a UPS with a Drive’s Load .......................................21 Fan Start Time and Torque .......................................................................21 Motor Efficiency Requirements...............................................................23 An Example ....................................................................................................24 Normal Operation .....................................................................................25 Time Where Load Exceeds Steady Torque ............................................27 Setting the Drive’s Torque Limit in the Drive’s Firmware ..................27 Sizing the UPS for Its Load ......................................................................27 Sizing the UPS Battery ..............................................................................29 Light Loads on Large Motors ..................................................................30 3. Storage Batteries ............................................................................................33 The DC System ...............................................................................................33 Valve-Regulated Lead–Acid Battery ...........................................................36 Battery Selection .............................................................................................37 vii viii Contents Battery Heat Flow ..........................................................................................39 The Battery .................................................................................................39 The Stack ....................................................................................................39 Heat Flow Analysis of the Stack .............................................................40 Exponential Temperature Response of the Stack .................................42 Battery Specific Heat .................................................................................42 Heat Flow Analysis of the Stack in the Cabinet ....................................43 A Different Use of This Battery ....................................................................45 Charging the Battery and Thermal Runaway ............................................46 Section II One-Line Designs 4. The Largest Demand for 13.8 kV Switchgear ..........................................49 Large-Motor Fault Current Contribution ...................................................50 Large Motors ..............................................................................................51 Small Motor Contribution ............................................................................51 Medium-Voltage Motor Control Centers ...................................................52 Maximum Plant Motor Load ...................................................................53 Fault Analysis of the Maximum Plant ...................................................54 Conclusions .....................................................................................................56 Exceptions .......................................................................................................57 5. The Minor Influence of the Grid Thevenin Impedance on Plant Faults ..........................................................................59 6. Use of a Three-Winding Step-Up Transformer .......................................61 Introduction ....................................................................................................61 The Small Off-Power Generating Unit .......................................................62 The Small-Unit Auxiliary Load ....................................................................62 The Transformer .............................................................................................64 Specifying the Transformer ..........................................................................66 Fault Current in the Auxiliary Distribution ...............................................66 Transformer Impedance Values ...................................................................68 Calculating Wye Values ................................................................................69 Values on the Transformer’s Nameplate ....................................................70 Fault-Current Analysis for the Protective Relay System ..........................71 Larger Units ....................................................................................................72 Section III Fast Transient Calculations 7. Analysis of Power Cables Conducting Fast Transient Loads ...............75 Cables in Air ...................................................................................................76 Cables Installed in Conduit ..........................................................................78 Underground Feeders ...................................................................................81 Contents ix Calculation of Time Constants .....................................................................81 Cooldown ........................................................................................................84 Simple Fast Transient Response ...................................................................86 Power Cables Rated 600 V ............................................................................89 Sizing Power Feeders Using the Tables ......................................................89 Cable Assemblies ...........................................................................................90 8. Sizing Power Cables for Fast Transient Loads ........................................91 Developing the Summary Tables 7.2 and 7.5 .............................................92 Low Voltage ....................................................................................................92 Fast Transient Loading of the Motor ...........................................................93 Fast Transient Loading of the Motor’s Feeder ...........................................93 Fast Transient Loading of Variable-Speed Drives .....................................94 Summary .........................................................................................................94 9. Introduction to Motor Fast Transient Loading ........................................95 A Mining Company Project ..........................................................................95 General Response ...........................................................................................96 10. Fast Transient Motor Analysis ....................................................................99 Background .....................................................................................................99 The Circuit Used for Analysis ....................................................................101 Varying Reactance ........................................................................................102 Torque ............................................................................................................103 Summary .......................................................................................................104 11. Calculation of the Motor’s Temperatures ...............................................105 Thermal Model .............................................................................................105 Motor Thermal Capacitances .....................................................................105 Temperature Rise Rating .............................................................................106 Evaluating Thermal Circuit Elements .......................................................107 Operating Time at 1300 lb-ft of Torque .....................................................107 Cooldown to 200 Hp Operation: Extended Cycle ...................................109 The More Severe Operating Cycle .............................................................110 Afterthought on the Thermal Resistances ................................................111 Summary .......................................................................................................112 12. Motor Conclusions .....................................................................................113 Frame Size .....................................................................................................113 Purchasing Requirements ...........................................................................114 13. Line Design ..................................................................................................117 The Load ........................................................................................................117 Cable Ampacity and Size ............................................................................118 Cable Temperature .......................................................................................119
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