Wilsonville SFRA.pdf

7/24/2019 Wilsonville SFRA.pdf

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Sweep Frequency Response Analysis (SFRA)

Assessing the Mechanical Integrity of Power Transformers



© OMICRON

What is SFRA?

• Powerful and sensitive tool to assess the

mechanical and electrical integrity of

power transformers active part

• Measurement of the transfer function

over a wide frequency range



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SFRA Discussion Outline

1. Basic SFRA Theory, History, and Evolution

2. SFRA Measurement Characteristics

3. Failure Modes4. Test Plans

5. Test Procedures

6. SFRA Relationship to Other TransformerDiagnostics

7. Analysis of Results



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Diagnostic Category

• Dielectric

• Thermal

• “Mechanical ”

• Use SFRA:

1. Transportation

2. Post Fault



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FRA Industry Groups

• CIGRE WG A2.26 (Guide)

• DL 911/2004 (Standard)

• IEC 60076-18 (Draft)

• IEEE WG PC57.149 (Guide) D8



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Standardization in the World

CHINA

DL 911/2004PC57.149/D8

WG A2.26

IEC 60076

-

18


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Available Documents

Cigré Brochure 342 DL 911/2004



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Available Documents

IEC 60076-18 IEEE PC57.149



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Transformer Tests

Dielectric Thermal Mechanical

DGA DGA SFRA

Oil Screen Oil Screen Leakage Reactance

PF/TD CAP IR PF/TD CAP

Exciting Ima DC Winding RES Exciting Ima

Turns Ratio Tests DC Winding RES

DFR

Insulation Resistance



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Transformer Test Protocol

1. Overall Power Factor and Capacitance

2. Bushings (C1, C2, Energized Collar)

3. Exciting Current

4. Surge Arresters

5. Insulating Fluids

6. Leakage Reactance

7. Turns Ratio Test

8. Insulation Resistance

9. IR

10. DFR

11. SFRA

12. DC Winding Resistance



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Life Cycle

Delivery Port

Reception Port

Manufacturer Workshop

•Quality Assuring

• After Short Circuit Test

•Failure Investigation

•Transport Checking

•Transport Checking

•Routine Measurement

• After Transients/Overcurrents

•Failure Investigation (DGA)

Truck Transport 1

Truck Transport 2

Ship Transport



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The SFRA Measurement Principle

Transformator

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

f in MHz

|TFU2/U1(f)|inV/V|

-200.0

-150.0

-100.0

-50.0

0.0

50.0

100.0

150.0

200.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

f in MHz

arc(TFU2/U1(f))indeg

Betragsfunktion

|TFU2/U1(f)|Phasenfunktion

arc(TFU2/U1(f))

Erregungssignal

(variable Frequenz)Antwortsignal

-3

-2

-1

0

1

2

3

0 50 100

Zeit t in µs

SpannungU1/U1inV/V

-3

-2

-1

0

1

2

3

0 50 100

Zeit t in µs

SpannungU/U1inV/V

U2^U1^

1-|TF(f1)|

U2^

U1^|TF(f1)| =

f1/2 f

arc(TF(f1 = (f1

-3

-2

-1

0

1

2

3

0 50 100

Zeit t in µs

SpannungU2/U1inV/V

Input signal

(sine wave of

variable frequency)

Output signal

PhaseMagnitude



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Measurement Setup

Power Transformer (complex RLC network)

U1 Rref=50Ω U2Rme=50Ω

50Ω

U

A B C

FRA Instrument

Output Reference

Channel

Measurement

Channel

Injection signal

Reference signal (Vin)

Measurement signal (Vout)



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Passive Components



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Low-Pass Filter

102

104

106

-150

-100

-50

0

Fre uenc Hz

Amplitude[dB]

L=200 mH

L=2 mH

L=20 H

=

= 0 , = 0 , = , =

= 1 = 0

= ∞ , = ∞ , = 0 , =

= 0

Rref

Rm



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High-Pass Filter

Rref Rm

102

104

106

-200

-150

-100

-50

0

Fre uenc Hz

Amplitude[dB]

C=1uF

C=20nF

C=1pF

=

1

= 0 , = ∞ , = 0 , =

= 0

= ∞ , = 0 , = = 1, =

= 1 = 0



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Band-Pass Filter – Series Resonance

Rref Rm

102

104

106

-140

-120

-100

-80

-60

-40

-20

Fre uenc Hz

Amplitude[dB]

C=1nF

C=10nF

C=50nF

=1

=

= , = , ℎ !

Inductor and Capacitor create short-circuit!



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Band-Stop Filter – Parallel Resonance

Rref Rm

102

104

106

-30

-25

-20

-15

-10

-5

0

5

Frequency (Hz)

Amplitude[dB]

C=1nF

C=10nF

C=50nF

=1

=

Inductor and Capacitor create open circuit!

= , = , !



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RLC Basics

• Parallel RLC - VALLEY

• Series RLC – PEAK

• 0 dB = 0 Ohms = Short

• -100 dB = = Open



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FRA Trace Example

Low-Pass!

Band-Pass!

Band-Stop!

High-Pass!

All 4 four filter types appear in SFRA traces!



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Typical Resultsf/Hz

5.000e+001 1.000e+002 5.000e+002 1.000e+003 5.000e+003 1.000e+004 5.000e+004 1.000e+005 5.000e+005 1.000e+006

dB

-70

-60

-50

-40

-30

-20

N W sec N V sec N U

f/Hz5.000e+001 1.000e+002 5.000e+002 1.000e+003 5.000e+003 1.000e+004 5.000e+004 1.000e+005 5.000e+005 1.000e+006

°

-100

-50

100

150



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Failure Mode Identified with SFRA

1. Radial “Hoop Buckling” Deformation of Winding2. Axial Winding Elongation “Telescoping”

3. Overall- Bulk & Localized Movement

4. Core Defects

5. Contact Resistance

6. Winding Turn-to-Turn Short Circuit

7. Open Circuited Winding

• Residual Magnetization

• Oil Status (With or Without)

• Grounding



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Radial Failure



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Axial Failure



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Conductor Tilting



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Core Failure Modes

• Over-Heating• Bulk Movement

• Multiple Core Grounding

• Lamination Gaps• Shorted Laminations

• Ungrounded Core



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Measurement Types

1. Open Circuit - Exciting Ima

2. Short Circuit - Leakage Reactance

3. Interwinding – CHL CAP

4. Transfer Voltage – Turns Ratio



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Measurement Setup – OPEN CIRCUIT



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HV vs. LV Winding Responses



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Open Circuit Tests



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Measurement Setup – SHORT CIRCUIT

Short Circuit Test



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> 12/08/2014

Open vs. Shorted tests



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Short Circuit Tests



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Measurement Setup

Inter-winding measurements: Capacitive (left) Inductive (right)



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Capacitive Inter-Winding Test



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> 12/08/2014

Inductive Inter-Winding Test



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> 12/08/2014

Usable Frequency Ranges



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Transformer Types

• 2 Winding (H, X) 3-H OC

3-X OC

3-HX SC

• 3 Winding (H, X, Y) 3-H OC

3-X OC

3-Y OC

3-HX SC

3-HY SC

• Auto Transformer (Series, Common, Tert)

3-H Series OC 3-X Common OC

3-Y Tert OC

3-HX SC

3-HY SC



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Test Connections



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Test Recommendations (IEEE)

• LTC Extreme Raise

• DETC as Found

• Open Circuit Test

• Short Circuit Test



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Series Winding Open Circuit Test

H1-X1 (A) H2-X2 (B) H3-X3(C)



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Common Winding Open Circuit Test

X1-X0 (A) X2-X0 (B) X3-X0 (C)



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Short Circuit Test

H1-H0X0 (A) H2-H0X0 (B) H3-H0X0(C)



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Overview of B Phase

H1-X2 (B) X2-X0 (B) H2-H0X0 (B)



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Analysis Strategies

1. Baseline

2. Similar Unit

3. Phase Comparison



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SFRA Interpretation

Fingerprint

Date X Date Y

T i m e

b a s e d c o m p a r i s

o n

P h a s e

b a s e d c o m p a r i s

o n

f/Hz1 . 0 00 e + 00 2 5 . 0 00 e + 00 2 1 . 0 0 0e + 0 03 5 . 0 0 0e + 0 03 1 . 0 00 e + 00 4 5 . 0 00 e + 00 4 1 . 0 0 0e + 0 05 5 . 0 00 e + 00 5 1 . 0 0 0e + 0 06

dB

-80

-70

-60

-50

-40

-30

-20

-10

U V

n u n v n

u v v u

U K nt t fli ß li rt v c n

f/H1. + . + 1. + . + 1. + . + 1. + . + 1. +

°

-1

-1

-

1

f/Hz1 . 00 0 e+ 0 02 5 . 00 0 e+ 0 02 1 . 00 0 e+ 0 03 5 . 00 0 e+ 0 03 1 . 00 0 e+ 0 04 5 . 00 0 e+ 0 04 1 . 00 0 e+ 0 05 5 . 00 0 e+ 0 05 1 . 00 0 e+ 0 06

dB

-80

-70

-60

-50

-40

-30

-20

-10

U V

n u n v n

u v v u


f/H1. . 1. . 1. . 1. . 1.

°

-1

-1

-

1

f/Hz1 . 0 00 e + 00 2 5 . 0 0 0e + 0 02 1 . 0 0 0e + 0 03 5 . 0 0 0e + 0 03 1 . 0 00 e + 00 4 5 . 0 00 e + 00 4 1 . 0 0 0e + 0 05 5 . 0 0 0e + 0 05 1 . 0 0 0e + 0 06

dB

-80

-70

-60

-50

-40

-30

-20

-10

U V

n u n v n

u v v u


f/H1. + . + 1. + . + 1. + . + 1. + . + 1. +

°

-1

-1

-

1

A B C A B C

f/Hz1 .0 0 0e + 0 02 5 .0 0 0e + 0 02 1.0 0 0 e+ 0 0 3 5 .0 00 e + 00 3 1 .0 0 0e + 0 04 5 .0 00 e + 00 4 1 .0 0 0e + 0 05 5 .0 0 0e + 0 05 1.0 0 0 e+ 0 0 6

dB

-80

-70

-60

-50

-40

-30

-20

-10

-U -V

f/1 .0 0 0e + 0 02 5 .0 0 0e + 0 02 1.0 0 0 e+ 0 0 3 5 .0 00 e + 00 3 1 .0 0 0e + 0 04 5 .0 00 e + 00 4 1 .0 0 0e + 0 05 5 .0 0 0e + 0 05 1.0 0 0 e+ 0 0 6

°

-150

-100

-50

100

A vs B vs C

A B C A B C

f/Hz1 . 0 00 e + 00 2 5 . 0 00 e +0 0 2 1 . 0 00 e +0 0 3 5 . 0 00 e +0 0 3 1 . 0 00 e +0 0 4 5 . 0 00 e + 00 4 1 . 0 00 e + 00 5 5 . 0 00 e +0 0 5 1 . 0 00 e +0 0 6

dB

-80

-70

-60

-50

-40

-30

-20

-10

U V

n u n v n

u v v u

U K n t k t fl i ß l i rt v c n

f/H1. + 5. + 1. + 5. + 1. + 5. + 1. + 5 5. + 5 1. +

°

-15

-1

-5

1

f/Hz1 . 0 00 e +0 0 2 5 . 0 00 e +0 0 2 1 . 0 00 e + 00 3 5 . 0 00 e +0 0 3 1 . 0 00 e +0 0 4 5 . 0 00 e + 00 4 1 . 0 00 e + 00 5 5 . 0 00 e +0 0 5 1 . 0 00 e + 00 6

dB

-80

-70

-60

-50

-40

-30

-20

-10

U V

n u n v n

u v v u

U K nt k t f li ß l i r t v c n

f/H1. + 5. + 1. + 5. + 1. + 5. + 1. + 5 5. + 5 1. +

°

-15

-1

-5

1

Construction based comparison



Initial Problem

Phase 1: Trip out of Service, Differential

Phase 2: DGA



Initial Problem

Phase 1: Trip out of Service, Differential

Phase 2: DGA

Phase 3: Test

-Visual Inspection

-Power Factor

-Exciting Current

-Transformer Turns Ratio

-SFRA

-Second DGA – 19 PPM of Acetylne

Phase 4: Reviewed SFRA data

HV O Ci t



HV Open Circut

LV O Ci t



LV Open Circut

Failure Modes due to Radial Forces



HV Short Circut

HV Short Circut Zoom In



HV Short Circut – Zoom In

~0.1db difference.. Not bad!




Phase 6: Perform Addition Test

-Leakage Reactance +FRSL

-Winding Resistance

Leakage Reactance 3 Phase Equivalent and Per Phase Test



Leakage Reactance – 3 Phase Equivalent and Per Phase Test

9.62% difference compared to average!

Leakage Reactance FRSL



Leakage Reactance – FRSL

Winding Resistance



Winding Resistance




Phase 5: Perform Addition Test

-Leakage Reactance +FRSL

-Winding Resistance

Phase 6: Tear down

During Tear Down, Transformer caught on fire

Tear Down



B Phase

Take a closer look

B phase Zoom In



From Left side of Buldge Right Side of Buldge



Thank You for Your Attention

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