Transcript TRANSFORMER DIAGNOSIS - Association of Municipal

Innovative Test Techniques & Diagnostic
Measurements to Improve the Performance
and Reliability of Power System Transformers
Dr. Michael Krüger, Alexander Kraetge – Omicron Electronics GmbH, Austria
Alexander Dierks – Alectrix (Pty) Ltd, South Africa
© OMICRON
7/7/2015
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The Switch Quiz
•
•
•
•
Room with one light
Three switches outside room
Which switch operates the light?
You are only allowed to open
and enter the room ONCE!
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The Switch Quiz
Turn Switch 1 & 2 ON and wait
Turn Switch 2 OFF, enter the room and check:
• If light is ON
 Switch 1
• If light is OFF and bulb is warm
 Switch 2
• If light is OFF and bulb is cold
 Switch 3
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Sources of Transformer Faults
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Classical Tests of Transformers
• Ratio Measurement (Tap changer dependant)
• Excitation Current Measurement
(Open Circuit Impedance)
• Short Circuit Impedance
• Winding Resistance (static)
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New Test Techniques: Summary
• Onload Tapchanger (OLTC) Testing
• SFRA Measurement
• Capacitance and Tan Delta Measurement
• Di-electric Response Measurement
• Partial Discharge Measurement
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Functioning of Tap changer
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OLTC Principle (1)
Tap Selector
Diverter
Resistors
A
B
Diverter
Switch
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OLTC Principle (2)
Tap Selector
Diverter
Resistors
A
B
Diverter
Switch
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OLTC Principle (3)
Tap Selector
Diverter
Resistors
A
B
Diverter
Switch
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OLTC Principle (4)
Tap Selector
Diverter
Resistors
A
B
Diverter
Switch
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OLTC Principle (5)
Tap Selector
Diverter
Resistors
A
B
Diverter
Switch
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OLTC Principle (6)
Tap Selector
Diverter
Resistors
A
B
Diverter
Switch
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Measurement of Winding Resistance
Measuring
Lines for U
Measuring
Lines for I
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New Voltage Selector Contact
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Testing of a new 500MVA Transformer
Resistance
285.00
280.00
Resistance [mW ]
275.00
270.00
KEMA
265.00
OMICRON 1…21
Ref. Temp.
OMICRON 21…1
Ref. Temp.
260.00
255.00
250.00
245.00
235.00
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
240.00
Taps
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220:110 kV 100MVA TRF: A-Phase
R L1 (referred to 20°C)
700.0
650.0
600.0
mOhm
R L1 1974
R L1 20.2.02 1...19
RL1 20.2.02 19…1
550.0
500.0
450.0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Taps
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Faulty Tap Selector Contact
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Winding Resistance A-Phase
After Repair
Resistance L1
650.0
630.0
Resistance [mW]
610.0
590.0
Factory Measurement
OMICRON 1…19
OMICRON 19…1
570.0
550.0
530.0
510.0
490.0
450.0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
470.0
Taps
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Delta R for U-Mp „UP“-„DOWN“
Before repair
Resistance Difference A Up-Down
2.0
(Delta R) / R [%]
1.5
1.0
After repair
0.5
0.0
-0.5
-1.0
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
-2.0
1
-1.5
Taps
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Transient Current during Switching Process
A
Slope

3
Ripple
1
4
2
1 = Diverter switch switches to the first commutating resistor
2 = Both commutating resistors are in parallel
3 = Final contact of the diverter contact B is reached
4 = Current control of the CPC 100 regulates the current to the nominal test current again
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Ripple of a Diverter Switch in a
Good Condition (1100MVA)
Ripple
2.5%
2.0%
A UP
A DOWN
B UP
B DOWN
C UP
C DOWN
1.5%
1.0%
0.5%
0.0%
000
005
010
015
020
025
030
Taps
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Ripple of an Aged Diverter Switch
Ripple
5.5%
5.0%
A UP
A DOWN
B UP
B DOWN
C UP
C DOWN
4.5%
4.0%
3.5%
3.0%
0
5
10
20
15
Taps
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Aged Diverter Switch
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New Test Techniques: Summary
• Onload Tapchanger Testing
• SFRA Measurement
• Capacitance and Tan Delta Measurement
• Di-electric Response Measurement
• Partial Discharge Measurement
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Transformer Model for SFRA
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Sweep Frequency Response Analysis (SFRA)
5.0
5.0
Transformer
U0*(1-K(f1))
3.0
3.0
1.0
1
N
-1.0 0
0.2
0.4
0.6
0.8
1
1
U
1
V
1.0
1
W
1/f1
-1.0 0
1.2
-3.0
0.2
0.4
-3.0
complex RLCM-Network
-5.0
0.6
0.8
1
1.2
(f1)
-5.0
sine generator
(variable frequency)
(f1)
K(f1)
Phase
Magnitude
transfer function (magnitude)
2.5
2.0
2.0
K(f)
transfer function (phase)
3.0
1.0
1.5
(f)
1.0
0.0
-1.0
0.5
-2.0
0.0
-3.0
0.0
0.2
0.4
0.6
0.8
Frequenz f
frequency f
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1.0
1.2
MHz
1.4
0.0
0.2
0.4
0.6 0.8
Frequenz f
1.0
MHz
1.2 1.4
frequency f
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SFRA Measurement: Test Set Up
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SFRA: Healthy transformer 33kV 10MVA
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SFRA: Damaged Winding 400kV 700MVA
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What can SFRA detect?
• Fingerprint (Reference Measurement) is important!!!
• Geometrical changes in the core and/or windings
due to transport or electrical faults:
• Core deformation / Core movement (clamping)
• Faulty core groundings
• Fault on magnetic cores (shorted laminates)
• Bulk winding movement
• Coil deformation - axial & radial
• Buckling of windings
• Broken or open internal connections
• Inter-winding / Inter-turn short circuits
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Radial Deformation (Buckling)
Source: G. Bertagnolli, Short Circuit Duty of Power Transformers, ABB Trasformatori, Legnano
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Damaged Winding (Axial Movement)
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Grounding of the Measurement Cables
Important for reproducible measurements
Braids for a low-inductive
connection cable screen flange
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New Test Techniques: Summary
• Onload Tapchanger Testing
• SFRA Measurement
• Capacitance and Tan Delta Measurement
• Di-electric Response Measurement
• Partial Discharge Measurement
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C / Tan Delta Progression of a Bushing
C Tan-Delta Progression of a 220 kV RBP (Hard Paper) Bushing
Year of Manufacturimg 1961, horizontal mounted, oil filled
Tan Delta
Change of Capacitance
30
Tan Delta x 10 -3
Change of Capacitance %
25
20
15
10
5
0
75
77
79
81
83
85
87
89
-5
Source: RWE
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Date of Measurement
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Bushing Fault
Source: RWE
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Bushing after Explosion
Source: RWE
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Tan Delta / Dissipation Factor
• Bushings:
• Aging and decomposition of insulation
• Water content
• Bad contacted electrodes or capacitive layers
• Cracks in the insulation
• Transformers:
• Aging
• Water content in oil and paper
• Contamination by particles
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Capacitance Measurement
• Bushings:
• Partial breakdowns between layers
• Oil ingress into cracks of solid insulation (RBP)
• Change of Geometry between:
• Transformer windings
• Windings and tank
• Windings and core
• Core and tank
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CPC 100 / TD 1
Tan-delta & Capacitance
Measurement
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220kV RIP Bushing Stored Outside
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220kV RIP Bushing Stored Outside
0.85 %
0.75 %
Minimum
Tan Delta
0.65 %
31.03.2004
15.07.2004
08.10.2004
0.55 %
0.45 %
Minimum
0.35 %
Minimum
0.25 %
0.0 Hz
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100.0 Hz
200.0 Hz
300.0 Hz
400.0 Hz
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New Test Techniques: Summary
• Onload Tapchanger Testing
• SFRA Measurement
• Capacitance and Tan Delta Measurement
• Di-electric Response Measurement
• Partial Discharge Measurement
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Design of the Winding Insulation
Measurement of Water Content in Paper & Pressboard
Source: Weidmann AG
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Frequency Domain Spectroscopy (FDS)
CN
ZN
ZX CX, LX
ICX
ICN
u0(t)
UN(t)
Z1
Reference path
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Z2
UX(t)
Measurement path
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PDC Analysis
Polarisation-Depolarisation-Current
Principle
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Recording of current
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Dirana: Combination of PDC and FDS
FDS  11 h Meas. Time
0.1 Hz – 5 kHz
PDC  Meas. only up to 1 Hz
0.1 mHz – 0.1 Hz
FDS+PDC  0.1 mHz – 5 kHz in
less than 3 hours meas. time
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PDC up to 0.1Hz und FDS above 0.1Hz
FDS
PDC
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FDS / PDC Measurements
on a 800 kVA Distribution Transformer
• 800 kVA
• 20 / 0.4 kV
• 1969
• Furan content:
12.27 mg/kg !!

DP  130
Decision:
transformer was
taken out of
service
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FDS / PDC Measurements
on a 800 kVA Distribution Transformer
50°C
FDS curves
for different
temperatures
25°C
12°C
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FDS / PDC Measurements
on a 800 kVA Distribution Transformer
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New Test Techniques: Summary
• Onload Tapchanger Testing
• SFRA Measurement
• Capacitance and Tan Delta Measurement
• Di-electric Response Measurement
• Partial Discharge Measurement
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Fault on a 25 MVA Furnace Transformer
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Fault on a 25 MVA Furnace Transformer
Overpressure valve
released 200l of oil
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Fault on a 25 MVA Furnace Transformer
DC insulation resistance
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Fault on a 25 MVA Furnace Transformer
Excitation Current
0.7
0.6
0.5
Io U
Io V
Io W
0.4
0.3
0.2
0.1
Taps
0
000
005
Angle of Excitation Current
010
015
020
Taps
0.0°
-10.0°
-20.0°
Phase (I) U
Phase (I) V
Phase (I) W
-30.0°
No-load
current
-40.0°
-50.0°
-60.0°
000
005
010
015
Taps 020
Taps
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Fault on a 25 MVA Furnace Transformer
6 0 0 0 .0 Ω
5 0 0 0 .0 Ω
4 0 0 0 .0 Ω
R0 W17
R0 V17
R0 U17
3 0 0 0 .0 Ω
2 0 0 0 .0 Ω
1 0 0 0 .0 Ω
0.0Ω
0.0Hz
100.0Hz
200.0Hz
300.0Hz
400.0Hz
500.0Hz
6 0 0 0 .0 Ω
5 0 0 0 .0 Ω
4 0 0 0 .0 Ω
Z0 (f) = R0 (f) + j X0 (f)
X0 W17
X0 V17
X0 U17
3 0 0 0 .0 Ω
2 0 0 0 .0 Ω
1 0 0 0 .0 Ω
0.0Ω
0.0Hz
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200.0Hz
300.0Hz
400.0Hz
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Fault on a 25 MVA Furnace Transformer
FRA (log view)
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Fault on a 25 MVA Furnace Transformer
Faulty B phase
FRA (lin view zoomed)
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Fault on a 25 MVA Furnace Transformer
Partial discharge measurement
Measuring
electrode
MPD
600
Optical fiber
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MPD
600
Optical fiber
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Fault on a 25 MVA Furnace Transformer
Partial discharge measurement
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Fault on a 25 MVA Furnace Transformer
Opened
transformer
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Fault on a 25 MVA Furnace Transformer
Melted screw
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Fault on a 25 MVA Furnace Transformer
Melted steel with copper marks
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Conclusions / Summary
• Defective contacts of the OLTC can be detected by measuring the
static winding resistance over all taps up- and down.
• Switching problems of the diverter switch of the OLTC can be found
through dynamic resistance measurements.
• The Sweep Frequency Response Analysis (SFRA) is a powerful tool for
detecting winding displacements, winding deformations and faulty core
and screen connections. Reproducible connection techniques are
important to ensure reliable and reproducible measurements.
• Tan Delta frequency sweeps are much more sensitive for investigating
insulation problems compared to measurements at 50Hz only.
• Polarization / Depolarization Current (PDC) and Frequency Domain
Spectroscopy (FDS) measurements are useful tools for determining
the water content in cellulose for deciding on further actions (e.g. drying).
• Partial Discharge (PD) measurements are an important tool for the
troubleshooting of insulation problems.
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Thank you for your interest !
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