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GENERATOR BASICS
GENERATOR BASICS
Chuck MozinaConsultant
Beckwith Electric
Basic Synchronous Generators
Connections to the system
Short Circuits
Generator Grounding
Device Numbers
Generator Basics
Generator Basics
Basic Synchronous Generator
Generator Basics
Gen.
AVR ExcitationTransformer
Generator Step-upTransformer
CT VTGenerator
Field
StaticExciter
Generator Excitation & AVR Control
Generator Basics
Synchronous Generator Types
Generator Basics
Generator Basics
Generator Basics
Generator Basics
Direct Connected Generator to Power System
Generator Basics
Unit Connected Generator to Power SystemUnit Connected Generator to Power System
Generator Basics
Symmetrical Trace of a GeneratorShort-Circuit Current
Generator Basics
Symmetrical Trace of a GeneratorShort-Circuit Current
Generator Basics
Generator Short-Circuit Currents Phase B
Generator Basics
Generator Terminal Fault Current
Generator Basics
High Side ofGeneratorBreakerCurrents
GeneratorNeutral
TerminalCurrents
Fault Inception
High Side Breaker Opens
Multi-Phase Generator Fault Oscillograph
Generator Basics
Low Impedance Grounding
Generator Basics
Low Impedance GroundingGenerators Bussed Together
Generator Basics
Most of the damage occurs in the period after the generator breaker opens
0
2000
4000
6000
8000
time, sec
0.01 0.1 1 10
watt seconds
Wat
t-sec
onds
Total
Generator
System
Accumulation of damage over time:
Generator Basics
Generator Basics
High Impedance Grounding
Generator Basics
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Dual (Hybrid) Grounding
“GROUNDING AND GROUND FAULT PROTECTION OF MULTIPLE GENERATOR INSTALLATIONS ON MEDIUM-VOLTAGE INDUSTRIAL AND COMMERICAL POWER SYSTEMS.” PART 1- 4.
IAS TRANSACTIONS JAN./FEB. 2004
Generator Basics
IEEE IAS PAPERS ON INDUSTRAL GENERATOR GROUNDING
Generator NeutralVoltage
GeneratorPhase
Currents
Fault Inception
Breaker Opens
Trip Command
Generator Basics
Oscillograph of Field Ground Fault
Generator Basics
Generator Basics
10Negative sequence unbalance current protection for the generator.
468Loss-of-field protection.40
14Reverse power relay. Anti-motoring protection.
32
6Volts/Hz protection for generator overexcitation.
24
11Distance Relay. Backup for system and generator zone phase faults.
21
Discussed in Tutorial Section
FunctionDevice
Generator Basics
4Overvoltage relay. Stator ground fault protection for a generator.
59GN
6Overvoltage protection.59
11Voltage-controlled or voltage-restrained time overcurrent relay. Backup for system and generator phase faults.
51V4 & 11Backup for ground faults.51TN4 & 11Time overcurrent ground relay.51GN
14Stator Thermal Protection.49
Discussed in Tutorial Section
FunctionDevice
Generator Basics
2Differential relay for overall generator and transformer protection.
87U
2Differential relay. Primary protection for the transformer.
87T4Stator ground fault differential . 87N
2Differential relay. Primary phase-fault protection for the generator.
87G14Hand-reset lockout auxiliary relay.86
5Frequency relay. Both underfrequency protection.
81
9Loss-of-synchronism protection.78
Discussed in Tutorial Section
FunctionDevice
Generator Basics
Generator Basics
Typical Unit Generator –Transformer Configuration
UTILITY TRANSMISSION SYSTEM
ST GT-1 GT-2G G G
AUX. TRANS. #1 AUX. TRANS. #2
M
A C
M M M M
BN.O.
Aux. Bus #1 Aux. Bus #2
V1 V2
GSU #1 GSU #2GSU
ST = STEAM TURBINEGT = GAS TURBINEGSU = GEN. STEP-UP UNIT TRANSFORMERN.0. = NORMALLY OPEN
Typical Combine Cycle Plant
Generator Basics
APPLICATION OF MULTIFUNCTION
DIGITAL GENERATOR PROTECTION
APPLICATION OF MULTIFUNCTION
DIGITAL GENERATOR PROTECTION
Generator Basics
Generator Basics
Evolution of Technology in Generator Protection
Single Function Electromechanical
Single Function Static
Single Function Microprocessor-Based
Multifunction Digital Relays
Almost all new generating facilities use this technology
All generator protection functions in on hardware platform
Generator Basics
Multifunction Digital Relays
AdvantagesReduced panel space: more economical, lower price per function.FlexibilityCommunication capabilitySelf-diagnostics = reduced maintenanceOscillographic capabilitySystem integration (DCS system)
Generator Basics
Appropriate Level of Redundancy for Generator Protection
Advanced Protection FunctionsField Ground (64F)
Brush lift off detection (64B)
Out-of-Step (78)
Stator Turn-to-Turn Fault Protection
Split-Phase Differential (87SP)
Zero Sequence Voltage Balance (59G)
Review generator VT connections
Multifunction Generator Protection Application Considerations
Generator Basics
Level of Redundancy Most new generators are gas turbines or steam unit as part of a combined cycle plant
On these projects - generator protection is “pre-packaged” by generator manufactures
Standard offering by many generator manufactures is a single multifunction relay package
Multifunction Generator Protection Application Considerations
Generator Basics
Level of Redundancy There is no remote backup protection for most generation fault/abnormal operation consideration
Utilities need to be aware that if more redundancy is desired -they need to ask for it before generator is ordered
Multifunction Generator Protection Application Considerations
Single Relay
Generator Basics
Generator Basics
Levels of Redundancy
Strategy #1Use a single multifunction relay
If you have a relay failure:
Rely on self-test features to detect failure (MTBF Typically 100 years)
Remove generator from service
Install spare relay
Recommission
Return generator to service
Generator Basics
Levels of Redundancy
Strategy #1Use a single multifunction relayIf you have a relay failure:
Rely on self-test features to detect failure (MTBF Typically 90 years)Remove generator from serviceInstall spare relayRecommissionReturn generator to service
Cost of Strategy #1No primary and backupProduction loss for generator during off periodModerately sized utility generators (150MW) can result in production losses of over $100,000/day or more.
Generator Basics
Dual Relay Approach
Generator Basics
Levels of Redundancy
Strategy #2Use duel relay approach
Have defined primary and backup systems
If you have a relay failure:
Continue to run the generator
Replace the failed relay
Recommission
Place the new relay in service
Generator Basics
Levels of Redundancy
Strategy #2Use duel relay approach
Have defined primary and backup systems
If you have a relay failure:Continue to run the generatorReplace the failed relayRecommissionPlace the new relay in service
Cost of Strategy #2Purchase and installation of a second relay
Generator Basics
Generator VT Connections
These major VT generator connections are widely usedline to line voltage
line to ground
4-wire
3-wire
line to ground VT connections have unique application considerations
Generator Basics
Line to Line VT’s
Common open delta VT connection
Relay VT inputs connected line to line
Generator Basics
Line to Ground VT’s
Relay VT input connected line to ground
4 Wire Connection
Generator Basics
Line to Ground VT’s
Relay VT input connected line to groundFor stator ground fault neutral shift can result in false indication ofovervoltage / overexcitation. Ideal solution is to supply voltage functions with phase tophase. If oscillograph monitors L-G voltage, it can be used to phase identify a statorand fault.
Generator Basics
Line to Ground VT’s
Relay VT input connected line to groundFor stator ground fault neutral shift can result in false indication ofovervoltage/overexcitation. Ideal solution is to supply voltage functions with phase tophase. If oscillograph monitors L-G voltage, it can be used to phase identify a stator andfault need to coordinate 59N relay with VT secondary fuses to avoid unit trip for a VTsecondary ground fault
Generator Basics
Line to Ground VT3 Wire Connection
Relay VT inputs connected line to lineThis VT connection avoids the need to coordinate 59N with VT fusingCan not phase identify stator ground faults
QUESTIONS ?
GENERATOR BASICS
GENERATOR BASICS
Generator Basics
©2008 Beckwith Electric Co., Inc.