3 6 field experience in sfra measurement on generator transformers
DESCRIPTION
SFRA generators and transformersTRANSCRIPT
Field Experience in SFRA Measurement on Generator Transformerson Generator Transformers
EuroDoble Conference 2009
M. BoltzeDoble LDIC
Germany
A. Saravanakumar S. MarkalousDoble LDIC
GermanyDoble LDIC
Germany
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Outline
• IntroductionIntroduction• Principle of SFRA• Interpretation Strategy• Interpretation Strategy• Sample results• Conclusion• Conclusion
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Diagnostic Testing Method
• Monitoringg– Sensor development– Data acquisition, noise suppression, filtering
• Diagnosis– Interpretation of monitored data
f• Benefits– Reduced risk of failure, better asset management
Better maintenance strategy– Better maintenance strategy
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DTCM Methods
Insulation System Winding/core arrangement
Partial discharge Leakage reactance
Dissolved gas analysis Low voltage impulse test
Top oil temperature Transfer function method
Degree of polymerisation Sweep Frequency Response Analysis (SFRA)(SFRA)
Furan analysis
Recovery voltage
Insulation resistance
tan(δ) or loss factor
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LVI and TF method
Tested winding
0.4
0.6
0.8
1
cita
tion
- v(t)
1.2μs / 50μs LV Impulse (V)
Non-Tested winding (shorted) 0 100 200 300 400 500 600 700 800 9000
0.2
Exc
0
5
se -
in(t)
Neutral Current (mA)
)(tv 0 100 200 300 400 500 600 700 800 900-10
-5
Res
pons
time (μs)
0.3 200Time domain data deconvoulted in frequency domain (TF method)
0
0.1
0.2M
agni
tude
-200
-100
0
100
Phas
e (d
eg)
0 4Direct frequency domain measurement (SFRA)
200
)(tin
)()()(
fVfIfH n
=0 500 1000 1500 20000
0.1
0.2
0.3
0.4
Mag
nitu
de
0 500 1000 1500 2000-200
-100
0
100
00
Phas
e (d
eg)
5
0 500 000 500 000Frequency (kHz)
0 500 000 500 000Frequency (kHz)
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Principle of SFRA
• Apply spectrally pure sinusoidal signal
• Measure excitation and response• Compute and store Gain/phase• Repeat measurement at next
di t fdiscrete frequency• Direct frequency domain
measurement• Better immunity to noise and• Better immunity to noise and
interference• Sensitive in detecting winding/core
movementmovement• An Draft on IEEE Guide for
performing SFRA exists
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Practical difficulties
• Ensure spectral purity of sourcep p y• Source harmonics exist & introduce problems• Excitation level low; SNR problem for on-site• Influence of cable length, bushing capacitance• Unshielded connecting leads cause problems
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Typical Response of winding
Magnitude Admittance – Y(f)
PhasePhase
+ 90
- 90
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SFRA and Natural frequencies
• Several factors affect natural
Equivalent circuit representation of a two winding single phase transformer
frequency– Winding type, position,
arrangement, clearance and t i l titerminal connection
– Terminal connection is the only factor that can be externally manipulatedexternally manipulated
• Some natural frequencies are non-excitable under certain terminal connectionsterminal connections
• Knowledge of all natural frequencies indicates highest sensitivitysensitivity
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Influence of Terminal Conditions
0.8
1(a) - Excitation with respect to ground
HVOC/Y(f)0.8
1 (b) - Excitation with respect to ground
)
HVSC/Y(f)
1
3 1
2
0.2
0.4
0.6
Mag
(p.u
)
0.2
0.4
0.6
Mag
(p.u
)
2
4
56
7
8
1
3
45
6
0 0
0 6
0.8
1 (c) - Excitation with respect to neutral
u)
HVOC/Y(f)
0 6
0.8
1 (d) - Excitation with respect to neutral
u)
HVSC/(Yf)
2
5
1
0.2
0.4
0.6
Mag
(p.u
0.2
0.4
0.6
Mag
(p.u
1
2 3
Fig. 1 Measured amplitude frequency response pertaining to terminal connection wherenon tested windings are – (a), (c) open circuited and floating (b), (d) shorted and floating
0 500 1000 1500 20000Frequency (kHz)
0 500 1000 1500 20000Frequency (kHz)
10
g ( ) ( ) p g ( ) ( ) g
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Pole-Zero
5
d/s)
-5
0
ω (M
rad
-0.1 -0.09 -0.08 -0.07 -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0.01σ (Mneper/s)
5
5
0
5
ω (M
rad/
s)
Fig 2 Pole Zero representation corresponding to Fig 1(a) and (d)
-0.1 -0.09 -0.08 -0.07 -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0.01
-5
σ (Mneper/s)
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Fig. 2 Pole-Zero representation corresponding to Fig. 1(a) and (d)
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All System Function Terminal Condition
0.5
1
Mag
1 2 3 4 67
8 910 11
125 Ig(ω)/Ip(ω)
0
M
0 5
1
ag
1 2 3 45
6 7 89
10 11 Vp(ω)/Ip(ω)
0
0.5
Ma
1 1
3Ip(ω)/Vp(ω)
7
0
0.5
Mag 2 3
4 5 68 9 10
11 Vsn(ω)/Vp(ω)
7
0 100 200 300 400 500 600 700 800 900 10000
0.5
Mag 2
3 4 5
Vsn(ω)/Vp(ω)
12
0 100 200 300 400 500 600 700 800 900 1000Frequency (kHz)
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Cable Terminations
0.8
1
)
(a)
Vout(f)/Vin(f)
1
0.2
0.4
0.6
Mag
(p.u
)
2 34
56
7
8
910
0
0 6
0.8
1
u)
(b)
Vout(f)/Vin(f)
1
0.2
0.4
0.6
Mag
(p.u
2
34 5 6 7
Measured amplitude frequency response pertaining to terminal connection where nontested windings are open circuited – (a) 50 Ω(b) 1 MΩ termination
0 100 200 300 400 500 600 700 800 900 10000Frequency(kHz)
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g p ) ( )
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Dynamic Range
1.5 (a)Vout(f)/Vin(f)
3
0.5
1
Mag
(p.u
) 1
24
5 6 7 89
0
1.5
(b)
Vout(f)/Vin(f)
5 6 7 8
3
0.5
1
Mag
(p.u
)
98765
42
1
0 100 200 300 400 500 600 700 800 900 10000Frequency(kHz)
Measured amplitude frequency response from a single phase two windingtransformer (a) with dynamic range (b) without dynamic range
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transformer – (a) with dynamic range (b) without dynamic range
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DOBLE SFRA EQUIPMENT
• Voltage – 10 V p-p (at 50 Ωimpedance)impedance)
• Frequency range – 10 Hz to 10 MHz
• Accuracy – ±1 dB to -70 dB• Accuracy ±1 dB to 70 dB• Input/Output impedance – 50 Ω
• Number of sample 1250• Number of sample – 1250 (logarthmically placed)
• Three lead measuring system
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Current practice (Doble)
Tested winding- Exciting Phase / Line end- Response measuredResponse measured
- Neutral (1 – phase)- Phase (3 – phase/ ∆ )- Neutral (3 – phase/ Y)
N d i diNon tested winding- Open circuited- Short circuited
Non tested terminals are floating
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Non tested terminals are floating
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Test and Analysis
• At factory– Before and after any destructive testing (like short circuit
strength assesment test)– Routine test (Baseline data)out e test ( ase e data)
• At Field– Routine test (after installing)
Before and after relocation– Before and after relocation– After any major event
• Analysis– With baseline data– Phase to phase– Sister unit measurements
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General Guideline
Screen captured from DOBLE SFRA ANALYZER (M5200)
SC response
Core Influence Bulk movement (Core/winding)Winding geometry
Magnitude
OC response
Winding geometryBushing, lead movement and so on
Phase
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Characterstics of windings
Open circuit response measured from 60 MVA, 128.36 / 20 kV transformer
H2 / Middle phaseH3 / Outer phase
Comparison of outer phases (H1 and H3)
Comparison of middle phase with outer phase (H2 and H3)
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Measurable Parameters
Open circuit responseExcitingcurrent
Sh t i itShort circuit response
Leakage reactance
Inductance
DC winding
resistanceresistance
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Certain type of faults
• With and without oil – spectrum remains same with increase in natural frequenciesincrease in natural frequencies
• Bad ground – shows notable differences at high frequencies (f>1 MHz)
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Core Magnetization
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Interpretation strategy (phase - phase)Interpretation strategy (phase phase)
Open circuit f 2 kH
Short circuitf 10 H• f<2 kHz
– Check for indications of core magentization
• 2 kHz<f<20 kHz
• f<10 Hz– Expect matching between traces.
If not, then winding resistance should be tested0
– Check for bulk winding movement• 20 kHz<f<400 kHz
– Identify frequency beyond which d ‘t i fl
• 10 Hz<f<100 Hz– Locate inductive roll off section
and identify the variation in dB (if any)core doesn‘t influence
– Look for variations in spectrum– Ensure quasi-matching of
spectrum
any)– Variation more than 0.1 dB
indicates variation in impedance• 20 kHz<f<800kHzp
• f>1 MHz– Incase of variations, check for
proper ground connections
– Variation in mid frequency range indicates axial movement of winding
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On-site SFRA Measurement
Connection from HV winding
3 phase, 2 winding, 40 MVA, 128 kV / 20 kV
HV winding
Test setup & IInstrumentation
M5200
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40 MVA, 128.36 kV/20 kV, 2-winding, 3 phase transformertransformer
core magnetization
Expected winding movement (H2 - Middle phase)
Confirm winding movement (H2 - Middle phase)
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60 MVA, 128.36 kV/20 kV, 2-winding, 3 phase transformertransformer
core magnetization
Expected winding movement (H2 - Middle phase)
core magnetization
Axial movement of winding
Winding movement detected (Outer phase - H3)
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Conclusion
• Being a non invasive technique, SFRA helps in better g q , passet management
• It also improves quality of maintenance program• Capable of early detection of any developing fault• On contrary, other diagnostic tests (like DGA, Furan
analysis PDC and so on) indicate only after the fault hasanalysis, PDC and so on) indicate only after the fault has occured
• M5200 is a popular SFRA equipment, proven to be accurate and repeatable in measurements
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Thank you for attendingThank you for attending
2009 EuroDoble Conference©Do
ble Engin
eering