electrical measurement methods i

New Experience in the Transformer Diagnosis Michael Krüger, OMICRON Austria

Annual Convention 2012 – Eilat, Israel PAGE 2

Measurement Method Application Indicated by Kind of Test*

on-/off-line

Winding resistance (static)

Contact problems,broken or loose connections,broken conductors

High internal temperatures, e.g. indicated by DGA results or Buchholz Relay

FRT off

Winding resistance (dynamic)Contact problems at the diverter switch, broken transition resistors

DGA, Buchholz Relay FRT off

Leakage reactance (stray reactance) Winding deformation High through-fault currents FRT off

Frequency Response of the Stray Losses (FRSL)

Shorted parallel strands of CTC's

High internal temperatures, e.g. indicated by DGA results FT off

No-load impedance Core problems, shorted turns


No-load current Core problems, shorted turns


*F=Fingerprint, R=Routine, T=Troubleshooting, S=Special

Electrical Measurement Methods I

Annual Convention 2012 – Eilat, Israel

Measurement Method Application Indicated by Kind of Test*

on-/off-line

Turns ratio After Buchholz Relay tripping Buchholz Relay has tripped T off

Frequency Response Analysis (FRA)

Winding deformation, winding displacement, core faults, faulty screen or core connections

High through-fault currents, transportation F(R)T off

Insulation resistance Insulation problems Breakdowns, Buchholz Relay tripping FRT off

Capacitance and Dielectric Dissipation Factor

Main insulation: ageing, moisture - Bushings: ageing, partial breakdowns

DGA FRT on/off

Dielectric Response Measurement (FDS and PDC)

Main insulation: ageing, moisture - Bushings: ageing, partial breakdowns

high water content in oil / high dielectric losses FRT off

Partial Discharge Insulation problems DGA T on/off *F=Fingerprint, R=Routine, T=Troubleshooting, S=Special

Electrical Measurement Methods II

PAGE 3


• Winding Resistance Measurement

• Fault Finding on Transformer Windings with FRA

• Moisture Measurement on Transformers

• Partial Discharge Measurement on Transformers

Content

PAGE 4


Winding Resistance Measurement

PAGE 5


Diverter Switch Contact of Phase V

PAGE 6


Winding Resistance after Repair

PAGE 7






Content

PAGE 8


Fault on a 115kV / 34.5kV Transformer

• There was a breakdown in phase B of the 34.5 kV busbar in the substation

• The differential protection relay of the faulty transformer tripped

PAGE 9


DGA

Phase 1: Trip out of Service, Differential

Phase 2: DGA

second DGA showed 19ppm C2H2

PAGE 10


Transformer Model for FRA


Swept Frequency Response Analysis (SFRA)

-5.0

-3.0

-1.0

1.0

3.0

5.0

0 0.2 0.4 0.6 0.8 1 1.2

Transformer

1N

1U

1V

1W

complex RLCM-Network -5.0

-3.0

-1.0

1.0

3.0

5.0

0 0.2 0.4 0.6 0.8 1 1.2

(f1)

U0*(1-K(f1))

1/f1

0.0

0.5

1.0

1.5

2.0

2.5

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4Frequenz f

K(f)

MHz

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4Frequenz f

(f)

MHz

sine generator (variable frequency)

transfer function (magnitude) transfer function (phase)

K(f1) (f1)

frequency f frequency f

H1 H2 H2 H3 H3 H1 f/Hz1.000e+002 1.000e+003 1.000e+004 1.000e+005 1.000e+006dB-120-110-100-90-80-70-60-50-40-30-20-10010 H1 H2 H2 H3 H3 H1 f/Hz1.000e+002 1.000e+003 1.000e+004 1.000e+005 1.000e+006°-200-150-100-50050100150Magnitude Phase


FRA LV Winding – Comparison of the 3 Phases

B Phase

PAGE 13


Buckling without innersupports

Buckling with inner supports

Higher order or forced Buckling

The conductors can bend between the supports all along the circumference

Free modeor free Buckling

Source: Brochure CIGRE WG 12.19 : The Short Circuit Performance of Power Transformers

Radial Forces


Radial Failure (Buckling)


Failure Modes due to Radial Forces

Source: Cigre Brochure 342 “ MECHANICAL-CONDITION ASSESSMENT OF TRANSFORMER WINDINGS USING FREQUENCY RESPONSE ANALYSIS (FRA)”

B phase with buckling C phase without buckling

PAGE 16


Comparison FRA LV Winding with Cigre Case Study of Buckling

B Phase

PAGE 17

www.e-cigre.org

Systematic shift of several resonances


B Phase

Take a closer look

PAGE 18


B Phase

PAGE 19






Content

PAGE 20


Water in the Transformer

Most of the water is contained in the paper!

Mass of the oil:100,000 kg = 220,000 Lbs

Water content at 60 °C:40 ppm

Mass of the water, dissolved in the oil:

4 kg = 8.8 Lbs

Mass of the solid insulation:13,000 kg = 20,000 Lbs

Water content at 60 °C:4 %

Mass of the water contained in the paper:

520 kg = 1200 Lbs

PAGE 21


Determination of the Water Content in Paper [Karl Fischer Titration and Equilibrium Curves]

0

1

2

3

4

5

6

7

8

9

[%]

11

0 10 20 30 40 50 60 70 [ppm] 90

Wat

er C

onte

nt in

the

Pape

r

Water Content in the Oil

20 °C 30 °C 40 °C

50 °C

60 °C

80 °C

100°C

Temperature

low

high

• Curves are only valid for new oil and new paper, for aged oil/paper different curves are necessary

• Oil sampling is critical (round robin tests)

• Balance between water content in the paper and in oil needs constant temperatures over a long period

• Only average measurement

PAGE 22


History of Dielectric Diagnostic Methods• 1960+• Dissipation factor at power

frequency• Polarization index• At that time: No reliable method for onsite moisture

diagnostics

• 2007 Combination of PDC and FDS

• 1991 RVM for water determination• Soon questioned by users (Kachler 1996)

U(t)

t c

t

U

t peakt d

Ur,max

• 1999+ Polarization Depolarization Currents• Technical University Zurich Switzerland

Uc (t)ipol (t)

idep (t)TC

t

U, I

• 1999+ Frequency Domain Spectroscopy• KTH Stockholm with ABB

Frequency

Dis

sipa

tion

fact

or

PAGE 23


Dielektric Response in the Time DomainPolarisation Depolarisation Current (PDC)

Current = f(t)

PAGE 24


Dielektric Response in the Frequency DomainFrequency Domain Spectroscopy (FDS) or Dielectric Frequency Response (DFR)

PAGE 25


Dielectric Response Measurement with Frequency Domain Spectroscopy (FDS) and Polarisation & Depolarisation Current (PDC)

PDC FDS

Combination of PDC und FDS reduces measurement time

Cur

rent

[nA

]

Time [s]

Trans-formation

Frequency [Hz]

Pow

er fa

ctor

0.0010.001

1

1000

10001

100

1Frequency [Hz]

Pow

er fa

ctor

1000

1

0.001 0.1

024

6

81012

14

PDCFDS DIRANAD

urat

ion

/ h

0,00010,0010,010,1

1101001000

Freq

uenc

y ra

nge

/ Hz

PAGE 26


Interpretation and Analysis

f/Hz0.001 0.01 0.1 1.0 10 100

Dis

sipa

tion

fact

or

0.0001

0.001

0.01

0.1

1

10

0.0001

Pressboard

0,51,0 2,0

Öl 1pS/m

Overall Response1%, 1pS/m, X30, Y15

1000

Oil: Carbon, Sludge, hmw Acids

Pressboard: Water, lmw

Acids

Transition from Capacitive to Resistive Voltage Distribution

Pressboard

PAGE 27


Analysis of the Water Content by Comparison to Model Results

Measurement Laboratory Results

Temperature

0,0001 0,01 1000,01

0,1

10

Frequency [Hz]

Tang

ent D

elta

Water Content Oil Conductivity

Comparison Fitting

X

Oil XY-ModelOil

Barriers

Spacers

Y

Source: Weidmann

PAGE 28


FDS / PDC Measurement on a 130 MVA Transformer – Situation 2006

• 130 MVA• 230 / 115 / 48 kV • Year of manf. 1967• Rubber membrane

in the expansion vessel

PAGE 29


FDS / PDC Measurement on a 130 MVA Transformer – Water Content Distribution

0

1

2

3

4

5M

oist

ure

in p

aper

[%]

FDS HV-LV OilsampleKarl Fischermg/kg(Oommenequilibrium)

FDS LV- Tertiary

FDSTertiary-Tank

Tertiary not in use

OilsampleRH %

Average

FDS/PDC1mHz-1kHz

PAGE 30


130 MVA Transformer On-Line Drying

PAGE 31


History 2006 – 2008 - 2010

PAGE 32






Content

PAGE 33


Diagnostic Measurement on a Cast Resin Type Transformer

PAGE 34


Cracks in the Epoxy

PAGE 35


PD Measurement Circuit

PAGE 36


Test Arangement

CPC100

CP CU1

Compensating Capacitors

PAGE 37


Test Arangement Coupling Capacitor and MPD600

PAGE 38


Separation of PD Sources in 3CFRD

2MHz

500kHz

8MHz

500kHz

2 MHz

8 MHz

3CFRD

timeframe 1 µs

500

kHz

2 M

Hz

8 M

Hz

3CFRD = 3 Center Frequency Relation DiagramPAGE 39


PD Measurement without 3CFRD Filtering

PAGE 40


3CFRD Filtering

PAGE 41


PD Measurement with 3CFRD Filtering

PAGE 42


PD Measurement without 3CFRD Filtering

PAGE 43


On-Line PD Measurement on a Transformer

PAGE 44


On-Line PD Measurement on a Transformer GIS - Cable Connection (GIS Side)

21

3

PAGE 45


Online PD Measurement at the GIS Side

yellow phase GIS

red phase GIS

blue phase GIS

PAGE 46


Sensors 1, 2 and 3 at the GIS Side and Sensor 4 at the Transformer Side

4

100m

PAGE 47


PD Measurement at the GIS and the Transformer Side

blue phase GIS

blue phase Tr

PAGE 48


PD Measurement at GIS and TR Side Trigger = TR Side - Delay on GIS Side

delayed signal blue phase GIS

trigger = blue phase Tr

PAGE 49


Jumper between Oil/Oil Bushing and Cable Termination

PAGE 50


Jumper between Oil/Oil Bushing and Cable Termination

PAGE 51

[email protected] and Remarks?

mailto:[email protected]


A last Example:Fault Investigation on a 220kV Transformer


DGA

Main Tank OLTCH2 1008.8 1183 ≤ 100 101 - 700 701 - 1800 > 1800CH4 67 65 ≤ 120 121 - 400 401 - 1000 > 1000C2H6 54.8 55 ≤ 65 66 - 100 101 - 150 > 150C2H4 668 710 ≤ 50 51 - 100 101 - 200 > 200C2H2 1130 1214 ≤ 1 2 - 9 10 - 35 > 35CO 95 107 ≤ 350 351 - 570 571 - 1400 > 1400CO2 720 740 ≤ 2500 2501 - 4000 4001 - 10000 > 10000TDCG 3024 3337 ≤ 720 721 - 1920 1921 - 4630 > 4630

Condition 3 Condition 4IEEE C57.104-2008Parameter DGA 7 Nov 2011

Condition 1 Condition 2


Ratio Measurement HV to LV


A:Tap V prim. Nom. Vsec.Nom. Ratio nom. V prim. Vsec. Ratio I prim.

A 001 165750.0/√3V 20000.0/√3V 8.2875:1 1999.5V 0.022947V 164.81° 87143.1684:1 1051401.28% 0.002665A 77.53°A 002 163500.0/√3V 20000.0/√3V 8.175:1 1999.57V 0.023128V 163.61° 86449.2002:1 1057382.57% 0.002657A 77.67°A 003 161250.0/√3V 20000.0/√3V 8.0625:1 1999.39V 0.022972V 164.95° 87043.535:1 1079509.74% 0.002673A 77.14°A 004 159000.0/√3V 20000.0/√3V 7.95:1 1999.35V 0.024964V 166.1° 80086.1206:1 1007272.59% 0.002634A 77.17°A 005 156750.0/√3V 20000.0/√3V 7.8375:1 1999.5V 0.024298V 163.59° 82283.9506:1 1049774.97% 0.002631A 77.06°A 006 154500.0/√3V 20000.0/√3V 7.725:1 1999.42V 0.023854V 162.68° 83815.5523:1 1084890.97% 0.002637A 77.55°A 007 152250.0/√3V 20000.0/√3V 7.6125:1 1999.58V 0.024173V 165.95° 82712.7198:1 1086438.19% 0.002651A 76.95°A 008 150000.0/√3V 20000.0/√3V 7.5:1 1999.74V 0.024195V 166.09° 82650.9609:1 1101912.81% 0.002648A 76.92°A 009 147750.0/√3V 20000.0/√3V 7.3875:1 1999.5V 0.02426V 163.8° 82419.6208:1 1115563.23% 0.002632A 77.03°A 010 145500.0/√3V 20000.0/√3V 7.275:1 1999.42V 0.022962V 164.95° 87082.7526:1 1196913.78% 0.00267A 77.19°A 011 143250.0/√3V 20000.0/√3V 7.1625:1 1999.4V 0.022158V 163.12° 90225.6318:1 1259594.68% 0.00267A 76.95°A 012 141000.0/√3V 20000.0/√3V 7.05:1 1999.43V 0.024335V 164.51° 82162.7286:1 1165328.77% 0.002629A 77.23°A 013 138750.0/√3V 20000.0/√3V 6.9375:1 1999.54V 0.024313V 163.74° 82234.8345:1 1185266.98% 0.002629A 77.03°A 014 136500.0/√3V 20000.0/√3V 6.825:1 1999.49V 0.023602V 165.97° 84724.1525:1 1241279.52% 0.002663A 77.14°A 015 134250.0/√3V 20000.0/√3V 6.7125:1 1999.49V 0.024304V 165.52° 82266.6118:1 1225473.36% 0.002641A 76.95°A 016 132000.0/√3V 20000.0/√3V 6.6:1 1999.5V 0.02426V 164.07° 82419.6208:1 1248682.13% 0.002625A 77.3°A 017 129750.0/√3V 20000.0/√3V 6.4875:1 1999.43V 0.024024V 166.21° 83222.8928:1 1282719.16% 0.002654A 76.97°A 018 127500.0/√3V 20000.0/√3V 6.375:1 1999.56V 0.023816V 166.46° 83962.2087:1 1316954.25% 0.002636A 76.95°

PAGE 56

Ratio HV to LV Phase A=R

2kV on HV -> 23mV on LV on all taps !


Ratio HV to LV Phase B=S

All taps have the same ratio 7.2:1 of position 11 !

B:Tap V prim. Nom. Vsec.Nom. Ratio nom. V prim. Vsec. Ratio I prim.

B 001 165750.0/√3V 20000.0/√3V 8.2875:1 999.76V 139.451279V -0.04° 7.1692:1 -13.49% 0.013008A -54.74°B 002 163500.0/√3V 20000.0/√3V 8.175:1 999.76V 139.450928V -0.03° 7.1693:1 -12.3% 0.013062A -54.89°B 003 161250.0/√3V 20000.0/√3V 8.0625:1 999.81V 139.457031V -0.03° 7.1693:1 -11.08% 0.013101A -54.94°B 004 159000.0/√3V 20000.0/√3V 7.95:1 999.79V 139.454666V -0.03° 7.1693:1 -9.82% 0.013075A -54.92°B 005 156750.0/√3V 20000.0/√3V 7.8375:1 999.71V 139.442612V -0.03° 7.1693:1 -8.53% 0.013093A -54.7°B 006 154500.0/√3V 20000.0/√3V 7.725:1 999.83V 139.460587V -0.03° 7.1693:1 -7.19% 0.013151A -54.94°B 007 152250.0/√3V 20000.0/√3V 7.6125:1 999.88V 139.466415V -0.02° 7.1693:1 -5.82% 0.013023A -54.64°B 008 150000.0/√3V 20000.0/√3V 7.5:1 999.62V 139.43132V -0.02° 7.1693:1 -4.41% 0.013017A -54.79°B 009 147750.0/√3V 20000.0/√3V 7.3875:1 999.78V 139.453995V -0.03° 7.1692:1 -2.95% 0.01313A -54.97°B 010 145500.0/√3V 20000.0/√3V 7.275:1 999.81V 139.453735V -0.03° 7.1695:1 -1.45% 0.013136A -54.96°B 011 143250.0/√3V 20000.0/√3V 7.1625:1 999.72V 139.43515V -0.03° 7.1698:1 0.1% 0.013087A -54.67°B 012 141000.0/√3V 20000.0/√3V 7.05:1 999.87V 139.456238V -0.03° 7.1698:1 1.7% 0.013013A -54.65°B 013 138750.0/√3V 20000.0/√3V 6.9375:1 999.82V 139.448944V -0.03° 7.1698:1 3.35% 0.013118A -54.87°B 014 136500.0/√3V 20000.0/√3V 6.825:1 999.82V 139.449051V -0.04° 7.1698:1 5.05% 0.013131A -54.94°B 015 134250.0/√3V 20000.0/√3V 6.7125:1 999.84V 139.452438V -0.04° 7.1698:1 6.81% 0.013061A -54.9°B 016 132000.0/√3V 20000.0/√3V 6.6:1 999.74V 139.436752V -0.02° 7.1698:1 8.63% 0.013088A -54.71°B 018 127500.0/√3V 20000.0/√3V 6.375:1 999.74V 139.438568V -0.03° 7.1698:1 12.47% 0.013088A -54.73°


C:Tap V prim. Nom. Vsec.Nom. Ratio nom. V prim. Vsec. Ratio I prim.

C 001 165750.0/√3V 20000.0/√3V 8.2875:1 999.87V 139.558258V -0.04° 7.1645:1 -13.55% 0.010944A -47.77°C 002 163500.0/√3V 20000.0/√3V 8.175:1 999.78V 139.544296V -0.02° 7.1646:1 -12.36% 0.011008A -47.85°C 003 161250.0/√3V 20000.0/√3V 8.0625:1 999.92V 139.565689V -0.03° 7.1645:1 -11.14% 0.010951A -47.68°C 004 159000.0/√3V 20000.0/√3V 7.95:1 999.93V 139.567307V -0.03° 7.1645:1 -9.88% 0.010956A -47.71°C 005 156750.0/√3V 20000.0/√3V 7.8375:1 999.74V 139.539001V -0.01° 7.1646:1 -8.59% 0.010937A -47.67°C 006 154500.0/√3V 20000.0/√3V 7.725:1 999.95V 139.569595V -0.04° 7.1645:1 -7.26% 0.010964A -47.73°C 007 152250.0/√3V 20000.0/√3V 7.6125:1 999.91V 139.553513V -0.04° 7.1651:1 -5.88% 0.01097A -47.83°C 008 150000.0/√3V 20000.0/√3V 7.5:1 999.68V 139.52594V -0.01° 7.1648:1 -4.47% 0.011007A -47.82°C 009 147750.0/√3V 20000.0/√3V 7.3875:1 999.85V 139.555328V -0.01° 7.1645:1 -3.02% 0.010945A -47.65°C 010 145500.0/√3V 20000.0/√3V 7.275:1 999.73V 139.538071V -0.01° 7.1646:1 -1.52% 0.010946A -47.7°C 011 143250.0/√3V 20000.0/√3V 7.1625:1 999.69V 139.533554V -0.01° 7.1645:1 0.03% 0.010938A -47.66°C 012 141000.0/√3V 20000.0/√3V 7.05:1 999.79V 139.544205V -0.01° 7.1647:1 1.63% 0.010944A -47.7°C 013 138750.0/√3V 20000.0/√3V 6.9375:1 999.77V 139.530441V -0.03° 7.1652:1 3.28% 0.010938A -47.58°C 014 136500.0/√3V 20000.0/√3V 6.825:1 999.67V 139.531235V -0.02° 7.1645:1 4.97% 0.011001A -47.81°C 015 134250.0/√3V 20000.0/√3V 6.7125:1 999.78V 139.54483V -0.01° 7.1646:1 6.73% 0.010996A -47.79°C 016 132000.0/√3V 20000.0/√3V 6.6:1 999.65V 139.529968V -0.03° 7.1644:1 8.55% 0.010932A -47.55°C 017 129750.0/√3V 20000.0/√3V 6.4875:1 999.85V 139.555405V -0.02° 7.1645:1 10.44% 0.010954A -47.68°

PAGE 58

Ratio HV to LV Phase C=T

All taps have the same ratio 7.2:1 of position 11 !


FRA HV

Interruption in phase R, HV side


FRA LV with HV open Short circuit in phase R, but on LV or HV side ???


FRA LV with HV Open and Shorted

A LV with open loop HV (red line)B LV with open loop HV (blue solid line)B LV with shorted HV (blue dashed line)


Winding Resistance of LV

Phase R LV doesn’t look damaged


Conclusions

• Phase R=A is interrupted on HV side

• The tap changer is broken – in position 11

• The limb R has a shorted winding

• The short circuit in limb R is not on the LV side but on the HV side


Opening of the OLTC Compartment


Opened OLTC Compartment

Interruption in phase R, HV side


Interruption due to Open OLTC Contacts


Removed OLTC – Cables to the Tap Winding


FRA on the Single Tap Winding Segments



Segments

11 - 13 9 - 11 8 - 9 7 - 8 6 - 7 5 - 6 4 - 5 3 - 4 2 - 314 - 2


Winding Resistance of the Tap Winding Segments

25mΩ

25mΩ

7mΩ

14mΩ

14mΩ

6mΩ

4

6

5

The fault was between tap conductor 4 and 6 !

[email protected] and Remarks?

mailto:[email protected]

electrical measurement methods i

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