Handbook of Large Turbo-Generator Operation and Maintenance

GEOFF KLEMPNER, BASc, is a large generator specialist, located in Toronto, Canada. He is an IEEE Fellow and has served on numerous IEEE committees and standards working groups for large generators and is also a contributor to CIGRE on large rotating electrical machines. ISIDOR KERSZENBAUM, PHD, is an IEEE Fellow, located in Irvine, CA. He is a generator specialist consulting to power plants on operation, maintenance and trouble-shooting of large motors and generators.

• Preface xxiAcknowledgments xxviiI THEORY, CONSTRUCTION, AND OPERATION1 PRINCIPLES OF OPERATION OF SYNCHRONOUS MACHINES 31.1 Introduction To Basic Notions On Electric Power 41.1.1 Magnetism and Electromagnetism 41.1.2 Electricity 71.2 Electrical–Mechanical Equivalence 81.3 Alternating Current (ac) 81.4 Three-Phase Circuits 201.5 Basic Principles of Machine Operation 221.5.1 Faraday’s Law of Electromagnetic Induction 221.5.2 Ampere–Biot–Savart’s Law of Electromagnetic-Induced Forces 221.5.3 Lenz’s Law of Action and Reaction 231.5.4 Electromechanical Energy Conversion 241.6 The Synchronous Machine 261.6.1 Background 261.6.2 Principles of Construction 281.6.3 Rotor Windings 321.6.4 Stator Windings 341.7 Basic Operation of The Synchronous Machine 371.7.1 No-Load Operation 441.7.2 Motor Operation 461.7.3 Generator Operation 471.7.4 Equivalent Circuit 471.7.5 Machine Losses 50Additional Reading 502 GENERATOR DESIGN AND CONSTRUCTION 532.1 Stator Core 552.1.1 General Construction Features 552.1.2 Insulated versus Noninsulated Cores 602.1.3 Cores Built with Consolidated “Donuts” 622.1.4 Robotic versus Hand Core Stacking 622.1.5 Core Stacking Pressure and Tightness 632.2 Stator Frame 642.2.1 General Construction Features 642.2.2 Caged Core Design 662.2.3 Grounding of Stator Frames 662.3 Flux and Armature Reaction 672.4 Electromagnetics 702.5 End-Region Effects and Flux Shielding 742.5.1 Stator Core-End Copper Flux Shields/Screens 752.5.2 Stator Core-End Flux Shunts 772.5.3 Combination Stator Core-End Flux Screens and Flux Shunts 782.5.4 Stator Core-End Packet Stepping 782.5.5 Stator Core-End Tooth Slitting 812.5.6 Keybar Shorting Straps 832.6 Stator Core and Frame Forces 842.7 Stator Windings 852.7.1 Stator Winding Configuration and Installation Overview 852.7.2 Overview of Stator Winding Design Considerations 892.7.3 Fundamental Concepts 932.7.4 Winding Structure 942.7.5 Winding Specific Layouts 952.7.6 Basic Formulae 962.7.7 Conductor Bar Construction 982.8 Stator Winding Wedges 1112.9 End-Winding Support Systems 1142.10 Stator Terminal Connections 1172.11 Rotor Forging 1182.12 Rotor Winding 1242.13 Rotor Winding Slot Wedges 1312.14 Amortisseur (Damper) Winding 1332.15 Retaining Rings 1332.16 Bore Copper and Terminal Connectors 1432.17 Slip/collector Rings and Brush Gear 1472.18 Rotor Couplings 1492.19 Rotor Turning Gear 1512.20 Bearings 1522.21 Air and Hydrogen Cooling 1522.21.1 Basic Cooling Arrangements 1552.22 Rotor Fans 1562.23 Hydrogen Containment 1582.23.1 Journal-Type Hydrogen Seals 1612.23.2 Thrust Collar-Type Hydrogen Seals 1612.24 Hydrogen Coolers 1622.25 Air Coolers 1642.26 Water-Cooled Rotors 165References 1663 GENERATOR AUXILIARY SYSTEMS 1693.1 Lube-Oil System 1703.2 Hydrogen Cooling System 1703.3 Seal-Oil System 1733.4 Stator Cooling Water System 1763.4.1 System Components 1773.4.2 Stator Cooling Water Chemistry 1803.4.3 Stator Cooling Water System Conditions 1853.5 Exciter Systems 1873.5.1 Types of Excitation Systems 1873.5.2 Excitation System Performance Characteristics 1923.5.3 Field Discharge Resistor 1933.5.4 Automatic Voltage Regulator 1963.5.5 Power System Stabilizer 1984 OPERATION AND CONTROL 2014.1 Basic Operating Parameters 2024.1.1 Machine Rating 2024.1.2 Apparent Power 2034.1.3 Power Factor 2054.1.4 Real Power 2084.1.5 Reactive Power 2094.1.6 Terminal Voltage 2104.1.7 Stator Current 2104.1.8 Field Voltage 2124.1.9 Field Current 2124.1.10 Speed 2124.1.11 Hydrogen Pressure 2124.1.12 Hydrogen Temperature 2134.1.13 Short-Circuit Ratio 2144.1.14 Volts Per Hertz and Overfluxing Events 2144.2 Operating Modes 2214.2.1 Shutdown 2214.2.2 Turning Gear 2224.2.3 Run-Up and Run-Down 2244.2.4 Field Applied Off-Line (Open Circuit) 2264.2.5 Synchronized and Loaded (Online) 2264.2.6 Start-Up Operation 2274.2.7 Online Operation 2284.3 Machine Curves 2294.3.1 Open-Circuit Saturation Characteristic 2294.3.2 Short-Circuit Characteristic 2294.3.3 Capability Curves 2294.3.4 V-Curves 2354.4 Special Operating Conditions 2374.4.1 Unexcited Operation (“Loss-of-Field” Condition) 2374.4.2 Negative-Sequence Currents 2414.4.3 Off-Frequency Currents 2424.4.4 Load Cycling and Repetitive Starts 2434.4.5 Overloading 2444.4.6 Extended Turning Gear Operation 2454.4.7 Loss of Cooling 2474.4.8 Overfluxing 2484.4.9 Overspeed 2564.4.10 Loss of Lubrication Oil 2564.4.11 Out-of-Step Synchronization and “Near” Short Circuits 2574.4.12 Ingression of Cooling Water and Lubricating Oil 2594.4.13 Under- and Overfrequency Operation (U/F and O/F) 2594.4.14 Brushes Bouncing Off the Sliprings due to Eccentricity and/or Vibration 2614.5 Basic Operation Concepts 2634.5.1 Steady-State Operation 2634.5.2 Equivalent Circuit and Vector Diagram 2644.5.3 Power Transfer Equations 2644.5.4 Working with the Fundamental Circuit Equation 2704.5.5 Parallel Operation of Generators 2734.5.6 Stability 2764.5.7 Sudden Short Circuits 2904.6 System Considerations 2914.6.1 Voltage and Frequency Variation 2924.6.2 Negative-Sequence Current 2924.6.3 Overcurrent 3024.6.4 Current Transients 3024.6.5 Overspeed 3034.7 Grid-Induced Torsional Vibrations 3034.7.1 Basic Principles of Shaft Torsional Vibration 3034.7.2 Spring Model of a Turbo-Generator Shaft Train 3054.7.3 Determination of Shaft Torque and Shaft Torsional Stress 3084.7.4 Material Changes Due to Torsional Vibrations 3084.7.5 Types of Grid-Induced Events 3084.7.6 Monitoring of Torsional Vibration Events 3154.7.7 Industry Experience and Alleviation Techniques 3154.8 Excitation and Voltage Regulation 3164.8.1 The Exciter 3164.8.2 Excitation Control 3174.9 Performance Curves 3184.9.1 Loss Curves 3184.9.2 Efficiency Curves 3194.10 Sample of Generator Operating Instructions 319References 3305 MONITORING AND DIAGNOSTICS 3315.1 Generator Monitoring Philosophies 3325.2 Monitoring Versus Protection: Definition and Practice 3335.3 Extent of Monitoring Versus Cost and Benefits 3355.4 Simple Monitoring With Static High-Level Alarm Limits 3355.5 Dynamic Monitoring With Load-Varying Alarm Limits 3365.6 Artificial Intelligence Diagnostic Systems 3425.7 Monitoring A Single Parameter Versus A Multifunction Instrument 3455.8 Monitored Parameters 3465.8.1 Generator Electrical Parameters 3475.8.2 Stator Core and Frame 3525.8.3 Stator Winding 3645.8.4 Rotor 3915.8.5 Excitation System 4095.8.6 Hydrogen Cooling System 4105.8.7 Lube-Oil System 4155.8.8 Seal-Oil System 4185.8.9 Stator Cooling Water System 421References 4276 GENERATOR PROTECTION 4296.1 Basic Protection Philosophy 4296.2 Generator Protective Functions 4316.2.1 Protection Alarm Response 4346.2.2 Protection Trip Response 4356.3 Brief Description of Protective Functions 4356.3.1 Synchronizer and Sync-Check Relays (Functions 15 and 25) 4366.3.2 Short-Circuit Protection (Functions 21, 50, 51, 51V, and 87) 4366.3.3 Volts/Hertz Protection (Function 24) 4396.3.4 Over- and Undervoltage Protection (Functions 59 and 27) 4436.3.5 Reverse Power Protection (Function 32) 4436.3.6 Loss-of-Field Protection (Function 40) 4456.3.7 Stator Unbalanced Current Protection (Function 46) 4456.3.8 Stator and Rotor Thermal Protection (Function 49) 4476.3.9 Voltage Balance Protection (Function 60) 4486.3.10 Time Overcurrent Protection for Detection of Turn-to-Turn Faults (Function 61) 4496.3.11 Breaker Failure Protection (Function 62B) 4506.3.12 Rotor Ground-Fault Protection (Function 64F) 4516.3.13 Stator Ground Fault Protection (Functions 27, 51, 59) 4536.3.14 Stator Ground Fault Protection Utilizing Third Harmonic-Based Relays 4546.3.15 Stator Ground Fault Protection by Low-Frequency Injection 4556.3.16 Over-/Underfrequency Protection (Function 81) 4556.3.17 Out-of-Step Operation (Loss of Synchronism, Function 78) 4566.4 Specialized Protection Schemes 4576.4.1 Protection against Accidental Energization 4576.4.2 dc Field Ground Discrimination 4596.4.3 Vibration Considerations 4626.4.4 Operation of the Isolated-Phase Bus (IPB) at Reduced Cooling and Risks from H2 Leaks into the IPB 4636.4.5 Calculation of the H2–Air Mixture in the IPB for a Given H2 Leak from the Generator into the IPB 4656.4.6 Calculation of Stator and Rotor Amortisseur Motoring Currents 4726.4.7 Numerical Example for Calculating Rotor Amortisseur Motoring Currents 4746.4.8 Voltage Across Field Terminals During an Induction Motoring or Generation Event 4746.5 Tripping and Alarming Methods 475References 477II INSPECTION, MAINTENANCE, AND TESTING7 INSPECTION PRACTICES AND METHODOLOGY 4817.1 Site Preparation 4817.1.1 Foreign Material Exclusion 4817.1.2 Foreign Material Exclusion: Procedures 4877.2 Experience and Training 4907.3 Safety Procedures 4917.3.1 Mechanical Obstacle Avoidance and Electrical Clearances 4917.3.2 Confined Space Entry 4957.3.3 Plan for Emergency Extraction 4967.4 Inspection Frequency 4967.5 Generator Accessibility 4977.6 Inspection Tools 4997.7 Inspection Forms 505References 5208 STATOR INSPECTION 5218.1 Stator Frame and Casing 5228.1.1 External Components 5228.1.2 Internal Components 5368.1.3 Caged Stator Cores–Inspection and Removal 5478.2 Stator Core 5498.2.1 Stator Bore Contamination 5498.2.2 Blocked Cooling Vent Ducts 5528.2.3 Iron Oxide Deposits 5538.2.4 Loose Core Iron/Fretting and Interlaminar Failures 5558.2.5 Bent/Broken Laminations in the Bore 5718.2.6 Space Block Support and Migration 5728.2.7 Migration of Broken Core Plate and Space Block Thick Plates 5738.2.8 Laminations Bulging into Air Vents 5748.2.9 Greasing/Oxide Deposits on Core Bolts 5758.2.10 Core-Compression Plates 5778.2.11 Core-End Flux Screens and Flux Shunts 5788.2.12 Frame-to-Core Compression (Belly) Bands 5798.2.13 Back-of-Core Burning 5808.2.14 Core-End Overheating 5838.3 Stator Windings 5868.3.1 Stator Bar/Coil Contamination (Cleanliness) 5868.3.2 End-winding Blocking and Roving 5878.3.3 Surge Rings 5898.3.4 Surge-Ring Insulation Condition 5938.3.5 End-winding Support Structures 5938.3.6 Ancillary End-Winding Support Hardware 5978.3.7 Asphalt Bleeding/Soft Spots 6008.3.8 Tape Separation/Girth Cracking 6028.3.9 Insulation Galling/Necking Beyond the Slot 6048.3.10 Insulation Bulging into Air Ducts 6058.3.11 Insulation Condition, Overheating, and Electrical Aging 6058.3.12 Cracked or Broken Strands 6088.3.13 Corona Activity 6098.3.14 Stator Wedges 6168.3.15 End-Wedge Migration Out of Slot 6208.3.16 Side-Packing Fillers 6208.3.17 Leaks in Water-Cooled Stator Windings 6218.3.18 Magnetic Termites 6248.3.19 Flow Restriction in Water-Cooled Stator Windings 6268.3.20 Hoses, Gaskets, and O-Rings in Water-Cooled Stator Windings 6298.4 Phase Connectors and Terminals 6338.4.1 Circumferential Bus Insulation 6338.4.2 Phase Droppers 6358.4.3 High-Voltage Bushings 6378.4.4 Standoff Insulators 6378.4.5 Bushing Vents 6398.4.6 Bushing-Well Insulators and Hydrogen Sealant Condition 6398.4.7 Generator Current Transformers (CTs) 6418.5 Hydrogen Coolers 644References 646Additional Reading 6479 ROTOR INSPECTION 6499.1 Rotor Cleanliness 6509.2 Retaining Rings 6529.2.1 Nonmagnetic 18–5 and 18–18 Retaining Rings 6579.2.2 Removal of Retaining Rings 6619.3 Fretting/movement At Interference-Fit Surfaces of Wedges and Rings 6699.3.1 Tooth Cracking 6699.4 Centering (Balance) Rings 6799.5 Fan Rings Or Hubs 6809.6 Fan Blades 6829.7 Bearings and Journals 6859.8 Balance Weights and Bolts 6899.9 End Wedges, Slot Wedges, and Damper Windings 6919.10 Other Wedges 6969.11 Windings: General 6969.11.1 Conductor Material 6999.12 Windings: Slot Region 7039.12.1 Slot Liner 7039.12.2 Turn Insulation 7059.12.3 Creepage Block and Top Channel 7079.12.4 C-Channel Subslot 7109.12.5 Radial-Tangential-Radial Cooling 7119.13 End Windings and Main Leads 7119.13.1 Retaining-Ring Liners 7129.13.2 End Turns and Blocking 7159.13.3 Shorted Turns 7199.13.4 Top-Turn Cracking 7219.13.5 dc Main Leads 7249.13.6 Coil and Pole Connections 7309.14 Collector Rings 7359.15 Collector Ring Insulation 7409.15.1 Collector Ring Surface Roughness 7419.16 Bore Copper and Radial (Vertical) Terminal Stud Connectors 7439.17 Brush-Spring Pressure and General Condition 7499.18 Brush Rigging 7529.19 Shaft Voltage Discharge (Grounding) Brushes 7539.20 Rotor Winding Main Lead Hydrogen Sealing: Inner and Outer 7559.21 Circumferential Pole Slots (Body Flex Slots) 7609.22 Blocked Rotor Radial Vent Holes: Shifting of Winding And/or Insulation 7629.23 Couplings and Coupling Bolts 7649.24 Bearing Insulation 7659.25 Hydrogen Seals 7679.25.1 Journal Seals 7689.25.2 Thrust-Collar Seals 7699.25.3 Carbon Seals 7719.26 Rotor Body Zone Rings 7729.27 Rotor Removal 774References 78210 AUXILIARIES INSPECTION 78510.1 Lube-Oil System 78510.2 Hydrogen Cooling System 78610.2.1 Hydrogen Desiccant/Dryer 78710.3 Seal-Oil System 78810.4 Stator Cooling Water System 79010.5 Exciters 79310.5.1 Rotating Systems Inspection 79310.5.2 Static Systems Inspection 79410.5.3 Brushless Systems Inspection 79410.5.4 Specific Inspection Items 79411 GENERATOR MAINTENANCE TESTING 80111.1 Stator Core Mechanical Tests 80111.1.1 Core Tightness 80111.1.2 Core and Frame Vibration Testing 80211.2 Stator Core Electrical Tests 80411.2.1 EL CID Testing 80411.2.2 Rated Flux Test with Infrared Scan 81611.2.3 Core Loss Test 82711.2.4 Through-Bolt Insulation Resistance 82811.2.5 Insulation Resistance of Flux Screens 82911.3 Stator Winding Mechanical Tests 82911.3.1 Wedge Tightness 82911.3.2 Stator End-Winding Vibration and Resonance (Bump) Testing 83211.4 Water-Cooled Stator Winding Tests 83611.4.1 Air Pressure Decay 83611.4.2 Tracer Gases 83711.4.3 Vacuum Decay 83811.4.4 Pressure Drop 83811.4.5 Flow Testing 83811.4.6 Capacitance Mapping 83811.5 Stator Winding Electrical Tests 83911.5.1 Pretesting Requirements 84011.5.2 Series Winding Resistance 84011.5.3 Insulation Resistance (IR) 84011.5.4 Polarization Index (PI) 84111.5.5 Dielectric Absorption During dc Voltage Application 84411.5.6 dc Leakage or Ramped Voltage 84511.5.7 dc Hi-Pot 84611.5.8 ac Hi-Pot 84711.5.9 Partial Discharge (PD) Off-Line Testing 85011.5.10 Capacitance Measurements 85311.5.11 Dissipation/Power Factor Testing 85411.5.12 Dissipation/Power Factor Tip-Up Test 85511.6 Rotor Mechanical Testing 85611.6.1 Rotor Vibration 85611.6.2 Rotor Nondestructive Examination Inspection Techniques 85711.6.3 Some Additional Rotor NDE Specifics 86711.6.4 Air Pressure Test of Rotor Bore 87111.7 Rotor Electrical Testing 87311.7.1 Winding Resistance 87311.7.2 Insulation Resistance (IR) 87311.7.3 Polarization Index (PI) 87311.7.4 dc Hi-Pot 87411.7.5 ac Hi-Pot 87511.7.6 Shorted Turns Detection: General 87511.7.7 Shorted Turns Detection by Recurrent Surge Oscillation (RSO) 87611.7.8 Shorted Turns Detection by Open-Circuit Test 87911.7.9 Shorted Turns Detection by Winding Impedance 88011.7.10 Shorted Turns Detection by Low-Voltage dc or Volt Drop 88211.7.11 Shorted Turns Detection by Low-Voltage ac or “C–Core” Test 88511.7.12 Shorted Turns Detection by Shorted Turns Detector (Flux Probe) 88511.7.13 Field-Winding Ground Detection by the Split-Voltage Test 90211.7.14 Field-Ground Detection by the Current-Through-Forging Test 90411.7.15 Shaft Voltage and Grounding 90411.8 Hydrogen Seals 90611.8.1 NDE 90611.8.2 Insulation Resistance 90611.9 Bearings 90611.9.1 NDE 90611.9.2 Insulation Resistance 90711.10 Thermal Sensitivity Testing and Analysis 90711.10.1 Background 90711.10.2 Typical Thermal Sensitivity Test 91011.11 Heat-Run Testing 91311.11.1 Test Procedure 91311.11.2 Acceptance Parameters 91511.12 Hydrogen Leak Detection 91611.12.1 Pressure Drop 91711.12.2 SF6 and CO2 Gas Detection 91811.12.3 Helium Gas Detection 91911.12.4 Snooping 92011.12.5 Ultrasonic 920References 92012 MAINTENANCE 92312.1 General Maintenance Philosophies 92312.1.1 Breakdown Maintenance 92512.1.2 Planned Maintenance 92512.1.3 Predictive Maintenance 92512.1.4 Condition-Based Maintenance (CBM) 92712.2 Operational and Maintenance History 92712.3 Maintenance Intervals/frequency 92812.4 Type of Maintenance 92912.4.1 Extent of Maintenance 92912.4.2 Repair or Replacement 93012.4.3 Rehabilitation/Upgrading/Uprating 93112.4.4 Obsolescence 93312.5 Work Site Location 93612.5.1 Transportation 93612.6 Workforce 93812.7 Spare Parts 93912.8 Uprating 94112.8.1 Drivers for Uprating 94112.8.2 Uprating Considerations 94312.8.3 Component Evaluations 94512.8.4 Reliability and Effect of Uprating on Generator Life 94912.8.5 Required Inspection and Tests Prior to Uprating 95112.8.6 Required Maintenance Prior to Uprating 95212.8.7 Heat-Run Testing After Uprating 95312.8.8 Maintenance Schedule After Uprating 95512.9 Long-Term Storage and Mothballing 95512.9.1 Reasons for Storage of Generator Equipment 95612.9.2 General Requirements 95612.9.3 Storage Requirements 95812.9.4 Monitoring and Maintenance During Storage 96312.9.5 Restoration from Storage 96512.9.6 Long-Term Storage Maintenance Procedures and Testing 96712.10 Life Cycle Management (LCM) 97012.11 Single-Point Vulnerability (SPV) Analysis 972References 97313 NEW GRID CODES 97513.1 New Grid Codes and Their Impact On Generators 97513.2 Regulatory Requirements For Turbo-Generators 98013.2.1 Verification of Real and Reactive Gross and Net Power Capacity 98013.2.2 Verification of Models for Excitation Control Systems and Protection 982References 984Index 985

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