Sweep Frequency Response Analysis (SFRA)

Assessing the Mechanical Integrity of Power Transformers

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 Modes
4. Test Plans

5. Test Procedures
6. SFRA Relationship to Other Transformer
Diagnostics
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

WG A2.26
PC57.149/D8

IEC 60076-18

DL 911/2004

CHINA

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Available Documents
Cigr Brochure 342

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DL 911/2004

Available Documents
IEC 60076-18

OMICRON

IEEE PC57.149

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

DFR

Insulation Resistance

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DC Winding RES

Transformer Test Protocol

1.

Overall Power Factor and Capacitance

9.

2.

Bushings (C1, C2, Energized Collar)

10. DFR

3.

Exciting Current

11. SFRA

4.

Surge Arresters

12. DC Winding Resistance

5.

Insulating Fluids

6.

Leakage Reactance

7.

Turns Ratio Test

8.

Insulation Resistance

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IR

Life Cycle
Manufacturer Workshop
Delivery Port

Quality Assuring

Truck Transport 1

Transport Checking

After Short Circuit Test

Failure Investigation
Ship Transport

Reception Port

Routine Measurement
After Transients/Overcurrents
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Failure

Truck Transport 2

Investigation (DGA)

Transport Checking

The SFRA Measurement Principle

3

Transformator

2
Spannung U2/U1 in V/V

Spannung U1/U1 in V/V

2
1

0
0

50

100

-1
-2

0
0

50

100

-1
-2

-3

-3
Zeit t in s

Zeit t in s

Erregungssignal
Input signal
(variable Frequenz)

OutputAntwortsignal
signal

(sine wave of
variable frequency)

Spannung U/U1 in V/V

1-|TF(f1)|
^
U1

^
U2

0
0
-1

50

(f1)/2f

-2

|TF(f1)| =

-3

arc(TF(f1)) =

100

^
U2
^
U1

(f1)
Zeit t in s

Betragsfunktion
|TFU2/U1(f)|Magnitude

Phasenfunktion

Phase
arc(TFU2/U1(f))

1.0

200.0
150.0

0.8

arc(TFU2/U1(f)) in deg

|TF U2/U1 (f)| in V/V|

100.0

0.6

0.4

50.0
0.0
-50.0
-100.0

0.2
-150.0
0.0

-200.0
0.0

0.2

0.4

0.6

0.8
f in MHz

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1.0

1.2

1.4

0.0

0.2

0.4

0.6

0.8
f in MHz

1.0

1.2

1.4

Measurement Setup

Power Transformer (complex RLC network)

Measurement
Channel

Reference
Channel

Output
50
U1

Rref=50

FRA Instrument
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U2

Rme=50

Injection signal
Reference signal (Vin)
Measurement signal (Vout)

Passive Components

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Low-Pass Filter

Rm

Rref

Amplitude [dB]

-50

-100

L=200 mH
L=2 mH
L=20 H

-150
10

= 0 , = 0 , = ,
= , = , = 0 ,

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10
Frequency (Hz)

=
= 1 = 0

=0

10

High-Pass Filter
1
=

Rm
Rref

Amplitude [dB]

0
-50
-100
C=1uF
C=20nF
C=1pF

-150

-200
10

= 0 , = , = 0 ,
= , = 0 , = = 1,

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10
Frequency (Hz)

=
=0

= 1 = 0

10

Band-Pass Filter Series Resonance

-20
-40

Rm
Rref

Amplitude [dB]

-60
-80

C=1nF
C=10nF
C=50nF

-100
-120
-140
10

= , = , !

Inductor and Capacitor create short-circuit!

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10
Frequency (Hz)

10

Band-Stop Filter Parallel Resonance

Rm
Rref

Amplitude [dB]

1
=

-5
-10
-15

C=1nF
C=10nF
C=50nF

-20
-25
-30
10

= , = , !

Inductor and Capacitor create open circuit!

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10

Frequency (Hz)

10

RLC Basics

Parallel RLC - VALLEY

Series RLC PEAK
0 dB = 0 Ohms = Short
-100 dB = = Open

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FRA Trace Example

All 4 four filter types appear in SFRA traces!

Band-Pass!
Low-Pass!

High-Pass!

Band-Stop!

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Typical Results
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

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

f/Hz

-20

-30

-40

-50

-60

-70

dB

150

100

-50

-100

N W sec

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N V sec

NU

f/Hz

Failure Mode Identified with SFRA

1.

Radial Hoop Buckling Deformation of Winding

2.

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

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Residual Magnetization

Oil Status (With or Without)

Grounding

Radial Failure

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Axial Failure

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Conductor Tilting

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Core Failure Modes

Over-Heating

Lamination Gaps

Bulk Movement

Shorted Laminations

Multiple Core Grounding

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Ungrounded Core

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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Open vs. Shorted tests

> 12/08/2014

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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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Inductive Inter-Winding Test

> 12/08/2014

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Usable Frequency Ranges

> 12/08/2014

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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)

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H2-X2 (B)

H3-X3(C)

Common Winding Open Circuit Test

X1-X0 (A)

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X2-X0 (B)

X3-X0 (C)

Short Circuit Test

H1-H0X0 (A)

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H2-H0X0 (B)

H3-H0X0(C)

Overview of B Phase

H1-X2 (B)

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X2-X0 (B)

H2-H0X0 (B)

Analysis Strategies

1. Baseline
2. Similar Unit
3. Phase Comparison

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Date X

1.000e+002

5.000e+002

1.000e+003

5.000e+003

Phase based comparison

Time based comparison

SFRA Interpretation

Date Y

1.000e+004

5.000e+004

1.000e+005

5.000e+005

1.000e+006

f/Hz

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

f/Hz

-10
-10

-20
-20

-30
-30

-40
-40

-50
-50

-60

-60

-70

-70

-80

-80

dB

dB

100

Fingerprint

1.000e+002

-50

100

5.000e+002

1.000e+003

5.000e+003

1.000e+004

5.000e+004

1.000e+005

5.000e+005

1.000e+006

f/Hz

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

f/Hz

-50
-100

-100

-150

-150

N-U

N-V

N-W

n-u

n-v

n-w

u2-v2

v2-w2

w2-u2

N-U Kontakte fliepoliert

v2-w2 second

N-U

N-V

N-W

n-u

n-v

n-w

u2-v2

v2-w2

w2-u2

N-U Kontakte fliepoliert

v2-w2 second

1.000e+002

5.000e+002

1.000e+003

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

5.000e+003

1.000e+004

5.000e+004

1.000e+005

5.000e+005

1.000e+006

f/Hz

-10

-20

-30

-40

-50

-60

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

-70

f/Hz

-10

-80
-20

dB

-30

100
-40

f/Hz

-50

-50
-60

-100
-150

-70

A vs B vs C

-80

dB

N-U

N-V

N-W

n-u

n-v

n-w

u2-v2

v2-w2

w2-u2

N-U Kontakte fliepoliert

v2-w2 second

100

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

f/Hz

-50
-100
-150

N-U

N-V

Construction based comparison

A

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

f/Hz

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

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

f/Hz

-10

-10
-20

-20
-30

-30
-40

-40
-50

-50
-60

-60
-70

-70
-80

dB
-80

dB

100

100

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

f/Hz

-50
-100

OMICRON
-50

-150

-100
-150

N-U

N-V

N-W

n-u

n-v

n-w

v2-w2

w2-u2

N-V

N-W

u2-v2

n-v

n-w

N-U Kontakte fliepoliert

v2-w2 second

u2-v2

v2-w2

w2-u2

N-U Kontakte fliepoliert

v2-w2 second

N-U
n-u

f/Hz

Radial Deformation (IEEE)

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IEEE WG PC57.149 (Guide) D8

Axial Deformation (IEEE)

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IEEE WG PC57.149 (Guide) D8

Core Defects (IEEE)

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IEEE WG PC57.149 (Guide) D8

CASE STUDY

1969 Transformer

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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 Open Circut

LV Open Circut

Failure Modes due to Radial Forces

Shift to the right

IEEE PC57.149
OMICRON

HV Short Circut

HV Short Circut Zoom In

~0.1db difference.. Not bad!

Phase 4: Reviewed SFRA data

Phase 6: Perform Addition Test

-Leakage Reactance +FRSL
-Winding Resistance

Leakage Reactance 3 Phase Equivalent and Per Phase Test

9.62% difference compared to average!

Leakage Reactance FRSL

Winding Resistance

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
B Phase

Take a closer look

B phase Zoom In

From Left side of Buldge

Right Side of Buldge

Thank You for Your Attention