generator basic concepts

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

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

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

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


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


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)

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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


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


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


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.

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Dual Relay Approach

Generator Basics


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


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

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Line to Line VT’s

Common open delta VT connection

Relay VT inputs connected line to line

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Line to Ground VT’s

Relay VT input connected line to ground

4 Wire Connection

Generator Basics


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


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

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