Large Turbo-Generators Malfunctions and Symptoms

This book presents a comprehensive, ordered relationship between malfunctions and symptoms occurring in large turbogenerators. With this book, the operator and/or engineer in a generating station could identify underlying causes of a developing component degradation or a failure quicker, which could potentially save both time and money and reduce the trial-and-error troubleshooting process. Large turbogenerators are the most important source of electricity. They can be found in thousands of power stations in every country. Forced outages, failures and degradation of these very expensive machines have an enormous aggregate cost to society. As such, any tool that can ameliorate loss of production by shaving time from troubleshooting activities, and avoiding unnecessary costs by detecting and promptly responding to component degradation, represents a step forward.

Preface.......................................................................................................................xi Caveat Emptor........................................................................................................xv Acknowledgments.............................................................................................. xvii List of Acronyms.................................................................................................. xix 1. Book Organization..........................................................................................1 2. Protective Functions........................................................................................5 2.1 Difference between Protection and Monitoring Functions.............5 2.2 Basic Protection Philosophy.................................................................6 2.3 Typical Protective Functions Applied to Large Turbogenerators............................................................................... 7 2.4 Primary and Backup Protective Functions........................................8 2.5 Identifying the Various Protected Zones......................................... 14 2.6 How to Identify Probable Causes from the Actuation of Protection Relays.................................................................................. 19 2.7 Essential Checks before Returning a Unit to Service after a Protection Trip......................................................................................22 2.8 Essential Checks before Returning a Unit to Service after Receiving an Alarm............................................................................. 24 2.9 Alarm Response Procedures.............................................................. 24 2.9.1 Rotor Grounds.............................................................. 24 2.9.2 Winding Temperature.............................................................. 26 2.9.3 End-Winding Vibration.............................................................. 26 2.9.4 Rotor Vibration.............................................................. 27 References........................................................................................................27 3. Monitored Parameters..................................................................................29 3.1 Typical Monitored Variables in Large Turbogenerators.................29 3.2 General Machine Variables.................................................................30 3.2.1 Stator Terminal Voltage..........................................................30 3.2.2 Stator Terminal Current.........................................................30 3.2.3 Generator Real and Reactive Power Output....................... 32 3.2.4 Generator Frequency..............................................................33 3.2.5 Rotor Field Voltage and Current...........................................34 3.2.6 Volts per Hertz........................................................................34 3.2.7 Negative Sequence Stator Current........................................35 3.2.8 Byproducts of Insulation Pyrolysis .....................................35 3.2.9 Liquids Inside the Generator................................................. 37 3.2.10 Ozone........................................................................................ 37 viii Contents 3.3 Stator (Frame, Core, and Winding) Variables.................................. 39 3.3.1 Frame Movement and/or Vibration..................................... 39 3.3.2 Core Vibration......................................................................... 39 3.3.3 Core Temperature...................................................................40 3.3.4 Flux Shield and Compression-Plate Temperatures............40 3.3.5 End-Winding Vibration..........................................................42 3.3.6 Stator Conductor Temperature and Differential Temperature...42 3.3.7 Partial Discharge Activity.....................................................43 3.4 Rotor Variables.....................................................................................45 3.4.1 Rotor Vibration........................................................................45 3.4.2 Rotor Winding Temperature.................................................45 3.4.3 Rotor Field Shorted Turns......................................................46 3.4.4 Rotor Ground Faults...............................................................46 3.4.5 Shaft Voltage and Current.....................................................46 3.4.6 Torsional Oscillation...............................................................48 3.5 Excitation Variables..............................................................................48 3.5.1 Brushgear Temperature and Condition of Air Filter.........50 3.5.2 Hydrogen in Brushgear Housing/Compartment..............50 3.5.3 Water Leaks in the Exciter/Rectifier Cubicle......................50 3.5.4 Exciter Temperature...............................................................50 3.5.5 PMG/HFG Voltage Output.................................................... 51 3.6 Hydrogen System Variables................................................................ 52 3.7 Stator Cooling Water System Variables.............................................54 3.8 Rotor Cooling Water System Variables.............................................56 3.9 Seal-Oil System Variables...................................................................56 3.10 Lubrication System Variables............................................................. 57 3.11 Identifying the Common Sources of Monitoring and Protection Variables.............................................................................58 References........................................................................................................66 4. List of Symptoms........................................................................................... 69 4.1 Definition of Symptom........................................................................ 69 4.2 List of Symptoms ................................................................................ 70 4.2.1 Core and Frame Symptoms................................................... 74 4.2.2 Stator Symptoms.....................................................................83 4.2.3 Rotor Symptoms.................................................................... 105 4.2.4 Excitation Symptoms............................................................ 114 4.2.5 Lubrication System Symptoms........................................... 125 4.2.6 Seal-Oil System Symptoms................................................. 128 4.2.7 Hydrogen System Symptoms.............................................. 134 4.2.8 Stator Cooling Water System Symptoms........................... 142 Contents ix 5. List of Malfunctions................................................................................... 153 5.1 Types of Malfunctions....................................................................... 160 5.1.1 Component Failure............................................................... 160 5.1.2 Component Degradation..................................................... 160 5.2 Core and Frame Malfunctions......................................................... 161 5.3 Stator Malfunctions........................................................................... 212 5.4 Rotor Malfunctions............................................................................ 331 5.5 Excitation System Malfunctions......................................................400 5.6 Hydrogen System Malfunctions......................................................440 5.7 Stator Cooling Water System Malfunctions...................................466 5.8 Seal-Oil System Malfunctions.........................................

Isidor Kerszenbaum, PhD, is an IEEE Fellow residing in Irvine, California. He is a generator specialist consulting to power plants on operation, maintenance and troubleshooting of large motors and generators. He is also active in the Electric Machinery Committee of the IEEE-PES. Geoff Klempner, BASc, is an IEEE Fellow and generator specialist residing in Toronto, Canada. He has served in numerous IEEE committees and standards working groups for large generators. He is also a contributor to CIGRE on large rotating electrical machines.