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Sweep Frequency Response Analysis (SFRA)
Assessing the Mechanical Integrity of Power Transformers
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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
U K nt t fli ß li rt v c n
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
U K nt t fli ß li rt v c n
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
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Radial Deformation (IEEE)
IEEE WG PC57.149 (Guide) D8
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Axial Deformation (IEEE)
IEEE WG PC57.149 (Guide) D8
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Core Defects (IEEE)
IEEE WG PC57.149 (Guide) D8
CASE STUDY
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1969 Transformer
CASE STUDY
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Initial Problem
Phase 1: Trip out of Service, Differential
Phase 2: DGA
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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
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HV Open Circut
LV O Ci t
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LV Open Circut
Failure Modes due to Radial Forces
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Failure Modes due to Radial Forces
IEEE PC57.149
Shift to the right
HV Short Circut
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HV Short Circut
HV Short Circut Zoom In
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HV Short Circut – Zoom In
~0.1db difference.. Not bad!
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Phase 4: Reviewed SFRA data
Phase 6: Perform Addition Test
-Leakage Reactance +FRSL
-Winding Resistance
Leakage Reactance 3 Phase Equivalent and Per Phase Test
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Leakage Reactance – 3 Phase Equivalent and Per Phase Test
9.62% difference compared to average!
Leakage Reactance FRSL
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Leakage Reactance – FRSL
Winding Resistance
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Winding Resistance
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Phase 4: Reviewed SFRA data
Phase 5: Perform Addition Test
-Leakage Reactance +FRSL
-Winding Resistance
Phase 6: Tear down
During Tear Down, Transformer caught on fire
Tear Down
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B Phase
Take a closer look
B phase Zoom In
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From Left side of Buldge Right Side of Buldge
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Thank You for Your Attention