abb-318-wpo field or factory testing-transformer pd testing at site

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© ABB Inc.May 10, 2012 | Slide 1

E397G & E408GField or Factory Testing- TransformerPD testing at Site

ABB Automation & Power World: April 23-26, 2012




E397G & E408GField or Factory Testing- Transformer PD testing at Site

Speaker name: Dr. Poorvi Patel

Speaker title: Manager, TRES EngineeringSolutions

Company name: ABB INC

Location: St. Louis, MO



Content

Why Test a Transformer

Typical Factory Testing

Testing in Field

Induced Testing

Case picture



Why Test Transformers?Part of Manufacturers QA Process

Verifies Design Criteria

Losses, Clearances, Impedances, BIL Rating, Impulse Withstand, Thermal Design,Insulation System Design, etc.

Verifies Manufacturing Criteria

Windings, Insulation System Assembly, Core Building, Processing, Accessories, CoolingSystem, etc.

Verification of Standards CriteriaIEEE/ANSI, IEC, CSA, etc.

Verification of Customer Requirements

Special Loading Capability

Dielectric Withstand Additional Operational Characteristics

Special Requirements



Actual Tested Values Product Quality Indicators

Review Tested Values of Performance Parameters verses CalculatedIncludes Winding Resistance, No-load losses, Exciting current, Load losses, Impedance, Soundlevel, and Temperature measurements

Agreement between calculated and measured values confirm the qualityof design, material, manufacturing, and testing

Hence, availability of calculated values for transformer performance parameters prior to the timeof test is recommended

Significant deviations between calculated and measured values couldindicate quality issue(s) and will need to be discussed with the

manufacturer

Tolerances, for different performance parameters which are not specified byIEEE C57.12.00 should be agreed upon with the manufacturer before the order isplaced



Types of Tests- Factory

Preliminary Tests (Low Voltage Tests)- screening of the assembyVoltage/Turns Ratio, Polarity, and Phase Displacement

Winding Resistance

LTC Tests (If Applicable)

Wiring Tests including Current Transformers

Performance Tests (Normal Voltage Tests) – verify if the TFO meets the spec

No-load and Load Loss Measurements, Impedance, etc.Cooling Losses

Temperature Rise

Sound Tests (Load & No-load)

Dielectric Tests (Above Normal Voltage Tests)- Verify the designPower Factor, Capacitance and Insulation Resistance

Typically performed with preliminary tests

Impulse Testing (Lightning and Switching)

Applied Tests

Induced Test with PD



Types of Tests (cont.) -Factory

Advanced Tests (Condition Assessment)

Frequency Response Analysis (FRA)

Dielectric Frequency Response (DR)

Acoustic Tests (Sonic)

Advanced PD Analysis

Test SequenceExtent of testing depends on size and voltage class as defined by ANSI standards

Class 1 <= 69 kV

Class II > 69 kV

Exact test sequences are not fully covered by standards

Follow IEEE and IEC Standard recommendations where practical

Final test sequence should be agreed to by both parties



Field Testing Power Transformers - On the Rail Car orTruck

Receiving Inspection And Tests

Visual Inspection

Look for visible dent, damage, or touchup paint

Dry air pressure in the transformer tank

Impact Recorder Tape reviewHorizontal, Vertical, Longitudinal

Dew Point (Internal pressure ≈ 3.5 psi) ABB acceptance limit is 0.8% surface moisture

What about 0.5% moisture?

Core Megger1000 VDC must be 100 Meg Ohms or better

Contact OEM if Lower

SFRA- Sweep Frequency Analysis



Final Testing After completing the assembly and oil filling operations, finalelectrical and oil tests should be conducted.

Electrical tests include:Power factor and capacitance of windings and bushings

Maximum of .5% PF

Winding excitation test

Insulation resistance (megger)Minimum of 1000 Mohms at 100V

Winding resistance

±2% phase-to-phase variation and compare to factory values

Controls checks and calibration of temperature devicesCT ratio and polarity

Transformer Turns Ratio



Insulation Power Factor & Capacitance

MethodInsulation power factor bridge is used to measure power factor andcapacitance of winding insulation and bushings. Test voltage is typically 10 kV(max Voltage) for windings and for bushings it is determined by the bushingdesign and construction. Readings are corrected to standard temperature.Testing is highly susceptible to temperature, humidity and contamination.

WhyCheck the condition of the transformer or bushing insulation. TypicallyPF should be ≤ 0.5%. Higher PF may be due to moisture or foreigncontamination in the insulation structure or excessive contamination tobushing surfaces.

Acceptance criteria ANSI power factor limit for bushings is .5% when corrected to 20°C. ABBrecommends that the readings be compared to nameplate values. Bushingsshould be replaced when the measured power factor doubles the nameplatevalue or capacitance is in excess of 110% of the nameplate value.



HV Cable

Guard LV Test Lead

ApparatusGround

Ground Lead

mA & W

Test Mode: UST

C1 Test Includes

•Core insulationbetween centerconductor andtapped layer.

C1 %PF is temperaturecorrected to 20 °C

using the average ofthe apparatus andambient temperature.

Connection toParent Apparatus

Insulation Power Factor & Capacitance-Bushings



Electrical Tests (Low Voltage Tests) when transformer is notfilled with oil.

Power Factor and capacitance of the bushings before installing intothe transformer (if applicable) Note: Bushings that are in cratesor laying down test results may not match the nameplate values.(Some problems usually are: bad ground, crates draw moisture,straps may effect the readings.)



Final Testing- After completing the assembly and oil filling operations, finalelectrical and oil tests should be conducted

Electrical tests include:

Power factor and capacitance of windings and bushings

Maximum of .5% PF


Insulation resistance (megger)

Minimum of 1000 Mohms at 100V

Winding resistance


Controls checks and calibration of temperature devices

CT ratio and polarity




Winding Excitation

Method

Voltage source is applied to winding and exciting current is measured.Test is most often done with power factor bridge test set at 10 kV.Residual magnetism greatly effects readings. Demagnetization ofcored may be required for acceptable results.

WhyMaintenance test generally recognized to detect any changes in themagnetic circuit.

Acceptance criteria

This is a repeat test. All subsequent tests are compared to originalbaseline test for indications of variance. Phase A and Phase C shouldbe close.






Maximum of .5% PF




Winding resistance







Core Resistance (Megger)

MethodUsing Megger instruments, 1000V is applied for one minute to coreground strap. Test is sensitive to temperature, moisture andcontamination. Some transformers may be constructed such that coreground strap is not accessible.

Why

Prove insulation integrity of core from ground potential and test forinadvertent core grounds.

Acceptance criteria

Minimum acceptance criteria is ≥2000 megaohms when corrected to20°C






Maximum of .5% PF




Winding resistance







Current Transformer Ratio, Polarity

MethodRatio can be verified either by primary current injection or secondaryvoltage injection. Polarity is verified by battery polarization orbuck/boost circuits.

WhyVerify proper ratio and polarity of current transformers.

Acceptance criteriaVaried depending on relay accuracy and burden rating of the CT.

Generally ± 1% of calculated ratio.






Maximum of .5% PF




Winding resistance








Method

Tests are conducted using low voltage ratio bridge or three phasepower supply and voltmeters. Voltage is applied to the primarywinding and the voltage is measured on a secondary winding. Test isconducted at all tap positions. Ratio is calculated in accordance withnameplate values.

WhyTest is done to verify all internal connections and windingconfigurations are correct

Acceptance criteria

ANSI limits that are measured ratio must be ±0.5% of calculated voltageratio



Advanced Testing in the field

Dielectric Frequency Response- DFR

Sweep Frequency Response Analysis- SFRA

HV-testing in the field




Dielectric Frequency Response- DFR



Dielectric Frequency Response

60 Hz1 mHz 1 kHz

Frequency (Hz)

Powerfactor



Dielectric Response of Power Transformers

Off-line diagnostics

Oil and cellulose insulation system

Dielectric properties are strongly affected bymoisture and ageing.

Dielectric response measurements can beused for diagnostic purposes.



Why Dielectric Response

Purpose of measurement

Diagnostic test of insulation systemMoisture content

Oil Conductivity

Diagnose defects in systemDiagnose high PF or tan

Contamination

Carbon Tracking

Resistance in core ground circuit

Quality control test of Factory and/or Field processing



Power Products where DFR is used

Transformer diagnostics

Power TransformersTransformer Bushings

Instrument Transformers

Cable diagnostics

XLPE cables

Oil/paper cables

Manufacturing controlling system

Trouble shooting electrical apparatus

Material chacterization




Sweep Frequency Response Analysis- SFRA



What is FRA?

FRA means: Frequency Response Analysis

FRA is : “An off -line, non- destructive diagnostic technique”

FRA shows: Spectrum changes mechanical deformation

FRA is: Comparative method (two spectra are compared)

FRA is: Measurement of electrical response(from 10 Hz to 2 MHz or more).

FRA can detect mechanicalproblems without opening thetransformer.



When should we perform FRA?

Prevention:

After manufacturingFingerprint measurement

Create first reference

As part of a routine diagnostic protocolTo check for changes during service time

After installation or relocationTo check for transformer integrity




High probability of mechanical movements:

After unusual disturbance during shipmentTo check for damages in the active part




Diagnostic purposes:

After a major change in on-line diagnostic condition

After a transformer alarm

After a significant through-fault event

After external failures compromising the transformer condition(short circuits, close lightning impact, ...)

To compare with a sister unit in troubles



Typical results: FRA frequency ranges

Core influence




Winding influence




Leads, grounding influence




HV-testing in the field



Reasons for Field Induced Test

After installation of critical HV transformers such as 500-kV

or 765-kV unitsWhen PD is indicated by DGA results (higher levels ofHydrogen gas)

When unusual sparking or popping sounds are heard frominside the unit

When oil results show corrosive sulfur or any othercontamination

After field repairs or internal inspections where the insulationis disturbed

To help determine the suitability for continued service orreplacement on older critical units such as generatortransformers at nuclear power plants



Transformer being set up for testing

Lift Vehicle

Bushing Shields

Good Weather ?



HV Cable Connections

Connection to HV Divider Connection to LV Bushing

d f



Adaption Transformer Connections

i b hi



PD connections to bushing tap

Connection to Bushing TapInput Quadrupole and

preamplifier

PD i i il



PD connections in test trailer

Computer PD Control Panel9 Channel ICM PD instrument

S d C lib i f PD



Setup and Calibration for PD

Connect Quadrupole and Preamplifier to HV bushingtaps

Windings rated 115-kV and above

Connect PD Calibrator to one Bushing

Inject 500-pC into Bushing Terminal

Use Spectrum Analyzer to locate minimum noiseband

Calibrate each PD Channel

Make Cross-calibration for other phases

Store calibration settings for report

S A l f N i R j i



Spectrum Analyzer for Noise Rejection

PD signal from Calibrator

Noise Signal

Band with best signalto noise ratio

CF

BW



PD M t Di l



PD Measurement Display

PD recording for

report

Continuous readout of PD

PD P tt Di l



PD Pattern Display

T i l tt f N2 b bbl i i di g



Typical pattern for N2 bubbles in winding



Conclusions



Conclusions

Field Induced test is an important diagnostictoolWhen the condition of the transformer issuspect

For Critical applicationsHigh Voltage Transformers (> 345 kV)

Important GSU Transformers

Transformers feeding critical loads

HVTMS standard of accuracy and safety

Tests that can be done with the HVTMS



Tests that can be done with the HVTMS

Induced Test with PD measurement

Applied test up to 500-kVNo-load loss test at rated frequency

Extended 110% voltage “gassing” test

Load loss test at rated frequency *

Temperature test (heat-run test)*

Extended load “gassing” test*

ABB can perform complete set of ANSI tests after on-siterepairs

* May require high MVAR capacitor bank trailer

Life Extension Options and Considerations



Life Extension Options and Considerations Verification: High Voltage Impulse Testing

Mobile Impulse Generator

Lightning impulse test up to 1800 kV

Switching impulse test up to 1300 kV

When required, failure localization during LI / SI test



Cases



Cases

Contact information




Contact information

If you have further questions , please contact me at:

PRESENTER Dr. Poorvi Patel

COMPANY ABB TRES, St. Louis

CONTACT PHONE (314)-679-4838 , (636)-328-6501

CONTACT E-MAIL [email protected]

Important reminders




Important reminders Automation & Power World 2012

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certificates for all the workshops you have attendedduring Automation & Power World 2012.

BE SURE YOU HAVE YOUR BADGE SCANNEDfor each workshop you attend. If you do not haveyour badge scanned you will not be able to obtainPDHs or CEUs credentials.

abb-318-wpo field or factory testing-transformer pd testing at site

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