upgrading gen protect and grounding
TRANSCRIPT
Upgrading Generator
Protection and Grounding for
Industrial Generators-Why & How
Chuck MozinaBeckwith Electric Co., Inc.
Section I
Introduction
A major US manufacturer of :
– Digital multifunction generator and transformer protection
– Generator synchronizing and bus transfer equipment
– Voltage control devices for LTC transformer, regulators, and capacitor banks
– Packaged systems using Beckwith products
– Family-owned company founded by Mr. Bob Beckwith
– Formed May 1967 in Chicago, Illinois
– Moved in 1974 to Largo, Florida
– Additional Facility in October 1992
– Temporary Facility in October 1992(Result of tornado damage)
– New facility November 1993
ISO Registered
The InstructorChuck Mozina is Manager of Application Engineering for Protection and Protection Systems at Beckwith Electric Co. He is responsible for the application of Beckwith products and systems used in generator protection and intertie protection, synchronizing and bus transfer schemes.
Chuck is an active member of the IEEE Power System Relay Committee and is the past chairman of the Rotating Machinery Subcommittee. He is active in the IEEE IAS I&CPS committee which addresses industrial system protection. He is the U.S. representative to the CIGRE Study Committee 34 on System Protection and chairs a CIGRE working group on generator protection. He also chaired the IEEE task force which produced the tutorial “The Protection of Synchronous Generators,” which won the PSRC‘s 1995 Outstanding Working Group Award. Chuck is the 1993 recipient of the PSRC‘s Career Service Award.
Chuck has a Bachelor of Science in electrical engineering from Purdue University and has authored a number of papers and magazine articles on protective relaying. He has over 25 years of experience as a protective engineer at Centerior Energy, a major investor-owned utility in Cleveland, Ohio where he was the Manager of the System Protection Section. He is also a former instructor in the Graduate School of Electrical Engineering at Cleveland State University as well as a registered Engineer in the state of Ohio.
Relay Seminar
October 14 – 19, 2001Clearwater, Florida
Beckwith Electric has announced a date forthe next Relay Seminar, which will cover Generator, Transformer, and Interconnection Protection.
To sign up to be on the mailing list and receive seminar details, please visit:www.beckwithelectric.com/semreg.htm
Seminar OutlineDay 1 — AM
Generator Protection M-3425Fundamentals of Digital Protection
• Generator basics and generator grounding– Generator fundamentals– Generator grounding
• Traditional• IAS proposed hybrid scheme
– Industry standards– Function numbers
• Developing a protection upgrade program– Why upgrade at all– Improved sensitivity– New protection areas– Special protection applications– Basic upgrade options
• Use of digital technology to upgrade– Beckwith M-3425– Features– Software, oscillograph demonstration
• Questions
Section II
Fundamentals of Digital Protection
General Information on Generator Protection
Generator fundamentals
Industry standards
Function numbers
Functional breakdown
Fundamentals
Fundamental Section
Basic synchronous generators
Connections to the system
Generator grounding
C37 guidelines
Device numbers
Ib
Basic Synchronous Generator
Gen3-Ø
Electrical Output
DC Field Source
Ia
Ic
Prime Mover(Mechanical Input)
Synchronous Generator Types
Direct Connected Generator to Power
System
G
POWER SYSTEM
LOAD BUS
AUXILIARYLOAD
LOAD LOAD
Unit Connected Generator to Power
System
GAUXILIARY
LOAD
POWER SYSTEM
Low Impedance Grounding
* RESISTOROR
REACTOR
*
GENERATORWINDINGS
High Impedance Grounding
* RESISTOR*
GENERATORWINDINGS
Generator Short-Circuit Current
(Xd” Tdo”)
(Xd’ Tdo’)
(I)
Generator Terminal Fault Current
Key Industry Guides & Standards
Key Industry Guides & Standards
IEEE/ANSI
C-37.102-1995
C-37.101-1992
C-37.106-1992
Guide for ACGenerator Protection
Guide for Generator Ground Protection
Guide for Abnormal Frequency Protection for Power Generating Plant
Relay Function Numbers
21 Distance relay. Backup for system and generator zone phase faults.
24 Volts/Hz protection for the generator.27 Undervoltage protection for the generator.27TN Third-Harmonic Undervoltage.32 Reverse power relay. Anti-motoring
protection.40 Loss-of-Field protection.50BF Instantaneous overcurrent relay used as
current detector in a breaker failure scheme.
51N Time overcurrent relay. Backup for ground faults.
51V Voltage-controlled or voltage-restrained time overcurrent relay. Backup for system and generator phase faults.
59 Overvoltage protection.59N Voltage relay. Primary status ground fault
protection for a generator.
60FL Voltage balance relay. Detection of blown potential transformer fuses.
62B Breaker failure timer.64F Primary protection for rotor ground
faults.78 Loss of synchronism protection.81O/U Frequency relay. Both under frequency
and overfrequency protection.86 Hand-reset lockout auxiliary relay.87G Differential relay. Primary phase-fault
protection for the generator. 87GD Sensitive ground fault protection for the
generator.87T Differential relay. Primary protection for
the transformer. May be used to provide phase fault backup for the generator in some station arrangements.
87U Differential relay for overall unit and transformer.
Relay Function Numbers
M-3425Typical Connection Diagram
Standard Protective Functions
This function provides control for thefunction to which it points: it cannot beused independently.
Premium Protective Functions
NOTE: Some functions are mutuallyexclusive; see Instruction Book for details.
Utility System
52Unit
3
IN
52Gen
M-3425
59 2481 27
50BF-Ph
46
87
CT
VT
78 51T
+
-
64F
GeneratorField
60FL 40
27
51V 50 21 32 50
27
51NCT
R
M-3425
Low-impedance Groundingwith Overcurrent StatorGround Fault Protection
50N
87GD
59N27TN
32
27
R
M-3425
High-impedance Stator GroundFault with Third Harmonic 100%Ground Fault Protection
3CT
50DT
50BF-N
Section IIIUpgrading Generator Protection
Using Digital Technology
Upgrading Generator Protection Using
Digital Technology
Charles J. MozinaBeckwith Electric Company
Why Upgrade Generator Protection?
• Generators fail due to:+Abnormal operating conditions+Internal short circuits
• Proper generator protection can prevent many failures or minimize damage when failures occur.
• Cost of generator loss can be substantial+Added purchase power costs+Cost associated with impact on plant production+Companies have found preventing one failure can pay for entire upgrade program
• Insurance companies base premiums on generators being protected to the level recommended by IEEE C-37.103
• Less skilled operators make sustained operation outside of generator capability more likely. This warrants upgraded protection.
• The longer you wait, the older equipment gets, the more likely the failure
• Upgrading with digital technology can reduce future relay maintenance and provide data (oscillographs)toreduce outage time.
Areas of Protection Upgrade OnOlder Generators
– Improved sensitivity– New or additional protection areas– Special protection application
considerations
MULTIFUNCTION DIGITAL RELAYS
Improved Sensitivity
– Negative sequence (unbalanced current)
– Field ground 100% fault detection+Brush pull-off detection
– Dual-level loss-of field protection– Sensitive overexcitation protection
MULTIFUNCTION DIGITAL RELAYS
New or Additional Protection Areas
– Inadvertent generator energizing
– VT fuse-loss protection– Sequential tripping– Oscillographic monitoring
MULTIFUNCTION DIGITAL RELAYS
MULTIFUNCTION DIGITAL RELAYS
Special Protection Application Special Protection Application ConsiderationsConsiderations
Generator breaker failureGenerator breaker failureOver/under frequencyOver/under frequency
Improved Sensitivity
• Negative sequence (unbalanced current)
• Field ground fault detection+ Brush pull-off detection
• Dual-level loss of field protection
• Sensitive overexcitationprotection
Negative Sequence
MULTIFUNCTION DIGITAL RELAYS
Negative Sequence (46)
– Unbalanced phase currents create negative sequence current in generator stator,
MULTIFUNCTION DIGITAL RELAYS
Negative Sequence (46)
– Negative sequence current interacts with normal positive sequence current to induce a double frequency current (120 Hz)
– Current (120 Hz) is induced into rotor causing surface heating
MULTIFUNCTION DIGITAL RELAYS
Currents in the Rotor Surface
MULTIFUNCTION DIGITAL RELAYS
Negative Sequence (46)
Salient PoleWith connected amortisseur
10With non-connected amortisseur
5Cylindrical
Indirectly10Directly cooled - to 960 MVA
8961 to 1200 MVA
61200 to 1500 MVA
5
% StatorRating
MULTIFUNCTION DIGITAL RELAYS
Negative Sequence (46)
– Generator has established short-time rating,
MULTIFUNCTION DIGITAL RELAYS
Negative Sequence (46)
Two Types of Relays
1. ELECTROMECHANICAL– Sensitivity restricted to about
60% I2 of generator ratings– Fault backup provided– Generally insensitive to load
balances or open conductors
MULTIFUNCTION DIGITAL RELAYS
Negative Sequence (46)
Two Types of Relays
1. DIGITAL AND STATIC–Protects generator down to
its continuous I2 rating–Can detect open conductor
conditions
MULTIFUNCTION DIGITAL RELAYS
Advanced Protection Functions
Field (Rotor) Ground Fault Protection (64F)
Insurance companies tell us this is the most frequent internal generator faultReview existing 64F voltage protection methodsDiscuss a new 64F injection method
Typical Generator Field Circuit
The first ground fault will:establish a ground reference making a second ground fault more likelyincrease stress to ground at other points in field winding
Ground #1
Typical Generator Field Circuit
The second ground fault will:short out part of field winding causing unit vibrationscause rotor heating from unbalanced currentscause arc damage at the points of fault
Ground #2
Ground #1
Field Ground Fault Protection
Detection Using a DC Source
Field Ground Fault Protection
Detection Using a Voltage Divider
Field Ground Fault Protection
Using Injection Voltage Signal
Field Ground Fault Protection
Real-Time Insulation Measurements
Field Insulation Real-Time Monitoring
Advanced Protection Functions
Brush lift-off detection (64B)– Brushes on older generators
are a maintenance headache for plant personnel
– When brushes should be replaced or re-adjusted is important diagnostic information
– If brushes open on an in-service generator they cause:
• arc damage to brush mounting structure
• eventual unit tripping by loss-of-field protection
Field Ground Fault Protection
Using Injection Voltage SignalBrush lift-off
Analyzer voltagereturn signal
Brush Lift-off Voltage Return Signal
Ground Brush Lift-off
When the ground brush lifts off the rotor
– Low resistance path to ground for stray rotor flux is removed
– Generator bearings carry stray shaft ground current
– Bearing will pit and will need to be replaced
Dual-LevelLoss-of-Field Protection
Older, Single-Zone Off-Set Mho Relay Loss-of-Field Characteristics
MULTIFUNCTION DIGITAL RELAYS
Loss-of-Field Using Two-Zone Off-Set Mho Method
MULTIFUNCTION DIGITAL RELAYS
SensitiveOverexcitation
Protection
MULTIFUNCTION DIGITAL RELAYS
Overexcitation /
Volts per Hertz (24)
GENERATORTRANSFORMER ≈EXCITATION
Voltage V
Freq. Hz
GENERATOR LIMITS (ANSI C 50.13)Full Load V/Hz = 1.05 puNo Load V/Hz = 1.05 pu
TRANSFORMER LIMITSFull Load V/Hz = 1.05 pu (HV Terminals)No Load V/Hz = 1.10 pu (HV Terminals)
MULTIFUNCTION DIGITAL RELAYS
Overexcitation/
Volts per Hertz (24)CAUSES OF V/HZ PROBLEMS
• Generator voltage regulator problems
- operating error during off-line manual regulator operation
- control failure
- loss of VT regulator supply voltage
- overexcitation when regulator is on–line
• System problems
- unit load rejection: full load, partial rejection
- power system islanding during major distrubances
MULTIFUNCTION DIGITAL RELAYS
Overexcitation/Volts per Hertz (24)
PHYSICAL INSIGHTS• As voltage rises above rating leakage flux increases
• Leakage flux induces current in transformer support structure causing rapid localized heating
MULTIFUNCTION DIGITAL RELAYS
Typical Relay Characteristics for Typical Relay Characteristics for DualDual--Level DefiniteLevel Definite--Time Time
V/Hz ProtectionV/Hz Protection
MULTIFUNCTION DIGITAL RELAYS
Optimum Optimum OverexcitationOverexcitationProtectionProtection
MULTIFUNCTION DIGITAL RELAYS
New or Additional Protection Areas
• Inadvertent generator energizing
• VT fuse-loss protection
• Sequential tripping
• Oscillographic monitoring
MULTIFUNCTION DIGITAL RELAYS
Inadvertent Generator Energizing
MULTIFUNCTION DIGITAL RELAYS
How Inadvertent Energizing Has Occurred
– Operating errors– Breaker head flashover– Control circuit malfunctions– Combination of above
MULTIFUNCTION DIGITAL RELAYS
Generator Response and Damage to Three-Phase Energizing
– Generator behaves as an induction motor
– Rotating flux induced into the generator rotor
– Resulting rotor current is forced into negative sequence path in rotor body
MULTIFUNCTION DIGITAL RELAYS
Inadvertent Energizing Equivalent Circuit
MULTIFUNCTION DIGITAL RELAYS
MULTIFUNCTION DIGITAL RELAYS
Inadvertent Energizing Function Logic Diagram
MULTIFUNCTION DIGITAL RELAYS
VT Fuse-Loss Protection
MULTIFUNCTION DIGITAL RELAYS
Application of Voltage Balance Relay Protection
MULTIFUNCTION DIGITAL RELAYS
Modern VT Fuse-Loss Detection
MULTIFUNCTION DIGITAL RELAYS
Sequential Tripping
MULTIFUNCTION DIGITAL RELAYS
Sequential Tripping Logic
– Used in steam turbine generators to prevent overspeed
– Recommended by manufacturers of steam turbine generators as a result of field experience
– This trip mode used only for boiler/reactor or turbine mechanical problems
– electrical protection should not trip through this mode
MULTIFUNCTION DIGITAL RELAYS
Sequential Tripping Logic
– STEP 1 Abnormal turbine/boiler/reactor condition is detected
– STEP 2 Turbine values are closed; generator allowed to briefly “motor” (i.e. take in power)
– STEP 3 A reverse power (32) relay in series with turbine valve positionswitches confirms all valves haveclosed
– STEP 4 Generator is separated from powersystem
MULTIFUNCTION DIGITAL RELAYS
Sequential Tripping Logic
MULTIFUNCTION DIGITAL RELAYS
OscillographicMonitoring
MULTIFUNCTION DIGITAL RELAYS
Benefits– Determine if relay and circuit breaker
operated properly– relay control problem – generator experience fault / abnormal
conditions– Speed generator return to service
– identify type of testing needed– provide data to generator manufacturer
– Gives relay engineer data to force unit off-line for inspection
– Uncovers unexpected problems: I.e. synchronizing
Oscillographic MonitoringOscillographicOscillographic MonitoringMonitoring
MULTIFUNCTION DIGITAL RELAYS
Digital Relay Oscillograph
MULTIFUNCTION DIGITAL RELAYS
Special ProtectionApplication
Considerations
Generator breaker failureOver/under frequency
MULTIFUNCTION DIGITAL RELAYS
Generator Breaker Failure
MULTIFUNCTION DIGITAL RELAYS
Typical Transmission Line Breaker Failure Functional Diagram
MULTIFUNCTION DIGITAL RELAYS
Functional Diagram of a Generator Breaker Failure Scheme
MULTIFUNCTION DIGITAL RELAYS
Under/Overfrequency(81U/81O)
MULTIFUNCTION DIGITAL RELAYS
Under/Overfrequency(81U/81O)
Underfrequency (81U)Generator Limits • Generator overloaded high strator
current
• Heating limits need to reduce output
•Overexcitation same as 24 Overvoltage (V/Hz)
•Turbine blade resonance
•All system generators are overloaded
•System load shedding via 81U to restore balance
•Need to coordinate tripping with system loadshedding.
Turbine Limits(Steam/GT)
System Problems
MULTIFUNCTION DIGITAL RELAYS
FIGURE 1 Generator Capability Versus Frequency
FIGURE 2 Generator Short-Term Thermal Capability
MULTIFUNCTION DIGITAL RELAYS
Under/Under/OverfrequencyOverfrequency(81U/81O)(81U/81O)
OverfrequencyOverfrequency (81O)(81O)
Generator LimitsTurbine Limits(Steam/GT)
System Problems
• None published
•Similar limits to underfrequency
•Overspeed trip at 110%
•More generation than load
•Governor actions to reduce MW output
MULTIFUNCTION DIGITAL RELAYS
FIGURE 3Steam Turbine Partial or Full-Load Operating
Limitations During Abnormal Frequency
MULTIFUNCTION DIGITAL RELAYS
ECAR Document # 3Generator Under Frequency
Tripping Requirements
0 minutesBelow 58.2 Hz
7.0 minutes58.5 - 58.2 Hz
30.0 minutes59.5 - 58.5 Hz
Unlimited60.0 – 59.5 Hz
Time DelayBefore Isolation
Frequency
MULTIFUNCTION DIGITAL RELAYS
FIGURE 4
Example of Trip Characteristics:
Overfrequency and Underfrequency
MULTIFUNCTION DIGITAL RELAYS
Use of Digital Technology to
Implement and Upgrade Program
MULTIFUNCTION DIGITAL RELAYS
Two Basic Design Options
– Retain Existing Protection– add additional functions to upgrade
to current standards
– Remove all existing protection– upgrade with all new protection
MULTIFUNCTION DIGITAL RELAYS
Dual-Relay Approach for Major Generators
MULTIFUNCTION DIGITAL RELAYS
Multifunction Relays Are The Right Choice, Either Way
– Panel space savings– Oscillographic capability– Communication (RS232 & RS485)– Low CT and VT burdens– Self diagnostic
MULTIFUNCTION DIGITAL RELAYS
Conclusions
– There are a number of serious protection shortcomings on generators with relays older than 20 years
– This paper attempted to bring those risks to the attention of utilities/generator owners
MULTIFUNCTION DIGITAL RELAYS
Conclusions
– Utilities/generator owners should address these risks through comprehensive upgrade programs to protect their generator investment
– Multifunction digital relays are an ideal, cost effective way to implement such a program
Section IVBeckwith M-3425Generator Relay
Function & Features
The World’s Leading Manufacturer of Digital Generator
Protection Proudly Presents the New
M-3425 Relay
The World’s Leading Manufacturer of Digital Generator
Protection Proudly Presents the New
M-3425 Relay
Digital Integrated Protection System® for Generators of All Sizes
What’s New from Beckwith in
Generator Protection
New Features
• Field Ground (64F)
• Out-of-Step(78)
• Split Phase Diff.. (50DT)
• Stator Thermal Overcurrent Protection (51T)
New FeaturesNew Features
•• Field Ground (64F)Field Ground (64F)
•• OutOut--ofof--Step(78)Step(78)
•• Split Phase Diff.. (50DT)Split Phase Diff.. (50DT)
•• Stator Thermal Overcurrent Protection Stator Thermal Overcurrent Protection (51T)(51T)
M-3420M-3420 M-3430M-3430
NewM-3425
NewM-3425
995 relays in service worldwide
489 relays in service worldwide
MM--34253425Typical Connection DiagramTypical Connection Diagram
Standard Protective Functions
This function provides control for thefunction to which it points: it cannot beused independently.
Premium Protective Functions
NOTE: Some functions are mutuallyexclusive; see Instruction Book for details.
Utility System
52Unit
3
IN
52Gen
M-3425
59 2481 27
50BF-Ph
46
87
CT
VT
78 51T
+
-
64F
GeneratorField
60FL 40
27
51V 50 21 32 50
27
51NCT
R
M-3425
Low-impedance Groundingwith Overcurrent StatorGround Fault Protection
50N
87GD
59N27TN
32
27
R
M-3425
High-impedance Stator GroundFault with Third Harmonic 100%Ground Fault Protection
3CT
50DT
50BF-N
Standard M-3425 Functions
• Overexcitation (V/Hz) protection (24)with both discrete time and inverse time curves
• 100% Stator Ground Fault Protection via third harmonic neutral undervoltage (27TN)
• Sensitive dual-setpoint reverse power, low forward power or over power detection, one of which can be used for sequential tripping (32)
• Dual-zone, offset-mho loss-of-field protection (40)• Sensitive negative sequence overcurrent
protection and alarm (46)• Generator Breaker Failure protection (50BF)• Inadvertant generator energizing protection
(50/27)• Definite Time Overcurrent (50DT) can be used for
split phase differential applications• Neutral inverse time overcurrent (51N) and
instantaneous overcurrent (50N) protection
Standard MStandard M--3425 Functions3425 Functions
ThreeThree--phase inverse time overcurrent phase inverse time overcurrent (51V) and instantaneous overcurrent (50) (51V) and instantaneous overcurrent (50) protectionprotectionPhase overvoltage (59) and undervoltage Phase overvoltage (59) and undervoltage (27) protection(27) protectionGenerator ground fault protection (59N)Generator ground fault protection (59N)VT fuseVT fuse--loss detection and blocking (60FL)loss detection and blocking (60FL)FourFour--step Over/Underfrequency (81) step Over/Underfrequency (81) protectionprotectionTwo step Rate of Change of Frequency Two step Rate of Change of Frequency (81R)(81R)Generator phase differential protection Generator phase differential protection (87) and ground differential (87GD) (87) and ground differential (87GD) protectionprotectionExternal Function allows external devices External Function allows external devices to trip through Mto trip through M--3425 Generator 3425 Generator Protection RelayProtection Relay
Premium MPremium M--3425 Functions3425 Functions
Field ground using advanced injection system (64F)
Stator thermal protection using positive sequence inverse overcurrent (51T)
Additional Standard M-3425 Functions• Eight programmable outputs and six
programmable inputs• Oscillography recording (170 cycles)• Time-stamped target storage for 24 events.• Metering of all measured parameters• Two RS-232C and one RS-485 communications
ports• M-3425 IPScom® Communications and Setting
Software• Includes Modbus and BECO2200 protocols• Standard 19" rack-mount design• Removable printed circuit board and power
supply• Both 50 and 60 Hz models available • Both 1 and 5 A rated CT inputs available • Additional trip inputs for externally connected
devices• IRIG-B time synchronization
MM--34253425External ConnectionsExternal Connections
ABC
50
LowImpedanceGrounding
52Gen
High Impedance Grounding
a b c
A B C
52b
2
M-3425 Three-Line Connection Diagram
M-3425OtherRelays
UTILITY SYSTEM
M-3425
Three VT Wye-WyeConnection
Three VT Wye-WyeConnection Ungrounded
Three VT Open-DeltaConnection
51
48 49
46 47 1011
OptionalField
GroundModule
58 59
56 57
54 55
M-3425
M-3425
52 53
M-3425
M-3425
M-3425
4544
42 43 40 41 38 39 42 43 40 41 38 39 42 43 40 41 38 39
Generator
OtherRelays
M-3425
Power Supply
Power Supply
(Optional)
ProgrammableGain Amplifier
MUX
Digital Signal Processor
(DSP) TMS 320C52
2K byte Dual-Ported
RAM
2-Line by 24-Character
Liquid Crystal Display
126K byte RAM
256K byte Flash-
Programmable ROM
Host Processor 10 MHz Zilog
64181
512 Byte EEPROM
8K byte RAM, Clock with
battery backup
MMI Module
(Optional)
Target Module
(Optional)
RS232 and RS485
Communi-cation ports
IRIG-B Time Code
input
Relay Outputs
Contact Inputs
Anti-Aliasing Low-Pass Filters (LPF)
Analog Multiplexer
VTs & CTs
Va
Vb
Vc
Vn
ia
ib
ic
iA
iB
iC
iN
32K X 16 RAM
Address/Data Bus
14-bit Analog-to-
Digital Converter
M-3425 Hardware Block Diagram