Generator System Testing - and Why! - Frame 6 Users...

Frame 6 User’s Group MeetingJune 14, 2006Phoenix, Arizona

Recommended Generator System Testing – and Why!

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Routine Maintenance Programfor the Generator System

Reliability of the Generating System

Dodge the costs associated with a Major Breakdown or Failure!

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MUST BE COST

$$$EFFECTIVE

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1. How Often?

2. What to Test?

3. Visual Exam / Inspection!

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During regularly scheduled Minor Maintenance Outages

(18 – 24 Month Cycle)

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Develop Records as a

Reference File.

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Record all incidents of mis-operation along with your MaintenanceRecords

40 Relay TripsShort Circuit Faults

Regulator ProblemsFull-Load RejectionLightning Strikes

Unexplained AlarmsOverload / AmpsOvervoltageMajor VAR Swings


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What to include?


64F GAC NGTROTATING DIODE BRIDGE

HV MAIN BUSFIELDSTATOR

HV NEUTRAL BUSLA / SURGE CAPS 52G

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What to include? (cont.)


RTD’S TRANSDUCERSPT PPT

SYNCHRONIZING SYSTEMALARMS

PROTECTIVE RELAYSMETERSCONTROL LOGIC

TRIP TESTS

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What to include? (cont.)


EXCITATION SYSTEMFUSE SIZING

VOLTAGE REGULATORSHAFT GROUNDINGNERC COMPLIANCE

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TESTING EQUIPMENT (calibrated)

VACUUMVACUUM

CLAMPCLAMP--ONONAMMETERSAMMETERS

RELAYRELAYTEST SETTEST SET

DC POWERDC POWERSUPPLYSUPPLY

TORQUETORQUEWRENCHWRENCH

mA / mVmA / mVSOURCESOURCE

CLEANINGCLEANINGSUPPLIESSUPPLIES

DUCTORDUCTOR

TTRTTRMEGGERMEGGER

CAMERACAMERA DVMDVM’’ss

OSCILLOSCOPEOSCILLOSCOPE

OSCILLOGRAPHOSCILLOGRAPH


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VISUAL INSPECTION / ODORS?(eyes, nose, cameras, boroscopes, mirrors, etc.)

LOOSE WIRES

OIL LEAKS

RUST

WATERLEAKS

RACCOONS

SNAKES

EXCESS HEATING

LOOSE COVERS

BRUSHCHATTER


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Generator FieldI. INSULATION TESTING (500 Volt Megger)

To determine the integrity (moisture, contamination, etc.) of the Generator Field Windings.Two factors:

1. Resistance level per megger reading.

2. P.I. Value

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Generator FieldI. INSULATION TESTING (500 Volt Megger) cont.

P.I. = Polarization Index

10 min Reading1 min Reading

P.I. for Field should be 1.25 or higher

= P.I.

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Generator Field

II. FIELD WINDING COPPERRESISTANCE CHECK

DLRO - Digital Low Resistance Ohmeter

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Generator FieldIII. BRUSH RIGGING & COLLECTOR RINGS

a) Clean

b) Surface Inspection

c) Check for Brush Wear & Spring Force

d) Check Clearances

e) Check Tightness

f) Check for brush bounce and sparking during operation

g) Brush Rigging Insulation check

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Generator FieldIV. SHORTED TURNS

High Field Amps to attain rated K.V.

Overexcitation Limiter pickups at low VAR levels.

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Generator FieldIV. SHORTED TURNS cont.

Impedance Testing

“Installed” Flux Probe

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64F Field Ground Detector

Field is Ungrounded!

“Field Ground” can be detected from rotating field back through the excitation system.

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64F Field Ground Detector

A “second” ground on the Generator Field is not a good thing.

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64F Field Ground DetectorMaintenance1. Operational Test –

solid ground at Collector Rings.

2. Verify minimum resistance-to-ground pickup.

3. Verify Output: Alarm & Trip.

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Generator Stator

AC Partial

Discharge

Dob

lePo

wer

Fac

tor

AC HIPOT

IR / PI Testing

DC HIPOT

EL Cid W

inding

Resistance

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Generator Stator

I. INSULTATION TESTING (5000 Volt Megger)

Two Factors:1. Resistance Level2. P.I. Value (2.5 or higher)

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Generator Stator

II. STATOR WINDING COPPER RESISTANCE CHECK

Use DLRO

Record Stator Temperature at various RTD locations.

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Generator Stator

III. END WINDING INSPECTION

CleanlinessOverheatingDamage, etc.

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Generator StatorIV. OPERATION CHECK OF THE

GENERATOR HEATERS

a) Sequence check by operating 52G Aux. Relay

b) Record Amps / Phase

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HV Neutral Bus

Inspect

Clean

Check Compartment Strip Heaters

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Neutral GroundingInspect

Clean

IR Checks with Megger; (1000 Volts)

H winding – GRDL winding – GRDH winding – L winding

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Neutral GroundingTransformer Turns Ratio CheckCheck Secondary ResistorVerify Proper Circuit Connections

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HV Main Bus

Inspect

Clean

Verify operation of all compartment strip heaters

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Lightning Arrestors / Surge Capacitors

InspectionAre ground connections tight?

Clean

Megger Checks(with Stator Windings)

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Generator Auxiliary Compartment

InspectCheck for water tightness of side walls, doors & roof joints.

CleanVerify all strip heaters are operating.AC Lights and Receptacles & DC Emergency Lights

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52G Generator BreakerMechanical Inspection of Breaker & Racking Mechanism

Binding?Grease as required

Hipot of the Vacuum Bottle**

Electrical Operational Checks

Close & tripSpring charging52GX Aux. Relays

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52G Generator BreakerInspection of the 52G Compartment

Evidence of waterTightness of connections

CleanRecord “Breaker Counter”

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Potential Transformers (PT)

Clean & Inspect the “Drawers”HV & LV Fuse CheckMegger ChecksTTR

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Power Potential Transformer (PPT)(Excitation Power Source)

Clean and inspectMegger Checks

HV Winding – GrdLV Winding – GrdHV – LV Winding

TTR

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Protective Relays

Inspect

Clean

Operational Tests

Settings/Calibration Tests

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Protective Relays

Record of all Relay “Trips”

Actions Taken following “Trip”

Causes Found

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Protective Relays“Settings” Review

System Changes to be accounted for

NERC, following August ‘03 blackout, recommends review of settings as they relate to performance during System Disturbances

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Protective Relays

On Digital Relays, check the set-up of the Oscillography & Events Recorder

Be prepared

Great troubleshooting tool for causes of “trips”.

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Generator RTD’s

Check calibration of all RTD’s at Incoming TB (Generator Control Panel).

Verify operation/calibration of the Generator Temperature Meter.

Verify “pickup” and operation of the 49G Generator Temperature Relay.

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MetersCalibration Check:

WMVARMAMVMFMFAMFVM

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Transducers

Transducer Outputs to:

Turbine ControlSCADA SystemMeters

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Transducers

Calibration Check:Zero & Range4-20mA Output(or 0-1mA)

Verify “Scaling Inputs” utilizing the 4-20mA Transducer Outputs.

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SynchronizingMeter Calibration Check

Incoming VMRunning VM

Monitor Synchroscope at “Closing”

Does it close at 12 o’clock?

Monitor VAR Flow at “Closing”

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Alarms / Annunciators

Gen Field GroundAlarm

Exciter Overvoltage

Alarm

Fault Transfer to Manual Regulator

Alarm

Rectifier Temperature

HI Alarm

Minimum Excitation

Limit Alarm

Bus Undervoltage

Alarm

Volts Per Hertz Alarm

Generator Over-

temperature Alarm

Sequence / Verify all Alarms

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Alarms / Annunciators cont.

Generator Ground Alarm

Generator Lockout

Trip Alarm

Loss of Excitation Trip Alarm

Over-frequency

Alarm

Loss of PT Alarm

Take Time to Re-familiarize YourselfWhat does this mean?Critical or Non-critical?Action required?

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Control SequencingProof Test of all Control Circuitry to verify even “seldom utilized” circuits.Examples:

AVR Setpoint R/L & Runback

MVR Setpoint R/L & Runback

Rectifier B-U Cooling Fan

59E Overvoltage Relay

All System TD Relays

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Control Sequencing cont.

Proof Test of all Control Circuitry to verify even “seldom utilized” circuits.Examples: cont.

Regulator Transfer Logic

Field Flashing / Startup

Power Supply Source Power Transfer

52G Breaker Close / Trip

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Trip Tests

TRIPTRIP52G52G TRIPTRIP

EXC.EXC.

86G86G

86T86T

86RE86RE

9494

5050

50/5150/5187T87T

52G52GTT

51V51V 4646

5959

64G64G

64B64B 40402424

64F64F

59E59E87G87G

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Fuse Sizing

Are they all in the correct location?

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Excitation / Voltage Regulators

“Pre-Excitation” System Checks(with Unit down)

“Off-Line” / FSNL System Checks

“On-Line” System Checks

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Excitation / Voltage RegulatorsPre-Excitation Checks:

PCB inspection

“Flashing” circuit check (resistor & diode)

Field OvervoltageProtection Calibration & Function check

Power Supply check

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Excitation / Voltage RegulatorsPre-Excitation Checks:

Verify all Potentiometer SetpointsVerify “Gain” SettingsTransducer (DCPT) Calibration checksFunctional Check of AVR

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Pre-Excitation Checks:

Functional Check of MVR

Inspection / tests of Power Rectifier Bridge(s)

Check integrity of the Shaft Voltage Suppression Circuit

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Verify “Flashing”Timing/Amps

Monitor MVR to AVR transfer

Verify VFNL Setpoint of AVR (Runback)

Off-Line Checks: (FSNL)

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Excitation / Voltage RegulatorsOff-Line Checks: (FSNL)

Record VFNL data for future reference:

KV, PT Volts, PPT Volts, PPT Amps, PCB Test Points, Field Amps, Field Volts, etc.

Check Field Voltage Waveshape & recordVerify ”Firing Circuit” Data

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Check/record all system gain, lead, lag, loop gain, etc.

Verify operation of all limiters (overexcitation, V/Hz, etc.)

Off-Line Checks: (FSNL)

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On-Line Checks: Monitor MVAR “bump”Verify operation and Proof Test of ALL limiters (URAL, overexcitation, etc.)Record operating data at varying load points (for future reference)

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Shaft Grounding Brush

Helps prevent damage to bearings via electrical discharge through the oil films.

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Shaft Grounding Brush

Provides a low impedance path to ground so current flow due to the 360 Hz ripple goes to ground, bypassing the bearings.

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Shaft Grounding BrushInspectionCleanRemove surface glaze on brushCheck spring force & brush holder gapUsing oscilloscope, check shaft-to-ground voltage (6 volts, 0-to-peak)

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NERC Compliance TestingNORTH AMERICAN ELECTRIC

RELIABILITY COUNCIL

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NERC Compliance Testing

Actual Reactive Capability Range

Excitation System Models (data validated by tests)

Generator characteristics (verified by tests)

Governor Droop / Deadband Proof Tests

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NERC Compliance TestingModel & Proof Test of Excitation Limiters

Generator Protective Relay Testing & verification that settings are coordinated with the Excitation Limiters

Operation in AVR only (Performance Proof Test)

Power System Stabilizer operating and verify Model (WECC)

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NERC Compliance Testing

An actual power swing test of a Power System Stabilizer. The voltage setpoint was given a 2% step up then 5 seconds later returned to normal. The red chart above shows the KW swing with the Power System Stabilizer turned off and the green chart shows the KW swing with the Power System Stabilizer enabled. Of note is the much faster damping of the stabilized wave form.

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Questions?

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Rotating Diode Bridge

Rectifies the AC output of the Rotating Exciter for direct input to the generator field.

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Stud Mounted

Press Pack (hockey puck)

Single or Dual Diode Modules

Fig 3: Westinghouse Mark III Exciter Diode Assembly

Variety of Packages & Configurations:

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Common Reasons for Failures

Transients on the Electrical Power Feed.

Faulty or wrong replacement component installed.

Surface leakage due to dirt & moisture.

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Common Reasons for Failures (cont.)

dV / dT

Low Resistance Short in Generator Field windings or leads.

Improper installation.

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One of the most important conditions for

testing the diodes is that the rated voltage

MUST NEVER

be exceeded.

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Meggers & Hi-Pot Test set should not

be used – they can easily damage

the components.

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Ohm meters are only reliable to detect a “Short”, since they do not have

enough voltage to properly energize the silicon wafer in a

Power Semiconductor.

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Test Diodes

Clean Components!!Dirt & moisture can cause surface leakage

Check ConnectionsVerify Assembly Components (Varisters, Resistors, Filtering Circuits, etc.)

Generator System Testing - and Why! - Frame 6 Users...

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