Protective Relaying for Power Generation Systems

by Reimert; Donald

• ISBN13: 9780824707002
• ISBN10: 0824707001
• eBook ISBN(s): 9781351836708
• Additional ISBN(s): 9781420030488
• Edition: 1st
• Format: Hardcover
• Copyright: 2005-12-09
• Publisher: CRC Press
• More Book Details

Summary

"This book, with 16 chapters and five appendices, arguably may be the most comprehensive single volume on generator and motor protection on the market. "…this book presents to practicing utility engineers a wealth of information that should be included in their library. Even those not directly involved in protection should have available to them the theory and practices associated with the protection described here"…Throughout the book, typical protective equipment settings are calculated with appropriate reference to electromechanical, solid-state, and digital protective devices. Where required, the author resorts to the application of Excel and Mathcad."Protective Relaying for Power Generation Systems is a recommended addition to every power engineer's library. The details may go beyond normal equipment protection requirements, but the depth of analysis, the data presented, and the qualitative discussion of all of the aspects involved in generator protection add a dimension not available in any single text.Reviewed by Stanley H. Horowitz in September/October 2006 Magazine of IEEE Power Engineering Society, Vol.4 No.5Organizing material in a structure that allows for quick and easy reference, Protective Relaying for Power Generation Systems features an in-depth presentation of topics and specific information related to generators and motors. This book provides coverage of protective component considerations, including explanations of potential damage. It explores a broad range of subjects including detailed time decrement generator fault calculations and minimum excitation limits. The text contains Excel® and Mathcad® workbook constructions for performing protection-related calculations. This is a valuable resource for electric utility engineers and those working in the power industry and at generation facilities.

Table of Contents

Generator Normal Operations	1	(14)
The Sample System	1	(1)
Generator Capability	1	(2)
Voltage Limitations	3	(1)
Sample System GSU Transformer Limits	3	(1)
System Limitations	4	(3)
Generator Capability Variations with Voltage	7	(2)
Excitation System	9	(6)
Reference	13	(2)
Generator Short Circuit Calculations	15	(32)
Introduction	15	(1)
Short-Circuit Current Characteristics	15	(1)
Generator Internal Magnetics	15	(4)
Generator Magnetic Structures	19	(4)
Generator Constants	23	(2)
Fault Current Calculations	25	(12)
Initial Load	26	(2)
Fault Calculation Overview	28	(2)
Determination of Xf and Fault Currents	30	(1)
Three-Phase Short Circuit	31	(1)
Phase-to-Phase Short Circuit	32	(1)
Phase-to-Ground Fault	33	(2)
Other Fault Conditions	35	(1)
DC Component of Short-Circuit Current	35	(2)
RMS Asymmetrical Current	37	(1)
Voltage Regulator	37	(1)
Practical Shortcuts	38	(2)
Short Circuit Calculation Example	40	(7)
Establish Prefault Conditions	40	(1)
Three-Phase Fault at Generator Terminals	41	(1)
Phase-to-Ground Fault on High-Voltage Terminals of GSU	42	(3)
Effects of the Automatic Voltage Regulator	45	(1)
References	46	(1)
Generator Differential Relay: 87G	47	(30)
Introduction	47	(1)
Ideal Differential Relay	47	(1)
Practical Considerations	47	(9)
CT Ratings	49	(1)
CT Saturation	50	(3)
CTs and Fault Current Replication	53	(3)
Percentage Differential Relay	56	(1)
Relay Characteristics	57	(2)
Electromechanical Relays	57	(1)
Solid-State and Microprocessor Relays	57	(2)
Minimum Operating Current Setting	59	(1)
Slope Setting	59	(9)
Requirements for Slope Setting	59	(1)
Advantage of Low Slope	60	(1)
Sensitivity and Load Current	60	(1)
Relay Response to Saturation	61	(2)
Methods of Choosing Slope Settings	63	(1)
Manufacturer's Recommendations	63	(1)
Qualitative Determination of Slope	63	(1)
Error Current Calculations for Unsaturated CT	63	(1)
Mason's Method	64	(1)
Example of Mason's Method	65	(1)
Fundamental Frequency Analysis	66	(2)
Sample System Differential Relay Settings	68	(2)
Sample System Differential Circuit	68	(1)
Electromechanical Relay	68	(1)
Specifications for Relay Chosen	68	(1)
Choosing Slope Static and Microprocessor Relays	69	(1)
Stabilizing Resistor	70	(3)
Balancing Burden	73	(1)
Time Delay	74	(1)
Frequency Response	74	(3)
References	75	(2)
Backup Fault Protection	77	(40)
Purpose and Implementation	77	(2)
Standard Overcurrent Relays	77	(1)
Voltage-Dependent Relays	78	(1)
Electromechanical vs. Electronic Relays	79	(1)
Voltage Supervised Overcurrent Relays	79	(26)
Voltage-Controlled and Voltage-Restrained Relays	79	(1)
Application Options and Fault Sensitivity	80	(1)
Scheme Sensitivity vs. Potential Transformer (PT) and Current Transformer (CT) Connection	80	(2)
Sensitivity Related to Relay Type	82	(1)
Delta Relay Currents	82	(1)
Settings Considerations	83	(1)
Basic Requirement	83	(1)
Automatic Voltage Regulator in Service	84	(1)
51 V Transmission System Backup Limitations	84	(2)
Effects of Wye-Delta Transformer	86	(1)
Self-Excitation Generators	87	(1)
Relay Response to Transient Current	88	(2)
Equipment Protection	90	(3)
Setting Criteria	93	(1)
Relay Current and Voltage Calculations	93	(1)
Relay Current and Voltage Equations	94	(1)
Sequence Currents and Voltages Calculations	95	(3)
Sample System 51 V Relay Settings	98	(1)
Fault Calculations	99	(3)
Choosing the Undervoltage Setting	102	(1)
Choosing Overcurrent Setting	103	(1)
Choosing Time Delay Setting	103	(1)
Auxiliary PTs to Correct for Wye-Delta Phase Shift	104	(1)
Distance Relays	105	(12)
Distance Relay Characteristics	105	(1)
Z Measured by Phase Distance Relay	105	(2)
Mho Distance Relay	107	(2)
System Impedance vs. Relay Characteristic	109	(2)
Setting Considerations	111	(1)
Load Limits	111	(1)
Apparent Impedance	112	(1)
Influence of an Interposing Wye-Delta Transformer	113	(2)
Auxiliary PTs to Correct for Wye-Delta Phase Shift	115	(1)
Other Distance Relay Applications	116	(1)
References	116	(1)
Generator Ground Fault Protection	117	(48)
Introduction	117	(1)
Generator Grounding Considerations	117	(4)
Ground Fault Current Limitation	117	(1)
Overvoltage Concerns	118	(2)
Core Damage Cause by Ground Fault	120	(1)
Methods of Grounding	121	(24)
Ungrounded System	121	(4)
Solidly Grounded/Effectively Grounded	125	(3)
High-Impedance Grounding	128	(1)
Distribution Transformer Grounding	128	(2)
High-Resistance Grounding on Sample System	130	(1)
Ground Fault Neutralizers	130	(11)
Low-Impedance Grounding	141	(2)
Low-Resistance Grounding	143	(1)
Low-Reactance Grounding	144	(1)
Grounding Transformers	144	(1)
Ground Fault Protection	145	(20)
Alarm vs. Tripping for High-Impedance Grounded System	146	(1)
Electromechanical and Electronic Relays	146	(1)
High-Impedance Ground Protection	146	(1)
Neutral Overvoltage Scheme	146	(2)
Application of 59GN on Sample System	148	(2)
Broken Delta Overvoltage Scheme	150	(1)
Overcurrent Scheme	151	(3)
Low-Impedance Ground Protection	154	(1)
Ground Differential	154	(1)
100% Stator Protection Schemes	155	(1)
Third-Harmonic Schemes	155	(2)
Third-Harmonic Undervoltage Scheme	157	(1)
Settings for Sample System 27H Scheme	158	(1)
Third-Harmonic Overvoltage Scheme	159	(1)
Third-Harmonic Voltage Ratio Scheme	159	(2)
Neutral Injection Scheme	161	(2)
References	163	(2)
Unbalanced Current Protection	165	(26)
Introduction	165	(1)
What Is Negative-Sequence Current?	165	(1)
Effects of Negative-Sequence Current	166	(3)
Rotor Heating	166	(1)
Cylindrical Rotor Generators	166	(2)
Salient Pole Generators	168	(1)
Pulsating Torque	169	(1)
Generator Negative-Sequence Capability	169	(2)
Continuous Unbalanced Capabilities	170	(1)
Short Time Unbalanced Currents	170	(1)
Sources of Negative Sequence Current	171	(1)
Unbalanced Faults	171	(1)
Open Phases	172	(1)
In-Service I2/2t Duty vs. Standards	172	(10)
Calculation of I2/2t Duty	174	(1)
Isolated Generator	174	(1)
The Interconnected Generator	174	(1)
The `venin's Equivalent Circuit	175	(1)
Unbalanced Duty on Sample System	175	(7)
Unbalanced Current Protection	182	(2)
Negative-Sequence Relay Settings	184	(7)
Calculation of Open-Circuit Current	184	(3)
Negative Sequence Relay Setting	187	(2)
References	189	(2)
Motoring Protection	191	(10)
Introduction	191	(1)
Effects of Motoring	191	(1)
Consequences for a Steam Turbine	192	(1)
Consequences for Other Prime Movers	192	(1)
Protection	192	(4)
Mechanical Protection: Steam Turbines	193	(1)
Electrical Protection	193	(3)
Sequential Trip Logic	196	(1)
Backup Protection	196	(1)
Setting Device 32	197	(1)
Applying Reversed Power Relay on the Sample System	197	(4)
References	199	(2)
Field Winding Protection	201	(20)
Field Ground Protection	201	(5)
Field Ground Hazard	201	(1)
Field Ground Protection	201	(1)
Field Ground Detection	202	(3)
Field Ground Relay Selection and Settings	205	(1)
Field Overcurrent Protection	206	(9)
Field Overcurrent Transients	206	(2)
Overcurrent Protection Schemes	208	(1)
Application of AC Relays to Protect the Field Winding	209	(1)
Basic Rectifier Operation	210	(3)
Relay Quantities	213	(2)
Settings For Field Overcurrent/Overvoltage Relays	215	(1)
Full Load Values	215	(1)
Maximum Field Current	215	(1)
Maximum Field Current from a Bridge Rectifier	215	(1)
Applying Field OC Protection on the Sample System	216	(5)
Rated Field Voltage	216	(1)
Maximum Available Field Current	217	(1)
Pickup Setting	217	(2)
Time Delay	219	(1)
References	220	(1)
Overexcitation	221	(16)
Introduction	221	(1)
Causes of Overexcitation	221	(2)
Damage	223	(1)
V/Hz Limits	224	(1)
Protection	225	(3)
Field Monitoring Relays	225	(1)
V/Hz Limiter	226	(1)
V/Hz Relay Applications	227	(1)
Settings	228	(5)
Generator V/Hz Settings	229	(1)
Transformer Settings	229	(1)
Generator/Transformer Settings	230	(1)
Setting Limitations	230	(1)
Time Delay Settings	231	(2)
Differential Relay Response to Overexcitation	233	(1)
Application of V/Hz Protection on the Sample System	234	(3)
References	236	(1)
Abnormal Frequency Protection	237	(12)
Introduction	237	(1)
Effect on Generator	237	(1)
Steam Turbines	237	(4)
Combustion Turbines	241	(1)
Hydro Generators	241	(1)
Excitation System	241	(3)
Protection and Settings	244	(5)
Primary Protection	244	(1)
Backup Protection	245	(3)
Combustion Turbine Generators Protection	248	(1)
References	248	(1)
Minimum Excitation Limiter	249	(38)
Overview of the Minimum Excitation Limiter Application	249	(2)
Operation in the Leading Mode	249	(1)
Limits on Leading Var Operation	250	(1)
Setting Criteria Background	251	(1)
Setting Criteria	252	(1)
Generator Leading Var Capability	253	(5)
Stator End-Core Heating in the Round Rotor Generator	254	(3)
Leading Var Capability of a Salient Pole Machine	257	(1)
Coordination with the LOF Relay	258	(2)
System Stability Limits	260	(10)
Classical View of Steady-State Stability	260	(2)
Manual Regulator Steady-State Stability Limit	262	(1)
Automatic Regulator Stability Limits	263	(7)
MEL Protective Characteristic	270	(7)
Straight Line Characteristic: Type UEL2 Model	272	(2)
Multisegment Straight Line Model Type UEL3	274	(1)
Circular Characteristic Type UEL1 Model	275	(2)
MEL Dynamic Performance	277	(2)
Problems with MEL Stability	277	(1)
Interaction with V/Hz	278	(1)
Isolated on Capacitive Load	278	(1)
MEL Application on the Sample System	279	(8)
References	284	(3)
Loss of Synchronism	287	(34)
Introduction	287	(1)
Turbine Generator Damage	288	(1)
Transient Stability	288	(4)
Out-of-Step Protection	292	(2)
Classical Swing Impedance Characteristic	294	(2)
Dynamic Swing Representation	296	(5)
Setting Consideration	301	(3)
Recoverable Swings	302	(1)
Current Limitation	303	(1)
Out-of-Phase Switching Rating for Breakers	303	(1)
Swing Velocity	303	(1)
Out-of-Step Relay: Device 78	304	(9)
Simple Mho Scheme	304	(3)
Single Blinder Scheme	307	(3)
Double Blinder	310	(1)
Double Lens and Concentric Circle Schemes	311	(1)
Detection Problems	312	(1)
Setting Out-of-Step on Sample System	313	(8)
References	319	(2)
Loss of Field Protection	321	(36)
General	321	(4)
Other Factors Affecting Loss of Field Severity	323	(2)
System Impact	325	(1)
Generator Damage	325	(6)
Stator Winding Overload	326	(1)
Rotor Damage	327	(3)
Stator End-Core Damage	330	(1)
Torque Pulsations	330	(1)
Loss of Field Protection: Device 40	331	(1)
Distance Relay Schemes	331	(11)
Distance Scheme 1: Unqualified Trip Scheme	331	(3)
Coordination for Stable Swings	334	(1)
Coordination with Minimum Excitation Limiter and Generator Capability Curve	335	(1)
Modified Scheme: Two Impedance Elements	336	(1)
Distance Scheme 2: Qualified Trip Scheme	337	(1)
Trip Delay Considerations	338	(1)
Criteria for Setting Mho Characteristic	339	(2)
Undervoltage Element	341	(1)
Modified Scheme	341	(1)
Special Consideration for Bussed Generators	341	(1)
Other Causes for LOF Relay Operations	342	(2)
Operator Error on Startup	342	(1)
Frequency-Sensitive Excitation Systems	343	(1)
LOF Relays During System Disturbances	344	(2)
Special Considerations for Hydro Units	346	(1)
Application of the LOF on the Sample System	346	(11)
Application of Scheme 1 on the Sample System Generator	347	(2)
Setting Review against Dynamic Data	349	(1)
Application of Scheme 2 on the Sample System Generator	350	(1)
Setting Review against Dynamic Data	351	(3)
References	354	(3)
Synchronization Protection	357	(32)
Introduction	357	(1)
Damage	357	(11)
Transformer Damage	358	(1)
Maximum Withstand Current	358	(1)
Maximum Synchronizing Current	359	(1)
Generator Damage	360	(1)
Shaft Torque	360	(3)
Fatigue Damage	363	(2)
Relative Damage Assessment	365	(1)
Considerations for Gas Turbines and Hydro Units	366	(1)
Breaker Considerations	367	(1)
Synchronizing Methods	368	(3)
Manual Synchronizing	369	(2)
Automatic Synchronizing	371	(1)
Synchronism Check Relays (Device 25)	371	(6)
Electromechanical Sync-Check Relays	372	(2)
Electronic-Based Sync-Check Relays	374	(1)
Phase Angle Supervision	375	(1)
Slip Frequency Limitation	375	(1)
Anticipatory Close Initiation	375	(1)
Minimum and Maximum Voltage Limits	375	(1)
Maximum Voltage Difference	376	(1)
Generator Voltage Priority	376	(1)
PT Phase Angle Compensation	376	(1)
Voltage Magnitude Compensation	376	(1)
Built-In Dead Bus Logic	377	(1)
Automatic Synchronizer (Device 25A)	377	(2)
Speed Control	377	(1)
Frequency Modulation Speed Control	378	(1)
Pulse Width Modulation Speed Control	379	(1)
Slow Breaker Protection	379	(1)
Settings	380	(1)
Synchronizing Equipment on the Sample System	381	(8)
Input Circuit Settings	382	(1)
Autosynchronizer Settings	383	(1)
Sync-Check Relay	384	(1)
Slow Close Protection	385	(1)
References	386	(3)
Accidental Energization Protection	389	(38)
Introduction	389	(1)
Generator State at Energization	389	(2)
Inadvertent Energization	391	(5)
Initial Current for a Three-Phase Energization from Standstill	392	(1)
Single-Phase Energization from Standstill	392	(2)
Initial Current for a Single-Phase Energization at Standstill	394	(2)
Breaker Flashover	396	(3)
Initial Single-Phase Flashover Current	396	(1)
Initial Current for Two-Phase Flashover	397	(2)
Dynamic Analysis of Three-Phase Energization from Standstill	399	(7)
System Voltage Impressed on d- and q-Axes	399	(1)
Axis Voltages Produced by Generator	400	(1)
Derivation of Axis Currents	400	(2)
Defining Generator Shaft Torque	402	(1)
d- and q-Axes Circuit Impedance	403	(2)
Acceleration	405	(1)
Generator Damage	406	(3)
Rotor Heating	406	(2)
Other Considerations	408	(1)
Turbine Damage	409	(1)
Energization Protection	410	(1)
Protection Provided by Native Schemes	411	(6)
Loss-of-Field Relay: Device 40	411	(1)
LOF Scheme 1	412	(1)
LOF Scheme 2	412	(1)
Backup Distance Protection: Device 21	413	(2)
Voltage Restraint/Voltage Control Relays: Device 51V	415	(1)
Motoring Protection: Device 32	415	(1)
Negative-Sequence Current Protection: Device 46	416	(1)
Backup Ground Relay: Device 51N	417	(1)
Dedicated Energization Protection	417	(3)
Dedicated Inadvertent Energization Schemes	417	(2)
Dedicated Breaker Flashover Protection	419	(1)
Applying Energization Protection on the Sample System	420	(7)
Inadvertent Energization Scheme Settings	420	(3)
Open Breaker Flashover	423	(1)
Initial Current for Single-Phase Flashover	423	(1)
Initial Current for Two-Phase Flashover	424	(1)
Setting the OBF Fault Detector (50N)	425	(1)
References	425	(2)
Motor Protection	427	(90)
Introduction	427	(1)
Motor Characteristics and Representation	427	(6)
Classical Motor Equivalent Circuit	427	(5)
Motor Torque	432	(1)
Motor Ratings	433	(2)
Rated Voltage and Frequency	434	(1)
Service Factor	435	(1)
Motor Characteristics	435	(3)
Motor Current	436	(1)
Speed--Torque Curves	436	(2)
Motor Applications	438	(3)
Horsepower Rating	438	(1)
Matching Motor and Load Torque Characteristics	439	(2)
Inertial Capability of NEMA Motors	441	(1)
Motor Starting	441	(20)
System Voltage Degradation during Starting	441	(2)
Starting Time Calculation	443	(1)
Motor Model for Starting Studies	444	(6)
Starting Calculation Example	450	(2)
Effect of Load Torque Characteristic	452	(1)
Centrifugal Pumps	453	(6)
Rotor Heating during Acceleration	459	(2)
Motor Overload Protection	461	(23)
Motor Thermal Limit Curves	461	(3)
Overcurrent Coordination	464	(1)
Thermal vs. Disk Elements	465	(2)
Time Overcurrent Trip Settings	467	(1)
Duty Cycle Motor Protection	467	(1)
Induction Disk Operating Characteristics	468	(2)
Dynamic Characteristic of the Disk Element	470	(1)
Practical Disk Element Model	470	(2)
Disk Element Response to Starting Current	472	(1)
Disk Element Response to Cyclic Load	473	(4)
Basic Thermal Element	477	(4)
Dynamic Characteristic of the Thermal Element	481	(1)
Thermal Element Response to Starting Current	482	(1)
Thermal Element Response to Cyclic Load	483	(1)
Multifunction Microprocessor Relays	484	(11)
Thermal Model Protection Scheme	486	(1)
Derivation of Model Parameters	487	(2)
Scheme Application Example	489	(1)
Thermal Limit Based Protection Scheme	490	(2)
Application of Thermal Limit Based Scheme	492	(3)
Unbalanced Current Protection	495	(1)
Special Schemes for Difficult Starts	495	(2)
Direct Temperature Measurement	497	(2)
Phase Fault Protection	499	(4)
Cable Protection	500	(2)
Upstream Coordination	502	(1)
Ground Fault Protection	503	(2)
Phase Unbalanced Protection	505	(4)
Current and Voltage Unbalanced Relays	508	(1)
Sample Setting Calculations	509	(8)
Set Device 51 Operating Current	510	(1)
Set Device 50 Operating Current	510	(1)
Checking the Maximum Three-Phase Fault Current at the Motor	511	(1)
Device 51 Time Delay	512	(1)
Coordination with Upstream Protection	513	(2)
References	515	(2)
Appendix A Generator Data Sheet	517	(2)
Appendix B CT Performance in Differential Relay Circuits	519	(8)
Appendix C Dynamic and Steady State Stability Limits	527	(6)
Appendix D Swing Impedance Locus Calculation Using Excel®	533	(12)
Appendix E Generator Shaft Torsional Transients	545	(18)
Index	563